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Inbreeding Depression (inbreeding + depression)
Selected AbstractsIS INBREEDING DEPRESSION LOWER IN MALADAPTED POPULATIONS?EVOLUTION, Issue 7 2009A QUANTITATIVE GENETICS MODEL Despite abundant empirical evidence that inbreeding depression varies with both the environment and the genotypic context, theoretical predictions about such effects are still rare. Using a quantitative genetics model, we predict amounts of inbreeding depression for fitness emerging from Gaussian stabilizing selection on some phenotypic trait, on which, for simplicity, genetic effects are strictly additive. Given the strength of stabilizing selection, inbreeding depression then varies simply with the genetic variance for the trait under selection and the distance between the mean breeding value and the optimal phenotype. This allows us to relate the expected inbreeding depression to the degree of maladaptation of the population to its environment. We confront analytical predictions with simulations, in well-adapted populations at equilibrium, as well as in maladapted populations undergoing either a transient environmental shift, or gene swamping in heterogeneous habitats. We predict minimal inbreeding depression in situations of extreme maladaptation. Our model provides a new basis for interpreting experiments that measure inbreeding depression for the same set of genotypes in different environments, by demonstrating that the history of adaptation, in addition to environmental harshness per se, may account for differences in inbreeding depression. [source] ENVIRONMENTAL CONDITIONS AFFECT THE MAGNITUDE OF INBREEDING DEPRESSION IN SURVIVAL OF DARWIN'S FINCHESEVOLUTION, Issue 6 2002Lukas F. Keller Abstract Understanding the fitness consequences of inbreeding (inbreeding depression) is of importance to evolutionary and conservation biology. There is ample evidence for inbreeding depression in captivity, and data from wild populations are accumulating. However, we still lack a good quantitative understanding of inbreeding depression and what influences its magnitude in natural populations. Specifically, the relationship between the magnitude of inbreeding depression and environmental severity is unclear. We quantified inbreeding depression in survival and reproduction in populations of cactus finches (Geospiza scandens) and medium ground finches (Geospiza fortis) living on Isla Daphne Major in the Galapagos Archipelago. Our analyses showed that inbreeding strongly reduced the recruitment probability (probability of breeding given that an adult is alive) in both species. Additionally, in G. scandens, first-year survival of an offspring withf= 0.25 was reduced by 21% and adults withf= 0.25 experienced a 45% reduction in their annual probability of survival. The magnitude of inbreeding depression in both adult and juvenile survival of this species was strongly modified by two environmental conditions, food availability and number of competitors. In juveniles, inbreeding depression was only present in years with low food availability, and in adults inbreeding depression was five times more severe in years with low food availability and large population sizes. The combination of relatively severe inbreeding depression in survival and the reduced recruitment probability led to the fact that very few inbred G. scandens ever succeeded in breeding. Other than recruitment probability, no other trait showed evidence of inbreeding depression in G. fortis, probably for two reasons: a relatively high rate of extrapair paternity (20%), which may lead to an underestimate of the apparent inbreeding depression, and low sample sizes of highly inbred G. fortis, which leads to low statistical power. Using data from juvenile survival, we estimated the number of lethal equivalents carried by G. scandens, G. fortis, and another congener, G. magnirostris. These results suggest that substantial inbreeding depression can exist in insular populations of birds, and that the magnitude of the inbreeding depression is a function of environmental conditions. [source] MAINTENANCE OF ANDRODIOECY IN THE FRESHWATER SHRIMP, EULIMNADIA TEXANA: ESTIMATES OF INBREEDING DEPRESSION IN TWO POPULATIONSEVOLUTION, Issue 3 2000Stephen C. Weeks Abstract., Androdioecy is an uncommon form of reproduction in which males coexist with hermaphrodites. Androdioecy is thought to be difficult to evolve in species that regularly inbreed. The freshwater shrimp Eulimnadia texana has recently been described as both androdioecious and highly selfing and is thus anomalous. Inbreeding depression is one factor that may maintain males in these populations. Here we examine the extent of "late" inbreeding depression (after sexual maturity) in these clam shrimp using two tests: (1) comparing the fitness of shrimp varying in their levels of individual heterozygosity from two natural populations that differ in overall genetic diversity; and (2) specifically outcrossing and selfing shrimp from these same populations and comparing fitness of the resulting offspring. The effects of inbreeding differed within each population. In the more genetically diverse population, fecundity, size, and mortality were significantly reduced in inbred shrimp. In the less genetically diverse population, none of the fitness measures was significantly lowered in selfed shrimp. Combining estimates of early inbreeding depression from a previous study with current estimates of late inbreeding depression suggests that inbreeding depression is substantial (,= 0.68) in the more diverse population and somewhat lower (,= 0.50) in the less diverse population. However, given that males have higher mortality rates than hermaphrodites, neither estimate of inbreeding depression is large enough to account for the maintenance of males in either population by inbreeding depression alone. Thus, the stability of androdioecy in this system is likely only if hermaphrodites are unable to self-fertilize many of their own eggs when not mated to a male or if male mating success is generally high (or at least high when males are rare). Patterns of fitness responses in the two populations were consistent with the hypothesis that inbreeding depression is caused by partially recessive deleterious alleles, although a formal test of this hypothesis still needs to be conducted. [source] Stress Resistance and Environmental Dependency of Inbreeding Depression in Drosophila melanogasterCONSERVATION BIOLOGY, Issue 4 2000Jesper Dahlgaard Two important issues are whether stress and inbreeding effects are independent as opposed to synergistic, and whether inbreeding effects are general across stresses as opposed to stress-specific. We found that inbreeding reduced resistance to acetone and desiccation in adult Drosophila melanogaster, whereas resistance to knockdown heat stress was not affected. Inbred flies, however, experienced a greater proportional decrease in productivity than outbreds following heat stress. Correlations using line means indicated that all resistance traits were uncorrelated in the inbred as well as in the outbred flies. Recessive, deleterious alleles therefore did not appear to have any general deleterious effects on stress resistance. Inbreeding within a specific environment and selection for resistant genotypes may therefore purge a population of deleterious genes specific to only one environmental stress. Resumen: Tanto la endogamia como el estrés ambiental pueden tener efectos adversos sobre la adaptabilidad afectando la conservación de especies en peligro de extinción. Dos temas importantes son determinar si los efectos del estrés y la endogamia son independientes en lugar de ser sinérgicos, y determinar si los efectos de la endogamia son generales para distintos tipos de estrés o si son específicos para un tipo determinado de estrés. Encontramos que la endogamia reduce la resistencia a la acetona y la desecación en adultos de Drosophila melanogaster, mientras que la resistencia al efecto demoledor del estrés por calor no fue afectada. Sin embargo, las moscas endogámicas experimentaron una disminución proporcionalmente mayor en la productividad que aquellas moscas sin endogamia después de experimentar un estrés por calor. Las correlaciones obtenidas usando líneas medias indicaron que las características de resistencia no estuvieron correlacionadas ni en moscas con endogamia, ni en moscas sin ella. Aparentemente los alelos nocivos recesivos no tuvieron ningún efecto nocivo general en la resistencia al estrés. La endogamia dentro de un ambiente específico y la selección por genotipos resistentes podrían, por lo tanto, eliminar una población de genes nocivos específicos a un solo estrés ambiental. [source] MAINTENANCE OF ANDRODIOECY IN THE FRESHWATER SHRIMP, EULIMNADIA TEXANA: ESTIMATES OF INBREEDING DEPRESSION IN TWO POPULATIONSEVOLUTION, Issue 3 2000Stephen C. Weeks Abstract., Androdioecy is an uncommon form of reproduction in which males coexist with hermaphrodites. Androdioecy is thought to be difficult to evolve in species that regularly inbreed. The freshwater shrimp Eulimnadia texana has recently been described as both androdioecious and highly selfing and is thus anomalous. Inbreeding depression is one factor that may maintain males in these populations. Here we examine the extent of "late" inbreeding depression (after sexual maturity) in these clam shrimp using two tests: (1) comparing the fitness of shrimp varying in their levels of individual heterozygosity from two natural populations that differ in overall genetic diversity; and (2) specifically outcrossing and selfing shrimp from these same populations and comparing fitness of the resulting offspring. The effects of inbreeding differed within each population. In the more genetically diverse population, fecundity, size, and mortality were significantly reduced in inbred shrimp. In the less genetically diverse population, none of the fitness measures was significantly lowered in selfed shrimp. Combining estimates of early inbreeding depression from a previous study with current estimates of late inbreeding depression suggests that inbreeding depression is substantial (,= 0.68) in the more diverse population and somewhat lower (,= 0.50) in the less diverse population. However, given that males have higher mortality rates than hermaphrodites, neither estimate of inbreeding depression is large enough to account for the maintenance of males in either population by inbreeding depression alone. Thus, the stability of androdioecy in this system is likely only if hermaphrodites are unable to self-fertilize many of their own eggs when not mated to a male or if male mating success is generally high (or at least high when males are rare). Patterns of fitness responses in the two populations were consistent with the hypothesis that inbreeding depression is caused by partially recessive deleterious alleles, although a formal test of this hypothesis still needs to be conducted. [source] Inbreeding depression and genetic load of sexually selected traits: how the guppy lost its spotsJOURNAL OF EVOLUTIONARY BIOLOGY, Issue 2 2003C. Van Oosterhout Abstract To date, few studies have investigated the effects of inbreeding on sexually selected traits, although inbreeding depression on such traits can play an important role in the evolution and ecology of wild populations. Sexually selected traits such as ornamentation and courtship behaviour may not be primary fitness characters, but selection and dominance coefficients of their mutations will resemble those of traits under natural selection. Strong directional selection, for instance, through female mate-choice, purges all but the most recessive deleterious mutations, and the remaining dominance variation will result in inbreeding depression once populations undergo bottlenecks. We analysed the effects of inbreeding on sexually selected traits (colour pattern and courtship behaviour) in the male guppy, Poecilia reticulata, from Trinidad, and found a significant decline in the frequency of mating behaviour and colour spots. Such effects occurred although the genetic basis of these traits, many of which are Y-linked and hemizygous, would be expected to leave relatively little scope for inbreeding depression. Findings suggest that these sexually selected traits could reflect the genetic condition or health of males, and thus may be informative mate-cue characters for female choice as suggested by the ,good genes' model. [source] Inbreeding depression by recessive deleterious genes affecting female fecundity of a haplo-diploid miteJOURNAL OF EVOLUTIONARY BIOLOGY, Issue 4 2000Saito The effect of inbreeding on haplo-diploid organisms has been regarded as very low, because deleterious recessive genes on hemizygous (haploid) males were immediately purged generation by generation. However, we determined such recessive genes to decrease female fecundity in a population of Schizotetranychus miscanthi Saito which is known in the Acari as a subsocial species with haplo-diploidy. In mother,son inbreeding experiments, there was no depression in egg hatchability nor in the larval survival of progeny over four generations. There was, on the other hand, significant inbreeding depression in the fecundity with increasing f -value. Crosses between two lineages, one having deleterious effects on the fecundity and the other having no such effects, established during the inbreeding, revealed heterosis, and backcrosses showed that the depression was caused by deleterious recessive(s). These results strongly suggest the existence of some deleterious genes governing only the traits of adult females in wild populations of haplo-diploid organisms. [source] Inbreeding Effects on Hatchery and Growout Performance of Pacific White Shrimp, Penaeus (Litopenaeus) vannameiJOURNAL OF THE WORLD AQUACULTURE SOCIETY, Issue 4 2008Dustin R Moss In animal breeding programs, selection coupled with a narrow genetic base can cause high levels of inbreeding to occur rapidly (in one or two generations). Although the effects of inbreeding have been studied extensively in terrestrial animals and to a lesser extent in aquaculture species, little is known about the effects of inbreeding on penaeid shrimp. The objective of this study was to investigate the effects of inbreeding on hatchery and growout performance of the Pacific white shrimp, Penaeus vannamei. The experiment was conducted over 2 yr, and data from two successive generations (G2 and G3) of inbred (sibling,sibling mating) and outbred families were analyzed. There were 11 inbred and 12 outbred families in G2 and 9 inbred and 10 outbred families in G3. Inbreeding coefficients (F) for outbred and inbred families were 0.00 and 0.25, respectively, for G2 and 0.00 and 0.375, respectively, for G3. Growth rates for outbreds and inbreds were similar in both G2 and G3. Hatch rate for inbred families was 33.1% lower than for outbred families in G2 and 47.1% lower in G3. Inbreeding depression (IBD) (relative change in phenotype per 0.1 increase in F) ± 95% CI for hatch rate was ,12.3 ± 10.1%. Hatchery survival for inbred families was 31.4% lower than for outbred families in G2 and 38.8% lower in G3. IBD for hatchery survival was ,11.0 ± 5.7%. Growout survival was 1.9% lower for inbred families than for outbred families in G2 and 19.6% lower in G3. IBD for growout survival was ,3.8 ± 2.9%. There was also a significant linear relationship between IBD estimates for survival traits and mean outbred survival. At high outbred survival, IBD was low (e.g., growout survival in G2), but IBD appeared to become more severe when outbred survival was lower. This suggests that stress (related to environment and/or life stage) may worsen IBD for survival traits. Results also indicate that moderate to high levels of inbreeding (>10%) should be avoided in commercial shrimp hatcheries because the cumulative effect of IBD on hatch rate and hatchery survival will significantly reduce postlarvae production. Thus, IBD can be significant enough to justify the use of inbreeding as a germplasm protection strategy (under certain scenarios) for genetic improvement programs. [source] Inbreeding depression and multiple regions showing heterozygote advantage in Drosophila melanogaster exposed to stressMOLECULAR ECOLOGY, Issue 13 2006ÁLVARO G. A. FERREIRA Abstract Recent studies that reveal a correlation between heterozygosity and fitness in natural populations have rekindled interest in whether balancing selection is widespread or an evolutionary oddity. We therefore quantified heterozygote advantage at 12 microsatellite markers in both inbred and outbred crosses of Drosophila grown under different forms of environmental stress. As expected, inbreeding depression reduces fitness relative to the outbred controls. In addition, many loci exhibit heterozygote advantage over and above any effect due to inbreeding, with ,30% of markers showing an effect in any given culture condition and ,75% of markers showing an effect in at least one of the four culture conditions. To explore the extent of linkage disequilibrium surrounding these loci we further typed four new markers close to each of the three strongest hits. We find a pattern where the extent of heterozygote excess tends to decline to nonsignificance within around 1.5 megabases (Mb) either side of the original hit. Crude extrapolation suggests 12 genes or regions experience detectable levels of heterozygote advantage in any one condition and as many as 25 overall. Thus, balancing selection is widespread and is likely to play an important role in maintaining genetic variability. [source] Effect of inbreeding depression on growth and fluctuating asymmetry in Turkish young malesAMERICAN JOURNAL OF HUMAN BIOLOGY, Issue 4 2010Özener This study sought to examine the effects of inbreeding on physical development and fluctuating asymmetry (FA). A total 144 male high-school students (mean age = 18.11 ± 0.52) whose parents are first cousins (F = 0.125) of low-socioeconomic status and 146 male students (mean age = 18.08 ± 0.54) from the same school who do not have any consanguineous parents (F = 0) were observed in Ankara. In addition to the weight and height measurements of the individuals, eight bilateral traits (hand width, elbow width, wrist width, knee width, ankle width, foot width, ear length, and ear width) were measured. Whereas the inbred group has lower values in terms of weight and height, the difference in body mass index between the groups is not significant. Although the inbred group is more asymmetric in terms of the observed bilateral traits, the differences are below the significance level. However, the composite FA index shows that the inbred group is more asymmetric and the difference is significant (P < 0.05). Inbreeding depression has a negative effect on weight and height development, and a negative effect on developmental stability.Am. J. Hum. Biol. 2010. © 2010 Wiley-Liss, Inc. [source] Heterosis performance of yield and fibre quality in F1 and F2 hybrids in upland cottonPLANT BREEDING, Issue 3 2004Y. T. Wu Abstract Because of the difficulty of producing F1 hybrid seeds by hand emasculation and pollination, wide use of heterosis in cotton production has been limited in China. The objective of this study was to evaluate the potential of F2 hybrids for yield and fibre quality. A half diallel involving eight parents and their F1 and F2 hybrids was grown in replicated studies at Linqing and Nanjing in 1999 and Nanjing in 2000. Yield and fibre quality was determined for all 64 entries. Fibre quality was also determined for parents and F1s, but only for Zhongmiansuo 28 (ZMS28), Xiangzamian 2 (XZM2) and Wanmian 13 (WM13) F2s. These three F2 hybrids are extensively planted in China and provide experimental controls with which to compare the performance of new hybrids. Average yield heterosis for F1s and F2s was 15.9 and 9.2%, respectively. Inbreeding depression for yield varied but some F2s greatly out-yielded the best variety. Average F1 heterosis was 6.7, 6.2 and 2.9%, respectively for number of bolls per unit area, boll weight, and lint percentage. The average F2 heterosis for the same traits was 4.4, 3.3 and 1.6%, respectively. F1 heterosis for fibre traits was low. In general, parental average was a good indicator of the yield and fibre quality of F1 hybrids. These encouraging results suggest there is sufficient heterosis for yield to use F2s in China. [source] Inbreeding depression and founder diversity among captive and free-living populations of the endangered pink pigeon Columba mayeriANIMAL CONSERVATION, Issue 4 2004Kirsty J. Swinnerton The endemic pink pigeon has recovered from less than 20 birds in the mid-1970s to 355 free-living individuals in 2003. A major concern for the species' recovery has been the potential genetic problem of inbreeding. Captive pink pigeons bred for reintroduction were managed to maximise founder representation and minimise inbreeding. In this paper, we quantify the effect of inbreeding on survival and reproductive parameters in captive and wild populations and quantify DNA sequence variation in the mitochondrial d-loop region for pink pigeon founders. Inbreeding affected egg fertility, squab, juvenile and adult survival, but effects were strongest in highly inbred birds (F,0.25). Inbreeding depression was more apparent in free-living birds where even moderate levels of inbreeding affected survival, although highly inbred birds were equally compromised in both captive and wild populations. Mitochondrial DNA haplotypic diversity in pink pigeon founders is low, suggesting that background inbreeding is contributing to low fertility and depressed productivity in this species, as well as comparable survival of some groups of non-inbred and nominally inbred birds. Management of wild populations has boosted population growth and may be required long-term to offset the negative effects of inbreeding depression and enhance the species' survival. [source] Population Size, Genetic Variation, and Reproductive Success in a Rapidly Declining, Self-Incompatible Perennial (Arnica montana) in The NetherlandsCONSERVATION BIOLOGY, Issue 6 2000Sheila H. Luijten In 26 populations in The Netherlands we investigated the relationship between population size and genetic variation using allozyme markers. Genetic variation was low in A. montana ( He = 0.088). There were positive correlations between population size and the proportion of polymorphic loci, the number of effective alleles, and expected heterozygosity, but not with observed heterozygosity. There was a significantly positive correlation between population size and the inbreeding coefficient. Generally, small populations showed heterozygote excess, which decreased with increasing population size. Possibly, the heterozygous individuals in small populations are survivors from the formerly larger populations with relatively high fitness. The F statistics showed a moderately high level of differentiation among populations ( FST = 0.140 ± 0.02), implying a low level of gene flow. For three out of four allozyme loci, we found significant inbreeding ( FIS = 0.104 ± 0.03). Only 14 of 26 populations were in Hardy-Weinberg equilibrium at all four polymorphic loci. In a subset of 14 populations of various size, we investigated natural seed production and offspring fitness. Population size was positively correlated with seed set, seedling size, number of flowering stems and flowerheads, adult survival, and total relative fitness, but not with the number of florets per flowerhead, germination rate, or the proportion of germination. Offspring performance in the greenhouse was not associated with genetic diversity measured on their mothers in the field. We conclude that the fitness of small populations is significantly reduced, but that there is as yet no evidence that this was caused by inbreeding. Possibly, the self-incompatibility system of A. montana has been effective in reducing selfing rates and inbreeding depression. Resumen:Arnica montana es una especie de planta rara, en declinación rápida y autoincompatible. En 26 poblaciones de los Países Bajos investigamos la relación entre el tamaño poblacional y la variación genética mediante el uso de alozimas marcadoras. La variación genética fue baja en A. montana ( He = 0.088). Existió una correlación positiva entre el tamaño poblacional y la proporción de emplazamientos polimórficos, el número de alelos efectivos y la heterocigocidad esperada, pero no con la heterocigocidad observada. Existió una correlación positiva significativa entre el tamaño poblacional y el coeficiente de endogamia. Generalmente, las poblaciones pequeñas mostraron una heterocigocidad excesiva con disminuciones en el tamaño poblacional. Posiblemente, los individuos heterocigóticos de poblaciones pequeñas son sobrevivientes de poblaciones anteriormente grandes con una adaptabilidad relativamente alta. Las pruebas de F mostraron un nivel de diferenciación moderadamente alto entre poblaciones ( FST = 0.140 ± 0.02) lo que implica un nivel bajo de flujo de genes. Para tres de cuatro de los emplazamientos de alozimas encontramos una endogamia significativa ( FIS = 0.104 ± 0.03). Solamente 14 de las 26 poblaciones estuvieron en equilibrio Hardy-Weinberg para los cuatro emplazamientos polimórficos. En un subconjunto de 14 poblaciones de varios tamaños, investigamos la producción natural de semillas y la adaptabilidad de la descendencia. El tamaño poblacional estuvo positivamente correlacionado con el juego de semillas, el tamaño del almácigo, el número de tallos en flor y de inflorescencias, la supervivencia de adultos y la adaptabilidad total relativa, pero no con el número de flores por inflorescencia, la tasa de germinación ni la proporción de la germinación. El rendimiento de la descendencia en invernaderos no estuvo asociado con la diversidad genética medida en sus madres en el campo. Concluimos que la adaptabilidad de poblaciones pequeñas está significativamente reducida, pero no existe aún evidencia de que esto sea ocasionado por endogamia. Es posible que el sistema de autoincompatibilidad de A. montana haya sido efectivo en la reducción de tasas de autofecundación y depresión de la endogamia. [source] IS INBREEDING DEPRESSION LOWER IN MALADAPTED POPULATIONS?EVOLUTION, Issue 7 2009A QUANTITATIVE GENETICS MODEL Despite abundant empirical evidence that inbreeding depression varies with both the environment and the genotypic context, theoretical predictions about such effects are still rare. Using a quantitative genetics model, we predict amounts of inbreeding depression for fitness emerging from Gaussian stabilizing selection on some phenotypic trait, on which, for simplicity, genetic effects are strictly additive. Given the strength of stabilizing selection, inbreeding depression then varies simply with the genetic variance for the trait under selection and the distance between the mean breeding value and the optimal phenotype. This allows us to relate the expected inbreeding depression to the degree of maladaptation of the population to its environment. We confront analytical predictions with simulations, in well-adapted populations at equilibrium, as well as in maladapted populations undergoing either a transient environmental shift, or gene swamping in heterogeneous habitats. We predict minimal inbreeding depression in situations of extreme maladaptation. Our model provides a new basis for interpreting experiments that measure inbreeding depression for the same set of genotypes in different environments, by demonstrating that the history of adaptation, in addition to environmental harshness per se, may account for differences in inbreeding depression. [source] EXPERIMENTAL EVIDENCE FOR FREQUENCY DEPENDENT SELF-FERTILIZATION IN THE GYNODIOECIOUS PLANT, SILENE VULGARISEVOLUTION, Issue 6 2009Keiko Miyake After over a half century of empirical and theoretical research regarding the evolution and maintenance of gynodioecy in plants, unexplored factors influencing the relative fitnesses of females and hermaphrodites remain. Theoretical studies suggest that hermaphrodite self-fertilization (selfing) rate influences the maintenance of gynodioecy and we hypothesized that population sex ratio may influence hermaphrodite selfing rate. An experimental test for frequency-dependent self-fertilization was conducted using replicated populations constructed with different sex ratios of the gynodioecious plant Silene vulgaris. We found that hermaphrodite selfing increased with decreased hermaphrodite frequency, whereas evidence for increased inbreeding depression was equivocal. We argue that incorporation of context dependent inbreeding into future models of the evolution of gynodioecy is likely to yield novel insights into sex ratio evolution. [source] EVOLUTIONARY ANALYSIS OF A KEY FLORAL TRAIT IN AQUILEGIA CANADENSIS (RANUNCULACEAE): GENETIC VARIATION IN HERKOGAMY AND ITS EFFECT ON THE MATING SYSTEMEVOLUTION, Issue 7 2007Christopher R. Herlihy The mating system of flowering plant populations evolves through selection on genetically based phenotypic variation in floral traits. The physical separation of anthers and stigmas within flowers (herkogamy) is expected to be an important target of selection to limit self-fertilization. We investigated the pattern of phenotypic and genetic variation in herkogamy and its effect of self-fertilization in a broad sample of natural populations of Aquilegia canadensis, a species that is highly selfing despite strong inbreeding depression. Within natural populations, plants exhibit substantial phenotypic variation in herkogamy caused primarily by variation in pistil length rather than stamen length. Compared to other floral traits, herkogamy is much more variable and a greater proportion of variation is distributed among rather than within individuals. We tested for a genetic component of this marked phenotypic variation by growing naturally pollinated seed families from five populations in a common greenhouse environment. For three populations, we detected a significant variation in herkogamy among families, and a positive regression between parental herkogamy measured in the field and progeny herkogamy in the greenhouse, suggesting that there is often genetic variation in herkogamy within natural populations. We estimated levels of self-fertilization for groups of flowers that differed in herkogamy and show that, as expected, herkogamy was associated with reduced selfing in 13 of 19 populations. In six of these populations, we performed floral emasculations to show that this decrease in selfing is due to decreased autogamy (within-flower selfing), the mode of selfing that herkogamy should most directly influence. Taken together, these results suggest that increased herkogamy should be selected to reduce the production of low-quality selfed seed. The combination of high selfing and substantial genetic variation for herkogamy in A. canadensis is enigmatic, and reconciling this observation will require a more integrated analysis of how herkogamy influences not only self-fertilization, but also patterns of outcross pollen import and export. [source] EVOLUTION UNDER RELAXED SEXUAL CONFLICT IN THE BULB MITE RHIZOGLYPHUS ROBINIEVOLUTION, Issue 9 2006Magdalena Tilszer Abstract The experimental evolution under different levels of sexual conflict have been used to demonstrate antagonistic coevolution in muscids, but among other taxa a similar approach has not been employed. Here, we describe the results of 37 generations of evolution under either experimentally enforced monogamy or polygamy in the bulb mite Rhizoglyphus robini. Three replicates were maintained for each treatment. Monogamy makes male and female interests congruent; thus selection is expected to decrease harmfulness of males to their partners. Our results were consistent with this prediction in that females from monogamous lines achieved lower fecundity when housed with males from polygamous lines. Fecundity of polygamous females was not affected by mating system under which their partners evolved, which suggests that they were more resistant to male-induced harm. As predicted by the antagonistic coevolution hypothesis, the decrease in harmfulness of monogamous males was accompanied by a decline in reproductive competitiveness. In contrast, female fecundity and embryonic viability, which were not expected to be correlated with male harmfulness, did not differ between monogamous and polygamous lines. None of the fitness components assayed differed between individuals obtained from crosses between parents from the same line and those obtained from crosses between parents from different lines within the same mating system. This indicates that inbreeding depression did not confound our results. However, interpretation of our results is complicated by the fact that both males and females from monogamous lines evolved smaller body size compared to individuals from polygamous lines. Although a decrease in reproductive performance of males from monogamous lines was still significant when body size was taken into account, we were not able to separate the effects of male body size and mating system in their influence on fecundity of their female partners. [source] THE EFFECT OF SELF-FERTILIZATION, INBREEDING DEPRESSION, AND POPULATION SIZE ON AUTOPOLYPLOID ESTABLISHMENEVOLUTION, Issue 9 2005Joseph H. Rausch Abstract The minority cytotype exclusion principle describes how random mating between diploid and autotetraploid cytotypes hinders establishment of the rare cytotype. We present deterministic and stochastic models to ascertain how selfing, inbreeding depression, unreduced gamete production, and finite population size affect minority cytotype exclusion and the establishment of autotetraploids. Results demonstrate that higher selfing rates and lower inbreeding depression in autotetraploids facilitate establishment of autotetraploid populations. Stochastic effects due to finite population size increase the probability of polyploid establishment and decrease the mean time to tetraploid fixation. Our results extend the minority cytotype exclusion principle to include important features of plant reproduction and demonstrate that variation in mating system parameters significantly influences the conditions necessary for polyploid establishment. [source] PERSPECTIVE: PURGING THE GENETIC LOAD: A REVIEW OF THE EXPERIMENTAL EVIDENCEEVOLUTION, Issue 12 2002Peter Crnokrak Abstract., Inbreeding depression, the reduction in fitness that accompanies inbreeding, is one of the most important topics of research in evolutionary and conservation genetics. In the recent literature, much attention has been paid to the possibility of purging the genetic load. If inbreeding depression is due to deleterious alleles, whose effect on fitness are negative when in a homozygous state, then successive generations of inbreeding may result in a rebound in fitness due to the selective decrease in frequency of deleterious alleles. Here we examine the experimental evidence for purging of the genetic load by collating empirical tests of rebounds in fitness-related traits with inbreeding in animals and plants. We gathered data from 28 studies including five mammal, three insect, one mollusc, and 13 plant species. We tested for purging by examining three measures of fitness-component variation with serial generations of inbreeding: (1) changes in inbreeding depression, (2) changes in fitness components of inbred lines relative to the original outbred line, and (3) purged population (outcrossed inbred lines) trait means as a function of ancestral outbred trait means. Frequent and substantial purging was found using all three measures, but was particularly pronounced when tracking changes in inbreeding depression. Despite this, we found little correspondence between the three measures of purging within individual studies, indicating that the manner in which a researcher chooses to estimate purging will affect interpretation of the results obtained. The discrepancy suggests an alternative hypothesis: rebounds in fitness with inbreeding may have resulted from adaptation to laboratory conditions and not to purging when using outcrossed inbred lines. However, the pronounced reduction in inbreeding depression for a number of studies provides evidence for purging, as the measure is likely less affected by selection for laboratory conditions. Unlike other taxon-specific reviews on this topic, our results provide support for the purging hypothesis, but firm predictions about the situations in which purging is likely or the magnitude of fitness rebound possible when populations are inbred remain difficult. Further research is required to resolve the discrepancy between the results obtained using different experimental approaches. [source] FAMILY-LEVEL COVARIATION BETWEEN PARASITE RESISTANCE AND MATING SYSTEM IN A HERMAPHRODITIC FRESHWATER SNAILEVOLUTION, Issue 7 2002Jürgen Wiehn Abstract Genetic compatibility, nonspecific defenses, and environmental effects determine parasite resistance. Host mating system (selfing vs. outcrossing) should be important for parasite resistance because it determines the segregation of alleles at the resistance loci and because inbreeding depression may hamper immune defenses. Individuals of a mixed mating hermaphroditic freshwater snail, Lymnaea ovata, are commonly infected by a digenetic trematode parasite, Echinoparyphium recurvatum. We examined covariation between quantitative resistance to novel parasites and mating system by exposing snail families from four populations that differed by their inbreeding coefficients. We found that resistance was unrelated to inbreeding coefficient of the population, suggesting that the more inbred populations did not carry higher susceptibility load than the less inbred populations. Most of the variation in resistance was expressed among the families within the populations. In the population with the lowest inbreeding coefficient, resistance increased with outcrossing rate of the family, as predicted if selfing had led to inbreeding depression. In the other three populations with higher inbreeding coefficients, resistance was unrelated to outcrossing rate. The results suggest that in populations with higher inbreeding some of the genetic load has been purged, uncoupling the predicted relationship between outcrossing rate and resistance. Snail families also displayed crossing reaction norms for resistance when tested in two environments that presented low and high immune challenge, suggesting that genotype-by-environment interactions are important for parasite resistance. [source] ENVIRONMENTAL CONDITIONS AFFECT THE MAGNITUDE OF INBREEDING DEPRESSION IN SURVIVAL OF DARWIN'S FINCHESEVOLUTION, Issue 6 2002Lukas F. Keller Abstract Understanding the fitness consequences of inbreeding (inbreeding depression) is of importance to evolutionary and conservation biology. There is ample evidence for inbreeding depression in captivity, and data from wild populations are accumulating. However, we still lack a good quantitative understanding of inbreeding depression and what influences its magnitude in natural populations. Specifically, the relationship between the magnitude of inbreeding depression and environmental severity is unclear. We quantified inbreeding depression in survival and reproduction in populations of cactus finches (Geospiza scandens) and medium ground finches (Geospiza fortis) living on Isla Daphne Major in the Galapagos Archipelago. Our analyses showed that inbreeding strongly reduced the recruitment probability (probability of breeding given that an adult is alive) in both species. Additionally, in G. scandens, first-year survival of an offspring withf= 0.25 was reduced by 21% and adults withf= 0.25 experienced a 45% reduction in their annual probability of survival. The magnitude of inbreeding depression in both adult and juvenile survival of this species was strongly modified by two environmental conditions, food availability and number of competitors. In juveniles, inbreeding depression was only present in years with low food availability, and in adults inbreeding depression was five times more severe in years with low food availability and large population sizes. The combination of relatively severe inbreeding depression in survival and the reduced recruitment probability led to the fact that very few inbred G. scandens ever succeeded in breeding. Other than recruitment probability, no other trait showed evidence of inbreeding depression in G. fortis, probably for two reasons: a relatively high rate of extrapair paternity (20%), which may lead to an underestimate of the apparent inbreeding depression, and low sample sizes of highly inbred G. fortis, which leads to low statistical power. Using data from juvenile survival, we estimated the number of lethal equivalents carried by G. scandens, G. fortis, and another congener, G. magnirostris. These results suggest that substantial inbreeding depression can exist in insular populations of birds, and that the magnitude of the inbreeding depression is a function of environmental conditions. [source] MAINTENANCE OF ANDRODIOECY IN THE FRESHWATER SHRIMP, EULIMNADIA TEXANA: ESTIMATES OF INBREEDING DEPRESSION IN TWO POPULATIONSEVOLUTION, Issue 3 2000Stephen C. Weeks Abstract., Androdioecy is an uncommon form of reproduction in which males coexist with hermaphrodites. Androdioecy is thought to be difficult to evolve in species that regularly inbreed. The freshwater shrimp Eulimnadia texana has recently been described as both androdioecious and highly selfing and is thus anomalous. Inbreeding depression is one factor that may maintain males in these populations. Here we examine the extent of "late" inbreeding depression (after sexual maturity) in these clam shrimp using two tests: (1) comparing the fitness of shrimp varying in their levels of individual heterozygosity from two natural populations that differ in overall genetic diversity; and (2) specifically outcrossing and selfing shrimp from these same populations and comparing fitness of the resulting offspring. The effects of inbreeding differed within each population. In the more genetically diverse population, fecundity, size, and mortality were significantly reduced in inbred shrimp. In the less genetically diverse population, none of the fitness measures was significantly lowered in selfed shrimp. Combining estimates of early inbreeding depression from a previous study with current estimates of late inbreeding depression suggests that inbreeding depression is substantial (,= 0.68) in the more diverse population and somewhat lower (,= 0.50) in the less diverse population. However, given that males have higher mortality rates than hermaphrodites, neither estimate of inbreeding depression is large enough to account for the maintenance of males in either population by inbreeding depression alone. Thus, the stability of androdioecy in this system is likely only if hermaphrodites are unable to self-fertilize many of their own eggs when not mated to a male or if male mating success is generally high (or at least high when males are rare). Patterns of fitness responses in the two populations were consistent with the hypothesis that inbreeding depression is caused by partially recessive deleterious alleles, although a formal test of this hypothesis still needs to be conducted. [source] Effects of inbreeding on immune response and body size in a social insect, Bombus terrestrisFUNCTIONAL ECOLOGY, Issue 5 2003C. U. Gerloff Summary 1Inbreeding can negatively affect various fitness components. Here we examine how immune response and body size of a social insect are affected by inbreeding, sex and ploidy. 2In the bumble-bee, Bombus terrestris (L.), the offspring of colonies resulting from brother,sister matings were compared with that of outbred colonies. Immune response was measured as the degree of encapsulation of a novel antigen, body size as the length of the radial cell in the forewings. 3Inbreeding affected neither immune response nor body size in either workers or haploid males under laboratory conditions. However, fitness characteristics varied significantly among maternal families and colonies. The lack of detectable inbreeding depression for two fitness components might help explain why B. terrestris is a good colonizer in nature. 4In addition, sex and ploidy strongly affected the fitness components studied: diploid males had a significantly lower immune response than haploid males, who in turn had a significantly lower immune response than workers of the same colony. The body size of diploid males was intermediate between the body size of workers and haploid males. [source] Interactive effects of environmental stress and inbreeding on reproductive traits in a wild bird populationJOURNAL OF ANIMAL ECOLOGY, Issue 6 2006A. B. MARR Summary 1Conservation biologists are concerned about the interactive effects of environmental stress and inbreeding because such interactions could affect the dynamics and extinction risk of small and isolated populations, but few studies have tested for these interactions in nature. 2We used data from the long-term population study of song sparrows Melospiza melodia on Mandarte Island to examine the joint effects of inbreeding and environmental stress on four fitness traits that are known to be affected by the inbreeding level of adult birds: hatching success, laying date, male mating success and fledgling survival. 3We found that inbreeding depression interacted with environmental stress to reduce hatching success in the nests of inbred females during periods of rain. 4For laying date, we found equivocal support for an interaction between parental inbreeding and environmental stress. In this case, however, inbred females experienced less inbreeding depression in more stressful, cooler years. 5For two other traits, we found no evidence that the strength of inbreeding depression varied with environmental stress. First, mated males fathered fewer nests per season if inbred or if the ratio of males to females in the population was high, but inbreeding depression did not depend on sex ratio. Second, fledglings survived poorly during rainy periods and if their father was inbred, but the effects of paternal inbreeding and rain did not interact. 6Thus, even for a single species, interactions between the inbreeding level and environmental stress may not occur in all traits affected by inbreeding depression, and interactions that do occur will not always act synergistically to further decrease fitness. [source] Inbreeding and inbreeding depression in a threatened endemic plant, the African violet (Saintpaulia ionantha ssp. grotei), of the East Usambara Mountains, TanzaniaAFRICAN JOURNAL OF ECOLOGY, Issue 3 2010Johanna Kolehmainen Abstract Mating among closely-related individuals in small and isolated plant populations may result in reduced vigour of the inbred offspring, i.e. inbreeding depression, especially in naturally outbreeding plants. Occurrence of inbreeding and inbreeding depression was studied in Saintpaulia ionantha ssp. grotei, a threatened endemic plant species with a narrow ecological amplitude from the East Usambara Mountains. The level of inbreeding (measured as the fixation index, F) was investigated in twelve populations by analyzing variation at one microsatellite marker locus. The effect of one generation of selfing and outcrossing on the progeny fitness was studied by controlled crosses in two small patches that differ in the level isolation. The fixation index (F) across the populations was on the average 0.21 and varied among the populations from substantial inbreeding (F = 0.58) to surplus heterozygosity (F = ,0.29). High inbreeding depression (,) was observed at early and late stages of the life-cycle. The isolated patch exhibited lower inbreeding depression than did the non-isolated patch. The results of this study suggest that inbreeding and subsequent inbreeding depression are potential threats to the survival of Saintpaulia populations. Résumé L'accouplement d'individus étroitement liés, dans des petites populations végétales isolées, peut aboutir à une vigueur moindre de la progéniture de même souche, c'est-à-dire une dépression due à l'endogamie, spécialement chez des plantes qui sont naturellement exogames. L'occurrence de l'endogamie et de la dépression qui y est liée a étéétudiée chez le Saintpaulia ionantha spp. grotei, une plante endémique menacée qui n'a qu'une faible amplitude écologique dans l'est des Usambara Mountains. On a recherché le taux d'endogamie (mesuré par l'indice de fixation F) dans 12 populations en analysant la variation d'un locus microsatellite marqueur. L'effet d'une génération d'auto- et d'allofécondation sur l'aptitude (fitness) de la progéniture a étéétudié par des croisements contrôlés dans deux petites parcelles dont le degré d'isolement différait. L'indice de fixation F dans les populations était en moyenne de 0,21 et il variait d'une autofécondation substantielle (F = 0,58) à une hétérozygosité en surplus (F = ,0,29). Une forte dépression due à l'endogamie (,) a été observée aux stades précoce et tardif du cycle vital. La parcelle isolée a présenté une dépression liée à l'endogamie moins forte que celle de la parcelle non isolée. Les résultats de cette étude suggèrent que l'auto-fécondation et la dépression qui en résulte sont des menaces potentielles pour la survie des populations de Saintpaulia. [source] The rough edges of the conservation genetics paradigm for plantsJOURNAL OF ECOLOGY, Issue 6 2006N. J. OUBORG Summary 1Small and isolated populations of species are susceptible to loss of genetic diversity, owing to random genetic drift and inbreeding. This loss of diversity may reduce the evolutionary potential to adapt to changing environments, and may cause immediate loss of fitness (cf. inbreeding depression). Together with other population size-dependent stochastic processes, this may lead to increased probabilities of population extinction. 2This set of processes and theories forms the core of conservation genetics and has developed into the conservation genetics paradigm. Many empirical studies have concentrated on the relationship between population size and genetic diversity, and in many cases evidence was found that small populations of plants do indeed have lower levels of genetic diversity and increased homozygosity. Although less empirical attention has been given to the relationship between low genetic diversity, fitness and, in particular, evolutionary potential, the paradigm is now widely accepted. 3Here we present five areas of the paradigm which could be refined, i.e. the ,rough' edges of the conservation genetics paradigm. 4Treating population size and isolation not as interchangeable parameters but as separate parameters affecting population genetics in different ways could allow more accurate predictions of the effects of landscape fragmentation on the genetic diversity and viability of populations. 5There is evidence that inbreeding depression may be a genotype-specific phenomenon, rather than a population parameter. This sheds new light on the link between population inbreeding depression and the expected increased probability of extinction. 6Modern eco-genomics offers the opportunity to study the population genetics of functional genes, to the extent that the role of selection can be distinguished from the effects of drift, and allowing improved insights into the effects of loss of genetic diversity on evolutionary potential. 7Incorporating multispecies considerations may result in the generally accepted notion that small populations are at peril being called into question. For instance, small populations may be less capable of sustaining parasites or herbivores. 8Comparative studies of endangered, common and invasive species may be a valuable approach to developing conservation biology from a phenomenological case study discipline into one investigating the general principles of what sustains biodiversity. 9The issues discussed set an agenda for further research within conservation genetics and may lead to a further refinement of our understanding and prediction of the genetic effects of habitat fragmentation. They also underline the need to integrate ecological and genetic approaches to the conservation of biodiversity, rather than regarding them as opposites. [source] Reduced fecundity and offspring performance in small populations of the declining grassland plants Primula veris and Gentiana luteaJOURNAL OF ECOLOGY, Issue 1 2000Marc Kéry Summary 1,We studied reproduction and offspring performance in relation to population size in the declining self-incompatible perennials Primula veris and Gentiana lutea. In both species, reproduction was strongly reduced in small populations, where plants produced fewer seeds per fruit and per plant. Total seed mass per plant was higher in large populations, but individual seeds were smaller, indicating a trade-off between seed number and size. Reproduction was depressed most strongly in populations consisting of less than c. 200 (P. veris) and c. 500 plants (G. lutea), respectively. 2,The inclusion of plant size (an integrated measure of habitat quality) in the statistical models did not change the relationships between fecundity and population size. Pollen limitation or inbreeding depression in small populations are therefore more likely explanations for these patterns than is habitat quality. 3,Germination rate and survival of seedlings in a common environment was not related to population size in either species, although P. veris developed into larger rosettes when seeds were derived from large populations. This suggests that inbreeding depression occurs in small populations of P. veris. 4,In a factorial fertilizer-by-competition experiment with P. veris, offspring from larger populations grew significantly larger and responded more strongly to fertilizer. For this declining species genetic deterioration as a result of habitat fragmentation may therefore aggravate the effects of environmental changes such as habitat eutrophication. 5,Our results suggest that small populations may face an increased short-term risk of extinction because of reduced reproduction, and an increased long-term risk because they are less able to respond to environmental changes. [source] Experimental infection magnifies inbreeding depression in house miceJOURNAL OF EVOLUTIONARY BIOLOGY, Issue 3 2008P. ILMONEN Abstract It is often assumed that inbreeding reduces resistance to pathogens, yet there are few experimental tests of this idea in vertebrates, and no tests for the effects of moderate levels of inbreeding more commonly found in nature. We mated wild-derived mice with siblings or first cousins and compared the resistance of their offspring to Salmonella infection with outbred controls under laboratory and seminatural conditions. In the laboratory, full-sib inbreeding reduced resistance to Salmonella and survivorship, whereas first-cousin inbreeding had no detectable effects. In competitive population enclosures, we found that first-cousin inbreeding reduced male fitness by 57% in infected vs. only 34% in noninfected control populations. Our study provides experimental evidence that inbreeding reduces resistance and ability to survive pathogenic infection, and moreover, it shows that even moderate inbreeding can cause significant fitness declines under naturalistic conditions of social stress, and especially with exposure to infectious agents. [source] The evolution of self-fertilization and inbreeding depression under pollen discounting and pollen limitationJOURNAL OF EVOLUTIONARY BIOLOGY, Issue 3 2005E. PORCHER Abstract We model the evolution of plant mating systems under the joint effects of pollen discounting and pollen limitation, using a dynamic model of inbreeding depression, allowing for partial purging of recessive lethal mutations by selfing. Stable mixed mating systems occur for a wide range of parameter values with pollen discounting alone. However, when typical levels of pollen limitation are combined with pollen discounting, stable selfing rates are always high but less than 1 (0.9 < s < 1 in most cases); in this situation, complete selfing does not evolve because pollen discounting becomes very large at high selfing rates, so that the automatic advantage of selfing changes to a disadvantage. These results suggest that mixed mating systems with high selfing rates can be maintained by selection, whereas mixed mating systems with low to moderate selfing rates are more likely attributable to unavoidable geitonogamous selfing. [source] Synergistic epistasis and alternative hypothesesJOURNAL OF EVOLUTIONARY BIOLOGY, Issue 6 2004S. Trouve Abstract Inbreeding generally results in deleterious shifts in mean fitness. If the fitness response to increasing inbreeding coefficient is non-linear, this suggests a contribution of epistasis to inbreeding depression. In a cross-breeding experiment, Salathé & Ebert (2003. J. Evol. Biol. 16: 976,985) tested and found the presence of this non-linearity in Daphnia magna. They argue that epistatic interactions cause this non-linearity. We argue here that their experimental protocol does not allow disentangling the effect of synergistic epistasis from two alternative hypotheses, namely hybrid vigour and statistical non-independence of data. [source] | |||||||||||||||||||||||||||||||