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Divergent Selection (divergent + selection)
Selected AbstractsTEMPORAL VARIATION IN DIVERGENT SELECTION ON SPINE NUMBER IN THREESPINE STICKLEBACKEVOLUTION, Issue 12 2002T. E. Reimchen Abstract., Short-term temporal cycles in ecological pressures, such as shifts in predation regime, are widespread in nature yet estimates of temporal variation in the direction and intensity of natural selection are few. Previous work on threespine stickleback (Gasterosteus aculeatus) has revealed that dorsal and pelvic spines are a defense against gape-limited predators but may be detrimental against grappling insect predators. In this study, we examined a 15-year database from an endemic population of threespine stickleback to look for evidence of temporal shifts in exposure to these divergent predation regimes and correlated shifts in selection on spine number. For juveniles, we detected selection for increased spine number during winter when gape-limited avian piscivores were most common but selection for decreased spine number during summer when odonate predation was more common. For subadults and adults, which are taken primarily by avian piscivores, we predicted selection should generally be for increased spine number in all seasons. Among 59 comparisons, four selection differentials were significant (Bonferroni corrected) and in the predicted direction. However, there was also substantial variability in remaining differentials, including two examples with strong selection for spine reduction. These reversals were associated with increased tendency of the fish to shift to a benthic niche, as determined from examination of stomach contents. These dietary data suggest that increased encounter rates with odonate predation select for spine reduction. Strong selection on spine number was followed by changes in mean spine number during subsequent years and a standard quantitative genetic formula revealed that spine number has a heritable component. Our results provide evidence of rapid morphological responses to selection from predators and suggest that temporal variation in selection may help maintain variation within populations. Furthermore, our findings indicate that variable selection can be predicted if the agents of selection are known. [source] EVOLUTION ON A LOCAL SCALE: DEVELOPMENTAL, FUNCTIONAL, AND GENETIC BASES OF DIVERGENCE IN BILL FORM AND ASSOCIATED CHANGES IN SONG STRUCTURE BETWEEN ADJACENT HABITATSEVOLUTION, Issue 8 2008Alexander V. Badyaev Divergent selection on traits involved in both local adaptation and the production of mating signals can strongly facilitate population differentiation. Because of its links to foraging morphologies and cultural inheritance song of birds can contribute particularly strongly to maintenance of local adaptations. In two adjacent habitats,native Sonoran desert and urban areas,house finches (Carpodacus mexicanus) forage on seeds that are highly distinct in size and shell hardness and require different bite forces and bill morphologies. Here, we first document strong and habitat-specific natural selection on bill traits linked to bite force and find adaptive modifications of bite force and bill morphology and associated divergence in courtship song between the two habitats. Second, we investigate the developmental basis of this divergence and find that early ontogenetic tissue transformation in bill, but not skeletal traits, is accelerated in the urban population and that the mandibular primordia of the large-beaked urban finches express bone morphogenetic proteins (BMP) earlier and at higher level than those of the desert finches. Further, we show that despite being geographically adjacent, urban and desert populations are nevertheless genetically distinct corroborating findings of early developmental divergence between them. Taken together, these results suggest that divergent selection on function and development of traits involved in production of mating signals, in combination with localized learning of such signals, can be very effective at maintaining local adaptations, even at small spatial scales and in highly mobile animals. [source] Serum insulin-like growth factor-1 concentration in pigs divergently selected for daily food intake or lean growth rateJOURNAL OF ANIMAL BREEDING AND GENETICS, Issue 4 2003N. D. Cameron Summary Divergent selection over seven generations for daily food intake (DFI) and for two lean growth rate (LGA and LGS) selection objectives in pigs produced correlated responses in serum insulin-like growth factor-1 (IGF-1) concentration. The LGA and LGS selection objectives were for lean growth, but with performance testing on ad libitum (LGA) or on restricted (LGS) feeding regimes. There were 342 animals in the study, with an average of 46 pigs in each selection line and 72 pigs in the control line. All animals were performance-tested from 30 to 90 kg on an ad libitum feeding regime. Selection on DFI increased IGF-1 at 6 weeks of age (158 versus 104 ,g/l, SED 21; control 136 ,g/l) and selection for high LGA increased IGF-1 at 30 kg liveweight (202 versus 161 ,g/l, SED 14; control 185 ,g/l). At 6 weeks of age and at 30 kg of weight, there was no response in IGF-1 with selection on LGS (128 versus 129 and 167 versus 153 ,g/l, respectively) suggesting that IGF-1 may not be a reliable physiological predictor of genetic merit for such a selection objective, which combined rate and efficiency of lean growth. IGF-1 measured immediately prior to the start of performance test may be useful in determining which animals to performance test for a lean growth selection objective, whereas IGF-1 measured at 6 weeks of age may be a useful physiological predictor of genetic merit for daily food intake during performance test. Zusammenfassung Serumkonzentrationen des insulinähnlichen Wachstumsfaktors-1 bei Schweinen, die entweder auf tägliche Futteraufnahme oder auf hohe Wachstumsrate für Magerfleischanteil selektiert wurden Die Selektion von Schweinen über sieben Generationen einerseits auf tägliche Futteraufnahme (DFI) und andererseits auf zwei Wachstumsraten für Magerfleischanteil (LGA, ad-libitum -Fütterung; LGS, rationierte Fütterung) ergab korrelierende Konzentrationen am insulinähnlichen Wachstumsfaktor (IGF-1). An der Studie waren 342 Tiere mit einer durchschnittlichen Tierzahl von 46 Schweinen pro Selektionsgruppe und 72 Schweinen als Kontrollgruppe beteiligt. Alle Tiere wurden zwischen 30 und 90 kg bei der ad-libitum Fütterung leistungsgeprüft. Die Selektion auf tägliche Futteraufnahme (DFI) erhöhte die IGF-1 Konzentrationen in der 6. Lebenswoche von 104 ,g/l auf 158 ,g/l (Kontrollgruppe 136 ,g/l) und die Selektion auf LGA bei der ad-libitum -Fütterung bei einem Lebendgewicht von 30 kg von 161 ,g/l auf 202 ,g/l (Kontrollgruppe 185 ,g/l). In der 6. Lebenswoche und bei 30 kg Lebendgewicht gab es keinen Anstieg der IGF-1 Konzentrationen in der Selektionsgruppe LGS mit rationierter Fütterung (128 ,g/l bzw. 129 ,fg/l in der 6. Lebenswoche; 167 ,g/l bzw. 153 ,g/l bei 30 kg),was darauf hinweisen könnte, dass IGF-1 wahrscheinlich kein verlässlicher, physiologischer Marker für den genetischen Erfolg für ein solches Selektionsziel, welches die Wachstumsrate und die Effizienz beim Magerfleischwachstum kombiniert, darstellt. Die direkt vor Prüfungsbeginn ermittelten IGF-1 Konzentrationen könnten bei der Auswahl der Tiere, die an einer Leistungsprüfung für die Wachstumsrate des Magerfleischanteils als Selektionsziel herangezogen werden sollten, hilfreich sein. Die IGF-1 Konzentrationen, die in der 6. Lebenswoche gemessen werden, sind wahrscheinlich ein hilfreicher physiologischer Marker für den genetischen Erfolg für DFI während einer Leistungsprüfung. [source] Spatially structured genetic variation in a broadcast spawning bivalve: quantitative vs. molecular traitsJOURNAL OF EVOLUTIONARY BIOLOGY, Issue 2 2003P. C. Luttikhuizen Abstract Understanding the origin, maintenance and significance of phenotypic variation is one of the central issues in evolutionary biology. An ongoing discussion focuses on the relative roles of isolation and selection as being at the heart of genetically based spatial variation. We address this issue in a representative of a taxon group in which isolation is unlikely: a marine broadcast spawning invertebrate. During the free-swimming larval phase, dispersal is potentially very large. For such taxa, small-scale population genetic structuring in neutral molecular markers tends to be limited, conform expectations. Small-scale differentiation of selective traits is expected to be hindered by the putatively high gene flow. We determined the geographical distribution of molecular markers and of variation in a shell shape measure, globosity, for the bivalve Macoma balthica (L.) in the western Dutch Wadden Sea and adjacent North Sea in three subsequent years, and found that shells of this clam are more globose in the Wadden Sea. By rearing clams in a common garden in the laboratory starting from the gamete phase, we show that the ecotypes are genetically different; heritability is estimated at 23%. The proportion of total genetic variation that is between sites is much larger for the morphological additive genetic variation (QST = 0.416) than for allozyme (FST = 0.000,0.022) and mitochondrial DNA cytochrome- c -oxidase-1 sequence variation (,ST = 0.017). Divergent selection must be involved and intraspecific spatial genetic differentiation in marine broadcast spawners is apparently not constrained by low levels of isolation. [source] Divergent selection and realized heritability for growth in the Japanese scallop, Patinopecten yessoensis JayAQUACULTURE RESEARCH, Issue 9 2010Jun Liang Abstract In order to improve the production and accurately estimate response to selection, divergent selection for growth in shell height was conducted in a cultured population of the Japanese scallop Patinopecten yessoensis. Applying the same selection intensity ± 1.756 in upward and downward directions, three groups including two selected groups of Fast and Slow and one non-selected Control group were created, which were reared under the same environmental conditions at any stage. Differences always significantly existed among the three groups (P<0.05), except for larvae at day 1 and at day 5, and in the order of Fast>Control>Slow. The average standardized response to selection (SR), realized heritability (hR2) and genetic gain (GG) was 0.473%, 0.269% and 7.85% for the Fast group and 0.381%, 0.217% and 6.60% for the Slow group respectively. Moreover, significant differences (P<0.05) were detected between the fast and the slow lines in both SR and hR2, providing evidence for an asymmetric response in two directions. Performance in shell height is improved by 7.85% in the fast line after one generation selection, suggesting that mass selection for faster growth in a cultured population of the Japanese scallop is effective. [source] Divergent selection for shell length in two stocks of small abalone Haliotis diversicolorAQUACULTURE RESEARCH, Issue 6 2010Wei-Wei You Abstract To determine whether genetic improvement can be attained through a selective breeding programme, divergent selection for shell length was applied to two stocks of Haliotis diversicolor. Stock A was descended from the cross between males from a Japanese wild population and females from a Taiwan aquacultured population and Stock B was from the Taiwan cultured population, which had been successively cultured in mainland China for about 10 generations. The 10% largest and 10% smallest abalones for each of these two stocks were selected as parents for the large-selected and small-selected lines respectively. Equal numbers of abalone were randomly chosen from the two stocks to serve as parents for the control lines before the selection. The selected and control lines were reared under the same conditions at early juvenile, later juvenile and grow-out stages. Stock A showed a significantly higher response to selection and realized heritability than Stock B (P<0.01). The large-selected line of Stock A and Stock B grew 12.79% and 4.58% faster than their control lines on shell length respectively. The average realized heritability for shell length was 0.441±0.064 for Stock A and 0.113±0.013 for Stock B. Responses to selection were different at different ages in each stock and the body weights of the selected lines were significantly different from the control lines in both stocks at the grow-out stage. Asymmetric responses to selection in the two directions were also observed in both stocks. Differences in response to selection and realized heritability between the two stocks are presumably due to genetic variability. [source] Letter to the editor: Chronicle for an orphan trait: Comment on Hofer, Shair, Masmela, & Brunelli, "Developmental effects of selective breeding for an infantile trait: The rat pup ultrasonic isolation call"DEVELOPMENTAL PSYCHOBIOLOGY, Issue 4 2001Pierre L. Roubertoux Abstract Hofer, Brunelli, Shair, and Masmela (2001) examined several behavioral and physiological measures in low, high, and unselected lines obtained from a divergent selection for ultrasound production (USP) in young rats. Although the response to selection was clear-cut, few correlated responses appeared. This surprising result could be explained by two reasons. USP has polygenic correlates in this population, and most of the chromosomal regions that are linked with these measures only contribute to a small part of the genetic variance. Therefore, correlated responses to selection might exist, but the common genetic variance between the trait under selection and the indirectly selected trait is too small to be detected by a selective breeding strategy. © 2001 John Wiley & Sons, Inc. Dev Psychobiol 39: 251,254, 2001.. [source] Genetic divergence and ecological specialisation of seed weevils (Exapion spp.) on gorses (Ulex spp.)ECOLOGICAL ENTOMOLOGY, Issue 3 2008MYRIAM BARAT Abstract 1.,Reproductive isolation of sympatric populations may result from divergent selection of populations in different environments, and lead to ecological specialisation. In Brittany (France), the gorse Ulex europaeus (Fabaceae, Genisteae), may be encountered in sympatry with one of the two other gorse species present: U. gallii and U. minor. A recent study based on morphological identification of seed predators of gorse has shown that two weevil species (Curculionoidea, Apionidae) infest gorse pods at different seasons and have different host ranges: Exapion ulicis infests U. europaeus in spring, whereas E. lemovicinum infests U. gallii and U. minor in autumn. Weevil populations may thus have diverged in sympatry. 2.,As morphological identification of weevils is often difficult and some of the characters used may exhibit individual or environmental variation, mitochondrial and nuclear sequences of weevils collected within pods of the three gorse species in 10 populations of Brittany were used to reconstruct their phylogeny. 3.,The results reveal that species differentiation based on morphological characters is confirmed by the two molecular data sets, showing that E. ulicis and E. lemovicinum are distinct species, and suggesting the absence of host races. Finally, E. ulicis was able to use U. gallii and U. minor pods in spring in some years in some populations, which appeared to depend on the availability of pods present during its reproductive period. 4.,Divergence between E. ulicis and E. lemovicinum may have resulted from temporal isolation of reproductive periods of weevil populations followed by specialisation of insects to host phenology. [source] Divergence in Female Duetting Signals in the Enchenopa binotata Species Complex of Treehoppers (Hemiptera: Membracidae)ETHOLOGY, Issue 12 2006Rafael L. Rodríguez Sexual communication often involves signal exchanges between the sexes, or duetting, in which mate choice is expressed through response signals. With both sexes acting as signalers and receivers, variation in the signals of males and females may be important for mate choice, reproductive isolation, and divergence. In the Enchenopa binotata species complex , a case study of sympatric speciation in which vibrational duetting may have an important role , male signals are species-specific, females choose among males on the basis of signal traits that reflect species and individual differences, and female preferences have exerted divergent selection on male signals. Here, we describe variation in female signals in the E. binotata species complex. We report substantial species differences in the spectral and temporal features of female signals, and in their timing relative to male signals. These differences were similar in range to differences in male signals in the E. binotata complex. We consider processes that might contribute to divergence in female signals, and suggest that signal evolution in the E. binotata complex may be influenced by mate choice in both sexes. [source] RELATIVE CONTRIBUTION OF ADDITIVE, DOMINANCE, AND IMPRINTING EFFECTS TO PHENOTYPIC VARIATION IN BODY SIZE AND GROWTH BETWEEN DIVERGENT SELECTION LINES OF MICEEVOLUTION, Issue 5 2009Reinmar Hager Epigenetic effects attributed to genomic imprinting are increasingly recognized as an important source of variation in quantitative traits. However, little is known about their relative contribution to phenotypic variation compared to those of additive and dominance effects, and almost nothing about their role in phenotypic evolution. Here we address these questions by investigating the relative contribution of additive, dominance, and imprinting effects of quantitative trait loci (QTL) to variation in "early" and "late" body weight in an intercross of mice selected for divergent adult body weight. We identified 18 loci on 13 chromosomes; additive effects accounted for most of the phenotypic variation throughout development, and imprinting effects were always small. Genetic effects on early weight showed more dominance, less additive, and, surprisingly, less imprinting variation than that of late weight. The predominance of additivity of QTL effects on body weight follows the expectation that additive effects account for the evolutionary divergence between selection lines. We hypothesize that the appearance of more imprinting effects on late body weight may be a consequence of divergent selection on adult body weight, which may have indirectly selected for alleles showing partial imprinting effects due to their associated additive effects, highlighting a potential role of genomic imprinting in the response to selection. [source] EVOLUTION ON A LOCAL SCALE: DEVELOPMENTAL, FUNCTIONAL, AND GENETIC BASES OF DIVERGENCE IN BILL FORM AND ASSOCIATED CHANGES IN SONG STRUCTURE BETWEEN ADJACENT HABITATSEVOLUTION, Issue 8 2008Alexander V. Badyaev Divergent selection on traits involved in both local adaptation and the production of mating signals can strongly facilitate population differentiation. Because of its links to foraging morphologies and cultural inheritance song of birds can contribute particularly strongly to maintenance of local adaptations. In two adjacent habitats,native Sonoran desert and urban areas,house finches (Carpodacus mexicanus) forage on seeds that are highly distinct in size and shell hardness and require different bite forces and bill morphologies. Here, we first document strong and habitat-specific natural selection on bill traits linked to bite force and find adaptive modifications of bite force and bill morphology and associated divergence in courtship song between the two habitats. Second, we investigate the developmental basis of this divergence and find that early ontogenetic tissue transformation in bill, but not skeletal traits, is accelerated in the urban population and that the mandibular primordia of the large-beaked urban finches express bone morphogenetic proteins (BMP) earlier and at higher level than those of the desert finches. Further, we show that despite being geographically adjacent, urban and desert populations are nevertheless genetically distinct corroborating findings of early developmental divergence between them. Taken together, these results suggest that divergent selection on function and development of traits involved in production of mating signals, in combination with localized learning of such signals, can be very effective at maintaining local adaptations, even at small spatial scales and in highly mobile animals. [source] THE EVOLUTION OF WING COLOR: MALE MATE CHOICE OPPOSES ADAPTIVE WING COLOR DIVERGENCE IN COLIAS BUTTERFLIESEVOLUTION, Issue 5 2003Jacintha Ellers Abstract Correlated evolution of mate signals and mate preference may be constrained if selection pressures acting on mate preference differ from those acting on mate signals. In particular, opposing selection pressures may act on mate preference and signals when traits have sexual as well as nonsexual functions. In the butterfly Colias philodice eriphyle, divergent selection on wing color across an elevational gradient in response to the thermal environment has led to increasing wing melanization at higher elevations. Wing color is also a long-range signal used by males in mate searching. We conducted experiments to test whether sexual selection on wing melanization via male mate choice acts in the same direction as natural selection on mate signals due to the thermal environment. We performed controlled mate choice experiments in the field over an elevational range of 1500 meters using decoy butterflies with different melanization levels. Also, we obtained a more direct estimate of the relation between wing color and sexual selection by measuring mating success in wild-caught females. Both our experiments showed that wing melanization is an important determinant of female mating success in C. p. eriphyle. However, a lack of elevational variation in male mate preference prevents coevolution of mate signals and mate preference, as males at all elevations prefer less-melanized females. We suggest that this apparently maladaptive mate choice may be maintained by differences in detectability between the morphs or by preservation of species recognition. [source] Genetic description of a divergent selection experiment in Angora rabbits with overlapping generationsJOURNAL OF ANIMAL BREEDING AND GENETICS, Issue 3 2009S.A. Rafat Summary The chief aims of this paper were the following: (i) to describe the demography and genetic structure in two divergent selected lines for total fleece weight (TFW) of French Angora rabbits with overlapping generations; (ii) to describe the effects of inbreeding during an experiment of divergent selection. A study of longevity with the survival kit showed that there was no significant difference in the risk of death or culling between the low line (LL) and high line (HL). A significant effect of inbreeding (p < 0.05) was observed with a 30% higher risk factor in the highest class of inbreeding coefficient compared with the other classes. The means of generation interval were 562 and 601 days in LL and HL, respectively. The numbers of generations for LL and HL were 3.90 and 3.64, respectively. Generation intervals decreased significantly from 1995 to 2000 (p < 0.05). The number of daughters in HL was very variable. The number of animals per generation was higher in HL than in LL. Each buck left nearly three daughters to the next generation (2.52 in LL, 3.24 in HL). In both lines, the effective number of ancestor genomes still present in the genetic pool of the generation was around eight from the reference population of 1995 to that of 2001. Inbreeding in HL was always higher than in LL. The effect of inbreeding was also significant (p < 0.05) on TFW and live weight. The animals with the lowest inbreeding category produced a higher TFW (p < 0.05) than the others. The observed selection differentials were lower than that expected owing to the breeding animal management rules in order to control inbreeding increase. [source] Evidence for selection on coloration in a Panamanian poison frog: a coalescent-based approachJOURNAL OF BIOGEOGRAPHY, Issue 5 2010Jason L. Brown Abstract Aim, The strawberry poison frog, Oophaga pumilio, has undergone a remarkable radiation of colour morphs in the Bocas del Toro archipelago in Panama. This species shows extreme variation in colour and pattern between populations that have been geographically isolated for < 10,000 years. While previous research has suggested the involvement of divergent selection, to date no quantitative test has examined this hypothesis. Location, Bocas del Toro archipelago, Panama. Methods, We use a combination of population genetics, phylogeography and phenotypic analyses to test for divergent selection in coloration in O. pumilio. Tissue samples of 88 individuals from 15 distinct populations were collected. Using these data, we developed a gene tree using the mitochondrial DNA (mtDNA) d-loop region. Using parameters derived from our mtDNA phylogeny, we predicted the coalescence of a hypothetical nuclear gene underlying coloration. We collected spectral reflectance and body size measurements on 94 individuals from four of the populations and performed a quantitative analysis of phenotypic divergence. Results, The mtDNA d-loop tree revealed considerable polyphyly across populations. Coalescent reconstructions of gene trees within population trees revealed incomplete genotypic sorting among populations. The quantitative analysis of phenotypic divergence revealed complete lineage sorting by colour, but not by body size: populations showed non-overlapping variation in spectral reflectance measures of body coloration, while variation in body size did not separate populations. Simulations of the coalescent using parameter values derived from our empirical analyses demonstrated that the level of sorting among populations seen in colour cannot reasonably be attributed to drift. Main conclusions, These results imply that divergence in colour, but not body size, is occurring at a faster rate than expected under neutral processes. Our study provides the first quantitative support for the claim that strong diversifying selection underlies colour variation in the strawberry poison frog. [source] The evolution of host-specific variation in cuckoo eggshell strengthJOURNAL OF EVOLUTIONARY BIOLOGY, Issue 8 2010C. N. SPOTTISWOODE Abstract Cuckoo eggs are renowned for their mimicry of different host species, leading to the evolution of host-specific races (or ,gentes') defined by egg colour and pattern. This study aims to test the prediction that another property of parasitic eggs, namely shell strength, might also have experienced divergent selection within cuckoo species. Host races of the common cuckoo Cuculus canorus encountering stronger host rejection have thicker-shelled eggs than those parasitising less discriminating species, as expected if egg strengthening discourages host rejection. Moreover, in the diederik cuckoo Chrysococcyx caprius, eggshell thickness was correlated across cuckoo gentes and host species, as expected if eggshell strength has been involved in coevolutionary interactions. This is the first report of host-specific differences in cuckoo egg properties other than colour and pattern and lends correlational support to the hypothesis that the strong eggshells of brood parasites are an adaptation to reduce host rejection. [source] Does character displacement initiate speciation?JOURNAL OF EVOLUTIONARY BIOLOGY, Issue 4 2010Evidence of reduced gene flow between populations experiencing divergent selection Abstract Character displacement , trait evolution stemming from selection to lessen resource competition or reproductive interactions between species , has long been regarded as important in finalizing speciation. By contrast, its role in initiating speciation has received less attention. Yet because selection for character displacement should act only where species co-occur, individuals in sympatry will experience a different pattern of selection than conspecifics in allopatry. Such divergent selection might favour reduced gene flow between conspecific populations that have undergone character displacement and those that have not, thereby potentially triggering speciation. Here, we explore these ideas empirically by focusing on spadefoot toads, Spea multiplicata, which have undergone character displacement, and for which character displacement appears to cause post-mating isolation between populations that are in sympatry with a heterospecific and those that are in allopatry. Using mitochondrial sequence data and nuclear microsatellite genotypes, we specifically asked whether gene flow is reduced between populations in different selective environments relative to that between populations in the same selective environment. We found a slight, but statistically significant, reduction in gene flow between selective environments, suggesting that reproductive isolation, and potentially ecological speciation, might indeed evolve as an indirect consequence of character displacement. Generally, character displacement may play a largely underappreciated role in instigating speciation. [source] Local adaptation at the range peripheries of Sitka spruceJOURNAL OF EVOLUTIONARY BIOLOGY, Issue 2 2010M. MIMURA Abstract High-dispersal rates in heterogeneous environments and historical rapid range expansion can hamper local adaptation; however, we often see clinal variation in high-dispersal tree species. To understand the mechanisms of the species' distribution, we investigated local adaptation and adaptive plasticity in a range-wide context in Sitka spruce, a wind-pollinated tree species that has recently expanded its range after glaciations. Phenotypic traits were observed using growth chamber experiments that mimicked temperature and photoperiodic regimes from the limits of the species realized niche. Bud phenology exhibited parallel reaction norms among populations; however, putatively adaptive plasticity and strong divergent selection were seen in bud burst and bud set timing respectively. Natural selection appears to have favoured genotypes that maximize growth rate during available frost-free periods in each environment. We conclude that Sitka spruce has developed local adaptation and adaptive plasticity throughout its range in response to current climatic conditions despite generally high pollen flow and recent range expansion. [source] Host-race formation: promoted by phenology, constrained by heritabilityJOURNAL OF EVOLUTIONARY BIOLOGY, Issue 4 2009A. V. WHIPPLE Abstract Host-race formation is promoted by genetic trade-offs in the ability of herbivores to use alternate hosts, including trade-offs due to differential timing of host-plant availability. We examined the role of phenology in limiting host-plant use in the goldenrod gall fly (Eurosta solidaginis) by determining: (1) whether phenology limits alternate host use, leading to a trade-off that could cause divergent selection on Eurosta emergence time and (2) whether Eurosta has the genetic capacity to respond to such selection in the face of existing environmental variation. Experiments demonstrated that oviposition and gall induction on the alternate host, Solidago canadensis, were the highest on young plants, whereas the highest levels of gall induction on the normal host, Solidago gigantea, occurred on intermediate-age plants. These findings indicate a phenological trade-off for host-plant use that sets up the possibility of divergent selection on emergence time. Heritability, estimated by parent,offspring regression, indicated that host-race formation is impeded by the amount of genetic variation, relative to environmental, for emergence time. [source] Five questions on ecological speciation addressed with individual-based simulationsJOURNAL OF EVOLUTIONARY BIOLOGY, Issue 1 2009X. THIBERT-PLANTE Abstract We use an individual-based simulation model to investigate factors influencing progress toward ecological speciation. We find that environmental differences can quickly lead to the evolution of substantial reproductive barriers between a population colonizing a new environment and the ancestral population in the old environment. Natural selection against immigrants and hybrids was a major contributor to this isolation, but the evolution of sexual preference was also important. Increasing dispersal had both positive and negative effects on population size in the new environment and had positive effects on natural selection against immigrants and hybrids. Genetic divergence at unlinked, neutral genetic markers was low, except when environmental differences were large and sexual preference was present. Our results highlight the importance of divergent selection and adaptive divergence for ecological speciation. At the same time, they reveal several interesting nonlinearities in interactions between environmental differences, sexual preference, dispersal and population size. [source] Migration load in plants: role of pollen and seed dispersal in heterogeneous landscapesJOURNAL OF EVOLUTIONARY BIOLOGY, Issue 1 2008S. LOPEZ Abstract Evolution of local adaptation depends critically on the level of gene flow, which, in plants, can be due to either pollen or seed dispersal. Using analytical predictions and individual-centred simulations, we investigate the specific influence of seed and pollen dispersal on local adaptation in plant populations growing in patchy heterogeneous landscapes. We study the evolution of a polygenic trait subject to stabilizing selection within populations, but divergent selection between populations. Deviations from linkage equilibrium and Hardy,Weinberg equilibrium make different contributions to genotypic variance depending on the dispersal mode. Local genotypic variance, differentiation between populations and genetic load vary with the rate of gene flow but are similar for seed and pollen dispersal, unless the landscape is very heterogeneous. In this case, genetic load is higher in the case of pollen dispersal, which appears to be due to differences in the distribution of genotypic values before selection. [source] Morphological and genetic divergence of intralacustrine stickleback morphs in Iceland: a case for selective differentiation?JOURNAL OF EVOLUTIONARY BIOLOGY, Issue 2 2007G. Á. ÓLAFSDÓTTIR Abstract The evolutionary processes involved in population divergence and local adaptation are poorly understood. Theory predicts that divergence of adjacent populations is possible but depends on several factors including gene flow, divergent selection, population size and the number of genes involved in divergence and their distribution on the genome. We analyse variation in neutral markers, markers linked to putative quantitative trait loci and morphological traits in a recent (< 10 000 years) zone of primary divergence between stickleback morphs in Lake Thingvallavatn, Iceland. Environmental factors, especially predation, are clearly implicated in reducing gene flow between morphs. There is continuous morphological and genetic variation between habitats with a zone centre similar to secondary contact zones. Individual microsatellite loci are implicated as being linked to adaptive variation by direct tests as well as by differences in cline shape. Patterns of linkage disequilibria indicate that the morphs have diverged at several loci. This divergence shows parallels and differences with the well-studied limnetic,benthic stickleback morphs, both in phenotypic divergence and at the genomic level. [source] Adaptive radiation in microbial microcosmsJOURNAL OF EVOLUTIONARY BIOLOGY, Issue 6 2005R. CRAIG MACLEAN Abstract It has often been argued that evolutionary diversification is the result of divergent natural selection for specialization on alternative resources. I provide a comprehensive review of experiments that examine the ecology and genetics of resource specialization and adaptive radiation in microbial microcosms. In these experiments, resource heterogeneity generates divergent selection for specialization on alternative resources. At a molecular level, the evolution of specialization is generally attributable to mutations that de-regulate the expression of existing biosynthetic and catabolic pathways. Trade-offs are associated with the evolution of resource specialization, but these trade-offs are often not the result of antagonistic pleiotropy. Replicate adaptive radiations result in the evolution of a similar assemblage of specialists, but the genetic basis of specialization differs in replicate radiations. The implications of microbial selection experiments for evolutionary theory are discussed and future directions of research are proposed. [source] Laboratory environments are not conducive for allopatric speciationJOURNAL OF EVOLUTIONARY BIOLOGY, Issue 1 2002A.-B. Florin We review published records of laboratory experiments on peripatric and vicariance allopatric speciation to address the following three questions: (1) What was the true effect size of reproductive isolation? (2) Was the reproductive isolation persistent? (3) What influenced the development of isolation? Contrary to popular belief, laboratory evidence for allopatric speciation is quite weak. Assortative mating was only found among derived populations in vicariance experiments. Reproductive isolation against control populations was only intermittent, so there is reason to doubt if some cases showing significant reproductive isolation really should be attributed to speciation. The method of testing was at least as important as the speciation model. Experimental populations tested against each other were the most likely to demonstrate reproductive isolation. This study suggests that allopatric speciation experiments are more likely to yield conclusive results under divergent selection than under drift, and points to the benefits of large populations and many generations. [source] Sexual selection on phenotypic traits in a hybrid zone of Littorina saxatilis (Olivi)JOURNAL OF EVOLUTIONARY BIOLOGY, Issue 5 2001R. Cruz Step clinal transitions in inherited character(s) between genetically distinct populations are usually referred to as hybrid zones. An example is found in the population of the intertidal snail Littorina saxatilis in Galicia (NW Spain). We studied the shape of the overall fitness surface for sexual selection in this hybrid zone, and the position of hybrids and pure morphs on this surface. We found that sexual divergent selection acted on a combination of phenotypic traits separating the pure morphs, and therefore that sexual selection contributed to morph differentiation. The average fitness of hybrids as a group was not significantly different from that of the pure morphs, but they did show divergent sexual selection in some traits. These results are in agreement with a model of divergent selection favouring both the pure morph as well as those hybrids most resembling each morph. The finding of divergent selection is remarkable because quadratic selection gradients are usually weak in nature. [source] Differential Appetite-Related Responses to Central Neuropeptide S in Lines of Chickens Divergently Selected for Low or High Body WeightJOURNAL OF NEUROENDOCRINOLOGY, Issue 7 2008M. A. Cline The anorexigenic 20 amino acid neuropeptide S (NPS) has not been studied in an animal model of hypo- or hyperphagia. The present study aimed to elucidate whether central NPS appetite-related effects are different in lines of chickens that had undergone long-term divergent selection for low (LWS) or high (HWS) body weight and that were hypo- and hyperphagic, respectively. It took a longer time for food intake to be reduced in LWS than HWS chicks administered the lowest dose of NPS tested (0.14 nmol) and, at the highest dose tested (0.56 nmol), they had a greater reduction in food intake than did HWS chicks. HWS chicks responded with a similar magnitude of food intake reduction that was independent of NPS dose. Although water intake was reduced concurrently with food intake after central NPS in both lines, blood glucose concentrations were not affected. Hypothalamic signalling was different between the lines. Although both lines respond to central NPS with decreased c-Fos immunoreactivity in the lateral hypothalamus, the periventricular nucleus had increased c-Fos immunoreactivity in LWS but not HWS chicks. After central NPS treatment, there was increased c-Fos immunoreactivity in the paraventricular nucleus in HWS but not LWS chicks. These data support the notion of differences in the central NPS system between the LWS and HWS lines and infer that central NPS may differentially affect appetite-related processes in other species that contain hypo- and hyperphagic individuals. [source] When can ecological speciation be detected with neutral loci?MOLECULAR ECOLOGY, Issue 11 2010XAVIER THIBERT-PLANTE Abstract It is not yet clear under what conditions empirical studies can reliably detect progress toward ecological speciation through the analysis of allelic variation at neutral loci. We use a simulation approach to investigate the range of parameter space under which such detection is, and is not, likely. We specifically test for the conditions under which divergent natural selection can cause a ,generalized barrier to gene flow' that is present across the genome. Our individual-based numerical simulations focus on how population divergence at neutral loci varies in relation to recombination rate with a selected locus, divergent selection on that locus, migration rate and population size. We specifically test whether genetic differences at neutral markers are greater between populations in different environments than between populations in similar environments. We find that this expected signature of ecological speciation can be detected under part of the parameter space, most consistently when divergent selection is strong and migration is intermediate. By contrast, the expected signature of ecological speciation is not reliably detected when divergent selection is weak or migration is low or high. These findings provide insights into the strengths and weaknesses of using neutral markers to infer ecological speciation in natural systems. [source] Genomic pattern of adaptive divergence in Arabidopsis halleri, a model species for tolerance to heavy metalMOLECULAR ECOLOGY, Issue 9 2009CLAIRE-LISE MEYER Abstract Pollution by heavy metals is one of the strongest environmental constraints in human-altered environments that only a handful of species can cope with. Identifying the genes conferring to those species the ability to grow in polluted areas is a first step towards a global understanding of the evolutionary processes involved and will eventually improve phytoremediation practices. We used a genome-scan approach to detect loci under divergent selection among four populations of Arabidopsis halleri growing on either polluted or nonpolluted habitats. Based on a high density of amplified fragment length polymorphism (AFLP) markers (820 AFLP markers, i.e. ~1 marker per 0.3 Mb), evidence for selection was found for some markers in every sampled population. Four loci departed from neutrality in both metallicolous populations and thus constitute high-quality candidates for general adaptation to pollution. Interestingly, some candidates differed between the two metallicolous populations, suggesting the possibility that different loci may be involved in adaptation in the different metallicolous populations. [source] Site-specific genetic divergence in parallel hybrid zones suggests nonallopatric evolution of reproductive barriersMOLECULAR ECOLOGY, Issue 13 2006M. PANOVA Abstract The evolution of reproductive isolation in the presence of gene flow is supported by theoretical models but rarely by data. Empirical support might be gained from studies of parallel hybrid zones between interbreeding taxa. We analysed gene flow over two hybrid zones separating ecotypes of Littorina saxatilis to test the expectation that neutral genetic markers will show site-specific differences if barriers have evolved in situ. Distinct ecotypes found in contrasting shore habitats are separated by divergent selection and poor dispersal, but hybrid zones appear between them. Swedish islands formed by postglacial uplift 5000 years ago provide opportunities to assess genetic structure in a recently evolved system. Each island houses a discrete population containing subpopulations of different ecotypes. Hybrid zones between ecotypes may be a product of ecological divergence occurring on each island or a consequence of secondary overlap of ecotypes of allopatric origin that have spread among the islands. We used six microsatellite loci to assess gene flow and genetic profiles of hybrid zones on two islands. We found reduced gene flow over both hybrid zones, indicating the presence of local reproductive barriers between ecotypes. Nevertheless, subpopulations of different ecotypes from the same island were genetically more similar to each other than were subpopulations of the same ecotype from different islands. Moreover, neutral genetic traits separating the two ecotypes across hybrid zones were site-specific. This supports a scenario of in situ origin of ecotypes by ecological divergence and nonallopatric evolution of reproductive barriers. [source] Variation at two flowering time genes within and among populations of Arabidopsis thaliana: comparison with markers and traitsMOLECULAR ECOLOGY, Issue 13 2005V. LE CORRE Abstract Flowering Locus C (FLC) and Frigida are two interacting genes controlling flowering time variation in Arabidopsis thaliana. Variation at these genes was surveyed in 12 A. thaliana populations sampled in France. These populations were also screened for variation at molecular markers [12 microsatellites and 19 cleaved amplified polymorphic sequence (CAPS) markers] and at seven quantitative traits measured with and without vernalization. Seven populations were highly polymorphic at markers (HS = 0.57 at microsatellites, 0.24 at CAPS) and showed heritable variation for bolting time and some other traits. Five populations were genetically fixed or nearly fixed. QST for bolting time without vernalization was significantly higher than FST, suggesting local divergent selection. One of the two haplotype groups at FLC (FLCA) was very predominant (frequency of 99%). The first exon of Frigida showed elevated nonsynonymous variation, and nine loss-of-function mutations were found throughout the gene. The association between loss-of-function and earlier bolting was confirmed. Overall, 18 Frigida haplotypes were detected. The pattern of variation at Frigida was largely similar to that found at markers and traits, with the same populations being fixed or highly diverse. Metapopulation dynamics is thus probably the main factor shaping genetic variation in A. thaliana. However, FST for functional (FRI) vs. nonfunctional (FRI,) haplotypes was significantly higher than FST at markers. This suggested that loss-of-function at Frigida is under local selection for flowering time. [source] Does natural selection promote population divergence?MOLECULAR ECOLOGY, Issue 12 2002A comparative analysis of population structure using amplified fragment length polymorphism markers, quantitative traits Abstract Divergent natural selection is considered an important force in plant evolution leading to phenotypic differentiation between populations exploiting different environments. Extending an earlier greenhouse study of population differentiation in the selfing annual plant Senecio vulgaris, we estimated the degree of population divergence in several quantitative traits related to growth and life history and compared these estimates with those based on presumably neutral molecular markers (amplified fragment length polymorphisms; AFLPs). This approach allowed us to disentangle the effects of divergent selection from that of other evolutionary forces (e.g. genetic drift). Five populations were examined from each of two habitat types (ruderal and agricultural habitats). We found a high proportion of total genetic variance to be among populations, both for AFLP markers (,ST = 0.49) and for quantitative traits (range of QST: 0.26,0.77). There was a strong correlation between molecular and quantitative genetic differentiation between pairs of populations (Mantel's r = 0.59). However, estimates of population differentiation in several quantitative traits exceeded the neutral expectation (estimated from AFLP data), suggesting that divergent selection contributed to phenotypic differentiation, especially between populations from ruderal and agricultural habitats. Estimates of within-population variation in AFLP markers and quantitative genetic were poorly correlated, indicating that molecular marker data may be of limited value to predict the evolutionary potential of populations of S. vulgaris. [source] | ||||||||||||||||