Home About us Contact
|
Home About us Contact | ||
|
|
||
Life-history Variation (life-history + variation)
Selected AbstractsPHYLOGENETIC COMPARATIVE ANALYSIS OF LIFE-HISTORY VARIATION AMONG POPULATIONS OF THE LIZARD SCELOPORUS UNDULATUS:AN EXAMPLE AND PROGNOSISEVOLUTION, Issue 3 2004Peter H. Niewiarowski Abstract Over the past 15 years, phylogenetic comparative methods (PCMs) have become standard in the study of life-history evolution. To date, most studies have focused on variation among species or higher taxonomic levels, generally revealing the presence of significant phylogenetic effects as well as residual variation potentially attributable to adaptive evolution. Recently, population-level phylogenetic hypotheses have become available for many species, making it possible to apply PCMs directly to the level at which experiments are typically used to test adaptive hypotheses. In this study, we present the results of PCMs applied to life-history variation among populations of the widespread and well-studied lizard Sceloporus undulatus. Using S. undulatus (which may represent four closely related species) as an example, we explore the benefits of using PCMs at the population level, as well as consider the importance of several thorny methodological problems including but not limited to nonindependence of populations, lack of sufficient variation in traits, and the typically small sample sizes dictated by the difficulty of collecting detailed demographic data. We show that phylogenetic effects on life-history variation among populations of S. undulatus appear to be unimportant, and that several classic trade-offs expected by theory and revealed by many interspecific comparisons are absent. Our results suggest that PCMs applied to variation in life-history traits below the species level may be of limited value, but more studies like ours are needed to draw a general conclusion. Finally, we discuss several outstanding problems that face studies seeking to apply PCMs below the species level. [source] Atlantic salmon Salmo salar L., brown trout Salmo trutta L. and Arctic charr Salvelinus alpinus (L.): a review of aspects of their life historiesECOLOGY OF FRESHWATER FISH, Issue 1 2003A. Klemetsen Abstract ,,,Among the species in the family Salmonidae, those represented by the genera Salmo, Salvelinus, and Oncorhynchus (subfamily Salmoninae) are the most studied. Here, various aspects of phenotypic and life-history variation of Atlantic salmon Salmo salar L., brown trout Salmo trutta L., and Arctic charr Salvelinus alpinus (L.) are reviewed. While many strategies and tactics are commonly used by these species, there are also differences in their ecology and population dynamics that result in a variety of interesting and diverse topics that are challenging for future research. Atlantic salmon display considerable phenotypic plasticity and variability in life-history characters ranging from fully freshwater resident forms, where females can mature at approximately 10 cm in length, to anadromous populations characterised by 3,5 sea-winter (5SW) salmon. Even within simple 1SW populations, 20 or more spawning life-history types can be identified. Juveniles in freshwater can use both fluvial and lacustrine habitats for rearing, and while most smolts migrate to sea during the spring, fall migrations occur in some populations. At sea, some salmon undertake extensive oceanic migrations while other populations stay within the geographical confines of areas such as the Baltic Sea. At the other extreme are those that reside in estuaries and return to freshwater to spawn after spending only a few months at sea. The review of information on the diversity of life-history forms is related to conservation aspects associated with Atlantic salmon populations and current trends in abundance and survival. Brown trout is indigenous to Europe, North Africa and western Asia, but was introduced into at least 24 countries outside Europe and now has a world-wide distribution. It exploits both fresh and salt waters for feeding and spawning (brackish), and populations are often partially migratory. One part of the population leaves and feeds elsewhere, while another part stays as residents. In large, complex systems, the species is polymorphic with different size morphs in the various parts of the habitat. Brown trout feed close to the surface and near shore, but large individuals may move far offshore. The species exhibits ontogenetic niche shifts partly related to size and partly to developmental rate. They switch when the amount of surplus energy available for growth becomes small with fast growers being younger and smaller fish than slow growers. Brown trout is an opportunistic carnivore, but individuals specialise at least temporarily on particular food items; insect larvae are important for the young in streams, while littoral epibenthos in lakes and fish are most important for large trout. The sexes differ in resource use and size. Females are more inclined than males to become migratory and feed in pelagic waters. Males exploit running water, near-shore and surface waters more than females. Therefore, females feed more on zooplankton and exhibit a more uniform phenotype than males. The Arctic charr is the northernmost freshwater fish on earth, with a circumpolar distribution in the Holarctic that matches the last glaciation. Recent mtDNA studies indicate that there are five phylogeographic lineages (Atlantic, Arctic, Bering, Siberian and Acadian) that may be of Pleistocene origin. Phenotypic expression and ecology are more variable in charr than in most fish. Weights at maturation range from 3 g to 12 kg. Population differences in morphology and coloration are large and can have some genetic basis. Charr live in streams, at sea and in all habitats of oligotrophic lakes, including very deep areas. Ontogenetic habitat shifts between lacustrine habitats are common. The charr feed on all major prey types of streams, lakes and near-shore marine habitats, but has high niche flexibility in competition. Cannibalism is expressed in several cases, and can be important for developing and maintaining bimodal size distributions. Anadromy is found in the northern part of its range and involves about 40, but sometimes more days in the sea. All charr overwinter in freshwater. Partial migration is common, but the degree of anadromy varies greatly among populations. The food at sea includes zooplankton and pelagic fish, but also epibenthos. Polymorphism and sympatric morphs are much studied. As a prominent fish of glaciated lakes, charr is an important species for studying ecological speciation by the combination of field studies and experiments, particularly in the fields of morphometric heterochrony and comparative behaviour. [source] PHYLOGENETIC COMPARATIVE ANALYSIS OF LIFE-HISTORY VARIATION AMONG POPULATIONS OF THE LIZARD SCELOPORUS UNDULATUS:AN EXAMPLE AND PROGNOSISEVOLUTION, Issue 3 2004Peter H. Niewiarowski Abstract Over the past 15 years, phylogenetic comparative methods (PCMs) have become standard in the study of life-history evolution. To date, most studies have focused on variation among species or higher taxonomic levels, generally revealing the presence of significant phylogenetic effects as well as residual variation potentially attributable to adaptive evolution. Recently, population-level phylogenetic hypotheses have become available for many species, making it possible to apply PCMs directly to the level at which experiments are typically used to test adaptive hypotheses. In this study, we present the results of PCMs applied to life-history variation among populations of the widespread and well-studied lizard Sceloporus undulatus. Using S. undulatus (which may represent four closely related species) as an example, we explore the benefits of using PCMs at the population level, as well as consider the importance of several thorny methodological problems including but not limited to nonindependence of populations, lack of sufficient variation in traits, and the typically small sample sizes dictated by the difficulty of collecting detailed demographic data. We show that phylogenetic effects on life-history variation among populations of S. undulatus appear to be unimportant, and that several classic trade-offs expected by theory and revealed by many interspecific comparisons are absent. Our results suggest that PCMs applied to variation in life-history traits below the species level may be of limited value, but more studies like ours are needed to draw a general conclusion. Finally, we discuss several outstanding problems that face studies seeking to apply PCMs below the species level. [source] Reproductive modes in lizards: measuring fitness consequences of the duration of uterine retention of eggsFUNCTIONAL ECOLOGY, Issue 2 2008R. S. Radder Summary 1One of the primary axes of life-history variation involves the proportion of embryonic development for which the offspring is retained within its parent's body; understanding trade-offs associated with prolonging that period thus is a critical challenge for evolutionary ecology. 2Prior to oviposition, most oviparous squamate reptiles retain developing eggs in utero for about one-third of embryogenesis; the strong conservatism in this trait is a major puzzle in reptilian reproduction. To clarify fitness consequences of this prolonged uterine retention, we need to experimentally modify the trait and examine the effects of our manipulation. 3We used transdermal application of corticosterone to induce gravid scincid lizards (Bassiana duperreyi) to lay their eggs ,prematurely', with relatively undeveloped embryos. Corticosterone application induced females to oviposit sooner (mean of 5·41 ± 0·51 days post-treatment) at earlier embryonic developmental stage (27 ± 0·21) than did controls (13·2 ± 1·22 days; embryonic stage 30·4 ± 0·16). 4Corticosterone levels in the egg yolk were unaffected by maternal treatment, so effects of earlier oviposition should not be confounded by endocrine disruption of embryogenesis. Nonetheless, early oviposition reduced hatchling fitness. Hatching success was lower, incubation periods post-laying were increased, and neonates from eggs laid at earlier embryonic stages were smaller and slower. 5These results suggest that retention of developing eggs in utero by oviparous squamates enhances maternal fitness, and does so via modifications to offspring phenotypes rather than (for example) due to accelerated developmental rates of eggs in utero compared to in the nest. 6More generally, our data support optimality models that interpret interspecific variation in the duration of maternal,offspring contact in terms of the selective forces that result from earlier vs. later termination of that maternal investment. [source] Testing the abundant-centre hypothesis using intertidal porcelain crabs along the Chilean coast: linking abundance and life-history variationJOURNAL OF BIOGEOGRAPHY, Issue 3 2010Marcelo M. Rivadeneira Abstract Aim, The abundant-centre hypothesis (ACH) is based on the assumption that physiological constraints limit populations at the edges of their distributional range, yet the geographical variation of physiological performance or life-history traits has rarely been examined. Here we examine the applicability of the ACH in a marine system by testing whether physiological predictions are reflected in large-scale variations of life-history traits. Location, The Chilean coast (18°,42° S), encompassing more than 2500 km along the Pacific coast of South America. Methods, Five porcelain crab species (Petrolisthes granulosus, Petrolisthes laevigatus, Petrolisthes tuberculatus, Petrolisthes violaceus and Allopetrolisthes angulosus) were sampled on intertidal boulder beaches at 13 sampling sites. For each species and site we evaluated: (1) relative abundance (density), (2) maximum size, (3) size at maturity, (4) sex ratio, (5) proportion of ovigerous females, and (6) presence of recruits. The shape of the spatial distribution of each trait was evaluated statistically against the prediction of four hypothetical models (normal, ramped-south, ramped-north and abundant-edge). Results, The relative abundance and life-history traits showed different spatial patterns among species. Relative abundance (across sites) was fitted by a normal model in only two species. No model fitted the spatial variation in body size and size at first maturity, which showed a slight but monotonic poleward increase in all species. Sex ratio showed a prominent hump-shaped pattern, with females prevailing in the centre of the ranges and males dominating towards the range boundaries; this pattern was statistically significant in three of the five studied species. The proportion of ovigerous females showed no clear latitudinal trends, and mature individuals were observed across most of the geographical range of the species. However, recruits tended to be absent towards the southern (poleward) boundaries of the distribution. Main conclusions, The ACH does not apply to all species equally. The link between abundance and life-history traits is complex and variable among the porcelain crab species studied. Overall, the observed patterns were consistent with the idea that equatorward boundaries might be controlled by physiological restrictions mainly affecting adult survival, whereas poleward boundaries might be shaped by limitations in reproductive output and larval survival. Our results underline the importance of incorporating ecological, physiological and life-history studies in future tests of the ACH. [source] Development and characterization of 14 polymorphic microsatellite loci in the raccoon tick (Ixodes texanus)MOLECULAR ECOLOGY RESOURCES, Issue 1 2009GUHA DHARMARAJAN Abstract Fourteen polymorphic microsatellite loci were developed for the raccoon tick (Ixodes texanus). Three multiplexed panels comprising the loci were developed and 50 ticks collected from two infected raccoons (Procyon lotor) were genotyped. The number of alleles per locus ranged from five to 22, and single locus heterozygosities ranged from 0.46 to 0.94. Future research will further our understanding of I. texanus biology and help in elucidating the effects of life-history variation on parasite population genetic structure, using I. texanus as a model organism. [source] Genetic variation in the life-history traits of Epiphyas postvittana: population structure and local adaptationAUSTRAL ECOLOGY, Issue 4 2000Hainan Gu Abstract The light brown apple moth, Epiphyas postvittana (Walker) shows high intraspecific variability in morphological, physiological, demographic and behavioural characters. To gain insight into the extent of adaptation and evolutionary changes in response to environmental heterogeneity in this species, quantitative genetic analyses of life-history variation were conducted for two natural populations under two thermal conditions (23°C and 28°C). Paternal half-sib heritability and genetic correlation in six life-history traits (i.e. development time, adult body weight, adult lifespan, age at first reproduction, the number of eggs laid during the first 5 days after emergence, and total fecundity) were compared. Significant heritabilities were shown consistently in development time; this is also true for adult body weight, except for the Canberra population at 23°C. However, neither population differences nor the effect of temperature were statistically detectable for any of these heritabilities, confirming the genetically determined flexibility. Positive genetic correlations between development time and adult body weight, and negative genetic correlations between the number of eggs laid during the first 5 days and adult lifespan were present for these populations at both temperatures, indicating the presence of genetic constraints. Pairwise comparisons of genetic correlations revealed the heterogeneity of the two populations and across temperatures. These results suggest that the structure of genetic covariance might have changed significantly during the divergence of natural populations and in response to the alteration of environmental conditions in E. postvittana. [source] Genetic variation in the life-history traits of Epiphyas postvittana: population structure and local adaptationAUSTRAL ECOLOGY, Issue 4 2000HAINAN GU Abstract The light brown apple moth, Epiphyas postvittana (Walker) shows high intraspecific variability in morphological, physiological, demographic and behavioural characters. To gain insight into the extent of adaptation and evolutionary changes in response to environmental heterogeneity in this species, quantitative genetic analyses of life-history variation were conducted for two natural populations under two thermal conditions (23°C and 28°C). Paternal half-sib heritability and genetic correlation in six life-history traits (i.e. development time, adult body weight, adult lifespan, age at first reproduction, the number of eggs laid during the first 5 days after emergence, and total fecundity) were compared. Significant heritabilities were shown consistently in development time; this is also true for adult body weight, except for the Canberra population at 23°C. However, neither population differences nor the effect of temperature were statistically detectable for any of these heritabilities, confirming the genetically determined flexibility. Positive genetic correlations between development time and adult body weight, and negative genetic correlations between the number of eggs laid during the first 5 days and adult lifespan were present for these populations at both temperatures, indicating the presence of genetic constraints. Pairwise comparisons of genetic correlations revealed the heterogeneity of the two populations and across temperatures. These results suggest that the structure of genetic covariance might have changed significantly during the divergence of natural populations and in response to the alteration of environmental conditions in E. postvittana. [source] Thermal effects on reptile reproduction: adaptation and phenotypic plasticity in a montane lizardBIOLOGICAL JOURNAL OF THE LINNEAN SOCIETY, Issue 3 2010RORY S. TELEMECO Interspecific comparisons suggest a strong association between cool climates and viviparity in reptiles. However, intraspecific comparisons, which provide an opportunity to identify causal pathways and to distinguish facultative (phenotypically plastic) effects from canalized (genetically fixed) responses, are lacking. We documented the reproductive traits in an alpine oviparous lizard, and manipulated thermal regimes of gravid females and their eggs to identify proximate causes of life-history variation. Embryonic development at oviposition was more advanced in eggs laid by females from high-elevation populations than in eggs produced by females from lower elevations. In the laboratory, experimentally imposed low maternal body temperatures delayed oviposition and resulted in more advanced embryonic development at oviposition. Warm conditions both in utero and in the nest increased hatching success and offspring body size. Our intraspecific comparisons support the hypothesis that viviparity has evolved in cold-climate squamates because of the direct fitness advantages that warm temperatures provide developing offspring. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 100, 642,655. [source] Identifying sources of variation in reproductive and life-history traits among five populations of a Chinese lizard (Takydromus septentrionalis, Lacertidae)BIOLOGICAL JOURNAL OF THE LINNEAN SOCIETY, Issue 4 2005WEI-GUO DU Research on life-history traits of squamate reptiles has focused on North American species, while Asian taxa have been virtually ignored. In order to understand general patterns in reptile life histories, we need a broader data base. Our study on the slender-bodied lacertid lizard Takydromus septentrionalis provides the first detailed information on factors responsible for intraspecific variation in reproductive output and life history in a Chinese reptile. Clutches of recently collected lizards from five widely separated localities in China revealed major divergences in female body size at maturation, mean adult female body size, body condition after oviposition, size-adjusted fecundity, relative clutch mass, and mass and shape of eggs. Most of these geographical differences persisted when the same groups of females were maintained in identical conditions in captivity. Additionally, reproductive frequency during maintenance under laboratory conditions differed according to the animals' place of origin. Thus, the extensive geographical variation in reproductive and life-history traits that occurs within T. septentrionalis is exhibited even in long-term captives, suggesting that proximate factors that vary among localities (local conditions of weather and food supply) are less important determinants of life-history variation than are intrinsic (presumably genetic) influences. The maternal abdominal volume available to hold the clutch may be one such factor, based on low levels of variation in Relative Clutch Mass among populations, and geographical variation in the position of trade-off lines linking offspring size to fecundity. © 2005 The Linnean Society of London, Biological Journal of the Linnean Society, 2005, 85, 443,453. [source] | ||||||||||||||||||||||