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Title Date Issued Date Released Description
Data from: The length of adaptive walks is insensitive to starting fitness in Aspergillus nidulans
06-07-2011 11-17-2011
Adaptation involves the successive substitution of beneficial mutations by selection, a process known as an adaptive walk. Gradualist models of adaptation, which assume that all mutations are small relative to the distance to a fitness optimum, predict that adaptive walks should be longer when the founding genotype is less well adapted. More recent work modelling adaptation as a sequence of moves in phenotype or genotype space predicts, by contrast, much shorter adaptive walks irrespective of the fitness of the founding genotype. Here we provide what is, to the best of our knowledge, the first direct test of these alternative models, measuring the length of adaptive walks in evolving lineages of fungus that differ initially in fitness. Contrary to the gradualist view, we show that the length of adaptive walks in the fungus Aspergillus nidulans is insensitive to starting fitness and involves just two mutations on average. This arises because poorly adapted populations tend to fix mutations of larger average effect than those of better-adapted populations. Our results suggest that the length of adaptive walks may be independent of the fitness of the founding genotype and, moreover, that poorly adapted populations can quickly adapt to novel environments.
Data from: A history of phenotypic plasticity accelerates adaptation to a new environment
06-08-2011 05-31-2017
Can a history of phenotypic plasticity increase the rate of adaptation to a new environment? Theory suggests it can through two different mechanisms. Phenotypically plastic organisms can adapt rapidly to new environments through genetic assimilation, or the fluctuating environments that result in phenotypic plasticity can produce evolvable genetic architectures. In this article, I studied a model of a gene regulatory network that determined a phenotypic character in one population selected for phenotypic plasticity and a second population in a constant environment. A history of phenotypic plasticity increased the rate of adaptation in a new environment, but the amount of this increase was dependent on the strength of selection in the original environment. Phenotypic variance in the original environment predicted the adaptive capacity of the trait within, but not between, plastic and non-plastic populations. These results have implications for invasive species, and ecological studies of rapid adaptation.
Data from: Genetic evidence for a Janzen-Connell recruitment pattern in reproductive offspring of Pinus halepensis trees.
07-29-2011 06-01-2017
Effective seed dispersal, combining both dispersal and post-dispersal (establishment) processes, determines population dynamics and colonization ability in plants. According to the Janzen-Connell (JC) model, high mortality near the mother plant shifts the offspring establishment distribution farther away from the mother plant relative to the seed dispersal distribution. Yet, extending this prediction to the distribution of mature (reproductive) offspring remains a challenge for long-living plants. To address this challenge we selected an isolated natural Aleppo pine (Pinus halepensis) population in Mt. Pithulim (Israel), expanded from five ancestor trees in the beginning of the 20th century into ~2000 trees today. Using nine microsatellite markers, we assigned parents to trees established during the early stages of population expansion. To elucidate the effect of the distance from mother plant on post-dispersal survival, we compared the effective seed dispersal kernel, constructed based on the distribution of mother-offspring distances, to the seed dispersal kernel, computed based on simulations of a mechanistic wind dispersal model. We found that the mode of the effective dispersal kernel is shifted farther away than the mode of the seed dispersal kernel, reflecting increased survival with increasing distance from the mother plant. The parentage analysis demonstrated a highly skewed reproductive success and a strong directionality in effective dispersal corresponding to the wind regime. We thus provide the first evidence that JC effects act also on offspring that become reproductive and persisted as adults for many decades, a key requirement in assessing the role of post-dispersal processes in shaping population and community dynamics.
Data from: Levels of clonal mixing in the black bean aphid Aphis fabae, a facultative ant mutualist
07-21-2011 10-02-2015
Aphids are a worldwide pest and an important model in ecology and evolution. Little is known, however, of the genetic structure of their colonies at a microgeographic level. For example, it remains largely unknown whether most species form monoclonal or polyclonal colonies. Here, we present the first detailed study on levels of clonal mixing in a nonsocial facultative ant mutualist, the black bean aphid Aphis fabae. In contrast to the earlier suggestion that colonies of this species are generally monoclonal, we found that across two subspecies of the black bean aphid, A. fabae cirsiiacanthoidis and A. fabae fabae, 32% and 77% of the aphid colonies were in fact polyclonal, consisting of a mix of up to 4 different clones, which resulted in an overall average relatedness within colonies of 0.90 and 0.79 in the two subspecies. Data further show that the average relatedness in A. f. cirsiiacanthoidis remained relatively constant throughout the season, which means that clonal erosion due to clonal selection more or less balanced with the influx of new clones from elsewhere. Nevertheless, relatedness tended to decrease over the lifetime of a given colony, implying that clonal mixing primarily resulted from the joining of preexisting colonies as opposed to via simultaneous host colonisation by several foundresses. Widespread clonal mixing is argued to affect the ecology and evolution of the aphids in various important ways, for example with respect to the costs and benefits of group living, the evolution of dispersal and the interaction with predators as well as with the ant mutualists.
Data from: An exceptionally high nucleotide and haplotype diversity and a signature of positive selection for the eIF4E resistance gene in barley are revealed by allele mining and phylogenetic analyses of natural populations.
08-02-2011 05-31-2017
In barley, the eukaryotic translation initiation factor 4E (eIF4E) gene situated on chromosome 3H is recognised as an important source of resistance to the bymoviruses Barley yellow mosaic virus and Barley mild mosaic virus. In modern barley cultivars two recessive eIF4E alleles, rym4 and rym5, confer different isolate-specific resistances. In this study the sequence of eIF4E was analysed in 1090 barley landraces and non-current cultivars originating from 84 countries. An exceptionally high nucleotide diversity was evident in the coding sequence of eIF4E but not in either the adjacent MCT-1 gene or the sequence related eIF(iso)4E gene situated on chromosome 1H. Surprisingly, all nucleotide polymorphisms detected in the coding sequence of eIF4E resulted in amino acid changes. A total of 47 eIF4E haplotypes were identified and phylogenetic analysis using maximum likelihood provided evidence of strong positive selection acting on this barley gene. The majority of eIF4E haplotypes were found to be specific to distinct geographic regions. Furthermore, the eIF4E haplotype diversity (uh) was found to be considerably higher in East Asia, whereas SNP genotyping identified a comparatively low degree of genome-wide genetic diversity in 16 out of 17 tested accessions (each carrying a different eIF4E haplotype) from this same region. In addition, selection statistic calculations using coalescent simulations showed evidence of non neutral variation for eIF4E in several geographic regions, including East Asia, the region with a long history of the bymovirus-induced yellow mosaic disease. Together these findings suggest eIF4E may play a role in barley adaptation to local habitats.
Data from: Clonal genetic variation in a Wolbachia-infected asexual wasp: horizontal transmission or historical sex?
06-14-2011 06-01-2017
Wolbachia are endocellular bacteria known for manipulating the reproductive systems of many of their invertebrate hosts. Wolbachia are transmitted vertically from mother to offspring. In addition, new infections result from horizontal transmission between different host species. However, to what extent horizontal transmission plays a role in the spread of a new infection through the host population is unknown. Here, we investigate whether horizontal transmission of Wolbachia can explain clonal genetic variation in natural populations of Leptopilina clavipes, a parasitoid wasp infected with a parthenogenesis-inducing Wolbachia. We assessed variance of markers on the nuclear, mitochondrial and Wolbachia genomes. The nuclear and mitochondrial markers displayed significant and congruent variation among thelytokous wasp lineages, showing that multiple lineages have become infected with Wolbachia. The alternative hypothesis in which a single female became infected, the daughters of which mated with males (thus introducing nuclear genetic variance) cannot account for the presence of concordant variance in mtDNA. All Wolbachia markers, including the hypervariable wsp gene, were invariant, suggesting that only a single strain of Wolbachia is involved. These results show that Wolbachia has transferred horizontally to infect multiple female lineages during the early spread through L. clavipes. Remarkably, multiple thelytokous lineages have persisted side-by-side in the field for tens of thousands of generations.
Data from: Temporal variation in genetic diversity and effective population size of Mediterranean and subalpine Arabidopsis thaliana populations
07-25-2011 09-14-2012
Currently there exists a limited knowledge on the extent of temporal variation in population genetic parameters of natural populations. Here we study the extent of temporal variation in population genetics by genotyping 151 genome-wide SNP markers polymorphic in 466 individuals collected from nine populations of the annual plant Arabidopsis thaliana during four years. Populations are located along an altitudinal climatic gradient from Mediterranean to subalpine environments in NE Spain, which has been shown to influence key demographic attributes and life-cycle adaptations. Genetically, A. thaliana populations were more variable across space than over time. Common multilocus genotypes were detected several years in the same population, whereas low-frequency multilocus genotypes appeared only one year. High-elevation populations were genetically poorer and more variable over time than low-elevation populations, which might be caused by a higher overall demographic instability at higher altitudes. Estimated effective population sizes were very low but also showed a significant decreasing trend with increasing altitude, suggesting a deeper impact of genetic drift at high-elevation populations. In comparison with single-year samplings, repeated genotyping over time captured substantially higher amount of genetic variation contained in A. thaliana populations. Furthermore, repeated genotyping of populations provided novel information on the genetic properties of A. thaliana populations and allowed hypothesizing on their underlying mechanisms. Therefore, including temporal genotyping programs into traditional population genetic studies can significantly increase our understanding of the dynamics of natural populations.
Data from: Mechanical reproductive isolation facilitates parallel speciation in western North American scincid lizards
07-28-2011 06-01-2017
Mechanical reproductive barriers have been dismissed as a major driver of animal speciation, yet the extent to which such barriers cause reproductive isolation in most animal groups is largely unknown and rarely tested. In this study, we used hierarchical Bayesian modeling of mate compatibility experiments to show that body size divergence in lizards of the Plestiodon skiltonianus complex contributes to reproductive isolation in at least three ways: males preferably court females that are more similar in size, females reject males that are highly divergent in size, and that the size difference of a male and female in copula constrains the ability to align the genitalia for intromission. We used a predictive model to estimate the contributions of behavioral and mechanical barriers to reproductive isolation between populations with differing degrees of size divergence. This model shows that the mechanical barrier is more important than the behavioral barriers at small and intermediate degrees of size divergence, suggesting that it acts earlier during speciation. As correlated divergence in size and ecology is common in animals, similar constraints imposed by the geometry of the mating posture may apply to a variety of major animal lineages and merit further attention in speciation research.
Data from: Population genomics of wild and laboratory zebrafish (Danio rerio)
09-16-2011 10-25-2011
Understanding a wider range of genotype-phenotype associations can be achieved through ecological and evolutionary studies of traditional laboratory models. Here, we conducted the first large-scale geographic analysis of genetic variation within and among wild zebrafish (Danio rerio) populations occurring in Nepal, India, and Bangladesh and we genetically compared wild populations to several commonly used lab strains. We examined genetic variation at 1,832 polymorphic EST-based SNPs and the cytb mitochondrial gene in 13 wild populations and three lab strains. Natural populations were subdivided into three major mtDNA clades with an average of 5.8% among-clade sequence divergence. SNPs revealed five major evolutionarily and genetically distinct groups with an overall FST of 0.170 (95% CI 0.105 - 0.254). Evolutionarily distinct groups corresponded to discrete geographic regions and appear to reflect isolation in refugia during past climate cycles. We detected 71 significantly divergent outlier loci (3.4 %) and nine loci (0.5%) with significantly low FST values. Valleys of reduced variation of up to 10 Mb in size surrounding divergent outliers were consistent with selective sweeps. The lab strains formed two additional groups that were genetically distinct from all wild populations. An additional subset of outlier loci was consistent with domestication selection within lab strains. Substantial genetic variation that exists in zebrafish as a whole is missing from lab strains that we analyzed. A combination of laboratory and field studies that incorporates genetic variation from divergent wild populations will be essential to understand the full range of genetic influences on phenotypic variation in this species.
Data from: Patterns of intra- and inter-population genetic diversity in Alaskan coho salmon: implications for conservation
07-13-2011 05-31-2017
Little is known about the genetic diversity of coho salmon in Alaska, although this area represents half of the species’ North American range. In this study, nine microsatellite loci were used to genotype 32 putative coho salmon populations from seven regions of Alaska. The primary objectives were to estimate and evaluate the degree and spatial distribution of neutral genetic diversity within and among populations of Alaskan coho salmon. Genetic analysis yielded four results that provide insight into forces influencing genetic diversity in Alaskan coho salmon and have important conservation implications: 1) significant population differentiation was found within each region; 2) the degree of differentiation (FST = 0.099) among populations was as large or larger than that reported for other Pacific salmon species in Alaska; 3) phenetic clustering of populations showed weak geographic concordance; 4) strong genetic isolation by distance was only apparent at the finest geographic scale (within a drainage). These results suggest that coho salmon populations are small relative to populations of other Pacific salmon, and the genetic diversity within and among coho salmon populations is influenced primarily by genetic drift, and not gene flow. Resource management and conservation actions affecting coho salmon in Alaska must recognize that the populations are generally small, isolated, and probably exhibit local adaptation to different spawning and freshwater rearing habitats. These factors justify managing and conserving Alaskan coho salmon at a fine geographic scale.
Data from: Effects of inversions on within- and between-species recombination and divergence
08-09-2011 05-31-2017
Chromosomal inversions disrupt recombination in heterozygotes by both reducing crossing over within inverted regions and increasing it elsewhere in the genome. The reduction of recombination in inverted regions facilitates the maintenance of hybridizing species, as outlined by various models of chromosomal speciation. We present a comprehensive comparison of the effects of inversions on recombination rates and on nucleotide divergence. Within an inversion differentiating Drosophila pseudoobscura and D. persimilis, we detected one double-recombinant among 9739 progeny from F1 hybrids screened, consistent with published double crossover frequencies observed within species. Despite similar rates of exchange within and between species, we found no sequence-based evidence of ongoing gene exchange between species within this inversion, but significant exchange was inferred within species. We also observed greater differentiation at regions near inversion breakpoints between species vs. within species. Moreover, we observed strong ‘interchromosomal effect’ (higher recombination in inversion heterozygotes between species) with up to 9-fold higher recombination rates along collinear segments of chromosome two in hybrids. Further, we observed that regions most susceptible to changes in recombination rates corresponded to regions with lower recombination rates in homokaryotypes. Finally, we showed that interspecies nucleotide divergence is lower in regions with greater increases in recombination rate, potentially resulting from greater interspecies exchange. Overall, we have identified several similarities and differences between inversions segregating within vs. between species in their effects on recombination and divergence. We conclude that these differences are most likely due to lower frequency of heterokaryotypes and to fitness consequences from the accumulation of various incompatibilities between species. Additionally, we have identified possible effects of inversions on interspecies gene exchange that had not been considered previously.
Data from: Using striated tooth marks on bone to predict body size in theropod dinosaurs: a model based on feeding observations of Varanus komodoensis, the Komodo monitor
01-05-2012 08-20-2015
Mesozoic tooth marks on bone surfaces directly link consumers to fossil assemblage formation. Striated tooth marks are believed to form by theropod denticle contact, and attempts have been made to identify theropod consumers by comparing these striations with denticle widths of contemporaneous taxa. The purpose of this study is to test whether ziphodont theropod consumer characteristics may be accurately identified from striated tooth marks on fossil surfaces. There are three major objectives; 1) experimentally produce striated tooth marks and explain how they form; 2) determine whether body size characteristics are reflected in denticle widths; 3) determine whether denticle characters are accurately transcribed onto bone surfaces in the form of striated tooth marks. Controlled feeding trials were conducted with the dental analogue Varanus komodoensis (the Komodo monitor). Goat (Capra hircus) carcasses were introduced to captive, isolated individuals. Striated tooth marks were then identified, and striation width, number, and degree of divergence were recorded for each. Denticle widths and tooth/body size characters were taken from photographs and published accounts of both theropod and V. komodoensis skeletal material, and regressions were compared among and between the two groups. Striated marks tend to be regularly striated with a variable degree of branching, and may co-occur with scores. Striation morphology directly reflects contact between the mesial carina and bone surfaces during the rostral reorientation when defleshing. Denticle width is primarily influenced by tooth size, and correlates well with body size displaying negative allometry in both groups regardless of taxon or position. When compared, striation widths fall within or below the range of denticle widths extrapolated for similar sized V. komodoensis individuals. Striation width is directly influenced by the orientation of the carina during feeding, and may underestimate but cannot overestimate denticle width. Although body size may theoretically be estimated solely by a striated tooth mark under ideal circumstances, many caveats should be considered. These include the influence of negative allometry across taxa and throughout ontogeny, the existence of theropods with extreme denticle widths, and the potential for striations to underestimate denticle widths. This method may be useful under specific circumstances, especially for establishing a lower limit body size for potential consumers.
Data from: The risk and intensity of sperm ejection in female birds
07-19-2011 05-31-2017
The way females utilise the gametes of different males has important consequences for sexual selection, sexual conflict and intersexual coevolution in natural populations. However, patterns of sperm utilisation by females are difficult to demonstrate, and their functional significance remains unclear. Here, we experimentally study sperm ejection in the fowl, Gallus gallus domesticus, where females eject preferentially the sperm of socially subordinate males. We study two measures of sperm ejection: (i) the probability that an ejaculate is ejected ('risk'), and (ii) the proportion of semen ejected ('intensity'), and show that both measures are strongly non-random with respect to characteristics of the ejaculate, the male and the female. Sperm ejection neutralised on average 80% of an ejaculate, and while larger ejaculates suffered a higher ejection risk, smaller ejaculates suffered more intense ejection. After controlling for ejaculate volume, socially subdominant males suffered higher ejection intensity. After controlling for male and ejaculate effects, ejection risk increased and intensity declined as females mated with successive males. Collectively, these results reveal that sperm ejection risk and intensity are at least partly actively caused by female behaviour, and generate independent selective pressures on male and ejaculate phenotypes.
Data from: A new species of marsupial frog (Anura: Hemiphractidae: Gastrotheca) from the Andes of southern Peru
11-10-2011 10-29-2012
Gastrotheca nebulanastes sp. nov. from cloud forests in the upper Kosñipata Valley, Manu National Park, in the Andes of southern Peru is similar to G. excubitor, which inhabits grasslands in higher elevations than the cloud forests. The two species differ in relative lengths of the fingers, skin texture, coloration, and advertisement call. Although the new species has an elevational range of 2000–3300 m, it is most abundant at 2400–2800 m. A phylogenetic analysis of a previously defined clade of Gastrotheca based on a fragment of 16S mitochondrial gene provides strong support that the sister taxon to the new species is G. atympana, a species from farther north in the Cordillera Oriental in Peru.
Data from: Data sharing by scientists: practices and perceptions
06-29-2011 05-31-2017
Background: Scientific research in the 21st century is more data intensive and collaborative than in the past. It is important to study the data practices of researchers –data accessibility, discovery, re-use, preservation and, particularly, data sharing. Data sharing is a valuable part of the scientific method allowing for verification of results and extending research from prior results. Methodology/Principal Findings: A total of 1329 scientists participated in this survey exploring current data sharing practices and perceptions of the barriers and enablers of data sharing. Scientists do not make their data electronically available to others for various reasons, including insufficient time and lack of funding. Most respondents are satisfied with their current processes for the initial and short-term parts of the data or research lifecycle (collecting their research data; searching for, describing or cataloging, analyzing, and short-term storage of their data) but are not satisfied with long-term data preservation. Many organizations do not provide support to their researchers for data management both in the short- and long-term. If certain conditions are met (such as formal citation and sharing reprints) respondents agree they are willing to share their data. There are also significant differences and approaches in data management practices based on primary funding agency, subject discipline, age, work focus, and world region. Conclusions/Significance: Barriers to effective data sharing and preservation are deeply rooted in the practices and culture of the research process as well as the researchers themselves. New mandates for data management plans from NSF and other federal agencies and world-wide attention to the need to share and preserve data could lead to changes. Large scale programs, such as the NSF-sponsored DataNET (including projects like DataONE) will both bring attention and resources to the issue and make it easier for scientists to apply sound data management principles.
n/a 08-19-2011
Data from: Reverse evolution: selection against costly resistance in disease-free microcosm populations of Paramecium caudatum
06-16-2011 12-15-2011
Evolutionary costs of parasite resistance arise if genes conferring resistance reduce fitness in the absence of parasites. Thus, parasite-mediated selection may lead to increased resistance and a correlated decrease in fitness, whereas relaxed parasite-mediated selection may lead to reverse evolution of increased fitness and a correlated decrease in resistance. We tested this idea in experimental populations of the protozoan Paramecium caudatum and the parasitic bacterium Holospora undulata. After 8 years, resistance to infection and asexual reproduction were compared among paramecia from (i) infected populations, (ii) uninfected naive populations and (iii) previously infected, parasite-free (recovered) populations. Paramecia from infected populations were more resistant (+12%), but had lower reproduction (-15%) than naive paramecia, indicating an evolutionary trade-off between resistance and fitness. Recovered populations showed similar reproduction to naive populations; however, resistance of recently (<3 years) recovered populations was similar to paramecia from infected populations, while longer (>3 years) recovered populations were as susceptible as naive populations. This suggests a weak, convex trade-off between resistance and fitness, allowing recovery of fitness, without complete loss of resistance, favouring the maintenance of a generalist strategy of intermediate fitness and resistance. Our results indicate that (co)evolution with parasites can leave a genetic signature in disease-free populations.
Data from: The quantitative genetics of incipient speciation: heritability and genetic correlations of skeletal traits in populations of diverging Favia fragum ecomorphs.
06-16-2011 12-15-2011
Recent speciation events provide potential opportunities to understand the microevolution of reproductive isolation. We used a marker-based approach and a common garden to estimate the additive genetic variation in skeletal traits in a system of two ecomorphs within the coral species Favia fragum: a Tall ecomorph that is a seagrass specialist, and a Short ecomorph that is most abundant on coral reefs. Considering both ecomorphs, we found significant narrow-sense heritability (h²) in a suite of measurements that define corallite architecture, and could partition additive and non-additive variation for some traits. We found positive genetic correlations for homologous height and length measurements among different types of vertical plates (costosepta) within corallites, but negative correlations between height and length within, as well as between costosepta. Within ecomorphs, h² estimates were generally lower, compared to the combined ecomorph analysis. Marker-based estimates of h² were comparable to broad-sense heritability (H) obtained from parent-offspring regressions in a common garden for most traits, and similar genetic co-variance matrices for common garden and wild populations may indicate relatively small G × E interactions. The patterns of additive genetic variation in this system invite hypotheses of divergent selection or genetic drift as potential evolutionary drivers of reproductive isolation.
Data from: Genetic and phenotypic variation across a hybrid zone between ecologically divergent tree squirrels (Tamiasciurus)
07-19-2011 05-31-2017
A hybrid zone along an environmental gradient should contain a clinal pattern of genetic and phenotypic variation. This occurs because divergent selection in the two parental habitats is typically strong enough to overcome the homogenizing effects of gene flow across the environmental transition. We studied hybridization between two parapatric tree squirrels (Tamiasciurus spp.) across a forest gradient over which the two species vary in coloration, cranial morphology, and body size. We sampled 397 individuals at 29 locations across a 600-km transect to seek genetic evidence for hybridization; upon confirming hybridization, we examined levels of genetic admixture in relation to maintenance of phenotypic divergence despite potentially homogenizing gene flow. Applying population assignment analyses to microsatellite data, we found that T. douglasii and T. hudsonicus form two distinct genetic clusters but also hybridize, mostly within transitional forest habitat. Overall, based on this nuclear analysis, 48% of the specimens were characterized as T. douglasii, 9% as hybrids, and 43% as T. hudsonicus. Hybrids appeared to be reproductively viable, as evidenced by the presence of later-generation hybrid genotypes. Observed clines in ecologically important phenotypic traits—fur coloration and cranial morphology—were sharper than the cline of putatively neutral mtDNA, which suggests that divergent selection may maintain phenotypic distinctiveness. The relatively recent divergence of these two species (probably late Pleistocene), apparent lack of pre-zygotic isolating mechanisms, and geographic coincidence of cline centers for both genetic and phenotypic variation suggest that environmental factors play a large role in maintaining the distinctiveness of these two species across the hybrid zone.
Data from: A century of genetic change and metapopulation dynamics in the Galápagos warbler finches (Certhidea)
06-16-2011 11-17-2011
Populations that are connected by immigrants play an important role in evolutionary and conservation biology, yet we have little direct evidence of how such metapopulations change genetically over evolutionary time. We compared historic (1895-1905) to modern (1988-2006) genetic variation in 11 populations of warbler finches at 14 microsatellite loci. Although several lines of evidence suggest that Darwin’s finches may be in decline, we found that the genetic diversity of warbler finches has not generally declined, and broad scale patterns of variation remained similar over time. Contrary to expectations, inferred population sizes have generally increased over time (6-8%) as have immigration rates (8-16%), which may reflect a recent increase in the frequency and intensity of El Niño events. Individual island populations showed significant declines (18-19%) and also substantial gains (18-20%) in allelic richness over time. Changes in genetic diversity were correlated with changes in immigration rates, but did not correspond to population size or human disturbance. These results reflect the expected stabilizing properties of whole metapopulations over time. However, the dramatic and unpredictable changes observed in individual populations during this short time interval suggests that care should be taken when monitoring individual population fragments with snapshots of genetic variation.