Congruent morphological and genetic differentiation as a signature of range expansion in a fragmented landscape

Phenotypic differentiation is often interpreted as a result of local adaptation of individuals to their environment. Here, we investigated the skull morphological differentiation in 11 populations of the white‐footed mouse (Peromyscus leucopus). These populations were sampled in an agricultural landscape in the Montérégie region (Québec, Canada), at the northern edge of the distribution of the white‐footed mouse. We found a strong pattern of phenotypic differentiation matching the genetic structure across these populations. Landscape fragmentation and the presence of geographic barriers, in particular north–south oriented rivers, contribute to this differentiation and modulate the pattern of rapid ongoing northward range expansion of the white‐footed mouse in response to climate warming. We conclude that while large rivers and postglacial recolonization routes have shaped the current pattern of distribution and differentiation of white‐footed mouse populations, further local differentiation is occurring, at the scale of the landscape. We posit that the northern expansion of the white‐footed mouse is achieved through successive independent founder events in a fragmented landscape at the northern range edge of the species. The phenotypic differentiation we observe is thus a result of a number of mechanisms operating at different spatial and temporal scales.     

Social Experience During Development and Female Offspring Aggression in Peromyscus Mice

Cross‐fostering between the highly aggressive, biparental California mouse (Peromyscus californicus) and the less aggressive, less parental white‐footed mouse (P. leucopus) influences female offspring attack latency in California mice, but not in white‐footed mice. Adult female California mice raised by white‐footed mice expressed longer attack latencies in a neutral‐arena test but not in a resident‐intruder test. One social cue that may be used by offspring to develop environmentally appropriate levels of aggression is the type of parental care during development. In California mice, a composite score of maternal behavior was positively associated with neutral‐arena aggression as indicated by decreased attack latency. In both species, paternal nest‐building was positively associated with neutral‐arena aggression and higher maternal retrieval behavior predicted higher offspring resident‐intruder aggression as indicated by decreased attack latency. Together, these results indicate that parental behavior has the potential to shape the development of attack latency in female offspring.     

Evaluating the influence of life‐history characteristics on genetic structure: a comparison of small mammals inhabiting complex agricultural landscapes

Conversion of formerly continuous native habitats into highly fragmented landscapes can lead to numerous negative demographic and genetic impacts on native taxa that ultimately reduce population viability. In response to concerns over biodiversity loss, numerous investigators have proposed that traits such as body size and ecological specialization influence the sensitivity of species to habitat fragmentation. In this study, we examined how differences in body size and ecological specialization of two rodents (eastern chipmunk; Tamias striatus and white‐footed mouse; Peromyscus leucopus) impact their genetic connectivity within the highly fragmented landscape of the Upper Wabash River Basin (UWB), Indiana, and evaluated whether landscape configuration and complexity influenced patterns of genetic structure similarly between these two species. The more specialized chipmunk exhibited dramatically more genetic structure across the UWB than white‐footed mice, with genetic differentiation being correlated with geographic distance, configuration of intervening habitats, and complexity of forested habitats within sampling sites. In contrast, the generalist white‐footed mouse resembled a panmictic population across the UWB, and no landscape factors were found to influence gene flow. Despite the extensive previous work in abundance and occupancy within the UWB, no landscape factor that influenced occupancy or abundance was correlated with genetic differentiation in either species. The difference in predictors of occupancy, abundance, and gene flow suggests that species‐specific responses to fragmentation are scale dependent.     

Sexual imprinting and speciation between two Peromyscus species

Sexual isolation, a reproductive barrier, can prevent interbreeding between diverging populations or species. Sexual isolation can have a clear genetic basis; however, it may also result from learned mate preferences that form via sexual imprinting. Here, we demonstrate that two sympatric species of mice—the white‐footed mouse (Peromyscus leucopus) and its sister species, the cotton mouse (P. gossypinus)—hybridize only rarely in the wild despite co‐occurrence in the same habitat and lack of any measurable intrinsic postzygotic barriers in laboratory crosses. We present evidence that strong conspecific mating preferences in each species result in significant sexual isolation. We find that these preferences are learned in at least one species: P. gossypinus sexually imprints on its parents, but in P. leucopus, additional factors influence mating preferences. Our study demonstrates that sexual imprinting contributes to reproductive isolation that reduces hybridization between otherwise interfertile species, supporting the role for learning in mammalian speciation.     

Mechanical thinning to restore oak savanna promoted predator assemblages of gypsy moth pupae in Michigan

相似文献   

Evaluation of the genetic management of the endangered black‐footed ferret (Mustela nigripes)

Empirical support for the genetic management strategies employed by captive breeding and reintroduction programs is scarce. We evaluated the genetic management plan for the highly endangered black‐footed ferret (Mustela nigripes) developed by the American Zoo and Aquarium Associations (AZA) as a part of the species survival plan (SSP). We contrasted data collected from five microsatellite loci to predictions from a pedigree‐based kinship matrix analysis of the captive black‐footed ferret population. We compared genetic diversity among captive populations managed for continued captive breeding or reintroduction, and among wild‐born individuals from two reintroduced populations. Microsatellite data gave an accurate but only moderately precise estimate of heterozygosity. Genetic diversity was similar in captive populations maintained for breeding and release, and it appears that the recovery program will achieve its goal of maintaining 80% of the genetic diversity of the founder population over 25 years. Wild‐born individuals from reintroduced populations maintained genetic diversity and avoided close inbreeding. We detected small but measurable genetic differentiation between the reintroduced populations. The model of random mating predicted only slightly lower levels of heterozygosity retention compared to the SSP strategy. The random mating strategy may be a viable alternative for managing large, stable, captive populations such as that of the black‐footed ferret. Zoo Biol 22:287–298, 2003. © 2003 Wiley‐Liss, Inc.     

Genetic structure of the white‐footed mouse in the context of the emergence of Lyme disease in southern Québec

The white‐footed mouse (Peromyscus leucopus) has expanded its northern limit into southern Québec over the last few decades. P. leucopus is a great disperser and colonizer and is of particular interest because it is considered a primary reservoir for the spirochete bacterium that causes Lyme disease. There is no current information on the gene flow between mouse populations on the mountains and forest fragments found scattered throughout the Montérégie region in southern Québec, and whether various landscape barriers have an effect on their dispersal. We conducted a population genetics analysis on eleven P. leucopus populations using eleven microsatellite markers and showed that isolation by distance was weak, yet barriers were effective. The agricultural matrix had the least effect on gene flow, whereas highways and main rivers were effective barriers. The abundance of ticks collected from mice varied within the study area. Both ticks and mice were screened for the presence of the spirochete bacterium Borrelia burgdorferi, and we predicted areas of greater risk for Lyme disease. Merging our results with ongoing Lyme disease surveillance programs will help determine the future threat of this disease in Québec, and will contribute toward disease prevention and management strategies throughout fragmented landscapes in southern Canada.     

Population Genetics of Indigenous Quercus robur L. Populations and of Derived Half‐Sib Families has Implications for the Reproductive Management of the Species

Abstract: In the Netherlands indigenous Quercus robur L. populations are rare and have been maintained as patches in ancient woodland. For adequate conservation of these populations, information about genetic variation and population structure is necessary. In order to assess the genetic variation and structure of these populations, microsatellite polymorphisms were studied in two autochthonous populations. These two populations differed slightly for their gene diversity, which was as high as was observed for Q. robur populations in France and Germany. For reforestation purposes there is an interest in the genetic variation of a half‐sib family harvested from one tree. The gene diversity of the two studied half‐sib families ‐ obtained from a forest and an urban area ‐ was similar, but relatively low. This indicates that, for reforestation purposes, seeds should be harvested from many different trees in order to obtain a population with a genetic variation as high as was observed for an autochthonous population.     

The Association Between Male Offspring Aggression and Paternal and Maternal Behavior of Peromyscus Mice

Parents influence offspring aggression through genetic and non‐genetic mechanisms, although the latter are less well understood. To examine potential non‐genetic effects of parents on offspring, we cross‐fostered the highly aggressive and biparental California mouse (Peromyscus californicus) and the less aggressive, less parental white‐footed mouse (Peromyscus leucopus). In‐fostered animals within each species were used as controls. We examined associations between the foster parents’ behavior and aggression of the fostered male offspring in resident–intruder (R–I) and neutral arena aggression tests. When both species and fostering groups were combined, R–I aggression of offspring was positively associated with paternal time spent retrieving pups. In contrast, aggression in a neutral arena was negatively associated with a composite score of maternal behavior. We discuss how our findings regarding paternal retrievals may explain previously reported effects of cross‐fostering on male aggression.     

Human activity and habitat type affect perceived predation risk in urban white‐footed mice (Peromyscus leucopus)

Predation risk is one of the largest costs associated with foraging in small mammals. Small mammals select microhabitat features such as tree and shrub canopy cover, woody debris and vegetative ground cover that can lower the risk of detection from predators and provide greater protection if discovered. Small mammals also increase foraging activity and decrease selection for cover when cloud cover increases and moon illumination is less. Often researchers assume small mammals in urban areas respond to these cues in the same manner as in natural areas, but these cues themselves are altered in urban zones. In this study, we investigated how Amur honeysuckle (Lonicera maackii) and coarse woody debris (CWD) affected giving‐up density (GUD) in white‐footed mice (Peromyscus leucopus). Each of three habitat treatments (open flood channel, the edge and interior of the honeysuckle patch) contained cover treatments with coarse woody debris present or absent. The six treatment combinations were compared to environmental variables (temperature, humidity and illumination) and habitat variables to test their effect on GUD. Peromyscus leucopus foraged to lower densities in areas with CWD present and also under the honeysuckle canopy, using this invasive shrub to decrease predation risk, potentially increasing survivability within this urban park. Increased human presence negatively affected foraging behavior across treatments. Human presence and light pollution significantly influenced P. leucopus, modifying their foraging behavior and demonstrating that both fine‐ and coarse‐scale urban factors can affect small mammals. Foraging increased as humidity increased, particularly under the honeysuckle canopy. Changes in illumination due to moonlight and cloud cover did not affect foraging behavior, suggesting urban light pollution may have altered behavioral responses to changes in light levels. Lonicera maackii seemed to facilitate foraging in P. leucopus, even though it adversely affects the plant community, suggesting that its impact may not be entirely negative.     

Extensive gene flow along the urban–rural gradient in a migratory colonial bird

Urban colonization by wildlife involves a combination of several different mechanisms, including phenotype or genotype sorting, phenotypic plasticity and microevolutionary adaptation. Combination of these processes can produce a rapid phenotypic, but also genetic divergence of urban versus rural populations. Here, we examined the pattern of genetic differentiation between urban and rural populations of a colonial migratory bird, the black‐headed gull Chroicocephalus ridibundus. To this end, we sampled ca 170 individuals from six (two urban and four rural) colonies in northern Poland, and genotyped them at ten microsatellite loci. Our analysis provided evidence for negligible genetic divergence of urban and rural colonies, as assessed with fixation index F_ST and Nei's unbiased genetic distance D (mean pairwise urban‐rural comparisons: F_ST = 0.003 ± 0.001 [SE] and D = 0.012 ± 0.006 [SE]). Bayesian clustering methods provided support for homogeneous genetic structure across all urban and rural populations. Also, we found no support for reduced allelic diversity in urban versus rural colonies. These results stand in a stark contrast to the previous findings on the genetic consequences of urbanization in birds. We hypothesize that this pattern could possibly be attributed to the important life‐history characters of the black‐headed gull, including coloniality, migratoriness, and high dispersal propensity. Our study provides a novel insight into the urban landscape genetics, underlining large variation in the mechanisms of urban colonization and its genetic consequences in wild animal populations.     

Pollen dispersal and genetic variation in an early‐successional forest herb in a peri‐urban forest

In order to conserve forest plant species under the particularly high constraints that represent urban surroundings, it is necessary to identify the key factors for population persistence. This study examined within‐ and between‐population pollen dispersal using fluorescent dye as pollen analogue, and genetic variation and structure using 15 allozyme loci in Centaurium erythraea, an insect‐pollinated, early‐successional forest biennial herb occurring in a peri‐urban forest (Brussels urban zone, Belgium). Dye dispersal showed an exponential decay distribution, with most dye transfers occurring at short distances (<15 m), and only a few long‐distance events (up to 743 m). Flowers of C. erythraea are mainly visited by Syrphids (Diptera) and small bees, which are usually considered as short‐distance pollen dispersers, and occasionally by bumblebees, which are usually longer‐distance pollen dispersers. Small and large dye source populations differed in dye deposition patterns. The populations showed low genetic diversity, high inbreeding coefficients (F_IS) and high genetic differentiation (F_ST), suggesting restricted gene flow, which can be expected for an early‐successional biennial species with a predominantly selfing breeding system and fluctuating population sizes. The positive relationship between recruitment rate and allelic richness and expected heterozygosity, and the absence of significant correlations between genetic variation and population size suggest seedling recruitment from the seed bank, contributing to maintain genetic diversity. Long‐distance dye dispersal events indicate pollinator movements along urban forest path and road verges. These landscape elements might therefore have a potential conservation value by contributing to connectivity of early‐successional species populations located in patchy open habitats.     

Low genetic diversity and local adaptive divergence of Dracaena cambodiana (Liliaceae) populations associated with historical population bottlenecks and natural selection: an endangered long‐lived tree endemic to Hainan Island,China

Historical population bottlenecks and natural selection have important effects on the current genetic diversity and structure of long‐lived trees. Dracaena cambodiana is an endangered, long‐lived tree endemic to Hainan Island, China. Our field investigations showed that only 10 populations remain on Hainan Island and that almost all have been seriously isolated and grow in distinct habitats. A considerable amount of genetic variation at the species level, but little variation at the population level, and a high level of genetic differentiation among the populations with limited gene flow in D. cambodiana were detected using inter‐simple sequence repeat (ISSR) and random amplified polymorphic DNA (RAPD) analyses. No significant correlation was found between genetic diversity and actual population size, as the genetic diversities were similar regardless of population size. The Mantel test revealed that there was no correlation between genetic and geographic distances among the 10 populations. The UPGMA, PCoA and Bayesian analyses showed that local adaptive divergence has occurred among the D. cambodiana populations, which was further supported by habitat‐private fragments. We suggest that the current genetic diversity and population differentiation of D. cambodiana resulted from historical population bottlenecks and natural selection followed by historical isolation. However, the lack of natural regeneration of D. cambodiana indicates that former local adaptations with low genetic diversity may have been genetically weak and are unable to adapt to the current ecological environments.     

Genetic diversity does not explain variation in extra‐pair paternity in multiple populations of a songbird

Many songbirds are socially monogamous but genetically polyandrous, mating with individuals outside their pair bonds. Extra‐pair paternity (EPP) varies within and across species, but reasons for this variation remain unclear. One possible source of variation is population genetic diversity, which has been shown in interspecific meta‐analyses to correlate with EPP but which has limited support from intraspecific tests. Using eight populations of the genetically polyandrous red‐winged blackbird (Agelaius phoeniceus), including an island population, we investigated whether population‐level differences in genetic diversity led to differences in EPP. We first measured genetic diversity over 10 microsatellite loci and found, as predicted, low genetic diversity in the island population. Additional structure analyses with multilocus genotypes and mtDNA showed the island population to be distinct from the continental populations. However, the island population's EPP rate fell in the middle of the continental populations' distribution, whereas the continental populations themselves showed significant variation in EPP. This result suggests that genetic diversity by itself is not a predictor of EPP rate. We discuss reasons for the departure from previous results, including hypotheses for EPP that do not solely implicate female‐driven behaviour.     

Genetic diversity,population structure and sex‐biased dispersal in three co‐evolving species

Genetic diversity and spatial structure of populations are important for antagonistic coevolution. We investigated genetic variation and population structure of three closely related European ant species: the social parasite Harpagoxenus sublaevis and its two host species Leptothorax acervorum and Leptothorax muscorum. We sampled populations in 12 countries and analysed eight microsatellite loci and an mtDNA sequence. We found high levels of genetic variation in all three species, only slightly less variation in the host L. muscorum. Using a newly introduced measure of differentiation (Jost’s D_est ), we detected strong population structuring in all species and less male‐biased dispersal than previously thought. We found no phylogeographic patterns that could give information on post‐glacial colonization routes – northern populations are as variable as more southern populations. We conclude that conditions for Thompson’s geographic mosaic of coevolution are ideal in this system: all three species show ample genetic variation and strong population structure.     

Low genetic diversity and strong but shallow population differentiation suggests genetic homogenization by metapopulation dynamics in a social spider

Mating systems and population dynamics influence genetic diversity and structure. Species that experience inbreeding and limited gene flow are expected to evolve isolated, divergent genetic lineages. Metapopulation dynamics with frequent extinctions and colonizations may, on the other hand, deplete and homogenize genetic variation, if extinction rate is sufficiently high compared to the effect of drift in local demes. We investigated these theoretical predictions empirically in social spiders that are highly inbred. Social spiders show intranest mating, female‐biased sex ratio, and frequent extinction and colonization events, factors that deplete genetic diversity within nests and populations and limit gene flow. We characterized population genetic structure in Stegodyphus sarasinorum, a social spider distributed across the Indian subcontinent. Species‐wide genetic diversity was estimated over approximately 2800 km from Sri Lanka to Himalayas, by sequencing 16 protein‐coding nuclear loci. We found 13 SNPs in 6592 bp (π = 0.00045) indicating low species‐wide nucleotide diversity. Three genetic lineages were strongly differentiated; however, only one fixed difference among them suggests recent divergence. This is consistent with a scenario of metapopulation dynamics that homogenizes genetic diversity across the species' range. Ultimately, low standing genetic variation may hamper a species' ability to track environmental change and render social inbreeding spiders ‘evolutionary dead‐ends’.     

Population size,center–periphery,and seed dispersers’ effects on the genetic diversity and population structure of the Mediterranean relict shrub Cneorum tricoccon

The effect of population size on population genetic diversity and structure has rarely been studied jointly with other factors such as the position of a population within the species’ distribution range or the presence of mutualistic partners influencing dispersal. Understanding these determining factors for genetic variation is critical for conservation of relict plants that are generally suffering from genetic deterioration. Working with 16 populations of the vulnerable relict shrub Cneorum tricoccon throughout the majority of its western Mediterranean distribution range, and using nine polymorphic microsatellite markers, we examined the effects of periphery (peripheral vs. central), population size (large vs. small), and seed disperser (introduced carnivores vs. endemic lizards) on the genetic diversity and population structure of the species. Contrasting genetic variation (H_E: 0.04–0.476) was found across populations. Peripheral populations showed lower genetic diversity, but this was dependent on population size. Large peripheral populations showed high levels of genetic diversity, whereas small central populations were less diverse. Significant isolation by distance was detected, indicating that the effect of long‐distance gene flow is limited relative to that of genetic drift, probably due to high selfing rates (F_IS = 0.155–0.887), restricted pollen flow, and ineffective seed dispersal. Bayesian clustering also supported the strong population differentiation and highly fragmented structure. Contrary to expectations, the type of disperser showed no significant effect on either population genetic diversity or structure. Our results challenge the idea of an effect of periphery per se that can be mainly explained by population size, drawing attention to the need of integrative approaches considering different determinants of genetic variation. Furthermore, the very low genetic diversity observed in several small populations and the strong among‐population differentiation highlight the conservation value of large populations throughout the species’ range, particularly in light of climate change and direct human threats.     

Bioclimatic regions influence genetic structure of four Jordanian Stipa species

Strong environmental gradients can affect the genetic structure of plant populations, but little is known as to whether closely related species respond similarly or idiosyncratically to ecogeographic variation. We analysed the extent to which gradients in temperature and rainfall shape the genetic structure of four Stipa species in four bioclimatic regions in Jordan. Genetic diversity, differentiation and structure of Stipa species were investigated using amplified fragment length polymorphism (AFLP) molecular markers. For each of the four study species, we sampled 120 individuals from ten populations situated in distinct bioclimatic regions and assessed the degree of genetic diversity and genetic differentiation within and among populations. The widespread ruderals Stipa capensis and S. parviflora had higher genetic diversity than the geographically restricted semi‐desert species S. arabica and S. lagascae. In three of the four species, genetic diversity strongly decreased with precipitation, while genetic diversity increased with temperature in S. capensis. Most genetic diversity resided among populations in the semi‐desert species (Φ_ST = 0.572/0.595 in S. arabica/lagascae) but within populations in the ruderal species (Φ_ST = 0.355/0.387 S. capensis/parviflora). Principal coordinate analysis ( PCoA) and STRUCTURE analysis showed that Stipa populations of all species clustered ecogeographically. A genome scan revealed that divergent selection at particular AFLP loci contributed to genetic differentiation. Irrespective of their different life histories, Stipa species responded similarly to the bioclimatic gradient in Jordan. We conclude that, in addition to predominant random processes, steep climatic gradients might shape the genetic structure of plant populations.     

The Kuroshio Current influences genetic diversity and population genetic structure of a tropical seagrass,Enhalus acoroides

Information on genetic diversity and differentiation of seagrass populations is essential for the conservation of coastal ecosystems. However, little is known about the seagrasses in the Indo‐West Pacific Ocean, where the world's highest diversity of seagrasses occurs. The influence of sea currents on these populations is also unknown. We estimated the genetic diversity and population genetic structure and identified reproductive features in Enhalus acoroides populations from the Yaeyama Islands, Hainan Island and the Philippines. The Philippines are situated at the centre of the E. acoroides range, Yaeyama and Hainan are peripheral populations, and the Yaeyama population is at the northern limit of the species range. The powerful Kuroshio Current flows from the Philippines to Yaeyama. Genetic analyses using nine microsatellite markers indicated that reproduction of E. acoroides is mostly sexual. Clonal diversity does not decrease in northern populations, although genetic diversity does. However, the genetic diversity of the Yaeyama populations is greater than that of the Hainan populations. Significant genetic differentiation among most populations was evident; however, the Yaeyama and north‐east Philippines populations were genetically similar, despite being separated by ~1100 km. An assignment test suggested that recruitment occurs from the north‐east Philippines to Yaeyama. The strong current in this region is probably responsible for the extant genetic diversity and recruitment patterns.