Genetic population structure of Natterer's bats explained by mating at swarming sites and philopatry

During autumn 'swarming', large numbers of temperate bats chase each other in and around underground sites. Swarming has been proposed to be a mating event, allowing interbreeding between bats from otherwise isolated summer colonies. We studied the population structure of the Natterer's bat (Myotis nattereri), a swarming species in northern England, by sampling bats at seven sites in two swarming areas and at 11 summer colonies. Analysis of molecular variance (amova) and genetic assignment analyses showed that the swarming areas (60 km apart) support significantly different populations. A negative correlation was found between the distance of a summer colony from a swarming area and the assignment of bats to that area. High gene diversity was found at all sites (HE = 0.79) suggesting high gene flow. This was supported by a low FST (0.017) among summer colonies and the absence of isolation by distance or substructure among colonies which visit one swarming area. The FST, although low, was significantly different from zero, which could be explained by a combination of female philopatry and male-mediated gene flow through mating at swarming sites with bats from other colonies. Modelling suggested that if effective size of the summer colonies (Ne) was low to moderate (10-30), all mating must occur at the swarming sites to account for the observed FST. If the Ne was higher (50), in addition to random mating during swarming, there may be nonrandom mating at swarming sites or some within-colony mating. Conservation of swarming sites that support potentially large populations is discussed.     

High gene diversity at swarming sites suggest hot spots for gene flow in the endangered Bechstein's bat

Our study shows that endangered Bechstein'sbats utilise distinct habitats at differentstages of their reproductive cycle, a findingthat has implications how habitat should beselected for preservation. Using nuclear andmitochondrial microsatellite DNA markers wecompared gene diversity of Bechstein's batswithin breeding colonies and at potentialmating sites. Bechstein's bat is one of themost threatened European bat species. Duringsummer it depends largely on mature deciduousforests. Females exhibit strict natalphilopatry. They form demographicallyindependent breeding colonies comprisingmaternally closely related bats. Males aresolitary. Like other temperate bats,Bechstein's bats swarm at the end of summer infront of caves. Because the sexes meet there,such swarming sites are potentially importantfor gene flow. Our genetic analyses reveal thatswarming sites have greater mitochondrial DNAgene diversity than colonies. Furthermore,field data on the phenology and reproductivestatus of several hundred individuals suggestthat Bechstein's bats mate during swarming. Incombination our field and genetic data showthat swarming sites provide the opportunity forgene flow among bats originating from differentcolonies. Therefore, we suggest that swarmingsites should be strictly protected to maintainthe observed high levels of gene flow amongcolonies.     

Genetic connectivity among swarming sites in the wide ranging and recently declining little brown bat (Myotis lucifugus)

Characterizing movement dynamics and spatial aspects of gene flow within a species permits inference on population structuring. As patterns of structuring are products of historical and current demographics and gene flow, assessment of structure through time can yield an understanding of evolutionary dynamics acting on populations that are necessary to inform management. Recent dramatic population declines in hibernating bats in eastern North America from white‐nose syndrome have prompted the need for information on movement dynamics for multiple bat species. We characterized population genetic structure of the little brown bat, Myotis lucifugus, at swarming sites in southeastern Canada using 9 nuclear microsatellites and a 292‐bp region of the mitochondrial genome. Analyses of F_ST, Φ_ST, and Bayesian clustering (STRUCTURE) found weak levels of genetic structure among swarming sites for the nuclear and mitochondrial genome (Global F_ST = 0.001, P < 0.05, Global Φ_ST = 0.045, P < 0.01, STRUCTURE K = 1) suggesting high contemporary gene flow. Hierarchical AMOVA also suggests little structuring at a regional (provincial) level. Metrics of nuclear genetic structure were not found to differ between males and females suggesting weak asymmetries in gene flow between the sexes. However, a greater degree of mitochondrial structuring does support male‐biased dispersal long term. Demographic analyses were consistent with past population growth and suggest a population expansion occurred from approximately 1250 to 12,500 BP, following Pleistocene deglaciation in the region. Our study suggests high gene flow and thus a high degree of connectivity among bats that visit swarming sites whereby mainland areas of the region may be best considered as one large gene pool for management and conservation.     

Population Genetic Structure Within and among Seasonal Site Types in the Little Brown Bat (Myotis lucifugus) and the Northern Long-Eared Bat (M. septentrionalis)

During late summer and early autumn, temperate bats migrate from their summering sites to swarming sites, where mating likely occurs. However, the extent to which individuals of a single summering site migrate to the same swarming site, and vice versa, is not known. We examined the migratory connectivity between summering and swarming sites in two temperate, North American, bat species, the little brown bat (Myotis lucifugus) and the northern long-eared bat (Myotis septentrionalis). Using mitochondrial and microsatellite DNA markers, we examined population structuring within and among summering and swarming sites. Both species exhibited moderate degrees of mitochondrial DNA differentiation (little brown bat: F_ST(SWARMING)= 0.093, F_ST(SWARMING)= 0.052; northern long-eared bat: F_ST(SWARMING)= 0.117, F_ST(SWARMING)= 0.043) and little microsatellite DNA differentiation among summering and among swarming sites. Haplotype diversity was significantly higher at swarming sites than summering sites, supporting the idea that swarming sites are comprised of individuals from various summering sites. Further, pairwise analyses suggest that swarming sites are not necessarily comprised of only individuals from the most proximal summering colonies.     

The role of swarming sites for maintaining gene flow in the brown long-eared bat (Plecotus auritus)

Bat-swarming sites where thousands of individuals meet in late summer were recently proposed as 'hot spots' for gene flow among populations. If, due to female philopatry, nursery colonies are genetically differentiated, and if males and females of different colonies meet at swarming sites, then we would expect lower differentiation of maternally inherited genetic markers among swarming sites and higher genetic diversity within. To test these predictions, we compared genetic variance from three swarming sites to 14 nursery colonies. We analysed biparentally (five nuclear and one sex-linked microsatellite loci) and maternally (mitochondrial D-loop, 550 bp) inherited molecular markers. Three mtDNA D-loop haplolineages that were strictly separated at nursery colonies were mixed at swarming sites. As predicted by the 'extra colony-mating hypothesis', genetic variance among swarming sites (V(ST)) for the D-loop drastically decreased compared to the nursery population genetic variance (V(PT)) (31 and 60%, respectively), and genetic diversity increased at swarming sites. Relatedness was significant at nursery colonies but not at swarming sites, and colony relatedness of juveniles to females was positive but not so to males. This suggests a breakdown of colony borders at swarming sites. Although there is behavioural and physiological evidence for sexual interaction at swarming sites, this does not explain why mating continues throughout the winter. We therefore propose that autumn roaming bats meet at swarming sites across colonies to start mating and, in addition, to renew information about suitable hibernacula.     

Gene flow is maintained by polyandry and male dispersal in the army ant <Emphasis Type="Italic">Eciton burchellii</Emphasis>

The combination of haplodiploidy, complementary sex determination and eusociality constrains the effective population size (N _e) of social Hymenoptera far more than in any other insect group. Additional limitations on N _e occur in army ants since they have wingless queens and colony fission, both of which are factors causing restricted maternal gene flow and high population viscosity. Therefore, winged army ant males gain a particular significance to ensure dispersal, facilitate gene flow and avoid inbreeding. Based on population genetic analyses with microsatellite markers, we studied a population of the Neotropical army ant Eciton burchellii, finding a high level of heterozygosity, weak population differentiation and no evidence for inbreeding. Moreover, by using sibship reconstruction analyses, we quantified the actual number of male contributing colonies represented in a queen’s mate sample, demonstrating that, through extreme multiple mating, the queens are able to sample the genes of males from up to ten different colonies, usually located within an approximate radius of 1 km. We finally correlated the individual mating success of each male contributing colony with the relative siring success of individual males and found a significant colony-dependent male fitness component. Our results imply that the dispersal and mating system of these army ants seem to enhance gene flow and minimise the deleterious effects associated with small effective population size. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Demographic bottlenecks and low gene flow in remnant populations of the critically endangered <Emphasis Type="Italic">Berchemiella wilsonii</Emphasis> var<Emphasis Type="Italic">. pubipetiolata</Emphasis> (Rhamnaceae) inferred from microsatellite markers

Berchemiella wilsonii var. pubipetiolata (Rhamnaceae) is an endangered plant with only four remnant populations in eastern China. Population genetic information is essential for understanding population history and formulating conservation strategies for this species. Thirteen microsatellite loci were used to investigate genetic variation and population structure of the four remnant populations. Moderate levels of expected heterozygosity (H _E = 0.466–0.543) and low allelic diversity (A = 3.1–3.6 and A _R = 2.2–2.4, respectively) were observed within populations. Bottleneck tests found three out of four populations to deviate from mutation-drift equilibrium under the two-phase model (TPM), suggesting a recent population decline, which is congruent with known demographic history. The evolutionary history of the species seems dominated by genetic drift rather than gene flow. Low historical gene flow was inferred from several different approaches and N _m ranged from 0.582 by the private allele method to 0.783 by the coalescent method. Contemporary gene flow was also found to be even lower for only one first generation migrant was detected with individual-based assignment analysis. Restricted pollen and seed dispersal as well as a recent decline in population size associated with habitat fragmentation may have contributed to low levels of historical and contemporary gene flow, and resulted in a high genetic differentiation. Under this scenario, Berchemiella wilsonii var. pubipetiolata populations are expected to display more pronounced population genetic structure in the future as a result of increased inbreeding and genetic drift.     

Genetic Diversity and Geographic Differentiation in the Threatened Species Dysosma pleiantha in China as Revealed by ISSR Analysis

Dysosma pleiantha, an important threatened medicinal plant species, is restricted in distribution to southeastern China. The species is capable of reproducing both sexually and asexually. In this study, inter-simple sequence repeat marker data were obtained and analyzed with respect to genetic variation and genetic structure. The extent of clonality, together with the clonal and sexual reproductive strategies, varied among sites, and the populations under harsh ecological conditions tended to have large clones with relatively low clonal diversity caused by vegetative reproduction. The ramets sharing the same genotype show a clumped distribution. Across all populations surveyed, average within-population diversity was remarkably low (e.g., 0.111 for Nei’s gene diversity), with populations from the nature reserves maintaining relatively high amounts of genetic diversity. Among all populations, high genetic differentiation (AMOVA: Φ_ST = 0.500; Nei’s genetic diversity: G _ST = 0.465, Bayesian analysis: Φ_B = 0.436) was detected, together with an isolation-by-distance pattern. Low seedling recruitment due to inbreeding, restricted gene flow, and genetic drift are proposed as determinant factors responsible for the low genetic diversity and high genetic differentiation observed.     

Comparisons of microsatellite variability and population genetic structure of two endangered wild rice species, <Emphasis Type="Italic">Oryza rufipogon</Emphasis> and <Emphasis Type="Italic">O. officinalis</Emphasis>, and their conservation implications

Conserving endangered wild rice species requires a thorough understanding of their population genetic structure and appropriate approaches. We applied six and seven microsatellite loci to study the genetic structure of six populations throughout the range of Chinese Oryza rufipogon and Oryza officinalis, respectively. The results showed that O. rufipogon possesses higher levels of genetic diversity but lower differentiation (R_S = 3.2713, P = 100.0%, H_O = 0.1401, H_S = 0.5800, F_ST = 0.271) than O. officinalis (R_S = 2.0545, P = 57.14%, H_O = 0.0470, H_S = 0.2830, F_ST = 0.554). Mean population F_IS was slightly larger for O. officinalis (F_IS = 0.844) than that for O. rufipogon (F_IS = 0.755), indicating that O. officinalis has slightly higher departures from Hardy–Weinberg expectations and heterozygosity deficits than O. rufipogon. In addition to different origins and evolutionary histories, O. officinalis has restricted gene flow, high inbreeding, isolated small populations and fewer opportunities of hybridization with other taxa, which may determine major differences in population genetic structure from O. rufipogon. Our results suggest the adoption of a plan of involving fewer populations but more individuals within populations for O. rufipogon, while both the number of populations and the individuals for a sampled population should be almost equally considered for O. officinalis. The known high degree of inbreeding in the populations of both species implies that conservation and restoration genetics should particularly focus on the maintenance of historically significant processes such as high levels of outbreeding, gene flow and large effective population sizes. We finally proposed to further estimate the role of rice gene flow in the conservation of O. rufipogon, and to perform detailed analysis of mating systems in both species for better conservation perspectives of their ecological and evolutionary processes.     

High gene flow between populations of Macrotermes michaelseni (Isoptera, Termitidae)

Termite alates are thought to be poor active flyers, and this should lead to considerable genetic differentiation on small spatial scales. However, using four microsatellite loci for the termite Macrotermes michaelseni we found low values of genetic differentiation (F_ST) across a spatial scale of even more than 50 km. Genetic differentiation between populations increased with spatial distance up to 50 km. Furthermore, up to this distance, the scatter around the linear regression of genetic differentiation versus spatial distance increased with spatial distance. This suggests that across such spatial distances gene flow and genetic drift are of about equal importance, and near equilibrium. Using a regional F_ST as well as the distance between populations with non-significant F_ST-values (up to 25 km), gene flow is sufficiently high so that populations may be regarded as panmictic on spatial scales of 25 to 50 km. The apparent contradiction between dispersal distances observed in the field and estimates of gene flow from genetic markers may be due to the masses of swarming alates. Assuming a leptokurtic distribution of dispersal distances, atleast some alates are expected to travel considerable distances, most likely by passive drift. Received 25 January 2005; revised 11 April 2005; accepted 26 April 2005.     

Population genetics and fitness in fragmented populations of the dioecious and endangered <Emphasis Type="Italic">Silene otites</Emphasis> (Caryophyllaceae)

Population fragmentation is often correlated with loss of genetic diversity and reduced fitness. Obligate out-crossing (dioecy) is expected to enhance genetic diversity, reduce genetic differentiation, and avoid inbreeding depression through frequent gene flow. However, in highly fragmented populations dioecy has only diminishing effects upon genetic structure as pollination limitations (e.g. flight distance of pollinators) most often restrict inter-population gene flow in insect pollinated species. In fragmented dry grasslands in northeastern Germany, we analysed genetic structure, fitness, and habitat quality of the endangered dioecious Silene otites (Caryophyllaceae). Using AFLP markers, a high level of differentiation among ten populations was found (F _st = 0.36), while the intra-population genetic diversities (H _E = 0.165–0.240) were similar as compared to hermaphroditic species. There was neither a correlation between geographic and genetic distance nor between genetic diversity and population size, which indicates reduced gene flow among populations and random genetic drift. Plant size was positively correlated with genetic diversity. Seed set and number of juveniles were positively related to population size. Higher total coverage resulted in reduced plant fitness, and the number of juveniles was negatively correlated to cryptogam cover. Additionally, we found a sex ratio bias towards more male plants in larger populations. Overall, our results indicate that on a regional geographic scale dioecy does not necessarily prevent genetic erosion in the case of habitat fragmentation, especially in the absence of long distance seed and pollen dispersal capacity.     

Isolated in an ocean of grass: low levels of gene flow between termite subpopulations

Habitat fragmentation is one of the most important causes of biodiversity loss, but many species are distributed in naturally patchy habitats. Such species are often organized in highly dynamic metapopulations or in patchy populations with high gene flow between subpopulations. Yet, there are also species that exist in stable patchy habitats with small subpopulations and presumably low dispersal rates. Here, we present population genetic data for the ‘magnetic’ termite Amitermes meridionalis, which show that short distances between subpopulations do not hinder exceptionally strong genetic differentiation (F_ST: 0.339; R_ST: 0.636). Despite the strong genetic differentiation between subpopulations, we did not find evidence for genetic impoverishment. We propose that loss of genetic diversity might be counteracted by a long colony life with low colony turnover. Indeed, we found evidence for the inheritance of colonies by so‐called ‘replacement reproductives’. Inhabiting a mound for several generations might result in loss of gene diversity within a colony but maintenance of gene diversity at the subpopulation level.     

Conservation genetics of the annual hemiparasitic plant <Emphasis Type="Italic">Melampyrum sylvaticum</Emphasis> (Orobanchaceae) in the UK and Scandinavia

Melampyrum sylvaticum is an endangered annual hemiparasitic plant that is found in only 19 small and isolated populations in the United Kingdom (UK). To evaluate the genetic consequences of this patchy distribution we compared levels of diversity, inbreeding and differentiation from ten populations from the UK with eight relatively large populations from Sweden and Norway where the species is more continuously distributed. We demonstrate that in both the UK and Scandinavia, the species is highly inbreeding (global F _IS = 0.899). Levels of population differentiation were high (F’_ST = 0.892) and significantly higher amongst UK populations (F’_ST = 0.949) than Scandinavian populations (F’_ST = 0.762; P < 0.01). The isolated populations in the UK have, on average, lower genetic diversity (allelic richness, proportion of loci that are polymorphic, gene diversity) than Scandinavian populations, and this diversity difference is associated with the smaller census size and population area of UK populations. From a conservation perspective, the naturally inbreeding nature of the species may buffer the species against immediate effects of inbreeding depression, but the markedly lower levels of genetic diversity in UK populations may represent a genetic constraint to evolutionary change. In addition, the high levels of population differentiation suggest that gene flow among populations will not be effective at replenishing lost variation. We thus recommend supporting in situ conservation management with ex situ populations and human-mediated seed dispersal among selected populations in the UK.     

Behavioural and Genetic Data Suggest that Bechstein's Bats Predominantly Mate Outside the Breeding Habitat

Investigating mating systems of species with a cryptic lifestyle often requires a combination of behavioural and genetic data. We used such a combined approach to investigate the mating system of the communal breeding Bechstein's bat (Myotis bechsteinii). Although females of this species are philopatric, gene flow among colonies is high. Gene flow occurs if dispersing males mate within the colony to which they moved. Males could gain local matings by defending resources or females in their breeding habitat. Alternatively, mating may take place at swarming sites, apart from the breeding habitat of the females, where males and females of several colonies meet. Whether or not males defend resources or females in the breeding habitat is of importance for understanding the mating system. Detailed observations of individual foraging and roosting behaviour over 4 yr suggest that males do not defend resources or females to gain matings. Moreover, paternity assignment based on microsatellite data of four complete juvenile cohorts showed that local males fathered less than 25% of the juveniles born in the colony where they settled. Even more striking, none of the males that had immigrated into our study area reproduced with the local females.     

Development of genetic diversity,differentiation and structure over 500 years in four ponderosa pine populations

Population history plays an important role in shaping contemporary levels of genetic variation and geographic structure. This is especially true in small, isolated range‐margin populations, where effects of inbreeding, genetic drift and gene flow may be more pronounced than in large continuous populations. Effects of landscape fragmentation and isolation distance may have implications for persistence of range‐margin populations if they are demographic sinks. We studied four small, disjunct populations of ponderosa pine over a 500‐year period. We coupled demographic data obtained through dendroecological methods with microsatellite data to discern how and when contemporary levels of allelic diversity, among and within‐population levels of differentiation, and geographic structure, arose. Alleles accumulated rapidly following initial colonization, demonstrating proportionally high levels of gene flow into the populations. At population sizes of approximately 100 individuals, allele accumulation saturated. Levels of genetic differentiation among populations (F_ST and Jost's D_est) and diversity within populations (F_IS) remained stable through time. There was no evidence of geographic genetic structure at any time in the populations' history. Proportionally, high gene flow in the early stages of population growth resulted in rapid accumulation of alleles and quickly created relatively homogenous genetic patterns among populations. Our study demonstrates that contemporary levels of genetic diversity were formed quickly and early in population development. How contemporary genetic diversity accumulates over time is a key facet of understanding population growth and development. This is especially relevant given the extent and speed at which species ranges are predicted to shift in the coming century.     

Drift happens: Molecular genetic diversity and differentiation among populations of jewelweed (Impatiens capensis Meerb.) reflect fragmentation of floodplain forests

Landscape features often shape patterns of gene flow and genetic differentiation in plant species. Populations that are small and isolated enough also become subject to genetic drift. We examined patterns of gene flow and differentiation among 12 floodplain populations of the selfing annual jewelweed (Impatiens capensis Meerb.) nested within four river systems and two major watersheds in Wisconsin, USA. Floodplain forests and marshes provide a model system for assessing the effects of habitat fragmentation within agricultural/urban landscapes and for testing whether rivers act to genetically connect dispersed populations. We generated a panel of 12,856 single nucleotide polymorphisms and assessed genetic diversity, differentiation, gene flow, and drift. Clustering methods revealed strong population genetic structure with limited admixture and highly differentiated populations (mean multilocus F_ST = 0.32, F_ST’ = 0.33). No signals of isolation by geographic distance or environment emerged, but alleles may flow along rivers given that genetic differentiation increased with river distance. Differentiation also increased in populations with fewer private alleles (R² = 0.51) and higher local inbreeding (R² = 0.22). Populations varied greatly in levels of local inbreeding (F_IS = 0.2–0.9) and F_IS increased in more isolated populations. These results suggest that genetic drift dominates other forces in structuring these Impatiens populations. In rapidly changing environments, species must migrate or genetically adapt. Habitat fragmentation limits both processes, potentially compromising the ability of species to persist in fragmented landscapes.     

Extreme isolation by distance in a montane frog <Emphasis Type="Italic">Rana cascadae</Emphasis>

Given the recent interest in declining amphibian populations, it is surprising that there are so few data on genetic drift and gene flow in anuran species. We used seven microsatellite loci to investigate genetic structure and diversity at both large and small geographic scales, and to estimate gene flow in the Cascades frog, Rana cascadae. We sampled 18 sites in a hierarchical design (inter-population distances ranging from 1–670 km) to test for isolation by distance and to determine the geographic scale over which substantial gene flow occurs. Eleven of these sites were sampled as three fine-scale clusters of three, three, and five sites separated by pairwise distances of 1–23 km to estimate number of migrants exchanged per generation via F _ST and by a coalescent approach. We found R. cascadae exhibits a strong pattern of isolation by distance over the entire species range, and that there is a sharp drop in migrants exchanged between sites separated by greater than 10 km. These data, in conjunction with results of other recent studies, suggest that montane habitats promote unusually strong genetic isolation among frog populations. We discuss our results in light of future management and conservation of R. cascadae.     

Genetic diversity in adult and seedling populations of <Emphasis Type="Italic">Primula vulgaris</Emphasis> in a fragmented agricultural landscape

Habitat fragmentation is known to generally reduce the size of plant populations and increase their isolation, leading to genetic erosion and increased between-population genetic differentiation. In Flanders (northern Belgium) Primula vulgaris is very rare and declining. Populations have incurred strong fragmentation for the last decades and are now restricted to a few highly fragmented areas in an intensively used agricultural landscape. Previous studies showed that small populations of this long-lived perennial herb still maintained high levels of genetic variation and low genetic differentiation. This pattern can either indicate recent gene flow or represent historical variation. Therefore, we used polymorphic microsatellite loci to investigate genetic variation and structure in adult (which may still reflect historical variation) and seedling (recent generation, thus affected by current processes) life stages. The recent generation (seedlings) showed a significant loss of observed heterozygosity (H _o) together with lower expected heterozygosity (H _e), a trend for higher inbreeding levels (F _IS) and higher differentiation (F _ST) between populations compared to the adult generation. This might result from (1) a reduction in effective population size, (2) higher inbreeding levels in the seedlings, (3) a higher survival of heterozygotes over time due to a higher fitness of heterozygotes (heterosis) and/or a lower fitness of homozygotes (inbreeding depression), (4) overlapping generations in the adult life stage, or (5) a lack of establishment of new (inbred) adults from seedlings due to degraded habitat conditions. Combining restoration of both habitat quality and gene flow between populations may be indispensable to ensure a sustainable conservation of fragmented populations.     

Genetic diversity and genotypic differentiation between the sexes in swarm aggregations decrease inbreeding in the Formosan subterranean termite

The life of a colony of subterranean termites, such as Coptotermes formosanus Shiraki (Isoptera: Rhinotermitidae), has natural inbreeding and outbreeding cycles. Reproductives of mature colonies can be replaced by their offspring, which increases the degree of inbreeding in each generation. High degrees of inbreeding may lead to inbreeding depression. In this study we focused on mechanisms for inbreeding avoidance during swarming that do not require kin recognition. We investigated genetic differentiation between swarm aggregations (isolation by distance), genetic diversity within swarm aggregations (multiple colony origin) and genetic differentiation between sexes. Alates were collected from five swarm aggregations in New Orleans, La. The genetic make-up of each swarm aggregation was then described by microsatellite genotyping. Alates from the different swarm aggregations were genetically differentiated; however, no isolation by distance up to at least 1000 m was detected. The dispersal distance of alates was sufficient to guarantee mixing of an average of 13 colonies within swarm aggregations. On average, eleven percent of all possible pairs of alates in each swarm aggregation were putative full siblings. Genotypic frequencies differed significantly between males and females. This could not be explained by sex-biased dispersal. We hypothesize sex-biased investment at the colony level to account for this difference. Genetic differentiation between the sexes and dispersal distances sufficient to promote high genetic diversity within swarm aggregations each facilitate inbreeding avoidance. These observations are consistent with the results of previous studies demonstrating that the majority of simple family colonies in Louisiana populations are headed by unrelated and outbred pairs of reproductives. Received 11 August 2005; revised 5 December 2005; accepted 20 December 2005.     

Genetic variation in populations of <Emphasis Type="Italic">Allothrombium pulvinum</Emphasis> (Acari: Trombidiidae) from Northern Iran revealed by mitochondrial <Emphasis Type="Italic">cox</Emphasis>I and nuclear rDNA <Emphasis Type="Italic">ITS</Emphasis>2 sequences

Allothrombium pulvinum Ewing is a common natural enemy of aphids and some other arthropods. So far, there are no studies that have addressed genetic variation of this predatory mite. We investigated genetic variation of A. pulvinum across its whole known range in Iran. A 410 bp portion of the mitochondrial cytochrome c oxidase subunit I gene (coxI) and 797–802 bp portion of the internal transcribed spacer 2 of rDNA (ITS2) were sequenced for 55 individuals from 11 populations, resulting in 12 and 26 haplotypes, respectively. In the coxI region, haplotype and nucleotide diversities varied among populations from 0.00 to 0.90 and from 0.0000 to 0.0110, respectively. In the ITS2 region they varied from 0.20 to 0.91 and from 0.0006 to 0.0023, respectively. For both gene regions the highest haplotype and nucleotide diversities were detected in population Mahmoud Abad from northern Iran. Statistically significant population differentiation (F _ST) was detected in most pair-wise population comparisons. The results of population differentiation for both gene regions were generally congruent indicating that A. pulvinum from Iran consists of genetically different populations. This suggests that A. pulvinum comprises at least two geographically distinct populations or even more than one species. This study is an initial step towards understanding genetic variation of A. pulvinum, a taxon for which little molecular information is available. More intensive sampling and analysis of additional DNA regions are necessary for more detailed classification of this taxon.