Development and characterization of microsatellite markers for a fig‐pollinating wasp (Ceratosolen sp. 1) of Ficus septica

For an undescribed fig‐pollinating wasp (Ceratosolen sp. 1) of Ficus septica, we isolated 15 polymorphic microsatellite markers from a genomic library partially enriched for GATA and CAG repeats. Polymorphism of these loci was evaluated by genotyping 40 female individuals collected from different fruits of host trees in southern Taiwan. The number of alleles per locus ranged from three to 15 and the observed heterozygosity of each locus ranged from 0.100 to 0.775. These loci would be suitable for further studies concerning population genetics, hybridization and sex ratio adjustment of the coexisting fig‐pollinating wasps.     

Predation on the pollinating fig wasp of Ficus erecta by larvae of Silba sp. (Diptera: Lonchaeidae)

This study examined the insect assemblage within the syconium of the dioecious fig Ficus erecta Thunb., 1786 (Moraceae) on Kii‐Oshima Island, Wakayama Prefecture, Japan. Species present included pollinating and non‐pollinating fig wasps Blastophaga nipponica Grandi, 1921 and Sycoscapter inubiae Ishii, 1934, respectively, as well as an undetermined species of Silba Macquart, 1851 (Diptera: Lonchaeidae). Larvae of Silba sp. were found only in fig syconia containing B. nipponica. Observations revealed that larvae of Silba sp. fed on female adults of B. nipponica within fig galls by thrusting their heads through the intersegmental membrane. Furthermore, larvae of Silba sp. had a high predation rate (90%). These observations suggest that larvae of Silba sp. are specialized for feeding on B. nipponica and have a negative effect on populations of this species.     

Patterns of spatial genetic structuring in a hydropsychid caddisfly (Cheumatopsyche sp. AV1) from southeastern Australia

We assessed levels of mitochondrial genetic spatial structuring in the hydropsychid caddisfly Cheumatopsyche sp. AV1 in southeastern New South Wales, Australia. No significant spatial structuring was detected within or between catchments using analysis of molecular variance, and nested clade contingency analysis suggested no strong relationship between haplotypes and geographical location, at any clade level. However, tests for association among haplotypes incorporating geographical distance in the nested clade analysis, revealed patterns of historical range expansion and recent restricted gene flow. Most likely, population fragmentation preceded range expansion, although subsequent recontact and gene flow among the previously sundered populations has apparently obscured the geographical signature of the former fragmentation. Taken together, our analyses suggest that a number of populations fragmented during the Pleistocene evolved in isolation for a time and subsequently expanded into secondary contact. Since expansion, there has apparently been substantial (albeit somewhat restricted) dispersal and gene flow of adult female Cheumatopsyche sp. AV1, throughout the study area.     

Spatial and temporal genetic structure of a river‐resident Atlantic salmon (Salmo salar) after millennia of isolation

The river‐resident Salmo salar (“småblank”) has been isolated from other Atlantic salmon populations for 9,500 years in upper River Namsen, Norway. This is the only European Atlantic salmon population accomplishing its entire life cycle in a river. Hydropower development during the last six decades has introduced movement barriers and changed more than 50% of the river habitat to lentic conditions. Based on microsatellites and SNPs, genetic variation within småblank was only about 50% of that in the anadromous Atlantic salmon within the same river. The genetic differentiation (F_ST) between småblank and the anadromous population was 0.24. This is similar to the differentiation between anadromous Atlantic salmon in Europe and North America. Microsatellite analyses identified three genetic subpopulations within småblank, each with an effective population size N_e of a few hundred individuals. There was no evidence of reduced heterozygosity and allelic richness in contemporary samples (2005–2008) compared with historical samples (1955–56 and 1978–79). However, there was a reduction in genetic differentiation between sampling localities over time. SNP data supported the differentiation of småblank into subpopulations and revealed downstream asymmetric gene flow between subpopulations. In spite of this, genetic variation was not higher in the lower than in the upper areas. The meta‐population structure of småblank probably maintains genetic variation better than one panmictic population would do, as long as gene flow among subpopulations is maintained. Småblank is a unique endemic island population of Atlantic salmon. It is in a precarious situation due to a variety of anthropogenic impacts on its restricted habitat area. Thus, maintaining population size and avoiding further habitat fragmentation are important.     

Intra‐ and interpopulation genetic differentiation and gene flow in a group of isolated populations of Bradybaena fruticum (O. F. Müller, 1774) in South Poland

Intra‐ and interpopulation variation was studied, by means of cellulose acetate allozyme electrophoresis, on 16 populations of helicoid snail Bradybaena fruticum (O. F. Müller, 1774) in South Poland. Four enzyme systems, coded by seven loci, were analysed. Calculated with Fisher's technique and Ohta's D‐statistics, four cases of linkage disequilibrium were detected, reflecting population subdivision. The mean number of alleles per locus equalled 2.16 and the mean expected heterozygosity was 0.287. Exact multipopulation and multilocus tests for Hardy–Weinberg equilibrium indicated a statistically significant homozygote excess in all the loci and all populations but three. Each population, however, was at Hardy–Weinberg equilibrium for most loci, though the values of f (F_IS) were usually high. Homozygote excess was ascribed partly to inbreeding and partly to Wahlund's effect (spatial subdivision of population; at least two cohorts of adult, reproducing snails), disrupting selection in this polymorphic species not excluded. F‐statistics showed relatively low values of θ (F_ST ; mean for all loci = 0.224) and those of Nm usually below 1 (mean 0.866). Pairwise values of either θ or Cavalli‐Sforza and Edwards arc distance were statistically significantly associated with geographic distances. Contrary to this, no geographic pattern of interpopulation differences was detected by correspondence analysis on allele frequencies, non‐linear multidimensional scaling, UPGMA clustering or neighbour‐joining trees constructed on θ and Cavalli‐Sforza and Edwards arc distance. Accordingly, some most distant populations were more similar to one another than the close ones.     

Microsatellite‐based analysis of genetic structure and gene flow of Mythimna separata (Walker) (Lepidoptera: Noctuidae) in China

The oriental armyworm, Mythimna separata, is a serious agricultural pest in China. Seasonal and roundtrip migration has recently led to sudden, localized outbreaks and crop losses. To evaluate genetic differentiation between populations in eastern and western China and elucidate gene flow, the genetic structure of 20 natural populations from nine provinces was examined using seven microsatellite markers. The results indicated high genetic diversity. However, little to moderate (0 < F_ST < 0.15) genetic differentiation was detected, and there was no correlation between genetic distance and geographical distance. Bayesian clustering analysis identified three groups whereas discriminant analysis of principal components identified ten clusters that were considered as two clear‐cut clusters and one admixed group. Gene flow occurred frequently in most population pairs, and an asymmetrical migration rate was detected in several pairwise population comparisons. The bottleneck test showed that few populations had experienced recent bottlenecks. Correspondingly, large‐scale and long‐distance migration of M. separata has caused low genetic differentiation and frequent gene exchange. Our findings are important for studying genetic evolution and help to improve predictions of M. separata outbreaks in China.     

Range‐wide analysis of genetic structure in a widespread,highly mobile species (Odocoileus hemionus) reveals the importance of historical biogeography

Highly mobile species that thrive in a wide range of habitats are expected to show little genetic differentiation across their range. A limited but growing number of studies have revealed that patterns of broad‐scale genetic differentiation can and do emerge in vagile, continuously distributed species. However, these patterns are complex and often shaped by both historical and ecological factors. Comprehensive surveys of genetic variation at a broad scale and at high resolution are useful for detecting cryptic spatial genetic structure and for investigating the relative roles of historical and ecological processes in structuring widespread, highly mobile species. In this study, we analysed 10 microsatellite loci from over 1900 samples collected across the full range of mule deer (Odocoileus hemionus), one of the most widely distributed and abundant of all large mammal species in North America. Through both individual‐ and population‐based analyses, we found evidence for three main genetic lineages, one corresponding to the ‘mule deer’ morphological type and two to the ‘black‐tailed deer’ type. Historical biogeographic events likely are the primary drivers of genetic divergence in this species; boundaries of the three lineages correspond well with predictions based on Pleistocene glacial cycles, and substructure within each lineage demonstrates island vicariance. However, across large geographic areas, including the entire mule deer lineage, we found that genetic variation fit an isolation‐by‐distance pattern rather than discrete clusters. A lack of genetic structure across wide geographic areas of the continental west indicates that ecological processes have not resulted in restrictions to gene flow sufficient for spatial genetic structure to emerge. Our results have important implications for our understanding of evolutionary mechanisms of divergence, as well as for taxonomy, conservation and management.     

Population genetic analysis of microsatellite variation of guppies (Poecilia reticulata) in Trinidad and Tobago: evidence for a dynamic source–sink metapopulation structure,founder events and population bottlenecks

Riverine fish populations are traditionally considered to be highly structured and subject to strong genetic drift. Here, we use microsatellites to analyse the population structure of the guppy (Poecilia reticulata), focussing on the headwater floodplain area of the Caroni drainage in Trinidad. We also analyse the population genetics of guppies in the Northern Drainage in Trinidad, a habitat characterized by rivers flowing directly into the sea, and a small isolated population in Tobago. Upland Caroni populations are highly differentiated and display low levels of genetic diversity. However, we found no evidence to suggest that these upland populations experienced recent population crashes and the populations appear to approach mutation–drift equilibrium. Dominant downstream migration over both short‐ and long‐time frames has a strong impact on the population genetics of lowland Caroni populations. This drainage system could be considered a source–sink metapopulation, with the tributary furthest downstream representing a ‘super sink’, receiving immigrants from rivers upstream in the drainage. Moreover, the effective population size in the lowlands is surprisingly low in comparison with the apparently large census population sizes.     

High gene flow in two thrips‐pollinated South‐East Asian pioneer trees: genetic diversity and population structure of Macaranga hypoleuca and M. beccariana (Euphorbiaceae)

As a result of intensive exploitation, disturbed forests now dominate large areas of lowland tropical rainforest in South‐East Asia. The genus Macaranga comprises some of the most important pioneer tree species of the region, among them M. beccariana and M. hypoleuca, two closely related obligate ant‐plants pollinated by thrips. We used nuclear and plastid DNA markers to address questions of genetic diversity and population structure. Twelve plastid haplotypes were detected among 281 samples, three of which were shared between the two study species. Hybrids between the two species appear to be rare. Overall, genetic diversity in both species was moderate to high, with low levels of population differentiation, consistent with other tropical pioneer trees. Genetic structure was generally more pronounced in plastid than in nuclear data, indicating that gene flow via pollen may be more efficient than via seeds. Thrips apparently also serve as efficient pollinators over long distances, perhaps through a combination of passive dispersal by wind and active search for inflorescences in the target area. Our results indicate that M. beccariana and M. hypoleuca populations from recently disturbed habitats do not yet suffer from reduced genetic diversity or increased inbreeding. © 2013 The Linnean Society of London, Botanical Journal of the Linnean Society, 2013, 173 , 606–621.     

Range‐wide genetic homogeneity in the California sea mussel (Mytilus californianus): a comparison of allozymes,nuclear DNA markers,and mitochondrial DNA sequences

We tested for genetic differentiation among six populations of California sea mussels (Mytilus californianus) sampled across 4000 km of its geographical range by comparing patterns of variation at four independent types of genetic markers: allozymes, single‐copy nuclear DNA markers, and DNA sequences from the male and female mitochondrial genomes. Despite our extensive sampling and genotyping efforts, we detected no significant differences among localities and no signal of isolation by distance suggesting that M. californianus is genetically homogeneous throughout its range. This concordance differs from similar studies on other mytilids, especially in the role of postsettlement selection generating differences between exposed coastal and estuarine habitats. To assess if this homogeneity was due to M. californianus not inhabiting estuarine environments, we reviewed studies comparing allozymes with other classes of nuclear DNA markers. Although both types of markers gave broadly consistent results, there was a bias favouring studies in which allozymes were more divergent than DNA markers (nine to three) and a disproportionate number of these cases involved marine taxa (seven). Furthermore, allozymes were significantly more heterogeneous than DNA markers in three of the four studies that sampled coastal and estuarine habitats. We conclude that the genetic uniformity exhibited by M. californianus may result from a combination of extensive gene flow and the lack of exposure to strong selective gradients across its range.