Gene Flow

In the Andes of Central Chile, flowering commences 1–2 months earlier on equatorial-(north-) facing than on polar-(south-) facing slopes, and pollinator assemblages also differ between these habitats. In order to understand the potential influence of these differences on gene flow, we monitored flowering periods and insect visitation rates to flowers of 60 individuals of Anarthrophyllum cumingii (Papilionaceae) on two equatorial-and two polar-facing slopes in the Andes of central Chile (33 35 0 S;70 32 0 W). Flowering began about 30 days earlier on equatorial-facing slopes. Flowering periods of individuals on slopes with the same aspect had a mean overlap of 0.52, while those on opposite slopes had a mean overlap of 0.15. On equatorial-facing slopes Yramea lathionoides (Lepidoptera) accounted for 60% of the visits to flowers of A. cumingii, while on polar-facing slopes Centris cineraria (Hymenoptera) was responsible for more than 80% of flower visits. Average similarities of visitor assemblages among individual plants on slopes with the same aspect was 0.83, while the mean similarity between individuals on opposite slopes was only 0.23. Within slopes fluorescent dyes were dispersed up to 40 m from the donor plants, but there was no movements of dyes between individuals growing on opposite slopes, even when they were separated by less than 10 m. Synchronous blooming and a common pollen vector are necessary conditions for pollen exchange between individuals. The overall probability of pollen exchange estimated by multiplying the inter-individual overlap for both factors, was nearly 0.5 for individuals growing on slopes with the same aspect, and less than 0.04 for individuals growing on opposite slopes. Consequently, at equivalent distances, the probability of pollen exchange between individuals growing on slopes of opposite aspect is more than 10-times lower than between those growing on the same slopes. Seed dispersal cannot compensate for restricted gene flow through pollination, because seeds of A. cumingii were dispersed less than 2 m away from a parent plant. Presumably, restricted gene flow could enhance genetic divergence between populations on slopes of contrasting aspects. This factor could be important in contributing to the high diversity and endemism in the Chilean Andes.

The stone marten is a widely distributed mustelid in the Palaearctic region that exhibits variable habitat preferences in different parts of its range. The species is a Holocene immigrant from southwest Asia which, according to fossil remains, followed the expansion of the Neolithic farming cultures into Europe and possibly colonized the Iberian Peninsula during the Early Neolithic (ca. 7,000 years BP). However, the population genetic structure and historical biogeography of this generalist carnivore remains essentially unknown. In this study we have combined mitochondrial DNA (mtDNA) sequencing (621 bp) and microsatellite genotyping (23 polymorphic markers) to infer the population genetic structure of the stone marten within the Iberian Peninsula. The mtDNA data revealed low haplotype and nucleotide diversities and a lack of phylogeographic structure, most likely due to a recent colonization of the Iberian Peninsula by a few mtDNA lineages during the Early Neolithic. The microsatel...

Genes involved in the reproductive isolation are particularly useful as molecular markers in speciation studies. Lutzomyia longipalpis (Diptera: Psychodidae: Phlebotominae), a putative species complex, is a vector of visceral leishmaniasis in Latin America. We isolated from this species a fragment homologous to cacophony, a Drosophila gene that encodes features of the lovesong, an acoustic signal that is important in the sexual isolation of closely related species and known to vary considerably among L. longipalpis putative siblings species. Using an intron of the sandfly cacophony as a marker, we analyzed the molecular variation and sequence divergence among five populations of L. longipalpis from Brazil, three allopatric (Jacobina, Lapinha and Natal) and two putative sympatric sibling species from the locality of Sobral. A high level of polymorphism was found and analysis of the data indicates that very little gene flow is occurring among the populations of Jacobina, Lapinha, and Natal. A high level of differentiation was also observed between the two putative sympatric species of Sobral, one of which seems to be the same sibling species found in Natal, while the other is somewhat more related to Jacobina and Lapinha. However, the amount of estimated gene flow among the Sobral siblings is about seven times higher than the previously estimated for period, another lovesong gene, perhaps indicating that introgression might be affecting cacophony more than period. The results suggest that L. longipalpis is not a single species in Brazil, but it is yet not clear whether the different populations studied deserve species status rather than representing an incipient speciation process.

Knowledge about current patterns of genetic structure of populations together with the evolutionary history of a species helps to understand and predict the adaptation of populations to future climate change. We assayed variation at nuclear microsatellite markers among peripheral vs. continuous populations of the temperate South American species Austrocedrus chilensis, to investigate the role of historical vs. demographical forces in shaping population genetic structure. This species occurs in continuous populations in the west and central distribution range, but becomes highly fragmented at the eastern limit, which comprised ice-free areas during Quaternary glaciations and has extreme climatic conditions at present times. Bayesian analysis methods identified two contrasting patterns of genetic structure; (I) populations from humid, mesic and peri-glacial regions formed a single deme with relatively low genetic differentiation and high admixture levels whereas (II) a highly heterogeneous genetic structure with low level of admixture was found in the steppe, towards the east and northeast limit of the distribution range. In the steppe, population fragmentation, restricted gene flow and isolation-by-distance were also inferred. In addition, several small steppe populations showed high genetic diversity and divergent gene pools, suggesting that they constitute ancient refuges from pre-Holocene glaciations with just a subgroup of them contributing significantly to post-glacial spread. These results are discussed in relation to patterns of genetic variation found for other temperate species and the contribution of the particular southern Andes topography and climate to post-glacial spread.

We assess craniometric variation in 153 individually dated human crania from South Africa with the aim of investigating genetic continuity/discontinuity during the Holocene. Evidence from the archaeological record is used to pinpoint likely episodes of genetic discontinuity. Craniometric data are then used to assess the likelihood of genetic change having occurred. Two periods of possible genetic discontinuity are identified: i) c. 4,000 BP, when an increase in overall population size, shifts in site organization and diet, and reduced mobility, were accompanied by reductions in stature; ii) c. 2,000 BP, when the herding of domesticates and the use of pottery vessels were introduced into the region. Results indicate that there was a decrease in cranial size and concomitant size-related changes in craniofacial shape between c.4,000 BP and 3,000 BP. This was followed almost immediately by a recovery in craniofacial size and a return to pre-4,000 BP craniofacial shape at c. 3,000 BP. This recovery continued gradually, extending into the herder period without any major shifts in morphology at 2,000 BP. It is suggested that the fluctuations in craniofacial size/shape were related to changes in environmental factors. Results obtained are consistent with long term continuity in South African Later Stone Age populations during the Holocene.

The Cape Dwarf Chameleon (Bradypodion pumilum) is an endemic South African species that is currently threatened by habitat loss and fragmentation of its natural habitat through urbanization and agriculture. To conduct studies that will assist in understanding these anthropogenic effects on gene flow, population structure, and genetic diversity, we developed eight microsatellite loci using an enrichment protocol. Number of alleles ranged from 5 to 26 with observed heterozygosities of 0.279–0.930. Several loci did not meet HW expectations, but this may be a result of extreme demographic fluctuations that have been noted for this species. These loci will prove useful to examine the population genetics of these threatened reptiles and for providing information that will be used for generating and updating conservation assessments.

A simultaneous survey of 14 protein loci, together with frequencies and within- and between-population allelism rates of lethal chromosomes, was carried out in five (four Japanese and one Korean) natural populations and one cage population of Drosophila melanogaster. It was found that lethal allelism rates decrease rapidly as geographic distance between two populations increases, while variation at protein loci shows a remarkable similarity over all populations examined. These findings suggest that there are very high levels of gene flow in these natural populations and that selection at protein loci which can maintain substantial geographic variation, if present, is overshadowed by gene flow. There is no indication that invasion of D. melanogaster to the Far East occurred so recently that the frequencies of lethal chromosomes are still in nonequilibrium.

Dispersal and gene flow within animal populations are influenced by the composition and configuration of the landscape. In this study, we evaluated hypotheses about the impact of natural and anthropogenic factors on genetic differentiation in two amphibian species, the spotted salamander (Ambystoma maculatum) and the wood frog (Lithobates sylvaticus) in a commercial forest in central Maine. We conducted this analysis at two scales: a local level, focused on factors measured at each breeding pond, and a landscape level, focused on factors measured between ponds. We investigated the effects of a number of environmental factors in six categories including Productivity, Physical, Land Composition, Land Configuration, Isolation and Location. Embryos were sampled from 56 spotted salamander breeding ponds and 39 wood frog breeding ponds. We used a hierarchical Bayesian approach in the program GESTE at each breeding pond and a random forest algorithm in conjunction with a network analysis b...

The transfer of genes between populations is increasingly important in a world where pollinators are declining, plant and animal populations are increasingly fragmented and climate change is forcing shifts in distribution. The distances that pollen can be transported by small insects are impressive, as is the extensive gene flow between their own populations. We compared the relative ease by which small insects introduce genetic markers into their own and host-plant populations. Gene flow via seeds and pollen between populations of an Asian fig species were evaluated using cpDNA and nuclear DNA markers, and between-population gene flow of its pollinator fig wasp was determined using microsatellites. This insect is the tree's only pollinator locally, and only reproduces in its figs. The plant's pollen-to-seed dispersal ratio was 9.183-9.437, smaller than that recorded for other Ficus. The relative effectiveness of the pollinator at introducing markers into its own populations...

Since the 1970s, when major improvements to the water quality were made, the River Thames has been subject to a high-profile project aimed at restoring Atlantic salmon to the catchment. Whilst initially successful, with hundreds of salmon returning each year in the late 1980s, the number of adults returning to the river has declined steeply again in recent years, reaching a low in 2005 when no salmon were recorded. Using a baseline of genetic information gathered from 3830 salmon from throughout their southern European range, and incorporating samples from the hatchery fish used to stock the Thames, all 10 tagged hatchery fish captured in 2003 and all 16 returning untagged adult salmon captured between 2005 and 2008 were assigned to their most likely river of origin. The results suggest that untagged salmon currently ascending the river originate not from exogenous fish stocked into the Thames, but predominantly from other rivers in southern England. This highlights the potential for natural processes of recolonisation to operate in rivers where salmon have become locally extirpated. These findings also underscore several important considerations when undertaking species restoration projects: (i) previous causes of declines must be sufficiently ameliorated to allow new/translocated individuals to thrive, (ii) introduced individuals should originate from a stock that is closely related to the extirpated population, according to the principles of contemporary conservation biology, and (iii) dispersal and gene-flow from neighbouring populations may play a significant role in establishing new populations.► Despite an intensive hatchery stocking programme, since 2005 no hatchery reared salmon have been caught in the Thames. ► Genetic assignment analysis indicates that wild salmon ascending the Thames originate from other rivers in southern England. ► Wild salmon returning to the Thames between 2005 and 2008 do not originate from exogenous fish stocked into the Thames. ► Such straying highlights the potential for natural recolonisation of rivers where salmon have become locally extirpated. ► Our findings highlight the futility of long-term stocking without corresponding improvements in habitat and water quality.

Twenty-two microsatellite loci were characterized in the soilborne plant pathogenic 8 fungus Verticillium dahliae by analysis of the genome sequence. All loci were 9 polymorphic in at least two of three populations of V. dahliae from lettuce, spinach and 10 tomato. These loci were useful in genotyping isolates and highlighting differences in 11 genetic diversity among the three tested populations.

To date, most assessments of coral connectivity have emphasized long-distance horizontal dispersal of propagules from one shallow reef to another. The extent of vertical connectivity, however, remains largely understudied. Here, we used newly-developed and existing DNA microsatellite loci for the brooding coral Porites astreoides to assess patterns of horizontal and vertical connectivity in 590 colonies collected from three depth zones (≤10 m, 15-20 m and ≥25 m) at sites in Florida, Bermuda and the U.S. Virgin Islands (USVI). We also tested whether maternal transmission of algal symbionts (Symbiodinium spp.) might limit effective vertical connectivity. Overall, shallow P. astreoides exhibited high gene flow between Florida and USVI, but limited gene flow between these locations and Bermuda. In contrast, there was significant genetic differentiation by depth in Florida (Upper Keys, Lower Keys and Dry Tortugas), but not in Bermuda or USVI, despite strong patterns of depth zonation in ...