PROGRAM NOTE: Kgtests: a simple Excel Macro program to detect signatures of population expansion using microsatellites

Pieces in a global puzzle: Population genetics at two whale shark aggregations in the western Indian Ocean

The whale shark Rhincodon typus is found throughout the world's tropical and warm-temperate ocean basins. Despite their broad physical distribution, research on the species has been concentrated at a few aggregation sites. Comparing DNA sequences from sharks at different sites can provide a demographically neutral understanding of the whale shark's global ecology. Here, we created genetic profiles for 84 whale sharks from the Saudi Arabian Red Sea and 72 individuals from the coast of Tanzania using a combination of microsatellite and mitochondrial sequences. These two sites, separated by approximately 4500 km (shortest over-water distance), exhibit markedly different population demographics and behavioral ecologies. Eleven microsatellite DNA markers revealed that the two aggregation sites have similar levels of allelic richness and appear to be derived from the same source population. We sequenced the mitochondrial control region to produce multiple global haplotype networks (based on different alignment methodologies) that were broadly similar to each other in terms of population structure but suggested different demographic histories. Data from both microsatellite and mitochondrial markers demonstrated the stability of genetic diversity within the Saudi Arabian aggregation site throughout the sampling period. These results contrast previously measured declines in diversity at Ningaloo Reef, Western Australia. Mapping the geographic distribution of whale shark lineages provides insight into the species' connectivity and can be used to direct management efforts at both local and global scales. Similarly, understanding historical fluctuations in whale shark abundance provides a baseline by which to assess current trends. Continued development of new sequencing methods and the incorporation of genomic data could lead to considerable advances in the scientific understanding of whale shark population ecology and corresponding improvements to conservation policy.

Phylogeographic reconstructions can be biased by ancestral shared alleles: The case of the polymorphic lichen Bryoria fuscescens in Europe and North Africa

Large phylogeographic studies on lichens are scarce, and none involves a single species within which different lineages show fixed alternative dispersal strategies. We investigated Bryoria fuscescens (including B. capillaris) in Europe and western North Africa by phenotypically characterizing 1400 specimens from 64 populations and genotyping them with 14 microsatellites. We studied population structure and genetic diversity at the local and continental scales, discussed the post-glacial phylogeography, and compared dispersal capacities of phenotypes with and without soralia. Our main hypothesis is that the estimated phylogeography, migration routes, and dispersal capacities may be strongly biased by ancestral shared alleles. Scandinavia is genetically the richest area, followed by the Iberian Peninsula, the Carpathians, and the Alps. Three gene pools were detected: two partially linked to phenotypic characteristics, and the third one genetically related to the American sister species B. pseudofuscescens. The comparison of one gene pool producing soredia and one not, suggested both as panmictic, with similar levels of isolation by distance (IBD). The migration routes were estimated to span from north to south, in disagreement with the assessed glacial refugia. The presence of ancestral shared alleles in distant populations can explain the similar IBD levels found in both gene pools while producing a false signal of panmixia, and also biasing the phylogeographic reconstruction. The incomplete lineage sorting recorded for DNA sequence loci also supports this hypothesis. Consequently, the high diversity in Scandinavia may rather come from recent immigration into northern populations than from an in situ diversification. Similar patterns of ancestral shared polymorphism may bias the phylogeographical reconstruction of other lichen species.

Propagule pressure and hunting pressure jointly determine genetic evolution in insular populations of a global frog invader

Islands are often considered to be more susceptible to biological invasions and to suffer greater impacts from invaders than mainland areas, and this difference is generally attributed to differences in species introductions, ecological factors or human activities between islands and mainland areas. Genetic variation, as a good estimate of evolutionary potential, can influence the invasion process and impacts of alien species. However, few studies have compared the genetic diversity of alien species between islands and a corresponding mainland. Here, we examined the genetic variation and differentiation in feral populations (30 sampled individuals/population) of a globally invasive species (the American bullfrog, Lithobates catesbeianus) that was extensively farmed on 14 islands in the Zhoushan Archipelago of China and in three nearby regions on the mainland. We quantified the relative importance of propagule pressure and hunting pressures on the genetic variation of bullfrog populations and found that insular populations have greater genetic variation than their mainland counterparts. Although genetic differentiation between the populations was observed, no evidence of recent bottlenecks or population expansion in any of the tested population was found. Our results suggest that the propagule pressures of bullfrogs escaping from farms, multiple releases and hunting pressure influence the genetic variation among bullfrog populations. These results might have important implications for understanding the establishment and evolution of alien species on islands and for the management of invasive species.

Insights into the introduction history and population genetic dynamics of the Argentine black-and-white tegu (Salvator merianae) in Florida

Invasive species are a major threat to global biodiversity. The US state of Florida is especially susceptible to the spread of exotic reptiles due to its subtropical climate, disturbed habitats, and robust pet trade. The Argentine black-and-white tegu (Salvator merianae) is a large, omnivorous lizard currently established in two different regions of Southern Florida. These two populations pose potential threats to sensitive ground nesting species such as gopher tortoises, American crocodiles, and migratory birds. At present, the introduction histories of these populations and the degree to which they are connected by gene flow are largely unknown. To address these issues, we genotyped S. merianae from Hillsborough and Miami-Dade Counties at ten microsatellite loci to assess intrapopulation genetic diversity, the degree of gene flow between populations, and compare the plausibilities of several potential introduction scenarios. Our results indicate that both populations have low genetic diversity [mean number of effective alleles across loci in both populations = 2.09 and are highly differentiated from each other (G_ST = 0.170; G″_ST = 0.545)]. In addition, our results suggest that these populations underwent a bottleneck event prior to their divergence. We discuss what our results suggest about the histories of Florida's invasive tegu populations, as well as how they inform ongoing management strategies.

Integrative inference of population history in the Ibero-Maghrebian endemic Pleurodeles waltl (Salamandridae)

Inference of population histories from the molecular signatures of past demographic processes is challenging, but recent methodological advances in species distribution models and their integration in time-calibrated phylogeographic studies allow detailed reconstruction of complex biogeographic scenarios. We apply an integrative approach to infer the evolutionary history of the Iberian ribbed newt (Pleurodeles waltl), an Ibero-Maghrebian endemic with populations north and south of the Strait of Gibraltar. We analyzed an extensive multilocus dataset (mitochondrial and nuclear DNA sequences and ten polymorphic microsatellite loci) and found a deep east-west phylogeographic break in Iberian populations dating back to the Plio-Pleistocene. This break is inferred to result from vicariance associated with the formation of the Guadalquivir river basin. In contrast with previous studies, North African populations showed exclusive mtDNA haplotypes, and formed a monophyletic clade within the Eastern Iberian lineage in the mtDNA genealogy. On the other hand, microsatellites failed to recover Moroccan populations as a differentiated genetic cluster. This is interpreted to result from post-divergence gene flow based on the results of IMA2 and Migrate analyses. Thus, Moroccan populations would have originated after overseas dispersal from the Iberian Peninsula in the Pleistocene, with subsequent gene flow in more recent times, implying at least two trans-marine dispersal events. We modeled the distribution of the species and of each lineage, and projected these models back in time to infer climatically favourable areas during the mid-Holocene, the last glacial maximum (LGM) and the last interglacial (LIG), to reconstruct more recent population dynamics. We found minor differences in climatic favourability across lineages, suggesting intraspecific niche conservatism. Genetic diversity was significantly correlated with the intersection of environmental favourability in the LIG and LGM, indicating that populations of P. waltl are genetically more diverse in regions that have remained environmentally favourable through the last glacial cycle, particularly southern Iberia and northern Morocco. This study provides novel insights into the relative roles of geology and climate on the biogeography of a biodiversity hotspot.

Extreme genetic diversity in asexual grass thrips populations

The continuous generation of genetic variation has been proposed as one of the main factors explaining the maintenance of sexual reproduction in nature. However, populations of asexual individuals may attain high levels of genetic diversity through within-lineage diversification, replicate transitions to asexuality from sexual ancestors and migration. How these mechanisms affect genetic variation in populations of closely related sexual and asexual taxa can therefore provide insights into the role of genetic diversity for the maintenance of sexual reproduction. Here, we evaluate patterns of intra- and interpopulation genetic diversity in sexual and asexual populations of Aptinothrips rufus grass thrips. Asexual A. rufus populations are found throughout the world, whereas sexual populations appear to be confined to few locations in the Mediterranean region. We found that asexual A. rufus populations are characterized by extremely high levels of genetic diversity, both in comparison with their sexual relatives and in comparison with other asexual species. Migration is extensive among asexual populations over large geographic distances, whereas close sexual populations are strongly isolated from each other. The combination of extensive migration with replicate evolution of asexual lineages, and a past demographic expansion in at least one of them, generated high local clone diversities in A. rufus. These high clone diversities in asexual populations may mimic certain benefits conferred by sex via genetic diversity and could help explain the extreme success of asexual A. rufus populations.

Reconstructing the invasion history of Heracleum persicum (Apiaceae) into Europe

Sparse, incomplete and inappropriate historical records of invasive species often hamper invasive species management interventions. Population genetic analyses of invaders might provide a suitable context for the identification of their source populations and possible introduction routes. Here, we describe the population genetics of Heracleum persicum Desf. ex Fisch and trace its route of introduction into Europe. Microsatellite markers revealed a significantly higher genetic diversity of H. persicum in its native range, and the loss of diversity in the introduced range may be attributed to a recent genetic bottleneck. Bayesian cluster analysis on regional levels identified three and two genetic clusters in the native and the introduced ranges, respectively. A global structure analysis revealed two worldwide distinct genetic groups: one primarily in Iran and Denmark, the other primarily in Norway. There were also varying degrees of admixture in England, Sweden, Finland and Latvia. Approximate Bayesian computation indicated two independent introductions of H. persicum from Iran to Europe: the first one in Denmark and the second one in England. Finland was subsequently colonized by English populations. In contrast to the contemporary hypothesis of English origin of Norwegian populations, we found Finland to be a more likely source for Norwegian populations, a scenario supported by higher estimated historical migration from Finland to Norway. Genetic diversity per se is not a primary determinant of invasiveness in H. persicum. Our results indicate that, due to either pre-adaptations or rapid local adaptations, introduced populations may have acquired invasiveness after subsequent introductions, once a suitable environment was encountered.

Multi-locus genotyping reveals absence of genetic structure in field populations of the brown ear tick (Rhipicephalus appendiculatus) in Kenya

Rhipicephalus appendiculatus is an important tick vector of several pathogens and parasitizes domestic and wild animals across eastern and southern Africa. However, its inherent genetic variation and population structure is poorly understood. To investigate whether mammalian host species, geographic separation and resulting reproductive isolation, or a combination of these, define the genetic structure of R. appendiculatus, we analyzed multi-locus genotype data from 392 individuals from 10 geographic locations in Kenya generated in an earlier study. These ticks were associated with three types of mammalian host situations; (1) cattle grazing systems, (2) cattle and wildlife co-grazing systems (3) wildlife grazing systems without livestock. We also analyzed data from 460 individuals from 10 populations maintained as closed laboratory stocks and 117 individuals from five other species in the genus Rhipicephalus. The pattern of genotypes observed indicated low levels of genetic differentiation between the ten field populations (FST=0.014±0.002) and a lack of genetic divergence corresponding to the degree of separation of the geographic sampling locations. There was also no clear association of particular tick genotypes with specific host species. This is consistent with tick dispersal over large geographic ranges and lack of host specificity. In contrast, the 10 laboratory populations (FST=0.248±0.015) and the five other species of Rhipicephalus (FST=0.368±0.032) were strongly differentiated into distinct genetic groups. Some laboratory bred populations diverged markedly from their field counterparts in spite of originally being sampled from the same geographic locations. Our results demonstrate a lack of defined population genetic differentiation in field populations of the generalist R. appendiculatus in Kenya, which may be a result of the frequent anthropogenic movement of livestock and mobility of its several wildlife hosts between different locations.

Contrasting patterns of genetic and phenotypic differentiation in two invasive salmonids in the southern hemisphere

Invasion success may be expected to increase with residence time (i.e., time since first introduction) and secondary releases (i.e., those that follow the original introduction), but this has rarely been tested in natural fish populations. We compared genetic and phenotypic divergence in rainbow trout and brown trout in Chile and the Falkland Islands to test the prediction that adaptive divergence, measured as P_ST/F_ST, would increase with residence time and secondary releases. We also explored whether interspecific competition between invaders could drive phenotypic divergence. Residence time had no significant effect on genetic diversity, phenotypic divergence, effective population size, or signatures of expansion of invasive trout. In contrast, secondary releases had a major effect on trout invasions, and rainbow trout populations mostly affected by aquaculture escapees showed significant divergence from less affected populations. Coexistence with brown trout had a positive effect on phenotypic divergence of rainbow trout. Our results highlight an important role of secondary releases in shaping fish invasions, but do not support the contention that older invaders are more differentiated than younger ones. They also suggest that exotic trout may not have yet developed local adaptations in these recently invaded habitats, at least with respect to growth-related traits.

Molecular markers reveal narrow genetic base and culturing-associated genetic drift in Teretrius nigrescens Lewis populations released for the biological control of the larger grain borer in Africa

In biological control, successful establishment of a natural enemy species depends on its adaptability in the introduced range including its ability to re-establish desired ecological interactions with the pest. These are affected by genetic parameters hitherto largely unresolved in biological control. The larger grain borer (LGB), Prostephanus truncatus, an invasive species from meso-America, is the most important post-harvest pest of maize in Africa. We studied the genetic structure of Teretrius nigrescens, a predatory beetle previously released for the control of the pest in Africa, to test the hypothesis that establishment patterns were a result of ecotype-environment mismatch and to follow up on our earlier reports of distinct lineages of the predator. We studied 13 populations of T. nigrescens, using 16 polymorphic microsatellite markers. Five genetic populations with a hierarchical structure and significant isolation by distance were detected. The most diverse population was found in southern Mexico, consistent with earlier lineage coexistence observations. Populations introduced to Africa maintained genetic similarity to local geographic populations of their area of origin. The more successful Benin releases were also more genetically diverse. Loss of rare alleles and a higher frequency of existing private alleles in some populations indicated population expansions following bottleneck events. Sustainable biological control should accommodate pest and natural enemy species, and monitor genetic changes associated with introduction and release.

Population history and pathways of spread of the plant pathogen Phytophthora plurivora

Human activity has been shown to considerably affect the spread of dangerous pests and pathogens worldwide. Therefore, strict regulations of international trade exist for particularly harmful pathogenic organisms. Phytophthora plurivora, which is not subject to regulations, is a plant pathogen frequently found on a broad range of host species, both in natural and artificial environments. It is supposed to be native to Europe while resident populations are also present in the US. We characterized a hierarchical sample of isolates from Europe and the US and conducted coalescent-, migration, and population genetic analysis of sequence and microsatellite data, to determine the pathways of spread and the demographic history of this pathogen. We found P. plurivora populations to be moderately diverse but not geographically structured. High levels of gene flow were observed within Europe and unidirectional from Europe to the US. Coalescent analyses revealed a signal of a recent expansion of the global P. plurivora population. Our study shows that P. plurivora has most likely been spread around the world by nursery trade of diseased plant material. In particular, P. plurivora was introduced into the US from Europe. International trade has allowed the pathogen to colonize new environments and/or hosts, resulting in population growth.

Reconstructing the origin and dispersal patterns of village chickens across East Africa: insights from autosomal markers

Unravelling the genetic history of any livestock species is central to understanding the origin, development and expansion of agricultural societies and economies. Domestic village chickens are widespread in Africa. Their close association with, and reliance on, humans for long-range dispersal makes the species an important biological marker in tracking cultural and trading contacts between human societies and civilizations across time. Archaezoological and linguistic evidence suggest a complex history of arrival and dispersion of the species on the continent, with mitochondrial DNA (mtDNA) D-loop analysis revealing the presence of five distinct haplogroups in East African village chickens. It supports the importance of the region in understanding the history of the species and indirectly of human interactions. Here, through a detailed analysis of 30 autosomal microsatellite markers genotyped in 657 village chickens from four East African countries (Kenya, Uganda, Ethiopia and Sudan), we identify three distinct autosomal gene pools (I, II and III). Gene pool I is predominantly found in Ethiopia and Sudan, while II and III occur in both Kenya and Uganda. A gradient of admixture for gene pools II and III between the Kenyan coast and Uganda's hinterland (P = 0.001) is observed, while gene pool I is clearly separated from the other two. We propose that these three gene pools represent genetic signatures of separate events in the history of the continent that relate to the arrival and dispersal of village chickens and humans across the region. Our results provide new insights on the history of chicken husbandry which has been shaped by terrestrial and maritime contacts between ancient and modern civilizations in Asia and East Africa.

Genetic variation in brown trout Salmo trutta across the Danube, Rhine, and Elbe headwaters: a failure of the phylogeographic paradigm?

Background

Brown trout Salmo trutta have been described in terms of five major mtDNA lineages, four of which correspond to major ocean basins, and one, according to some authors, to a distinct taxon, marbled trout Salmo marmoratus. The Atlantic and Danubian lineages of brown trout meet in a poorly documented contact zone in Central Europe. The natural versus human mediated origin of the Atlantic lineage in the upper Danube is a question of both theoretical and practical importance with respect to conservation management. We provide a comprehensive population genetic analysis of brown trout in the region with the aim of evaluating the geographic distribution and genetic integrity of these two lineages in and around their contact zone.

Results

Genetic screening of 114 populations of brown trout across the Danube/Rhine/Elbe catchments revealed a counter-intuitive phylogeographic structure with near fixation of the Atlantic lineage in the sampled portions of the Bavarian Danube. Along the Austrian Danube, phylogeographic informative markers revealed increasing percentages of Danube-specific alleles with downstream distance. Pure Danube lineage populations were restricted to peri-alpine isolates within previously glaciated regions. Both empirical data and simulated hybrid comparisons support that trout in non-glaciated regions north and northeast of the Alps have an admixed origin largely based on natural colonization. In contrast, the presence of Atlantic basin alleles south and southeast of the Alps stems from hatchery introductions and subsequent introgression. Despite extensive stocking of the Atlantic lineage, little evidence of first generation stocked fish or F₁ hybrids were found implying that admixture has been established over time.

Conclusions

A purely phylogeographic paradigm fails to describe the distribution of genetic lineages of Salmo in Central Europe. The distribution pattern of the Atlantic and Danube lineages is extremely difficult to explain without invoking very strong biological mechanisms.

The peri-alpine distribution of relict populations of pure Danubian lineage brown trout implies that they colonized headwater river courses post-glacially ahead of the expansion of the Atlantic lineage. The recognition of natural as opposed to anthropogenic introgression of the Atlantic lineage into Danubian gene pools is of fundamental importance to management strategies.

Russian wheat aphids (Diuraphis noxia) in China: native range expansion or recent introduction?

In this study, we explore the population genetics of the Russian wheat aphid (RWA) (Diuraphis noxia), one of the world's most invasive agricultural pests, in north-western China. We have analysed the data of 10 microsatellite loci and mitochondrial sequences from 27 populations sampled over 2 years in China. The results confirm that the RWAs are holocyclic in China with high genetic diversity indicating widespread sexual reproduction. Distinct differences in microsatellite genetic diversity and distribution revealed clear geographic isolation between RWA populations in northern and southern Xinjiang, China, with gene flow interrupted across extensive desert regions. Despite frequent grain transportation from north to south in this region, little evidence for RWA translocation as a result of human agricultural activities was found. Consequently, frequent gene flow among northern populations most likely resulted from natural dispersal, potentially facilitated by wind currents. We also found evidence for the long-term existence and expansion of RWAs in China, despite local opinion that it is an exotic species only present in China since 1975. Our estimated date of RWA expansion throughout China coincides with the debut of wheat domestication and cultivation practices in western Asia in the Holocene. We conclude that western China represents the limit of the far eastern native range of this species. This study is the most comprehensive molecular genetic investigation of the RWA in its native range undertaken to date and provides valuable insights into the history of the association of this aphid with domesticated cereals and wild grasses.

Microsatellite variation suggests a recent fine-scale population structure of Drosophila sechellia, a species endemic of the Seychelles archipelago

Drosophila sechellia is closely related to the cosmopolitan and widespread model species, D. simulans. This species, endemic to the Seychelles archipelago, is specialized on the fruits of Morinda citrifolia, and harbours the lowest overall genetic diversity compared to other species of Drosophila. This low diversity is associated with a small population size. In addition, no obvious population structure has been evidenced so far across islands of the Seychelles archipelago. Here, a microsatellite panel of 17 loci in ten populations from nine islands of the Seychelles was used to assess the effect of the D. sechellia's fragmented distribution on the fine-scale population genetic structure, the migration pattern, as well as on the demography of the species. Contrary to previous results, also based on microsatellites, no evidence for population contraction in D. sechellia was found. The results confirm previous studies based on gene sequence polymorphism that showed a long-term stable population size for this species. Interestingly, a pattern of Isolation By Distance which had not been described yet in D. sechellia was found, with evidence of first-generation migrants between some neighbouring islands. Bayesian structuring algorithm results were consistent with a split of D. sechellia into two main groups of populations: Silhouette/Mahé versus all the other islands. Thus, microsatellites suggest that variability in D. sechellia is most likely explained by local genetic exchanges between neighbouring islands that have recently resulted in slight differentiation of the two largest island populations from all the others.

Inter-island divergence within Drosophila mauritiana, a species of the D. simulans complex: Past history and/or speciation in progress?

Speciation with gene flow may be more common than generally thought, which makes detailed understanding of the extent and pattern of genetic divergence between geographically isolated populations useful. Species of the Drosophila simulans complex provide a good model for speciation and evolutionary studies, and hence understanding their population genetic structure will increase our understanding of the context in which speciation has occurred. Here, we describe genetic diversity and genetic differentiation of two distant populations of D. mauritiana (Mauritius and Rodrigues Islands) at mitochondrial and nuclear loci. We surveyed the two populations for their mitochondrial haplotypes, eight nuclear genes and 18 microsatellite loci. A new mitochondrial type is fixed in the Rodrigues population of D. mauritiana. The two populations are highly differentiated, their divergence appears relatively ancient (100,000 years) compared to the origin of the species, around 0.25MYA, and they exhibit very limited gene flow. However, they have similar levels of divergence from their sibling, D. simulans. Both nuclear genes and microsatellites revealed contrasting demographic histories between the two populations, expansion for the Mauritius population and stable population size for the Rodrigues Island population. The discovery of pronounced geographic structure within D. mauritiana combined to genetic structuring and low gene flow between the two island populations illuminates the evolutionary history of the species and clearly merits further attention in the broad context of speciation.

Population structure, demographic history, and selective processes: contrasting evidences from mitochondrial and nuclear markers in the European spiny lobster Palinurus elephas (Fabricius, 1787)

The European spiny lobster Palinurus elephas (Fabricius, 1787) is an ecologically and economically important species inhabiting a wide geographic range that extends from the North-east Atlantic and Azores to the Eastern Mediterranean. We investigated the population structure and evolutionary history of this species by both mitochondrial and microsatellite markers. Ten population samples covering a large part of the species distribution range (three samples from the Atlantic Ocean and seven from the Mediterranean Sea) were analyzed for a portion of the mitochondrial control region and seven polymorphic microsatellite loci. Both markers rejected the hypothesis of panmixia identifying two differentiated gene pools. The control region clearly distinguished the Atlantic and Mediterranean populations in two genetically separated groups. Microsatellites, also revealed two groups roughly associated to the Atlantic-Mediterranean separation, however, the Azores sample did not conform to this geographic scheme. Discrepancy between mitochondrial and nuclear markers emerged also when reconstructing the history of the species. Neutrality tests of the mitochondrial sequences indicated a departure from mutation-drift equilibrium that, combined to the mismatch analysis, pointed toward a sudden population expansion in both Atlantic and Mediterranean gene pools. Unexpectedly, microsatellites did not identify any signal of population expansion neither in the Atlantic pool nor in the Mediterranean one.

Spatial genetic structure of Aedes aegypti mosquitoes in mainland Southeast Asia

Aedes aegypti mosquitoes originated in Africa and are thought to have spread recently to Southeast Asia, where they are the major vector of dengue. Thirteen microsatellite loci were used to determine the genetic population structure of A. aegypti at a hierarchy of spatial scales encompassing 36 sites in Myanmar, Cambodia and Thailand, and two sites in Sri Lanka and Nigeria. Low, but significant, genetic structuring was found at all spatial scales (from 5 to >2000 km) and significant F IS values indicated genetic structuring even within 500 m. Spatially dependent genetic-clustering methods revealed that although spatial distance plays a role in shaping larger-scale population structure, it is not the only factor. Genetic heterogeneity in major port cities and genetic similarity of distant locations connected by major roads, suggest that human transportation routes have resulted in passive long-distance migration of A. aegypti. The restricted dispersal on a small spatial scale will make localized control efforts and sterile insect technology effective for dengue control. Conversely, preventing the establishment of insecticide resistance genes or spreading refractory genes in a genetic modification strategy would be challenging. These effects on vector control will depend on the relative strength of the opposing effects of passive dispersal.

Ustilago maydis populations tracked maize through domestication and cultivation in the Americas

The domestication of crops and the development of agricultural societies not only brought about major changes in human interactions with the environment but also in plants' interactions with the diseases that challenge them. We evaluated the impact of the domestication of maize from teosinte and the widespread cultivation of maize on the historical demography of Ustilago maydis, a fungal pathogen of maize. To determine the evolutionary response of the pathogen's populations, we obtained multilocus genotypes for 1088 U. maydis diploid individuals from two teosinte subspecies in Mexico and from maize in Mexico and throughout the Americas. Results identified five major U. maydis populations: two in Mexico; two in South America; and one in the United States. The two populations in Mexico diverged from the other populations at times comparable to those for the domestication of maize at 6000-10000 years before present. Maize domestication and agriculture enforced sweeping changes in U. maydis populations such that the standing variation in extant pathogen populations reflects evolution only since the time of the crop's domestication.

Population history of Berthelot's pipit: colonization, gene flow and morphological divergence in Macaronesia

The fauna of oceanic islands provide exceptional models with which to examine patterns of dispersal, isolation and diversification, from incipient speciation to species level radiations. Here, we investigate recent differentiation and microevolutionary change in Berthelot's pipit (Anthus berthelotii), an endemic bird species inhabiting three Atlantic archipelagos. Mitochondrial DNA sequence data and microsatellite markers were used to deduce probable colonization pathway, genetic differentiation, and gene flow among the 12 island populations. Phenotypic differentiation was investigated based on eight biologically important morphological traits. We found little mitochondrial DNA variability, with only one and four haplotypes for the control region and cytochrome b, respectively. However, microsatellite data indicated moderate population differentiation (FST=0.069) between the three archipelagos that were identified as genetically distinct units with limited gene flow. Both results, combined with the estimated time of divergence (2.5 millions years ago) from the Anthus campestris (the sister species), suggest that this species has only recently dispersed throughout these islands. The genetic relationships, patterns of allelic richness and exclusive alleles among populations suggest the species originally colonized the Canary Islands and only later spread from there to the Madeiran archipelago and Selvagen Islands. Differentiation has also occurred within archipelagos, although to a lesser degree. Gene flow was observed more among the eastern and central islands of the Canaries than between these and the western islands or the Madeiran Islands. Morphological differences were also more important between than within archipelagos. Concordance between morphological and genetic differentiation provided ambiguous results suggesting that genetic drift alone was not sufficient to explain phenotypic differentiation. The observed genetic and morphological differences may therefore be the result of differing patterns of selection pressures between populations, with Berthelot's pipit undergoing a process of incipient differentiation.