Independent introductions and sequential founder events shape genetic differentiation and diversity of the invasive green anole (Anolis carolinensis) on Pacific Islands

Genomic signatures of admixture and selection are shared among populations of Zaprionus indianus across the western hemisphere

Introduced species have become an increasingly common component of biological communities around the world. A central goal in invasion biology is therefore to identify the demographic and evolutionary factors that underlie successful introductions. Here we use whole genome sequences, collected from populations in the native and introduced range of the African fig fly, Zaprionus indianus, to quantify genetic relationships among them, identify potential sources of the introductions, and test for selection at different spatial scales. We find that geographically widespread populations in the western hemisphere are genetically more similar to each other than to lineages sampled across Africa, and that these populations share a mixture of alleles derived from differentiated African lineages. Using patterns of allele‐sharing and demographic modelling we show that Z. indinaus have undergone a single expansion across the western hemisphere with admixture between African lineages predating this expansion. We also find support for selection that is shared across populations in the western hemisphere, and in some cases, with a subset of African populations. This suggests either that parallel selection has acted across a large part of Z. indianus's introduced range; or, more parsimoniously, that Z. indianus has experienced selection early on during (or prior‐to) its expansion into the western hemisphere. We suggest that the range expansion of Z. indianus has been facilitated by admixture and selection, and that management of this invasion could focus on minimizing future admixture by controlling the movement of individuals within this region rather than between the western and eastern hemisphere.

An island-hopping bird reveals how founder events shape genome-wide divergence

When populations colonize new areas, both strong selection and strong drift can be experienced due to novel environments and small founding populations, respectively. Empirical studies have predominantly focused on the phenotype when assessing the role of selection, and limited neutral-loci when assessing founder-induced loss of diversity. Consequently, the extent to which processes interact to influence evolutionary trajectories is difficult to assess. Genomic-level approaches provide the opportunity to simultaneously consider these processes. Here, we examine the roles of selection and drift in shaping genomic diversity and divergence in historically documented sequential island colonizations by the silvereye (Zosterops lateralis). We provide the first empirical demonstration of the rapid appearance of highly diverged genomic regions following population founding, the position of which are highly idiosyncratic. As these regions rarely contained loci putatively under selection, it is most likely that these differences arise via the stochastic nature of the founding process. However, selection is required to explain rapid evolution of larger body size in insular silvereyes. Reconciling our genomic data with these phenotypic patterns suggests there may be many genomic routes to the island phenotype, which vary across populations. Finally, we show that accelerated divergence associated with multiple founding steps is the product of genome-wide rather than localized differences, and that diversity erodes due to loss of rare alleles. However, even multiple founder events do not result in divergence and diversity levels seen in evolutionary older subspecies, and therefore do not provide a shortcut to speciation as proposed by founder-effect speciation models.

Genetic Diversity and Thermal Performance in Invasive and Native Populations of African Fig Flies

During biological invasions, invasive populations can suffer losses of genetic diversity that are predicted to negatively impact their fitness/performance. Despite examples of invasive populations harboring lower diversity than conspecific populations in their native range, few studies have linked this lower diversity to a decrease in fitness. Using genome sequences, we show that invasive populations of the African fig fly, Zaprionus indianus, have less genetic diversity than conspecific populations in their native range and that diversity is proportionally lower in regions of the genome experiencing low recombination rates. This result suggests that selection may have played a role in lowering diversity in the invasive populations. We next use interspecific comparisons to show that genetic diversity remains relatively high in invasive populations of Z. indianus when compared with other closely related species. By comparing genetic diversity in orthologous gene regions, we also show that the genome-wide landscape of genetic diversity differs between invasive and native populations of Z. indianus indicating that invasion not only affects amounts of genetic diversity but also how that diversity is distributed across the genome. Finally, we use parameter estimates from thermal performance curves for 13 species of Zaprionus to show that Z. indianus has the broadest thermal niche of measured species, and that performance does not differ between invasive and native populations. These results illustrate how aspects of genetic diversity in invasive species can be decoupled from measures of fitness, and that a broad thermal niche may have helped facilitate Z. indianus's range expansion.

Genetic Variation May Have Promoted the Successful Colonization of the Invasive Gall Midge, Obolodiplosis robiniae, in China

Invasive species often cause serious economic and ecological damage. Despite decades of extensive impacts of invasives on bio-diversity and agroforestry, the mechanisms underlying the genetic adaptation and rapid evolution of invading populations remain poorly understood. The black locust gall midge, Obolodiplosis robiniae, a highly invasive species that originated in North America, spread widely throughout Asia and Europe in the past decade. Here, we used 11 microsatellite DNA markers to analyze the genetic variation of 22 O. robiniae populations in China (the introduced region) and two additional US populations (the native region). A relatively high level of genetic diversity was detected among the introduced populations, even though they exhibited lower diversity than the native US populations. Evidence for genetic differentiation among the introduced Chinese populations was also found based on the high Fst value compared to the relatively low among the native US populations. Phylogenetic trees, structure graphical output, and principal coordinate analysis plots suggested that the Chinese O. robiniae populations (separated by up to 2,540 km) cluster into two main groups independent of geographical distance. Genetic variation has been observed to increase rapidly during adaptation to a new environment, possibly contributing to population establishment and spread. Our results provide insights into the genetic mechanisms underlying successful invasion, and identify factors that have contributed to colonization by an economically important pest species in China. In addition, the findings improve our understanding of the role that genetic structure plays during invasion by O. robiniae.

Genetic diversity and inferred dispersal history of the Schlegel's Japanese Gecko (Gekko japonicus) in Northeast Asia based on population genetic analyses and paleo-species distribution modelling

To understand the genetic diversity and dispersal history of Schlegel's Japanese gecko (Gekko japonicus), we performed genetic analyses and paleo-species distributional modelling. For the genetic analysis, we analyzed mitochondrial DNA (mtDNA) (cytochrome b [Cytb] and NADH dehydrogenase 2 [ND2]) and seven microsatellite loci of 353 individuals from 11 populations (2 east coast China, 4 west and central coast Japan and 5 Korea). For the paleo-species distribution modelling, we used 432 occurrence data points (125 China, 291 Japan and 16 Korea) over the Pleistocene and Holocene. China is inferred to be the source population, which had higher genetic diversity (mtDNA) and more private alleles (mtDNA) compared to Japanese and Korean populations. Differences between the three counties were very small in the mtDNA haplotype network despite some genetic structure among the three countries. Microsatellite analysis inferred that genetic exchange has actively occurred among the Chinese, Japanese and Korean populations. Suitable habitats in Japan should have been plentiful by the mid-Holocene, but have only recently become available in Korea. These results suggest that dispersal of G. japonicus occurred after the Holocene warming from the east coast of China to the west and central coasts of Japan and Korea, and gene flow is actively occurring among the three countries.