Contrasting Historical and Recent Gene Flow among African Buffalo Herds in the Caprivi Strip of Namibia

There is widespread concern about impacts of land-use change on connectivity among animal and plant populations, but those impacts are difficult to quantify. Moreover, lack of knowledge regarding ecosystems before fragmentation may obscure appropriate conservation targets. We use occurrence and population genetic data to contrast connectivity for a long-lived mega-herbivore over historical and contemporary time frames. We test whether (i) historical gene flow is predicted by persistent landscape features rather than human settlement, (ii) contemporary connectivity is most affected by human settlement and (iii) recent gene flow estimates show the effects of both factors. We used 16 microsatellite loci to estimate historical and recent gene flow among African elephant (Loxodonta africana) populations in seven protected areas in Tanzania, East Africa. We used historical gene flow (FST and G'ST ) to test and optimize models of historical landscape resistance to movement. We inferred contemporary landscape resistance from elephant resource selection, assessed via walking surveys across ~15400km(2) of protected and unprotected lands. We used assignment-based recent gene flow estimates to optimize and test the contemporary resistance model, and to test a combined historical and contemporary model. We detected striking changes in connectivity. Historical connectivity among elephant populations was strongly influenced by slope but not human settlement, whereas contemporary connectivity was influenced most by human settlement. Recent gene flow was strongly influenced by slope but was also correlated with contemporary resistance. Inferences across multiple timescales can better inform conservation efforts on large and complex landscapes, while mitigating the fundamental problem of shifting baselines in conservation.

The populations of goitered gazelle suffered significant decline due to natural and anthropogenic factors over the last century. Investigating the effects of barriers on gene flow among the remaining populations is vital for conservation planning. Here we adopted a landscape genetics approach to evaluate the genetic structure of the goitered gazelle in Central Iran and the effects of landscape features on gene flow using 15 polymorphic microsatellite loci. Spatial autocorrelation, isolation by distance (IBD) and isolation by resistance (IBR) models were used to elucidate the effects of landscape features on the genetic structure. Ecological modeling was used to construct landscape permeability and resistance map using 12 ecogeographical variables. Bayesian algorithms revealed three genetically homogeneous groups and restricted dispersal pattern in the six populations. The IBD and spatial autocorrelation revealed a pattern of decreasing relatedness with increasing distance. The distribution of potential habitats was strongly correlated with bioclimatic factors, vegetation type, and elevation. Resistance distances and graph theory were significantly related with variation in genetic structure, suggesting that gazelles are affected by landscape composition. The IBD showed greater impact on genetic structure than IBR. The Mantel and partial Mantel tests indicated low but non-significant effects of anthropogenic barriers on observed genetic structure. We concluded that a combination of geographic distance, landscape resistance, and anthropogenic factors are affecting the genetic structure and gene flow of populations. Future road construction might impede connectivity and gene exchange of populations. Conservation measures on this vulnerable species should consider some isolated population as separate management units.

Sorbus domestica (Rosaceae) is one of the rarest deciduous tree species in Europe and is characterized by a scattered distribution. To date, no large-scale geographic studies on population genetics have been carried out. Therefore, the aims of this study were to infer levels of molecular diversity across the major part of the European distribution of S. domestica and to determine its population differentiation and structure. In addition, spatial genetic structure was examined together with the patterns of historic and recent gene flow between two adjacent populations. Leaf or cambium samples were collected from 17 populations covering major parts of the European native range from north-west France to south-east Bulgaria. Seven nuclear microsatellites and one chloroplast minisatellite were examined and analysed using a variety of methods. Allelic richness was unexpectedly high for both markers within populations (mean per locus: 3·868 for nSSR and 1·647 for chloroplast minisatellite). Moreover, there was no evidence of inbreeding (mean Fis = -0·047). The Italian Peninsula was characterized as a geographic region with comparatively high genetic diversity for both genomes. Overall population differentiation was moderate (FST = 0·138) and it was clear that populations formed three groups in Europe, namely France, Mediterranean/Balkan and Austria. Historic gene flow between two local Austrian populations was high and asymmetric, while recent gene flow seemed to be disrupted. It is concluded that molecular mechanisms such as self-incompatibility and high gene flow distances are responsible for the observed level of allelic richness as well as for population differentiation. However, human influence could have contributed to the present genetic pattern, especially in the Mediterranean region. Comparison of historic and recent gene flow may mirror the progress of habitat fragmentation in eastern Austria.

Rafting has been proposed as an effective mechanism for species without free-living pelagic larvae to achieve long-distance dispersal, theoretically preventing population differentiation over wide distributional ranges. Moreover, rafting has been advocated as a main dispersal mechanism for marine invertebrates with sub-Antarctic distributions, because of abundant buoyant kelps, driven by the Antarctic Circumpolar Current. Nonetheless, little attention has been given to the role of rafting to establish regular gene flow across the sub-Antarctic, and the geographic and temporal scales at which it occurs. Aiming to unravel these major questions about the extent of genetic connectivity across the Southern Ocean (SO), we studied the pulmonate limpet Siphonaria lateralis, a benthic species with encapsulated larvae, found on the rocky intertidal of sub-Antarctic islands and southern South America. Since S. lateralis is closely associated with D. antarctica, dispersal by rafting is plausible, as revealed by the absence of phylogeographic structure across the sub-Antarctic. We sampled 116 individuals from eight localities across the SO, and used 5,515 SNPs obtained through Genotyping-by-Sequencing, to determine contemporary genetic diversity, structure, and gene flow at two spatial scales; global, across the SO, and regional, within Kerguelen. Results identified substantial genetic structure, differentiating Patagonia, Falklands/Malvinas Islands, South Georgia and the Kerguelen archipelago, and low levels of contemporary gene flow. The most notable genetic differentiation was found between Patagonia/Falklands and South Georgia/Kerguelen. Structure was also significant between Patagonia and the Falkland/Malvinas Islands. Conversely, South Georgia and Kerguelen exhibited closer genetic affinity, and indications of recent but limited gene flow. Moreover, historical gene flow estimates between the four populations were low. At regional scale, noteworthy genetic structure persisted, and gene flow was insufficient to prevent genetic differentiation within Kerguelen. Consequently, rafting’s potential may be overestimated as a contemporary mechanism promoting gene flow across the SO, as these events may be sporadic, irregular, and unpredictable for marine invertebrates lacking a larval dispersal stage, since contemporary dispersal events don’t seem to facilitate high gene flow at both scales. Accordingly, other oceanographic factors or processes may hinder the establishment of species associated with macroalgae, and as consequence, contemporary genetic connectivity in the sub-Antarctic.

Over 95% of the currently cultivated cotton was domesticated from Gossypium hirsutum, which originated and diversified in Mexico. Demographic and genetic studies of this species at its centre of origin and diversification are lacking, although they are critical for cotton conservation and breeding. We investigated the actual and potential distribution of wild cotton populations, as well as the contribution of historical and recent gene flow in shaping cotton genetic diversity and structure. We evaluated historical gene flow using chloroplast microsatellites and recent gene flow through the assessment of transgene presence in wild cotton populations, exploiting the fact that genetically modified cotton has been planted in the North of Mexico since 1996. Assessment of geographic structure through Bayesian spatial analysis, BAPS and Genetic Algorithm for Rule-set Production (GARP), suggests that G. hirsutum seems to conform to a metapopulation scheme, with eight distinct metapopulations. Despite evidence for long-distance gene flow, genetic variation among the metapopulations of G. hirsutum is high (He = 0.894 ± 0.01). We identified 46 different haplotypes, 78% of which are unique to a particular metapopulation, in contrast to a single haplotype detected in cotton cultivars. Recent gene flow was also detected (m = 66/270 = 0.24), with four out of eight metapopulations having transgenes. We discuss the implications of the data presented here with respect to the conservation and future breeding of cotton populations and genetic diversity at its centre of crop origin.

The relationship between genes and behaviour has been of longstanding interest to evolutionary biologists. Certain behaviours can shape the genetic structure of natural populations, thereby altering their genetic diversity and influencing their evolutionary fate. Dispersal is the behaviour that mediates gene flow, the extent of which determines population genetic structure. Because both historic and contemporary gene flow are considered to have greatly impacted their evolutionary history, baboons (genus Papio) are especially intriguing to study the relationship between behaviour and population genetic structure. Both species-specific male- and female-biased dispersal can be observed in this genus, their current distribution was shaped by range expansion and contraction, and interspecific gene flow is prevalent. In this thesis, I investigated how different dispersal patterns influence gene flow in baboons to contribute to a better understanding of the interrelation between behavioural ecology and genetic makeup of natural populations. I specifically addressed how differences in the social system of baboon species impact their genetic structure and also used the observed patterns to draw inferences about sex-biased dispersal in Guinea baboons, one of the least known members of the genus. I examined in detail how both historic and contemporary gene flow shape the genetic structure of Guinea baboons and whether we can draw inferences about human evolution from the analysis of range expansions in baboons. To answer these questions, I used a population genetic approach based on distribution-wide, geo-referenced faecal samples of baboons for which I analysed both autosomal microsatellites and part of the mitochondrial hypervariable region I. I could show that the genetic structure of Guinea baboons is best explained by female-biased dispersal, both on a local and a distribution-wide scale. Female gene flow results in high intrapopulation diversity and a lack of genetic-geographic structuring in mitochondrial DNA. In contrast, there is significant structuring of nuclear markers on a global scale and males exhibit higher population structuring than females on a local scale, as expected if males are the more philopatric sex. Over the whole distribution, locally restricted dispersal appears to limit effective gene flow to a distance of below 200 km, resulting in a strong isolation-by-distance effect and genetically divergent populations. Signatures of population expansion, the clinal structure of genetic variation, and potential traces of allele surfing, point to an historic west-ward expansion of Guinea baboons. Introgressive hybridization with olive baboons can be invoked to explain genetic patterns in the contact zone, but warrant further investigation. Additionally I could show the ‘southern route’ from Africa to Arabia could have been used by hamadryas baboons during the same time period in the Late Pleistocene as proposed for modern humans. My study is the first comprehensive analysis of the genetic population structure in Guinea baboons and provides evidence for female-biased dispersal in this species. It corroborates the notion that the Guinea baboons’ social system shares some important features with that of hamadryas baboons, suggesting similar evolutionary forces have acted to distinguish them from all other baboons. In conjunction with the importance of range expansions in shaping their distribution and genetic diversity, this strengthens baboons as an intriguing model to elucidate the processes that also influenced the evolution of our own species.

Mountains and refuges: Genetic structure and evolutionary history in closely related, endemic Centaurea in continental Greece

Biological invasions of pests into climatically unsuitable areas can be facilitated by human‐regulated environments, in which case there may be an impact on genetic structure through population processes and/or adaptation. Here, we investigated the population genetic structure of an invasive agricultural pest, Thrips palmi, in China, which has expanded its distribution range through using greenhouses. Early invaded populations showed a relatively higher level of genetic diversity than recently expanded greenhouse populations. Strong population genetic structure corresponded to a pattern of isolation by distance, with no recent gene flow and low historical gene flow among populations, reflecting limited ongoing dispersal. A genetic signature of population expansion was detected in early invaded populations and three northern populations from greenhouses, suggesting that the greenhouse environments facilitated expansion of this species. Redundancy analysis showed that the independent effects of environment and geography could explain 51.68% and 32.06% of the genetic variance, respectively. These findings point to climate‐ and greenhouse‐related spatial expansion, with the potential for adaptation by T. palmi. They emphasize the contribution of human‐regulated environments on the successes of this invasive species, a situation likely to apply to other invasive species that use greenhouse environments.

The reintroduction of a species into its historical range can present challenges for wildlife managers, particularly when it occurs near the edge of that species’ range and the population is isolated from others. One important aspect of reintroductions is the selection of source populations that best suit local conditions. Additionally, movement and gene flow between reintroduced and extant populations is important for maintaining genetic diversity and evolutionary processes but can be highly influenced by habitat quality, quantity, intactness, and landscape permeability. The reintroduction of pronghorn (Antilocapra americana) into the Flint Hills region of east-central Kansas from the late 1970s through the early 1990s resulted in the establishment of a small population (~ 30 individuals) originating from southwest Wyoming and southeast Colorado. We collected pronghorn fecal samples from the Flint Hills region and from a historical population in western Kansas for DNA analysis to compare, predict, and model genetic diversity, gene flow, isolation, and genetic drift within the Flint Hills population since reintroduction. Our results indicated the average observed heterozygosity from the Flint Hills (0.68) was slightly higher than in western Kansas (0.61), and the average number of alleles per locus were similar (6.1 and 6.2 respectively). Pairwise FST (0.09, p = 0.00001) and G”ST (0.15) indicated slight restriction of gene flow, but not complete isolation between the two groups. Shared ancestry was detected between both groups which may be either through recent gene flow, historical gene flow or similar source populations. The higher genetic diversity found in the Flint Hills population may be attributed to behavioral isolation between the two source populations, the underestimation of their population size, or long-distance immigration from other populations. Additionally, changes in agricultural practices and higher habitat fragmentation in western Kansas may be limiting local and regional pronghorn movement and gene flow. Our results provide additional insight into potential factors influencing the diversity and structure within small, isolated populations when considering future reintroductions of pronghorn and other wildlife species.

Despite recent advances in population genetic theory and empirical research, the extent of genetic differentiation among natural populations of animals remains difficult to predict. We reviewed studies of geographic variation in mitochondrial DNA in seabirds to test the importance of various factors in generating population genetic and phylogeographic structure. The extent of population genetic and phylogeographic structure varies extensively among species. Species fragmented by land or ice invariably exhibit population genetic structure and most also have phylogeographic structure. However, many populations (26 of 37) display genetic structure in the absence of land, suggesting that other barriers to gene flow exist. In these populations, the extent of genetic structure is best explained by nonbreeding distribution: almost all species with two or more population-specific nonbreeding areas (or seasons) have phylogeographic structure, and all species that are resident at or near breeding colonies year-round have population genetic structure. Geographic distance between colonies and foraging range appeared to have a weak influence on the extent of population genetic structure, but little evidence was found for an effect of colony dispersion or population bottlenecks. In two species (Galapagos petrel, Pterodroma phaeopygia, and Xantus's murrelet, Synthliboramphus hypoleucus), population genetic structure, and even phylogeographic structure, exist in the absence of any recognizable physical or nonphysical barrier, suggesting that other selective or behavioural processes such as philopatry may limit gene flow. Retained ancestral variation may be masking barriers to dispersal in some species, especially at high latitudes. Allopatric speciation undoubtedly occurs in this group, but reproductive isolation also appears to have evolved through founder-induced speciation, and there is strong evidence that parapatric and sympatric speciation occur. While many questions remain unanswered, results of the present review should aid conservation efforts by enabling managers to predict the extent of population differentiation in species that have not yet been studied using molecular markers, and, thus, enable the identification of management units and evolutionary significant units for conservation.

The disjunctive distribution of Fagus hayatae between Taiwan and mainland China provides a unique framework for understanding phylogeographic patterns and evolutionary processes in relict tree species. This study investigated the genetic diversity, population structure, and phylogeographic history of F. hayatae using microsatellite and chloroplast DNA markers. Analysis of 249 samples from nine populations revealed that Taiwanese populations possess higher genetic diversity with significant inbreeding, while mainland Chinese populations showed lower diversity and inbreeding levels. Chloroplast DNA analysis identified eight haplotypes, with unique variants in Taiwanese populations. AMOVA confirmed significant genetic differentiation between the two regions, revealing four distinct clustering patterns and three clear phylogenetic clades, including an early-diverging Taiwanese TS population. Molecular divergence time estimation based on chloroplast DNA sequences indicates a temporal divergence pattern within F. hayatae populations, with the Taiwanese TS lineage exhibiting an earlier separation event, followed by subsequent divergence between other Taiwanese populations (PCTS and AW) and mainland Chinese populations (CH). These phylogeographic events temporally correspond with significant paleoclimatic and geotectonic episodes in East Asia. Demographic and historical biogeography inference revealed a recent population decline in Taiwan, in contrast to more stable population dynamics on the mainland, while historical gene flow between the regions remains limited, and suggested several dispersals and vicariant events influencing the current genetic structure. These findings not only delineate the genetic structure shaped by historical geographic isolation and contemporary evolutionary processes but also emphasize Taiwan's role as a genetic refugium for F. hayatae.

In landscapes shaped by intense agriculture, even common bee species may face limits to their dispersal capacity. We explored how spatial isolation and land-use types influence the genetic population structure of two generalist mining bees — Andrena haemorrhoa and A. nigroaenea —which differ in body size and putative dispersal potential, yet sharing similar ecological niches. Using a network of isolated wetland patches as a model for fragmented habitats, we hypothesized that body size, spatial isolation, and landscape features, such as intensive crop production, affect genetic structure. We expected the larger-bodied A. nigroaenea to show less genetic differentiation due to higher dispersal potential, while gene flow in the smaller A. haemorrhoa would be constrained by landscape resistance and isolation. Using nine microsatellite markers per species, we found low genetic differentiation, with no consistent link between body size and genetic structure. Genetic clusters did not align with spatial clustering, suggesting that factors beyond geographic isolation — like mating systems, male-biased dispersal, and female philopatry — may shape genetic structure. Landscape resistance, i.e. species-specific habitat permeability, showed a weak influence on gene flow, more evident in A. haemorrhoa, indicating some, albeit limited landscape impact on dispersal. Despite evidence for inbreeding, both species maintained high allelic richness. Our results highlight how species life-histories, ecological factors, and landscape features interact to shape population structure. Despite considerable landscape fragmentation, generalist bees showed little spatial genetic structure, emphasizing the value of high-quality habitat patches and corridors for supporting gene-flow, especially in smaller-bodied species.

Janzen's influential "mountain passes are higher in the tropics" hypothesis predicts restricted gene flow and genetic isolation among populations spanning elevational gradients in the tropics. Few studies have tested this prediction, and studies that focus on population genetic structure in Southeast Asia are particularly underrepresented in the literature. Here, we test the hypothesis that mountain treeshrews (Tupaia montana) exhibit limited dispersal across their broad elevational range which spans ~2,300m on two peaks in Kinabalu National Park (KNP) in Borneo: Mt Tambuyukon (MT) and Mt Kinabalu (MK). We sampled 83 individuals across elevations on both peaks and performed population genomics analyses on mitogenomes and single nucleotide polymorphisms from 4,106 ultraconserved element loci. We detected weak genetic structure and infer gene flow both across elevations and between peaks. We found higher genetic differentiation on MT than MK despite its lower elevation and associated environmental variation. This implies that, contrary to our hypothesis, genetic structure in this system is not primarily shaped by elevation. We propose that this pattern may instead be the result of historical processes and limited upslope gene flow on MT. Importantly, our results serve as a foundational estimate of genetic diversity and population structure from which to track potential future effects of climate change on mountain treeshrews in KNP, an important conservation stronghold for the mountain treeshrew and other montane species.

Single-nucleotide polymorphisms (SNPs) represent the most prevalent form of genomic polymorphism and are extensively used in population genetics research. Using dd-RAD sequencing, a high-throughput sequencing method, we investigated the genome-level diversity, population structure, and phylogenetic relationships among three morphological forms of the widely distributed taxon Cryptotaenia japonica Hassk., which is native to East Asia. Our study aimed to assess the species status of C. japonica according to its genetic structure and genetic diversity patterns among 66 naturally distributed populations, comprising 26C. japonica f. japonica, 36C. japonica f. dissecta (Y. Yabe) Hara and 4C. japonica f. pinnatisecta S. L. Liou accessions. Based on genomic SNP data generated by dd-RAD sequencing, we conducted genetic diversity, principal component, neighbor-joining (NJ) phylogenetic, admixture clustering, and population differentiation analyses. The findings revealed the following: (1) 5,39,946 unlinked, high-quality SNPs, with mean π, H O, H E and F IS values of 0.062, 0.066, 0.043 and -0.014, respectively, were generated; (2) population divergence was unaffected by isolation through distance; (3) six main distinct regions corresponding to geographic locations and exhibiting various levels of genetic diversity were identified; (4) pairwise F ST analysis showed significant (P < 0.05) population differentiation in 0%-14% of populations among the six regions after sequential Bonferroni correction; and (5) three migration events (historical gene flow) indicated east‒west directionality. Moreover, contemporary gene flow analysis using Jost's D, Nei's G ST, and Nm values highlighted the middle latitude area of East Asia as a significant contributor to genetic structuring in C. japonica. Overall, our study elucidates the relatively low genetic differentiation and population structure of C. japonica across East Asia, further enhancing our understanding of plant lineage diversification in the Sino-Japanese Floristic Region.

Understanding the ecological and evolutionary processes occurring during species range shifts is important in the current context of global change. Here, we investigate the interplay between recent expansion, gene flow and genetic drift, and their consequences for genetic diversity and structure at landscape and local scales in European beech (Fagus sylvatica L.) On Mont Ventoux, South-Eastern France, we located beech forest refugia at the time of the most recent population minimum, ~150 years ago, and sampled 71 populations (2042 trees) in both refugia and expanding populations over an area of 15,000 ha. We inferred patterns of gene flow and genetic structure using 12 microsatellite markers. We identified six plots as originating from planting, rather than natural establishment, mostly from local genetic material. Comparing genetic diversity and structure in refugia versus recent populations did not support the existence of founder effects: heterozygosity (He = 0.667) and allelic richness (Ar = 4.298) were similar, and FST was low (0.031 overall). Still, significant spatial evidence of colonization was detected, with He increasing along the expansion front, while genetic differentiation from the entire pool (βWT) decreased. Isolation by distance was found in refugia but not in recently expanding populations. Our study indicates that beech capacities for colonization and gene flow were sufficient to preserve genetic diversity despite recent forest contraction and expansion. Because beech has long distance pollen and seed dispersal, these results illustrate a 'best case scenario' for the maintenance of high genetic diversity and adaptive potential under climate-change-related range change.