Restricted Gene Flow Research Articles

Does coevolution in refugia drive mimicry in bumble bees? Insights from a South Asian mimicry group.

Müllerian mimicry was proposed to be an example of a coevolved mutualism promoted by population isolation in glacial refugia. This, however, has not been well supported in butterfly models. Here, we use genomic data to test this theory while examining the population genetics behind mimetic diversification in a pair of co-mimetic bumble bees, Bombus breviceps Smith and Bombus trifasciatus Smith. In both lineages, populations were structured by geography but not as much by color pattern, suggesting sharing of color alleles across regions of restricted gene flow and formation of mimicry complexes in the absence of genetic differentiation. Demographic analyses showed mismatches between historical effective population size changes and glacial cycles, and niche modeling revealed only mild habitat retraction during glaciation. Moreover, mimetic subpopulations of the same color form in the two lineages only in some cases exhibit similar population history and genetic divergence. Therefore, the current study supports a more complex history in this comimicry than a simple refugium-coevolution model.

Evidence for gene flow and trait reversal during radiation of Mexican Goodeid fish

Understanding the phylogeographic history of a group and identifying the factors contributing to speciation is an important challenge in evolutionary biology. The Goodeinae are a group of live-bearing fishes endemic to Mexico. Here, we develop genomic resources for species within the Goodeinae and use phylogenomic approaches to characterise their evolutionary history. We sequenced, assembled and annotated the genomes of four Goodeinae species, including Ataeniobius toweri, the only matrotrophic live-bearing fish without a trophotaenia in the group. We estimated timings of species divergence and examined the extent and timing of introgression between the species to assess if this may have occurred during an early radiation, or in more recent episodes of secondary contact. We used branch-site models to detect genome-wide positive selection across Goodeinae, and we specifically asked whether this differs in A. toweri, where loss of placental viviparity has recently occurred. We found evidence of gene flow between geographically isolated species, suggesting vicariant speciation was supplemented by limited post-speciation gene flow, and gene flow may explain previous uncertainties about Goodeid phylogeny. Genes under positive selection in the group are likely to be associated with the switch to live-bearing. Overall, our studies suggest that both volcanism-driven vicariance and changes in reproductive mode influenced radiation in the Goodeinae.

Embracing biodiversity: multispecies population genomics of leafless Bossiaea species shows novel taxa, population dynamics and conservation strategies

Leafless Bossiaea species are a unique group of plants endemic to Australia that present intriguing challenges in taxonomy and conservation because of their morphological simplicity and often small, disjunct populations. We employed whole genome reduced representation sequencing (DArTseq) to enhance our understanding of the population dynamics, diversity and taxonomy of leafless Bossiaea species. Our dataset comprised 52,539 single-nucleotide polymorphisms across 283 samples from 7 leafless Bossiaea species, including 6 listed threatened species. We examined population structure, phylogenetic relationships, kinship and gene flow within and among populations. On the basis of our population-genomic analyses, we propose recognition of the novel taxon Bossiaea vombata subsp. orientalis and a change in status from species (B. milesiae) to subspecies for B. fragrans subsp. milesiae. Additionally, we show extensive clonal reproduction across species and limited gene flow at distances of >1 km, shedding light on the challenges faced by these species. We advocate a coordinated approach to conservation, focusing on restoring self-sustaining populations and leveraging genetic rescue strategies. By addressing the population dynamics of multiple species simultaneously in taxonomically challenging lineages, we can make informed choices to safeguard biodiversity and evolutionary potential.

Genetic Diversity, Mating System, and Seed Viability Reveal a Trade-Off between Outcrossing and Inbreeding in Pinus yunnanensis var. tenuifolia, an Ecologically Important Conifer Species Growing in a Hot-Dry River Basin Habitat in Southwest China

Revealing the relationship between the mating system (i.e., the outcrossing/inbreeding degree) and the fitness of seeds in tree species under wild conditions is essential for understanding the ecological adaptability and evolutionary stability of the species. This study collected open-pollinated seeds from seven wild populations of Pinus yunnanensis var. tenuifolia that exhibited fragmentation in the Nanpan–Hongshui River basin, an ecologically fragile area in China. The seeds and sprouts (germinated seeds) from 20 families were genotyped (24 seeds and 24 sprouts per family) using twelve microsatellite loci to reveal the genetic diversity, mating status, and effect of inbreeding on the three seed quality indicators (thousand-seed weight, germination rate, and germination potential). The three seed quality indicators differed significantly between families (p < 0.001). Higher values of genetic diversity (except the observed heterozygosity) were observed in the sprout group than those in the seed group. Families from different populations showed a notable genetic differentiation (Φst = 0.12), and a large part of families from the common populations had a high degree of coancestry, which signified that the current habitat fragmentation is limiting gene flow between populations. High levels of outcrossing rates (tm) were observed in both the seed group (tm = 0.974) and the sprout group (tm = 0.978), indicating that a low proportion of seeds were self-fertilized. Although there was a slightly higher single outcrossing rate (ts = 0.888) and a lower proportion of biparental inbreeding (tm − ts = 0.077) in sprouts compared to the seeds (ts = 0.871, tm − ts = 0.091), indicating that a part of inbred seeds were purged during the germination stage, curve fitting between the outcrossing rate and seed quality indicators showed that a certain degree of biparental inbreeding (ts between 0.89 and 0.91 and tm − ts between 0.09 and 0.11) did have a positive effect on seed germination ability. This highlights that excessive inbreeding or outbreeding seems to be unfavorable to seed viability. The peculiar relationship between seed viability and the mating system in P. yunnanensis var. tenuifolia was likely an evolutionary consequence of a trade-off between the nature of mixed mating and its specific ecological niche.

Pleistocene climate oscillations have shaped the expansion and contraction speciation model of the globose Eriosyce sect. Neoporteria cacti in Central Chile.

Pleistocene climatic oscillations, characterized by arid (interglacial) and pluvial (glacial) phases, have profoundly impacted the floras of Mediterranean climates. Our study investigates the hypothesis that these climatic extremes have promoted phases of range expansion and contraction in the Eriosyce sect. Neoporteria, resulting in pronounced genetic structuring and restricted gene flow. Utilizing nuclear microsatellite markers, we genotyped 251 individuals across 18 populations, encompassing all 14 species and one subspecies within the Eriosyce sect. Neoporteria. Additionally, Species Distribution Models (SDMs) were employed to reconstruct past (Last Interglacial, Last Glacial Maximum, Mid-Holocene) and current potential distribution patterns, aiming to delineate the climatic influences on species' range dynamics. The gene flow analysis disclosed disparate levels of genetic interchange among species, with marked restrictions observed between entities that are geographically or ecologically separated. Notably, E. subgibbosa from Hualpen emerged as genetically distinct, warranting its exclusion for clearer genetic clustering into north, central, and south clusters. The SDMs corroborated these findings, showing marked range expansions during warmer periods and contractions during colder times, indicating significant shifts in distribution patterns in response to climatic changes. Our findings emphasize the critical role of Pleistocene climatic fluctuations in driving the dynamic patterns of range expansions and contractions that have led to geographic isolation and speciation within the Eriosyce sect. Neoporteria. Even in the face of ongoing gene flow, these climate-driven processes have played a pivotal role in sculpting the species' genetic architecture and diversity. This study elucidates the complex interplay between climatic variability and evolutionary dynamics among Mediterranean cacti in central Chile, highlighting the necessity of considering historical climatic millenial oscillations in conservation and evolutionary biology studies.

Fine-scale genetic structure and phenotypic divergence of a passerine bird population inhabiting a continuous Mediterranean woodland.

Genetic differentiation between populations inhabiting ecologically different habitats might appear because of limited dispersal and gene flow, which may lead to patterns of phenotypic divergence and local adaptation. In this study, we use dispersal, genotypic (24 microsatellite loci) and phenotypic (body size and clutch size) data to analyse patterns of genetic structuring and phenotypic divergence in a blue tit (Cyanistes caeruleus) population inhabiting a continuous and heterogeneous woodland along a valley. The two slopes of the valley differ in their forest formations and environmental conditions. Findings showed that most blue tits reproduced within their natal slope. Accordingly, microsatellite analyses revealed that populations of blue tits established in the two slopes show subtle genetic differentiation. The two genetic populations diverged in clutch size, exceeding the level of differentiation expected based on genetic drift, hence suggesting divergent selection (or other processes promoting divergence) on this life-history trait. Our findings reveal that restricted dispersal and spatial heterogeneity may lead to genetic differentiation among bird populations at a surprisingly small scale. In this respect, it is worth highlighting that such differentiation occurs for an organism with high dispersal capacity and within a continuous woodland. Moreover, we show that small-scale ecological differences, together with limited gene flow, can result in selection favouring different phenotypes even within the same continuum population.

Genetic differentiation at extreme latitudes in the socially plastic sweat bee Halictus rubicundus.

The sweat bee Halictus rubicundus is an important pollinator with a large latitudinal range and many potential barriers to gene flow. Alongside typical physical barriers, including mountain ranges and oceans, the climate may also impose restrictions on gene flow in this species. The climate influences voltinism and sociality in H. rubicundus, which is bivoltine and can nest socially at warmer lower latitudes but tends to be univoltine and solitary in the cooler north. Variation in voltinism could result in phenological differences, potentially limiting gene flow, but a previous study found no evidence for this in H. rubicundus populations in mainland Britain. Here we extend the previous study to consider populations of H. rubicundus at extreme northern and southern latitudes in the UK. We found that bees from a population in the far north of Scotland were genetically differentiated from bees collected in Cornwall in the south-west of England. In contrast, bees collected across the Irish Sea in Northern Ireland showed slight genetic overlap with both the Scottish and Cornish bees. Our results suggest that when populations at extreme latitudes are considered, phenology and the climate may act alongside physical barriers such as the Scottish Highlands and the Irish Sea to restrict gene flow in H. rubicundus. We discuss the implications of our results for local adaptation in the face of rapidly changing selection pressures which are likely under climate change.

Correction to: Limited interspecific gene flow in the evolutionary history of the icefish genus Chionodraco

Correction to: Limited interspecific gene flow in the evolutionary history of the icefish genus <i>Chionodraco</i>

Phylogenomics, Lineage Diversification Rates, and the Evolution of Diadromy in Clupeiformes (Anchovies, Herrings, Sardines, and Relatives).

Migration independently evolved numerous times in animals, with a myriad of ecological and evolutionary implications. In fishes, perhaps the most extreme form of migration is diadromy, the migration between marine and freshwater environments. Key and longstanding questions are: how many times has diadromy evolved in fishes, how frequently do diadromous clades give rise to non-diadromous species, and does diadromy influence lineage diversification rates? Many diadromous fishes have large geographic ranges with constituent populations that use isolated freshwater habitats. This may limit gene flow among some populations, increasing the likelihood of speciation in diadromous lineages relative to non-diadromous lineages. Alternatively, diadromy may reduce lineage diversification rates if migration is associated with enhanced dispersal capacity that facilitates gene flow within and between populations. Clupeiformes (herrings, sardines, shads and anchovies) is a model clade for testing hypotheses about the evolution of diadromy because it includes an exceptionally high proportion of diadromous species and several independent evolutionary origins of diadromy. However, relationships among major clupeiform lineages remain unresolved and existing phylogenies sparsely sampled diadromous species, limiting the resolution of phylogenetically-informed statistical analyses. We assembled a phylogenomic dataset and used multi-species coalescent and concatenation-based approaches to generate the most comprehensive, highly-resolved clupeiform phylogeny to date, clarifying associations among several major clades and identifying recalcitrant relationships needing further examination. We determined that variation in rates of sequence evolution (heterotachy) and base-composition (non-stationarity) had little impact on our results. Using this phylogeny, we characterized evolutionary patterns of diadromy and tested for differences in lineage diversification rates between diadromous, marine, and freshwater lineages. We identified thirteen transitions to diadromy, all during the Cenozoic Era (ten origins of anadromy, two origins of catadromy, and one origin of amphidromy), and seven losses of diadromy. Two diadromous lineages rapidly generated non-diadromous species, demonstrating that diadromy is not an evolutionary dead-end. We discovered considerably faster transition rates out of diadromy than to diadromy. The largest lineage diversification rate increase in Clupeiformes was associated with a transition to diadromy, but we uncovered little statistical support for categorically faster lineage diversification rates in diadromous versus non-diadromous fishes. We propose that diadromy may increase the potential for accelerated lineage diversification, particularly in species that migrate long distances. However, this potential may only be realized in certain biogeographic contexts, such as when diadromy allows access to ecosystems in which there is limited competition from incumbent species.

Soil Requirements, Genetic Diversity and Population History of the Juniperus sabina L. Varieties in Europe and Asia

Trees and shrubs belonging to the genus Juniperus L. are pivotal species in arid and semiarid ecosystems in the Northern Hemisphere. However, unfavourable phenomena are observed in their populations due to global warming. We aimed to investigate the soil requirements, genetic diversity and population history of Juniperus sabina L. from Europe, Georgia, and Kyrgyzstan. Genetic resources were evaluated in 16 populations using nuclear microsatellites, while past demographic events were described based on the chloroplast DNA haplotypes. Seven chemical parameters in 36 soil samples from the European range of J. sabina were compared. In the studied area, three distinct phylogenetic lineages corresponding to different varieties of J. sabina, namely var. sabina, var. balkanensis, and the Asian variety, were revealed. Unimodal mismatch distributions and significantly negative Tajima’s D and Fu’s Fs parameters indicated that the sabina and balkanensis varieties underwent a population expansion. Microsatellite variation was moderate, potentially influenced by inbreeding, clonal propagation, and limited gene flow between populations. Bayesian clustering revealed five genetic groups. Compared to var. sabina, the balkanensis variety occupies areas with significantly higher potassium content in the soil, which probably mitigates the adverse effects of drought in its localities.

Deep genetic divergence among bluefish (Pomatomus saltatrix) of the Southwestern Atlantic

AbstractNeglected cryptic diversity can lead to the permanent loss of locally adapted alleles, which can reduce resilience to rapid environmental change. It can also result in overestimation of fisheries stock sizes that can result from treating different species as if they belonged to one. Bluefish (Pomatomus saltatrix) is considered a circumtropical and subtropical species and an important fishery resource all over the world. Differences in ecologically relevant traits are observed among isolated populations. Also, in the Southwestern Atlantic, molecular data suggest multiple populations, but these are treated as a single fish stock by regulatory agencies due to a lack of definitive information. We used whole mitogenome sequences, nuclear (rho) and mitochondrial (coxI and cytb) genes, as well as microsatellites to investigate historical and current genetic population structure and parameters of bluefish in the Western Atlantic. A total of 263 samples were collected along the Brazilian coast and in the USA (New Jersey, Northwest Atlantic). Data revealed the existence of two evolutionarily significant units (ESU) of bluefish along the South American coast, later confirmed by whole mitogenome sequencing of both haplogroups. These two ESUs have a mostly parapatric distribution, with some areas of overlap, which vary along the year. We also conducted seasonal sampling in Brazil to investigate migration patterns. ESUs occur mostly north and south of parallel 23° 40′ S, with an overlap area that varied seasonally. The level of differentiation between those two ESUs in the SW Atlantic, even in sympatry, is as high as that found between them and those from the NW Atlantic and Europe. Parapatric distribution and restricted gene flow suggest the existence of ecological barriers and local adaptation. The splitting of an ancient population from the Southwestern Atlantic into two putative species is important to understand bluefish evolutionary diversification and has implications for fishery regulatory measures in Brazil.

Genomic landscapes of divergence among island bird populations: Evidence of parallel adaptation but at different loci?

When populations colonise new environments, they may be exposed to novel selection pressures but also suffer from extensive genetic drift due to founder effects, small population sizes and limited interpopulation gene flow. Genomic approaches enable us to study how these factors drive divergence, and disentangle neutral effects from differentiation at specific loci due to selection. Here, we investigate patterns of genetic diversity and divergence using whole-genome resequencing (>22× coverage) in Berthelot's pipit (Anthus berthelotii), a passerine endemic to the islands of three north Atlantic archipelagos. Strong environmental gradients, including in pathogen pressure, across populations in the species range, make it an excellent system in which to explore traits important in adaptation and/or incipient speciation. First, we quantify how genomic divergence accumulates across the speciation continuum, that is, among Berthelot's pipit populations, between sub species across archipelagos, and between Berthelot's pipit and its mainland ancestor, the tawny pipit (Anthus campestris). Across these colonisation timeframes (2.1 million-ca. 8000 years ago), we identify highly differentiated loci within genomic islands of divergence and conclude that the observed distributions align with expectations for non-neutral divergence. Characteristic signatures of selection are identified in loci associated with craniofacial/bone and eye development, metabolism and immune response between population comparisons. Interestingly, we find limited evidence for repeated divergence of the same loci across the colonisation range but do identify different loci putatively associated with the same biological traits in different populations, likely due to parallel adaptation. Incipient speciation across these island populations, in which founder effects and selective pressures are strong, may therefore be repeatedly associated with morphology, metabolism and immune defence.

Phylogenomic perspectives on speciation and reproductive isolation in a North American biodiversity hotspot: an example using California sages (Salvia subgenus Audibertia: Lamiaceae).

The California Floristic Province (CA-FP) is the most species-rich region of North America north of Mexico. One of several proposed hypotheses explaining the exceptional diversity of the region is that the CA-FP harbours myriad recently diverged lineages with nascent reproductive barriers. Salvia subgenus Audibertia is a conspicuous element of the CA-FP, with multiple sympatric and compatible species. Using 305 nuclear loci and both organellar genomes, we reconstruct species trees, examine genomic discordance, conduct divergence-time estimation, and analyse contemporaneous patterns of gene flow and mechanical reproductive isolation. Despite strong genomic discordance, an underlying bifurcating tree is supported. Organellar genomes capture additional introgression events not detected in the nuclear genome. Most interfertility is found within clades, indicating that reproductive barriers arise with increasing genetic divergence. Species are generally not mechanically isolated, suggesting that it is unlikely to be the primary factor leading to reproductive isolation. Rapid, recent speciation with some interspecific gene flow in conjunction with the onset of a Mediterranean-like climate is the underlying cause of extant diversity in Salvia subgenus Audibertia. Speciation has largely not been facilitated by gene flow. Its signal in the nuclear genome seems to mostly be erased by backcrossing, but organellar genomes each capture different instances of historical gene flow, probably characteristic of many CA-FP lineages. Mechanical reproductive isolation appears to be only part of a mosaic of factors limiting gene flow.

Distribution pattern of large old Ginkgo biloba in China under climate change scenarios.

Large old Ginkgo biloba trees (LOGTs), with profound ecological and cultural significance in China, face increasing threats from climate change and human activities. We employed the BIOCLIM and DOMAIN species distribution models to predict their spatial patterns under the present climate and doubled-CO2 climate change scenario in 2100. We collected 604 validated LOGT occurrence records and data on 19 bioclimate factors for the analysis. Our study yielded a LOGT geographic distribution pattern covering a wide latitudinal belt extending from south subtropical to temperate zones in central and eastern China, concentrating in low elevations and coastal regions. The principal component analysis identified the dominant bioclimatic factors shaping their distribution, namely annual precipitation and low winter temperatures. BIOCLIM and DOMAIN generated predicted suitable habitats that match the present distribution range well. However, under the future climate scenario, the models indicated habitat retentions mainly in the core distribution areas and habitat losses mainly in the southern edge of the present range and scattered pockets elsewhere. Some retained habitats, including excellent ones, will suffer from fragmentation. The predicted new habitats may permit some range expansion and migration but are beset by small patch size and large interpatch distance, bringing fragmentation and gene flow restrictions. The anticipated projected range decline highlights considerable threats climate change poses to the long-term survival of the precious natural-cum-cultural resource. Understanding the distribution patterns and underlying drivers and distillation of practical conservation measures can foster sustainable management vis-a-vis the looming global change.

Effects of landscape, resource use, and body size on genetic structure in bee populations.

Quantifying genetic structure and levels of genetic variation are fundamentally important to predicting the ability of populations to persist in human-altered landscapes and adapt to future environmental changes. Genetic structure reflects the dispersal of individuals over generations, which can be mediated by species-level traits or environmental factors. Dispersal distances are commonly positively associated with body size and negatively associated with the amount of degraded habitat between sites, motivating the investigation of these potential drivers of dispersal concomitantly. We quantified genetic structure and genetic variability within populations of seven bee species from the genus Euglossa across fragmented landscapes. We genotyped bees at SNP loci and tested the following predictions: (1) deforested areas restrict gene flow; (2) larger species have lower genetic structure; (3) species with greater resource specialization have higher genetic structure; and (4) sites surrounded by more intact habitat have higher genetic diversity. Contrasting with previous work on bees, we found no associations between body size and genetic structure. Genetic structure was higher for species with greater resource specialization, and the amount of intact habitat between or surrounding sites was positively associated with parameters reflecting gene flow and genetic diversity. These results challenge the dominant paradigm that individuals of larger species disperse farther, and they suggest that landscape and resource requirements are important factors mediating dispersal.

Intraspecific divergence in a coastal plant, Euphorbia jolkinii, at a major biogeographic boundary in East Asia.

Quaternary climatic fluctuations and long-distance seed dispersal across the sea are critical factors affecting the distribution of coastal plants, but the spatiotemporal nature of population expansion and distribution change of East Asian coastal plants during this period are rarely examined. To explore this process, we investigated the genome-wide phylogenetic patterns of Euphorbia jolkinii Boiss. (Euphorbiaceae), which grows widely on littoral areas of Japan, Korea, and Taiwan. We used plastome sequences and genome-wide single nucleotide polymorphisms in samples across the species range to reveal phylogeographic patterns and spatiotemporal distributional changes. We conducted ecological niche modeling for the present and the last glacial maximum (LGM). Genetic differentiation was observed between the northern and southern populations of E. jolkinii, separated by the major biogeographic boundary, the Tokara Gap. These two groups of populations differentiated during the glacial period and subsequently intermingled in the intermorainic areas of the central Ryukyu Islands after the LGM. Ecological niche models suggested that the potential range of E. jolkinii was restricted to southern Kyushu; however, it was widespread in the southern Ryukyu Islands and Taiwan during the LGM. This study provides evidence of genetic differentiation among coastal plant populations separated by the prominent biogeographical boundary. Although coastal plants are typically expected to maintain population connectivity through sea-drifted seed dispersal, our findings suggest that genetic differences may arise because of a combination of limited gene flow and changes in climate during the glacial period.

Genetic variation of English yew (Taxus baccata L.) in the Bavarian Forest National Park, Germany

AbstractTaxus baccata L. is a highly valuable species with wide distribution but scattered and locally rare occurrence. Human intervention, including forest management practices and fragmentation, can significantly impact the species’ genetic diversity, structure, and dynamics. In this study, we investigated these factors within T. baccata populations in the Bavarian Forest National Park (NP) in Germany and their implications for conservation. We used 13 EST-SSRs to assess the genetic diversity and structure of the population. Our analysis revealed a scarcity of small-diameter trees, indicating limited natural regeneration over time. However, conservation efforts, like selectively removing competitor species and using protective fencing, have improved growth conditions and promoted seedling emergence. The NP’s natural zone has no active management, which is confined to the development and management zones. Genetic diversity assessments revealed high genetic diversity (He: 0.612 and 0.614 for seedlings and adults, respectively) compared to other studies in Taxus baccata, dispelling concerns of significant inbreeding and showcasing a stable genetic structure. However, significant spatial clustering of related individuals (family structures) in both cohorts and low effective population size in the progeny hints at restricted gene flow, necessitating conservation efforts prioritizing safeguarding and promoting natural regeneration in development and management zones. Limited natural regeneration and the recent decrease in effective population size in the NP populations indicate habitat fragmentation and human interventions. Effective population size estimates emphasize the need for diverse conservation strategies. Conservation efforts should prioritize protecting natural regeneration and enhancing gene flow by actively promoting European yew, e.g., by shelterwood cutting, to ensure the long-term viability of T. baccata in the region outside the NP.

Combining population genomics and biophysical modelling to assess connectivity patterns in an Antarctic fish.

Connectivity is a fundamental process of population dynamics in marine ecosystems. In the last decade, with the emergence of new methods, combining different approaches to understand the patterns of connectivity among populations and their regulation has become increasingly feasible. The Western Antarctic Peninsula (WAP) is characterized by complex oceanographic dynamics, where local conditions could act as barriers to population connectivity. Here, the notothenioid fish Harpagifer antarcticus, a demersal species with a complex life cycle (adults with poor swim capabilities and pelagic larvae), was used to assess connectivity along the WAP by combining biophysical modelling and population genomics methods. Both approaches showed congruent patterns. Areas of larvae retention and low potential connectivity, observed in the biophysical model output, coincide with four genetic groups within the WAP: (1) South Shetland Islands, (2) Bransfield Strait, (3) the central and (4) the southern area of WAP (Marguerite Bay). These genetic groups exhibited limited gene flow between them, consistent with local oceanographic conditions, which would represent barriers to larval dispersal. The joint effect of geographic distance and larval dispersal by ocean currents had a greater influence on the observed population structure than each variable evaluated separately. The combined effect of geographic distance and a complex oceanographic dynamic would be generating limited levels of population connectivity in the fish H. antarcticus along the WAP. Based on this, population connectivity estimations and priority areas for conservation were discussed, considering the marine protected area proposed for this threatened region of the Southern Ocean.

Tasmanian devil (Sarcophilus harrisii) gene flow and source-sink dynamics

Increased access to genetic data has substantially improved how we manage threatened species. The Tasmanian devil (Sarcophilus harrisii) is listed as endangered due to the ongoing threat of a highly contagious cancer, devil facial tumour disease (DFTD), causing more than 80% population reductions. To assist future management interventions (e.g. releases into wild sites) we expanded upon previous studies of gene flow for the devil by assessing more recent and broad-scale patterns. We use genome-wide single nucleotide polymorphisms generated via DArTSeq across 21 devil sites to delineate source-sink dynamics across the species’ range. Our findings revealed gene flow is stronger on the northeast and central regions of Tasmania, with high rates of bidirectional gene flow among central sites. The northwest exhibits weaker connectivity relative to other regions of Tasmania, while gene flow appears to be non-existent between the southwest and other areas. Northeast coastal sites tend to serve as ‘sources’ for inland central sites, whereas gene flow appears restricted to the coastline in the northwest. These results are consistent with genetic structure of devil sites and spatial spread of DFTD, which has yet to arrive in the southwest region of Tasmania. Southwest isolation is probably due to mountain ranges and lack of roadways. Interestingly, some waterbodies did not appear to restrict devil movement among sites. Conversely, areas of high elevation act as apparent barriers, as evidenced by limited gene flow observed between eastern and western sites. Integrating source-sink dynamics into conservation management planning will be crucial in developing effective strategies to safeguard the Tasmanian devil and other threatened species facing similar threats (i.e. disease, habitat loss).

The Andes as a semi-permeable geographical barrier: Genetic connectivity between structured populations in a widespread spider.

Geographical barriers like mountain ranges impede genetic exchange among populations, promoting diversification. The effectiveness of these barriers in limiting gene flow varies between lineages due to each species' dispersal modes and capacities. Our understanding of how the Andes orogeny contributes to species diversification comes from well-studied vertebrates and a few arthropods and plants, neglecting organisms unable to fly or walk long distances. Some arachnids, such as Gasteracantha cancriformis, have been hypothesized to disperse long distances via ballooning (i.e. using their silk to interact with the wind). Yet, we do not know how the environment and geography shape its genetic diversity. Therefore, we tested whether the Andes contributed to the diversification of G. cancriformis acting as an absolute or semi-permeable barrier to genetic connectivity between populations of this spider at opposite sides of the mountain range. We sampled thousands of loci across the distribution of the species and implemented population genetics, phylogenetic, and landscape genetic analyses. We identified two genetically distinct groups structured by the Central Andes, and a third less structured group in the Northern Andes that shares ancestry with the previous two. This structure is largely explained by the altitude along the Andes, which decreases in some regions, possibly facilitating cross-Andean dispersal and gene flow. Our findings support that altitude in the Andes plays a major role in structuring populations in South America, but the strength of this barrier can be overcome by organisms with long-distance dispersal modes together with altitudinal depressions.