Biology subjects

Wapstra, E.

Publications and source records attributed to Wapstra, E..

8 recordsLinked to original sources

bioRxiv2026

Thermally driven sex reversal reveals divergent sex determination dynamics in wild viviparous reptile populations

Climate change can threaten population viability by disrupting sex ratios in species whose sex is influenced by temperature. While species with sex chromosomes were historically considered immune, in some species, temperatures can override genetic sex determination via sex reversal, leaving them vulnerable to climate-driven sex ratio shifts. The Tasmanian spotted snow skink (Carinacincus ocellatus), a viviparous reptile with an XX/XY system, provides a compelling case study. While laboratory studies demonstrated that extreme thermal conditions induce female-to-male sex reversal (XX males), its occurrence in the wild remains unexplored, limiting our understanding of actual climate impacts. Integrating 23 years of phenotypic and genetic sexing data across two climatically distinct populations, we provide the first evidence of sex reversal in a wild viviparous reptile. XX reversal occurred in both populations, affecting up to 23.5% of XX births in the warmer population, and was associated with colder minimum daily temperatures. Despite high birth rates in some years, sex-reversed adults were rare. We also identified putative XY females, suggesting bidirectional sex reversal and reinforcing the extreme plasticity of reptilian sex determination. Ultimately, sex reversal could act as an evolutionary trap, potentially compromising population viability as climate instability increases.

evolutionary biology↗

bioRxiv2026

Genomic consequences of admixture in an experimentally founded sand lizard population

Conservation interventions are increasingly required for species threatened by population declines and isolation due to anthropogenic pressures. Small, isolated populations are particularly vulnerable to the loss of genetic diversity, increased inbreeding, and the accumulation of deleterious mutations. Translocations or supplementation of allopatric individuals for genetic rescue may be the only way to increase genetic diversity to increase population persistence via increased adaptive potential. Here, we use an experimentally admixed population of sand lizards on a small island in Sweden as a valuable model of genetic rescue. This population was established approximately 20 years ago (5-6 generations) resulting in increased fecundity and hatchling viability. This population was founded from crossings between individuals from an inbred population from the nearby mainland and individuals sourced from populations in southern Sweden. Low-coverage whole-genome sequencing revealed elevated genetic diversity and reduced realized genetic load in this admixed population relative to the source populations. Ancestry analyses indicated a greater contribution of southern Swedish genetic variation, potentially reflecting contribution of beneficial adaptive variation from this region that may underlie the positive population effects. This system provides valuable empirical insights into the long-term genomic consequences of genetic rescue in this model vertebrate population.

genomics↗

bioRxiv2025

Large scale, low coverage population genomics approach to assess genetic variation and structure across vulnerable Swedish sand lizard populations

Genomics has emerged as a powerful tool in conservation biology, offering valuable insights into the genetic diversity, population connectivity and adaptive potential of threatened species. Here, we apply a large-scale, low-coverage whole genome sequencing approach to the conservation genomics of the Swedish sand lizard (Lacerta agilis). Sand lizards occur in fragmented populations across Sweden, with varying population sizes and degrees of isolation, and face significant threats from habitat degradation and land use change. In this study, we sequenced 139 individuals to investigate genetic diversity, population structure and genetic load. We reveal strong population structure among Swedish sand lizards and identify populations with low genetic diversity and realised high genetic load. Genetic diversity in populations declined with increasing latitude, likely reflecting the historical northward expansion process and the subsequent population fragmentation and isolation. We observe strong population structure and reveal genetic distinctiveness of populations; findings with significant conservation implications. For example, the Sormon population, a relict population in central Sweden, appears genetically distinct from all other populations. Further, the northern-most populations in Dalarna appear relatively small, with high genetic load, and thus may require intensive management via e.g., restored open successional habitat to aid population recovery. Our study adds to the growing field of conservation genomics and demonstrates the value of high-resolution whole genome approaches to the conservation efforts for threatened populations. Finally, our research contributes crucial insights for the conservation management of this vulnerable species in Sweden.

genomics↗

bioRxiv2025

Gene traffic mediated by transposable elements shaped the dynamic evolution of ancient sex chromosomes of varanid lizard

Lizards exhibit rapid turnovers and a much greater diversity of sex determination mechanisms compared to birds and eutherians. This makes the conserved ZW sex chromosomes of anguimorph lizards originated over 115 million years ago a seeming exception. We recently discovered in an anguimorph lizard Varanus acanthurus (Vac) that its entire W chromosome (chrW), but not chrZ is homologous to part of the chr2 by cytogenetic mapping, suggesting a complex history of its sex chromosome evolution yet to be elucidated. To address this, we assembled a chromosome-level genome, and provided evidence that the Vac sex chromosome pair had undergone at least three times of recombination suppression, forming a similar pattern of evolutionary strata to that of birds or mammals. We identified the putative sex-determining genes in the oldest evolutionary stratum that had first lost recombination. Comparison to other lizard genomes dated the stepwise propagation of specific retrotransposon subfamilies shared by chrW and chr2 to the varanid ancestor. These retrotransposons are also enriched near the duplicated genes shared by the two chromosomes and probably mediated the recruitment of many autosomal genes that rejuvenated the degenerating chrW, including members of a large vomeronasal chemosensory receptor gene family V2R. Our results challenge the canonical model of sex chromosome evolution, and suggest that the W or Y chromosome as a refugium of repetitive elements, may recurrently recruit short-lived functional genes responsible for sexual dimorphisms during its long-term course of degeneration.

evolutionary biology↗

bioRxiv2023

Using a handful of transcriptomes to detect sex-linked markers in a lizard with homomorphic sex chromosomes

To understand the biology of a species it is often crucial to be able to differentiate males and females. Many species lack distinguishable sexually dimorphic traits, but in those that possess sex chromosomes, molecular sexing offers a good alternative. Designing molecular sexing assays is typically achieved through the comparison of male and female genomic sequences, often from reduced-representation sequencing. However, in many non-model species sex chromosomes are poorly differentiated, and identifying sex-limited sequences and developing PCR-based sexing assays is challenging without additional genomic resources. Here we highlight a simple procedure for detection of sex-linked markers based on transcriptomes that circumvents limitations of other approaches. We apply it to the spotted snow skink Carinascincus ocellatus, a lizard with homomorphic XY chromosomes that also experiences environmentally-induced sex reversal. With transcriptomes from 3 males and 3 females alone, we identify thousands of putative Y-linked sequences. We confirm linkage through alignment of assembled transcripts to a distantly related genome, and readily design PCR primers to sex C. ocellatus and related species. In addition to providing an important molecular sexing tool for these species, this approach also facilitated valuable comparisons of sex determining systems on a large taxonomic scale.

genetics↗

bioRxiv2021

Diversity of reptile sex chromosome evolution revealed by cytogenetic and linked-read sequencing

Reptile sex determination is attracting much attention because the great diversity of sex-determination and dosage compensation mechanisms permits us to approach fundamental questions about sex chromosome turnover and evolution. However, reptile sex chromosome variation remains largely uncharacterized and no reptile master sex determination genes have yet been identified. Here we describe a powerful and cost-effective "chromosomics" approach, combining probes generated from the microdissected sex chromosomes with transcriptome sequencing to explore this diversity in non-model Australian reptiles with heteromorphic or cryptic sex chromosomes. We tested the pipeline on a turtle, a gecko, and a worm-lizard, and we also identified sequences located on sex chromosomes in a monitor lizard using linked-read sequencing. Genes identified on sex chromosomes were compared to the chicken genome to identify homologous regions among the four species. We identified candidate sex determining genes within these regions, including conserved vertebrate sex-determining genes pdgfa, pdgfra amh and wt1, and demonstrated their testis or ovary-specific expression. All four species showed gene-by-gene rather than chromosome-wide dosage compensation. Our results imply that reptile sex chromosomes originated by independent acquisition of sex-determining genes on different autosomes, as well as translocations between different ancestral macro- and micro-chromosomes. We discuss the evolutionary drivers of the slow differentiation, but rapid turnover, of reptile sex chromosomes.

genomics↗

bioRxiv2019

Phylogeographic parallelism: concordance of patterns in closely related species illuminates underlying mechanisms in the historically glaciated Tasmanian landscape

Phylogeography provides a means to understand mechanisms that shaped the distribution and abundance of species, including the role of past climate change. While concordant phylogeographic relationships across diverse taxa suggest shared underlying mechanisms ("phylogeographic parallelism"), it is also possible that similar patterns are the product of different mechanisms ("phylogeographic convergence"), reflecting variation among taxa in factors such as environmental tolerances, life histories, and vagility. Hence, phylogeographic concordance among closely related and ecologically similar species can yield a more confident understanding of the past mechanisms which shaped their distribution and abundance. This study documented mitochondrial and nuclear phylogeographic patterns in the ectotherm skink, Niveoscincus metallicus, which occupies historically glaciated regions of Tasmania, and contrasted these with the closely related and broadly sympatric N. ocellatus. Major phylogeographic breaks were similar in location between the two species, and indicative of isolation caused by retreat from high elevation areas during glaciations, but with long-term persistence at multiple low elevation sites. Hence, Pleistocene glacial refugia were altitudinal rather than latitudinal, a pattern mirrored in other temperate Southern Hemisphere taxa. This study also examined phylogeographic patterns across the intermittently inundated Bassian Isthmus between mainland Australia and the island of Tasmania, and revealed that structuring is similarly maintained when populations were physically isolated during interglacial rather than glacial stages.

evolutionary biology↗

bioRxiv2018

Conservation of sex-linked markers among conspecific populations of a viviparous skink, Niveoscincus ocellatus, exhibiting genetic and temperature dependent sex determination

Sex determination systems are exceptionally diverse and have undergone multiple and independent evolutionary transitions among species, particularly reptiles. However, the mechanisms underlying these transitions have not been established. Here we tested for differences in sex-linked markers in the only known reptile that is polymorphic for sex determination system, the spotted snow skink, Niveoscincus ocellatus, to quantify the genomic differences that have accompanied this transition. In a highland population, sex is determined genetically, whilst in a lowland population, offspring sex ratio is influenced by temperature. We found a similar number of sex-linked loci in each population, including shared loci, with genotypes consistent with male heterogamety (XY). However, population-specific linkage disequilibrium suggests greater divergence of sex chromosomes in the highland population. Our results suggest that transitions between sex determination systems (GSD and TSD-like systems) can be facilitated by subtle genetic differences.

evolutionary biology↗