Biology subjects

Denton, R. D.

Publications and source records attributed to Denton, R. D..

6 recordsLinked to original sources

bioRxiv2026

Range-wide validation of reduced locomotor endurance in unisexual Ambystoma salamanders

O_LILocomotor endurance is a critical physiological trait dictating terrestrial dispersal and metapopulation connectivity, especially in amphibians. C_LIO_LIThe unisexual Ambystoma complex is an ancient, all-female polyploid lineage that reproduces via kleptogenesis. This unique reproductive mode creates an evolutionary mismatch between a conserved mitochondrial genome and divergent nuclear subgenomes that are taken from sympatric, sexual species. This provides a compelling system for testing the physiological limits of polyploidy and how subgenome composition influences phenotypes. Previous locomotor assessments of this lineage demonstrate that polyploid salamanders display reduced locomotor endurance compared to sexual species. To overcome previous limitations in geographic sampling and sample size, we conducted standardized treadmill endurance trials on a broad geographic sampling of 110 salamanders, comparing the performance of triploid unisexual biotypes (LJJ and LLJ) directly to their sexually reproducing parental species (A. jeffersonianum and A. laterale). C_LIO_LIWe found that biotype significantly dictates endurance performance. Both sexual species demonstrated significantly greater total distance traveled prior to exhaustion compared to the unisexual hybrids. But within the unisexual cohort, subgenome dosage influenced performance: LJJ individuals outperformed LLJ individuals, aligning with A. jeffersonianum demonstrating greater endurance than A. laterale. C_LIO_LIWe propose that the aerobic capacity of unisexual salamanders is limited, potentially due to mitonuclear mismatch or the biophysical constraints of increased cellular volume. This endurance deficit is likely to restrict unisexual salamanders dispersal capabilities, leaving populations uniquely vulnerable to ongoing habitat fragmentation compared to more mobile, sexual species C_LI

zoology↗

bioRxiv2024

The Amphibian Genomics Consortium: advancing genomic and genetic resources for amphibian research and conservation

Amphibians represent a diverse group of tetrapods, marked by deep divergence times between their three systematic orders and families. Studying amphibian biology through the genomics lens increases our understanding of the features of this animal class and that of other terrestrial vertebrates. The need for amphibian genomic resources is more urgent than ever due to the increasing threats to this group. Amphibians are one of the most imperiled taxonomic groups, with approximately 41% of species threatened with extinction due to habitat loss, changes in land use patterns, disease, climate change, and their synergistic effects. Amphibian genomic resources have provided a better understanding of ontogenetic diversity, tissue regeneration, diverse life history and reproductive modes, anti-predator strategies, and resilience and adaptive responses. They also serve as essential models for studying broad genomic traits, such as evolutionary genome expansions and contractions, as they exhibit the widest range of genome sizes among all animal taxa and possess multiple mechanisms of genetic sex determination. Despite these features, genome sequencing of amphibians has significantly lagged behind that of other vertebrates, primarily due to the challenges of assembling their large, repeat-rich genomes and the relative lack of societal support. The emergence of long-read sequencing technologies, combined with advanced molecular and computational techniques that improve scaffolding and reduce computational workloads, is now making it possible to address some of these challenges. To promote and accelerate the production and use of amphibian genomics research through international coordination and collaboration, we launched the Amphibian Genomics Consortium (AGC, https://mvs.unimelb.edu.au/amphibian-genomics-consortium) in early 2023. This burgeoning community already has more than 282 members from 41 countries. The AGC aims to leverage the diverse capabilities of its members to advance genomic resources for amphibians and bridge the implementation gap between biologists, bioinformaticians, and conservation practitioners. Here we evaluate the state of the field of amphibian genomics, highlight previous studies, present challenges to overcome, and call on the research and conservation communities to unite as part of the AGC to enable amphibian genomics research to "leap" to the next level.

genomics↗

bioRxiv2024

Characterizing population structure and documenting rapid loss of genetic diversity in Chiricahua Leopard Frogs (Lithobates chiricahuensis) with high throughput microsatellite genotyping

The use of molecular markers to assess genetic diversity has become a common component of recovery action plans for threatened and endangered species. In this study, we use an unusually large number of microsatellite markers (N=91) to characterize the genetic variation of Chiricahua Leopard Frogs (Lithobates chiricahuensis) across their range in order to understand their distribution of genetic variation, identify genetic bottlenecks, and measure genetic changes over time in a single, highly-managed population. Populations were best divided into three genetically distinct clusters, with the southeastern Arizona and New Mexico populations forming distinct genetic clusters. While there is moderate genetic variation distributed across the sampled populations, each population on its own shows relatively low allelic diversity. Most populations displayed strong genetic signals of recent genetic bottlenecks or a deficiency of heterozygous genotypes that is typically associated with frequent inbreeding. Populations that have a history of no management through translocations harbored the greatest number of unique alleles and overall allelic richness, especially in a subset of the Mexican populations. Finally, long-term cohort sampling at one specific site (the Southwestern Research Station in Portal, Arizona) allowed us to demonstrate how rapidly genetic diversity can decrease across a matter of years in a population with few founders. This work shows how microsatellite markers can provide important context for conservation agencies, but even a large suite of markers beyond what is typical may not be enough for populations that are extremely bottlenecked and have low levels of standing genetic diversity.

genetics↗

bioRxiv2021

Conserved chromatin and repetitive patterns reveal slow genome evolution in frogs

Frogs are an ecologically diverse and phylogenetically ancient group of living amphibians that include important vertebrate cell and developmental model systems, notably the genus Xenopus. Here we report a high-quality reference genome sequence for the western clawed frog, Xenopus tropicalis, along with draft chromosome-scale sequences of three distantly related emerging model frog species, Eleutherodactylus coqui, Engystomops pustulosus and Hymenochirus boettgeri. Frog chromosomes have remained remarkably stable since the Mesozoic Era, with limited Robertsonian (i.e., centric) translocations and end-to-end fusions found among the smaller chromosomes. Conservation of synteny includes conservation of centromere locations, marked by centromeric tandem repeats associated with Cenp-a binding, surrounded by pericentromeric LINE/L1 elements. We explored chromosome structure across frogs, using a dense meiotic linkage map for X. tropicalis and chromatin conformation capture (HiC) data for all species. Abundant satellite repeats occupy the unusually long ([~]20 megabase) terminal regions of each chromosome that coincide with high rates of recombination. Both embryonic and differentiated cells show reproducible association of centromeric chromatin, and of telomeres, reflecting a Rabl configuration similar to the "bouquet" structure of meiotic cells. Our comparative analyses reveal 13 conserved ancestral anuran chromosomes from which contemporary frog genomes were constructed.

genomics↗

bioRxiv2021

Gigantic Genomes of Salamanders Indicate Body Temperature, not Genome Size, is the Driver of Global Methylation and 5-Methylcytosine Deamination in Vertebrates

Methylation of cytosines at CpG dinucleotide sites silences transposable elements (TEs), sequences that replicate and move throughout genomes. TE abundance drives differences in genome size, but TE silencing variation across genomes of different sizes remains largely unexplored. Salamanders include most of the largest C-values -- 9 to 120 Gb. We measured CpG methylation levels in salamanders with genomes ranging from 2N = ~58 Gb to 4N = ~116 Gb. We compared these levels to results from endo- and ectothermic vertebrates with more typical genomes. Salamander methylation levels are ~90%, higher than all endotherms. However, salamander methylation does not differ from the other ectotherms, despite a ~100-fold difference in nuclear DNA content. Because methylation affects the nucleotide compositional landscape through 5-methylcytosine deamination to thymine, we quantified salamander CpG dinucleotide levels and compared them to other vertebrates. Salamanders have comparable CpG levels to other ectotherms, and ectotherm levels are higher than endotherms. These data show no shift in global methylation at the base of salamanders, despite a dramatic increase in TE load and genome size. This result is reconcilable with previous studies by considering endothermy and ectothermy, which may be more important drivers of methylation in vertebrates than genome size.

evolutionary biology↗

bioRxiv2018

The African Bullfrog (Pyxicephalus adspersus) genome unites the two ancestral ingredients formaking vertebrate sex chromosomes

Heteromorphic sex chromosomes have evolved repeatedly among vertebrate lineages despite largely deleterious reductions in gene dose. Understanding how this gene dose problem is overcome is hampered by the lack of genomic information at the base of tetrapods and comparisons across the evolutionary history of vertebrates. To address this problem, we produced a chromosome-level genome assembly for the African Bullfrog (Pyxicephalus adspersus)--an amphibian with heteromorphic ZW sex chromosomes--and discovered that the Bullfrog Z is surprisingly homologous to substantial portions of the human X. Using this new reference genome, we identified ancestral synteny among the sex chromosomes of major vertebrate lineages, showing that non-mammalian sex chromosomes are strongly associated with a single vertebrate ancestral chromosome, while mammals are associated with another that displays increased haploinsufficiency. The sex chromosomes of the African Bullfrog however, share genomic blocks with both humans and non-mammalian vertebrates, connecting the two ancestral chromosome sequences that repeatedly characterize vertebrate sex chromosomes. Our results highlight the consistency of sex-linked sequences despite sex determination system lability and reveal the repeated use of two major genomic sequence blocks during vertebrate sex chromosome evolution.

genomics↗