Biology subjects

Hillis, D. M.

Publications and source records attributed to Hillis, D. M..

5 recordsLinked to original sources

bioRxiv2025

Parallel Sensory Compensation following Independent Subterranean Colonization by Groundwater Salamanders (Eurycea )

Lineages that have invaded subterranean environments have repeatedly evolved remarkable adaptations to life in darkness. However, observational and experimental studies in additional natural systems are needed to further our understanding of repeated evolution and convergence. In Texas, a radiation of groundwater salamanders (genus Eurycea), with independent invasions of subterranean karstic environments, offers an opportunity to investigate phenotypic convergence, parallel evolution, and the enhancement and regression of sensory systems. Adaptations to a troglobitic life in this clade includes morphological, behavioral, and physiological changes within and among species. Intraspecific and interspecific variation in morphology to the selective pressures of life underground allows for detailed examination of physical, behavioral, and physiological changes associated with subterranean adaptation within a comparative phylogenetic framework. We find a tradeoff between two sensory systems repeated across multiple subterranean Eurycea lineages: the degeneration of the eye and the expansion of the mechanosensory lateral line. The increase in anterior neuromast organs in subterranean lineages was positively correlated with the expression of paired box protein Pax-6, a conserved transcription factor important for vertebrate neurogenesis. Our results show a decreasing trend of PAX-6 labeling in the neuromasts of adult surface salamanders (E. nana) relative to the maintained labeling in subterranean species (E. rathbuni). Our results suggest a tradeoff in resource allocation between the development of optic and anterior lateral line sensory systems in surface and subterranean salamander lineages and provide a starting point for future evolutionary developmental investigations examining the genetic underpinnings of adaptive, repeated evolution in a novel system. Significance StatementUnder-explored subterranean environments in Central Texas harbor a phenotypically and taxonomically diverse radiation of groundwater salamanders, which we used to test the molecular and developmental bases for adaptive evolution in extreme environments. Using an integrative approach, we quantify the divergence and convergence of two sensory modalities: vision loss and mechanoreception. The divergent developmental and phenotypic tradeoffs have evolved several times in parallel among populations and species in this group. Understanding the evolutionary developmental processes responsible for these changes will further our understanding of adaptive, repeated evolution in a natural system.

evolutionary biology↗

bioRxiv2023

PAX6 protein in neuromasts of the lateral line system of salamanders (Eurycea)

PAX6 is well known as a transcription factor that drives eye development in animals as widely divergent as flies and mammals. In addition to its localization in eyes, PAX6 expression has been reported in the central nervous system, the pancreas, testes, Merkel cells, nasal epithelium, and developing cells of the inner ear. Here we show that PAX6 is also found in the mechanosensory neuromasts of the lateral line system in paedomorphic salamanders of the genus Eurycea. Using immunohistochemistry and confocal microscopy, we found that PAX6 is extranuclear, and antibody labeling is most intense in the apical appendages of the hair cells of the neuromast. This extranuclear localization raises the possibility of an as yet undescribed function for PAX6 as a cytoskeleton-associated protein.

cell biology↗

bioRxiv2022

A tale of two paths: The evolution of mitochondrial recombination in bivalves with doubly uniparental inheritance

In most animals, mitochondrial DNA is strictly maternally inherited and non-recombining. One exception to these assumptions is called doubly uniparental inheritance (DUI): a phenomenon involving the independent transmission of female and male mitochondrial genomes. DUI is known only from the molluscan class Bivalvia. The phylogenetic distribution of male mitochondrial DNA in bivalves is consistent with several evolutionary scenarios, including multiple independent gains, losses, and varying degrees of recombination with female mitochondrial DNA. In this study, we use phylogenetic methods to test male mitochondrial DNA origination hypotheses and infer the prevalence of mitochondrial recombination in bivalves with DUI. Phylogenetic modeling using site concordance factors supported a single origin of male mitochondrial DNA in bivalves coupled with recombination acting over long evolutionary timescales. Ongoing mitochondrial recombination is present in Mytilida and Venerida, which results in a pattern of concerted evolution of female and male mitochondrial DNA. Mitochondrial recombination could be favored to offset the deleterious effects of asexual inheritance and maintain mitonuclear compatibility across tissues. Cardiida and Unionida have gone without recent recombination, possibly due to an extension of the COX2 gene in male mitochondrial DNA. The loss of recombination may be neutral but could be connected to the role of M mtDNA in sex determination or sexual development. Our results support recombination events in DUI species may occur throughout their genomes. Future investigations may reveal more complex patterns of inheritance of recombinants, which could explain the retention of signal for a single origination of male mitochondrial DNA in protein coding genes.

evolutionary biology↗

bioRxiv2019

Does breeding season variation affect evolution of a sexual signaling trait in a tropical lizard clade?

Sexually selected traits can be expected to increase in importance when the period of sexual behavior is constrained, such as in seasonally restricted breeders. Anolis lizard male dewlaps are classic examples of multifaceted signaling traits, with demonstrated reproductive function reflected in courtship behavior. Fitch and Hillis found a correlation between dewlap size and seasonality in mainland Anolis using traditional statistical methods. Here, we present two tests of the Fitch-Hillis Hypothesis using new phylogenetic and morphological data sets for 44 species of Mexican Anolis. A significant relationship between dewlap size and seasonality is evident in phylogenetically uncorrected analyses but erodes once phylogeny is accounted for. This loss of statistical support for a relationship between a key aspect of dewlap morphology and seasonality also occurs within a species complex (A. sericeus group) that inhabits seasonal and aseasonal environments. Our results fail to support seasonality as a strong driver of evolution of Anolis dewlap size. We discuss the implications of our results and the difficulty of disentangling the strength of single mechanisms on trait evolution when multiple selection pressures are likely at play.

evolutionary biology↗

bioRxiv2017

Evolution of Animal Neural Systems

Nervous systems are one of the most spectacular products of evolution. Their provenance and evolution have been an area of interest and often intense debate since the late 19th century. The genomics era has provided researchers with a new set of tools with which to study the early evolution of neurons, and recent progress on the molecular evolution of the first neurons has been both exciting and frustrating. It has become increasingly obvious that genomic data is often insufficient to reconstruct complex phenotypes in deep evolutionary time. We review this recent progress and its attendant challenges, and suggest ways forward.

evolutionary biology↗