Biology subjects

McDole, B.

Publications and source records attributed to McDole, B..

4 recordsLinked to original sources

bioRxiv2021

Characterizing the genetic basis of trait evolution in the Mexican cavefish

Evolution in response to a change in ecology often coincides with various morphological, physiological, and behavioral traits. For most organisms little is known about the genetic and functional relationship between evolutionarily derived traits, representing a critical gap in our understanding of adaptation The Mexican tetra, Astyanax mexicanus, consists of largely independent populations of fish that inhabit at least 30 caves in Northeast Mexico, and a surface fish population, that inhabits the rivers of Mexico and Southern Texas. The recent application of molecular genetic approaches combined with behavioral phenotyping have established A. mexicanus as a model for studying the evolution of complex traits. Cave populations of A. mexicanus are interfertile with surface populations and have evolved numerous traits including eye degeneration, insomnia, albinism and enhanced mechanosensory function. The interfertility of different populations from the same species provides a unique opportunity to define the genetic relationship between evolved traits and assess the co-evolution of behavioral and morphological traits with one another. To define the relationships between morphological and behavioral traits, we developed a pipeline to test individual fish for multiple traits. This pipeline confirmed differences in locomotor activity, prey capture, and startle reflex between surface and cavefish populations. To measure the relationship between traits, individual F2 hybrid fish were characterized for locomotor behavior, prey-capture behavior, startle reflex and morphological attributes. Analysis revealed an association between body length and slower escape reflex, suggesting a trade-off between increased size and predator avoidance in cavefish. Overall, there were few associations between individual behavioral traits, or behavioral and morphological traits, suggesting independent genetic changes underlie the evolution of behavioral and morphological traits. Taken together, this approach provides a novel system to identify genes that underlie naturally occurring genetic variation in morphological and behavioral traits.

evolutionary biology↗

bioRxiv2021

Blind cavefish retain functional connectivity in the tectum despite loss of retinal input

Sensory systems display remarkable plasticity and are under strong evolutionary selection. The Mexican cavefish, Astyanax mexicanus, consists of eyed river-dwelling surface populations, and multiple independent cave populations which have converged on eye loss, providing the opportunity to examine the evolution of sensory circuits in response to environmental perturbation. Functional analysis across multiple transgenic populations expressing GCaMP6s showed that functional connectivity of the optic tectum largely did not differ between populations, except for the selective loss of negatively correlated activity within the cavefish tectum, suggesting positively correlated neural activity is resistant to an evolved loss of input from the retina. Further, analysis of surface-cave hybrid fish reveals that changes in the tectum are genetically distinct from those encoding eye-loss. Together, these findings uncover the independent evolution of multiple components of the visual system and establish the use of functional imaging in A. mexicanus to study neural circuit evolution.

neuroscience↗

bioRxiv2019

Evolution of the acoustic startle response of Mexican cavefish

The ability to detect threatening sensory stimuli and initiate an escape response is essential for survival and under stringent evolutionary pressure. In diverse fish species, acoustic stimuli activate Mauthner neurons, which initiate a stereotypical C-start escape response. This reflexive behavior is highly conserved across aquatic species and provides a model for investigating the neural mechanism underlying the evolution of escape behavior. Here, we define evolved differences in the C-start response between populations of the Mexican cavefish, Astyanax mexicanus. Cave populations of A. mexicanus inhabit in an environment devoid of light and macroscopic predation, resulting in evolved differences in diverse morphological and behavioral traits. We find that the C-start is present in multiple populations of cavefish and river-dwelling surface fish, but response kinematics and probability differ between populations. The Pachon population of cavefish have an increased response probability, a slower response and reduction of the maximum bend angle, revealing evolved differences between surface and cave populations. In two other independently evolved populations of cavefish, the response probability and the kinematics of the response differ from one another, as well as from surface fish, suggesting the independent evolution of differences in the C-start response. Investigation of surface-cave hybrids reveals a relationship between angular speed and peak angle, suggesting these two kinematic characteristics are related at the genetic or functional levels. Together, these findings provide support for the use of A. mexicanus as a model to investigate the evolution of escape behavior.

neuroscience↗

bioRxiv2019

Stable transgenesis in Astyanax mexicanus using the Tol2 transposase system.

Astyanax mexicanus is a well-established and widely used fish model system for evolutionary and developmental biology research. These fish exist as surface forms that inhabit rivers and 30 different populations of cavefish. The establishment of A. mexicanus as an emergent model organism for understanding the evolutionary basis of development and behavior has been accelerated by an increasing availability of genomic approaches to identify genotype-phenotype associations. Despite important progress in the deployment of new technologies, deep mechanistic insights into A. mexicanus evolution and development have been limited by a lack of transgenic lines commonly used in genetic model systems. Here, we expand the toolkit of transgenesis by characterizing two novel stable transgenic lines that were generated using the highly efficient Tol2 system, commonly used to generate transgenic zebrafish. A stable transgenic line consisting of the zebrafish ubiquitin promoter fused to eGFP expressed eGFP ubiquitously throughout development in a surface population of Astyanax. To define specific cell-types, we injected fish with a Cntnap2-mCherry construct that labels lateral line mechanosensory neurons in zebrafish. Strikingly, both constructs appear to label the predicted cell types, suggesting many genetic tools and defined promoter regions in zebrafish are directly transferrable to cavefish. The lines provide proof-of-principle for the application of Tol2 transgenic technology in A. mexicanus. Expansion on these initial transgenic lines will provide a platform to address broadly important problems in the quest to bridge the genotype to phenotype gap.

developmental biology↗