Subterranean Fishes of the World

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2022

bioRxiv preprint May 02 2022

Now published in BMC Ecology and Evolution (2022) 22:116 https://doi.org/10.1186/s12862-022-02069-8

The copyright holder for this preprint (which was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is made available under aCC-BY-NC-ND 4.0 International license

Aggression is a complex behavior that is observed across the animal kingdom, and plays roles in 6 resource acquisition, defense, and reproductive success. While there are many individual 7 differences in propensity to be aggressive within and between populations, the mechanisms 8 underlying differences in aggression between individuals in natural populations are not well 9 understood. We addressed this using the Mexican tetra, Astyanax mexicanus, a powerful model 10 organism to understand behavioral evolution. A. mexicanus exists in two forms: a river-dwelling 11 surface form and multiple populations of a blind cave form. We characterized aggression in 12 surface fish and cavefish in a resident/intruder assay through quantifying multiple behaviors 13 occurring during social interactions. Surface fish, which are aggressive, display multiple social 14 behaviors in this context, which we characterized into two types of behaviors: aggression-15 associated and escape-associated behaviors. The majority of these behaviors were reduced or 16 lost in Pachón cavefish. Further, both aggression-associated and escape-associated behaviors 17 were not dependent on the presence of light, and both surface fish and cavefish remained 18 aggressive or non-aggressive, respectively, when opposed to fish from a different population. 19 Additionally, we found that within populations, levels of stress response were not correlated with 20 aggression- or escape-associated behaviors. Finally, when we compared aggression- and escape-21 associated behaviors across four cavefish populations, we found that both types of behaviors are 22 reduced in three cave populations, while still present in one. Together, these results reveal that 23 multiple cavefish populations have repeatedly evolved reduced aggression through shared 24 behavioral components, while other cavefish have retained aggression.

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