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Abstract Evolution in similar environments often leads to convergence of behavioral and anatomical traits. A classic example of convergent trait evolution is the reduced traits that characterize many cave animals: reduction or loss of pigmentation and eyes. While these traits have evolved many times, relatively little is known about whether these traits repeatedly evolve through the same or different molecular and developmental mechanisms. The small freshwater fish,Astyanax mexicanus, provides an opportunity to investigate the repeated evolution of cave traits.A. mexicanusexists as two forms, a sighted, surface‐dwelling form and at least 29 populations of a blind, cave‐dwelling form that initially develops eyes that subsequently degenerate. We compared eye morphology and the expression of eye regulatory genes in developing surface fish and two independently evolved cavefish populations, Pachón and Molino. We found that many of the previously described molecular and morphological alterations that occur during eye development in Pachón cavefish are also found in Molino cavefish. However, for many of these traits, the Molino cavefish have a less severe phenotype than Pachón cavefish. Further, cave–cave hybrid fish have larger eyes and lenses during early development compared with fish from either parental population, suggesting that some different changes underlie eye loss in these two populations. Together, these data support the hypothesis that these two cavefish populations evolved eye loss independently, yet through some of the same developmental and molecular mechanisms.
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Convergence on reduced aggression through shared behavioral traits in multiple populations of Astyanax mexicanus
Abstract BackgroundAggression is observed across the animal kingdom, and benefits animals in a number of ways to increase fitness and promote survival. While aggressive behaviors vary widely across populations and can evolve as an adaptation to a particular environment, the complexity of aggressive behaviors presents a challenge to studying the evolution of aggression. The Mexican tetra,Astyanax mexicanusexists as an aggressive river-dwelling surface form and multiple populations of a blind cave form, some of which exhibit reduced aggression, providing the opportunity to investigate how evolution shapes aggressive behaviors. ResultsTo define how aggressive behaviors evolve, we performed a high-resolution analysis of multiple social behaviors that occur during aggressive interactions inA. mexicanus.We found that many of the aggression-associated behaviors observed in surface-surface aggressive encounters were reduced or lost in Pachón cavefish. Interestingly, one behavior, circling, was observed more often in cavefish, suggesting evolution of a shift in the types of social behaviors exhibited by cavefish. Further, detailed analysis revealed substantive differences in aggression-related sub-behaviors in independently evolved cavefish populations, suggesting independent evolution of reduced aggression between cave populations. We found that many aggressive behaviors are still present when surface fish fight in the dark, suggesting that these reductions in aggression-associated and escape-associated behaviors in cavefish are likely independent of loss of vision in this species. Further, levels of aggression within populations were largely independent of type of opponent (cave vs. surface) or individual stress levels, measured through quantifying stress-like behaviors, suggesting these behaviors are hardwired and not reflective of population-specific changes in other cave-evolved traits. ConclusionThese results reveal that loss of aggression in cavefish evolved through the loss of multiple aggression-associated behaviors and raise the possibility that independent genetic mechanisms underlie changes in each behavior within populations and across populations. Taken together, these findings reveal the complexity of evolution of social behaviors and establishA. mexicanusas a model for investigating the evolutionary and genetic basis of aggressive behavior.
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- Award ID(s):
- 2202359
- PAR ID:
- 10376017
- Publisher / Repository:
- Springer Science + Business Media
- Date Published:
- Journal Name:
- BMC Ecology and Evolution
- Volume:
- 22
- Issue:
- 1
- ISSN:
- 2730-7182
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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