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Abstract Studying how different genotypes respond to environmental variation is essential to understand the genetic basis of adaptation. The Mexican tetra,Astyanax mexicanus, has cave and surface‐dwelling morphotypes that have adapted to entirely different environments in the wild, and are now successfully maintained in lab conditions. While this has enabled the identification of genetic adaptations underlying a variety of physiological processes, few studies have directly compared morphotypes between lab‐reared and natural populations. Such comparative approaches could help dissect the varying effects of environment and morphotype, and determine the extent to which phenomena observed in the lab are generalizable to conditions in the field. To this end, we take a transcriptomic approach to compare the Pachón cavefish and their surface fish counterparts in their natural habitats and the lab environment. We identify key changes in expression of genes implicated in metabolism and physiology between groups of fish, suggesting that morphotype (surface or cave) and environment (natural or lab) both alter gene expression. We find gene expression differences between cave and surface fish in their natural habitats are much larger than differences in expression between morphotypes in the lab environment. However, lab‐raised cave and surface fish still exhibit numerous gene expression changes, supporting genetically encoded changes in livers of this species. From this, we conclude that a controlled laboratory environment may serve as an ideal setting to study the genetic underpinnings of metabolic and physiological differences between the cavefish and surface fish.
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Defining the Unseen: Population-Specific Markers for Astyanax mexicanus Blind Cavefish
Astyanax mexicanus is an emerging model system used to study development, evolution, and behavior of multiple cavefish populations that have repeatedly evolved from conspecific surface fish. Although surface and cavefish live and breed in the laboratory, there are no rapid methods for distinguishing between different cavefish populations. We present 2 methods for genotyping fish for a total of 16 population-specific markers using methods that are easy and inexpensive to implement in a basic molecular biology laboratory. This resource will help researchers maintain independent stocks within the laboratory and distinguish between fish from different populations.
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- PAR ID:
- 10550477
- Publisher / Repository:
- Mary Ann Liebert, Inc.
- Date Published:
- Journal Name:
- Zebrafish
- Volume:
- 21
- Issue:
- 3
- ISSN:
- 1545-8547
- Page Range / eLocation ID:
- 255 to 258
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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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.more » « less
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ABSTRACT Cave‐dwelling animals thrive in isolated caves despite the pressures of darkness, starvation, and reduced oxygen. Prior work revealed thatAstyanaxcave‐dwelling morphs derived from different cave localities express significantly higher levels of blood hemoglobin compared to surface‐dwelling fish. Interestingly, this elevation is maintained in different populations of cavefish, despite captive rearing in normal oxygen conditions. We capitalized on the consistent response of elevated hemoglobin in captive cavefish, which were derived from geographically distinct regions, to determine if this elevation is underpinned by expression of the sameHbgenes. Blood hemoglobin proteins are encoded by a large family ofhemoglobin(Hb) gene family members, which demonstrate coordinated expression patterns, subject to various organismal (e.g., period of life history) and environmental influences (e.g., oxygen availability). Surprisingly, we found that geographically distinct populations showed mostly divergent patterns ofHbgene expression. Cavefish from two cave localities, Pachón and Tinaja, have a more recent shared origin, and show more similarHbexpression patterns as adults. However, during embryonic phases, Pachón and Tinaja show significant variability in timing of peak expression ofHbfamily members. In sum, the transcriptomic underpinnings ofHbgene expression represents a complex composite of shared and divergent expression patterns across three captive cavefish populations. We conclude that these differential patterns are likely influenced by life history, and the unique cave conditions in which these animals evolved.more » « less
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Abstract Animals respond to sleep loss with compensatory rebound sleep, and this is thought to be critical for the maintenance of physiological homeostasis. Sleep duration varies dramatically across animal species, but it is not known whether evolutionary differences in sleep duration are associated with differences in sleep homeostasis. The Mexican cavefish,Astyanax mexicanus, has emerged as a powerful model for studying the evolution of sleep. While eyed surface populations ofA. mexicanussleep approximately 8 hr each day, multiple blind cavefish populations have converged on sleep patterns that total as little as 2 hr each day, providing the opportunity to examine whether the evolution of sleep loss is accompanied by changes in sleep homeostasis. Here, we examine the behavioral and molecular response to sleep deprivation across four independent populations ofA. mexicanus. Our behavioral analysis indicates that surface fish and all three cavefish populations display robust recovery sleep during the day following nighttime sleep deprivation, suggesting sleep homeostasis remains intact in cavefish. We profiled transcriptome‐wide changes associated with sleep deprivation in surface fish and cavefish. While the total number of differentially expressed genes was not greater for the surface population, the surface population exhibited the highest number of uniquely differentially expressed genes than any other population. Strikingly, a majority of the differentially expressed genes are unique to individual cave populations, suggesting unique expression responses are exhibited across independently evolved cavefish populations. Together, these findings suggest sleep homeostasis is intact in cavefish despite a dramatic reduction in overall sleep duration.more » « less
- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1089/zeb.2023.0105
