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1. Postprandial Sleep in Short‐Sleeping Mexican Cavefish

   https://doi.org/10.1002/jez.2880  

   Gallman, Kathryn; Rastogi, Aakriti; North, Owen; O'Gorman, Morgan; Hutton, Pierce; Lloyd, Evan; Warren, Wesley C; Kowalko, Johanna E; Duboue, Erik R; Rohner, Nicolas; et al (December 2024, Journal of Experimental Zoology Part A: Ecological and Integrative Physiology)

   ABSTRACT Interactions between sleep and feeding behaviors are critical for adaptive fitness. Diverse species suppress sleep when food is scarce to increase the time spent foraging. Postprandial sleep, an increase in sleep time following a feeding event, has been documented in vertebrate and invertebrate animals. While interactions between sleep and feeding appear to be highly conserved, the evolution of postprandial sleep in response to changes in food availability remains poorly understood. Multiple populations of the Mexican cavefish,Astyanax mexicanus, have independently evolved sleep loss and increased food consumption compared to surface‐dwelling fish of the same species, providing the opportunity to investigate the evolution of interactions between sleep and feeding. Here, we investigate the effects of feeding on sleep in larval and adult surface fish, and in two parallelly evolved cave populations ofA. mexicanus. Larval surface and cave populations ofA. mexicanusincrease sleep immediately following a meal, providing the first evidence of postprandial sleep in a fish model. The amount of sleep was not correlated to meal size and occurred independently of feeding time. In contrast to larvae, postprandial sleep was not detected in adult surface or cavefish, which can survive for months without food. Together, these findings reveal that postprandial sleep is present in multiple short‐sleeping populations of cavefish, suggesting sleep‐feeding interactions are retained despite the evolution of sleep loss. These findings raise the possibility that postprandial sleep is critical for energy conservation and survival in larvae that are highly sensitive to food deprivation. 

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2. Unique transcriptional signatures of sleep loss across independently evolved cavefish populations

   https://doi.org/10.1002/jez.b.22949  

   McGaugh, Suzanne E.; Passow, Courtney N.; Jaggard, James Brian; Stahl, Bethany A.; Keene, Alex C. (April 2020, Journal of Experimental Zoology Part B: Molecular and Developmental Evolution)

   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. 

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3. Widespread loss of sleep in independently evolved populations of wild-caught cavefish

   https://doi.org/10.1016/j.isci.2025.113940  

   North, Owen W; Maza-Castañeda, Lourdes Citlalli; Manning, Aubrey E; Rastogi, Aakriti; Gluesenkamp, Andrew; Gluesenkamp, Leah; Swanson, Nathan; Hernández-Lozano, Jorge; Garduño-Sánchez, Marco A; Díaz-Cruz, Jesús Alberto; et al (December 2025, iScience)

   Sleep is an evolutionarily ancient behavior, yet multiple cave-dwelling populations of the Mexican tetra, Astyanax mexicanus, have converged on sleep loss compared to surface fish. However, most of the 34 cave populations remain unstudied, and sleep in natural habitats is largely unknown. To address this, we measured sleep and activity in 15 representative populations of surface, cave, and hybrid populations. All cavefish and hybrid populations tested exhibited drastically reduced sleep, including hybrid populations with diverse eye and pigmentation phenotypes. Mapping behavior onto the A. mexicanus phylogeny revealed that reduced sleep and elevated locomotor activity evolved independently multiple times. Field experiments confirmed that wild fish also exhibit sleep loss, paralleling laboratory findings. These results demonstrate deep evolutionary convergence on sleep loss across cavefish lineages and suggest that sleep reduction is a primary trait contributing to adaptation in subterranean environments. 

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4. Repeated evolution of eye loss in Mexican cavefish: Evidence of similar developmental mechanisms in independently evolved populations

   https://doi.org/10.1002/jez.b.22977  

   Sifuentes‐Romero, Itzel; Ferrufino, Estephany; Thakur, Sunishka; Laboissonniere, Lauren A.; Solomon, Michael; Smith, Courtney L.; Keene, Alex C.; Trimarchi, Jeffrey M.; Kowalko, Johanna E. (July 2020, Journal of Experimental Zoology Part B: Molecular and Developmental Evolution)

   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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5. Cavefish brain atlases reveal functional and anatomical convergence across independently evolved populations

   https://doi.org/10.1126/sciadv.aba3126  

   Jaggard, James B.; Lloyd, Evan; Yuiska, Anders; Patch, Adam; Fily, Yaouen; Kowalko, Johanna E.; Appelbaum, Lior; Duboue, Erik R.; Keene, Alex C. (September 2020, Science Advances)

   null (Ed.)

   Environmental perturbation can drive behavioral evolution and associated changes in brain structure and function. The Mexican fish species, Astyanax mexicanus , includes eyed river-dwelling surface populations and multiple independently evolved populations of blind cavefish. We used whole-brain imaging and neuronal mapping of 684 larval fish to generate neuroanatomical atlases of surface fish and three different cave populations. Analyses of brain region volume and neural circuits associated with cavefish behavior identified evolutionary convergence in hindbrain and hypothalamic expansion, and changes in neurotransmitter systems, including increased numbers of catecholamine and hypocretin/orexin neurons. To define evolutionary changes in brain function, we performed whole-brain activity mapping associated with behavior. Hunting behavior evoked activity in sensory processing centers, while sleep-associated activity differed in the rostral zone of the hypothalamus and tegmentum. These atlases represent a comparative brain-wide study of intraspecies variation in vertebrates and provide a resource for studying the neural basis of behavioral evolution. 

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