While it is widely accepted that sleep is conserved throughout the animal kingdom, very little is known about the genetic mechanisms driving the behavior or the evolutionary forces shaping it. This dissertation aims to investigate both the genetic and the evolutionary mechanisms underlying sleep using the Mexican Blind Cavefish, Astyanax mexicanus. Astyanax is unique among vertebrate organisms in that it has two drastically different forms, an eyed surface dwelling form and 29 cave dwelling populations which have all evolved from the surface fish.
We have first established sleep in the surface dwelling population and three cavefish populations. We find that a clearly defined change in ecological conditions, from surface to cave, is correlated with a dramatic reduction in sleep in all three independently derived cave populations of A. mexicanus.
We next show that blockade of β-adrenergic receptors with propranolol rescues the decreased-sleep phenotype of cavefish. Morphological analysis of catecholamine circuitry reveals conservation of gross catecholaminergic neuroanatomy between surface and cave morphs. Taken together these findings suggest that evolutionarily derived changes in adrenergic signaling affect the reduced sleep of cave populations.
Analyses of surface × cave hybrids show that the alleles for reduced sleep in the Pachón and Tinaja cave populations are dominant in effect to the surface alleles. Genetic analysis of hybrids between surface and Pachón cavefish suggests that only a small number of loci with dominant effects are involved. Our results demonstrate that sleep is an evolutionarily labile phenotype, highly responsive to changes in ecological conditions.
Finally, we show that in an unrelated cavefish species, the Hillstream loach, that four cave populations have greatly reduced rest times in comparison to rest times of their surface relatives. All four cave species retained rhythmicity, and in three of the four there is a pronounced 24-hour rhythm; in the fourth there is an altered rhythmicity of 38-40 hours. Thus, consistent changes in total rest have evolved in these species independent of circadian rhythmicity. Taken together, our data suggest that consistent reduction in total rest times were accomplished evolutionarily through alterations in rest homeostasis.
|Advisor:||Borowsky, Richard L.|
|Commitee:||Blau, Justin, Desplan, Claude, Purugganan, Michael, Vosshall, Leslie|
|School:||New York University|
|School Location:||United States -- New York|
|Source:||DAI-B 73/07(E), Dissertation Abstracts International|
|Subjects:||Neurosciences, Evolution and Development|
|Keywords:||Behavioral evolution, Cavefish, Circadian rythms, Quantitative trait loci, Sleep loss|
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