Meeting Abstract

P3-110    How hot is too hot for pupfish reproduction? Effects of thermal environment on reproductive physiology in Amargosa pupfish, Cyprinodon nevadensis amargosae Housh, MJ*; Lema, SC; California Polytechnic State University, San Luis Obispo; California Polytechnic State University, San Luis Obispo maddiehoush@gmail.com

Desert pupfishes (genus Cyprinodon) of the North American southwest present an ideal system for examining how thermal environment shapes physiology. As a consequence of being confined to isolated habitats, many of which show extreme environmental fluctuations, pupfishes have evolved some of the highest thermal maxima and broadest temperature ranges among freshwater fishes. However, pupfish reproduction is impaired at temperatures well below thermal maxima, and ~40% of pupfish are already endangered, putting them in a precarious situation given projected climate warming. Physiologically, reproduction is regulated by the hypothalamic-pituitary-gonadal (HPG) hormone axis, and chronic high temperature exposure can reduce circulating steroid hormones, affecting gonad development and mating behavior. Here, we examined the effects of elevated temperatures on the reproductive physiology of Amargosa pupfish (C. n. amargosae) by maintaining adult fish for 44 d under conditions of stable 25^°C, stable 35^°C, or a regime that fluctuated diurnally between ~25-35^°C (mean: 30.5^°C). Female pupfish at 35^°C and fluctuating had lower gonadosomatic index (GSI) values compared to females at 25^°C. Temperature did not affect GSI in males. In females, hepatic expression of genes involved in egg development, vitellogenin A (vtgA) and choriogenin L (cgL), were reduced at 35^°C and fluctuating compared to 25^°C. These findings suggest that oogenesis is more sensitive to inhibition at elevated temperatures than spermatogenesis in pupfishes and demonstrate that oogenesis can be affected by short-term high temperature exposure— reflective of ecologically relevant fluctuating temperature regimes that occur in stream and spring outflow channel pupfish habitats.