Results

1. The impacts of food restriction on reproductive development in a seasonally-reproducing mammal, the Siberian hamster (Phodopussungorus) Carlisha A. Hall1, Allison M. Bailey 2,3, Gregory E. Demas2,3 1University of North Carolina Pembroke, Pembroke, NC 2Department of Biology, Indiana University, Bloomington, IN 3Center for the Integrative Study of Animal Behavior, Indiana University, Bloomington, IN Results Introduction Discussion • Seasonal reproduction is a strategy that maximizes reproductive success by ensuring offspring are born during favorable environmental conditions [1]. • Seasonally reproducing animals face unique challenges in changing environments because they have evolved robust physiological responses to environmental cues, like food availability [2]. • Neuroendocrine mechanisms controlling the onset of puberty are the same as those that control the onset of seasonal reproduction [3,4]. A B B • The food-restricted animals exhibited physiological delays in development compared to the ad libitum-fed animals. Ad libitum-fed animals gained more body mass than food-restricted animals Sex differences in ad libitum intake • By day 30 all ad libitum-fed males achieved reproductive maturity and by day 40 all food restricted males achieved reproductive maturity. • By day 40 all ad libitum-fed females achieved vaginal patency and at day 50 the food-restricted females achieved vaginal patency. • Out of 62 females, only two females from the ad libitum group had an estrous cycle. • All ad libitum males and females had more reproductive fat than their counterparts and no significant differences were found in the other reproductive organs. Hypotheses • If a seasonally breeding animal experiences limited food availability during development, reproductive development will be delayed. • Because the same neural mechanisms are involved in reproductive development and seasonal reproduction, responses to seasonal cues as an adult will subsequently be impaired. Ad libitum-fed hamsters achieved reproductive maturity earlier than food-restricted hamsters Ad libitum-fed hamsters had more reproductive fat than food-restricted hamsters. Male reproductive organ mass Reproductive Maturity in Males Future Directions Study System • Kisspeptin is a peptide hormone that acts in the brain to promote reproduction by responding to internal and environmental cues [5]. • Siberian hamsters (Phodopussungorus), were used to examine the effects of food availability on seasonal reproductive development. • We hypothesize that our food restriction treatment influenced kisspeptinactivity, contributing to delayed reproductive development. • Expression of kisspeptin mRNA in the brain will be assessed in a subset of hamsters at day 60. • Another subset of hamsters from this study are currently involved in a follow-up experiment investigating their adult seasonal reproductive responses as well as mRNA expression of kisspeptin and its receptor underlying these responses. Methods • Hamsters received either ad libitum food or 70% of ad libitum intake from weaning until early adulthood. • We monitored ad libitum food intake every two days and body mass every five days. • To assess reproductive maturity in male hamsters, we calculated the estimated testis volume (ETV; testis length x testis width2) every five days until ETV was greater than or equal to 400. • To assess reproductive maturity in female hamsters, we recorded the presence or absence of vaginal patency every five days. • At 60 days, we measured reproductive organ mass and collected tissues for subsequent gene expression analysis. Reproductive Maturity in Females Female reproductive organ mass References • [1] Bronson FH. 1985. Mammalian reproduction: An ecological perspective. Biology of Reproduction 32: 1-26. [2] Bronson FH, Heideman PD. 1994. Seasonal regulation of reproduction in mammals. In: Knobil E and Neill JD, ed. The Physiology of Reproduction, Second Edition. New York: Raven Press, Ltd. 541-583 pp. [3] Castellano JM et al. 2005. Changes in hypothalamic KiSS-1 system and restoration of pubertal activation of the reproductive axis by kisspeptin in undernutrition. Endocrinology 146: 3917-25. [4] Greives TJ et al. 2007. Environmental control of kisspeptin: Implications for seasonal reproduction. Endocrinology 148: 1158-66. [5] Clarke IJ, Caraty A. 2013. Kisspeptin and seasonality of reproduction. Advances in experimental medicine and biology 784: 411-30. Acknowledgements This work is funded by the NSF-REU program in Animal Behavior at Indiana University. Thank you to the members of the Demas lab for their support throughout the study.