Meeting Abstract

P2.154  Tuesday, Jan. 5  Sexual dimorphisms in visceral organ mass, metabolism, and energetics in pre-breeding American Toads (Anaxyrus americanus). FINKLER, M.S.*; HAYES, C.J.; Indiana Univ. Kokomo mfinkler@iuk.edu

Sexual dimorphisms in body size are common in many species of anurans, and have often been ascribed to different selective forces that influence reproductive success in males and females. However, little is known about dimorphisms in whole-organism physiology or in internal morphology in anurans. In this study, we investigated potential differences in visceral organ mass, hematology, metabolism, and stored energy content between reproductive male and female American Toads (Anaxyrus americanus) collected en route to breeding areas during the spring. Female toads were both longer and more massive than males, but males tend to have larger somatic masses (i.e., sans reproductive organs) at a given snout-vent length. Females had proportionately greater kidney masses than males, whereas males demonstrated larger increases in heart mass with body mass than did females. Liver mass did not differ between the sexes once somatic body mass was accounted for. None of the hematological parameters examined (RBC counts, Hct, and [Hb]) differed between the sexes, but oxygen consumption rates increased with increasing somatic body mass in males but not in females. The caloric content of the carcass (sans the heart, liver, kidneys, and reproductive organs) and the did not differ between males and females once corrected for carcass mass. The relevance of these observed differences towards increasing reproductive success in each sex will be discussed.