SREL Reprint #3037

Reproductive and resource benefits to large female body size in a mammal with female-biased sexual size dimorphism

H. Bobby Fokidis1, Thomas S. Risch1, and Travis C. Glenn2

1Department of Biological Sciences, Arkansas State University, State University, AR 72467, USA
2Savannah River Ecology Laboratory, The University of Georgia, Aiken, SC 29802, USA

Abstract: Factors underlying the evolution of female-biased sexual size dimorphism in mammals are poorly understood. In an effort to better understand these factors we tested whether larger female southern flying squirrels, Glaucomys volans, gained reproductive advantages (larger litters or more male mates) and direct resource benefits, such as larger home ranges or access to more food (i.e. mast-producing trees). As dimorphism can vary with age in precocial breeding species, we compared females during their first reproduction and during a subsequent breeding attempt. Females were not significantly larger or heavier than males at first reproduction, but became about 7% heavier and 22% larger than males at subsequent breeding. Larger females produced larger litters and had home ranges containing a greater proportion of upland hardwood trees. Female body size was not associated with either multiple male mating or home range size, but females with larger home ranges had higher indexes of body condition. Females in precocial breeding flying squirrels initiate reproduction before sexual size dimorphism is evident, and thus, may be allocating resources to both reproduction and growth simultaneously, or delaying growth entirely. Larger females produce more pups and have access to more food resources. Thus, selection for increased female size may partly explain how female-biased sexual size dimorphism is maintained in this species.

Keywords: benefits of age, body condition and body size; female-biased sexual size dimorphism; Glaucomys volans; multiple paternity; precocial breeding; home range size; southern flying squirrel

SREL Reprint #3037

Fokidis, H. B., T. S. Risch, and T. C. Glenn 2007. Reproductive and resource benefits to large female body size in a mammal with female-biased sexual size dimorphism. Animal Behavior 73:479-488.

This information was provided by the University of Georgia's Savannah River Ecology Laboratory (srel.uga.edu).