Meeting Abstract
Marsh rice rats reportedly are excellent swimmers with swimming largely confined to the nighttime. I examined whether photoperiod, castration, and melatonin implants affect growth, pelage, reproduction, and the swimming behavior of rice rats. Juvenile males housed on 14L:10D (a long photoperiod) were weaned at 21 days of age, weighed, and left on 14L:10D or transferred to 11L:13D (a short photoperiod). On day 68 of age, rice rats were weighed and swum for ten minutes in a ten gallon glass aquarium. Animals were videotaped while swimming in order to quantify the swimming and floating times. Animals were reweighed after the swim to determine whether water absorption by the pelage caused a change in body mass. On day 69 of age, rice rats were sacrificed and the following organs removed and weighed: both testes, seminal vesicles (SV), spleen, and Harderian glands (HG). Photoperiod significantly affected body mass and the masses of the testes, SV, and HG. The pelage absorbed more water on 14L:10D than on 11L:13D, but pelage lengths were not different between the two photoperiods. The swimming and floating times also were not different between the two photoperiods. Castration affected body mass and the growth of the SV, HG, and spleen only. Lastly, melatonin implants affected body mass, the growth of the testes, SV, HG, pelage length, and absorption of water by the pelage. Taken together, these results show that photoperiod, castration, and melatonin, although they affect growth and reproduction, do not affect swimming behavior in rice rats. It is hypothesized that changes characteristic of winter (short photoperiod, decreased testes size and testosterone, and increased melatonin) are not sufficient to alter aspects of swimming behavior. (Supported by the Indiana Academy of Science)
