Circadian locomotor activity and response to different light conditions in the Volcano mouse, Neotomodon alstoni (Merriam, 1898)

Abstract

The volcano mouse, Neotomodon alstoni, was studied in order to describe basic circadian behavior during free running and entrainment to parametric and non-parametric photoperiods. Responses to short and long days were also tested to ascertain any potential photoperiodic response. This species is endemic to the high grasslands of central Mexico. Its breeding peaks during summer, indicating a possible circannual regulation of reproduction. Our results indicate that locomotor activity in Neotomodon alstoni is typical of a nocturnal rodent when studied using running wheels, however, when activity was observed in freely moving recordings with no running wheel, locomotor activity shifts to a semidiurnal architecture when exposed to long day photoperiods. When gonadal activity was studied in males exposed to short and long days, significant differences were observed in testis size, nevertheless levels of testosterone and seminiferous tubuli indicated that day length does not inhibit sexual maturity in this species. The results indicated that N. alstoni may not be photoperiodic with regard to gonadal activity, however it does display photoperiodic differences with regard to behavior, body weight and testis size.