Seasonal breeding in the Western Mexican whiptail lizard Aspidoscelis costata on Isla Isabel,Nayarit, Mexico

Timing of sexual activity by males and females is a critical aspect of mating systems. We analyzed whether reproduction in western Mexican whiptail lizards, Aspidoscelis costata, on a tropical Pacific island in Mexico is seasonal or continuous, and whether it is linked to certain meteorological factors. Macroscopic and microscopic analyses of monthly samples of gonads showed that reproductive cycles of males and females were seasonal (FebruarySeptember) and significantly associated with day length. Necropsies did not evidence an overlap between successive reproductive events in females. However, our observations of free-ranging females showed that 35% of them were accompanied by males >1 time/season, with intervals between accompaniments of 1431 days. In addition, observations of captive females and males revealed that accompaniment lasted 25 days, seemingly coincided with female receptivity and was broken 812 days before egg-laying. Repeated accompaniment by males suggests females have successive reproductive events within a season.