VITOUSEK, Maren N.*; MITCHELL, Mark A.; Princeton University; Louisiana State University: Reproductive pattern and follicular development in the Galapagos marine iguana (Amblyrhynchus cristatus)

Female Galapagos marine iguanas (Amblyrhynchus cristatus) typically reproduce biennially, producing a clutch that represents 18-28% of female body weight. During periods of plentiful food availability females may reproduce in consecutive years; when conditions are poor few females visit male display territories or are observed to copulate. We attempted to determine how and when reproductive status is established in a given year. We assessed female follicular development through the use of ultrasonography, a method that produced highly repeatable measures of follicular dimensions. Twenty-four females were marked at Bahia Paraiso, Isla Santa Fe, Galapagos Archipelago, and followed throughout the mate choice period. Females were recaptured at 10-day intervals to assess follicular development and measure circulating levels of reproductive hormones (estradiol, progesterone, testosterone and dihydrotestosterone), as well as corticosterone. Immediately prior to the mate choice period (which lasts approximately 30 days) all adult-sized females had developing follicles. During the first week of male assessment approximately half of the females began to resorb their follicles. All of the females who did not resorb during this interval continued to grow their follicles throughout the remainder of the mating season. We will correlate follicular size and number with female condition and hormonal profiles to show how and when reproductive and non-reproductive females begin to diverge.