Laparoscopy, radiography, and blood analyses as techniques for identifying the reproductive condition of female tuatara

Abstract

Female tuatara (Sphenodon punctatus) nest on Stephens Island, New Zealand, in spring (October-December). Previous radiographic surveys in September-October have suggested that only about one-fourth or less of mature-sized females nest each year, but these studies have assumed that ovulation in all females nesting that year has occurred by September-October and that no females X-rayed in September-October carry unshelled, radio-transparent eggs. We used a combination of radiography and laparoscopy to test these inferences in September-October 1987. We X-rayed 173 tuatara that we assumed to be female and performed laparoscopies on 29 of the tuatara identified by X-raying as non-gravid (i.e., not carrying oviducal eggs). The results indicate that about 5.3% of radiographed tuatara were small males misidentified as females. Of the females, about 22.2% were in early vitellogenesis, 22.2% were in mid-vitellogenesis, 25.0% were in late vitellogenesis, 25.0% were gravid, and 5.6% were non-gravid females with atretic but no vitellogenic follicles. No females examined in September-October were in pre-ovulatory condition and none contained unshelled, radio-transparent eggs. Subsequent laparoscopic observations at other times revealed that females in pre-ovulatory condition are present in February-March, that ovulation occurs between March and April, and that shells are radio-opaque by July. We conclude that radiographic surveys of female tuatara in September-October reasonably estimate the proportion of females ovulating and nesting each year. Furthermore, we suggest that the reproductive cycle of female tuatara has an average length of about 4 yr, with vitellogenesis being spread over the first 3 yr and ovulation occurring in the fourth. Plasma concentrations of estradiol, progesterone, testosterone, calcium, and total protein, and the presence/absence of plasma vitellogenin were not useful indicators for distinguishing between gravid and non-gravid females in September-October.