Reproductive Correlates of Abdominal Fat Body Mass in Niveoscincus occellatus, a Skink with an Asynchronous Reproductive Cycle
Wapstra, E and Swain, R, Reproductive Correlates of Abdominal Fat Body Mass in Niveoscincus occellatus, a Skink with an Asynchronous Reproductive Cycle, Journal of Herpetology, 35, (3) pp. 403-409. ISSN 0022-1511 (2001) [Refereed Article]
The relationship between the annual cycle of energy storage, in the form of abdominal fat bodies, and reproduction was studied in lowland and subalpine populations of the viviparous skink, Niveoscincus ocellatus. This species displays an unusual asynchronous reproductive pattern in which male and female preparations for reproduction are separated temporally, thereby providing an opportunity to clarify our understanding about the energy demands of squamate reproduction. Abdominal fat bodies in both sexes showed distinct annual cycles that were positively correlated with resource availability, peaking in summer. In males, fat body mass was correlated positively with testes development and negatively with plasma testosterone concentrations and mating behavior. This is in contrast to the pattern observed in species with synchronous breeding cycles, where there is generally a negative relationship between testis size and lipid storage. We concluded that N. ocellatus is able to produce spermatozoa and develop abdominal fat reserves concurrently, and therefore testis size is unlikely to be constrained by energetic costs. In contrast, mating behavior appears to rely on stored energy, even though this results in reduced fat reserves for winter hibernation. Female fat bodies were smallest in midspring, coinciding with the end of vitellogenesis and early pregnancy. Vitellogenesis and early pregnancy appear to be energetically expensive and are reliant on stored energy in this species. Large fat bodies at the end of pregnancy in both populations are surprising given the reported high costs of reproduction. Two factors may contribute to this: resource availability may be greater in late summer, and the energetic costs associated with pregnancy appear to be highest in the early to midstages of gestation.