Abstract
Common geckos, Hoplodactylus maculatus, inhabit a cool-temperate region and are nocturnal; some populations have pregnancies lasting up to 14 months. This thesis investigates the effects of pregnancy on thermoregulation and the effects of temperature on gestation length and offspring quality.
Selected body temperatures (Tsel) were compared between pregnant females, males and non-pregnant females from two different sites: a cool site with a biennial reproductive cycle (Macraes), and a warm site with annual reproduction (Alexandra). Tsel varied with time of day in all comparisons; however, the effect of reproductive condition on Tsel differed between sites and seasons. Pregnant females generally exhibited the highest Tsel and it appeared that stage of pregnancy affected the degree of elevation. Measurement of microhabitat temperatures revealed that both sites experienced extreme seasonal and daily variation in temperature, and geckos at the cool site rarely had opportunity to achieve Tsel (in contrast with geckos at the warm site). The elevation of Tsel with pregnancy is extreme in this species (up to 8°C at Macraes), suggesting that it is crucial to successful reproduction.
Field body temperature (Tb) was examined in relation to microhabitat temperature at the Macraes site; both spot Tb measurements and temperature-sensitive radio telemetry were used to measure differences between reproductive conditions. Both techniques indicated that common geckos often face low microhabitat temperatures and have low mean Tbs (that are affected by season and time of day); however, they (particularly pregnant females) will generally thermoregulate maximally to achieve the warmest temperatures available. Tsel ' spot Tb and microhabitat temperatures were combined mathematically to produce an index of thermoregulatory effectiveness; these indices confirmed that pregnant females devote the most effort to thermoregulation, particularly in late summer, during the last stages of embryogenesis.
The effect of temperature on duration and success of gestation was compared between Macraes and Alexandra by maintaining females ( collected just after ovulation) throughout their pregnancy under a warm or a cool laboratory temperature regime. Pregnancy was significantly lengthened by cool temperatures and success was markedly reduced under the cool temperature regime. Alexandra females were less successful than Macraes females in advancing embryogenesis under the cool regime. Failure of successful pregnancies under the cool regime occurred at temperatures recorded within Macraes microhabitat, indicating that precise thermoregulation is necessary for successful pregnancy. Comparisons made between Alexandra and Macraes juveniles from the warm regime revealed differences in life history traits including body size and growth rates. Adult females also differed in traits such as body size and relative clutch mass.
Although they remain in utero for another 8-9 months, embryos at Macraes are fully developed and viable before winter. The effect of prolonged gestation on offspring quality was examined in Macraes geckos, by comparing body size, lipid content and sprint speed between autumn-born and spring-born neonates. No clear differences in offspring quality were observed, with the exception of
depletion of residual yolk over winter. Proximate explanations for prolonged pregnancy were examined; females were responsive to AVT inducement of birth in both seasons and there were no obvious differences in environmental temperature that might inhibit parturition. Ultimate causes which relate to aspects of vitellogenesis and female reproductive output are also considered.