Modelling exposure to selected temperature during pregnancy: the limitations of squamate viviparity in a cool-climate environment

Abstract

Behavioural thermoregulation is important for the success of cool-climate lizards, and a basis of the cold-climate hypothesis for the evolution of viviparity in squamate reptiles. The temperature (Tsel) selected by pregnant females in a thermal gradient is considered to be optimal for embryonic development; however, exposure to Tsel throughout pregnancy has been difficult to estimate in small-bodied lizards as temperature-sensitive telemetry is impractical. In addition, the value of maternal thermophily during pregnancy is controversial: some studies have shown elevated Tsel, whereas others have found lowered Tsel or no change during pregnancy. We estimated indirectly the overall exposure to Tsel during the 4–5 months of pregnancy of the cool-climate, sub-alpine species Oligosoma maccanni (McCann's skink, 3–6 g) from southern New Zealand. The thermal environment available to skinks was modelled using temperature loggers inside validated copper models in basking and retreat sites. Pregnant skinks were able to achieve mean Tsel (28.9 °C) in the field very infrequently (4–15% of each month during the final 4 months of pregnancy). In field thermoregulatory studies, pregnant females did not bask more frequently and did not show altered field body temperature compared with non-pregnant adults, suggesting that all skinks (whether pregnant or not) thermoregulate maximally whenever conditions allow. Further research on cool-climate lizards should address the significance for offspring phenotypes of low and variable exposure to Tsel during pregnancy, as well as the significance of temperatures for embryos in maternal bodies (viviparity) versus nest sites (oviparity) arising from differences in maternal body size. © 2009 The Linnean Society of London, Biological Journal of the Linnean Society, 2009, 96, 541–552.