Saturday, November 6, 2010

Cloud Cover, Basking, & Squamate Offspring

Basking turtles on logs, basking lizards on tree trunks, and basking snakes on the ground or at the water's edge are common sites. It is basking behavior that makes otherwise secretive reptiles most visible in their environments. While tropical species sometimes bask, temperate species do so more frequently because they are often in environments with daily changes in temperature that require them to raise their body temperatures for hunting, digesting food, finding mates and avoiding predators. Females of viviparous squamate reptiles also bask to regulate the temperature of their developing embryos. While the focus of climate change predictions is often on temperature, a warming climate also means increased humidity and increased cloud cover in some areas. In a forthcoming paper Kelly M. Hare and Alison Cree of the University of Otago, in New Zealand report on experimental manipulation of basking opportunities on gravid female McCann's Skinks (Oligosoma maccanni)and the impact basking time has on their offspring. Southern New Zealand, is predicted to undergo changes in mean annual air temperature over the next 100 years that are slightly below the average for global predictions, although predicted changes in cloud cover vary greatly. Cloud cover changes will alter basking opportunities at many locations, and the authors were interested in measuring the phenotypic consequences of  increased or reduced basking times experienced by the offspring of the viviparous, temperate skink. Female skinks were  housed in identical  containers, with a basking site and cool retreat site. Ambient room temperatures simulated a 1–2 °C increase in current mean day-time air temperatures as predicted under global warming scenarios, with 16-18 °C temperatures during the day and about 12 °C at night. When heat lamps were on, skinks could bask at their preferred temperature range or remain at room temperature They set-up three regimes for the lizards to bask. High basking females could bask  8 hours a day for 7 days a week,  mid-basking females could bask 5 days week–or 3.5 days week for a total of  56 or 40 hours (a regime similar to that used by females in the wild, low regime females could bask 28 hours per week.  The low regime group showed reduced success carrying embryos full term. After several late-stage abortions (nonviable offspring at near full-term/ development), the basking access of the remaining females was raised to 5 days week for the remainder of the pregnancy so that  viable offspring could be obtained for phenotypic study. They had 33 of the 51 females gave birth to 116 viable offspring. In addition, 15 stillbirths and nonviable embryos were obtained from eight of the 51 females. Measurements included: the sex, size, growth, survival, emergence behavior, morphotype, pigmentation, and locomotor performance of offspring up to 3 months of age. Most offspring characteristics were not influenced by the maternal basking regime. However, they found high cloud cover regimes lowered the success of pregnancy and female offspring grew more slowly, and were smaller. In McCann's Skinks, female offspring from the two warmer incubation regimes grew faster and attained significantly longer lengths than the other individuals. Like all lizards, female McCann Skinks must reach a minimum size before they are able to reproduce  and the increase in growth rate would potentially enable them to reproduce earlier and produce more offspring. Thus, changes in cloud cover have potentially long-term influences on population dynamics.

Hare, K. M. and A. Cree. 2010. Exploring the consequences of climate-induced changes in cloud cover on offspring of a cool-temperate viviparous lizard. Biological Journal of the Linnean Society. DOI: 10.1111/j.1095-8312.2010.01536.x

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