Crocker-1 - NEWS VIEWS NATURE|Vol 451|31 January 2008 with...

Info iconThis preview shows pages 1–2. Sign up to view the full content.

View Full Document Right Arrow Icon
with steroid hormone biosynthesis, in this instance the aromatase inhibitor fadrozole 8 . Eggs were incubated in the lab at one of three temperatures (low, intermediate, warm), and the hatchlings were released into outdoor enclosures (about 30 lizards in each of 6 enclo- sures). The lizards were allowed to grow up, mate and produce offspring in these enclosures over a period of 3.5 years. To measure fitness — reproductive success — Warner and Shine established parentage of each of the offspring by genotyping DNA microsatellites. All offspring born in the enclosures were unambiguously assigned to specific parents, thus bypassing any indirect measures of presumed mating success and fecundity. Lifetime reproductive success showed some surprises. For females, it was expected, first, that warmer incubation temperatures would lead to larger body size (because warmer tempera- tures lead to earlier hatching); and, second, that body size would correlate strongly with fecun- dity. Thus female fecundity should increase with incubation temperature. This compound expectation was only partly supported: female lifetime fitness was highest at the warmest tem- perature, but no appreciable fitness difference was found between the intermediate and low temperatures. For males, there was no obvious basis for prediction, but males from intermedi- ate temperatures had appreciably higher fitness than males from low and warm extremes. In all, the fitness measures matched the theory, but most of the fitness effects of temperature defied intuition. The study 1 provides directions for future work. The most important concerns the mechanistic bases by which incubation temperature affects male versus female fitness. There is accumulating evidence that incubation temperature in TSD liz- ards has a variety of behavioural, anatomical and physiological effects, including directly acting on brain development 9,10 . In addition, even though offspring are either male or female in terms of their gonads, hormone levels throughout life vary according to the individual’s incubation temperature, further contributing to a gradation of attributes that translate into fitness differences within a sex caused by incubation temperature. To the extent that such interactions exist, TSD may have evolved to be somewhat self-reinforc- ing, in essence providing the basis for much of its own benefit. It will thus be interesting to solve the mechanistic link between temperature and fitness, to augment the observations that Warner and Shine have at last provided to resolve the rid- dle of reptilian sex determination. There is also a wider picture to this line of research. It has been suggested that sex determi- nation by temperature or other environmental factors is ancestral to genotypic sex determina- tion, and that elements of TSD can be found in mammals 11 . Even in humans, conditions dur- ing gestation have lasting effects throughout life, with recent work indicating a connection with coronary disease, obesity, diabetes, cancer, cognitive dysfunction and infertility 12 .
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Image of page 2
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}

Page1 / 2

Crocker-1 - NEWS VIEWS NATURE|Vol 451|31 January 2008 with...

This preview shows document pages 1 - 2. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online