Wednesday, October 22, 2008

Poached Eggs & Embryo Death in Modern Dinosaurs

Temperature-dependent sex-biased embryo mortality in a bird. 2008. Y. Eiby et al. Proceedings of the Royal Society B 275: 2703-2706.

The idea that extreme temperature changes during the extinction event at the end of the Cretaceous played a role in the demise of the non-avian dinos has been mentioned a number of times over the past 20 years. Here’s some experimental evidence for the effect of temperature on the incubation of eggs from living birds.
Abstract: Sex ratios have important evolutionary consequences and are often biased by environmental factors. The effect of developmental temperature on offspring sex ratios has been widely documented across a diverse range of taxa but has rarely been investigated in birds and mammals. However, recent field observations and artificial incubation experiments have demonstrated that the hatching sex ratio of a megapode, the Australian brush-turkey (Alectura lathami), varied with incubation temperature; more females hatched at high incubation temperatures and more males hatched at low temperatures.

Here, we investigated the causes of this temperature-dependent sex-biasing system. Molecular sexing of chicks and embryos confirmed that male embryo mortality was greater at high temperatures while female embryo mortality is greater at low temperatures, with mortality in both sexes similar at intermediate incubation temperatures. Temperature-dependent sex-biased embryo mortality represents a novel mechanism of altering sex ratios in birds. This novel mechanism, coupled with the unique breeding biology of the brush-turkey, offers a potentially unparalleled opportunity in which to investigate sex allocation theory in birds.