Sex controls
نویسنده
چکیده
There have been a number of recent reports suggesting that birds may be able to manipulate the sex ratio of their offspring in relation to a variety of social and environmental factors. But, from several of the studies of sex-ratio bias, it has been difficult to tell whether the observed ratio was the result of hormonal changes. To test this explicitly, two researchers from the University of Newcastle-upon-Tyne experimentally manipulated hormone levels to look at the effects on offspring sex. Thomas W. Pike and Marion Petrie manipulated circulating levels of testosterone, 17β β-oestradiol and corticosterone in breeding female Japanese quail using implants and looked for effects on the sex ratio of offspring they produced. Artificially elevating levels of corticosterone via implants caused females to produce significantly female-biased offspring sex ratios, while decreasing circulating corticosterone caused females to produce slightly more sons than controls, although this result was not significant. Corticosterone is commonly found to be raised in the plasma of birds in poor body condition, which is associated with sex-ratio biases in a variety of species. Concerns about sex-ratio biases in offspring have been raised by conservationists tending the critically endangered New Zealand kakapo parrot, Strigops habroptilus, comprising less than 100 individuals in the wild. Conservationists began a programme of supplementary feeding female parrots in 1989, in the hope of bolstering breeding success. But early results revealed the the sex ratio of offspring was biased towards males, a major problem in such a tiny breeding population. The female parrots achieve prime breeding condition when they achieve a weight of 1.5 kg ahead of the breeding season. So, instead of feeding all the birds, a team led by Bruce Robertson at Letters of the Royal Society (published online), decided to target only those birds that were not otherwise expected to reach this weight by the onset of the breeding season. Birds considered to be able to achieve this weight by themselves were given only the minimal supplementary feeding. The revised programme started in 2001, and the team have found that the previous male bias sex ratio of offspring in the extremely well-fed females, which was running at 70 per cent, was reduced to a more equal value under the modified feeding regime. The team raised " all predicted-underweight female kakapo above the 1.5 kg breeding threshold, thereby potentially stimulating breeding ". The authors believe their modified feeding programme has helped achieved …
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عنوان ژورنال:
- Current Biology
دوره 16 شماره
صفحات -
تاریخ انتشار 2006