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Embryonic Mortality...
Embryonic Mortality and Sex Ratios in the Tree Sparrow
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- Svensson, Magnus, 1976- (author)
- Uppsala universitet,Institutionen för ekologi och evolution
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Ekman, Jan (thesis advisor)
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Höglund, Jacob (thesis advisor)
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- Arnold, Kathryn, Associate professor (opponent)
- Environmental and Evolutionary Biology, University of Glasgow, Glasgow
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(creator_code:org_t)
- ISBN 9155467652
- Uppsala : Acta Universitatis Upsaliensis, 2006
- English 42 s.
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Series: Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, 1651-6214 ; 258
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https://uu.diva-port... (primary) (Raw object)
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Abstract
Subject headings
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- Tree sparrows (Passer montanus) have been studied in two areas in Sweden since 1997. At both sites, tree sparrow eggs had remarkably low hatching success. On average only 60% of the eggs hatched. Analyses have shown that this was caused by embryonic mortality, which was highly sex biased. About 70 % of the dead embryos were males, while about 65 % of all fledged nestlings were females. Impaired hatching success here related to two factors. Hatching success was lower for pairs with a male in poor body condition, and it was lower in areas with a high local population density. A sex bias in the mortality early in life has been demonstrated in several species. Since the competitive ability of males is determined by conditions early in life, parents with poor provisioning capacity should prefer to produce female offspring in broods reared under poor conditions. The body condition of a tree sparrow during the nestling stage was well correlated to the condition as an adult, and pairs in which the male parent was in poor condition produced chicks in poor condition. Since the breeding success of a pair depended more on the condition of the male, females appear less affected by conditions early in life. Parents with poor provisioning capacity appear to bias offspring survival towards females, and a difference in the early susceptibility may be adaptive. Changes in birth sex ratios have in some cases been suspected to result from exposure to estrogenic environmental pollutants. This was examined by exposing great- and blue tit embryos to a synthetic estrogen. Although there was a difference in the mortality rate, the difference was present also in the control groups, why this could not be attributed to estrogen exposure.
Keyword
- Ecology
- Hatching success
- Embryonic mortality
- Sex ratio
- Density dependence
- Parasites
- Ekologi
- Passer montanus
Publication and Content Type
- vet (subject category)
- dok (subject category)
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