However, meta-analyses find weak support, if any, for the Trivers-Willard hypothesis ( Ewen, Cassey & Moller, 2004 Cassey, Ewen & Moller, 2006 Booksmythe et al., 2017).įemale birds are often used as a model for testing primary sex ratio manipulation. There is evidence that the offspring sex ratio in birds can vary adaptively according to maternal condition, mate quality, mate competition, resource availability, seasonal effects, hatching order, clutch size, parental compatibility and parental age ( Ewen, Cassey & Moller, 2004 Booksmythe et al., 2017), and references therein). This sex bias could also be enhanced by male sexually-selected traits: the attractive ornaments of males are signals of their high quality, so females should produce sons with these high-quality fathers but daughters from low-quality fathers ( Burley, 1981). Hence, a mother in better condition should invest more in sons but if the mother is in poor condition, daughters ought to be preferred ( Myers, 1978 Cockburn, Legge & Double, 2002 Merkling et al., 2015). This is because the maternal condition more profoundly affects sons which, raised in good conditions, will have a superior breeding success than females raised in the same conditions ( Trivers & Willard, 1973). But according to another model, the Trivers-Willard hypothesis ( Trivers & Willard, 1973 Ewen, Cassey & Moller, 2004 Cassey, Ewen & Moller, 2006 Booksmythe et al., 2017), selection under different maternal conditions should promote deviations from the equal offspring sex ratio. We consider that in our Blackbird population, parental age could make a more significant contribution to shaping offspring sex and reproductive success.įisher’s theory states that natural selection should promote investment in equal sex ratios of offspring: any deviation from equality should not be selected because of negative frequency-dependent selection (simple deviation from equality cancels out in a population, so the best strategy is to produce offspring with an equal sex ratio) ( Fisher, 1930). We found that neither offspring hatching sequence nor hatching date or clutch sequence were significant for sex determination.
Older females mated with younger males produced more daughters, which could have been due to the lesser attractiveness of the males and the mothers’ poorer condition caused by accelerated senescence. Accordingly, the sons’ breeding success increased with the father’s age, but this relationship was close to non-linear, which may indicate that the transgenerational effect of paternal senescence could negatively affect progeny fitness despite the high-quality of older fathers. We found that the overall sex ratio did not differ statistically from 50:50, but that younger females bonded with older mates did tend to produce more sons, probably because of the greater fitness of male descendants. During the breeding season we inspected the study area to locate the pairs’ territories and to track their nests and clutches. Data on the offspring sex and fitness were collected in five years, 2005–20–2017. The study was conducted in the city-centre Stefan Żeromski Park in Szczecin, NW Poland, where the local population of Blackbirds has been studied since 1996. On the basis of long-term research, we first evaluated the possible influence of parental age difference and brood characteristics on offspring sex and fitness in multi-brooded Blackbirds Turdus merula. Many studies of birds have indicated that offspring sex ratios can vary with environmental and parental traits. The effects of parental age difference on the offspring sex and fitness of European blackbirds. Cite this article Cholewa M, Jankowiak Ł, Szenejko M, Dybus A, Śmietana P, Wysocki D. For attribution, the original author(s), title, publication source (PeerJ) and either DOI or URL of the article must be cited. Licence This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, reproduction and adaptation in any medium and for any purpose provided that it is properly attributed.
4 Department of Genetics, Faculty of Biotechnology and Animal Husbandry, West Pomeranian University of Technology, Szczecin, Poland DOI 10.7717/peerj.10858 Published Accepted Received Academic Editor Xavier Harrison Subject Areas Animal Behavior, Ecology, Molecular Biology, Zoology Keywords Transgenerational effect, Senescence, Trivers-Willard hypothesis, Male attractiveness, Parental age, Good genes hypothesis Copyright © 2021 Cholewa et al.
0 kommentar(er)
