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Identifying Targets of Selection: A Multivariate Analysis of Reproductive Traits in the Great Tit

1997; Wiley; Volume: 78; Issue: 3 Linguagem: Inglês

10.2307/3545622

1600-0706

Peeter Hõrak, Raivo Mänd, I. Ots, Peeter Hõrak, Raivo Mänd,

Bird parasitology and diseases

In order to identify the true targets of phenotypic selection, we carried out a multivariate analysis on three reproductive traits in an urban population of great tits in Tartu, south-east Estonia, using data collected during 1987-1994. Individuals laying large eggs consistently recruited more offspring into the breeding population, independent of the simultaneous effects of clutch size and laying date. However, the mean egg size of a clutch was not related to the occurrence of embryonal or nestling mortality, which points to the possibility that the relationship between egg size and recruitment rate was due to the effects of female quality. Early breeders tended to recruit more offspring into the breeding population, but the effect of laying date disappeared when egg size was incorporated into the model. This fact indicates that the primary target of selection was not laying date per se but some property of the female affecting both laying date and egg size. Selection on clutch size fluctuated in direction between years. Selection against large clutches operated above all on individuals with small eggs, suggesting that the fitness consequences of similar reproductive decisions are different for individuals of different quality.