Delayed cost of reproduction and senescence in the willow tit Parus montanus

Abstract

Summary 1.We studied age-specific survival rates in the willow tit Parus montanus in northern Finland using 15 years of capture-recapture data obtained from birds during the breeding seasons 1986-2000. In addition, short-and long-term costs of reproduction were investigated by comparing survival probabilities of breeding and non-breeding individuals. 2. We did not find evidence supporting age-specific survival probabilities in males. However, in females there was a significant decline in survival after the age of 5 years. 3. Reproduction did not impair individuals' chances of being alive in the subsequent year (short-term cost) because breeding males and females had similar survival rates as non-breeders. 4. Demographic costs of breeding appeared later in life. Females skipping breeding earlier in life showed a higher probability of survival after the age of 5 years than females that bred every year until that age. This effect was non-significant in males. 5. The observed decline in survival probability late in life is likely to result from an increased cost of reproduction due to higher allocation of resources to breeding earlier in life, i.e. increased effort early in life is traded with survival late in life. The results also suggest that income breeders, such as small passerines, may pay long-term costs of reproduction. This is in agreement with the disposable soma theory of ageing.

Experimental evidence of a link between breeding conditions and the decision to breed or to help in a colonial cooperative bird

“…As a corollary of this, it has recently been shown that when faced with an artificial life-threatening risk during reproduction, individuals from species with high survival and low fecundity reacted by changing their behaviour to reduce risks to themselves, whereas individuals from low survival-high fecundity species would expose themselves to a higher risk to decrease the risk to their offspring (Ghalambor & Martin 2001;Martin 2002). Reducing the risks associated with breeding activity might be particularly important for young individuals for two reasons: they probably incur disproportionately high costs of breeding through reduced survival, as suggested in two recent studies (Tavecchia et al 2001;Orell & Belda 2002), and they may experience comparatively lower reproductive output (Green 2001;Magrath 2001). Thus, long-lived cooperative (or non-cooperative) species should be particularly reluctant to breed in suboptimal habitats or under suboptimal conditions, as indicated by several correlative studies (Emlen 1990;Koenig et al 1992;Komdeur et al 1995;Frederiksen & Bregnballe 2001;Ekman et al 2001).…”

Reproductive costs in terrestrial male vertebrates: insights from bird studies

“…It is noteworthy that in this review, we reported opposite results in terms of reproductive costs in two populations of the same species, the willow tit (Parus montanus). In one of them, survival costs of reproduction have been detected [31], but not in the other one [63]. Whether these two populations differ in their level of paternal care, polygyny or pace of life, and whether these differences are translated into different costs of reproduction, remain to be explored.…”

Early-late life trade-offs and the evolution of ageing in the wild

“…However, contrasting patterns can sometimes emerge when senescence is investigated jointly in males and females. For instance, in willow tits (Parus montanus), early reproduction and survival in late life are independent in males, whereas females that do not breed during early life survive better in late life [18]. Overall, this emphasizes the need to test evolutionary theories of ageing in both sexes to identify the nature of the reproductive costs that influence performance in late life, and then the evolution of sex-differences in ageing patterns (see §4b for a specific discussion on this topic).…”