American Society of Naturalists

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“Helping relatives survive and reproduce: inclusive fitness and reproductive value in brood parasitism”

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Malte Andersson

Some females lay eggs in nests of other females of same species, and can gain fitness if the parasite is a relative

Brood parasitism by a relative can benefit the host

Comon eider, incubating female and a pair, Svalbard.<br />(Credit: Malte Andersson)
Comon eider, incubating female and a pair, Svalbard.
(Credit: Malte Andersson)

In many egg-laying animals, parasitic females increase their reproduction by laying eggs in nests of other females, to the disadvantage of the host. But if the females are related, parasitism can be genetically advantageous also for the host.

In conspecific brood parasitism some females lay eggs parasitically in nests of other females of the same species, ‘hosts’ that alone take care of the joint brood. Being parasitized usually impairs the reproduction of the host. But mathematical models suggest that a host can gain a genetic advantage if parasitized by a relative whose reproduction or survival is thereby increased, as suggested by Hamilton’s rule.

Incubating eider female, Svalbard.<br />(Credit: Malte Andersson)
Incubating eider female, Svalbard.
(Credit: Malte Andersson)

These predictions are explored in waterfowl, which differ from other birds in that host and parasite females are often related. Estimates based on life history data from common eiders and other ducks suggest that hosts can increase their genetic success (inclusive fitness) if parasitized by a close relative. The largest gains can be achieved through increased parasite reproduction, but gain is also possible through higher survival of parasites that avoid increased predation and other risks of nesting. Being parasitized can be particularly favorable for females with small own clutches, hosting eggs from young related parasites with high reproductive value. The research, from the University of Gothenburg, suggests that being ‘parasitized’ in waterfowl is sometimes neutral or even advantageous owing to genetic benefits to host as well as parasite, contributing to evolution of frequent brood parasitism in these birds. Read the Article