American Society of Naturalists

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“The evolution of clutch size in hosts of avian brood parasites”

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Iliana Medina, Naomi E. Langmore, Robert Lanfear, and Hanna Kokko

Avian brood parasites, like cuckoos, could be selecting for larger clutches in their hosts

Coping with brood parasites: Changes in clutch size?

Clutch of white-plumed honeyeater (<i>Lichenostomus penicillatus</i>) parasitized by a pallid cuckoo (<i>Cuculus pallidus</i>).<br />(Credit: Naomi Langmore)
Clutch of white-plumed honeyeater (Lichenostomus penicillatus) parasitized by a pallid cuckoo (Cuculus pallidus).
(Credit: Naomi Langmore)

Clutch size is a very important and variable trait in birds. Some birds, such as albatrosses and petrels, lay only one egg per breeding season, while pheasants usually lay around ten. Researchers have found that latitude and nest type are important predictors of avian clutch size, and species at higher latitudes and with cavity nests have larger clutches. In a recent article, Medina et al. explore whether the interaction between brood parasites and hosts could also affect the evolution of clutch size.

Superb fairy-wren male (<i>Malurus cyanus</i>). This species is the main host of the Horsfield’s bronze-cuckoo (<i>Chalcites basalis</i>) in Australia.<br />(Credit: Naomi Langmore)
Superb fairy-wren male (Malurus cyanus). This species is the main host of the Horsfield’s bronze-cuckoo (Chalcites basalis) in Australia.
(Credit: Naomi Langmore)

Avian brood parasites lay their eggs in the nests of other species, their hosts. There are ~100 species of brood parasites and more than 500 species of hosts. The most famous brood parasites are cuckoos, and cuckoo chicks evict all the other host eggs from the nest, being left to receive all the parental care of their foster parents. By using a mathematical model, Medina et al. found that selection can potentially favor the evolution of larger clutches, in hosts of brood parasites. This result was further complemented by current information on clutch size in over 800 species, which revealed that species that suffer larger costs from parasitism (e.g. smaller species exploited by large cuckoos) tend to have larger clutches.

These results suggest that brood parasitism could be an important force in driving the evolution of clutch size in species that are hosts of brood parasites. This interesting possibility should be further explored with field and experimental data in different species. Read the Article