The evolution of traits in hosts may be influenced by their parasites and vice versa and a coevolutionary arms race often develops between the two. As part of such an arms race, the common cuckoo mimics the eggs of its hosts to avoid egg rejection. Traits related to this arms race may also be influenced by climatic conditions, such as temperature, affecting, for example, food availability and, thus, female condition and egg size (therefore may reflect Bergmann’s rule or the resource rule). The potential interaction between coevolution and climate has rarely been studied. We investigated whether egg and body size of cuckoos and reed warblers from Britain and Denmark had undergone change between 1868 and 1956, and whether such changes were correlated with climatic factors. Cuckoo egg size decreased during the studied period while warbler egg size remained stable. Hence, cuckoo and warbler eggs have become more similar in size over time. Cuckoo egg volume decreased with increasing annual precipitation, but annual precipitation decreased over time. Warbler egg volume increased with spring temperatures (which could not reflect Bergmann’s rule, but may support the resource rule). Hence, it seems that the measured climatic indices did not affect cuckoo egg size but may in part affect warbler egg size. Therefore, the decrease in cuckoo egg size may be the result of the coevolutionary arms race. Body and egg sizes in the cuckoos were negatively correlated whereas warbler body and egg sizes were uncorrelated, suggesting that selection probably acted on egg size directly and not via selection on body size. Taken together, these findings may indicate that climate change, the coevolutionary arms race, or both, affected egg sizes. It is suggested that drawing conclusions regarding the arms race without taking into account other selective pressures (e.g., climate) may confound conclusions regarding parasite-host systems.
Bibliographical noteFunding Information:
Comments made by four anonymous referees significantly improved the manuscript. This research received support from the SYNTHESYS Project: http://www.synthesys.info , which was financed by the European Community Research Infrastructure Action under the FP7 “Capacities” Program. BGS was funded by the Research Council of Norway (218144). The research was further funded by a seed money grant from Oranim College awarded to Shai Markman. We thank Arnon Lotem and Tamar Dayan for valuable comments on an earlier version of this manuscript. We also thank Rainee Kaczorowski, Oliver Tallowin and Naomi Paz for going over the final version of this manuscript. We are grateful to the collection managers and curators at the Natural History museums: in Tring, UK—to Robert Prys-Jones, Mark Adams, and especially to Douglas Russell, the curator of the egg collection; in Copenhagen—to Jon Fjeldså, and Jan Bolding Kristensen, and in Berlin—to Sylke Frahnert and Pascal Eckhoff. We thank Oliver Tallowin and Uri Obolski for statistical advice.
© 2015, Springer International Publishing Switzerland.
- Body size
- Brood parasitism
- Climate change
- Egg size
ASJC Scopus subject areas
- Ecology, Evolution, Behavior and Systematics