Scrutinizing assortative mating in birds

PLoS Biol. 2019 Feb 21;17(2):e3000156. doi: 10.1371/journal.pbio.3000156. eCollection 2019 Feb.

Abstract

It is often claimed that pair bonds preferentially form between individuals that resemble one another. Such assortative mating appears to be widespread throughout the animal kingdom. Yet it is unclear whether the apparent ubiquity of assortative mating arises primarily from mate choice ("like attracts like"), which can be constrained by same-sex competition for mates; from spatial or temporal separation; or from observer, reporting, publication, or search bias. Here, based on a conventional literature search, we find compelling meta-analytical evidence for size-assortative mating in birds (r = 0.178, 95% CI 0.142-0.215, 83 species, 35,591 pairs). However, our analyses reveal that this effect vanishes gradually with increased control of confounding factors. Specifically, the effect size decreased by 42% when we used previously unpublished data from nine long-term field studies, i.e., data free of reporting and publication bias (r = 0.103, 95% CI 0.074-0.132, eight species, 16,611 pairs). Moreover, in those data, assortative mating effectively disappeared when both partners were measured by independent observers or separately in space and time (mean r = 0.018, 95% CI -0.016-0.057). Likewise, we also found no evidence for assortative mating in a direct experimental test for mutual mate choice in captive populations of Zebra finches (r = -0.020, 95% CI -0.148-0.107, 1,414 pairs). These results highlight the importance of unpublished data in generating unbiased meta-analytical conclusions and suggest that the apparent ubiquity of assortative mating reported in the literature is overestimated and may not be driven by mate choice or mating competition for preferred mates.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Animals
  • Body Size*
  • Female
  • Finches / physiology*
  • Male
  • Mating Preference, Animal / physiology*
  • Observer Variation
  • Pair Bond
  • Phenotype
  • Sample Size

Associated data

  • Dryad/10.5061/dryad.7jd76kq

Grants and funding

This work was supported by the Max Planck Society (to BK) and the China Scholarship Council (CSC; stipend to DW). Work for the monitoring of Blue-footed boobies on Isla Isabel was supported by the Universidad Nacional Autónoma de México (PAPIIT, IN211491, IN-200702-3, IN206610-3, IN205313), the Consejo Nacional de Cienciay Tecnología (CONACYT, 81823, 47599, 34500-V, 4722-N9407, D112-903581, 31973H and 104313) and the National Geographic Society to Dr. Hugh Drummond. Work of Western bluebirds was supported by US National Science Foundation grants (DEB-0918095 and DEB-1350107 to RAD). Work of Pied flycatchers was supported by a VIDI-grant from the Netherlands Organisation for Scientific Research (NWO) to CB. Work of Tawny owls was supported by the Academy of Finland (project 314108) to PK. Work of Barn swallows was supported by the Czech Science Foundation project No. 15-11782S to TA. Work of Semipalmated sandpiper was supported by the EU Horizon 2020 Marie Curie individual fellowship (4231.1 SocialJetLag; to MB) and the Czech University of Life Sciences (CIGA 2018421; to MB). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.