A comparative study of the structural and mechanical properties of avian eggshells among hosts of obligate brood parasitic cowbirds (genus Molothrus )

LÓPEZ, ANALÍA V; REBOREDA, JUAN C; FIORINI, VANINA D; GERSCHENSON, LÍA N; HAUBER, MARK E

BIOLOGICAL JOURNAL OF THE LINNEAN SOCIETY

WILEY-BLACKWELL PUBLISHING, INC

Lugar: Londres; Año: 2021 vol. 133 p. 1057 - 1076

0024-4066

Obligate avian brood parasites depend on hosts for parental care, which in turn suffer fitness losses as a result ofparasitism. Mechanisms by which brood parasitic cowbirds (Molothrus spp.) reduce host breeding success include thepuncture (M. rufoaxillaris and M. bonariensis) or removal (M. ater) of the eggs of the host. Our working hypothesisis that the host eggs? mechanical strength and their size and shape in species with higher frequency of parasitismcovaries with the cowbird?s strategy to reduce host clutch size. Our results, obtained through phylogenetic analysesbased on egg 2D geometric morphometry and eggshell mechanical and ultrastructural measurements, suggest thategg-puncturer behaviour has led to an increase in the strength of the host?s eggshell, which might make them moredifficult to be pierced. We also characterized larger, more rounded and asymmetrical eggs in frequent hosts of M. ater,which might be more difficult to be removed. These interspecific host egg and shell traits were also positively affectedby the frequency of parasitism, indicating that species-specific patterns of parasitic costs select for respective antiparasiticdefences in hosts.