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Physiological costs and age constraints of a sexual ornament: an experimental study in a wild bird

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journal contribution
posted on 2021-03-01, 00:00 authored by Alexandra McQueenAlexandra McQueen, Kaspar Delhey, Beatrice Szecsenyi, Andrea Crino, Michael J Roast, Anne Peters
Sexual ornaments are often considered honest signals of quality because potential costs or constraints prevent their display by low-quality individuals. Testing for potential physiological costs of ornaments is difficult, as this requires experimentally forcing individuals to produce and display elaborate ornaments. We use this approach to test whether a sexually selected trait is physiologically costly to male superb fairy-wrens (Malurus cyaneus). Male fairy-wrens molt from brown to blue breeding plumage at different times of the year, and females strongly prefer the few males that are blue early, during winter. We used short-acting testosterone implants to stimulate males to produce “early-blue” plumage and assessed costs during and after molt using a panel of physiological indices. Testosterone-implanted, T-males molted in winter and produced blue plumage 6 weeks before control-implanted, C-males. T-males molted while in lower body condition, tended to have lower fat reserves, and were more likely to be parasitized by lice. However, we detected no negative effects on immune function, blood parasites, exposure to stressors, or survival. Juvenile males never naturally display early-blue plumage, but we found no evidence for increased costs paid by juvenile T-males. Instead, juvenile T-males molted later than adult T-males, suggesting that age presents an absolute constraint on ornament exaggeration that cannot be fully overcome by testosterone treatment. Together, these small costs and large, age-related constraints may enforce signal honesty, and explain female preference for early-blue males.

History

Journal

Behavioral ecology

Volume

32

Issue

2

Season

Mar/Apr

Pagination

327 - 338

Publisher

Oxford University Press

Location

Oxford, Eng.

ISSN

1045-2249

eISSN

1465-7279

Language

English

Publication classification

C1 Refereed article in a scholarly journal