Assortative mating, sexual size dimorphism and sex determination in a seabird with plumage polymorphism

ABSTRACT

Intraspecific plumage polymorphism in seabirds is often attributed to advantages in foraging activities and escape from predators, but its role in sexual selection is not well understood. The Trindade petrel (Pterodroma arminjoniana) presents morphs varying from pale to whole dark, with no apparent sexual size dimorphism (SSD). We tested assortative mating in Trindade petrels based on plumage colours and body size. In addition, genders of Trindade petrels were identified molecularly aiming to test SSD based on morphometrics, which was also used to generate a discriminant function for sex assignment. Within-pair consistency in plumage colour (i.e. birds paired with mates of the same morph) was detected in 9 out of 10 pairs, but not in morphometric traits. Minimum bill depth and bill depth at unguis were traits significantly larger in males. The best model was adjusted with Bill depth at unguis, wing chord and body mass, with global discriminatory power of 78.4%. Our results suggest that plumage colours may be sexually selected in Trindade petrels, which brings evolutionary implications on the persistence of plumage polymorphism. Discriminatory power of the best discriminant function was similar to those found in other Procellariiformes and also among datasets obtained by distinct researchers, demonstrating its robustness.

KEYWORDS:

• Discriminant function
• gadfly petrel
• morphometrics
• Pterodroma arminjoniana
• researcher bias
• sexual selection

SUBJECT EDITOR:

• Audrey Geffen

Acknowledgements

We are grateful to Brazilian Navy and Comissão Interministerial para os Recursos do Mar (CIRM/SECIRM) for logistic support during sampling expeditions. Ecomega Research Group for contributing to the logistics and funding for this study through grants (CNPq and Projeto Talude). We also thank André Guaraldo, Carlos Zavalaga, Eduardo R. Secchi, Luciano Dalla Rosa, Manuel Haimovici and two anonymous reviewers, for the revision and comments on the manuscript, and Ruth M. Brown for sexing some petrels. This research is part of the PhD thesis written by G.R.L. under the guidance of L.B.

Disclosure statement

No potential conflict of interest was reported by the authors.

Ethical approval

This study was authorized under the license number 22697-5 (SISBIO – Sistema de Autorização e Informação em Biodiversidade).

ORCID

Leandro Bugoni http://orcid.org/0000-0003-0689-7026

Additional information

Funding

This study was supported by the Brazilian CNPQ - Conselho Nacional de Desenvolvimento Científico e Tecnológico (Grants 557152/2009-7 and 405555/2012-1). G.R. Leal received PhD Grant from the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES). L. Bugoni received a Research Fellowship from CNPq (PQ 310550/2015-7).