Titre du document / Document title

Testicular volume and asymmetry are age-dependent in black-throated blue warblers (Dendroica caerulescens)

Auteur(s) / Author(s)

GRAVES Gary R. ;

Résumé / Abstract

Passerine birds are favored models for studies of sperm competition and extrapair paternity, yet the intraspecific chronology of testicular maturation and its empirical and theoretical consequences in avian mating systemshave been largely ignored. I analyzed age-dependent variation in testicular morphology in 25 breeding populations of the Black-throated Blue Warbler (Dendroica caerulescens) distributed throughout its geographic range in eastern North America. Yearlings (first breeding season) had significantly smaller testes than older males (≥2 years). Latitude, altitude, and Julian date had negligible effects on testicular morphology when effects of core body size were controlled. Preparator effects had significant influence on the estimation of testicular volume and asymmetry. Contrary to Møller's hypothesis that the smaller testis compensates for deficiencies in the larger, the volumes of the left and right testes were positively correlated in both yearlings and older males. Older males exhibited a higher degree of directional asymmetry because of the disproportionate enlargement of the left testis. These data suggest that testicular morphology and reproductive capacities of yearling passerines may not be equivalent to those of older males. In a broader context, these findings demonstrate that age class should be factored into quantitative models of sperm competition in birds.

Revue / Journal Title

The Auk    ISSN  0004-8038   CODEN AUKJAF 

Source / Source

2004, vol. 121, n^o2, pp. 473-485 [13 page(s) (article)]

Langue / Language

Anglais

Editeur / Publisher

Ornithological Societies North America, Lawrence, KS, ETATS-UNIS  (1884) (Revue)

Localisation / Location

INIST-CNRS, Cote INIST : 3366, 35400011360386.0190