Simultaneous age-dependent and age-independent sexual selection in the lekking black grouse (Lyrurus tetrix)

Type Article
Date 2016-05
Language English
Author(s) Kervinen MattiORCID1, Lebigre Christophe2, Soulsbury Carl D.3
Affiliation(s) 1 : Univ Jyvaskyla, Dept Biol & Environm Sci, POB 35, FI-40014 Jyvaskyla, Finland.
2 : Earth & Life Inst, Pl Croix Sud 4,Carnoy Bldg, B-1348 Louvain La Neuve, Belgium.
3 : Lincoln Univ, Sch Life Sci, Joseph Banks Labs, Lincoln LN6 7TS, England.
Source Journal Of Animal Ecology (0021-8790) (Wiley-blackwell), 2016-05 , Vol. 85 , N. 3 , P. 715-725
DOI 10.1111/1365-2656.12496
WOS© Times Cited 19
Keyword(s) annual reproductive success, fitness, lek, long-term data, mating success, selection differential, selection gradient, senescence, Tetrao tetrix
Abstract Individuals' reproductive success is often strongly associated with their age, with typical patterns of early-life reproductive improvement and late-life senescence. These age-related patterns are due to the inherent trade-offs between life-history traits competing for a limited amount of resources available to the organisms. In males, such trade-offs are exacerbated by the resource requirements associated with the expression of costly sexual traits, leading to dynamic changes in trait expression throughout their life span. Due to the age dependency of male phenotypes, the relationship between the expression of male traits and mating success can also vary with male age. Hence, using longitudinal data in a lekking species with strong sexual selection - the black grouse Lyrurus tetrix - we quantified the effects of age, life span and age of first lek attendance (AFL) on male annual mating success (AMS) to separate the effects of within-individual improvement and senescence on AMS from selective (dis)appearance of certain phenotypes. Then, we used male AMS to quantify univariate and multivariate sexual selection gradients on male morphological and behavioural traits with and without accounting for age and age-related effects of other traits. Male AMS increased with age, and there was no significant reproductive senescence. Most males never copulated, and of the ones that did, the majority had only one successful year. Life span was unrelated to AMS, but early AFL tended to lead to higher AMS at ages 1-3. AMS was related to most morphological and behavioural traits when male age was ignored. Accounting for age and age-specific trait effects (i.e. the interaction between a trait and age) reduced the magnitude of the selection gradients and revealed that behavioural traits are under consistent sexual selection, while sexual selection on morphological traits is stronger in old males. Therefore, sexual selection in black grouse operates primarily on male behaviour and morphological traits may act as additional cues to supplement female choice. These results demonstrate the multifaceted influence of age on both fitness and sexual traits and highlight the importance of accounting for such effects when quantifying sexual selection.
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