Daniel Pincheira-Donoso | bioRxiv Science

bioRxiv2015

Fecundity selection theory: concepts and evidence

Fitness results from the optimal balance between survival, mating success and fecundity. The interactions between these three components of fitness vary importantly depending on the selective context, from positive covariation between them, to antagonistic pleiotropic relationships when fitness increases in one reduce fitness of others. Therefore, elucidating the routes through which selection shapes life history and phenotypic adaptations via these fitness components is of primary significance to understand ecological and evolutionary dynamics. However, while the fitness components mediated by natural (survival) and sexual (mating success) selection have extensively been debated from most possible perspectives, fecundity selection remains considerably less studied. Here, we review the theory, evidence and implications of fecundity selection as a driver of sex-specific adaptive evolution. Based on accumulating literature on the life-history, phenotypic and ecological aspects of fecundity, we (i) suggest that fecundity is restricted to refer to brood size per reproductive episode, while annual and lifetime fecundity should not be used interchangeably with fecundity as they represent different life history parameters; (ii) provide a generalized redefinition of fecundity selection that encompasses any traits that influence fecundity in any direction (from high to low) and in either sex; (iii) review the (macro)ecological basis of fecundity selection (e.g., ecological pressures that influence predictable spatial variation in fecundity); (iv) suggest that most ecological theories of fecundity selection should be tested in organisms other than birds; (v) argue that the longstanding fecundity selection hypothesis of female-biased sexual size dimorphism (SSD) has gained inconsistent support, that strong fecundity selection does not necessarily drive female-biased SSD, and that this form of SSD can be driven by other selective pressures; and (vi) discuss cases in which fecundity selection operates on males.

Evolutionary Biology↗

bioRxiv2014

A quantitative analysis of objective feather colour assessment: measurements in the lab are more reliable than in the field

The evolution of animal colouration is importantly driven by sexual selection operating on traits used to transmit information to rivals and potential mates, which therefore, have major impacts on fitness. Reflectance spectrometry has become a standard colour-measuring tool, especially after the discovery of tetrachromacy in birds and their ability to detect UV. Birds plumage patterns may be invisible to humans, necessitating a reliable and objective way of assessing colouration not dependent on human vision. Plumage colouration measurements can be taken directly on live birds in the field or in the lab (e.g. on collected feathers). Therefore, it is essential to determine which sampling method yields more repeatable and reliable measures, and which of the available quantitative approaches best assess the repeatability of these measures. Using a spectrophotometer, we measured melanin-based colouration in barn swallows (Hirundo rustica) plumage. We assessed the repeatability of measures obtained with both traditional sampling methods separately to quantitatively determine their reliability. We used the ANOVA-based method for calculating the repeatability of measurements from two years separately, and the GLMM-based method to calculate overall adjusted repeatabilities for both years. We repeated the assessment for the whole reflectance spectrum range and only the human-visible part, to assess the influence of the UV component on the reliabilities of sampling methodologies. Our results reveal very high repeatability for lab measurements and a lower, still moderate to high repeatability, for field measurements. Both increased when limited to only the human-visible part, for all plumage patches except the throat, where we observed the opposite trend. Repeatability between sampling methods was quite low including the whole spectrum, but moderate including only the human-visible part. Our results suggest higher reliability for measurements in the lab and higher power and accuracy of the GLMM-based method. They also suggest UV reflectance differences amongst different plumage patches.

Animal Behavior and Cognition↗