Field evidence challenges the often-presumed relationship between early male maturation and female-biased sexual size dimorphism

Authors

Marie Claire Chelini, University of California, MercedFollow
Eileen Hebets, University of Nebraska - LincolnFollow

ORCID IDs

Marie-Claire Chelini http://orcid.org/0000-0001-8375-2985

Date of this Version

10-2017

Citation

Ecology and Evolution. 2017;7:9592–9601.

DOI: 10.1002/ece3.3450

Comments

© 2017 The Authors. Ecology and Evolution published by John Wiley & Sons Ltd. This is an open access article under the terms of the Creative Commons Attribution License,

Abstract

Female-biased sexual size dimorphism (SSD) is often considered an epiphenomenon of selection for the increased mating opportunities provided by early male maturation (i.e., protandry). Empirical evidence of the adaptive significance of protandry remains nonetheless fairly scarce. We use field data collected throughout the reproductive season of an SSD crab spider, Mecaphesa celer, to test two hypotheses: Protandry provides fitness benefits to males, leading to female-biased SSD, or protandry is an indirect consequence of selection for small male size/large female size. Using field-collected data, we modeled the probability of mating success for females and males according to their timing of maturation. We found that males matured earlier than females and the proportion of virgin females decreased abruptly early in the season, but unexpectedly increased afterward. Timing of female maturation was not related to clutch size, but large females tended to have more offspring than small females. Timing of female and male maturation was inversely related to size at adulthood, as early-maturing individuals were larger than late-maturing ones, suggesting that both sexes exhibit some plasticity in their developmental trajectories. Such plasticity indicates that protandry could co-occur with any degree and direction of SSD. Our calculation of the probability of mating success along the season shows multiple male maturation time points with similar predicted mating success. This suggests that males follow multiple strategies with equal success, trading-off access to virgin females with intensity of male–male competition. Our results challenge classic hypotheses linking protandry and female-biased SSD, and emphasize the importance of directly testing the often-assumed relationships between co-occurring animal traits.