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

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.