The intensity of sexual selection, body size and reproductive success in a mating system with male-male combat: Is bigger better?

Body size is a key selected trait in many animal systems: larger size is
sexually selected for in males because it confers a reproductive advantage
during contest competition for access to females, and larger females are
naturally selected for fecundity. Herein, we used radio-telemetry to
gather a large dataset of male-female interactions and DNA paternity
analyses to characterize the intensity of sexual selection and the link
between two body size metrics (body length and condition, the latter
manipulated experimentally for males) and reproductive success in a
population of puff adders (Bitis arietans). Our multiple estimates of the
intensity of sexual selection generally indicated that males experienced
stronger sexual selection than females. However, the Bateman gradients did
not differ by sex, despite the fact that males increased reproductive
success by mating with multiple females while females did not. We also
found no strong evidence that females experienced indirect fitness
benefits through multiple matings. Body size was not a key predictor of
male reproductive success, and for females, body condition—but not body
length—was the critical fecundity trait. Altogether, a combination of
factors suggests that post–copulatory mechanisms of sexual selection
(e.g., sperm competition, cryptic female choice) may play critical roles
in this mating system and perhaps that of other snakes. We interpret our
findings in the context of sexual conflict—a ubiquitous and potent driver
of mating strategy evolution—to propose a scenario for the evolution of
female promiscuity that is applicable to many other animal systems where
males roam widely to locate females at high costs.