2010년 11월 20일
Han et al 2010 BMC Evolutionary Biology
Size-assortative mating and sexual size dimorphism are predictable from simple mechanics of mate-grasping behavior
A major challenge in evolutionary biology is to understand the typically complex interactions between diverse counter-balancing factors of Darwinian selection for size-assortative mating and sexual size dimorphism. It appears that rarely a simple mechanism could provide a major explanation of these phenomena. Mechanics of behaviors can predict animal morphology, such like adaptations to locomotion in animals from various of taxa, but its potential to predict size-assortative mating and its evolutionary consequences has been less explored. Mate-grasping by males, using specialized adaptive morphologies of their forelegs, midlegs or even antennae wrapped around female body at specific locations, is a general mating strategy of many animals, but the contribution of the mechanics of this wide-spread behavior to the evolution of mating behavior and sexual size dimorphism has been largely ignored.
Here, we explore the consequences of a simple, and previously ignored, fact that in a grasping posture the position of the male's grasping appendages relative to the female's body is often a function of body size difference between the sexes. Using an approach taken from robot mechanics we model coercive grasping of females by water strider Gerris gracilicornis males during mating initiation struggles. We determine that the male optimal size (relative to the female size), which gives the males the highest grasping force, properly predicts the experimentally measured highest mating success. Through field sampling and simulation modeling of a natural population we determine that the simple mechanical model, which ignores most of the other hypothetical counter-balancing selection pressures on body size, is sufficient to account for size-assortative mating pattern as well as species-specific sexual dimorphism in body size of G. gracilicornis.
The results indicate how a simple and previously overlooked physical mechanism common in many taxa is sufficient to account for, or importantly contribute to, size-assortative mating and its consequences for the evolution of sexual size dimorphism.
Han CS, Jablonski PG, Kim B & Park FC. 2010. Size-assortative mating and sexual size dimorphism are predictable from simple kinematics of mate-grasping behavior. BMC Evolutionary Biology 10:359.
http://www.biomedcentral.com/1471-2148/10/359
Han_Jablonski_2010_BMCEvobio.pdf
# by | 2010/11/20 21:37 | PUBLICATIONS | 트랙백(1) | 덧글(4)
Despite recent advances in our understanding of sexual conflict and antagonistic coevolution between sexes, the role of interspecific interactions, such as predation, in these evolutionary processes remains unclear. In this paper, we present a new male mating strategy whereby a male water strider Gerris gracilicornis intimidates a female by directly attracting predators as long as she does not accept the male's coercive copulation attempt. We argue that this male strategy is a counteradaptation to the evolution of the female morphological shield protecting her genitalia from coercive intromission by water strider males. The G. gracilicornis mating system clearly represents an effect expected from models of the coevolutionary arms race between sexes, whereby one sex causes a decrease in the fitness component of the other sex. Moreover, our study demonstrates a crucial role that interspecific interactions such as predation can have in the antagonistic coevolution between sexes.
Water striders are a model system for the study of sexual size dimorphism, but the effect of body size on the dominance relationship between individuals has not been experimentally tested. In 34 staged contests between males of the water strider Aquarius paludum , we determined the effect of body size difference between contestants on the outcome of the aggressive interactions. In contests between a large and a small male, the larger individuals won the interactions significantly more often than expected by chance. This is the first experimental evidence for the importance of body size in pair-wise contests among water striders.
