The effect of size and autotomies on sexual competition between males of the mud crab Cyrtograpsus angulatus DANA

PEDRO DALEO; TOMÁS LUPPI; AGUSTINA MENDEZ CASARIEGO; CARLOS MAURICIO ESCAPA; PABLO RIBEIRO; PAOLA SILVA; OSCAR IRIBARNE

Coquimbo. Chile.

Congreso; The crustacean society mid-year meeting; 2007

Distribucin y efectos ecolgicos de la ostra introducida Crassostrea gigas en Bahia Anegada <!-- /* Style Definitions */ p.MsoNormal, li.MsoNormal, div.MsoNormal {mso-style-parent:""; margin:0cm; margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:12.0pt; font-family:"Times New Roman"; mso-fareast-font-family:"Times New Roman";} p.MsoBodyTextIndent, li.MsoBodyTextIndent, div.MsoBodyTextIndent {margin:0cm; margin-bottom:.0001pt; text-indent:42.55pt; line-height:200%; mso-pagination:widow-orphan; font-size:12.0pt; font-family:"Times New Roman"; mso-fareast-font-family:"Times New Roman"; mso-ansi-language:EN-US;} @page Section1 {size:612.0pt 792.0pt; margin:70.85pt 3.0cm 70.85pt 3.0cm; mso-header-margin:36.0pt; mso-footer-margin:36.0pt; mso-paper-source:0;} div.Section1 {page:Section1;} --> Size advantage in male-male competition over mates, combined with male preference over large females, is a common feature that can drive to size assortative mating and, eventually, sexual selection. In crabs, limb autotomies can affect assortative mating and opportunity for sexual selection by affecting size advantage in matting contests. In this work we evaluate the effect of size and autotomies in generating assortative mating in the mud crab Cyrtograpsus angulatus. Field observations of guarding pairs in 2 different populations show a positive correlation between carapace width of males and females in both populations. In one of the populations, incidence of autotomies was low and the variability in size of reproductive males was lower than the variability in size of randomly collected males (i.e., only larger males were successful in getting a female), whereas there was no differences in the other population (i.e., most male sizes were successful) where the incidence of autotomies was very high, indicating that the importance of size is higher when incidence of autotomies is low. In this context, experiments (in both populations) show that, in contests for a female, larger males outcompete smaller ones only when they were without autotomies. When males were with autotomies, wining or loosing against smaller males was at random. This may lead to a decrease in the importance of male size in populations with high incidence of autotomies, affecting assortative mating and opportunity for selection and, thus, affecting selective pressures.