Harvesting changes mating behaviour in European lobster.

Tonje K Sørdalen,Kim T Halvorsen,Hugo B Harrison,Esben M Olsen,Charlie D Ellis,Halvor Knutsen,Leif Asbjørn Vøllestad,Even Moland

doi:10.1111/eva.12611

Abstract

Removing individuals from a wild population can affect the availability of prospective mates and the outcome of competitive interactions, with subsequent effects on mating patterns and sexual selection. Consequently, the rate of harvest‐induced evolution is predicted to be strongly dependent on the strength and dynamics of sexual selection, yet there is limited empirical knowledge on the interplay between selective harvesting and the mating systems of exploited species. In this study, we used genetic parentage assignment to compare mating patterns of the highly valued and overexploited European lobster (Homarus gammarus) in a designated lobster reserve and nearby fished area in southern Norway. In the area open to fishing, the fishery is regulated by a closed season, a minimum legal size and a ban on the harvest of egg‐bearing females. Due to the differences in size and sex‐specific fishing mortality between the two areas, males and females are of approximately equal average size in the fished area, whereas males tend to be larger in the reserve. Our results show that females would mate with males larger than their own body size, but the relative size difference was significantly larger in the reserve. Sexual selection acted positively on both body size and claw size in males in the reserve, while it was nonsignificant in fished areas. This strongly suggests that size truncation of males by fishing reduces the variability of traits that sexual selection acts upon. If fisheries continue to target large individuals (particularly males) with higher relative reproductive success, the weakening of sexual selection will likely accelerate fisheries‐induced evolution towards smaller body size.

Highlights

Humans depend on healthy ecosystems for valuable goods and services, but human activities are considered to be one of the strongest selective forces in nature (Palumbi, 2001)
We investigated the mating system of the exploited European lobster in its natural environment inside and outside a coastal marine reserve to establish whether harvesting can affect mating patterns and sexual selection
Our genetic parentage assignment clearly demonstrates a positive size-assortative mating pattern, where females have a strong disposition to mate with comparatively larger males

Summary

| INTRODUCTION

Humans depend on healthy ecosystems for valuable goods and services, but human activities are considered to be one of the strongest selective forces in nature (Palumbi, 2001). The potential contribution of male phenotype to populations’ reproductive success, and factors underlying variation in the intensity of sexual selection on male traits, remains largely ignored (Uusi-Heikkilä et al, 2015). This paucity of research is surprising for several reasons. Hutchings and Rowe’s (2008) modelling work on the Atlantic cod (Gadus morhua) showed that if reproductive success increases with body size and harvesting decreases its mean and variation, the overall strength of selection for smaller body size is stronger than expected by fishing alone. We argue that fisheries targeting large males with high reproductive success can lead

| MATERIALS AND METHODS

| DISCUSSION

Findings

CONFLICT OF INTEREST