Asymmetrical costs of sexual conflict in the seaweed fly, Coelopa frigida

Abstract

1. Sexual conflict can play an important role in the evolution of animal life history characteristics, including lifespan. Seaweed flies show an increase in mortality rates when exposed to brown algae. The seaweed stimulates females to oviposit and males to mount females. Females typically respond to male mounts by performing a violent rejection response. 2. Here the contribution of sexual conflict to the increase in mortality seen in the presence of seaweed was determined. The survival of single and mixed sex pairs of flies was followed in the presence and absence of seaweed. 3. The two sexes showed differential survival rates, with females living longer in the absence of seaweed. The presence of seaweed reduced survival in both sexes. In the presence of seaweed, female survival was lower when paired with a male. Over 40% of the reduction in survival in females in the presence of seaweed appears to be attributable to sexual conflict. 4. The presence of a female did not significantly affect male survival. Thus the mortality cost of being in the presence of the opposite sex and seaweed appears highly asymmetric. 5. In the presence of seaweed, female survival was lower when females were paired with small males. Small males exhibit higher levels of harassment of females, thus it is argued that pre-copulatory sexual conflict is the probable cause of the increased mortality cost to females of being in the presence of both males and seaweed.