Wing Muscle Dimorphism: Two Reproductive Pathways of the Waterstrider Gerris Thoracicus in Relation to Habitat Instability

Abstract

cles. In the laboratory when food was abundant, non-flyer females laid 60-100% more eggs than flyer females. When food was scarce, non-flyer females survived longer than flyer females. There were no differences in longevity between non-flyer males and flyer males. Even when starved some females and most males maintained flight muscles. The occurrence of the two morphs was related to habitat stability. Flyers were more common in temporary rock pools. Non-flyers were abundant in brackish sea bays, which are cool and stable habitats. In nature histolysis of flight muscles was more common among females than males. I conclude that G. thoracicus females have two different reproductive pathways in the Finnish archipelago. Flyers are able to lay their eggs in many places, to search for the best possible site each time, and to colonize newly filled vacant rock pools throughout the summer. Non-flyers have a high reproductive output when food is abundant, and they survive better when food is scarce. This tactic is advantageous in permanent sea habitats.