Dispersal and life-history differences between waterstrider (Aquarius najas) populations

Abstract

The main objective of this thesis was to study dispersal, colonization success and life-history differences among different waterstrider Aquarius najas populations. Life-history studies were carried out in an artificial stream system, and studies on dispersal and colonization success were performed in field. Genetic variation and gene flow within and between different watersheds were studied using RAPD markers. Field studies indicated dispersal differences between populations. Dispersal distances of common garden reared waterstriders were dependent on the size of the habitat patches and the size of dispersal barriers between patches. Individuals that originated from small and isolated patches dispersed less than those originated from long and connected streams. Among laboratory reared waterstriders several winged individuals appeared. The relative frequency of winged individuals was highest in the southern as compared to northern populations. Overwintering survival under laboratory conditions was higher among the wingless individuals. Thus, the survival cost may explain why the proportion of winged individuals was lower in the northern populations. Data from the colonization experiment indicates that genetic variation together with the founder population size is important for the colonization success. Populations founded by large propagule sizes and by individuals of different origins had the highest colonization success. This is a central result for conservation biology as it indicates the value of intraspecific variation for the colonization success. According to the RAPD data, occasional gene flow between streams seems to exist, but mainly to downstream direction within a watershed. Results from life-history studies indicate that waterstriders of different origins have only slightly differing life-histories. The slightness of observed latitudinal differences makes sense, since life-history traits need to be plastic due to temporally varying conditions.