Gene flow in the Daphnia longispina hybrid complex (Crustacea, Cladocera) inhabiting large lakes

Abstract

The significance of short-term exchange between populations relative to long-term local selection was evaluated in the Daphnia longispina hybrid complex. In a hierarchical analysis, the genetic structure of D. cucullata, D. hyalina and their interspecific hybrid c x h was studied by allozyme electrophoresis. Two data sets based on the variation at three and nine loci revealed high genetic variation in all populations. Significant genetic differentiation, FST, was found between lakes that are less than 14 km apart. FST between subpopulations was around 0.2 for D. hyalina and D. cucullata averaged over three and nine loci. Selection on hybrid genomes may explain why, in c x h hybrids, only 10 per cent of the total genetic variation found was attributable to differences between populations. FST and genetic distances, Dnej,were compared between pairs of populations from different hierarchical levels. In both data sets, differences were highest between species. Between parent species and hybrids, they were intermediate, and they were lowest within species. A regression of log Nm against log distance was used to test for isolation by distance. Mantel tests showed a highly significant decrease in Nm with distance for populations of D. hyalina in both data sets. A negative trend was also found for populations of D. cucullata and c x h. Thus, in contrast to littoral cladoceran species, the pattern of geographical variation between populations of pelagic species seems to be more strongly influenced by gene flow.

The interplay between colonization history and gene flow in passively dispersing zooplankton: microsatellite analysis of rotifer resting egg banks

“…Clear patterns of isolation by distance are rare in zooplanktonic organisms (Lynch & Spitze, 1994). The strongest patterns have been found for zooplankters inhabiting large lakes, but the F st involved were low (Gießler, 1997; Naihong et al ., 2000). However, weaker or no patterns of isolation by distance have been found in pond D. pulex (Innes, 1991; Pálsson, 2000).…”

Morphological evolution and genetic differentiation in Daphnia species complexes

“…In most of the lakes two or more species coexist that are known to hybridize (cf. Woltereck, 1919; Baumbach, 1922; Aurich, 1933; Gessner, 1953; Jacobs, 1977; Seitz, 1980; Müller, 1993; Gießler, 1997b), and thus our samples are supposed to include a large number of hybrids. One hundred and fifty‐eight laboratory clones were established and raised under standardized conditions (19 °C; 16 : 8 h light/dark; well‐fed with the green alga Ankistrodesmus gracilis ) in a common environment.…”

“…Here, we present morphological and genetic data on species and interspecific hybrids from one of the most diverse Daphnia groups in Europe, the Daphnia longispina group. This group comprises several species complexes known to form hybrids across large geographical areas ( Wolf & Mort, 1986; Gießler, 1987; Hebert et al ., 1989 ; 1993b; Taylor & Hebert, 1993a; Schwenk & Spaak, 1995, 1997a) and isolation by distance was detected in some parental species and hybrids ( Gießler, 1997b). Most data exist for the traditional species D. cucullata , D. galeata and D. hyalina which are common in large lakes, whereas little is known from D. longispina and D. rosea which are mainly restricted to pond habitats ( Brooks, 1957; Flößner, 1972).…”