The contribution of differential hatching success to the fitness of species and interspecific hybrids

Abstract

Resting egg banks of microcrustaceans have been used to reconstruct the evolutionary and ecological history of species. However, recent studies provided evidence for a discrepancy between dormant propagules in the sediment and the planktonic population. This pattern raises two questions: First, what is the value of data on resting egg banks for population dynamics over time and second, which component of the reproductive cycle causes the observed inconsistency? In our study we focussed on the second question by comparing the taxon composition of a resting egg bank with the reproductive success of ex-ephippial hatchlings. Species and interspecific hybrid identification of dormant and hatched stages was achieved through the application of restriction fragment length polymorphism analysis of an internal transcribed spacer region. We found no significant deviation between the proportion of hatched Daphnia galeata, D. galeata · hyalina and D. hyalina individuals and the observed taxon composition of the resting egg bank. However, species and hybrids differed in their mode and relative success of reproduction. We conclude that the components of reproductive success in Daphnia contribute differentially to the fitness of species and interspecific hybrids. The discrepancy between resting egg banks and ''active'' planktonic populations results not from differential hatching of species but from the reproductive success of ex-ephippial females and the timing and frequency of sexual reproduction of the different taxa.

Phenotypic plasticity in life‐history traits of Daphnia galeata in response to temperature – a comparison across clonal lineages separated in time

“…In our experiment, genotyping of laboratory‐hatched and wild populations showed no significant differences in the genetic variability (Brede et al. ). However, we were not able to include all clonal lineages established in the laboratory in our experiments.…”

The impact of human-made ecological changes on the genetic architecture of Daphnia species

“…Alternatively to the ''simultaneous invasion'' hypothesis, D. galeata might have been present in the lake for a long time already but ceased or at least strongly reduced ephippial production during the first part of the past century. A change in the frequency of sexual reproduction with eutrophication (17), as well as differential hatching success of parental and hybrid taxa (28), has also been observed in Lake Constance. This hypothesis is supported by the presence of a few interspecific hybrids in Greifensee sediment layers of the 1920s, which suggests that D. galeata was present in Greifensee during this time but did not reproduce sexually (i.e., make ephippia).…”

Modes and mechanisms of aDaphniainvasion

“…In Lake Constance, D. longispina persisted in the water column but ceased making diapausing eggs [42,43]. Because diapausing egg production in other species of Daphnia is induced at least in part by crowding and food scarcity [44], it may be that eutrophication eliminated the stimulus for diapause in this species.…”