Incidence of diapause varies among populations of Daphnia pulicaria

Abstract

Dormancy is a common way in which organisms survive environmental conditions that would be lethal to the active individual. However, while dormant, individuals forego reproduction. Hence theory suggests an optimal time in which to enter dormancy, depending on risks associated with both remaining active and entering dormancy. When these relative risks differ among habitats, dormancy strategies are predicted to vary as well. For freshwater zooplankton, it has been suggested that sensitivity to the cues that initiate dormancy should be selected against when females have the opportunity to remain in the water column year round. We tested this prediction with 12 populations of lake-dwelling Daphnia pulicaria (Crustacea: Cladocera). Differences among lakes in basin morphometry, predators and resources create a gradient of risk for Daphnia in the water column. Some populations persist in high numbers year round while others are abundant only in spring. We used this difference in persistence ability as an estimate of risk in the water-column. For 3 years of field sampling we found consistent differences among the lake populations in the incidence of dormancy. In some populations, only a small fraction of females switched to producing dormant eggs each year whereas in others the majority of eggs produced in the late spring were dormant. In general, populations that experienced predictably low abundances in the active form exhibited higher incidence of dormancy than did populations that persisted in high abundance year round, but there were exceptions. Our results confirm that the incidence of dormancy varies considerably among populations in a fashion consistent with general theory, but suggest that persistence in the water column is not the sole predictor of the diapause strategy found in any particular lake.

Both Costs and Benefits of Sex Correlate With Relative Frequency of Asexual Reproduction in Cyclically ParthenogenicDaphnia pulicariaPopulations

“…We tested this hypothesis using four natural lake populations (Caceres and Tessier 2004) of the cyclically parthenogenic microcrustacean Daphnia pulicaria that differ consistently and predictably in their frequency of sexual reproduction. Although all four populations are capable of sexual reproduction, the actual frequency of sex, previously calculated using the proportion of males and sexually reproducing females (Caceres and Tessier 2004), spans an $30-fold difference between the high-and low-sex populations (Caceres and Tessier 2004).…”

“…Although all four populations are capable of sexual reproduction, the actual frequency of sex, previously calculated using the proportion of males and sexually reproducing females (Caceres and Tessier 2004), spans an $30-fold difference between the high-and low-sex populations (Caceres and Tessier 2004). The D. pulicaria system offers extraordinary power because in addition to variation in the frequency of sex in nature, sampled individuals can be maintained clonally in the laboratory, allowing the essentially permanent propagation of wild-caught parental genotypes along with their sexually produced offspring.…”

Effects of physical interference on life history shifts in Daphnia pulex

“…In this study, Daphnia pulex did produce diapausing eggs, but these represented only a small percentage of the cumulative number of parthenogenetic eggs. Variability in diapausing egg production among clones has been shown in Daphnia pulex (Innes and Singleton, 2000;Berg et al, 2001), Daphnia pulicaria (Caceres and Tessier, 2004) and Daphnia magna (Carvalho and Hughes, 1983). Our Daphnia pulex clones are probably less sensitive to crowding in terms of diapausing egg production.…”

Ecological genomics in Daphnia: stress responses and environmental sex determination

“…Implications of migration through time, or the effects of overlapping generations on population dynamics, are an active research area (for example, Cáceres and Tessier, 2004). In addition, hatching dormant propagules may compare ancestral populations and their descendents, for example before and after introduction of a novel predator or toxicant, to measure genetic differences related to the environmental change (Weider et al, 1997;Hairston et al, 1999).…”