Inter-genotype variation in reproductive response to crowding among Daphnia pulex

Abstract

Crowding is known to have a major influence on reproduction in the freshwater microcrustacean Daphnia pulex. We analyzed reproductive output of six different D. pulex genotypes under two different density regimes in the laboratory. Four of these genotypes reproduce via obligate parthenogenesis, allowing thorough analysis of the life history strategies of some asexual lines. Among 30,109 neonate offspring and 1041 resting egg ephippia collected, several trends were evident. Crowding induced increased resting egg production and reduced neonate offspring production among all genotypes. Offspring sex ratios grew more male-biased with maternal age. The extent, but not direction, of each of these trends varied among genotypes. Offspring sex ratios, and the very direction in which they changed in response to crowding, differed significantly among genotypes with some genotypes producing more and others fewer males in response to crowding. Obligately parthenogenetic genotypes seemed to respond to the crowding stimulus in similar ways as the facultatively parthenogenetic genotypes, as expected from the sexual origins of their genomes. The inter-genotype variation in life-history traits observed in this and other investigations calls into question the common practice of extrapolating results from a single Daphnia genotype to an entire species. Our findings are considered in the context of other research in the field of environmental influences on Daphnia reproduction with a review of representative literature.

All Eggs Are Not Equal: The Maternal Environment Affects Progeny Reproduction and Developmental Fate in Caenorhabditis elegans

“…Further, low maternal food availability is shown to decrease the likelihood that progeny will develop as dauer larvae (Figure 3). These observed effects of maternal conditions on progeny life history in C. elegans could represent a switch to the production of fewer, better provisioned eggs, in poor conditions and would mirror observations in Daphnia [6]–[10]. As such they would represent attempts to match progeny development to the expected environmental conditions and are therefore likely to be adaptive [1], [4].…”

Effects of physical interference on life history shifts in Daphnia pulex

“…As shown in the literature, crowding by conspecifics reduces adult growth and egg production rates in Daphnia pulex (Nishikawa and Ban, 1998) and Simocephalus vetulus (Lee and Ban, 1999), clutch size in Daphnia pulex (Fitzsimmons and Innes, 2006), Daphnia hyalina (Seitz, 1984), Daphnia carinata (Matveev, 1993) and Daphnia magna (Guisande, 1993) given excess food. What causes such negative effects on demographic parameters?…”

“…The evidence indicates that a reduction in feeding due to crowding does not necessarily cause a diminution of clutch size in older animals. Since inter-genotype variation in reproductive responses to crowding has been shown in Daphnia pulex (Fitzsimmons and Innes, 2006), smaller clutch sizes at older age under crowded conditions may be a reproductive feature of the clone used in this study, but is not attributable to food shortage. If the reproductive responses to crowded conditions adapt to forthcoming severe food conditions as described above, the reduction in offspring numbers may also be adaptive.…”

“…Carvalho and Hughes (Carvalho and Hughes, 1983) reported that diapausing egg production in Daphnia magna correlated positively with female density in a culture vessel with excess food. Recently, Fitzsimmons and Innes (Fitzsimmons and Innes, 2006) used six different clones to show that per capita diapausing egg production in Daphnia pulex was significantly higher for crowded daphniids than for individual animals. In this study, Daphnia pulex did produce diapausing eggs, but these represented only a small percentage of the cumulative number of parthenogenetic eggs.…”

An experimental test of the ability of Daphnia galeata resting egg production in Lake Biwa

“…The frequency of resting egg production was found to be lower in Daphnia populations that persist with high numbers all through the year than in those that disappear from the water column during some seasons Tessier, 2004a, 2004b). Furthermore, recent studies have shown intra-specific variation in sexual reproduction in response to given conditions (Tessier and Cáceres, 2004;Fitzsimmons and Innes, 2006). If harsh seasons were to disappear due to environmental changes that enable Daphnia to persist through the year in the water column, then genetic strains that are sensitive to environmental stimuli for triggering sexual reproduction may be outcompeted by less sensitive lines because of decreased individual fitness, at least with respect to resting egg production.…”