Sex allocation variation in Daphnia pulex

Abstract

Duphniu (Crustacea: Cladocera) reproduce by cyclical parthenogenesis in which the sex of offspring is environmentally determined. Although numerous studies have demonstrated that factors such as crowding and short-day photoperiod stimulate male production, there is limited information on variation in allocation to male and female offspring for any species of Duphniu. The present study assessed the presence or absence of male production in 96 isofemale lines (clones) from each of eight populations of Duphniu pulex. An average of 37% (range l&51%) of clones failed to produce males under crowded conditions in the laboratory. A subset of 14 of these non-male-producing clones also failed to produce males under short-day photoperiod (8L: 16D). Three male-producing clones were within-clone mated as well as crossed to three non-male-producing clones to study the inheritance of the failure to produce males. The average frequency of non-male-producing F, progeny was significantly higher (58%, N = 486) among the outcrossed progeny than the inbred progeny (5%, N = 86). In addition, when sixteen of the male-producing outcrossed progeny were withinclone mated, only 7% (N = 106) of the resulting F, progeny failed to produce males. These results are consistent with a genetic basis for the absence of male production. Average survival of the progeny from the nine outcrossed matings was more than twice (67%) that of the inbred progeny from the three withinclone matings (30%) suggesting that within-clone mating would result in significant inbreeding depression. We present a model that suggests that even low levels of inbreeding could allow non-male-producing females to be maintained in a population. The co-occurrence of non-male-producing females and females that produce both males and females in Duphniu p&x bears a similarity to the gynodioecious breeding system found in some plant species. 560Innes and Dunbrack

Localization of the Genetic Determinants of Meiosis Suppression in Daphnia pulex

“…Only a fraction of D. pulex are capable of male production, and although the genetic details remain to be worked out, the limited crosses that have been made between maleand nonmale-producing clones appear to be qualitatively consistent with a single-locus model in which individuals with male/female function are either MM or Mm and those incapable of male production are mm, with a dominant allele (or tight linkage group) M conferring the ability to produce males (Innes and Dunbrack 1993;Innes 1997;Tessier and Cáceres 2004). However, none of the significant markers that we identified in obligate asexuals were associated with the ability to produce males (revealed by application of male-inducing methyl farnesoate; Olmstead and Leblanc 2002).…”

Reproduction of Daphnia pulex in a Northern Italy pond

“…In most Cladocera, sexual phase and male production begin after several generations of parthenogenetic reproduction with the production of subitaneously developing eggs. Switch to sexual reproduction and resting egg production is generally cued by a number of factors that are indicative of environmental deterioration (i.e., crowding and short-day photoperiod) and by maternal environmental conditions (Stross, 1987;Hobaek and Larsson, 1990;Innes and Dunbrack, 1993;Innes, 1997;LaMontagne and McCauley, 2001;Koch et al, 2009). In the bodrio, a very early investment in sexual reproduction, independent of population density, was observed.…”

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

“…Disp and Morg occur in woodlots, while VBA and War ponds are in more open areas. At least a dozen clonal isolates were individually maintained from each of these ponds in synthetic zooplankton media (Lynch et al, 1986) in conditions described elsewhere (Innes & Dunbrack, 1993). Cups of clonal strains were fed 3.5 mL of algal slurry from an aquarium system daily.…”

“…Studies that have tested for inter-clonal variation in sex ratios have found it, among clones of D. pulex (Innes & Dunbrack, 1993;Innes, 1997;Innes & Singleton, 2000), clones of D. pulicaria , and both clones (Korpelainen, 1986) and populations (Ferrari & Hebert, 1982) of D. magna. In fact, the significant cloneÂdensity interaction affecting sex ratios in the present study was also found to significantly influence sex ratios in other studies on D. pulex (Ruvinsky et al, 1986;Innes & Singleton, 1994) and D. magna (Yampolsky, 1992).…”

“…Within-clone matings are known to produce offspring with fitness that is variable but reduced on average (Innes, 1989;Innes & Dunbrack, 1993;Deng, 1997a;Salathe´& Ebert, 2003). Perhaps D. pulex adjusts its reproduction in response to outbreeding opportunities, just as female ambrosia beetles adjust their offspring sex ratio depending on outbreeding opportunities (Peer & Taborsky, 2004).…”