Biochemical food quality effects on a Daphnia hybrid complex

Abstract

Correlative field studies have shown that the food quality of natural seston for Daphnia is highly correlated with the content of eicosapentaenoic acid (EPA), indicating that the growth of Daphnia in nature is at least seasonally limited by a low availability of this polyunsaturated fatty acid. Here we test the hypothesis that a putative limitation due to limited availability of EPA in natural seston should lead to genetic adaptation in physiological traits reflected in genotype-dependent differences in the ability of sympatric clones of Daphnia to cope with these shortages. We further test if this adaptation to the low availability of EPA provides another explanation for the coexistence of hybrids with their parental taxa. Standardized growth experiments were performed with and without dietary EPA using clones of three taxa from the Daphnia longispina complex: Daphnia galeata, Daphnia hyalina, and their interspecific hybrids. Fitness was estimated from juvenile somatic growth rates, g, and from intrinsic population growth rates, r. There was marked interclonal variability in the susceptibilities of g and r to the absence of EPA from the food, with considerable intraspecific variability. At the taxon level, we noted differences in susceptibility to EPA limitation with regard to the intrinsic rate of population increase r, which demonstrates that the availability of EPA affects the relative fitness of hybrids, but not of the parental species. On average, hybrids seemed less susceptible to the absence of EPA than do parental species. Environmental heterogeneity driven by EPA-mediated changes in the quality of food may in consequence contribute to the maintenance of genetic diversity in Daphnia and may be a reason for the temporal dominance of hybrids.

Single dietary amino acids control resting egg production and affect population growth of a key freshwater herbivore

“…is due to a deficiency in essential long chain PUFAs (Weers and Gulati 1997;Von Elert 2002;Brzeziński and Von Elert 2007). Taking Liebig's law of the minimum into consideration, this explanation appears to be incompatible with our data, which imply that the performance of daphnids feeding on S. obliquus is constrained by a deficiency in specific amino acids.…”

Interspecific hybridization in sympatric species of Daphnia inhabiting lakes in northeastern Poland

“…The high deficiencies of heterozygotes observed in this study may indicate that hybridization mating is not random or that amphigonic egg production by hybrids is constrained . Indeed, hybrids of the D. longispina complex are sometimes fitter than individuals of parental species (Spaak & Hoekstra 1995, Brzeziński & Von Elert 2007. Hence, clonal reproduction of the most succesfull hybrid genotypes and the inferiority of other hybrid clones in amphigonic reproduction may contribute to the observed deviations from HWE.…”

“…Morphological identification of hybrids within the D. longispina complex is difficult (Giessler 2001), so it is necessary to apply molecular markers such as allozymes (Wolf & Mort 1986, Giessler 1997 (Spaak 1996), which may result in merging of gene pools and genetic swamping of two or more species. Hybrids are reported to be more fit than parental individuals under certain environmental conditions (Spaak & Hoekstra 1995, Brzeziński & Von Elert 2007, which may result in local competitive exclusion of parental species. On the other hand, hybrids seem to be inferior compared to parentals with regard to amphigonic reproduction , which can lower their success under conditions favouring this mode of reproduction (eg.…”

Temperature‐ and cholesterol‐induced changes in eicosapentaenoic acid limitation of Daphnia magna determined by a promising method to estimate growth saturation thresholds

“…Consulting outcomes of published laboratory studies we derived mechanisms of how these factors might influence EPA-dependent growth responses and hypothesized how differences between species or clones may affect these interactions (Table 3). EPA requirements and, thus, EPA growth thresholds might vary between Daphnia species and clones, as it was shown that the growth response of different Daphnia species was differently affected by the presence or absence of dietary EPA (Brzezinski and Von Elert 2007). A difference in EPA requirements for species or clones can affect competition-driven selection, which would lead to locally or temporally adapted clones.…”

“…Other factors potentially influencing growth, e.g., temperature or the availability of other food constituents, may have interactive effects on the nutrientdependent growth responses Martin-Creuzburg et al 2010). Intra-and interspecific variation in Daphnia's sensitivity to nutritional limitations (Brzezinski and Von Elert 2007;Seidendorf et al 2007) may also cause differences in nutrient thresholds.…”