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Filamentous cyanobacteria alter the relative fitness in a Daphnia hybrid species complex

Brzeziński, Tomasz
Freshwater biology 2015 v.60 no.1 pp. 101-110
Cylindrospermopsis raciborskii, Daphnia galeata, Daphnia longispina, Scenedesmus obliquus, animals, clones, diet, food quality, freshwater, hybrids, interspecific hybridization, intraspecific variation, lakes
Interspecific hybridisation is common in freshwater cladocerans. Within the Daphnia longispina complex hybrids frequently dominate over parental species, and environmental heterogeneity in the pelagial of lakes has been invoked to explain the coexistence of hybrids and parental species. In laboratory conditions, I investigated the effects of filamentous cyanobacteria on the relative fitness of Daphnia hyalina, Daphnia galeata and Daphnia hyalina×galeata hybrids. For each taxon, the performance of three clones was measured using animals fed with two diets: (i) a mixture of the filamentous cyanobacterium Cylindrospermopsis raciborskii and the green alga Scenedesmus obliquus and (ii) Scenedesmus obliquus in non‐limiting concentration. Inter‐ and intraspecific differences in ability to cope with cyanobacterial filaments were found; hybrids were, on average, superior to parental species in the absence of filaments, but in the presence of filaments one of the parental species (D. hyalina) was superior, while performance of hybrids did not differ from D. galeata. No relationship was found between size at first reproduction (range 1.3–2.0 mm) and reduced fitness due to the presence of cyanobacterial filaments. Shifts in relative fitness of daphnids due to variation in food quality, mediated by the presence of filamentous cyanobacteria, may promote coexistence of hybrids and parental species of the D. longispina complex.