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Non-indigenous freshwater bivalves negatively affect invaded ecosystems through different mechanisms, including inter-specific competition for trophic resources. Here, we investigated in Lake Trasimeno (Central Italy) the diet of the invasive Dreissena polymorpha and the native Anodonta anatina. δ15N and δ13C stable isotopes were measured in winter and summer in bivalves, phytoplankton, and sedimentary organic matter (SOM); the relative dietary contributions of the two resources were determined using Bayesian mixing models. To elucidate the different carbon and nitrogen pools characterizing the study site, isotopic analyses were extended to zooplankton and to representatives of the benthic flora and macroinvertebrate fauna. Independently from the season, the two bivalves showed a limited trophic overlap, as mixing models indicated for D. polymorpha a diet based primarily on phytoplankton, while A. anatina relied mainly on SOM. Dietary differences were less marked in summer, when comparable isotopic values characterized phytoplankton and SOM. In winter, conversely, the trophic differentiation between the two species was more evident, and corresponded with a significant enrichment in SOM δ13C values, likely due to a substantial contribution of carbon deriving from decaying macrophytes. Whether differences in ecological and behavioral traits alone can explain the observed trophic segregation between the two species, or if they have actively shifted their diet to reduce competition for food is discussed. We conclude emphasizing the need of an advanced resolution of the influence of non-indigenous species on the flux of energy and matter in invaded lentic systems, including Lake Trasimeno.

In animals, doubly uniparental inheritance (DUI) is a major exception to the common strict maternal inheritance of mitochondria. To date, DUI has only been found in many bivalve species, but its distribution is still unclear. Given the great species richness of the class, much effort is needed to further investigate the occurrence of DUI in unsampled species. A compelling evidence of DUI is generally the presence of a sex-linked heteroplasmy, where two divergent mitochondrial lineages are found: One is isolated from the male germline, and the other one is isolated from the female germline and, normally, from the soma of both sexes. In the present study, we investigated the sex-linked heteroplasmy in the razor clam Solen marginatus Pulteney, 1799 and in the lagoon cockle Cerastoderma glaucum (Bruguière, 1789) using two mitochondrial markers (cox1 and rrnL). We found evidence of DUI in the species S.marginatus, with a divergence up to 21% for the rrnL gene, but not in C.glaucum. Moreover, our phylogenetic reconstruction includes all the available data for heterodont species with sex-linked heteroplasmy and suggests multiple origins of DUI in this subclass, as well as the presence of DUI in other species of the genus Solen.