Mechanisms of coexistence of cryptic species

Cryptic species are species which differ in their genes, ecology, physiology or any other traits that are invisible to the human eye. They are typically discovered and identified by genetic analysis, which reveal them as evolutionary entities that may have been separated from each other for millions of years. When individuals of cryptic species co-occur in the same place, they may employ different ecological strategies to share the available resources among them, and they also require some means of recognizing each other as suitable or unsuitable mating partners. Amphipods are small crustaceans that are known for their diversity of cryptic species in European freshwater systems and provide excellent opportunities for testing hypothesis on the co-existing of cryptic species. They fulfill immensely important ecological functions by devouring large amounts of leaf litter and other organic material and themselves serving as food source for fish and birds. The project investigates whether and how different cryptic species of the amphipod Gammarus fossarum diverge in resource use, recognize mating partners of their own species and compete with individuals of the other species, and differ in their susceptibility to parasites. Experiments will be conducted with multiple cryptic species representing a range of more closely to more distantly related species, and originating from the eastern European Alps and the Western Carpathians. Both regions are hotspots of cryptic diversity in these amphipods, where the cryptic species have already been shown to live together in the same small streams. Detailed measurements of body parts are taken to examine whether the cryptic species are indeed cryptic, or whether differences in size or shape have only been overlooked so far. Analyses of the food ingested by the amphipods examine whether the co-occurring species differ in resource use. Mating preferences among different species are revealed by collecting mated pairs, which cling together for some time before reproduction, and identifying the partners based on their species-specific DNA sequences. Courtship and reproduction between species are studied in the lab to infer reproductive barriers between species. Lab experiments also examine competitive interactions in order to inform about dominance relationships between species. Infection levels with certain parasites are estimated in the different species to assess their relative health status. The project combines fieldwork, behavioral experiments, stable isotope analysis, DNA sequencing and morphological analyses to elucidate the mechanisms of coexistence of species that have, for the longest time, defied our traditional means of detection.