title: Morphological evolution of coexisting amphipod species pairs from sulfidic caves suggests competitive interactions and character displacement, but no environmental filtering and convergence.
abstract: Phenotypically similar species coexisting in extreme environments like sulfidic water are subject to two opposing eco-evolutionary processes: those favoring similarity of environment-specific traits, and those promoting differences of traits related to resource use. The former group of processes includes ecological filtering and convergent or parallel evolution, the latter competitive exclusion, character displacement and divergent evolution. We used a unique eco-evolutionary study system composed of two independent pairs of coexisting amphipod species (genus Niphargus) from the sulfidic caves Movile in Romania and Frasassi in Italy to study the relative contribution and interaction of both processes. We looked at the shape of the multifunctional ventral channel as a trait ostensibly related to oxygenation and sulfide detoxification, and at body size as a resource-related trait. Phylogenetic analysis suggests that the sulfidic caves were colonized separately by ancestors of each species. Species within pairs were more dissimilar in their morphology than expected according to a null model based on regional species pool. This might indicate competitive interactions shaping the morphology of these amphipod species. Moreover, our results suggest that the shape of the ventral channel is not subject to long-term convergent selection or to the process of environmental filtering, and as such probably does not play a role in sulfide tolerance. Nevertheless, the ancestral conditions reconstructed using the comparative method tended to be more similar than null-model expectations. This shift in patterns may reflect a temporal hierarchy of eco-evolutionary processes, in which initial environmental filtering became later on superseded by character displacement or other competition-driven divergent evolutionary processes.
authors.affiliation: Department of Biology, Biotechnical Faculty, University of Ljubljana, 1000 Ljubljana, Slovenia.
authors.forename: Cene
authors.initials: C
authors.lastname: Fišer
authors.affiliation: Department of Biology, Biotechnical Faculty, University of Ljubljana, 1000 Ljubljana, Slovenia.
authors.forename: Roman
authors.initials: R
authors.lastname: Luštrik
authors.affiliation: Grupul de Explorări Subacvatice şi Speologice, Strada Frumoasă 31, 010986 Bucureşti, Romania.
authors.forename: Serban
authors.initials: S
authors.lastname: Sarbu
authors.affiliation: Department of Genetics, Evolution and Environment, University College London, Darwin Building, Gower Street, London WC1E 6BT, United Kingdom.
authors.forename: Jean-François
authors.initials: JF
authors.lastname: Flot
authors.affiliation: Department of Biology, Biotechnical Faculty, University of Ljubljana, 1000 Ljubljana, Slovenia; Museum für Naturkunde, Leibniz-Institut für Evolutions- und Biodiversitätsforschung an der Humboldt-Universität zu Berlin, Invalidenstrasse 43, Berlin 10115, Germany.
authors.forename: Peter
authors.initials: P
authors.lastname: Trontelj
mesh_terms: D033304:Amphipoda / Q000145:classification; D000818:Animals; D005075:Biological Evolution; D059552:Caves; D010802:Phylogeny; D013440:Sulfides
chemical_list: D013440:Sulfides