title: Are sympatrically speciating Midas cichlid fish special? Patterns of morphological and genetic variation in the closely related species Archocentrus centrarchus.
abstract: Established empirical cases of sympatric speciation are scarce, although there is an increasing consensus that sympatric speciation might be more common than previously thought. Midas cichlid fish are one of the few substantiated cases of sympatric speciation, and they formed repeated radiations in crater lakes. In contrast, in the same environment, such radiation patterns have not been observed in other species of cichlids and other families of fish. We analyze morphological and genetic variation in a cichlid species (Archocentrus centrarchus) that co-inhabits several crater lakes with the Midas species complex. In particular, we analyze variation in body and pharyngeal jaw shape (two ecologically important traits in sympatrically divergent Midas cichlids) and relate that to genetic variation in mitochondrial control region and microsatellites. Using these four datasets, we analyze variation between and within two Nicaraguan lakes: a crater lake where multiple Midas cichlids have been described and a lake where the source population lives. We do not observe any within-lake clustering consistent across morphological traits and genetic markers, suggesting the absence of sympatric divergence in A. centrarchus. Genetic differentiation between lakes was low and morphological divergence absent. Such morphological similarity between lakes is found not only in average morphology, but also when analyzing covariation between traits and degree of morphospace occupation. A combined analysis of the mitochondrial control region in A. centrarchus and Midas cichlids suggests that a difference between lineages in the timing of crater lake colonization cannot be invoked as an explanation for the difference in their levels of diversification. In light of our results, A. centrarchus represents the ideal candidate to study the genomic differences between these two lineages that might explain why some lineages are more likely to speciate and diverge in sympatry than others.
authors: Department of Biology Chair of Zoology and Evolutionary Biology University of Konstanz Universitätsstrasse 1078457 Konstanz Germany; School of Earth, Environmental & Biological Sciences Queensland University of Technology Brisbane Qld 4000 Australia.
authors: Carmelo
authors: C
authors: Fruciano
authors: Department of Biology Chair of Zoology and Evolutionary Biology University of Konstanz Universitätsstrasse 10 78457 Konstanz Germany.
authors: Paolo
authors: P
authors: Franchini
authors: Department of Biology Chair of Zoology and Evolutionary Biology University of Konstanz Universitätsstrasse 1078457 Konstanz Germany; International Max Planck Research School (IMPRS) for Organismal Biology Max-Planck-Institut für Ornithologie Am Obstberg 178315 Radolfzell Germany.
authors: Francesca
authors: F
authors: Raffini
authors: Department of Biology Chair of Zoology and Evolutionary Biology University of Konstanz Universitätsstrasse 10 78457 Konstanz Germany.
authors: Shaohua
authors: S
authors: Fan
authors: Department of Biology Chair of Zoology and Evolutionary Biology University of Konstanz Universitätsstrasse 10 78457 Konstanz Germany.
authors: Axel
authors: A
authors: Meyer
keywords: Adaptive radiation; geometric morphometrics; phylogeography; sympatric speciation