Combining geometric morphometrics with molecular genetics to investigate a putative hybrid complex: a case study with barbels Barbus spp. (Teleostei: Cyprinidae).

This integrative study examined the morphological and genetic affinities of three endemic barbel species from Italy (brook barbel Barbus caninus, Italian barbel Barbus plebejus and horse barbel Barbus tyberinus) and of putative hybrid specimens to their species of origin. Two of the species frequently occur together with the non-native barbel Barbus barbus. DNA barcoding indicates that mitochondrial (mt) haplotypes often do not match the species expected from morphology. Linear distance measurements and meristics are not informative for discrimination of the species and putative hybrids, but a discriminant analysis of principal components (DAPC) of geometric landmark data produces reassignments largely in congruence with mt and nuclear genetic data. Cyto-nuclear conflicts confirm the presence of hybridization in B. plebejus and B. tyberinus and identify additional introgressed specimens. A comparison between mixed genotypes and their morphology-based assignment reveals no predictable pattern. The finding that most individuals of the morphologically similar B. plebejus and B. tyberinus have very high assignment probabilities to their respective species suggests that the presented approach may serve as a valuable tool to distinguish morphologically very similar taxa.