We conducted a comparative (2D landmark-based geometric and traditional) morphometric analysis on tadpoles at early developmental stages. Two species of brown frog (Rana dalmatina and R. temporaria) and the common toad (Bufo bufo) were involved, all raised in the laboratory from fertilized eggs collected in their natural habitat. Taxonomic identification was confirmed by the DNA barcoding method with the 16S rRNA sequence as the gene marker. Interested to compare the methodologies for quantification and description of morphological differences among tadpoles of mentioned species, we aimed to: 1) calculate interspecies genetic distances as the most relevant measurement for species differentiation, 2) determine and describe size and shape variation, 3) identify relationships among the analyzed species at the morphological level and 4) assess their classification accuracy. Within the framework of the specified aims, both methodologies produced very similar results, i.e., the smallest divergence was between R. dalmatina and R. temporaria, while the most discriminative were B. bufo and R. temporaria. However, we observed subtle shape variation of the distal region of the tail that was detected only by the geometric morphometrics. Our findings support the following. Geometric morphometric method captures more subtle shape differences that were unable to be recovered from linear measurements. It performs slightly better in classification rate. Although it was not quantified, it stands to reason that there is no difference in time investment between the two approaches. Geometric morphometrics provides more information that can be leveraged to answer further questions and it has a clear advantage in visualizing.
To elucidate the historical biogeography of a species, the patterns of population divergence must be understood, and the evolutionary history of the species must be accurately known. For brown trout (Salmo trutta complex), estimating divergence times remains a challenge due to the lack of well-defined time calibration points and insufficient phylogeographic coverage in previous studies. The present work aims to improve molecular dating of mitochondrial control region sequences by using a multicalibration framework based on the latest paleogeological evidence for dating the origin of Lake Ohrid and two available Salmo fossils, including the overlooked Salmo immigratus. Our results clearly show that, contrary to common belief, the major divisions within the brown trout occurred in the Late Pliocene, not the Pleistocene. The Pliocene origin suggests that the brown trout lineages did not form because of geo(hydro)morphological changes during glaciation cycles but may be the result of orogeny and drainage evolution. In addition, increased sampling, particularly in Serbia, led to the identification of a new haplogroup (da-int) occupying an intermediate position with respect to da-es and da-bs haplogroups. While the control region can delineate brown trout lineages, its phylogenetic resolution is limited, so even extensive sampling could not further resolve the lineage level polytomies.