Cryptic species of the genus Pimelodella (Siluriformes: Heptapteridae) from the Miranda River, Paraguay River basin, Pantanal of Mato Grosso do Sul, Central Brazil

Abstract

Specimens of Pimelodellacaptured in the Miranda River, Pantanal of Mato Grosso do Sul State, present morphological features that could indicate at least four species. Therefore, karyotype analysis and molecular biology provided evidence that they were only two species, one showing 2n = 46, and the other, 2n = 52 chromosomes, with only 18% genetic similarity. The morphological analysis evidenced that the dorsal filament is a male characteristic and that the upper lobe of the caudal fin was variable and might or might not be elongated in both species. With respect to morphometric characters, the formation of two groups was evident, but with a small overlap of specimens between them. Among the species with filaments on the dorsal fin observed in the Pantanal, the one with the lesser length of adipose fin base is P. griffini, which corresponds to that with 2n = 46 chromosomes, whereas the species P. taenioptera has 2n = 52 chromosomes. Thus, the accurate detection of these cryptic taxonomic units was only possible with the use of various analysis techniques. Furthermore, it is worth noting that the identification of cryptic species is important for obtaining correct estimates of fish diversity in the Pantanal

Description of a new Pimelodella (Siluriformes: Heptapteridae) species with a discussion on the upper pectoral girdle homology of Siluriformes

“…A century has passed since the last taxonomic revision of Pimelodella (Eigenmann, ). Despite subsequent efforts (Bockmann & Slobodian, ; Leiva, ; Mees, ; Souza‐Shibatta et al ., ; Slobodian et al ., ; G. M. Guazzelli, unpublished data), the species boundaries within this genus remain unclear. Most species assigned to the genus have never been subject to rigorous taxonomic study and those currently considered as valid are a testament only to the list of available names.…”

Trends of karyotypical evolution in the pearl cichlid, Geophagus brasiliensis, from southern Brazil

“…Thus, this group is a good model for elucidating the genetic mechanisms behind biodiversity (Albertson and Kocher, 2006;Gross, 2006;Meadows, 2009). In this respect, cytogenetic studies can help provide markers that may be employed in speciation analysis and assist in taxonomic problems, such as complex or cryptic species (Nakayama et al, 2001;Souza-Shibatta et al, 2013).…”

Structure, composition, mechanics and growth of spines of the dorsal fin of blue tilapia Oreochromis aureus and common carp Cyprinus carpio

“…Their conical shape, which ends distally in an extremely sharp free end, also forms an effective defence mechanism (Claes et al, 2013). The spine of C. carpio additionally possesses recurved serrations that are located on the caudal aspect of the distal third of the spine, similar to spines of Siluriformes (Trapani, 2008;Souza-Shibatta et al, 2013;Vanscoy et al, 2015), several fishes from the Tetraodontiformes and Gasterosteiformes (Bannikov & Tyler, 2006) and spines in the dorsal fin of some shark species (Maisey, 1979). Although the function of these serrations is not entirely clear, the most reasonable speculation is that they are also part of a defence mechanism (Maisey, 1979), injuring attacking predators and allowing the prey to escape (Alexander, 1981).…”