Genetic variability in three species of Gymnotus Linnaeus, 1758 (Gymnotiformes: Gymnotidae) from Caracu stream of the upper Paraná River basin, Brazil

Abstract

The genetic variability of three Gymnotus species from the Caracu stream, a small tributary of the left margin of Paraná River (Brazilian upper Paraná River floodplain), was estimated with data of 17 putative allozyme loci, which were obtained by using corn starch gel electrophoresis of 10 enzymatic systems: Aspartate aminotransferase (E. C. 2.6.1.1), Alcohol dehydrogenase (E. C. 1.1.1.1), Esterase (E. C. 3.1.1.1), Glucose dehydrogenase (E. C. 1.1.1.118), Glycerol-3-phosphate dehydrogenase (E. C. 1.1.1.8), Isocitrate dehydrogenase (E. C. 1.1.1.42), L-Lactate dehydrogenase (E. C. 1.1.1.27), Malate dehydrogenase (E. C. 1.1.1.37), Superoxide dismutase (E. C. 1.15.1.1) and Sorbitol dehydrogenase (E. C. 1.1.1.14). The genetic diversity was estimated as He = 0.3458 for G. pantanal, He = 0.2481 for G. inaequilabiatus, and He = 0.3152 for G. sylvius. The most divergent species were G. sylvius and G. pantanal (D = 0.117), and the most similar were G. inaequilabiatus and G. pantanal (D = 0.051). The data indicates that the observed genetic variability was very low and the expected variability estimated for these three species is very high, and the genetic differences among them are small. The data suggest that the process of speciation which produced these three species is recent.

Ocorrência de espécies de peixes não nativos em um rio Neotropical sob a influência da atividade aquí­­cola

“…The representatives of the Gymnotiformes order have specific characteristics, such as the capacity to emit electrical pulses used in communication, foraging, navigation and orientation in relation to the substrate (CRAMPTON and ALBERT, 2006). These characteristics facilitate the establishment of the species in environments with high turbidity and the presence of aquatic vegetation (REZENDE et al, 2009), as observed at the sites sampled in this study. The Azul River microbasin, which is widely exploited by agriculture and livestock activities, is characterized by a reduced area of riparian vegetation, causing high turbidity of the water and the development of dense marginal aquatic vegetation, which enables the successful colonization by the representatives of the Gymnotiformes order.…”

Gymnotus paraguensis, a Good Example of Phenotypic Plasticity in the Pantanal Biome, Brazil

“…61 Previous studies of several Neotropical fish species have reached similar conclusions, with a mean genetic divergence among congeners of *5%, 60 and exclusive alleles being found in many cases, confirming the low genetic variability found in these species. 62 Similar values were recorded in the basin of the Itapecuru River, 63 in northeastern Brazil, which permitted the reliable identification of 92.19% of the fish species, with interspecific differences of <3% in most cases, demonstrating considerable potential for the discrimination of cryptic species. In the present study, the variation found among congeners was much FIG.…”

Characterization of the agonistic behavior of the weakly electric fish Gymnotus sylvius

“…Only four species of Gymnotus occur in the southernmost freshwater environments of Argentina. Gymnotus inaequilabiatus is found in lotic environments and cannot survive in poorly oxygenated waters, whereas Gymnotus omarorum , Gymnotus pantanal , and Gymnotus sylvius usually inhabit in sympatry in environments such as marshes or ponds with dense floating aquatic vegetation and poorly oxygenated water (Casciotta et al., 2013; Rezende et al., 2009).…”

“…Although all species of the genus Gymnotus are considered aggressive and territorial, Gymnotus omarorum is the only species inhabiting the southernmost boundary of gymnotiforms in South America in which its agonistic behavior has been carefully addressed (Batista et al., 2012; Perrone & Silva, 2018; Quintana et al., 2016). In contrast, little is known about the natural history and social behavior of the sexually monomorphic Gymnotus sylvius , which occurs in sympatry with Gymnotus omarorum in freshwater environments of Argentina (Albert et al., 1999; Casciotta et al., 2013; Rezende et al., 2009). In this study, we describe the agonistic behavior of Gymnotus sylvius in dyadic encounters in laboratory settings.…”