Hematological and plasma biochemical profile of two species of freshwater stingrays from the Amazon

The evaluation of hematological and plasma biochemical parameters and the subsequent establishment of reference intervals facilitate the diagnosis of the health status of animals. This work aimed to determine the blood parameters of wild specimens of the stingrays Potamotrygon motoro and Potamotrygon orbignyi from the lower Solimões River region, Amazonas, Brazil. One hundred forty-one stingrays were captured, 92 specimens of P. motoro and 49 of P. orbignyi, of both sexes and at different stages of development. No effect of sex was observed on the blood parameters of juvenile animals for both species. P. motoro neonates presented a distinct hematological and biochemical profile, with significantly lower hematocrit values, hemoglobina, number of erythrocytes, mean corpuscular hemoglobin concentration, monocytes, plasma glucose, total proteins, albumin, and globulin. On the other hand, total cholesterol and urea levels were significantly higher in this same group compared to juveniles of the same species. Comparison between species revealed lower values of triglycerides and total cholesterol in P. orbignyi of both sexes. The results obtained are pioneering for these Amazonian species in white water environments and will serve as a basis for evaluating the health status of wild stingrays. Thus, from the analysis of the blood of the P. motoro and P. orbignyi stingrays, it was possible to observe good health conditions.

First Karyotypic Insights into Potamotrygon schroederi Fernández-Yépez, 1958: Association of Different Classes of Repetitive DNA

INTRODUCTION

Currently, there are 38 valid species of freshwater stingrays, and these belong to the subfamily Potamotrygoninae. However, cytogenetic information about this group is limited, with studies mainly using classical techniques, Giemsa, and C-banding.

METHODS

In this study, we used classical and molecular cytogenetic techniques - mapping of 18S and 5S rDNA and simple sequence repeats (SSRs) - in order to investigate the karyotypic composition of Potamotrygon schroederi and reveal the karyoevolutionary trends of this group.

RESULTS

The species presented 2n = 66 chromosomes with 18m + 12sm + 16st + 20a, heterochromatic blocks distributed in the centromeric regions of all the chromosomes, and terminal blocks in the q arm of pairs 2 and 3. Mapping of 18S rDNA regions revealed multiple clusters on pairs 2 and 7 and a homolog of pair 24. The 5S rDNA region was found in the pericentromeric portion of the subtelocentric pair 16. Furthermore, dinucleotide SSRs sequences were found in the centromeric and terminal regions of different chromosomal pairs, with preferential accumulation in pair 17. In addition, we identified conspicuous blocks of (GATA)n and (GACA)n sequences colocalized with the 5S rDNA (pair 16).

CONCLUSION

In general, this study corroborates the general trend of a reduction in 2n in the species of Potamotrygoninae subfamily. Moreover, we found that the location of rDNA regions is very similar among Potamotrygon species, and the SSRs accumulation in the second subtelocentric pair (17) seems to be a common trait in this genus.

Foreign stingers: South American freshwater river stingrays Potamotrygon spp. established in Indonesia

The pet trade is known to be one of the most important pathways of aquatic non-native species introduction and Indonesia is a significant trade partner. Popular ornamental South American river stingrays (Potamotrygon spp.) were introduced to Indonesia in the 1980s and the culture was established. Here we present a detailed Indonesian market and aquaculture survey, the volume of trade between January 2020 and June 2022, and the list of customer countries with the total amount of imported stingrays. Climate similarities between the native range of P. motoro and P. jabuti and Indonesia were analysed. A significant number of areas of Indonesian islands were identified as suitable for the establishment of this species. This was confirmed by the first record of probably established populations in the Brantas River (Java). In total 13 individuals including newborns were captured. The culture of potamotrygonid stingrays is unregulated in Indonesia, and the risk of the establishment of this predator and its potential spread is alarming for wildlife. Moreover, the first case of envenomation caused by Potamotrygon spp. in the wild outside of South America was recorded. The current condition is predicted as the 'tip of the iceberg' and continuous monitoring and mitigation of risks are strongly recommended.

Signatures of positive selection in the mitochondrial genome of neotropical freshwater stingrays provide clues about the transition from saltwater to freshwater environment

Neotropical freshwater stingrays (subfamily Potamotrygoninae) are carnivorous bottom feeder batoids widely distributed in most river basins of South America. They represent the unique extant group of elasmobranchs that evolved to live exclusively in freshwater environments. These species are exploited either by commercial fisheries (e.g., for food or ornamental industry) or by indigenous communities allocated along with their natural range. Restrictive life history characteristics coupled with habitat degradation make Potamotrygoninae species highly vulnerable to human impacts and highlight the necessity of studies to inform basic biological aspects, from ecology to genetics, to guide their conservation and clarify the molecular basis of adaptation to the freshwater environment. We used available and newly assembled Potamotrygon spp. mitogenomes to perform a comparative investigation of their molecular evolution. A phylogenetic estimation using the mitogenome of Potamotrygon falkneri and other Elasmobranchii supports monophyly for Potamotrygonidae and indicates a close relationship to Dasyatidae. A synteny analysis comprising 3 Potamotrygon and other 51 batoids revealed a highly conserved mitogenomic context. We detected various amino acid sites under positive selection exclusively in Potamotrygon spp., within the sequences of ND4, ND5, ND6, and COXII genes. Positively selected mutational events in key genes of energetic metabolism may be related to the physiological adaptation of Potamotrygon spp. during the ancient incursion into freshwater. This broad comparative mitogenomic study provides novel insights into the evolutionary history of neotropical freshwater stingrays and their relatives and stands out as a valuable resource to aid in current and future research on elasmobranch molecular evolution.

Patterns of Phenotypic Evolution Associated with Marine/Freshwater Transitions in Fishes

Evolutionary transitions between marine and freshwater ecosystems have occurred repeatedly throughout the phylogenetic history of fishes. The theory of ecological opportunity predicts that lineages that colonize species-poor regions will have greater potential for phenotypic diversification than lineages invading species-rich regions. Thus, transitions between marine and freshwaters may promote phenotypic diversification in trans-marine/freshwater fish clades. We used phylogenetic comparative methods to analyze body size data in nine major fish clades that have crossed the marine/freshwater boundary. We explored how habitat transitions, ecological opportunity, and community interactions influenced patterns of phenotypic diversity. Our analyses indicated that transitions between marine and freshwater habitats did not drive body size evolution, and there are few differences in body size between marine and freshwater lineages. We found that body size disparity in freshwater lineages is not correlated with the number of independent transitions to freshwaters. We found a positive correlation between body size disparity and overall species richness of a given area, and a negative correlation between body size disparity and diversity of closely related species. Our results indicate that the diversity of incumbent freshwater species does not restrict phenotypic diversification, but the diversity of closely related taxa can limit body size diversification. Ecological opportunity arising from colonization of novel habitats does not seem to have a major effect in the trajectory of body size evolution in trans-marine/freshwater clades. Moreover, competition with closely related taxa in freshwaters has a greater effect than competition with distantly related incumbent species.

Evidence of multiple paternity for the endemic Xingu River stingray

Multiple paternity (MP) is a phenomenon observed for more than 30 elasmobranch species. The Batoidea is more specious than the Selachii, but only three studies of MP have been conducted on batoids. The occurrence of MP in freshwater stingrays was tested using microsatellite markers, which were developed for Potamotrygon leopoldi. Six mothers and their litters were genotyped, providing the first evidence of MP for Potamotrygonidae, with an MP frequency of 33%.

Ecological and Phenotypic Diversification after A Continental Invasion in Neotropical Freshwater Stingrays

Habitat transitions are key potential explanations for why some lineages have diversified and others have not - from Anolis lizards to Darwin's finches. The ecological ramifications of marine-to-freshwater transitions for fishes suggest evolutionary contingency: some lineages maintain their ancestral niches in novel habitats (niche conservatism), whereas others alter their ecological role. However, few studies have considered phenotypic, ecological, and lineage diversification concurrently to explore this issue. Here, we investigated the macroevolutionary history of the taxonomically and ecologically diverse Neotropical freshwater river rays (subfamily Potamotrygoninae), which invaded and diversified in the Amazon and other South American rivers during the late Oligocene to early Miocene. We generated a time-calibrated, multi-gene phylogeny for Potamotrygoninae and reconstructed evolutionary patterns of diet specialization. We measured functional morphological traits relevant for feeding and used comparative phylogenetic methods to examine how feeding morphology diversified over time. Potamotrygonine trophic and phenotypic diversity are evenly partitioned (non-overlapping) among internal clades for most of their history, until 20-16 mya, when more recent diversification suggests increasing overlap among phenotypes. Specialized piscivores (Heliotrygon and Paratrygon) evolved early in the history of freshwater stingrays, while later trophic specialization (molluscivory, insectivory, and crustacivory) evolved in the genus Potamotrygon. Potamotrygonins demonstrate ecological niche lability in diets and feeding apparatus; however, diversification has mostly been a gradual process through time. We suggest that competition is unlikely to have limited the potamotrygonine invasion and diversification in South America.

Environmentally-induced osmoregulation in Neotropical freshwater stingrays (Myliobatiformes: Potamotrygoninae) after controlling for phylogeny

The osmotic physiology of freshwater stingrays was investigated in fifteen species from white (WW), black (BW), and clearwater (CW) rivers of Brazilian hydrographic basins. Regardless of phylogeny, potamotrygonids collected in the BW (Negro, Jutai, Nhamunda, and Manacapuru rivers), and CW (Tapajos, Parana, Mutum, Demeni, and Branco rivers) exhibited lower levels of osmolytes and plasma osmolality than those from WW (Amazon estuary, Solimoes, and Tarauaca rivers). However, the gill and kidney Na⁺/K⁺-ATPase activities were higher in the potamotrygonid species from BW and CW than those from WW. These results may be related to the ability of the potamotrygonids to achieve high ion uptake from ion-poor waters, such as those of BW and/or CW. Additionally, the high kidney Na⁺/K⁺-ATPase activity may help to minimize ion loss and generate diluted urine. Thus, diffusional losses of salts are balanced by uptake of ions in the gill, and reabsorption by the kidney. The physiological traits showed a weak phylogenetic signal, which indicates a strong evolutionary convergence. Multivariate analyses revealed that variations in physiological traits has a significant association with the type of water, as well as its physical and chemical characteristics such as electric conductivity and pH. Therefore, the South American Neotropical freshwater stingrays adjust their osmoregulatory mechanisms according to the environment in which they live.