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•Hyalella curvispina is a good model species for the assessment of sediment quality.•Boana pulchella provided additional, complementary and significant information.•High-frequency ...abnormalities coincide with the presence of persistent endosulfan.•Boana pulchella is a good indicator of sediment toxicity.
In a study area chosen outside the city of La Plata (Buenos Aires, Argentina), two zones were selected having different types and magnitudes of agrarian activity: one represented mainly by grasslands with a low degree of anthropic influence, the other by intensive cultivation under cover with a high level of anthropic impact. The first objective was to assess the toxicity of the sediments from the study areas to two local species and compare the responses of both bioassays (assessing mortality and growth inhibition) in a standardized test protocol. Hyalella curvispina (Hc) is a validated indicator of sediment toxicity; Boana pulchella (Bp) has likewise proven useful as a study model through its sensitivity to different pollutants. The comparison was performed by multivariate analyses at the time of evaluating sediment toxicity in a stretch of the Carnaval Stream that flows through an agroecosystem. The second objective was to evaluate the presence of morphologic abnormalities, among other supplemental endpoints (behavior and development), in tadpoles of Bp since those features are good indicators of sublethal effects. Hc turned out to be the more sensitive to the chemical profile of the agroecosystem. We detected two herbicides, trifluralin and acetochlor, and three insecticides, chlorpyrifos, endosulfan, and lambda-cyhalothrin and in this test proposed Bp as a second indicator of sediment toxicity. This research was the first to use larvae of Bp to evaluate the toxicity of sediments of a particular site. The analysis of the occurrence of morphologic abnormalities enabled the detection of toxicities in locations where other endpoints remained unaffected. We intend to incorporate this species into sediment testing since Bp is a prominent anuran in pampean agroecosystems whose utility in toxicity bioassays has been verified by numerous ecotoxicological studies. In conclusion, both the species Hc and Bp should be considered appropriate as tests organisms for the assessment of sediment quality as well as effective and promising environmental indicators.
The aim of this study was to analyze the seasonal distribution of the nematode Hedruris dratini parasitizing the South American Snake-necked turtle Hydromedusa tectifera and the amphipod Hyalella ...spp. in an urban stream. We focused on understand which strategies parasite population displays to get through the host's hibernation period.
The highest prevalence and abundance of H. dratini were found in summer. The parasitic load was lower in winter, however there were no significant differences when it was compared with autumn and spring. Generalized linear model identified the temperature as a determining factor for the presence of parasites in turtles.
Our results indicate that, beside turtles enter in a diapause state, the life cycle of H. dratini never stop throughout the year, being a continuous transmission between both the intermediate and final host throughout the year. Turtles feed and become infected with parasite larvae even in winter although with a lower ingestion rate.
Habitat requirements of
Hydromedusa tectifera
from an urban impacted stream from the Buenos Aires province, the Rodriguez stream, are here studied. We describe the type of underwater refuges, how ...they are used in different stream sections, stream margins, year season, size class and sex of the individuals, and analyze patterns of recurrence and aggregative use of refuges. Fieldwork was carried out from March 2017 to January 2018. Turtles were caught manually recording the following variables: site, transect and margin, sex, straight carapace length, and weight. Substrate types are differently used according to stream section, stream margin, year season and size class of individuals, but no difference was found between sexes. In the whole stream, most used refuges were the hollows on the margins (55.05%), followed by marginal aquatic vegetation (19.27%). Turtles of all class sizes and both sexes refuge into hollows on the stream margins. Despite different microhabitats provide refuge to turtles during all year seasons, hollows are the most important refuge during extreme cold and extreme hot seasons. In addition, turtle recaptures evidence a recurrence and aggregative pattern in the use of refuges. This information provides insight into the key aspects of the microhabitat requirements of the species and will be certainly useful in mitigating and preventing negative effects of the current stream management policies. It is worth highlighting the need to keep the stream margins unaltered to favor the presence of turtles in urban environments.
Abstract Two dimensions of the ecological niche (diet and habitat) of a snake assemblage from an endemic rich area in east-central Argentina, the Sierras de Ventania mountain chain, were analyzed. ...Field data collection was performed in 15-week study periods between 2010 and 2014. Snakes were hand-captured using transect surveys. Field observations on diet were analyzed together with stomach content data from museum specimens. Our results supported the partitioning of the snake assemblage by both habitat use and diet into at least three functional groups: species restricted to microhabitats under rocks and with a diet composed exclusively of ants (Epictia australis); species found mostly in stream microhabitats and feeding mainly upon anurans (Erythrolamprus poecilogyrus and Lygophis elegantissimus); and species found mostly in grassland microhabitats, with specialized diets of terrestrial prey items (Philodryas patagoniensis and Bothrops alternatus). Consistent with previous work, diet was more important than habitat in explaining ecological niche partitioning of this snake assemblage. Our results showed that high overlap values of microhabitat use were compensated by low overlap values of the trophic niche dimension, thus matching the traditional complementary niches hypothesis.
Bufonid toads of the Rhinella granulosa species group are reported to have paired prenasal bones typically absent in other bufonids. The homology of the prenasal bone is explored throughout ontogeny ...herein by studying larvae, froglets, and adult R. fernandezae. I found that these putative bones are actually part of the enlarged and exposed anterior ends of the septomaxillae. An unpaired prenasal bone not previously described for other toads was found at the anterior end of the snout of R. fernandezae. Its position, origin, and shape indicate this bone is a homologue with the prenasal described for some casque-headed hylids.
Knowledge of parasites in turtles is scarce, particularly with regard to freshwater turtles of South America. Here, we describe the association of Spiroxys contortus (Rudolphi, 1819)in Phrynops ...hilarii (Duméril & Bibron, 1835) and S. contortus and Hedruris orestiae (Moniez, 1889) in Hydromedusa tectifera (Cope, 1870). The presence of S. contortus in P. hilarii represents a new host record and also the southernmost geographic record for this species. More interestingly, the presence of H. orestiae in H. tectifera represents the first record of this helminth species from a reptilian host.
We here describe the skull in four species of the three genera of the tribe Hydropsini (Serpentes: Dipsadidae: Xenodontinae): Helicops infrataeniatus, H. leopardinus, Hydrops caesurus and Pseudoeryx ...plicatilis. We compare them with several genera of Dipsadidae. We found that the unpaired foramen on the parabasisphenoid with anterior position is the only skull feature shared by all Hydropsini genera. This feature also occurs in semi-aquatic (Erythrolamphrus semiaureus) and fully-aquatic (Farancia abacura) dipsadids. All species of Hydrops with available skull descriptions and Pseudoeryx plicatilis share four features: (1) The anterior border of the angular is higher than the posterior border of the splenial, (2) the vomerine processes of the premaxilla are long, (3) the ascending process of the premaxilla overlaps the horizontal lamina of the nasals, and (4) an anterior projection of the prefrontal is present. All species of Helicops with available skull descriptions and Pseudoeryx plicatilis share three features: (1) A vertical lamina of the nasal with a notch, (2) a single foramen rotundum, and (3) the presence of a ventral projection of the transverse crista of the basioccipital. Finally, we found small, paired parietal foramina in most of the dipsadids studied here, which are filled with a Sudan-Black-positive tissue of possible nervous origin.
In this study we describe some ecological features of Kinosternon scorpioides scorpioides from a section of the Argentina's Chaco ecoregion encompassing the provinces of Salta, Chaco, and Formosa, ...including the description of the capture sites and an analysis of the feeding ecology of the species. Six field trips were made during the spring and summer months from 2016 to 2020. We captured 23 turtles: 8 in Salta, 8 in Chaco, and 7 in Formosa; all corresponding to the dry portion of the Chaco ecoregion. They were found in a variety of aquatic environments (including those with considerable waste and human disturbance), and they also seemed to tolerate some fragmentation of the forest matrix. The analysis of 20 stomach contents and 14 fecal samples corroborated that K. s. scorpioides is predominantly an opportunistic omnivore, capable of feeding upon a diverse variety of invertebrates, some small vertebrates, and large volumes of vegetal material. The present study provides some baseline information about habitat requirements and feeding habits of the southernmost known populations of K. s. scorpioides.
Abstract Introduction: The frequent use of pesticides is currently considered a cause of environmental pollution due to the high rate of entry of these substances into agroecosystems. This ...constitutes a risk for the species that inhabit these ecosystems, in particular anurans whose characteristics make them prone to exposure to and interaction with environmental pollutants. Objective: To report the occurrence of abnormalities in larvae of the common toad Rhinella arenarum inhabiting ponds surrounded by agroecosystems. Methods: In two consecutive springs (2015 and 2016), reproductive events of common toads were monitored in temporary pond systems in agricultural and non-agricultural areas, located near the city of La Plata (Buenos Aires, Argentina). The physicochemical parameters of the ponds were measured, and the stage of each reproductive event was recorded, such as the numbers of adult toads, amplexus and clutches. In the laboratory, the larvae were measured and photographed, their stage of development was recorded, and their morphology was examined under a stereomicroscope. Representative samples (normal and abnormal) from each pond studied were processed for histopathological analysis. Results: In the field studies carried out on a population of R. arenarum collected in an agroecosystem, a lower number of reproductive adults and clutches were observed in relation to the population of a non-agricultural pond. A total of 1 910 larvae were collected: 529 and 1 381 larvae from ponds located in non-agricultural and agricultural areas, respectively. Larvae from the agroecosystem showed two types of abnormalities: severe tail flexure and abdominal bloating. In addition, five degrees of severity could be determined in relation to abdominal bloating. Conclusions: This work reports the high frequency and severity of abnormalities observed in the early stages of R. arenarum larvae living within an agroecosystem, providing evidence of the negative impact that agricultural activities cause on aquatic ecosystems surrounded by farming areas.
Six species of freshwater turtles dominate the Chaco-Pampa Plain in southern South America and their parasites have been relatively understudied, with most records concentrated in Brazil. ...Particularly in Argentina, there are only scattered records of parasites for most of the turtles that inhabit the region, leaving a large knowledge gap. The purpose of the present contribution is to increase the knowledge of the internal parasites of six species of freshwater turtles from Argentina, after 15 years of fieldwork, by providing new hosts and additional geographic records for many host-parasite relationships. Some molecular sequences of the studied parasites were provided as a tool for better species identification. We processed 433 stomach and fecal samples from live individuals and visceral and soft tissue samples from 54 dissected turtles collected from a wide range and different ecoregions. We found 6230 helminths belonging to 18 taxa (one cestode, 11 digeneans and six nematodes). Fourteen new parasite-host associations are reported here, and for the first time parasites are recorded for
This work contributes significantly to the knowledge of the parasitofauna in freshwater turtles in Argentina, providing a detailed list of parasites present in each turtle species and reporting molecular characters for future studies.
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