Variation in body size represents one of the crucial raw materials for evolution. However, at present, it is still being debated what is the main factor affecting body size or if the final body size is the consequence of several factors acting synergistically. To evaluate this, widespread species seem to be suitable models because the different populations occur along a geographical gradient and under contrasted climatic and environmental conditions. Here we describe the spatial pattern of variation in body size and sexual size dimorphism in the snouted treefrog Scinax fuscovarius (Anura, Hylidae) along a 10°range in latitude, 25°longitude, and 2000 m in altitude from Argentina, Brazil and Paraguay using an information-theoretic approach to evaluate the support of the data for eight a priori hypotheses proposed in the literature to account for geographical body size, and three hypotheses for sexual size dimorphism variation. Body size of S. fuscovarius varied most dramatically with longitude and less so with latitude; frogs were largest in the northwestern populations. Body size was positively related with precipitation seasonality, and negatively with annual precipitation. Furthermore, the degree of sexual size dimorphism was greatest in the western populations with less annual precipitation, as the increase in body size was stronger for females. Our results on body size variation are consistent with two ecogeographical hypotheses, the starvation resistance and the water availability hypotheses, while our results on sexual size dimorphism in S. fuscovarius supports the differential-plasticity hypothesis but the inverse to Rensch's rule and the parental investment hypothesis. Due to the weak association between environmental variables and body size and sexual size dimorphism variation, we stress that there are other factors, mainly those related to the life history, driving the geographical variation of S. fuscovarius.
ABSTRACT Species tend to be less abundant at the limits of their geographic distribution. Giant and lesser anteaters have their southernmost limits in Argentina and Paraguay, where scarce information exists regarding their ecology and conservation. We present a study carried out in the Paraguay River floodplain, in an area dedicated to cattle rearing using native grasses in a subtropical flooded savanna associated with naturally occurring forest islets, wetlands and palm groves. Using camera-traps within three different forest types, we estimated parameters related to habitat preference, social behavior and activity patterns of both species. Results show that capture success was greater in the Floodable sub-humid forest islets (FSF), compared to other types of forests: Riparian forests associated with wetlands (W-RF) and Mesoxerophytic semi-deciduous forests dominated by Schinopsis balansae (MXF). Most detections corresponded to solitary anteaters, although mother-young pairs were occasionally observed during summer. Both species showed a nocturnal and crepuscular activity pattern with a peak of records around midnight. Myrmecophaga tridactyla was detected between 11°C and 26°C, while Tamandua tetradactyla occurred between 15°C and 23°C. Future research that incorporates systematically taken data in other different habitats, including grasslands and shrublands, during all seasons of the year is recommended.
Four species of Pseudopaludicola, Pseudopaludicola boliviana, P. falcipes, P. mystacalis and P. ternetzi, are usually cited for Paraguay. However, after analyzing 407 specimens assigned to this genus in herpetological collections of the country, we conclude that there are no specimens of P. falcipes in Paraguayan collections or vouchers cited in the literature, and almost all individuals referred to P. ternetzi are most probably P. ameghini. At the same time, a recently described species, P. motorzinho, is recorded for the first time in the country. Information on the distribution of these and the remaining species of Pseudopaludicola in Paraguay (P. boliviana and P. mystacalis) is provided.
Ontogenetic colour change (OCC) is defined as the progressive and non-reversible process of changes in colouration of organisms associated with their development. Among the many vertebrate groups, amphibians are particularly impressive for their strikingly wide variety of colours, colour patterns, and signals, whose evolutionary and ecological significance have been poorly studied. Elachistocleis comprises 18 species currently separated into two main groups based on their ventral colour pattern: one immaculate and the other with specks and/or colour patches. Elachistocleis haroi is a small-sized species within the immaculate venter group, distributed in the Yungas and Dry Chaco ecoregions from which little information is known. In a comprehensive sampling of post-metamorphic individuals of E. haroi at different stages of development we identified a significant variation in ventral colour pattern, which could denote a progressive filling of yellow colour according to an ontogenetic pattern. To test this hypothesis, we analysed 39 post-metamorphic individuals of E. haroi at different stages of development with imaging procedures. We found that yellow spots and their intensity are significantly related to snout-vent length, as major expansion of colour on the sides, gular region and male chest, as almost no development on the belly. We briefly discuss our findings in relation to sexual display and predation avoidance. To our knowledge, this is the first analysis of post-metamorphic OCC in ventral colouration in the genus Elachistocleis.
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