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Phenotypic plasticity has been suggested as the main mechanism for species persistence under a global change scenario, and also as one of the main mechanisms that alien species use to tolerate and invade broad geographic areas. However, contrasting with this central role of phenotypic plasticity, standard models aimed to predict the effect of climatic change on species distributions do not allow for the inclusion of differences in plastic responses among populations. In this context, the climatic variability hypothesis (CVH), which states that higher thermal variability at higher latitudes should determine an increase in phenotypic plasticity with latitude, could be considered a timely and promising hypothesis. Accordingly, in this study we evaluated, for the first time in a plant species (Taraxacum officinale), the prediction of the CVH. Specifically, we measured plastic responses at different environmental temperatures (5 and 20°C), in several ecophysiological and fitness-related traits for five populations distributed along a broad latitudinal gradient. Overall, phenotypic plasticity increased with latitude for all six traits analyzed, and mean trait values increased with latitude at both experimental temperatures, the change was noticeably greater at 20° than at 5°C. Our results suggest that the positive relationship found between phenotypic plasticity and geographic latitude could have very deep implications on future species persistence and invasion processes under a scenario of climate change.

Several studies have claimed that reduction in body size comprises a nearly universal response to global warming; however, doubts about the validity of this pattern for endothermic species have been raised recently. Accordingly, we assessed temporal changes in body mass for 27 bird and 17 mammal species, to evaluate if a reduction in body size during the 20th century is a widespread phenomenon among endothermic vertebrates. In addition, we tested if there are differences in the temporal change in size between birds and mammals, aquatic and terrestrial species, and the first and second half of the 20th century. Overall, six species increased their body mass, 21 species showed no significant changes in size, and 17 species decreased their body mass during the 20th century. Temporal changes in body mass were similar for birds and mammals, but strongly differ between aquatic and terrestrial species: while most of the aquatic species increased or did not change in body mass, most terrestrial species decreased in size. In addition, we found that, at least in terrestrial birds, the mean value of the correlation between body mass and year of collection differs between the first half and the second half of the 20th century, being close to zero for the former period but negative for the later one. To our knowledge, this is the first study showing that temporal changes in body mass differ between aquatic and terrestrial species in both mammals and birds.

One of the most generalized conclusions arising from studies analyzing the ecological variation of energy metabolism in endotherms is the apparent negative correlation between ambient temperature and mass-independent basal metabolic rate (residual BMR). As a consequence, ambient temperature has been considered the most important external factor driving the evolution of residual BMR. It is not clear, however, whether this relationship is size dependent, and artifacts such as the biased sampling of body masses in physiological data sets could cause us to overstate the ubiquity of the relationship. Accordingly, here we used published data on body mass (m b), BMR, and annual mean temperature (Tmean) for 458 mammal species (and/or subspecies) to examine the size dependence of the relationship between temperature and BMR. We found a significant interaction between m b and Tmean as predictors of residual BMR, such that the effect of Tmean on residual BMR decreases as a function of m b. In line with this, the amount of residual variance in BMR explained by Tmean decreased with increasing m b, from 20%–30% at body sizes of less than 100 g to almost 0 at body sizes greater than 1,000 g. These data suggest that our current understanding of the importance of broad-scale variation in ambient temperature as a driver of metabolic evolution in endotherms probably is affected by the large number of small species in both nature and physiological data sets.

Abrothrix olivacea (Waterhouse, 1837), the olive grass mouse, is a widely distributed sigmodontine rodent that inhabits a broad range of environments, from the hyper arid deserts of southernmost Perú and northern Chile to the Patagonian steppe to the humid temperate rainforests of southern South America. Its extensive ecological breadth, coupled with physiological adaptations to water scarcity, makes it an ideal model for studying environmental responses and phenotypic plasticity. Here, we present the first de novo scaffold-level genome assembly of A. olivacea , generated from short-read DNA sequencing. The 2.25 Gb assembly achieved a scaffold N50 of 123 Mb and a BUSCO completeness score of 98.61%, indicating high sequence completeness. Genome annotation identified 21,476 protein-coding genes, providing a valuable resource for evolutionary, ecological, and functional genomics. As a case study, we used this reference genome to explore gene expression and genetic divergence in kidney tissue from individuals inhabiting contrasting environments: the southern Andean rainforest and the Patagonian steppe. By integrating single-cell transcriptomic data from Mus musculus , we performed cell type deconvolution, revealing environment-specific expression patterns linked to renal function. This new genomic resource opens avenues for investigating local adaptation, population structure, and conservation genetics in one of South America's most ecologically versatile and widely distributed rodents.

Since the Asian golden mussel, Limnoperna fortunei, was first reported in the Río de la Plata in the 90’s, its invasion has continuously expanded throughout South America, promoting several negative ecosystem consequences. Several fish species consume and assimilate large fractions of L. fortunei in their biomass, partially controlling the abundance of this invader, but potential fish dietary and trophic niche modifications caused by the invasion have not been studied in deep. Through gut content, stable isotopes and gut morphometry analysis of field-collected and historical museum samples, the potential dietary, trophic niche and physiological consequences of the invasion for two predatory fish of the golden mussel were surveyed. The analysis of historical samples of some of the most frequent and abundant L. fortunei consumers, such as Megaleporinus obtusidens and Pimelodus maculatus, revealed changes in trophic niche when fish started to incorporate L. fortunei. Specifically, an increase in trophic position and a reduction in diet diversity was observed for both predators. Also, a reduction in dietary generalism occurred for M. obtusidens. Furthermore, the digestive tract mass of this species decreased after the invasion, that is, in parallel to a markedly increase in the consumption of animal material. This research raised several questions about the potential effect of L. fortunei on growth rates and abundances of M. obtusidens and P. maculatus, two of the most important species in commercial fisheries in the Uruguay river. Also, it may assist in predicting food web changes to be expected in newly invaded areas.

The number of individuals to be sampled is a key element in the sampling design of any study as it directly affects the estimations and inferences made. Additionally, in cases where several replicates per individual can be taken, it is important to define how the sampling effort will be distributed between the intraindividual and interindividual components (within and between individuals, respectively). Determining how samples should be distributed among these components can help optimize the available resources and reduce bias in the estimations. To study population trophic diversity, the total niche width (TNW) is usually estimated, which is an approximation of resource diversity at the population level. TNW is the sum of the resource diversity consumed at the intraindividual (replicates) and interindividual (individuals) level. In this study, the effect of prioritizing the number of individuals or the number of replicates on the accuracy and precision of TNW estimations was tested. Multiple isotopic ( δ 13 C and δ 15 N) values per individual in populations with different degree of individual specialization were simulated. Then, isotopic data from natural populations within the same species (available published studies) were used to assess the results obtained with simulated data. It was found that TNW estimations were more accurate and precise when prioritizing the number of individuals over the replicates, along the entire individual gradient of trophic specialization. Therefore, it is advisable to prioritizing the number of individuals. This methodological contribution should be considered in future studies that use repeated measures of isotopic data to estimate TNW.

Individual trophic specialization (ITS) refers to the trophic diversification amongst individuals within a population. The gentoo penguin ( Pygoscelis papua ) is considered a trophic generalist at the population level, but little is known about its individual trophic differentiation. We assessed the degree of ITS at one of its main breeding colonies: Ardley Island, South Shetland Islands. We used skin from 19 dead individuals to determine species and sex by molecular methods and a nail for stable isotope analysis of δ 15 N and δ 13 C. Isotopic niche metrics and ITS were estimated for the population and for each sex. We found a moderately high degree of ITS associated with the trophic position of the resources consumed (δ 15 N) for the population and both sexes, as well as a moderate degree of ITS in the foraging habitat (δ 13 C) for the population and females. Females showed a higher exclusive niche area, suggesting that they use resources and foraging areas that males do not, probably related to reproductive energy demands. Given the high population density of this species, ITS could function as a mechanism to decrease intraspecific competition. This combination of genetic and isotopic tools allowed us to provide relevant information on the trophic ecology of the gentoo penguin without manipulating animals or using invasive methods.

The uneven spatial distribution of biodiversity is a defining feature of nature. In fact, the implementation of conservation actions both locally and globally has progressively been guided by the identification of biodiversity ‘hotspots’ (areas with exceptional biodiversity). However, different regions of the world differ drastically in the availability of fine-scale data on the diversity and distribution of species, thus limiting the potential to assess their local environmental priorities. Within South America—a megadiverse continent—Uruguay represents a peculiar area where multiple tropical and non-tropical eco-regions converge, creating highly heterogeneous ecosystems, but where the systematic quantification of biodiversity remains largely anecdotal. To investigate the constraints posed by the limited access to biodiversity data, we employ the most comprehensive database for tetrapod vertebrates in Uruguay (spanning 664 species) assembled to date, to identify hotspots of species-richness, endemism and threatened species for the first time. Our results reveal negligible spatial congruence among biodiversity hotspots, and that tetrapod sampling has historically concentrated in only a few areas. Collectively, our study provides a detailed account of the areas where urgent biodiversity monitoring efforts are needed to develop more accurate knowledge on biodiversity patterns, offering government and environmental bodies a critical scientific resource for future planning.

Metabolic rates are related to the pace of life. Hence, research into their variability at global scales is of vital importance for several contemporary theories in physiology, ecology, and evolution. Here we evaluated the effect of latitude, climate, primary productivity, habitat aridity, and species trophic habits, on mass-independent basal metabolic rates (BMRs) for 195 rodent species. The aims of this article were twofold. First, we evaluated the predictive power of different statistical models (via a model selection approach), using a dimensional reduction technique on the exogenous factor matrix to achieve a clear interpretation of the selected models. Second, we evaluated three specific predictions derived from a recently proposed hypothesis, herein called the \"obligatory heat\" model (OHM), for the evolution of BMR. Obtained results indicate that mean/minimum environmental temperature, rainfall/primary productivity and, finally, species trophic habits are, in this order, the major determinants of mass-independent BMR. Concerning the mechanistic causes behind this variation, obtained data agree with the predictions of the OHM: (1) mean annual environmental temperature was the best single predictor of residual variation in BMR, (2) herbivorous species have greater mass-independent metabolic rates, and tend to be present at high-latitude cold environments, than species in other trophic categories.

Abstract Plasticity of resource use represents an important strategy for fish species living in unstable freshwater environments. Trophic polymorphism (i.e. variation in the morphology of the alimentary tract) has been observed in dozens of vertebrate species in response to diet variation. The digestive tract has been reported as one of the most reactive systems. The Digestion Theory predicts that consumption of food with a high proportion of indigestible material would produce an increase in the length of the digestive tract. This response allows individuals to get energy enough even when consuming a low-quality diet. We evaluated the diet—using classical stomach content analysis and stable isotopes (nitrogen and carbon)—and the length of digestive organs of an abundant and ubiquitous fish species, the La Plata croaker (Pachyurus bonariensis Steindachner, 1879). A total of 95 individuals were captured at three sites of the lower Uruguay River, with different food supply during two sampling campaigns. We found larger digestive organs (stomach and intestine) at the site with higher sediment vegetal matter availability and, consequently, with the highest vegetal matter consumption. However, these differences in food consumption were not observed with the stable isotope analysis, probably due to the different temporal resolution of this technique. The results presented herein support one prediction of the Digestion Theory, confirming digestive flexibility as an intraspecific compensatory mechanism in a freshwater fish species.