Variação latitudinal nos limites de tolerância e plasticidade térmica em anfíbios em um cenário de mudanças climáticas: efeito dos micro-habitats, sazonalidade e filogenia

Abstract

Under the current scenario of climate change, the inclusion of precise knowledge of individually-based thermal exposures estimates with physiological traits, allows to formulate objective metrics to assess present ectotherm vulnerability to climate change. The variation of thermal tolerance boundaries (CTmax and CTmin) can help to understand the mechanisms underlying macroecological and biogeographical patterns regarding species distributional range, species richness gradients, physiological barriers and dispersal capacities. However, there are disparities in CTmax estimates, depending on ramping rates. There are controversies about whether the benefits by employing realistic slow heating against a fast rate which avoid collateral nuisance processes that affect thermal resistance. Nevertheless, the ability of organisms to deal physiologically with global warming basically relies on two factors: (i) how close organisms are to their thermal limits in nature and, (ii) the degree to which organisms can adjust, or acclimatize, their thermal sensitivity. In the present thesis, we tested the macrophysiological hypotheses related to the physiological thermal limits and the ability to adjust them (thermal plasticity), including, whenever possible, the effect of the microhabitat structure, the thermal seasonality at different spatial scales and the phylogenetic history of species. Since the dynamic model for estimating the thermal physiological limits inherently includes an interaction between time and temperature, we will also test the latitudinal variation in the expression of hardening estimating this metric at different heating rates (fast and slow) that incorporate, simultaneously, the ability to adjust CTmax and cumulative damage to extreme temperatures. Our results showed that thermal tolerance range is higher according latitude increase due the drop of minimum temperatures which promote adaptation in cold resistance in subtropical community and for highly distributed species. The spatial and temporal thermal heterogeneity occurring in tropical and subtropical habitats, validated by our microclimatic predictors, determined species thermal adaptation and vulnerability, which reflect in the observed interspecific divergence of physiological limits within microhabitats and between seasons. That is, species tadpoles living in open areas or in hot seasons tend to have greater vulnerability and higher CTmax when compared to forest species or that reproduce in cold seasons, without variation along the studied latitudinal gradient. Although subtropical and mainly temperate species are exposed to higher thermal variability than tropical ones, hot (ARRmax) and cold (ARRmin) thermal plasticity not differed between regions, whereas were slightly higher in tropical species. We did not find relationship between basal CTmax and ARRmax, as well as, ARRmax and ARRmin. In any case, acclimation response found for CTmax was rather small in magnitude and probably insufficient to compensate alone, increased temperatures caused by climate change. The results using different rates of temperature changes unfit the predictions of greater losses in CTmax in tropical and subtropical species and are more compatible with the adaptive scenario of greater hardening compensation in most of tropical and subtropical species, mainly in the high thermotolerant species (HTS). In this context, when assessed at realistic conditions, our estimates of warming tolerances showed that amphibian tadpole species will increase vulnerability and decrease hardening expression with latitude. Our results allowed testing macrophysiological hypotheses in a refined way, including the environmental thermal heterogeneity, the species evolutionary history and the physiological traits particularities of communities and species of each of the studied regions, which contributed to the discussion about the pertinence of current macrophysiological hypotheses, generated new questions and perspectives for the continuity of research in this area.