Simon Monique Nouailhetas, Ribeiro Pedro Leite, Navas Carlos Arturo
Department of Physiology, Institute of Biosciences, University of São Paulo, Rua do Matão, travessa 14, CEP: 05508-090 São Paulo, Brazil.
J Therm Biol. 2015 Feb;48:36-44. doi: 10.1016/j.jtherbio.2014.12.008. Epub 2014 Dec 16.
Tropical ectothermic species are currently depicted as more vulnerable to increasing temperatures because of the proximity between their upper thermal limits and environmental temperatures. Yet, the acclimatory capacity of thermal limits has rarely been measured in tropical species, even though they are generally predicted to be smaller than in temperate species. We compared critical thermal maximum (CTmax) and warming tolerance (WT: the difference between CTmax and maximum temperature, Tmax), as well as CTmax acclimatory capacity of toad species from the Atlantic forest (AF) and the Brazilian Caatinga (CAA), a semi-arid habitat with high temperatures. Acclimation temperatures represented the mean temperatures of AF and CAA habitats, making estimates of CTmax and WT more ecologically realistic. CAA species mean CTmax was higher compared to AF species in both acclimation treatments. Clutches within species, as well as between AF and CAA species, differed in CTmax plasticity and we discuss the potential biological meaning of these findings. We did not find a trade-off between absolute CTmax and CTmax plasticity, indicating that species can have both high CTmax and high CTmax plasticity. Although CTmax was highly correlated to Tmax, CTmax plasticity was not related to Tmax or Tmax coefficients of variation. CAA species mean WT was lower than for AF species, but still very high for all species, diverging from other studies with tropical species. This might be partially related to over-estimation of vulnerability due to under-appreciation of realistic acclimation treatments in CTmax estimation. Thus, some tropical species might not be as vulnerable to warming as previously predicted if CTmax is considered as a shifting population parameter.
由于热带变温动物的热上限与环境温度接近，目前它们被认为更容易受到气温上升的影响。然而，尽管通常预计热带物种的热限适应能力比温带物种小，但很少对热带物种的热限适应能力进行测量。我们比较了来自大西洋森林（AF）和巴西卡廷加（CAA，一个高温半干旱栖息地）的蟾蜍物种的临界热最大值（CTmax）和耐热性（WT：CTmax与最高温度Tmax之间的差值），以及CTmax的适应能力。适应温度代表了AF和CAA栖息地的平均温度，使得对CTmax和WT的估计更符合生态实际情况。在两种适应处理中，CAA物种的平均CTmax均高于AF物种。物种内部以及AF和CAA物种之间的窝卵数在CTmax可塑性方面存在差异，我们讨论了这些发现的潜在生物学意义。我们没有发现绝对CTmax与CTmax可塑性之间存在权衡，这表明物种可以同时具有高CTmax和高CTmax可塑性。尽管CTmax与Tmax高度相关，但CTmax可塑性与Tmax或Tmax变异系数无关。CAA物种的平均WT低于AF物种，但对所有物种来说仍然非常高，这与其他关于热带物种的研究结果不同。这可能部分与在CTmax估计中由于对实际适应处理的认识不足而导致的对脆弱性的高估有关。因此，如果将CTmax视为一个动态变化的种群参数，一些热带物种可能不像之前预测的那样容易受到气候变暖的影响。
