Abstract
Thermal tolerance underpins most biogeographical patterns in ectothermic animals. Macroevolutionary patterns of thermal limits have been historically evaluated, but a role for the phylogenetic component in physiological variation has been neglected. Three marine zoogeographical provinces are recognized throughout the Neotropical region based on mean seawater temperature (T m): the Brazilian (T m = 26 °C), Argentinian (T m = 15 °C), and Magellanic (T m = 9 °C) provinces. Microhabitat temperature (MHT) was measured, and the upper (UL 50) and lower (LL 50) critical thermal limits were established for 12 eubrachyuran crab species from intertidal zones within these three provinces. A molecular phylogenetic analysis was performed by maximum likelihood using the 16S mitochondrial gene, also considering other representative species to enable comparative evaluations. We tested for: (1) phylogenetic pattern of MHT, UL 50, and LL 50; (2) effect of zoogeographical province on the evolution of both limits; and (3) evolutionary correlation between MHT and thermal limits. MHT and UL 50 showed strong phylogenetic signal at the species level while LL 50 was unrelated to phylogeny, suggesting a more plastic evolution. Province seems to have affected the evolution of thermal tolerance, and only UL 50 was dependent on MHT. UL 50 was similar between the two northern provinces compared to the southernmost while LL 50 differed markedly among provinces. Apparently, critical limits are subject to different environmental pressures and thus manifest unique evolutionary histories. An asymmetrical macroevolutionary scenario for eubrachyuran thermal tolerance seems likely, as the critical thermal limits are differentially inherited and environmentally driven.
Highlights
Thermal tolerance in animals depends on systemic through subcellular functions of resistance, entailing complex physiological interactions that underpin most biogeographical distribution patterns of life on Earth
Upper critical thermal limits (UL50) can predict latitude, vertical position in an intertidal environment, or the biotope occupied by different species, as they correlate positively with microhabitat temperature and are associated with mechanisms of thermal tolerance
Hypotheses regarding the effect of zoogeographical province and microhabitat temperature on the evolution of upper and lower critical thermal limits were tested using a phylogenetic generalized least squares (PGLS) model
Summary
Thermal tolerance in animals depends on systemic through subcellular functions of resistance, entailing complex physiological interactions that underpin most biogeographical distribution patterns of life on Earth. KEYWORDS 16Smt gene, comparative methods, evolutionary physiology, temperature, thermal limits, zoogeographical province, Crustacea, Decapoda Upper critical thermal limits (UL50) can predict latitude, vertical position in an intertidal environment, or the biotope occupied by different species, as they correlate positively with microhabitat temperature and are associated with mechanisms of thermal tolerance.
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