Upper thermal tolerances and vulnerability to global warming in a Brazilian Caatinga fishAstyanax bimaculatus (Linnaeus, 1758) population

Abstract

Global warming is predicted to increase both average temperatures and the frequency and duration of heat waves. Tropical ectotherms, particularly those living in warm environments are more prone to receive heat impacts. Then, it is crucial to identify those populations already exposed to high temperatures that may be at risk of decimation by ongoing warming. We assessed heating risk in a population of the fish species Astyanax bimaculatus, inhabiting hot pools in intermittent streams in the Brazilian Caatinga ecoregion. We experimentally examined the upper thermal tolerance (CT max ), and provided estimates of warming tolerance (WT), as the difference between CT max and micro-environmental peak temperatures (T max ). Two CT max estimates ranged between 37.6 and 40.6°C, whereas pond T max ranged between 34.6 and 41.3°C. This determines very narrow, even negative WTs, for these extreme heated A. bimaculatus populations, which ultimately may determine their local extinction in the coming decades. Abstract in Portuguese is available with online material.Prevê-se que o aquecimento global aumente tanto as temperaturas m edias como a frequência e durac ßão das ondas de calor. Ectot ermicos tropicais, principalmente aqueles que habitam ambientes temperados, estão mais expostos a impactos t ermicos. Portanto, identificar populac ßões que j a estão expostas a temperaturas altas o suficiente para serem ameac ßadas pelo aquecimento atual e crucial. O risco de exposic ßão a altas temperaturas foi estabelecido na esp ecie de peixe Astyanax bimaculatus, que habita poc ßas quentes nos rios intermitentes presentes na ecorregião conhecida como Caatinga. A tolerância t ermica superior (CT max ) foi aferida experimentalmente e apresentamos medidas de tolerância t ermica (WT), definida como a diferenc ßa entre a CT max e as temperaturas m aximas registradas na escala microambiental (T max ). Duas estimativas de CT max ficaram entre 37,6°C e 40,6°C, enquanto o T max das poc ßas variou entre 34,6°C e 41,3°C. Isso determina valores muito estreitos, e at e mesmo negativos, de WTs para a populac ßão de A. bimaculatus estudada, o que pode vir a determinar sua extinc ßão em d ecadas futuras.

Plasticity of upper thermal limits of Australian Paratya spp. (Decapoda, Atyidae) and considerations of climate-change adaptation

“…The range where increasing water temperatures affect organisms is linked to their ability to survive future warming. The consequences expected will be more intense in tropical and subtropical streams as generally, stream invertebrates in these streams live closer to their physiological thermal limits (Egea-Serrano et al 2022). We observed a 2°C difference between LT 10 and LT 90 for warm water-acclimated shrimp and a 5.2°C difference for winter-acclimatised shrimp.…”