Especialização fisiológica e bioquímica por adaptação térmica em duas espécies simpátricas da Amazônia central (Paracheirodon axelrodi Schultz, 1956 e Paracheirodon simulans Géry, 1963) (Charachidae)

Abstract

A central question in evolutionary biology is to understand phenotypic and genetic diversity throughout natural selection, especially regarding sympatric diversification. Sympatric species are used as model to study the causes and mechanisms of ecological and evolutionary diversification. Paracheirodon axelrodi and Paracheirodon simulans are simpatric and sintopic species that inhabit floodplain areas in the medium Negro River. Previous works show that these two species have nearly identical life cycles and feeding strategies, suggesting that niche segregation relies on thermal microhabitats. We have investigated the physiological and biochemical divergence in these congeners. It was hypothesized that these species differ in physiology with respect to the experienced temperature of acclimatization, i.e., the experienced temperature in their natural habitats. Therefore, the present work aimed to describe the biochemical and physiological adjustments to temperature in these species, and point the possible effects of future climate changes. Comparison between these two species was done for: thermal tolerance; critical oxygen tension; metabolic rate; and enzymes of energy metabolic pathways (CS, MDH and LDH) in fishes acclimated to different temperatures. Our results show a larger thermal tolerance in P. simulans, high energetic metabolic rate and enzymes activity. These results showed that P. simulans has a better energy budget that provide them adaptation to survive at higher temperatures. In conclusion, temperature gradient is a plausible scenario for sympatric speciation of neon’s tetra in floodplain areas of Negro River.