engleski

The role of phenotypic plasticity in the evolution of cave-adapted traits in Astyanax mexicanus

Cave dwellers are equipped with a suite of troglomorphic traits associated with survival in the highly specialized dark environment. A widely accepted model for the evolution of cave animals posits cave colonization by surface dwelling ancestors followed by the acquisition of adaptations over many generations until fully troglomorphic forms are achieved. However, the speed of troglomorphic evolution in some species is difficult to reconcile with this scenario, suggesting the importance of alternative mechanisms operating over shorter timescales. To obtain insight into these mechanisms, we exposed Astyanax mexicanus surface fish (SF) to completely dark (D/D) conditions as embryos or larvae and compared them to siblings placed on a standard photoperiod (L/D SF). We identified multiple traits that were altered in D/D SF compared to L/D SF adults raised in complete darkness for up to 2 years. These changes include differences in the expression of genes related to sensory systems, endocrine signaling, circadian rhythms, the circulatory system, and numerous metabolic changes, especially in lipids. In addition, on a phenotypic level we find alterations in metabolic rates, starvation resistance, neurotransmitter levels, and hormone levels. Remarkably, most of these traits are associated with known adaptations to caves and change in the direction of the cavefish phenotype. Therefore, contrary to the widely-accepted scenario, our results indicate that the appearance of some cave- associated traits can occur within a single generation by phenotypic plasticity. The results suggest that phenotypic plasticity followed by genetic assimilation may be an important mechanism for the rapid evolution of cave-related traits in A. mexicanus.

adaptation ; environmental change ; cave-adapted animal

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