Biomarker-based assessment of the muscle maintenance and energy status of anurans from an extremely seasonal semi-arid environment, the Brazilian Caatinga.

Strongly seasonal environments pose challenges for performance and survival of animals, especially when resource abundance seasonally fluctuates. We investigated the seasonal variation of key metabolic biomarkers in the muscles of males from three species (Rhinella jimi, R. granulosa and Pleurodema diplolister) of anurans from the drastically seasonal Brazilian semi-arid area, Caatinga. We examined the expression of proteins regulating energy turnover (AMP-activated protein kinase [AMPK] and protein kinase B [AKT]), protein synthesis and homeostasis (total and phosphorylated eukaryotic initiation factor 2α [eIF2α and p-eIF2α] and chaperone proteins [HSP 60, 70, and 90]) in muscles predominantly related to reproduction and locomotion. Cytochrome c oxidase (COX) activity was also assessed as an index of the muscle aerobic capacity. The expression pattern of metabolic biomarkers indicates that the maintenance of muscular function is regulated in a species-specific manner during the drastic seasonal variation. Rhinella jimi and R. granulosa that remain active during the drought appear to maintain muscles through more energy expensive pathways including elevated protein synthesis, while the aestivating P. diplolister employs energy conservation strategy suppressing protein synthesis, decreasing chaperone expression and increasing expression of AMPK. Two (P. diplolister and R. granulosa) of the three studied species activate cell survival pathways during the drought likely to prevent muscle atrophy, and all three studied species maintain the muscle aerobic capacity throughout the year, despite the resource limitation. These strategies are important considering the unpredictability of the reproductive event and high demand on muscular activity during the reproductive season in these amphibians. SUMMARY STATEMENT: We studied seasonal variation of key metabolic biomarkers in the muscles of anurans that experience drastic variation in environmental conditions and differ in seasonal activity patterns.

Seasonal Patterns of Variation in Steroid Plasma Levels and Immune Parameters in Anurans from Brazilian Semiarid Area.

Elevated androgens and glucocorticoids displayed by males during the reproductive season have been proposed to mediate a possible trade-off between reproduction and immunocompetence. Anurans living in arid and semiarid environments display a strong seasonal reproduction, which could accentuate the variation in physiological, immunological, and behavioral parameters. We studied covariation between steroid plasma levels, morphometric variables associated with body condition and immunity, leukocyte profile, parasite load, and response to an immunological challenge across different phases of the annual life-history cycle of three anuran species from a Brazilian semiarid area. Our results showed a seasonal pattern of covariation among leukocyte parameters, kidney mass, and steroid plasma levels, with higher values measured during the reproductive season, particularly when males were sampled during calling activity. Moreover, these anurans showed a stronger response to an immunological challenge during the reproductive period. The immunosuppression during the dry period was particularly evident for the species that aestivate, indicating that the availability of energetic resources might be an important factor determining seasonal variation in inflammatory response. Intensity of the helminth infection was associated with eosinophil count but showed a more complex pattern with regard to androgens levels. These data emphasize that variations in the intensity of helminth infection might be more closely related to specific aspects of the immune response than to the general seasonal patterns of variation in steroid plasma levels, total circulating leukocytes, and inflammatory response.