Renal morphology, phylogenetic history and desert adaptation of South American hystricognath rodents

1. To determine whether variation in kidney morphology is associated with environmental aridity in South American hystricognaths, we used conventional and phylogenetic analysis (independent contrasts) to correlate mass-independent renal variables (kidney size; relative medullar thickness, RMT; medulla/cortex ratio, MC; inner medulla/ cortex ratio, MIC; relative medullar area, RMA) with environmental variables such as precipitation, temperature and a measure of primary productivity (NDVI). 2. Body mass and most renal indexes showed significant phylogenetic signal (the tendency of closely related species to resemble each other), as well as latitude, one index of minimum daily temperature (Tmin) and NDVI, indicating that correcting for phylogenetic effects is necessary, hence results from independent contrasts are more reliable for these traits. 3. All renal indexes except RMA and MIC were significantly correlated with body mass. After correcting for size effects, inclusion of precipitation or NDVI improved significantly the regression model for kidney size and MIC regardless of the analyses employed, whereas Tmin was also a significant predictor of both indices according to independent contrasts. Precipitation was the best predictor of kidney size, with animals from dryer environments having larger kidneys. RMT was not correlated with any of the environmental indexes employed here. 4. Our results suggest that hystricognaths from environments with lower rainfall have evolved larger kidneys, probably to cope with aridity. Additional renal indices (RMT, MC and RMA) were not correlated with any environmental variable, and their relative importance as predictors of urine concentration ability for this group of rodents remains unclear.