Phylogenetic signal and evolutionary relationships among traits of inland fishes along elevational and longitudinal gradients

Understanding the main drivers of species distributions is one of the main goals of ecology. However, the relationships between traits and elevational and longitudinal distributions in inland fishes, as well as their underlying evolutionary processes, have been less investigated. Thus, we aimed to quantify and assess the relationships among several types of traits resulting from species’ evolutionary histories by measuring their phylogenetic signal across inland fishes of the Iberian Peninsula. We also aimed to test for correlated evolution of these traits with elevation and stream size (i.e. stream order), to test whether a species’ suite of traits and their elevational and longitudinal niche tend to evolve together. We compiled data on 23 fish biological and ecological traits for 30 inland fish species present in the Iberian Peninsula. We quantified their phylogenetic signal using four complementary indices (Pagel’s λ, Blomberg’s K, and Abouheif’s Cmean for continuous and −D + 1 for binary traits). We used both phylogenetic and non-phylogenetic methods to evaluate the relationship among traits and their relationship with elevation and stream order. We found a significant phylogenetic signal for 65% of the studied traits. Phylogenetic signals were quite variable, but we did not detect clear differences between continuous and binary traits or among trait types (i.e. morphological, trophic, reproductive, and habitat use). Evolutionary models revealed that elevational and longitudinal distribution showed little evidence for directional trends of evolution. Hence, species elevational and longitudinal niches tend to resemble to those of the common ancestor. Many fish traits were inter-correlated as revealed by phylogenetic methods, indicating correlated evolution of pairs of traits. For example, reproductive traits such as maximum longevity, fecundity and age at maturity tended to evolve together with fish maximum length. Consequently, certain orders of fish showed shared suites of traits. Comparative methods revealed a significant positive relationship of parental care with elevation and stream order. By contrast, non-phylogenetic analyses and multivariate analyses indicated positive relationships between elevation and rheophily and lithophily, and a negative relationship between stream order and invertivory and rheophily. Overall, our results point to a notable phylogenetic signal in many traits of inland fishes and a strong phylogenetic structure in their functional traits along their elevational and longitudinal gradients. Thereby, our results contribute to an improved understanding of species’ adaptations to environmental changes with important conceptual and practical implications for minimising further species losses ​
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