Variability of earthworm's functional traits in eastern Amazon is more species-dependent than environment-dependent

Understanding the causes of variability in functional traits is an important question in earthworm ecology. While interspecific variation in anatomical dimensions for the same trait is well accepted, the role of environmental filters, soil degradation, and environmental stress in affecting the variability of functional traits is not well understood. In this study, we sought to determine the relative importance of environmental factors and earthworm species taxonomy on the variability in functional traits within species (intraspecific variability). We focused on eight functional traits including body mass, body length, body diameter, gizzard, gizzard thickness, septum thickness, typhlosole, and gut organic matter. We sampled earthworms of 11 different species in various regions of the eastern Amazon to determine the general responses of different species' characteristics when exposed to various ecosystem and soil conditions. Our results suggest that the functional traits of earthworms are influenced in different ways by environmental conditions. One set of traits, including body mass, body length, and body diameter, was more constant and independent of environmental variability, while another set, including gizzard diameter and length, gizzard muscle thickness, septum thickness, typhlosole, and intestinal organic matter, was more sensitive. The most affected by different environmental variables was septum thickness. We also examined which environmental factors are most important for trait variability. Our study highlights the importance of considering both environmental factors and taxonomic classification when studying the variability of functional traits within earthworm species. Overall, our results suggest that taxonomic classification alone is a good guide for estimating the major functional traits of earthworms in the Brazilian Amazon, but local conditions can their variability is which is essential for informing conservation efforts and maintaining ecosystem function. •Earthworm traits variability are better explained by accounting for soil conditions.•Body mass, length and diameter are less sensitive to variability of soil conditions.•Septa thickness variability is the most affected by environmental variables.•Taxonomic classification is a good guide to estimate functional traits.•Morphometric features should be used for gizzard development and body thickness.