Phylogenetic structure shapes body-mass variation in soil nematodes

Abstract

Soil nematodes are abundant metazoans and widely used as bioindicators in terrestrial ecosystems, yet the influence of evolutionary history on their functional traits remains poorly understood. Here, we investigated whether phylogenetic relatedness structures body mass variation in soil nematodes, a key trait integrating form and function. Using a comprehensive dataset comprising 2554 species and a synthetic phylogeny, we conducted phylogenetic comparative analyses to quantify the phylogenetic signal in body mass and to evaluate the contributions of gender, colonizer-persister (cp) value, and trophic group. Our results revealed a significant phylogenetic signal in body mass, demonstrating that body mass was non-randomly structured with respect to phylogeny. Although body mass varied significantly with gender, cp value, and trophic group, the apparent effects of cp value and trophic group were attenuated after accounting for phylogenetic non-independence. In contrast, a significant interaction between gender and trophic group emerged only in the phylogenetically informed model, revealing context-dependent patterns of sexual size dimorphism across phylogenetically structured lineages. These results indicate that evolutionary history contributes to the observed structure of body-mass variation, and that ignoring phylogenetic relatedness can lead to biased ecological inference by conflating functional effects with lineage dependence. Our findings underscore the need to integrate phylogenetic comparative methods into soil ecology to accurately disentangle the evolutionary and ecological patterns of functional trait variation.