Strong phylogenetic signal and models of trait evolution evidence phylogenetic niche conservatism for seagrasses

Abstract

Phylogenetic signal (PS) is the propensity of closely related species to resemble each other. PS has been tested across clades of terrestrial plants; however, insight for seagrasses is still lacking. Signatures of PS and models of niche (trait) evolution can help to detect phylogenetic niche conservatism (PNC), that is, close relatives live in comparable niches. The initial goal of this study was to assess the pattern of PS for the world's seagrasses, by testing the non-independence of phylogenetic relatedness and seagrass species traits. A phylogeny of 49 seagrasses was constructed, together with a matrix of nine traits covering morphological, life-history and reproductive attributes. PS of traits was tested through complementary indices (Pagel's λ, Blomberg's K, Moran's I and Abouheif's Cmean). Three models of niche evolution (Brownian Motion, BM; Ornstein–Uhlenbeck, OU; Early Burst, EB) were then fitted to each trait and the multivariate trait matrix. Results supported the existence of strong PS for seagrasses, with a particularly large effect size for seagrass reproductive traits, which followed an EB evolution model. Local Indicators of Phylogenetic Association (local autocorrelation metrics that can help to identify areas of large autocorrelation) supported the presence of PS across seagrass lineages/clades, supported by the dominance of OU as the most parsimonious trait evolution model. The pattern of strong PS seems to be a consequence of long-term PNC of seagrass traits after initial radiation. Synthesis: Our study highlights the relevance of evolution from common ancestors and shared history underpinning large seagrass phylogenetic structuring.