Joint effect of phylogenetic relatedness and trait selection on the elevational distribution of Rhododendron species

Abstract

Congeneric species may coexist at fine spatial scales through niche differentiation, however, the magnitude to which the effects of functional traits and phylogenetic relatedness contribute to their distribution along elevational gradients remains understudied. To test the hypothesis that trait and elevational range overlap can affect local speciesʼ coexistence, we first compared phylogenetic relatedness and trait (including morphological traits and leaf elements) divergence among closely related species of Rhododendron L. on Yulong Mountain, China. We then assessed relationships between the overlap of multiple functional traits and the degree of elevational range overlap among species pairs in a phylogenetic context. We found that phylogeny was a good predictor for most functional traits, where closely related species showed higher trait similarity and occupied different elevational niches at our study site. Species pairs of R. subgen. Hymenanthes (Blume) K. Koch showed low elevational range overlap and some species pairs of R. subgen. Rhododendron showed obvious niche differentiation. Trait divergence is greater for species in R. subgen. Rhododendron, and it plays an important role between species pairs with low elevational range overlap. Trait convergent selection takes place between cooccurring closely related species that have high elevational range overlap, which share more functional trait space due to environmental filtering or ecological adaptation in more extreme habitats. Our results highlight the importance of evolutionary history and trait selection for species coexistence at fine ecological scales along environmental gradients.

Evidence for divergence in phenology over morphology in response to limiting similarity in montane communities of Rhododendron

“…A common pattern across previous studies and ours is that at higher elevations, alpine species of Rhododendron tend to be more synchronized in their flowering (Hart & Salick, 2018) and more similar in morphology, for example, have smaller leaves (Zou et al, 2021). These patterns likely reflect the shorter flowering season and environmental filtering of harsher alpine climates.…”

“…Studies of Rhododendron co‐occurrence in relation to phenology, traits and relatedness have been carried out at sites elsewhere in the Hengduan Mountains (Hart & Salick, 2018; Zou et al, 2021) and the eastern Himalaya (Basnett et al, 2021; Basnett, Ganesan, et al, 2019; Basnett, Nagaraju, et al, 2019). While the methods of these studies varied and differed from ours, some pertinent comparisons can be made.…”

Testing genome skimming for species discrimination in the large and taxonomically difficult genus Rhododendron

“…Rhododendron is one of the most taxonomically difficult and speciesrich groups for species identification and phylogenetic inference due to its complex evolutionary history (Yan et al, 2015). Numerous species of Rhododendron occur sympatrically and undergo extensive interspecific hybridization and/or introgression (Ma et al, 2010;Milne et al, 2010;Yan et al, 2017Yan et al, , 2019Zou et al, 2020). Hybridization/ introgression can result in the sharing of maternally inherited plastid genomes between closely related species (Du et al, 2009), and thus the plastid genome may not track species boundaries (Hollingsworth et al, 2016;Petit & Excoffier, 2009).…”

Plant diversity and ecology on the Qinghai–Tibet Plateau

“…Therefore, monsoon duration seems to be a major factor in determining the distribution limit of this species. In the third paper, Zou et al (2021) explored the relationship between functional traits and phylogenetic relatedness along altitudinal distributions of the Rhododendron species. They found that closely related species had high trait similarity.…”