Genetic insights into the evolution of genera with the eastern Asia–eastern North America floristic disjunction: a transcriptomics analysis

Abstract

Premise Large disjunctions in species distributions provide excellent opportunities to study processes that shape biogeographic patterns. One such disjunction is the eastern Asia–eastern North America (EA‐ENA) floristic disjunction. For many genera with this disjunction, species richness is greater in EA than in ENA; this pattern has been attributed, in part, to higher rates of molecular evolution and speciation in EA. Longer branch lengths have been found in some EA clades, relative to their ENA sister clades, suggesting that the EA lineages have evolved at a higher rate, possibly due to environmental heterogeneity, potentially contributing to the species richness anomaly. Methods To evaluate whether rates of molecular evolution are elevated in EA relative to ENA, we used transcriptomes from species in 11 genera displaying this disjunction. Rates of molecular evolution were estimated for up to 385 orthologous nuclear loci per genus. Results No statistically significant differences were identified in pairwise comparisons between EA and ENA sister species, suggesting equal rates of molecular evolution for both species; the data also suggest similar selection pressures in both regions. For larger genera, evidence likewise argues against more species‐rich clades having higher molecular evolutionary rates, regardless of region. Our results suggest that genes across multiple gene ontology categories are evolving at similar rates under purifying selection in species in both regions. Conclusions Our data support the hypothesis that greater species richness in EA than ENA is due to factors other than an overall increase in rates of molecular evolution in EA.

An updated phylogeny, biogeography, and PhyloCode‐based classification of Cornaceae based on three sets of genomic data

“…With better data and methodologies available today, biogeographic studies of individual clades can provide a more accurate picture of their dynamic histories on range expansion and restriction and provide solid baseline data for understanding the origin of disjunctions and the assembly of the Earth's phytogeography. The origin of the floristic disjunction/floristic similarity between eastern Asia and North America has been of interest for the past three decades (e.g., Qian and Ricklefs, 2000; Xiang and Soltis, 2001; Donoghue and Smith, 2004; Ricklefs et al, 2004; Harris et al, 2013; Dong et al, 2019; Melton et al, 2020, 2022; see reviews by Wen, 1999; Wen et al, 2010, 2016). Clearly, detailed biogeographic studies of disjunct clades based on robust, dated, comprehensive phylogenies inferred from genome‐wide data using modern methodology are particularly valuable for evaluating hypotheses derived from previous meta‐analyses or synthesis (e.g., Donoghue and Smith, 2004; Wen et al, 2010) that were based on early methodology.…”

“…An updated classification is proposed using the PhyloCode with the hope to stabilize the names of this taxonomically highly controversial group. During the past two decades, the dogwood genus has become a model clade for bridging macro‐ and microevolution (Fan et al, 2004, 2007; Xiang et al, 2005, 2008; Xiang and Thomas, 2008; Zhang et al, 2008; Yu et al, 2017; Dong et al, 2019; Lindelof et al, 2020; Melton et al, 2020), for integrating phylogenetics, evolution, and developmental biology and molecular genetics (Feng et al 2009b, 2011, 2012, 2013; Liu et al, 2013; Zhang et al, 2013; Geng et al, 2016; Liu et al, 2016, 2017, 2019; Ma et al, 2017), and for integrating evolution with genetics, metabolomics, physiology, and/or ecology (Karlson et al, 2004; Sarnighausen et al, 2004; Call et al, 2016; Pais et al, 2017, 2018, 2020; Zhou 2021). Our study is also an important step facilitating further comparative studies, via a robust phylogeny that we provide as a framework for synthesizing different dimensions of dogwood biology that have been studied for many decades (e.g., Bate‐Smith et al, 1975; Eyde, 1988; Murrell, 1993, 1994; Xiang et al, 1993, 1998; Noshiro and Baas, 1998, 2000, and subsequent publications from the Xiang lab).…”

Species in lichen-forming fungi: balancing between conceptual and practical considerations, and between phenotype and phylogenomics

“…org] is an excellent source. When considering potentially applicable names, always take into account the geographic origin but consider known broad disjunctions, such as western North American vs. Central Asia (Weber 2003;Melton et al 2020) 5. If the degree of non-fittingness of the sample is deemed sufficient to consider a novelty and no applicable name appears to exist, the sample should be formally described.…”

Phylogenetic diversity of eastern Asia–eastern North America disjunct plants is mainly associated with divergence time

“…Some have suggested that floristic regions in EA possess more complex habitats, larger spans of vegetational continuity, and more connections with tropical floristic elements than those in ENA ( Wen, 1999 ; Milne and Abbott, 2002 ). Moreover, a higher rate of molecular evolution in EA has been proposed to be tightly linked to the species diversity anomaly in the EA−ENA disjuncts ( Xiang et al., 2004 ), although recent work indicates that such a pattern does not hold for all disjunct genera ( Melton et al., 2020 ).…”