Species Delimitation and Conservation in Taxonomically Challenging Lineages: The Case of Two Clades of Capurodendron (Sapotaceae) in Madagascar

Abstract

Capurodendron is the largest endemic genus of plants from Madagascar, with around 76% of its species threatened by deforestation and illegal logging. However, some species are not well circumscribed and many of them remain undescribed, impeding a confident evaluation of their conservation status. Here we focus on taxa delimitation and conservation of two species complexes within Capurodendron: the Arid and Western complexes, each containing undescribed morphologies as well as intermediate specimens alongside well-delimited taxa. To solve these taxonomic issues, we studied 381 specimens morphologically and selected 85 of them to obtain intergenic, intronic, and exonic protein-coding sequences of 794 nuclear genes and 227 microsatellite loci. These data were used to test species limits and putative hybrid patterns using different approaches such as phylogenies, PCA, structure analyses, heterozygosity level, FST, and ABBA-BABA tests. The potential distributions were furthermore estimated for each inferred species. The results show that the Capurodendron Western Complex contains three well-delimited species, C. oblongifolium, C. perrieri, and C. pervillei, the first two hybridizing sporadically with the last and producing morphologies similar to, but genetically distinct from C. pervillei. The Arid Complex shows a more intricate situation, as it contains three species morphologically well-delimited but genetically intermixed. Capurodendron mikeorum nom. prov. is shown to be an undescribed species with a restricted distribution, while C. androyense and C. mandrarense have wider and mostly sympatric distributions. Each of the latter two species contains two major genetic pools, one showing interspecific admixture in areas where both taxa coexist, and the other being less admixed and comprising allopatric populations having fewer contacts with the other species. Only two specimens out of 172 showed clear genetic and morphological signals of recent hybridization, while all the others were morphologically well-delimited, independent of their degree of genetic admixture. Hybridization between Capurodendron androyense and C. microphyllum, the sister species of the Arid Complex, was additionally detected in areas where both species coexist, producing intermediate morphologies. Among the two complexes, species are well-defined morphologically with the exception of seven specimens (1.8%) displaying intermediate patterns and genetic signals compatible with a F1 hybridization. A provisional conservation assessment for each species is provided.

A 638‐gene phylogeny supports the recognition of twice as many species in the Malagasy endemic genusCapurodendron(Sapotaceae)

“…These data suggest the possibility of reticulate evolution highly influenced by recurrent hybridization between the three taxa, which present overlapping distribution ranges (Christe & al., 2021). A more detailed revision of the complex has been presented in a separate study using additional samples and more variable genetic markers (Boluda & al., 2021).…”

“…Further collections and genetic analysis have clearly demonstrated that they are two different species. In the phylogeny, C. oblongifolium is not sister to C. perrieri , but to the third species of the clade, C. pervillei , which is clearly morphologically distinct (Boluda & al., 2021). Capurodendron oblongifolium is not sympatric with C. perrieri , but instead with C. pervillei , and its entire range is included within that of C. pervillei .…”

One in, one out: Generic circumscription within subtribe Manilkarinae (Sapotaceae)

“…Both clades have a radiation‐like topology (Glor, 2010) which is known to result in unresolved polytomies (Naciri & Linder, 2020). Recent studies suggest that this type of rapid radiation might be common in Malagasy Sapotaceae (Boluda & al., 2021, 2022; Christe & al., 2021) as well as in other Malagasy tree genera (e.g., Canarium – Federman & al., 2018; Dalbergia – Crameri, 2020). Weak support for species relationships was expected, considering that the current sampling was designed to resolve generic issues and not interspecific relationships within each genus, which will require further sampling and more analyses.…”

Two further new species in the highly-diverse Malagasy endemic genus Capurodendron (Sapotaceae)

“…It is however closely related to C. mandrarense. Together with the very distinctive C. androyense, these three species form the core of what has been referred as the "Arid Complex" (Boluda et al, 2021(Boluda et al, , 2022. 130 m, 17.II.2017, old fl.…”

“…The analysis of 638 genes (Christe et al, 2021;Boluda et al, 2022) confirmed the placement of the genus in the tribe Tseboneae (Gautier et al, 2013) and showed a massive radiation with numerous new species, upgrading Capurodendron as the richest endemic Malagasy genus with 33 described species so far. Boluda et al (2021) characterized the so-called "Arid Complex", comprising Capurodendron androyense Aubrév., C. mandrarense Aubrév., and some specimens collected north of the city of Toliara which were morphologically hypothesised to be hybrids between C. mandrarense and C. greveanum Aubrév. This complex was part of a lineage containing also C. microphyllum (Scott-Elliott) Aubrév., C. nanophyllum L. Gaut.…”