Resolving the Tetrastigma loheri s. l. Species Complex (Vitaceae) in the Philippines: No Evidence for Recognizing More than One Species

Abstract

Tetrastigma loheri (Vitaceae) is a vine species native to Borneo and the Philippines. Because it is a commonly encountered forest species in the Philippines, T. loheri is potentially suitable for studying patterns of genetic diversity and connectivity among fragmented forest ecosystems in various parts of this country. However, previous research suggests that T. loheri is part of a species complex in the Philippines (i.e. the T. loheri s. l. complex) that potentially also contains Philippine plants identified as T. diepenhorstii, T. philippinense, T. stenophyllum, and T. trifoliolatum. This uncertainty about its taxonomic delimitation can make it challenging to draw conclusions that are relevant to conservation from genetic studies using this species. Here, we tested the hypothesis that T. loheri s. l. is composed of more than one species in the Philippines. For this, we used generalized mixed Yule coalescent (GMYC) and Poisson tree process (PTP) species delimitation models to identify clades within DNA sequence phylogenies of T. loheri s. l. that might constitute species within this complex. Although these methods identified several putative species, these are statistically poorly supported and subsequent random forest analyses using a geometric morphometric leaf shape dataset and several other vegetative characters did not result in the identification of characters that can be used to discriminate these putative species morphologically. Furthermore, the results of principal component and principal coordinates analyses of these data suggest the absence of morphological discontinuities within the species complex. Under a unified species concept that uses phylogenetic and morphological distinction as operational criteria for species recognition, we therefore conclude that the currently available data do not support recognizing multiple species in the T. loheri s. l. complex. This implies that T. loheri is best considered as a single, morphologically variable species when used for studying patterns of genetic diversity and connectivity in the Philippines.