Unravelling a vine : a taxonomic and conservation genetics study of Tetrastigma loheri Gagnep. (Vitaceae) in the Philippines. (2019)
Type of ContentElectronic Thesis or Dissertation
Thesis DisciplinePlant Biology
Degree NameDoctor of Philosophy
PublisherUniversity of Canterbury
AuthorsObico, Jasper John Aragonshow all
Conservation genetic studies inform conservation management that aims to maintain genetic diversity for the long-term persistence of species. To my knowledge, published conservation genetic studies are currently lacking in Cebu, a Philippine island that has a long history of deforestation and has lost nearly all of its forest cover. Consequently, the effects of habitat fragmentation on patterns of genetic diversity and genetic connectivity among the remaining forests of Cebu remain unknown. As a first step towards filling this knowledge gap, microsatellite data from Tetrastigma loheri Gagnep. (Vitaceae), a commonly encountered woody vine species in the forests of Cebu, was used in Chapter 4 of this thesis to study patterns of genetic diversity and genetic connectivity among the four largest of the few remaining forested areas in Cebu. However, indications that Philippine T. loheri is a member of a species complex, referred to as the T. loheri s.l. complex, currently complicate this effort. In Chapters 2 and 3 of this thesis, I therefore used morphological and phylogenetic approaches to test the hypothesis that T. loheri s.l. is composed of more than one species. In Chapter 2, the results of unsupervised clustering analyses of geometric morphometric and other morphological datasets of vegetative characters revealed the absence of morphologically distinct clusters of individuals. In Chapter 3, several putative species were identified by species delimitation models from DNA sequence phylogenies of T. loheri s.l., but these were statistically poorly-supported and a supervised clustering method did not result in the identification of vegetative characters that characterise them. The results of the morphometric and phylogenetic analyses presented in Chapters 2 and 3 therefore do not provide conclusive evidence in support of recognizing more than one species within T. loheri s.l. in the Philippines. Even if this conclusion proves incorrect following future research, the results still suggest that the T. loheri specimens that were sampled from Cebu for the conservation genetic study in Chapter 4 are conspecific because these specimens were resolved as part of the same clades identified by species delimitation models as putative species. This means that the microsatellite dataset that I compiled for T. loheri samples from Cebu can be used for studying patterns of genetic diversity and genetic connectivity among the remaining forested areas in Cebu. The results of these analyses did not reveal evidence of low genetic diversity, despite suggesting a relatively high level of inbreeding in each of the four forested areas. Furthermore, low levels of genetic connectivity were evident among these areas, as inferred from identifying significant genetic differentiation among them. The negative consequences of habitat fragmentation, such as inbreeding and low genetic connectivity, are likely to be greater for plant species that are less common than T. loheri and that have smaller population sizes or more restricted distributions. I therefore recommend the establishment of ecological corridors to increase genetic connectivity between the remaining forested areas with the aim of reducing the risk of inbreeding and loss of genetic diversity.