Floral biology and taxonomic complexity in the genus Alpinia Roxb. (Zingiberaceae)
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07/12/2021Item status
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07/12/2022Author
Ranavat, Surabhi
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Abstract
The tropics harbour the highest number of species in the world. Uncovering why and
how these regions are so species-rich has been a central theme in evolutionary
biology. When it comes to plants, about two-thirds of the plant species are present in
the tropics. Research on tropical plants is impeded by an array of taxonomic
challenges. To understand these challenges in more detail, I have focused on the
genus Alpinia Roxb. from the Zingiberaceae. It is the largest genus in the ginger
family (c.250 species) and one of the most taxonomically complex. Molecular
phylogenetic studies have revealed that this genus is polyphyletic. Moreover,
nomenclatural confusion is an issue in Alpinia as many species with validly
published names were described before the development of the type concept which
has led to taxonomic confusion regarding species identities. Several Alpinia species
also possess intermediate morphological characters that cause difficulty in delimiting
species. Understanding the extent of reproductive isolation and hybridisation is
crucial in this case. These species also possess a unique stylar dimorphism termed
flexistyly, a strategy used to promote outcrossing. Many studies have investigated
the reproductive biology of flexistylous species in Alpinia, but not much is known
about the genetic basis of this trait.
Accordingly, the aims of my thesis are:
• To understand the taxonomic challenges present in the tropics.
• To resolve taxonomic uncertainty in a group of Indian Alpinia species.
• To investigate the crossing barriers and the potential for hybridisation in the
genus Alpinia.
• To elucidate the genetic basis of flexistyly.
I conducted a survey of plant biologists to investigate the taxonomic problems faced
when working on tropical taxa, and reviewed the literature to find case studies where
taxonomic issues impede research. I found that taxonomic challenges in the tropics
are caused by practical issues associated with fieldwork and herbarium collections
and biological factors such as rapid radiations, hybridisation, and phenotypic
plasticity. To resolve the nomenclatural confusion in a group of Indian Alpinia
species, I examined a range of original material and have resolved the confusion
associated with the name A. bracteata used by Roscoe and Roxburgh. I have also
assigned a lectotype for the name A. calcarata (Haw.) Roscoe. To investigate
crossing barriers, I performed artificial hybridisation between and within clades of
Alpinia s.l. I found that Alpinia species show widespread interspecific cross
compatibility, especially within clades, and in a few instances, between divergent
clades as well as genera. I also found a negative correlation between the genetic
distance and the seed set, but this correlation was not significant. To investigate the
genetic basis of flexistyly, I assembled a draft genome of Alpinia nigra that served as
a reference for downstream analysis. I used a Pool-Seq approach to investigate the
allele frequency differences between bulks of the anaflexistylous and cataflexistylous
morphs. Most of the genome showed low differentiation (average genome-wide
FST=0.04), with no clear outlier regions. This is consistent with the lack of evidence
for a large inversion. This might be due to the complex nature of the genomic
region(s) that govern this trait or it could be a single gene that might be difficult to
detect. The potential for hybridisation and the lack of reproductive isolation might be
common in gingers, and overlooked in many tropical taxa. It may be a critical factor
that caused taxonomic complexity within this tropical genus.