Taxonomy & Evolution

Clonal female populations dominate the tropical herb genus, Hanguana

Can apomixis explain the distribution of Hanguana individuals in Singapore?

Clonal reproduction is common in plants. Apomixis is a specialised form of clonal reproduction whereby viable seeds are produced without sexual reproduction. Apomixis involves the development of seeds from fruit tissue, resulting in clonal offspring. Over a hundred tropical plant genera are included in the apomixis database but little is known about the prevalence of apomictic species within these genera. Hanguana is a genus of dioecious monocots native to southeast Asia and the Pacific islands. In Singapore, despite extensive surveys male plants have only been reported for one out of the five native Hanguana species since herbarium records began in the 1820s. The distribution of native Hanguana species in Singapore can only be explained by seed dispersal, yet the lack of male plants begs the question, is apomixis at play?

A female plant of Hanguana rubinea in habitat in Singapore. Image credit: Niissalo et al.

In their new study published in AoBP, Niissalo et al. used reduced representation genomics to observe population diversity and apomictic status of the dioecious herb genus Hanguana in Singapore. Their results suggest that most of the studied species reproduce exclusively via apomictic seeds, and form populations that are composed of single, widely distributed clones. This explains the lack of records of male plants in the area. The relationships of apomictic clones to sexual populations, for example possible hybridisation, requires further study. In this study, several triploid and pentaploid genomes were characteristic of apomictic Hanguana plants. The authors conclude that population genomics tools offer a quick and cost-effective way of detecting excess clonality and thereby inferring apomixis. In the case of Hanguana, the presence of male plants is a strong indicator of sexual reproduction, whereas genome triplication is indicative of apomictic reproduction.

Researcher highlight

Matti Niissalo comes from Finland, and he moved to the UK in 2006 to study the cultivation and taxonomy of plants, leading to his PhD in Botany at the National University of Singapore starting in 2012. Matti now works as a researcher in the molecular laboratory at Singapore Botanic Gardens.

Matti’s research focuses on the genetics of the Flora of Singapore and the plant diversity in South East Asia. His main interests are the understanding of genomic diversity across Singapore’s plant species, and in population genetic patterns of threatened species and fragmented landscapes. He hopes to contribute to the understanding of plant speciation and diversity in tropical forests, as well as to advice conservation actions in the region.

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