Botany Curator Heidi Meudt and colleagues have published a paper on what is special about the diversification of plants on islands, based on an investigation of the five best-studied island archipelagos, including New Zealand. Read on to find out more about their findings on the role of whole genome duplication – also known as polyploidy – in these island floras.
Comparing the floras of five archipelagos
Islands are special places, and their remarkable native floras – and the evolutionary forces that have shaped them – are of particular interest to biologists. On islands, polyploidy may facilitate long-distance dispersal, the survival of small populations, the evolution of novel traits, increased genetic diversity, and species diversification.
We aimed to test the role of polyploidy in contributing to the diversification of plants on islands by focusing on five island systems: Hawai‘i, New Zealand, Galápagos Islands, Canary Islands and Juan Fernández Islands.
The five archipelagos vary in area, distance to the nearest continent and number of islands. By compiling available data for all native and endemic plant species and genera over these five archipelagos, we found that the islands show a 5-fold difference in the number of native genera, a 10-fold difference in the number of native species, and a 20-fold difference in the number of endemic species.
For example, the Juan Fernández Islands have the smallest flora whereas New Zealand has the largest. New Zealand and the Canary Islands have the highest prevalence of polyploidy and also the most data available for further analysis.
Testing our hypothesis on island diversification
We then came up with a conceptual model to statistically test how species diversity in island lineages varies with polyploidy and extrinsic colonization history.
Our main hypothesis is that polyploidy has played an important role in the diversification of island floras by facilitating dispersal and establishment of plants to islands, and also by generating additional diversity through varying ploidy levels.
We assembled a final dataset comprising 150 lineages representing 1,805 endemic species over four of the fie island systems.
Based on data availability of published dated phylogenies and chromosome numbers, the majority of the 150 lineages analysed were from New Zealand (66%) followed by the Canary Islands and Hawai‘i (15% each), and Juan Fernández (4%). No lineages from the Galápagos Islands could be included due to a lack of data.
Polyploidy promotes endemic diversity on islands
Overall, our statistical analysis supported the hypothesis that polyploidy contributes significantly to dispersal, colonization, and diversification of island lineages on all islands studied here. In summary, we found:
- Greater levels of polyploidy directly promoted endemic diversity on islands.
- Island lineages whose original colonizers have sister groups with many species, that had already undergone polyploidization after diverging from their sister group, and that showed increasing ploidy levels over time, had more endemic island species.
- Our results overturn the “chromosomal stasis” model for islands, as at least 12% of lineages have undergone polyploidization after arrival on the island.
- There is a surprising lack of basic data for some “classic” island systems, like the Galápagos Islands. Generating such fundamental data for additional lineages and islands is important and should be prioritised.
This research was funded by Te Apārangi Royal Society of New Zealand Marsden Fund for the project, “Whole-genome duplication in plants: what is the pathway to success?” which was granted to PI Bill Lee (Manaaki Whenua – Landcare Research) in 2017. This international collaboration has also supported other published papers including student research such as Liddell et al. (2021) and Thomas et al. (2021).
Thanks to my collaborators on this paper: Dirk C. Albach (University of Oldenburg, Germany), Andrew J. Tanentzap (University of Cambridge, UK), Javier Igea (University of Cambridge, UK), Sophie C. Newmarch (Massey University, New Zealand), Angela J. Brandt (Manaaki Whenua – Landcare Research, New Zealand), William G. Lee (Manaaki Whenua – Landcare Research, New Zealand) and Jennifer A. Tate (Massey University, New Zealand).
- Liddell LG, Lee WG, Dale EE, Meudt HM, Matzke NJ. 2021. Pioneering polyploids: the impact of whole-genome duplication on biome shifting in New Zealand Coprosma (Rubiaceae) and Veronica (Plantaginaceae). Biology Letters 17(9):2021.0297.
- Meudt HM, Albach DC, Tanentzap AJ, Igea J, Newmarch SC, Brandt AJ, Lee WG, Tate JA. 2021. Polyploidy on Islands: Its Emergence and Importance for Diversification. Frontiers in Plant Science 12:637214.
- Thomas AE, Igea J, Meudt HM, Albach DC, Lee WG, Tanentzap AJ. 2021. Using target sequence capture to improve the phylogenetic resolution of a rapid radiation in New Zealand Veronica. American Journal of Botany 108(7):1289-306.