Palms of Madagascar meeting in Leipzig

In the beginning of February, I organised a kick-off meeting for Laura Mendez‘ PhD project on “Genomic signatures of palms on Madagascar” – 3 days of discussions at iDiv in Leipzig (Germany). The team includes palm, frugivory and Madagascar experts from Kew Botanical Gardens, Aarhus University, University of Amsterdam, Bochum Botanical Gardens and iDiv – all important collaborators on Laura’s PhD project. The discussions ranged from deciding which species she will sample on Madagascar next summer, to clarifying the specific hypotheses and learning about historical demographic modelling techniques using Rad-seq data. A couple of very valuable and ‘fruitful’ days.

IMG_5798From left to right: John Dransfield, Chris Barratt, Daniel Kissling, Laura Mendez, Renske Onstein, Alex Zizka, Adriana Alzate, Wolf Eiserhardt, Wolfgang Stuppy, Jun Lim, Bill Baker.

New article published in Proceedings of the Royal Society B

Also see the press release from the University of Amsterdam.

Global change, such as climate changes, may have two outcomes with respect to biodiversity: species will adapt, or they will go extinct. In this article, we address this question from a historical perspective, focusing on the Quaternary (the last 2.6 Ma), a period characterised by rapid global changes. We show that in some parts of the world palm trees with very large fruits have adapted to global change, whereas in other parts they seem to have gone extinct.  The results were published in the journal Proceedings of the Royal Society B.

Palmplants crow smaller fruits

Global change – such as climate change, habitat fragmentations or the extinction of large-bodied animals , such as giant sloths, may force species to adapt or go extinct. In particular, plants with very large fruits that rely on large-bodied animals for the dispersal of their seeds may face a problem: can they adapt quick enough, or will global change drive them ultimately to extinction?

During the last 2.6 million years,  Latin American palms with the largest fruits seem to have gone extinct with increasing rates, whereas large-fruited palms in South-East Asian regions seem to be adapting by producing smaller fruits. Small enough to be eaten and dispersed by birds and bats. These were the results of Onstein and her team which consisted of researchers from the Netherlands, UK, France, Sweden and Denmark. They collected data for more than 2000 palm species across the globe.

Fruits need to become smaller

The absence of certain fruit-eaters, such as large hornbills, elephants or giant tortoises, may require plants with large, ‘megafaunal’ fruits to evolve ‘new’ fruits. This is similar to the selection by humans for fruits (such as papayas or mangos) to become bigger and bigger. However, instead of becoming bigger, these fruits naturally have to become smaller, to adapt to the small-bodied animals that are still there to disperse their seeds. A lack of dispersal may, alternatively, lead to their extinction.

‘Although it is difficult to see the long-term results of current global change, global change has been happening in the deep past as well, especially during the last 2,6 million years,’ says Onstein. ‘We therefore use the past as our experimental set-up to understand how current and future global change may affect these palms with very large fruits.’

Onstein thinks that the dramatic changes in climate, habitat fragmentation and megafauna extinctions that have happened in Latin America over the last 2.6 million years may have been the cause of the increasing extinction of palms. In South-East Asian regions, on the other hand, palm dispersal by flying animals such as birds and bats may have been important to escape the dramatic effects of global change. Palms seem to have had enough time to adapt to these flying animals by evolving smaller fruits.

The future of palms

How does the future of these palms with big fruits look like? There are still at least 220 palm species worldwide that bear these massive fruits larger than 4 cm in length. ‘Large-fruited plants have it increasingly difficult to survive in our human dominated world’, says Daniel Kissling, associate professor and senior author of the study. ‘The loss of large animals in tropical rainforests, e.g. due to hunting, illegal trade, and habitat loss, has a massive effect on tropical biodiversity. It leads to a reduced seed dispersal and less regeneration of these tall and massive plants. This has even the potential to significantly erode the carbon storage of tropical rainforest because large-fruited trees also store most carbon.’

The increasing human pressure and hunting of the still existing megafauna will certainly have cascading effects on the plants they feed on. Whether all palms will be able to adapt to the loss of large-bodied animal dispersers has to be seen.

Publication

Onstein RE, Baker WJ, Couvreur TLP, Faurby S, Herrera-Alsina L, Svenning J-C, Kissling WD. ( 2018 ). To adapt or go extinct? The fate of megafaunal palm fruits under past global change. Proceedings of the Royal Society BBiological Sciences, 285, 20180882.

New article published in Nature Ecology & Evolution

rainforest Borneo2 editBy dispersing the seeds of plants, fruit-eating animals contribute to the possibility of increased plant speciation and thus biodiversity. These are the findings of our study published on Monday, 23 October (2017) in Nature Ecology & Evolution.

The article is available here, and I wrote a blog post on the Nature community website. Other outreach is available from here (in English) and here (in Dutch). In case you do not have access to the pdf, send me an email and I’ll happily send it to you (onsteinre@gmail.com).

My first time in the rain forest was during a gap year after high school, now more than 12 years ago. My parents had inspired me to follow in their footsteps, and when arriving at Bangkok airport, Thailand, I immediately took a bus up north, to see the remaining rain forest and its treasures with my own eyes.

Fruits of the palm Cryosophila warscewiczii

The diversity of plants and animals, the rain forest sounds and smells, as well as the alarming noise of chainsaws, all encouraged me to study biology in the years that followed. Palms, amongst the most charismatic and recognisable elements of rain forests, immediately caught my attention. They appeared in so many shapes and forms, and I found out that in total there are almost 2600 species worldwide. Their fruits in particular intrigued me: ranging from tiny red berries to huge brown ‘megafaunal’ fruits, up to 12 cm in length. Almost all palm species depend on fruit-eating animals such as chimpanzees, elephants or hornbills for their seed dispersal. Interestingly, palms with large, megafaunal fruits are exclusively dispersed by large-bodied mammals (‘megafauna’) that were highly diverse in the past, but have nowadays gone largely extinct. My trip to the rain forest inspired me to ask questions that ultimately led to his study. Why are palms so diverse? Has their intricate relationship with fruit-eating animals perhaps contributed to their diversification?

Although palms are extraordinarily species-rich, it remains unclear which factors are responsible for this diversity. I expected that the historical interaction of megafaunal-fruited palms with megafaunal animals likely reduced their speciation rate as compared to smaller-fruited palms, because of increased gene flow between populations, reducing the chances of geographic speciation. With this study we show that small fruit sizes do indeed increase speciation rates in palms. However, fruit size is not the only important driver of speciation: understory growth form and the colonisation of islands also contribute to increased speciation. The highest speciation rate was found for palms that are dispersed by birds and bats that are able to fly long distances across oceanic barriers, allowing them to colonise isolated islands in South-East Asia and the Pacific.

These results provide important insights for the future of biodiversity. The ongoing extinction of biodiversity worldwide has dramatic consequences for ecosystem functioning and human well-being. Our study emphasises the need to protect not just single species or habitats, but also to restore interactions between species, such as those between fruit-eating animals and their food plants, in areas where these have been lost.

Publication: https://www.nature.com/article…

R.E. Onstein, W.J. Baker, T.L.P. Couvreur, S. Faurby, J.-C.Svenning & W.D. Kissling: ‘Frugivory-related traits promote speciation of tropical palms’, in Nature Ecology & Evolution (23 october 2017). DOI: 10.1038/s41559-017-0348-7

rainforest Borneo edit

IBS conference, Tucson

Last week I attended the 8th Biennial conference of the International Biogeography Society in Tucson, Arizona (U.S.A.). The conference included symposia on modelling large scale ecological and evolutionary dynamics, experimental macroecology and building up biogeography from process to pattern. I presented the first results of my work on what may happen to megafaunal-fruited palm lineages under rapid global environmental change. These species with anachronistic fruits (> 4 cm in length) suffer from dispersal limitation because of recent extinctions of their large-bodied (megafauna) fruit and seed dispersers, such as gomphotheres, ground sloths and glyptodonts. However, we do not know how these palms have survived and evolved in the past – and whether they have suffered from extinction previously, during Quaternary climate change for example. In this talk I showed how over the last 2.6 million years (the Quaternary) these megafaunal-fruited palm lineages have experienced increasing extinction rates, but only in the Americas, and how they have evolved smaller fruits in Southeast Asia and Australasia. These smaller fruits may be adaptations to bird-dispersal in these dynamic island systems.