Anina Coetzee: Diversity is about sharing colours

In this post Anina Coetzee, lecturer at Nelson Mandela university presents her latest work ‘’Facilitation and competition shape a geographical mosaic of flower colour polymorphisms’, discusses when it is important for plants to be similar and shares her passion for fynbos.

Anina with Erica fascicularis in the Kogelberg
Anina with Erica fascicularis in the Kogelberg

Our study investigated the phenomenon of morphological diversity that is maintained in the absence of obvious divergent selective pressures. Specifically, in a group of congeneric species sharing a pollinator species.

In the fynbos biome in South Africa, sunbird-pollinated Erica species often co-occur and sometimes flower simultaneously. The unusual thing about them is that almost half of them are flower colour polymorphic (different populations of a species can have different flower colours), despite sharing a habitat and a pollinator species (the orange-breasted sunbird Anthobaphes violacea). In some species, colour polymorphisms may result from populations diverging in pollination syndrome and adapting to pollinators with different visual systems (i.e. birds and insects) that select for different flower colours. However, this could not explain the variation in bird-pollinated ericas.

Erica coccinea and Erica mammosa co-occur at the Cape of Good Hope section of Table Mountain National Park and share a pollinator species.
Erica coccinea and Erica mammosa co-occur at the Cape of Good Hope section of Table Mountain National Park and share a pollinator species.

The spatial distribution of flower colours in these ericas led us to the hypothesis that local colour convergence could help species to attract more pollinators. However, we also recognised the potential for conflict (through reproductive interference) because these congeneric species have similar flower morphologies. A sunbird could thus mix pollen between co-flowering Erica species if it visits both.

We tested whether colour similarity provided a selective advantage to the less-preferred species in each community and which factors limit colour similarity. The patterns that we found suggest that an Erica species experienced higher fitness if it mimicked the flower colour of a more preferred species to, presumably, attract more pollinators. This mimicking was only beneficial under certain conditions: when different flower morphologies or flowering patterns prevent pollen mixing of co-occurring Erica species by sunbirds.

This work helps us to understand how high levels of species and morphological diversity can be maintained. Species radiations remain a fascinating mystery and our results indicate that a combination of spatial processes and species interactions could contribute to this process.

Orange-breasted Sunbird visiting Erica coccinea (credit Callan Cohen)
Orange-breasted Sunbird visiting Erica coccinea (credit Callan Cohen)

I enjoyed this project since it combined two of my favourite study subjects:  fynbos plants and birds. I have always had an interest in understanding why species occur where they do and how species depend on each other. My exposure to research as an undergrad student fuelled these interests and led to my own research pursuits.

Currently, I am a lecturer at Nelson Mandela University, South Africa, based at the George campus which is probably one of the most beautiful places in our country. Here we are spoilt with fynbos and forest vegetation at our doorstep. I continue exploring my research interests in plant-animal interactions, conservation biology, community ecology and urban ecology. My present research focus is on the ecology and conservation of pollination systems in the fynbos and forest.

My advice to young ecologists would be to be confident in your work and persevere until you develop the skills you want. Do not lose hope when things get tough and remind yourself that everybody struggles similarly. Be humble enough to take advice and admit mistakes, this is what makes us strong and successful.

Read the article in full here.

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