[This was written by Fran Siebrits and published online by Wild Magazine http://www.wildcard.co.za/, 2012]

The cluster disa, a Western Cape endemic, changes its flower colour according to the area in which it grows. This chameleon-like adaptation is all in an effort to fool the iconic mountain pride butterfly into visiting it.

The mountain pride butterfly (Aeropetes tulbaghia) is the only insect that pollinates the cluster disa (Disa ferruginea). It is therefore imperative for survival that the cluster disa attracts this specific butterfly. Adding to the complexity, the mountain pride butterfly is quite fickle when it comes to feeding, preferring orange flowers in one area and red ones in another.

A recent study on the interaction between this butterfly and the cluster disa was done on Table Mountain and in Grootvadersbosch Nature Reserve in the Langeberg mountains. This research revealed the adaptability of the cluster disa to meet the fickle feeding tastes of the mountain pride butterfly.

Cluster disas have cleverly adapted to the mountain pride butterfly’s regional colour preference by developing two colour variations (or phenotypes). A red version of the cluster disa grows in the western areas of the Western Cape, while an orange variety is found towards the east of its range.

“Because the mountain pride butterfly has such localised, specific colour preferences, the cluster disa literally had to adapt to its pollinator and has changed its colours to survive,” explained Ethan Newman, researcher at Stellenbosch University.

Nectar of the cluster disa is not high in nutrients. There would therefore be little attraction for insects if the disa did not evolve to become a master of mimicry. In order to lure pollinators, the disa disguises itself to have the appearance of more nutritional, nectar-producing plants in the area. This is known as floral Batesian mimicry.

The cluster disa mimics the red-flowering iris (Tritoniopsis triticea) in the western areas of the province, and the orange-flowered red-hot poker (Kniphofia uvaria) in the eastern areas. These two plants constitute the majority of the mountain pride butterfly’s diet, hence the reason for the cluster disa mimicking the red colour of the iris in the west and the orange colour of the red-hot poker in the east.

“Because the cluster disa has responded admirably to the local colour preferences of its only pollinator, we now find two colour variations in nature,” Ethan said.

Above: Ethan Newman spends a lot of his time in the field collecting data on the cluster disa (Disa ferruginea). Photograph by Bruce Anderson.

Fun facts:

  • The largest butterfly on Table Mountain is the mountain pride butterfly (Aeropetes tulbaghia) which has a wingspan of 80mm. It is easy to identify as there are blue “eyespots” on its brown wings.
  • The cluster disa (Disa ferruginea) prefers to grow on stony slopes where there is little competition from surrounding vegetation. It ranges from the Cape Peninsula to Albertinia.
  • Floral Batesian mimicry is the adaptive resemblance of flowers from plants that don’t produce nectar or pollen to plants that do produce nectar or pollen. This functions to deceive pollinators such as insects into visiting the plant that uses this form of mimicry, which can take on similarities in floral shape, scent or colour.

Sources: Research project from Stellenbosch University – findings published in the leading scientific journal Proceedings of the Royal Society B. For more information on the Animal-Plant Interaction Research Group at Stellenbosch University, visit http://academic.sun.ac.za/botzoo/APIR/index.htm.