Cape Town - A sandy patch outside of Mamre has become the hotbed of plant evolution and observing how plants speciate.
Professor Bruce Anderson, an evolutionary ecologist in the department of botany and zoology at Stellenbosch University, said this was the third time in his research career that he has found a contact zone where speciation is happening “before our eyes”.
Using quantum dots as a tool to trace the pollen of the long-tubed iris, Lapeirousia anceps, evolutionary ecologists have succeeded in capturing a snapshot of a plant in the process of speciation. “Contact zones of entities in the process of diverging may actually be quite common, but they are hard to find because you really need to know what to look for.”
Anderson and his associates have been visiting a West Coast sandplain with fynbos in Mamre for the past 15 years. This is one of the prime spots where the long-tubed iris can be found, as well as its pollinator, the long-tongue fly - Moegistorhynchus longirostris.
“Think of the famous example of the Madagascar star orchid with its 30cm nectar tube, and Darwin’s moth with an almost equally long tongue, where the orchid and moth have co-evolved in an escalating race scenario,” said Anderson.
The same evolutionary mechanism behind the matching of pollinator tongues and floral tubes is true for the Lapeirousia. In 2009 a fellow researcher, Professor Anton Pauw, found that Lapeirousia had tube lengths which have co-evolved with the tongue lengths of its fly pollinator, Moegistorhynchus longirostris, where tongues and tubes can vary from 43mm to 86mm.
The tube length of the plants matched perfectly with the tongue-length of the pollinators, depending on the geographical location of the different populations. But in 2003, Anderson stumbled upon a strange population of Lapeirousia anceps in the Mamre area. “Some plants had short floral tubes, others long tubes, while few had tubes of intermediate length. Yet these plants were visited by only a single species of the long-tongued fly, Moegistorhynchus longirostris.”
For the next 15 years, Anderson and his colleagues studied this population and found there was a little gene flow between the two plants forms, which explained why they had remained as two separate entities for so long.
In one of the many photographs from his field work, he noticed a long-tongued fly from that area with pollen on the top of its head and then another clump of pollen halfway down its tongue. But because these plants are so recently diverged, they couldn’t tell the pollen apart.
When Corneile Minnaar joined the group as a PhD student in 2015, he decided to try to find a reliable method to label and track pollen in order to answer this question. By the end of his first year, he succeeded in using quantum dots to label pollen grains, thereby breaking new ground in a field of research that had been hampered by the lack of a universal method to track pollen for over a century.
From November 2015 to 2016, the team set off to Mamre to test the newly designed method in the field, and more importantly to test Anderson’s hypothesis. In the case of Lapeirousia and the long-tongued fly, Minnaar and Anderson showed conclusively that long- and short-tubed flowers placed and received pollen from different parts of the fly’s long tongue: short tubed flowers mostly midway and long-tubed flowers on or near the head.