THE INTERACTION BETWEEN THE FIRST PLANTS AND ANIMALS
Terrestrial plants first evolved without flowers. The first land plants evolved around 400 million years ago and were probably mosses. They used a mechanism of a sexual and an asexual cycle to reproduce. Then at around 350 million years ago the cycads came along and with them a different reproductive mechanism developed. They evolved into male and female plants, both producing a huge central cone, which evolved from the previous spores. The male plants produced huge amounts of pollen which is mostly wind dispersed. But little insects also started feasting on the nutritious pollen and along with that a strategy developed to attract these creatures that were now helping the process of pollen dispersal. One species of cycad even today practises a strategy where the temperature in the cone is raised by about 2 degrees when the pollen is ready for distribution. This attracts weevils, which come to feast on the pollen, get themselves covered in the process and then deliver the pollen to another cycad in search of another meal. This way of pollen dispersal is a lot more economical than the wind and both the cycads and the weevils are winners (1).
It is only about 100 million years ago when the first flowering plants evolved. This was an advertisement strategy and still is today. Pollen is nutritious and insects long learned to utilise this food source. Now plants developed more strategies to attract the pollinators and the flowering plants were born. Water-lilies and magnolias are descendants of some of the oldest plant families that first produced true flowers. They still reward the little beetles that visit them with little more than the pollen, but this has served to be successful enough for these plants to be around still today.
Some plants developed an exclusive relationship with just one species of insect. One such example present today is of the pink Orphiump frutescence that is only pollinated by carpenter bees. The flower holds its pollen inside its hollow anthers and the only way the pollen can escape is through a tiny hole at the top of the anther. The carpenter bee has perfected its technique of extracting the pollen by alighting on an anther and then beating its wings at a certain frequency, just right to make the pollen spout out of the hole at the top. As only the carpenter bees can buzz at this frequency, they alone can extract the pollen. They however do not know if a flower has been visited before and so they move from flower to flower, shaking the anthers and in the process pollinating the flowers with the pollen that has collected on their furry bodies (2).
Another such example of a specialized partnership is seen in the twinspurs (Diascia) in South Africa. There reward is oil which is secreted at the far end of the spurs. Several species of solitary bees have developed brushes on there forelegs to collect the oil. For each species of twinspur there is a corresponding species of oil-collecting bee with forelegs that exactly match the length of the spurs (1).
Some flowers started producing nectar as a reward to attract insects and some produced scented chemical to attract their pollen couriers and yet another advertisement is colour. Many even developed “landing strip marks” or nectar guides that help the insects guide their tongues into the flowers to collect their reward and often also parcels of pollen which they then carry to the next flower.
Some plants even mimic others to try and trick a pollinator to visit. One such example is the cluster disa (Disa ferruginea) on Table Mountain. It has a bright red colour and closely resembles the red Tritoniopsis triticea (alongside it also grows), which produces a rich nectar reward. The disa however produces none, but manages to trick the mountain pride butterfly who repeatedly visits the empty flowers and thereby pollinating it (2).
There are many more examples of how plants and insects have evolved together, adapting together to serve each other. Some are extremely bizarre, but all serving a purpose of fulfilling a life-cycle, all part of a functional ecosystem.
1. Attenborough D. 1995. The Private Life of Plants. Pages 95-106 in Flowering. London: BBC Books.
2. Pauw A, Johnson S. 1999. Table Mountain. A Natural History. Pages 55-67 in Delicate Partnerships. Cape Town: Fernwood Press.