Main Club

Our speaker was Professor Byron Lamont, an expert on the adaptations of Mediterranean floras, especially those in south-west Australia. His special interests within that field are the evolution of the Proteaceae or Banksia family and the role of fire in the evolution of plants. He studied Agricultural Science and Botany at UWA. Since “retirement”, he has published fifty papers and a book on plant adaptations in the south-west.

Byron began by saying that one of his interests as an ecologist is plant-animal relationships, and that he would talk about the influence of Carnaby’s Black-cockatoos on the WA flora, particularly on Hakeas. Hakeas and cockatoos have both existed in WA for 15 to 20 million years.

The 100 species of Hakea in the south-west can be put into two groups or “syndromes”—bird-pollinated and insect-pollinated. Bird-pollinated Hakeas usually have larger inflorescences with larger flowers that are red and accessible to birds, have larger, softer leaves and longer internodes (for birds to perch on). Insect-pollinated species typically have cream or white flowers and smaller, spinier leaves. The first group is typified by Hakea francisiana and the second by H. auriculata.

The red flowers contain cyanide, so the birds learn not to eat these flowers, only the nectar. This brings a new explanation for redness in flowers—that it may be a predator warning rather than (solely) to attract pollinators such as honeyeaters. There is no cyanide in the nectar.

Byron pointed out that there is an evolutionary dilemma here: having highly exposed, accessible flowers has the disadvantage that their fruits are now easily accessible to birds that are looking for seeds to eat. Cockatoos are very efficient at extracting seeds from the woody Hakea fruits, and in sharp contrast to seeds in other parts of the world, the seeds contain as much protein as in food animals such as insect larvae.

Hakeas have adapted to frequent fire and poor soils by storing their seeds on the plant for a long time and dropping them onto the ash bed after a fire. (Holding the fruits on the plant is called serotiny and happens more often in the south-west than anywhere else in the world.) This seed-storage regime is very convenient for the cockatoos as it means that the seeds are always available for them. It seems that, as a response, Hakeas have evolved features that discourage the birds from stealing the seeds: they often have spiny leaves surrounding the fruit; some disguise their fruits in a number of ways; some have large, woody fruits that are very difficult to break open. And a few species have tightly-clustered fruits that restrict beak access. Many Hakeas also have a low seed store, meaning that many plants produce few or no fruits, making them hard to find.

This leads to the hypothesis that species with serotinous fruits should be better defended. But careful investigations carried out by Byron together with Mick Hanley, Phil Groom and Tianhua He have indicated that it is not as simple as that. While large fruits are very effective against seed-loss to birds and clustering is fairly effective, having spiny leaves or camouflage does not really work. But it is possible that spiny leaves and camouflage have evolved to stop insects (beetles, moths) eating the seeds—not birds. (Insect larvae mostly reach the seeds by boring into the unripe fruit.) Insects lack good eyesight and are often night-active so camouflaged fruits hidden beneath spiny leaves would be difficult to detect; by contrast, cockatoos have excellent eyesight are very clever at locating fruits and snipping spiny leaves away to gain access. However, this is only a hypothesis, and  would require investigation and strong evidence to confirm or refute.

This cocky’s skull covered with blue plasticine was a tool used to measure the damage that would be inflicted on a cockatoo searching for Hakea seeds among spiny leaves. (It’s okay, it was road-kill.)

Byron’s research aid Norwegian Blue was the star of the show.

So a possible evolutionary process emerges, consisting of a chain of environmental agents of selection and Hakea responses, as follows. Honeyeaters are attracted to exposed flowers. Having exposed flowers means that the fruits will be exposed. Cockatoos have the habit of eating flowers. Hakeas evolve red flowers with cyanide that discourage them from being eaten. Because of the poor soils and seasonal fires, Hakeas evolve nutritious seeds to assist their establishment, which they retain until after a fire when conditions for recruitment are ideal. So cockatoos become seed-eaters. In response, Hakeas evolve large, strong, woody fruits, sometimes tightly-clustered, to discourage seed-stealing.

Thanks go to Byron for a fascinating talk, presented in an interesting way that provoked plenty of questions and was backed up with scientific data. It gave an insight into the influence of honeyeaters and cockatoos and a harsh environment on the evolution of Hakeas in the South-West, and an explanation of why they are as they are today.

Mike Gregson