2023 SERVENTY MEMORIAL LECTURE , 5 APRIL 2023

The Serventy Memorial Lecture is held annually in honour of the contribution made to Natural History in Australia and to our Club by the Serventy family. The lecture is the primary source of funding to award prizes to students. The prizes aim to encourage and assist young people in studying natural history at the four WA universities.

Before the talk, past president Mandy Bamford outlined the work of the Serventy family, the foundation of the WA Naturalists’ Club by Dom Serventy in 1924, and some of the achievements of our Club. Then our co-patron Lyn Beazley introduced the speaker. After the talk, our other co-patron Kerry Sanderson thanked the speaker on behalf of the appreciative audience.

Our speaker was Professor Leigh Simmons, a naturalist and evolutionary biologist currently working at UWA in the Centre for Evolutionary Biology. Originally from the UK, Leigh visited WA to study the singing insects of Kings Park. Once here, he became fascinated by the biodiversity of this state and moved here permanently to study its rich diversity, particularly the evolutionary biology of reproduction. His main study area is sexual selection and the understanding of mate-choice.

Leigh began by explaining what makes WA a biodiversity hotspot, defined not only by very high biodiversity and endemism but also by high numbers of endangered species and high extinction rates. He said we hear about the extinction of cute and cuddly mammals but less about the loss of invertebrates, which are vital parts of ecosystems.

He then reminded us that Charles Darwin and Alfred Russel Wallace almost simultaneously proposed the idea that we can only explain the distribution of living things by the natural selection of traits that help the species survive. But he added that Darwin later came up with a second evolutionary force – sexual selection. (Wallace dismissed the latter.) Darwin realised that reproduction was important – not just survival.

Leigh then looked at an example from WA – one which some of us have seen on excursions to the Kennedy Ranges – Dawson’s Burrowing Bee Amegilla dawsoni. They are solitary nesters, like most WA native bees, but their nests are aggregated, giving the impression of a colony. The females build the nests on claypans and compacted dirt roads in arid regions such as the Gascoyne. New males emerge in mid-July, and 2-3 weeks later, the females emerge.

Then there is a battle to the death among a big crowd of major males, after which the prevailing males can mate with the females. But there is a different type of male – the minor males, which wait on the sidelines and try to mate with escaping females. Pheromones signal to the male whether the female is receptive or not. When laying eggs, the female determines whether the progeny will be female, major male or minor male. (>80% of males are minors, but these only get 13% of the mating). This is an example of strong sexual selection.

The second example that Leigh discussed was the rapid ongoing evolution in the Oceanic Field Cricket Teleogryllus oceanicus of northern Australia and the western Pacific. These have sound-producing structures on modified wings. The males produce two types of calls, one of which is a courtship call. Calling is energetically expensive, and females respond to high-quality songs. But on some islands, a parasitic fly appeared, which responds to the sound of the male cricket, and lays its eggs on it. The larva buries into the body of the cricket.

On some islands, mutations occurred, which modified the wings so that the sound was quieter. This was selected because it made them harder to be found by the parasite. Thus the new cricket genes survived because of the fly. So, the female crickets faced selection pressure to respond to quieter calling. This is an example of sexual selection by the female crickets interacting with a natural selection from the flies. And it is an example of how new species might emerge on some of those islands.

Leigh studied the Spring Bush Cricket Kawanaphila nartee at sites including Kings Park. It feeds on the pollen of spring flowers such as Milkmaids and Kangaroo Paws. The male chooses a mate and gives his mate an edible nuptial gift. This extra food facilitates the creation of eggs, so the females fight over access to males, and there is selection for better hearing sensitivity by which to hear the males calling. However, when the grass trees flower, the females have a surplus of food, so they don’t have to fight over males. Then it’s the males that compete for females. One result is that in places with few grass trees (e.g. Koondoola), the females need their nuptial gifts, so there is pressure for their “ears” to become more sensitive.

Leigh also mentioned examples of sexual selection in the frog Crinia georgiana, the Western Whistler, Whistling Moths, and Marri Millipedes. He said that, unlike well-known examples, most sexual selection doesn’t involve exaggerated weapons like antlers or decorations like peacock feathers.

In conclusion, Leigh referred to the global decline in invertebrate fauna, particularly insect fauna. Primary causes are habitat destruction (70% in WA), pesticide use and climate change (hot, arid conditions can sterilise insects). And he pointed out the importance of invertebrate biodiversity: it provides pollination services in the natural world and commercial crops, controls pest insect populations (e.g. wasps preying on aphids), promotes nutrient recycling (e.g. dung beetles), and provides critical links in food chains to keep ecosystems functioning.

This fascinating lecture emphasised that the endless battle to reproduce contributes greatly to high biodiversity, such as in WA.

Mike Gregson