Shi-Xiao Luo, et al.
By Colin Barras
Species: Leafflower moths, specifically Epicephala lanceolaria
Habitat: Forests of East Asia
Visit a forest in south-east China, say, in mid-March and you might catch one of the more unusual sights in the natural world. The ripe fruit of one species of tree burst open at that time each year – and fully developed moths fly out.
Leafflower moths have a special relationship with leafflower trees, of the genus Glochidion. The trees produce male and female flowers in April and May. Most insects overlook them by day, perhaps because they don’t produce nectar.
At night, though, the flowers release a perfume that is irresistible to leafflower moths. Females flock to the trees and perform a very specific routine. First, they visit the male flowers, where they carefully collect pollen on their proboscis. Then they head to a female flower, using the pollen to fertilise the bloom. Pollination complete, they lay one egg in the flower.
A few months later, the egg hatches. By that time, the fertilised flower should have matured into a fruit, providing the larva with food – it eats two or three of the half-dozen seeds inside.
Under the surface: Cushion plants harbour tiny mountain worlds inside
Eventually the intimate relationship with the trees ends when the larva chews its way out of the fruit, pupates on the forest floor over winter and emerges as an adult moth in the spring.
One species – E. lanceolaria – does things a little differently. It still lays its eggs in April and May, but the species of tree it chooses – G. lanceolarium – takes ages to bear fruit. In fact, it isn’t until January of the following year that the fruit begin to develop. Only at this point do the larvae emerge from their eggs and begin to feed on the fruit.
With their development squeezed into a few short months, the larvae simply metamorphose into adults while still inside the fruit. A few weeks later, in March, the fruits mature – and the moths fly out, just in time to mate and lay their eggs in the tree’s new blooms.
“The moth turns to an adult in the fruit, and then flies out when the mature fruit opens on the branches,” says Shi-Xiao Luo at the Chinese Academy of Sciences in Guangzhou. He says the behaviour is unique among leafflower moths.
Atsushi Kawakita at Kyoto University, Japan, agrees. He was a member of the team that discovered the relationship between leafflower trees and leafflower moths in 2003. “I know of no other example where a [butterfly or moth] matures as a winged adult literally inside the host plant tissue,” he says.
Unusually intimate
The fact that they do means this relationship between plant and moth is unusually intimate – which might be of particular benefit to the G. lanceolarium tree.
“The host plant has the ultimate control of when the moths will be in flight. This [seems to] coincide with the next flowering period of the host plant,” says Kawakita. “So the findings point to the possibility that the plants are ‘hoarding’ their mutualist partners until the plants themselves are ready for the next reproduction event.”
The relationship is the “next step forward in terms of intimacy”, he says.
Read more: Armoured wasps chop off opponents’ heads in brutal fig wars
Biologists are still trying to understand how this sort of mutualistic relationship arises. One idea is that it appears gradually as a result of a long period of co-evolution involving the two lineages. This does seem to be the case for leafflower trees and moths in general. The evolutionary histories of the two groups match each other almost perfectly.
But E. lanceolaria doesn’t fit. It lies at the very base of the leafflower moth “evolutionary tree”, but the species of leafflower tree it partners with isn’t similarly basal – it is one of the more recent species of leafflower tree to evolve. In other words, E. lanceolaria and G. lanceolarium don’t seem to have co-evolved over a long period in the same way that other leafflower trees and moths have.
Luo and his colleagues think the moth might have begun laying eggs in G. lanceolarium trees relatively recently, perhaps displacing another species of leafflower moth in the process. “Highly intimate and coevolved associations may be more evolutionarily dynamic than had been previously realised,” he says.
It’s a view shared by Guillaume Chomicki at the University of Munich in Germany, who studies the evolutionary dynamics of mutualism. He agrees that the new findings suggest intimate mutualism is not just about the gradual co-diversification of two evolutionary lineages.
“It’s a major leap forward,” he says. “We know so little about the evolution and stability of mutualism over geological time.”
Journal reference: The American Naturalist, DOI: 10.1086/690623
No comments:
Post a Comment