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Oh, those blue butterflies are so near the brink

By Dave Armstrong - 28 Nov 2012 15:31:0 GMT
Oh, those blue butterflies are so near the brink

Maculinea rebeli with closed wings; Credit: © Shutterstock

Do you know about the Large Blue and its begging habit? Maculinea rebeli (also known as Phengaris) is one of those cute blue butterflies that hang out with ants. What I mean is they eat them, but don't tell the ants. In different European countries, they parasitise different species of the Myrmica red ant. Interest in this butterfly is partly ignited by the loss in 1979 of the British sub-species. Because the ant species on which it depends lost much of its habitat. Maculinea arion eutyphron is now extinct, although 10,000 of the Swedish subspecies now fly about in its "niche!"

Jeremy Thomas is one of those responsible for the conservation classic of the Somerset Large Blues in England. He's written this paper with several Polish and German colleagues, to illustrate the nightmare of matching blue butterfly sub-species with ant species. He publishes today in the Proc Roy Soc B. and works at Oxford University and Wallingford's Centre for Ecology and Hydrology, both UK.

Conservation often fails. Different genotypes from that of the main species' can be to blame, but even neighbouring niches are seen here to cause variation within this parasite. Its recent evolution seems so far to be undetectable with DNA analysis, despite its great effect on the understanding of speciation. One or two genes seem to be able to affect the phenotype (basically, the appearance) so that six morpho-species of the Large Blue have developed a differing chemical and acoustic mimicry. Even two different species, M.rebeli and M. alcon could not be easily distinguished genetically. That certainly explains a lot of conservation failure with smaller animals.

When they are disturbed, red ants move their brood quickly. It was a simple measurement for these researchers to check how quickly the mimicking caterpillars were picked up and moved, as opposed to how the natural grubs of the ants themselves were treated in an experiment. Of 20 in each artificial brood in the experiments, the caterpillars were the last to be "rescued" at first. After a week, the status of the parasite had risen to joint first, alongside host pupae, through the "emergency exit door." When they had the wrong host ant, (ie. Spanish caterpillars in Poland or Polish caterpillars in Spain), only 20% of caterpillars were taken at all and they were never given "high status."

Together with natural observations of 100% mortality with the wrong hosts, Jeremy and his researchers' experimentation led to the discovery that each morpho-species produced its own hydrocarbon profile to match the different ant species' smell. After five years of successful retrieval by ants of both species' caterpillars in both countries, it was realised that at retrieval, no problems were being encountered by the caterpillar.

Immediately afterwards, however, it was discovered that corpses were being discarded from nests, with many signs of ant attack. Those ants in the lab experiments were better fed and more kindly. Research showed that after 5 days, the secreted hydrocarbons from the caterpillar matched the host ant better and they were carried about with high status. In nature, this didn't seem to happen, unfortunately for the butterfly!

The relevance of this research to all endangered sub-species and species is that chemical and acoustic relationship are rarely measurable. In insects like these and many other animals, the survival of a "cuckoo" species may depend upon maintaining the host in its suitable niche, just like the two ant species. They require different grassland and grass heights and therefore differing grazing regimes. How many will share the fate of the British Large Blue sub-species? Perhaps all the Larger Blue species if we're not careful. Then we have an almost unique life-style to mourn.

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Topics: Insects