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Frog Discoveries
Warning: Killer Flies eat WA frog eggs! 22 February 2006 Anyone that has spent any time in the Australian bush on a hot summer’s day, probably has many unprintable names for flies! For the most part however, our infamous bush flies do little harm to humans and perform an essential role in breaking down dead animals. Well, did you know that our local frogs are bugged by pesky flies too, only these flies can be deadly! In a great example of international detective work, recent research by Dr. Robert Davis at The University of Western Australia’s Frog Lab uncovered a new species of fly that parasitises the eggs of our Western Spotted Frog Heleioporus albopunctatus. During his PhD research on this species Dr. Davis was examining the survival of egg clutches. Unlike many other frogs, the Western Spotted Frog has a unique breeding system. Males call from a tunnel-like burrow up to 2m long, which they excavate in a depression in the landscape during autumn. If a female is attracted by the male’s call, mating occurs in a chamber at the base of the burrow and about 400 eggs are laid in a foamy mass. Tadpoles develop within the egg until the burrow is flooded by winter rains. When this happens, tadpoles burst free from the egg capsule and swim out into their newly-formed pond. As part of his frog research, Dr. Davis dug up a number of Western Spotted Frog burrows across the wheatbelt region. His interest was sparked one day when he noticed that some burrows contained a number of small black flies that escaped as soon as the sandy burrow entrance was excavated. He also noticed that when he took frog eggs back to the lab and looked at them under the microscope some clutches were full of small white maggots and even contained a few adult flies. He initially had the flies identified by UWA Forensic Entomologist Dr. Ian Dadour as phorid flies. Upon further investigation it turned out that there was only one man in the world who had made the study of these tiny flies his passion – Dr. Henry Disney from Cambridge University in England. With the next piece of the puzzle in place, these frog-flies were sent off to England for further examination by Dr. Disney. An excited email a few days later established that the fly was a female phorid fly (also known as “scuttle flies”) of a species that was only known from male specimens. There were certainly no records of male flies from frog eggs! This special fly had only been recorded from Tasmania and New Zealand and the find represented a huge range extension. Some further investigative work found that similar flies had been collected from burrows of the Moaning Frog Heleioporus eyrei at Jandakot in 1983 by Dale Roberts of the UWA Frog Lab. Identification by Dr. Disney revealed that these were also the same species of fly. It was apparent by this stage that this special scuttle fly lived in the egg masses of frogs of our local Heleioporus species. A request put out to the Australian frog community did not reveal any similar observations of flies in the eggs of any other burrow-depositing species. It seems that our unlucky frogs have this unique predatory fly to contend with all to themselves! |
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