Museum material reveals a frog parasite emergence after the invasion of the cane toad in Australia

Ashlie Hartigan,David N Phalen,Jan Šlapeta

doi:10.1186/1756-3305-3-50

Abstract

BackgroundA parasite morphologically indistinguishable from Myxidium immersum (Myxozoa: Myxosporea) found in gallbladders of the invasive cane toad (Bufo marinus) was identified in Australian frogs. Because no written record exists for such a parasite in Australian endemic frogs in 19th and early 20th century, it was assumed that the cane toad introduced this parasite. While we cannot go back in time ourselves, we investigated whether material at the museum of natural history could be used to retrieve parasites, and whether they were infected at the time of their collection (specifically prior to and after the cane toad translocation to Australia in 1935).ResultsUsing the herpetological collection at the Australian Museum we showed that no myxospores were found in any animals (n = 115) prior to the cane toad invasion (1879-1935). The green and golden bell frog (Litoria aurea), the Peron's tree frog (Litoria peronii), the green tree frog (Litoria caerulea) and the striped marsh frog (Limnodynastes peronii) were all negative for the presence of the parasite using microscopy of the gallbladder content and its histology. These results were sufficient to conclude that the population was free from this disease (at the expected minimum prevalence of 5%) at 99.7% confidence level using the 115 voucher specimens in the Australian Museum. Similarly, museum specimens (n = 29) of the green and golden bell frog from New Caledonia, where it was introduced in 19th century, did not show the presence of myxospores. The earliest specimen positive for myxospores in a gallbladder was a green tree frog from 1966. Myxospores were found in eight (7.1%, n = 112) frogs in the post cane toad introduction period.ConclusionAustralian wildlife is increasingly under threat, and amphibian decline is one of the most dramatic examples. The museum material proved essential to directly support the evidence of parasite emergence in Australian native frogs. This parasite can be considered one of the luckiest parasites, because it has found an empty niche in Australia. It now flourishes in > 20 endemic and exotic frog species, but its consequences are yet to be fully understood.

Highlights

A parasite morphologically indistinguishable from Myxidium immersum (Myxozoa: Myxosporea) found in gallbladders of the invasive cane toad (Bufo marinus) was identified in Australian frogs
No gallbladder myxospores found in frogs prior to 1935 A catalogue of the Australian Museum, Sydney was queried for five frog species; the green and golden bell frog (Litoria aurea), the green tree frog (Litoria caerulea), the Peron's tree frog (Litoria peronii), the striped marsh frog (Limnodynastes peronii), and the introduced cane toad
The museum specimens were from eastern Australia, mostly from New South Wales (Figure 1)

Summary

Introduction

A parasite morphologically indistinguishable from Myxidium immersum (Myxozoa: Myxosporea) found in gallbladders of the invasive cane toad (Bufo marinus) was identified in Australian frogs. Because no written record exists for such a parasite in Australian endemic frogs in 19th and early 20th century, it was assumed that the cane toad introduced this parasite. While we cannot go back in time ourselves, we investigated whether material at the museum of natural history could be used to retrieve parasites, and whether they were infected at the time of their collection ( prior to and after the cane toad translocation to Australia in 1935). Museum collections of amphibians have been used effectively in the global investigation into amphibian decline and historical emergence of external frog malformations [1,3]. The myxosporean, Myxobolus cerebralis (Plehn 1905), which causes whirling disease in salmonid fish was introduced from Europe to 26 other countries [5] and has significantly impacted wild and farmed fish populations in North America significantly [6]

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