The cane toad: a new host for helminth parasites in Australia

Barton, Diane Patricia (1995) The cane toad: a new host for helminth parasites in Australia. PhD thesis, James Cook University.

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Abstract

The helminth fauna of native Australian amphibians and the introduced toad, Bufo marinus was studied. Species composition and ecological relationships of the helminths were considered in detail. In addition, the relationship of one helminth species, Rhabdias sp., to the health of the toad was considered.

A total of 27 helminth species (14 Nematoda, 8 Digenea, 2 Cestoda, 2 Acanthocephala, 1 Monogenea) was collected from both the toad and native amphibians in this study. Six helminth species were found to only infect toads in this study: Dolichosaccus juvenilis, Zeylanurotrema spearei, Cosmocerca sp. 2, Cosmocerca sp. 3, Austraplectana sp., adult acanthocephalans. Two of these species (D. juvenilis and adult acanthocephalans) had been reported from native fauna in previous studies. Three species were found to infect only native amphibians in this study: Parapolystoma sp., Seuratascaris numidica, and Onchocercidae gen. sp.

All of the helminth species collected from B. marinus in this study, with the possible exception of Rhabdias sp. and Mesocoelium sp. for taxonomic reasons, can be determined as having an Australian origin. The majority were acquired by the toad from native amphibians. Some species, however, were thought to have transferred to the toad from native reptiles.

At least 70% of toads and native frogs were infected with at least one helminth species. Maximum number of helminth species for an individual toad was 6, whereas for native frogs it was 4.

Bufo marinus had a more diverse helminth community than native frogs at both a host individual and host population level. The use of diversity indices in helminth community ecology and the concept of core and satellite species, particularly in relation to amphibian helminth communities, is discussed.

Comparison of the helminth fauna of B. marinus and a native frog, Litoria inermis, was undertaken in detail. Relationships of total helminth intensity and species richness to various factors, including host sex and snout-vent length and month of collection were calculated for both host species. Reasons for the possible disparity between helminth infection levels for B. marinus and Lit. inermis are discussed.

Only one helminth species, Rhabdias sp., was thought to have potential as a biological control agent for the toad in Australia. Detailed studies of the life cycle of Rhabdias sp., natural infection levels within a population of B. marinus and its relationship with the health of the toad were undertaken.

Rhabdias sp. infected over 80% of toads collected from QDPI, with a mean intensity of 16 nematodes per infected toad. Intensity of infection had a significant relationship with length of toad for subadult toads only. Average length of Rhabdias sp. within an infrapopulation had a significant relationship to host length for subadult and middle size class toads.

Distribution of Rhabdias sp. within the toad population was aggregated, with degree of aggregation increasing with toad size class.

Sex of toad had a significant relationship with average length of Rhabdias sp. only in Class II toads, where male toads had larger nematodes.

Rainfall was an important environmental factor influencing infection of toads with Rhabdias sp. The majority of Rhabdias sp. recruitment into the toad population occurred during the late wet season, although small amounts of recruitment occurred throughout the year.

Development of Rhabdias sp. from embryonated egg to infective third stage larva, in the laboratory, took 4 days at 24°C. Development was only observed via a free-living sexual cycle, with only one larva produced per free-living female.

Experimental infections were hampered by a high death rate among the metamorph B. marinus and Limnodynastes ornatus used. Over 50% of metamorphs exposed to infective larvae of, Rhabdias sp. became infected. Number of larvae penetrating the metamorph was significantly related to the success of infection. Lower infection dosages produced proportionately higher levels of infection.

Haematological data for B. marinus in Australia is presented for the first time. Presence of a Rhabdias sp. infection significantly decreased levels of red blood cells, packed cell volume and haemoglobin concentration. Level of Rhabdias sp. infection also significantly decreased these levels, but not to the same extent as presence of Rhabdias sp. alone.

Item ID: 24098
Item Type: Thesis (PhD)
Keywords: Australia; Bufo; cane toads; frogs; helminths; internal parasites; Limnodynastes; Litoria; nematodes; Rhabdias
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Date Deposited: 11 Dec 2012 07:08
FoR Codes: 06 BIOLOGICAL SCIENCES > 0608 Zoology > 060899 Zoology not elsewhere classified @ 34%
05 ENVIRONMENTAL SCIENCES > 0501 Ecological Applications > 050103 Invasive Species Ecology @ 33%
06 BIOLOGICAL SCIENCES > 0603 Evolutionary Biology > 060307 Host-Parasite Interactions @ 33%
SEO Codes: 96 ENVIRONMENT > 9608 Flora, Fauna and Biodiversity > 960808 Marine Flora, Fauna and Biodiversity @ 100%
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