Food spectrum analysis of the Asian toad, Duttaphrynus melanostictus (Schneider, 1799) (Anura: Bufonidae), from Timor Island, Wallacea

ABSTRACT

The Asian toad, Duttaphrynus melanostictus (Schneider, 1799), is widespread throughout tropical Asia and very abundant where it occurs. It was relatively recently introduced to Timor, the second largest island in the biogeographic region called Wallacea. Timor Island shows an exceptionally high level of endemism in a wide range of faunal groups and there are concerns that D. melanostictus may have a negative impact on this diversity, including vertebrates, through direct predation. To evaluate the impact the diet of D. melanostictus might have on the local fauna, gut contents of 83 preserved toad specimens from five habitat types in Timor-Leste, a country occupying the eastern half of Timor Island, were examined. We identified 5581 prey items, comprising the following animal groups: annelids; snails and slugs; spiders and harvestmen; woodlice; millipedes and centipedes; grasshoppers, crickets and earwigs; termites; thrips and true bugs; beetles; ants; hymenopterans other than ants; true flies; butterflies; unidentified insects; and insect larvae. Small eusocial insects (ants and termites) constituted the major part of the diet (61.6% and 23.4%, respectively). No vertebrate prey was recorded. Prey item composition did not differ between habitats. The wide prey spectrum well indicates that D. melanostictus is a generalist invertebrate feeder, as other studies, from regions where this species occurs naturally, have already shown. Although the Asian toad seems to not generally prey on vertebrates, vertebrate species that are morphologically similar to invertebrates in their overall appearance may be consumed. Hence, a negative effect on some taxa (e.g. blindsnakes) may be possible. We also present some limited data on intestinal parasites occurring in D. melanostictus.

KEYWORDS:

• Amphibia
• Duttaphrynus melanostictus
• Timor-Leste
• trophic ecology
• gut contents analysis

Acknowledgements

We are very grateful for the personal support of Timor-Leste’s political leadership, particularly Their Excellencies former President José Ramos-Horta, former Prime Minister Xanana Gusmão and Minister Ágio Pereira. Our research in Timor-Leste would not have been possible without the networking skills of Claudia Abate-Debat, former Special Advisor in the Prime Minister’s Office. Fieldwork in Timor-Leste in Summer 2013 was facilitated by a research and collecting permit (No. 24/DAPPN-DNF-MAP/VI/2013) issued by the Timor-Leste Ministry of Agriculture and Fisheries, wherein we are especially grateful for the years of support provided by Manuel Mendes, Director of National Parks. For their enthusiastic efforts during our fieldwork we thank the participants of the Victor Valley Tropical Research Initiative (Herpetofauna of Timor-Leste, Phase VIII), Kevin Burns, Claudia Rivas, Jay Paris, Julia Pozo and Franziska Wagner. We particularly thank our Timorese companions and friends Paulo Pinto and Agivedo Varela Ribeiro. We are grateful for the logistical assistance provided by Paulo Aniceto (Rentló Car Rental) and the hospitality of the management and staff of the Timor Lodge Hotel, Dili, especially the late Kemal Baser. We thank Steve Gotte, Jeremy Jacobs and Robert Wilson (USNM) for the loan of specimens under their care. We are grateful to Hans Wilhelm Bohle and Martin Brändle (Philipps-Universität Marburg, Germany) for the identification of some of the prey items, and to Julian Münster (Goethe-Universität, Frankfurt, Germany) for the identification of some of the parasites found. We sincerely acknowledge Theresa Graf, Ka Schuster and Heike Worth (Philipps-Universität Marburg, Germany), Raffael Ernst (MTD) and the two anonymous reviewers for providing comments and/or helpful information on an earlier version of this publication. Financial assistance for student travel from California to Timor-Leste was provided by the Associated Student Body at Victor Valley College. This paper is contribution no. 21 from the Tropical Research Initiative at Victor Valley College.

Disclosure statement

No potential conflict of interest was reported by the authors.

Notes

1. Jamdar and Shinde (2013) presented a gut content analysis of Duttaphrynus melanostictus from Aurangabad, Maharashtra, India. However, their article was printed in a ‘predatory journal’ (a journal that does not offer peer review but charges for article processing), the Indian Journal of Scientific Research and Technology (according to Beall’s (2016) list of standalone journals), and contains sentences and paragraphs that are identical or similar to ones in Berry and Bullock (1962), who were not cited by Jamdar and Shinde (2013). This identifies Jamdar and Shinde’s work as plagiarism. For this reason we do not consider their paper herein.

2. Duttaphrynus melanostictus presumably arrived in West Timor, Indonesia, around 1999–2000, entered Timor-Leste shortly afterwards (Trainor 2009) and was recorded in Timor-Leste’s easternmost district (Lautém) for the first time in August 2014 (MCZ A-149329 from Com).

3. The myrmecophagous horned lizards (genus Phrynosoma) incapacitate their prey by binding them with mucus secreted by distinct papillae within their pharynx (Schwenk and Sherbrooke 2003). A similar mechanism may exist in toads that consume ants in high numbers, but this has not yet been documented.