Historical perspectives on global exports and research of African clawed frogs (Xenopus laevis)

Abstract

Trade in live animals has been associated with populations of invasive species as well as the spread of disease. The African clawed frog, Xenopus laevis, was exported from its native region of southern Africa for use in pregnancy testing, and later for laboratory use as the model amphibian. We use historical export figures and publication records to detail the size and extent of the global trade. In addition, we explore the link between exports, scientific use, and invasive populations and chytrid outbreaks. Exports reached 400 000 animals in the first 30 years from 1940, but only 86 000 were sent outside Africa. Exports out of Africa peaked in the 1950s, while scientific publications using Xenopus laevis grew in the 1970s, coinciding with a rise in invasive populations and chytrid outbreaks. We show a lag between exports of Xenopus laevis and a rise in invasive populations of around 15 years. Our data demonstrate the global reach of the exports of Xenopus laevis from South Africa, and a later, much wider distribution via the scientific network which was supplied by secondary means outside of South Africa. We contend that our data demonstrate that by 1970, Xenopus laevis was the world’s most widely distributed amphibian: institutions in 48 countries were supplied with live colonies on all continents except Antarctica. There is some evidence linking exports and scientific studies with invasive populations, but others appear to be linked to secondary distributors of this species.

Keywords:

• African clawed frog
• Anura
• historical biology
• invasion biology
• invasion debt
• propagules
• trade
• Xenopus

ACKNOWLEDGEMENTS

We would like to thank Philip Purnell (Thomson Reuters) for facilitating access to early WoK searches. Hendré van Rensburg (NRF student assistantship) and Marié Theron for their help with address searches from early published literature. John Wilson, Rui Rebelo, Thalassa Matthews and two anonymous reviewers gave helpful comments on an earlier version of this manuscript. JM would like to thank the DST-NRF Centre of Excellence for Invasion Biology for making this study possible.

SUPPLEMENTAL DATA

Supplemental data for this article can be accessed here.

ORCID

G. John Measey http://orcid.org/0000-0001-9939-7615

Additional information

Funding

This research was funded by the National Research Foundation of South Africa (NRF grant no. 87759 to GJM) and NRF incentive funding to GJM.