Back to the future? Unravelling current and potential future declines of the common toad, Bufo bufo, in the UK

Abstract

Large scale and unexplained declines of the common toad, Bufo bufo, have been recorded in the UK for over two decades, especially in southern and central England. However, the extent of these declines and their causes are poorly understood. Except for “toad patrols” taking place in many parts of the UK, B. bufo has been relatively neglected by conservationists and many aspects of the species demography and population structure at local scale are unknown. In this thesis, neutral genetic markers were used to investigate broad scale genetic diversity and population structure of B. bufo populations across Great Britain. This project relied partially on citizen volunteers to allow for quick data collection over a large geographic area. Careful considerations had to be given to the most cost-effective approach to gather large amounts of genetic samples using buccal swabbing as a minimally invasive sampling method (Chapter 2). Based on this method, the genetic data collected throughout the project revealed large scale admixture and low genetic structuring over most of British populations (Chapter 3). In a local area of Central England, presence of heavy metals and nutrients in the environment correlated with trends of B. bufo declines. Local population structuring remains low, and genetic estimates of effective population size supported empirical observations. Adult and larvae telomeres were measured as a possible indicator of environmental stress affecting populations. Although population variations were found in telomere length, it did not unambiguously correlate with presence of chemicals in the environment or observed population trends (Chapter 4). My results shed new light on the state of B. bufo in Great Britain and despite declines, genetic diversity and connectivity between populations is reasonably high. The factors driving declines need more careful examination; however, it is likely a combination of factors that need to be addressed to stop further declines.