Exploring the invasion dynamics and impacts of the invasive Asian common toad in Madagascar

Investigating the invasion dynamics and impacts of understudied invasive amphibians can be relevant to improving our understanding and management of amphibian invasions worldwide. In 2014, an invasive population of the toxic Asian common toad Duttaphrynus melanostictus has been reported in Madagascar, raising concerns about the potential impacts it could have on its megadiverse ecosystems. In my thesis, I investigate the invasion dynamics of the Asian common toad in Madagascar examining: (1) range expansion, (2) morphology, and (3) spatial ecology. Lastly, I explore (5) the toad poisoning effect on a native predator, (6) and the potential socioeconomic impacts on local populations. Initially, the invasive population showed an apparent accelerating range expansion. I conducted morphological and spatial analyses to test whether this could be determined by spatial evolutionary processes at the invasion front. I found no evidence of such processes, on the contrary, the findings supported an invasion scenario dominated by short-distance leading-edge dispersal. Spatiotemporal analyses of public surveys data confirmed the limited rate of spread of the species (2 km per year), however, showed that man-mediated dispersal facilitates the long-distance spread of the species. I found that toad poisoning of native predators —the most feared impact on ecosystems— could cause the local extinction of the cat-eyed snake Madagascarophis colubrinus, which could lead to potential trophic cascades across ecosystems, and possible implications also for human health. Public surveys revealed potentially major socioeconomic impacts —loss of domestic apiaries, poisoning of poultry, and decline of snakes— which cause the greatest societal concerns and, if confirmed, can deepen the systemic socioeconomic vulnerabilities in Madagascar. This thesis provides important baseline information for the management of the invasive Asian toad both in Madagascar and elsewhere, highlighting the importance of investigating fundamental aspects of biology to understand the mechanisms underlying invasion dynamics and impacts.

Fulvio Licata is a BIODIV Ph.D. candidate who will defend his Ph.D. thesis entitled ‘Exploring the invasion dynamics and impacts of the invasive Asian common toad in Madagascar’. His work was supervised by Dr. Angelica Crottini (CIBIO-InBIO/UP), Prof. Gentile Francesco Ficetola (UNIMI, Italy), and Dr. Franco Andreone (Turin MRSN, Italy). Fulvio’s research focuses on the invasion dynamics and impacts of the invasive Asian common toad in Madagascar, where it has been accidentally introduced. Using a multi-analytical approach to modelling morphological, spatial, and public surveys data, Fulvio’s work investigates the extrinsic and intrinsic determinants of range expansion, and the major impacts on the ecosystems and societies of Madagascar, to provide important baseline information for the management of this invasive species.

[Host: Angelica Crottini, Biogeography and Evolution - BIOEVOL, Applied Phylogenetics - AP]