Resumen de Biological invasions: a temporal, spatial and plastic point of view
The rates at which allochthonous species are introduced and become invasive worldwide are unprecedented, and the economic and ecological losses linked to these processes are overwhelming. Accordingly, the number of studies on invasion biology have increased during the past years. However, despite great opportunities for the study of phenotypic or genetic evolution, biological invasions are still seemingly underused as natural laboratories to test essential biological theory. In this sense, the nine studies presented in this thesis try to globally give an evolutionary – apart from ecologic – point of view on the ongoing invasion of the Mediterranean Painted Frog (Discoglossus pictus) in Europe. This frog is native to Northern Africa and was introduced from Algeria in Banyuls de la Marenda (Southern France) approximately a century ago, being nowadays present on a wide coastal stripe of approximately 250km from Montpellier (SE France) to Sant Celoni (Barcelona, NE Spain).
The aim of “PART A: Intraspecific variation along the invasive range of Discoglossus pictus” is the examination – at a phenotypic and genomic level – of possible differences across populations within the invasive range of the species. We observe that the Mediterranean Painted Frog is not a uniform unit in its invasive range in Europe, neither from a phenotypic nor a genomic point of view: mean size of adults and life-history traits related to mean annual precipitation, while substantial genetic differences among populations are most probably created by the expansion history itself.
The aim of “PART B: Intraguild competition in tadpoles of Discoglossus pictus” is to study and discuss the role of Discoglossus pictus tadpoles as potential competitors for the larvae of native anurans. In this section, we see that the Mediterranean Painted Frog represents, physiologically, a unique addition to the local tadpole guild, characterized by a very rapid and consumption-oriented growth, and that these tadpoles are able also to increase the quality and quantity of its food intake when these possibilities are provided. This poses these tadpoles as potentially very disruptive of the natural dynamics of native anurans. Concerning the competitive relationship between the Natterjack Toad (Epidalea calamita) and the Mediterranean Painted Frog, we can observe that it changes according to previous evolutionary history of populations. In this sense, populations of the native toad that have had a greater number of generations of contact with the invasive frog are able to inflict a greater competitive distress on the invasive tadpoles, pointing at an optimistic long-term scenario in this case. Both competitors also differ mildly in their breeding preferences, and direct competitor avoidance seems also plausible according to results here presented. Nevertheless, both species seem forced to end up competing very often at a pond level. Within ponds, the trophic position of both species can respond either to evolutionary or to ecological patterns with the data gathered hitherto, and data from the most genetically differentiated population with isotopic data – La Jonquera – will probably disentangle which is the dominant pattern.
Finally, in “PART C: Tadpoles of Discoglossus pictus as prey for aquatic native predators” two studies examine the degree in which tadpoles modify its phenotypes in front of a chosen array of – native and invasive – predators. Interestingly, the invasive frog presents a pattern of inducible defences which would be expected for a native anuran, responding to all native predators effectively, while lacking responses in front of introduced or invasive predators. This makes us discard additional predation costs on the invasive frog in comparison to native species due to lack of previous knowledge of the native predators.
Globally, the complex evolutionary history of the local anuran assemblages poses the Mediterranean Painted Frog as a very particular case of invasive species, in which effects of previous recurrent shared evolutionary history with similar competitor / predator species are probably present. Hence, the Mediterranean Painted Frog is a good model for ecological and evolutionary studies reaching beyond invasion biology, and signals that an evolutionary focus is probably essential for realistic long-term predictions of the impacts and ecological role of any invasive species.
