Biological invasions: a temporal, spatial and plastic point of view: the case of Discoglossus pictus in Europe = Invasions biològiques: un punt de vista temporal, espaial i plàstic : el cas de Discoglossus pictus a Europa

Abstract

The rates at which allochthonous species are introduced and become invasive worldwide are unprecedented and accordingly, the number of studies on invasion biology have increased during the past years. However, biological invasions are still seemingly underused as natural laboratories to test essential biological theory. In this sense, the nine studies – ordered in three parts, which function as thematic blocks – 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 Southern France approximately a century ago, being nowadays present on a wide coastal strip of approximately 250km in SE France and NE Spain, constantly colonizing new areas. 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: 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. We here 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 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. Both competitors also differ mildly in their breeding preferences, but 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. Finally, in “PART C: Tadpoles of Discoglossus pictus as prey for aquatic native predators”, two studies examine if invasive tadpoles modify its phenotypes in front of an array of – native and invasive – predators, testing also the effectiveness of the possible changes. 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. Globally, the complex evolutionary history of the local anuran assemblages poses the Mediterranean Painted Frog as a good model for ecological and evolutionary studies reaching beyond invasion biology, as it is very particular case of invasive species, in which effects of previous recurrent shared evolutionary history with similar competitor / predator species are probably present.

Les invasions biològiques estan essent aparentment infrautilitzades com a laboratoris naturals per investigar certs aspectes teòrics fonamentals de la biologia. En aquest sentit, els nou estudis presentats en aquesta tesi – ordenats en tres blocs temàtics – intenten donar un punt de vista evolutiu – a part d'ecològic – sobre la invasió de la granota pintada (Discoglossus pictus) a Europa. Aquesta granota es va introduir des d'Algèria a Banyuls de la Marenda (Catalunya Nord) fa aproximadament un segle, arribant ara des de Montpeller fins a Sant Celoni, colonitzant contínuament noves àrees. A la "PART A: variabilitat intraespecífica al llarg de la distribució invasora de Discoglossus pictus" observem que la granota pintada no forma un conjunt uniforme de poblacions en la seva distribució invasora europea, ni fenotípica ni genòmicament: la mida i els trets de la història vital dels adults es relacionen amb la precipitació mitjana de cada zona, mentre que la diferenciació genètica entre poblacions ha estat molt probablement creada pel procés d'expansió en sí. A la "PART B: Competència intra-gremi en capgrossos de Discoglossus pictus" veiem que la granota pintada representa, fisiològicament, una addició única al gremi local de capgrossos, caracteritzada per un creixement molt ràpid i orientat al consum, amb bones capacitats d'augmentar la qualitat i quantitat de la ingesta d'aliments quan n'hi ha possibilitats. Pel que fa a la freqüent relació de competència entre Epidalea calamita i Discoglossus pictus, podem observar que els capgrossos autòctons que han tingut un major nombre de generacions de contacte amb els invasors són capaços d'infligir un major estrès competitiu en aquests. Els dos competidors també difereixen lleugerament en les seves preferències de cria, però semblen estar obligats a acabar competint molt sovint a nivell de bassa. Dins d'aquestes, la posició tròfica d'ambdues espècies pot respondre tant a patrons evolutius com a patrons ecològics amb les dades recollides fins ara. Finalment, a la "Part C: Capgrossos de Discoglossus pictus com a presa per depredadors aquàtics autòctons" veiem que la granota invasora presenta un patró de defenses induïbles que s'emmotlla al que s'esperaria per a un anur autòcton, responent a tots els depredadors nadius eficaçment, mancant respostes davant de depredadors introduïts. La complexa història evolutiva dels conjunts d'anurs del mediterrani occidental posa la granota pintada com un cas molt particular d'espècie invasora, on no ses poden descartar els efectes d'una història co-evolutiva prèvia entre espècies similars.