The western area of the Iberian Peninsula could be determinant in the original place of the ancestral population of Drosophila subobscura, an invasive species widely spread around different latitudes. This conclusion results from a study based on the study of adaptive genetic markers, published in the journal Proceedings of the Royal Society B and led by Marta Pascual, expert from the Faculty of Biology and the Biodiversity Research Institute (IRBio) of the University of Barcelona.
The study supports the use of adaptive genetic markers combined with genetically informed environmental niche modelling as the scientific methodology to help determine the potential areas of origin of the colonizer species. Moreover, these indicators could be useful to define areas that are not colonized yet and of potential interest for the invasive species. The study counts on the participation of experts from the University of Oporto (Portugal) and the University of Washington and National Science Foundation (United States), among others.
Drosophila subobscura: from the Mediterranean basin to the American continent
The study confirms the hypothesis that marks the Mediterranean basin as the original place for the D. subobscura colonizer individuals, a native species from the palearctic area which colonized the American continent in the late seventies, in the 20th century. Like other invasive species, an anthropic environment (freight traffic, etc.) would have made it easier for the species to spread.
According to the experts, during the colonizing process of D. subobscura, North and South America underwent a bottleneck effect, and both hemispheres were colonized in a sequential manner. The study confirms the influence of the origin and the genetic composition of the founding individuals in the dispersal of the species. Compared to other previous modelling studies on the potential distribution of the species, this study model considers the existence of local adaptations that can allow a bigger adaptation to certain environmental conditions.
“Genetic data enabled determining that chromosomal arrangements of the species are adaptive –in particular, to cold and warm environments–, and their frequencies vary quickly depending on the environment”, notes Pascual, lecturer at the Department of Genetics, Microbiology and Statistics of the UB.
“This knowledge –she continues– has been determining to design different models and assess how they behave to predict the biogeographical distribution of the species”.
The current distribution in the American continent could not be completely explained if the origins of the colonizers were in northern Europe, whereas if these were from the south, there would be a better explanation, according to the authors. Therefore, the model that better predicts the colonized region by D. subobscura is the one based on populations with a high frequency of warm chromosomal arrangements.
Apart from inferring potential areas of origin of the colonizers, the distribution models of the species combined with adaptive genetic markers can contribute to identify future situations of introduction and spread of a new invasive species.
“If the colonizers come from a specific area, we can predict the potential distribution of the species. If they come from different environments, the dispersal potential can be very powerful. With this knowledge, measures could be taken to prevent invasive species from reaching certain areas of the world. Once they colonize an environment, it is very hard to remove them from there”, concludes the researcher
«Si los colonizadores proceden de una zona determinada, podemos predecir cuál puede ser la distribución potencial de la especie. Si vienen de zonas con ambientes distintos, el potencial de dispersión puede ser muy potente. Con este conocimiento, se podrían tomar medidas para evitar la llegada de especies invasoras a determinadas regiones del mundo. Una vez han colonizado un ambiente, es muy difícil erradicarlas», concluye la investigadora.
Sillero, N.; Huey, R. B.; Gilchrist, G.; Rissler, L.; Pascual, M. “Distribution modelling of an introduced species: do adaptive genetic markers affect potential range?”. Proceedings of the Royal Society B, 2020, September 2020. Doi: https://dx.doi.org/10.1098/rspb.2020.1791