Efecto de los procesos demográficos recientes en los patrones genéticos de las poblaciones del abejorro nativo Bombus dahlbomii y del abejorro exótico Bombus terrestris (Hymenoptera: Apidae) en Chile
Fecha
2019Autor
Poulin, Elie
UNIVERSIDAD DE CHILE
Institución
Resumen
Invasive species have been recognized as a significant component on biodiversity declines in the world. However, invasive species offer an excellent opportunity to study biological processes in populations. Genetic diversity may play a key role in establish and spread of invasive species. Colonization events may involve a population bottleneck because the number of initial colonists is often small (founder effect). This effect may be especially strong when all colonists are drawn from the same source population. However, how do invasive species spread and adapt to new conditions if they have low genetic diversity (Genetic paradox of biological invasions)? Multiple introductions can create invasive populations that are much more genetically diverse than any single source population. Different colonizing populations of the same species are likely to be genetically divergent with different levels of genetic variation and therefore have different capacities to promote invasiveness. Native species could have their population size reduced, given the interspecific competition or pathogen infections from invasive species, specially, if the invasive species is congeneric. Small populations tend to lose genetic diversity more quickly than large populations due to genetic drift effects. Also, small population sizes may cause inbreeding depression (increase of homozigosity), which can reduces the survival of the population and thereby increases the risk of extinction. Bombus dahlbomii is a native bumblebee from Chile and Argentina, and in Chile has had a drastic reduction of its population size in the last 20 years, coincident with the introduction of Bombus terrestris into Chile in 1997. B. terrestris was introduced to pollinate tomatoes and has had a quick demographic and geographic expansion in Chile. Decline of B. dahlbomii populations may be explained for habitat loss by land-use change and disturbance by fires in Chile, competition with no-native pollinators, climate change and, above all, parasite transmission from exotic bumblebee (B. terrestris). Using molecular markers (microsatellite genotyping) we evaluated the effect of population decline of B. dahlbomii and demographic and geographic expansion of B. terrestris on the genetic patterns (genetic diversity, genetic structure and gene flow) of its populations in Chile. Additionally, we evaluate and compare the current geographic distribution of B. terrestris and B. dahlbomii in Chile by SMDs analysis and compare the parasites prevalence (C. bombi and N. bombi) in B. terrestris and B. dahlbomii populations from Chile by molecular detection. 9 Our results suggest that there is a low effect of population decline on genetic diversity and genetic structure in B. dahlbomii populations. We found high levels of genetic diversity, especially, allelic richness. On the other hand, we detected evidence of a strong genetic bottleneck in Pichiquillaipe population; and reduced gene flow between B. dahlbomii populations. In B. terrestris our results showed high levels of genetic structure and high genetic differentiation in populations from central and central-south of Chile. On the other hand, we found reduced gene flow between B. terrestris populations. These results are consistent with multiple introductions hypothesis, which could play a key role in establish and spread of B. terrestris in Chile. Finally, we found a range contraction in B. dahlbomii, mainly in Patagonian region and along the Andes and valley in central Chile and in invasive bumblebee our results suggest that B. terrestris not being at equilibrium yet in Chile. Parasite detection showed high levels of N. bombi and C. bombi prevalence in B. dahlbomii and B. terrestris populations. N. bombi was found for first time in B. dahlbomii populations by molecular methods. It is remarkable the high values of C. bombi and N. bombi prevalence for population Pichiquillaipe. Both pathogens have the highest values of prevalence for B. dahlbomii populations in Pichiquillaipe. Also, Pichiquillaipe show significantly reduced genetic diversity, evidence of genetic bottleneck, and high genetic differentiation. This detection of C. bombi and N. bombi in B. dahlbomii is consistent with the hypothesis of a pathogen spillover from B. terrestris