From where, how and how many times? History of the invasion of Senecio madagascariensis (Asteraceae) in South America

COULLERI, JUAN PABLO; BREM, MARTA CAROLINA; MAYER, JOAQUÍN ; ROBLEDO DOBLADEZ, GERMÁN

Puerto Iguazú

Simposio; XVI International Symposium on Biological Control of Weeds; 2023

ISBCW

Senecio madagascariensis commonly named fireweed, is a southern Africa native species,recognized as invasive in Australia, south-east Asia, South America and the HawaiianIslands. This species occurs in roadsides, fallows, wastelands and anthropized areas. Anindividual of S. madagascariensis can produce up to 18.000 seeds that are dispersed bywind. Unfortunately, these plants contain pyrrolizidine alkaloids that cause cumulativechronic liver damage and fatality, especially in monogastric livestock. Phylogeographicand population genetic analyses can provide important insights into the dynamics ofbiological invasions by elucidating geographical source(s), dispersal route(s), spread andthe roles of evolutionary processes in invasion success. Thus, in order to have a morecomprehensive understanding of the invasion of S. madagascariensis in southern SouthAmerica, we aimed a) to clarify the origin of introduced genotypes and b) determine thegenetic diversity and the structure of the invasive populations. To achieve our goals, weused a genetic characterization with internal transcribed spacer (ITS) from 57 populationsbelonging to Argentina and Brazil and 26 others populations? available in Genebankbelonging to different parts of the world of both native and invasive range. We analyzedthe haplotype and nucleotide diversity and an AMOVA among collection sites. Theevolutionary relationships among the sequences were performed, sequences of S.inaequidens from GenBank were used as outgroup. In addition, we used 8 microsatellitemarkers in 342 individuals for the 57 populations through which the genetic diversity wasestimated using the parameters: number of alleles, allelic richness, expected and observedheterozygosity, deviations of the genotype frequencies Hardy-Weinberg equilibrium andthe inbreeding coefficient (FIS). Moreover, the relationships between geographic andgenetic (FST) distances among populations were tested at the structure and scale ofgeographic differentiation among populations. The phylogeographic results indicate thatthe Argentinian populations are originating from South Africa, while the Brazilian one’srepresent diverse provenances. These results become more relevant with the evidence frompopulation genetic studies from which Argentinian populations are represented by only onedeme, whereas the populations that are present in Brazil are split into 2 demes representedby populations that occurred in the center of the distribution area and the other deme isrepresented in the coastal area of the country.