Microsatellite DNA analysis of population structure in Cornops aquaticum (Orthoptera: Acrididae), over a cline for three Robertsonian translocations

Abstract

The grasshopper Cornops aquaticum occurs between Mexico (23°N) and Uruguay and Central Argentina (35°S). It was recently introduced as a pest control agent of the neotropical water-hyacinth Eichhornia crassipes in South Africa. The information about the amount and distribution of genetic variability of the native populations may optimise the results of biological control programmes. Here we analyse microsatellite variability at the south of C. aquaticum’s distribution, coinciding with a cline for three polymorphic Robertsonian translocations along the Paraná River in order to: (1) estimate the amount of intrapopulation variation and its correlation with geographic/climatic variables, (2) infer interpopulation genetic variation and assess connectivity between local populations and (3) compare chromosome, morphometric and molecular variation patterns to analyse the probable causes involved in the maintenance of intraspecific variation. Our sample of 170 individuals of C. aquaticum from seven Argentine populations between latitudes 27°S to 34°S showed 211 alleles across seven microsatellite loci. Genetic diversity was estimated through average number of alleles, allelic richness, expected heterozygosity and observed heterozygosity. The analysis of molecular variance showed significant genetic differentiation among populations. Pairwise comparisons of FST/RST and Bayesian population assignment method and the discriminant analysis of principal components revealed that the two southernmost populations are more differentiated. Genetic diversity is negatively correlated with Southern latitude and with Robertsonian translocation frequencies. Our results showed that the Paraná River’s middle course populations are genetically undifferentiated and more genetically diverse than the highly chromosomally polymorphic downstream ones. The chromosomal polymorphisms are associated with increased body size in the direction in which larger size is adaptive. This may be relevant for C. aquaticum’s role as a pest control agent, since chromosome variability would enhance the ability of the species for a successful settlement in its new habitats, especially in temperate regions of the world.