Genetic Differentiation of a New World Screwworm Fly Population from Uruguay Detected by SNPs, Mitochondrial DNA and Microsatellites in Two Consecutive Years

Geographic Population Genetic Structure of the New World Screwworm, Cochliomyia hominivorax (Diptera: Calliphoridae), Using SNPs

The New World screwworm, Cochliomyia hominivorax (Coquerel 1858) (Diptera: Calliphoridae), is a serious parasite of livestock, humans, and other warm-blooded animals. It has been eradicated from the northern parts of its historical range down to the Panama-Colombian border where a permanent barrier zone is maintained. This eradication was accomplished through using the sterile insect technique (SIT). In 2016 there was an outbreak of C. hominivorax in the Florida Keys. In only six months, this pest was successfully re-eradicated using SIT, but the geographic origin of the invasion has yet to be resolved. It was previously determined that the Florida flies most likely represented a single invasion, and it was recommended that a finer-scale genetic assessment should be completed. Thus, this current proof-of-concept study aimed to develop a population genetic database using single nucleotide polymorphisms (SNPs) to reference outbreaks and potentially identify the origin of the Florida outbreak. This initial database consists of wild-caught samples from 4 geographic locations as well as laboratory colony samples that originated from 7 additional locations using a genotyping by sequencing (GBS) approach. Geographic population structuring was identified for twelve populations that clustered according to geographic location. The Florida outbreak samples appeared similar to samples from the outer Caribbean cluster which included samples from Dominican Republic and Trinidad and Tobago, however, these results will be further clarified with the replacement of laboratory colony samples with future wild-caught samples.

Temporal Analysis of Effective Population Size and Mating System in a Social Wasp

Highly social species are successful because they cooperate in obligately integrated societies. We examined temporal genetic variation in the eusocial wasp Vespula maculifrons to gain a greater understanding of evolution in highly social taxa. First, we wished to test if effective population sizes of eusocial species were relatively low due to the reproductive division of labor that characterizes eusocial taxa. We thus estimated the effective population size of V. maculifrons by examining temporal changes in population allele frequencies. We sampled the genetic composition of a V. maculifrons population at 3 separate timepoints spanning a 13-year period. We found that effective population size ranged in the hundreds of individuals, which is similar to estimates in other, non-eusocial taxa. Second, we estimated levels of polyandry in V. maculifrons in different years to determine if queen mating system varied over time. We found no significant change in the number or skew of males mated to queens. In addition, mating skew was not significant within V. maculifrons colonies. Therefore, our data suggest that queen mate number may be subject to stabilizing selection in this taxon. Overall, our study provides novel insight into the selective processes operating in eusocial species by analyzing temporal genetic changes within populations.