Print PageGenetic population structure is the organization of individuals into genetically distinct sub-populations. Population structure could be a function of ecological characteristics. Agro-ecosystems are characterized by extensive monocultures of crops over large areas, under managed environment. Cultivated cotton (Gossypium hirsutum) is an introduced crop into the United States. Its cultivation as a vast monoculture only dates back to late 1700’s. A native insect, Pseudatomoscelis seriatus is currently pest of cotton in the United States, besides being associated with several native wild host plants. P. seriatus provides the opportunity to study genetic variation within an extensive geography and in multiple host plant species. Specifically, we wanted to know if P. seriatus has any population structure with respect to geography and host plant species.
We used both nuclear molecular markers (AFLP) and mitochondrial gene (COI) sequences to assess genetic variation of different geographic and host-associated populations. This study included 11 geographic locations distributed across the cotton growing states in the US, and 5 different locations within the state of Texas in which P. seriatus was collected from 3 host plants.
Results/Conclusions
Bayesian analysis of AFLP markers showed no geographic population structure of P. seriatus populations associated with only cotton across 11 states in the United States. P. seriatus populations associated with two native host plants (Monarda punctata and Croton capitatus) in Texas revealed host-associated differentiation in M. punctata and G. hirsutum. Interestingly, this host-associated genetic differentiation was observed in only 3 out of the 5 locations in Texas in which host-plant populations were sampled. In the other two locations, fleahopper populations were not structured by host-plant. The COI sequence of individuals from different host-associated populations did not show any genetic differentiation.
The result of no geographic population structure among P. seriatus populations associated with cotton in a large geographic scope (from Arizona to North Carolina) indicates that the different geographic populations are either connected by gene flow and/or there is a single genotype infesting cotton without much evolution over a short time period since expansion of cotton cultivation throughout US. The observed genetic differentiation in P. seriatus populations associated with different hosts in 3 locations within Texas is an interesting pattern. Future studies should explore the ecological and evolutionary mechanisms explaining this pattern.
