Molecular study of systematics and biogeography of sunflower seed weevils in North America

Shujuan Li, Purdue University

Abstract

Sunflower (Helianthus annuus L.) has had a long association with the native pests, red sunflower seed weevil ( Smicronyx fulvus L.) and gray sunflower seed weevil (Smicronyx sordidus L.). We investigated the phylogenetic relationships and population structures of red and gray sunflower seed weevil populations collected on either side of the Rocky Mountains using nuclear 18S rDNA, mitochondrial ribosomal DNA, and microsatellites. The results showed that the sunflower seed weevils are sister taxa in a monophyletic clade. No significant relationships attributable to geographic barriers were found. Thirty-three unique mitochondrial 16S rDNA sequences (haplotypes) were identified and the sequence divergence among haplotypes ranged from 0.2 to 3.68%. Because more individuals per population could be collected for gray sunflower seed weevil than for red, a more detailed study of population structure was possible for this species. Most of the genetic variation observed in gray sunflower seed weevil resulted from variation within populations. Contiguous range expansion appeared to be the main mechanism for increased variability within the species. Significant differences were found in analyses of five polymorphic microsatellite loci in four geographically separated field populations from which multiple individuals could be collected. More genetic differences occurred among weevil populations collected from sunflowers along the East-West axis than among weevil populations collected on a North-South axis. The overall results are consistent with current theories concerning the origin of the sunflower. The population represented by haplotype 33 from Texas is likely a new species that evolved independently. The sample size for this species was limited and additional studies are needed.

Degree

Ph.D.

Advisors

Oseto, Purdue University.

Subject Area

Entomology

COinS