Morphology delimits more species than molecular genetic clusters of invasive Pilosella

Authors: MOFFAT, CHANDRA - University Of British Columbia; ENSING, DAVID - University Of British Columbia; Gaskin, John; DE CLERCK-FLOATE, ROSEMARIE - Agri Food - Canada; PITHER, JASON - University Of British Columbia

Submitted to: American Journal of Botany
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/17/2015
Publication Date: 7/13/2015
Publication URL: http://handle.nal.usda.gov/10113/61246
Citation: Moffat, C.E., Ensing, D.J., Gaskin, J.F., De Clerck-Floate, R.A., Pither, J. 2015. Morphology delimits more species than molecular genetic clusters of invasive Pilosella. American Journal of Botany. 102(7):1145–1159. DOI: 10.3732/ajb.1400466.

Interpretive Summary: Reliable identifications of invasive species are essential for effective management. Several species of hawkweeds invade North America, where unreliable identification hinders their control. Here we ask (i) do morphological traits dependably discriminate among species? (ii) if so, which traits are most reliable? (ii) are putative species supported by genetic clustering? (iv) how strong is the association between morphological and genetic variation? and (v), are novel hybridizations occurring in the invaded range? We sampled 353 individuals of six hawkweed species throughout the invaded range of British Columbia, Canada. Key results: We found (i) that field-identified specimens could be reliably distinguished using morphology, with eight traits being especially discerning; (ii) strong species-level differentiation in the genetic data, though six putative species consistently grouped into four species; and (iii) a reasonably strong association between morphological and genetic dissimilarity. By identifying highly discerning morphological characters, and by clarifying patterns of variation among populations of invasive hawkweeds, we have provided the foundations for more focused and effective hawkweed control efforts.

Technical Abstract: Premise of the study: Reliable identifications of invasive species are essential for effective management. Several species of Pilosella (syn. Hieracium, Asteraceae) hawkweeds invade North America, where unreliable identification hinders their control. Here we ask (i) do morphological traits dependably discriminate among putative (field-identified) species? (ii) if so, which traits are most reliable? (ii) are putative species supported by genetic clustering? (iv) how strong is the association between morphological and genetic variation? and (v), are novel hybridizations occurring in the invaded range? Methods: We sampled 353 individuals of six Pilosella species throughout the invaded range of British Columbia, Canada. We assessed 33 morphometric characters for their discriminatory power using the randomForest classifier and, using amplified fragment length polymorphism (AFLP) techniques, we evaluated genetic cluster support in STRUCTURE, CLUMPP and DISTRUCT, and via analysis of molecular variance. We assessed the strength of the association between morphological and genotypic dissimilarity using a Mantel test. Key results: We found (i) that field-identified specimens could be reliably distinguished using morphology, with eight traits being especially discerning; (ii) strong species-level differentiation in the AFLP loci tested, though six putative species consistently grouped into four clusters; and (iii) a reasonably strong association between morphological and genetic dissimilarity. Our findings were more consistent with multiple introductions for some species of Pilosella than with novel hybridizations. Conclusions: By identifying highly discerning morphological characters, and by clarifying patterns of genotypic variation among populations of invasive Pilosella, we have provided the foundations for more focused and effective hawkweed control efforts.