Seed production and floral visitors to Pityopsis ruthii (Asteraceae: Asterales), an endangered aster native to the Southern Appalachians

Authors: MOORE, PHILIP - University Of Tennessee; Wadl, Phillip; TRIGIANO, ROBERT - University Of Tennessee; SKINNER, JOHN - University Of Tennessee; KLINGEMAN, WILLIAM - University Of Tennessee

Submitted to: Journal of Kansas Entomological Society
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/1/2021
Publication Date: 11/16/2021
Citation: Moore, P.A., Wadl, P.A., Trigiano, R.N., Skinner, J.A., Klingeman, W.E. 2021. Seed production and floral visitors to Pityopsis ruthii (Asteraceae: Asterales), an endangered aster native to the Southern Appalachians. Journal of Kansas Entomological Society. 93(4):327-348. https://doi.org/10.2317/0022-8567-93.4.327.
DOI: https://doi.org/10.2317/0022-8567-93.4.327

Interpretive Summary: Pityopsis ruthii, is a federally endangered herbaceous perennial species that is only known to grow along two rivers in the world, both in southeastern Tennessee. There has been documented inbreeding and small population sizes for the species which has contributed to reproductive capacity leading to concern for the long-term survival of the species. A gap in knowledge regarding the floral visitors to Pityopsis ruthii exists and an assessment can be used to support conservation management for the species. Therefore, researchers at the University of Tennessee and the USDA completed a floral visitor survey for the species within naturally occurring plant populations and at a common garden planting over two years. Forty-seven insect species, representing 15 families and 3 orders were recovered across 2 years during more than 70 hours of observation and specimen collection. Honeybees and the common eastern bumble bee were common in the natural populations, whereas Toxomerus geminatus (a fly species that mimics stinging bees and wasps) was the most abundant floral visitor. Evidence for inbreeding depression was validated through investigating seed germination from controlled crosses between geographically dissimilar parent plants from distal ranges of the river systems where the species occurs. Our study provides critical knowledge that was lacking for Pityopsis ruthii floral visitors and should be used to assist breeding efforts intended to increase genetic diversity through ongoing efforts in plant reintroduction and habitat management.

Technical Abstract: Pityopsis ruthii (Small) Small (Asteraceae: Asterales) is a federally endangered, grass-leaved golden aster that only grows along short stretches of the Hiwassee and Ocoee Rivers in southeastern Tennessee, U.S.A. The species is self-incompatible and small populations of plants have experienced genetic drift and inbreeding depression. Multiple investigators have observed highly variable sexual reproductive capacity of P. ruthii. To assist in conservation management, an assessment of floral visitors to P. ruthii plants was undertaken at in situ and ex situ locations. Forty-seven insect species, representing 15 families and 3 orders were recovered across 2 years during more than 70 hours of observation and specimen collection. Greater abundance of P. ruthii inflorescences did not reliably influence floral visitation during observations made during flowering at both in situ and ex situ locations. Megachile brevis Say specimens carried the most pollen across two years of sampling, yet just three specimens were collected, all from the ex situ location. In both years, Halictidae were common at the ex situ location, but infrequently collected or observed at the in situ locations. Apis mellifera L. and Bombus impatiens Cresson were commonly observed at in situ locations in both years, and at the ex situ location only in 2013. Toxomerus geminatus (Say), which was the most abundant floral visitor in both years and particularly at in situ locations, carried very little pollen. Floral visiting lepidopteran species carried no pollen. Assessments of filled seed yielded low germination rates. Hybridization between geographically disparate parent plants propagated from the distal ranges of Hiwassee River distribution yielded an average of 33 percent germination, validating evidence of inbreeding depression. Knowledge of P. ruthii floral visitors at in situ and ex situ locations can be employed to assist breeding efforts intended to increase genetic diversity through ongoing efforts in plant re-introduction and habitat management.