Seed Production and Floral Visitors to Pityopsis ruthii (Asteraceae: Asterales), an Endangered Aster Native to the Southern Appalachians

Abstract

Pityopsis ruthii (Small) Small (Asteraceae: Asterales) is a federally endangered 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 genetic drift and inbreeding depression have been reported. Multiple investigators have observed highly variable sexual reproductive capacity of P. ruthii. To better understand which insect species may be contributing roles as potential pollinators, floral visitation to P. ruthii was assessed at in situ and ex situ locations. Forty-seven insect species in 15 families and 3 orders were recovered across 2 years during more than 70 hours of observation and specimen collection. Megachile brevis Say (Megachilidae: Hymenoptera) carried the most pollen, yet just three specimens were collected, all from the ex situ location. In both years, Halictidae were common at the ex situ location and were infrequently collected at the in situ location. Apis mellifera L. (Apidae: Hymenoptera) and Bombus impatiens Cresson (Apidae: Hymenoptera) were commonly observed at in situ locations in both years, and in 2013 at the ex situ location. Toxomerus geminatus (Say) (Syrphidae: Diptera) was the most abundant floral visitor in both years but carried very little pollen. Floral visiting lepidopteran species carried no pollen. Greater numbers of P. ruthii inflorescences did not reliably influence Apoidea or Syrphidae floral visitor abundance in either the in situ or ex situ locations. Assessments of filled seeds revealed 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.