Conservation assessment of a range-edge population of Trichophorum planifolium (Cyperaceae) reveals range-wide inbreeding and locally divergent environmental conditions

Abstract

Peripheral populations hold special conservation significance as repositories of genetic diversity, while they may also be at increased risk of extirpation. We collected genetic, ecological, and distributional data to evaluate an endangered range-edge population of Trichophorum planifolium (Sprengel) Palla. Our data show that, range-wide, T. planifolium has remarkably low within-population diversity, and most populations are dominated by a small number of unique genotypes. However, the extremely low observed and expected heterozygosity we document is comparable to results from other woodland sedges. The life history of this species results in high levels of inbreeding. The low diversity of the single remaining Canadian population is therefore not unusual for this species and does not support suggestions that this population suffers from elevated inbreeding depression. However, it is geographically isolated, and its soil environment is unusual for the species. These conditions may have facilitated local adaptation of conservation value for the long-term persistence of this species. In addition, we identified populations within the core range of this species that are comparably isolated to the peripheral population or that demonstrate greater genetic divergence. Consequently, while distinctions between core and peripheral populations are important for conservation management, understanding variation across the range of a species is key to effective protection.