Breeding system and inbreeding depression in the rare orchid,Platanthera praeclara, in a fragmented grassland landscape

Abstract

An important consequence of self-compatibility in plants is that self-pollination can have deleterious effects on plant fitness due to inbreeding. We conducted a hand pollination experiment under field conditions to measure the magnitude of inbreeding depression associated with self-pollination in the rare western prairie fringed-orchid Platanthera praeclara Sheviak and Bowles. By comparing capsules and seeds resulting from cross versus self-pollination treatments, we determined that self-pollination reduces seed quality while having no detectable effect on capsule production or seed numbers. A smaller percentage of seeds resulting from self-pollination contained an embryo (18%) relative to seeds from cross-pollination (46%). Seeds that had an embryo were scored for the size of the embryo, small or large. A smaller proportion of seeds from self-pollination contained a large embryo (75%) relative to seeds from cross-pollination (92%).These results suggest that sexual reproduction and recruitment in this rare plant are dependent on the frequency of pollinator visitations that result in outcrossing.

Anthropogenic fragmentation increases risk of genetic decline in the threatened orchid Platanthera leucophaea

“…The reduction in fitness associated with elevated homozygosity, known as inbreeding depression, is commonly seen in orchids (Juillet et al, 2007; Ortiz‐Barney & Ackerman, 1999; Sletvold et al, 2012). Several studies have shown a reduced seed production in selfed plants, including orchids (Sletvold et al, 2012), the genus Platanthera (Gregg, 1990; Nilsson, 1983; Patt et al, 1989; Travers et al, 2018), and more specifically this species (Wallace, 2003). However, inbreeding depression can also express itself in other demographic life stages including germination, seedling performance, and survival (Juillet et al, 2007; Sletvold et al, 2012).…”

A novel case of autogamy and cleistogamy in Dendrobium wangliangii: A rare orchid distributed in the dry‐hot valley

“…This mode may be beneficial to enhance the adaptability of D. wangliangii to adverse environments, such as drought, short florescence, and pollinator‐scarce conditions (Abdel‐Ghani, Parzies, Omary, & Geiger, ; Miranda & Vieira, ). In addition, cleistogamy reduces the threat of genetic contamination and gene flow through crossing with other plants of the same species (Faisal et al, ; Travers, Anderson, Vitt, & Harris, ; Zou et al, ). Outcrossing has a selective advantage, such as maintaining high genetic diversity and avoiding sibling competition (Antlfinger, ; Cozzolino & Widmer, ; Culley & Klooster, ; Schmitt, Ehrhardt, & Swartz, ).…”

“…In general, cleistogamy is favored under adverse and stressful conditions (e.g., scarce-pollinator, water deficiencies), which are unsuitable for cross-pollination (Schemske, 1978;Solbrig, 1976 (Faisal et al, 2018;Travers, Anderson, Vitt, & Harris, 2018;Zou et al, 2018). Outcrossing has a selective advantage, such as maintaining high genetic diversity and avoiding sibling competition (Antlfinger, 1986;Cozzolino & Widmer, 2005;Culley & Klooster, 2007;Schmitt, Ehrhardt, & Swartz, 1985).…”

We know very little about pollination in the Platanthera Rich (Orchidaceae: Orchidoideae)

“…The most TA B L E 2 Associated floral visitor and pollinator information for various Platanthera species obtained from literature sources. (1971), Dobson (1988), Vogt (1990), Boland (1993), Catling and Catling (1991), Larson (1992) few studies that reported the amount of nectar present, it seems that nectar quantity is highly variable, with reports of 2-4 mm in the spur (Nilsson, 1978) and 3.3 mg (Stpiczynska, 2001) for P. chlorantha, 20 μL (Travers et al, 2018) for P. praeclara, and 0.1 μL (Patt et al, 1989) for P. stricta. Platanthera nectar typically has a high sugar concentration, and sucrose concentrations are much higher than fructose or glucose, according to the few sources available.…”