Pollen thieving and pollen limitation in gynodioecious <i>Polemonium foliosissimum</i> (Polemoniaceae)

Abstract

The limitation of pollen available to pollinators and visitors alike may potentially direct pollinator visitation choice as well as the plant’s ability to provide pollen rewards, nectar rewards, and plant defense mechanisms. Such trade-offs exist in Polemonium foliosissimum A. Gray (Polemoniaceae) a gynodioecious perennial plant in that we tested the hypothesis that pollen limitation would correlate to differences in stigma pollen deposition and plant fitness between females and hermaphrodites within a population sampled off of Kebler Pass Road near Crested Butte, CO (38.86301,-107.12087). As theory dictates that females must either produce more seeds, seeds of higher quality, or render themselves less attractive to herbivores and pre- dispersal seed predators to compensate for loss of male fitness in order to persist in gynodioecious populations (Burd 1994). The role of trade-offs effectively can alter plants’ choices of resource allocation between attracting pollinators and limiting harm from enemies. As such this balance has been investigated for herbivores, florivores, and pre-dispersal seed predators such as Hylemya (Delia) sp. (Diptera: Anthomyiidae), yet there has been insufficient attention in regards to these trade-offs in response to pollen thieves. Pollen thieving muscid flies (Diptera: Muscidae) consume protein-rich pollen with little to no direct pollination. Within hermaphroditic and female P. foliosissimum hermaphroditic advantages of offering protein-rich pollen and male siring capabilities are essentially lost to pollen thieves. This therefore allots females representative equal fitness amongst the gynodioecious population and can potentially warrant correlation with differences in fitness via seed-set quality and quantity between P. foliosissimum. Nevertheless, throughout the manipulation of pollen neighborhoods by removing half of the available pollen from Polemonium in ten 2m 2 plots we saw significant differences in pollen deposition between hermaphroditic and female flowers (p<0.001), but not between manipulation treatments, as denoted as “pre-treatment” and “post- treatment” (p=0.3892) Pollinator visitation rate as well substantiated that pollinators and pollen thieving muscid flies on average spend 95% more time upon hermaphroditic flowers as compared to female flowers (p<0.001). Yet, pollinators and enemies significantly visit more hermaphrodites than females on average (p<0.001), but do not significantly discriminate between number of flowers visited between hermaphrodites and females (p=0.0539) as analyzed in a One-way ANOVA using JMP.

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