What We Think We Know vs. What We Need to Know About Orchid Pollination and Conservation: Cypripedium L. as a Model Lineage

Abstract

While Darwin (1862Darwin ( , 1877 showed that reproductive success in orchid populations depended on adaptive floral morphology coupled with pollinator visitation a more recent review of the literature (Tremblay et al., 2005) confirmed that many out-breeding species are pollinator-limited because most orchid species showing low fecundity also lack rewards. The absence of rewards depresses both pollinator fidelity and the frequency of pollinator visits to an orchid population even though orchid flowers that lack rewards retain the same interlocking floral structures for precise pollinia removal and deposition found in related species that offer rewards. Using the genus, Cypripedium, as a model lineage of non-rewarding flowers this study also shows that the correlation between low fruit set in a Cypripedium sp. and its specific pollinator(s) is insufficient to predict specific frequencies of low fecundity. Annual rates of fruit set often vary broadly between populations of the same species and within the same population over several seasons. We speculate that fruit-set rates also decline when orchid demography and additional biotic and abiotic factors interrupt rates of pollinator activity (pre-zygotic) and fertilization/fruit maturation (post-zygotic). We suggest that that traditional field studies on pollination ecology and breeding systems be combined with data sets recording genetic variation and orchid flower demography in relation to seasonal variation in climate. We also propose that the same information be collected in regard to genetic variation, demography and phenology of populations of known orchid pollinators and co-blooming angiosperm species native to orchid habitats.

Flowers ofCypripedium fargesii(Orchidaceae) fool flat-footed flies (Platypezidae) by faking fungus-infected foliage

“…With a few important exceptions (10,11), bees of various sizes dominate the pollination of Cypripedium spp. (6,7,12,13).…”

“…The genus Cypripedium is regarded as a model lineage of fooddeceptive orchids restricted to temperate regions of the Northern Hemisphere (6,7). No Cypripedium flower studied to date has been found to secrete nectar or to offer accessible, granular pollen.…”

“…No Cypripedium flower studied to date has been found to secrete nectar or to offer accessible, granular pollen. However, observers continue to record insects entering their inflated labellum sacs (6), with the exception of three autonomously self-pollinating species (8,9). The flower often produces a discernible and pleasant aroma, whereas the labellum is often a vivid and contrasting color from that of the broad, solitary staminode and the other five perianth segments.…”

Pollination of slipper orchids (cypripedioideae): a review

“…Despite their wide geographical distribution, diverse habitats, and sizes, all species have the same basic floral morphology and pollination mechanism (Cribb 1987(Cribb , 1997bBernhardt and Edens-Meier 2010;Edens-Meier et al, in press). Species are selfcompatible but require insects to transfer pollen from the anther to the stigma (Edens-Meier et al 2011).…”

Comparative Reproductive Biology of a Rare Endemic Orchid and its Sympatric Congeners in Southwestern China

“…In the plant kingdom, intrinsic traits and factors that are related to breeding systems, pollination patterns, dispersal, competitive ability, and resource use capability can critically influence population abundance (Burne et al, 2003;Gaston and Kunin, 1997). Generally speaking, species having more specific requirements from the surrounding environments will be more vulnerable to becoming rare or endangered (Darwin, 1877;Van der Pijl and Dodson, 1966;Dressler, 1981;Tremblay et al, 2005;Bernhardt et al, 2010) because being "picky" makes them more vulnerable to natural or human-induced environmental changes. Examples of these specific requirements include complete dependency on one or a few species for pollination, particular seed dispersal requirements, or specific nutrient needs.…”