The bracts of the alpine 'glasshouse' plant R heum alexandrae ( Polygonaceae) enhance reproductive fitness of its pollinating seed-consuming mutualist.

Environmental conditions are known to affect the reproductive fitness of insects, as do host plants. Although the highly specialized bracts of Himalayan 'glasshouse' plants are thought to be an adaptive morphology that allows the plant to reproduce in harsh alpine environments, little information appears to exist concerning the benefit of these bracts for the pollinating insects. In this study, we examine whether the semi-translucent bracts of R heum alexandrae, a giant herb endemic to the alpine zone of the Hengduan Mountains in south-western China, enhance the reproductive fitness of its pollinator. R heum alexandrae depends mainly on mutualistic seed-consuming B radysia flies for pollination. Bracts increased interior temperature on sunny days, acted as a buffer against fluctuating air humidity, greatly decreased the intensities of ultraviolet B/ C radiation and provided shelter from strong winds. Bract removal significantly decreased adult oviposition and offspring performance of pollinators during flowering and fruiting, respectively. Our results indicate that the bracts of R. alexandrae enhance the reproductive fitness of its pollinating seed-consuming mutualist in alpine environments, which may be attributed to the positive effects of the bracts on the interior microenvironment. © 2015 The Linnean Society of London, B otanical J ournal of the L innean S ociety, 2015, 179, 349-359. [ABSTRACT FROM AUTHOR]