Divergence in floral scent and morphology but not thermogenic traits associated with pollinator shift in two brood-site mimicking Typhonium (Araceae) species.

Abstract

BACKGROUND\nFlowers which imitate insect oviposition sites likely represent the most widespread form of floral mimicry, exhibit the most diverse floral signals and are visited by two of the most speciose and advanced taxa of insect - beetles and flies. Detailed comparative studies on brood-site mimics pollinated exclusively by each of these insect orders are lacking, limiting our understanding of floral trait adaptation to different pollinator groups in these deceptive systems.\n\n\nMETHODS\nTwo closely related and apparent brood-site mimics Typhonium angustilobum and T. wilbertii (Araceae) observed to trap these distinct beetle and fly pollinator groups were used to investigate potential divergence in floral signals and traits most likely under pollinator-mediated selection. Trapped pollinators were identified and their relative abundances enumerated, and thermogenic, visual, and chemical signals and morphological traits were examined using thermocouples and qRT-PCR, reflectance, gas chromatography-mass spectrometry, floral measurements and microscopy.\n\n\nKEY RESULTS\nT. angustilobum and T. wilbertii were functionally specialised to trap saprophagous Coleoptera and Diptera, respectively. Both species shared similar colour and thermogenic traits and contained two highly homologous AOX genes (AOX1a and AOX1b) most expressed in the thermogenic tissue and stage (unlike pUCP). Scent during the pistillate stage differed markedly - T. angustilobum emitted a complex blend of sesquiterpenes, and T. wilbertii, a dung mimic, high relative amounts of skatole, p-cresol, and irregular terpenes. Species differed significantly in floral morphology related to trapping mechanisms.\n\n\nCONCLUSIONS\nFunctional specialisation and pollinator divergence were not associated with differences in anthesis rhythm and floral thermogenic or visual signals between species, but with significant differences in floral scent and morphological features, suggesting these floral traits are critical for the attraction and filtering of beetle or fly pollinators in these two brood-site mimics.