Despite their apparent integration, spur length but not perianth size affects reproductive success in the moth-pollinated orchid Platanthera bifolia

• The evolution of many floral traits is thought to have been shaped  by pollinator-mediated selection for increased attractiveness or an   improved mechanical fit of flowers to pollinators. Yet, few studies have examined experimentally the independent and interactive effects of   different aspects of flower morphology on plant reproductive success.   In the orchid Platanthera bifolia, perianth size and spur length are   positively correlated within and among populations. To test the hypothesis that pollination success and seed output increases with   increasing perianth size and spur length, we manipulated the two traits   in a factorial design in a long-spurred population of P. bifolia   pollinated by long-tongued hawkmoths. Additionally, to determine   whether differences in selfing rate can explain variation in fruit set   and fruit size, we performed controlled self- and cross-pollination.   Plants with long spurs had more flowers pollinated, more pollen removed   and produced more and larger fruits compared to plants with short   spurs. In contrast, perianth size did not affect the pollination   success or fruit production of P. bifolia.   Fruit production and fruit size did not differ among flowers pollinated   with self- and cross pollen, respectively. This indicates that reduced   pollen deposition rather than pollinator-mediated self-pollination   caused the reduction in fruit set and fruit volume observed after   shortening of the spur.   The results demonstrate that spur length, but not perianth size, is   critical for reproductive success in P. bifolia, and suggest that   among-population differentiation in perianth size may reflect a  correlated response to selection on spur length. The results are  consistent with the hypothesis that visual display is less important   than other cues for the reproductive success of P. bifolia, and   underscore the necessity to experimentally examine the functional   significance of putatively adaptive traits.

Ämnesord

NATURVETENSKAP  -- Biologi (hsv//swe)

NATURAL SCIENCES  -- Biological Sciences (hsv//eng)

Nyckelord

pollination success

seed output

floral evolution

floral display

flower morphology

pollen removal

Biology

Biologi

Publikations- och innehållstyp

ref (ämneskategori)

art (ämneskategori)