Vulnerability of a specialised pollination mechanism to climate change revealed by a 356-year analysis

Pollination of Ophrys sphegodes by sexual deception of male Andrena nigroaenea bees depends both on male bees emerging before female bees and before flowering, and on the orchid flowering before female bee emergence, so that competition for the services of naïve male bees is avoided. Using previously-established relationships between the timing of these phenological events and spring temperature, we model flowering and bee emergence dates from 1659-2014, using Central England Temperature records. All phenological events were predicted to advance significantly over this period, accompanying a trend towards warmer springs. The interval between male and female flight decreased over time, whereas that between male flight and flowering increased. In addition, female flight preceded orchid flowering after warm springs, and it preceded both flowering and male bee flight following the warmest springs. Such reversals in phenology have increased in frequency over the last 356 years. In most years, the Ophrys/Andrena pollination system achieves very limited pollination success. The results presented here suggest that climate warming has changed the timing of the phenological events that are critical to reproductive success in O. sphegodes, and that continuing warming will increase the frequency of years in which this rare orchid suffers complete reproductive failure.