Expanding Floral Multimodality
: Floral Temperature and Floral Humidity

  • Mike Harrap

Student thesis: Doctoral ThesisDoctor of Philosophy (PhD)


Flowering plants produce floral displays that both attract pollinators and allow them to learn flower identity. How well these displays do this can be critically important to pollinator and plant success, and thus is also important to the evolution of both mutualists. Floral displays are multimodal, they produce many complex floral signals through different sensory modes (such as visual, olfactory and tactile) simultaneously. Why floral displays are multimodal is not fully understood. This is due to the majority of research focusing upon pollinator responses to single signalling modalities, but also due to the majority of research focusing upon scent and visual signals. This has a consequence that we do not yet know the extent of floral multimodality. While scent and visual modalities are obviously of great importance, in order to fully understand the reasons behind the evolution of floral multimodality we must gain a better understanding of other signalling modalities. In this thesis I investigate two floral signalling modalities further, floral temperature and floral humidity. Through investigation of the traits floral displays produce I show that the temperature across floral displays differs, flowers show temperature patterns. Additionally, I show that elevated floral humidity about the flower is not limited to the single specialist species on which it has been recorded previously. Using captive bumblebees and established behavioural techniques I show that bumblebees can respond to and learn floral temperature pattern and floral humidity differences. This shows floral displays to be more multimodal than previously thought, with floral temperature showing a greater level of complexity and floral humidity having potential to be more widely used. In addition to this I investigate further how floral temperature may function within a multimodal display by testing its capacity to perform roles other than floral recognition which have previously been observed in visual patterns.
Date of Award25 Jun 2019
Original languageEnglish
Awarding Institution
  • The University of Bristol
SupervisorHeather M Whitney (Supervisor), Sean A Rands (Supervisor) & Natalie Hempel de Ibarra (Supervisor)


  • Pollination
  • Bumblebee
  • Infrared
  • Thermal cues
  • Humidity cues
  • Floral signalling
  • Angiosperms
  • Multimodality

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