Ambient Temperature Influences Australian Native Stingless Bee (Trigona carbonaria) Preference for Warm Nectar

The interaction between flowers and insect pollinators is an important aspect of the reproductive mechanisms of many plant species. Several laboratory and field studies indicate that raising flower temperature above ambient can be an advantage in attracting pollinators. Here we demonstrate that this preference for warmer flowers is, in fact, context-dependent. Using an Australian native bee as a model, we demonstrate for the first time a significant shift in behaviour when the ambient temperature reaches 34°C, at which point bees prefer ambient temperature nectar over warmer nectar. We then use thermal imaging techniques to show warmer nectar maintains the flight temperature of bees during the period of rest on flowers at lower ambient temperatures but the behavioural switch is associated with the body temperature rising above that maintained during flight. These findings suggest that flower-pollinator interactions are dependent upon ambient temperature and may therefore alter in different thermal environments

evolutionary pressures linked to hymenopteran vision Parallel evolution of angiosperm colour signals: common References Subject collections Parallel evolution of angiosperm colour signals: common evolutionary pressures linked to hymenopteran vision

Flowering plants in Australia have been geographically isolated for more than 34 million years. In the Northern Hemisphere, previous work has revealed a close fit between the optimal discrimination capabilities of hymenopteran pollinators and the flower colours that have most frequently evolved. We collected spectral data from 111 Australian native flowers and tested signal appearance considering the colour discrimination capabilities of potentially important pollinators. The highest frequency of flower reflectance curves is consistent with data reported for the Northern Hemisphere. The subsequent mapping of Australian flower reflectances into a bee colour space reveals a very similar distribution of flower colour evolution to the Northern Hemisphere. Thus, flowering plants in Australia are likely to have independently evolved spectral signals that maximize colour discrimination by hymenoptera. Moreover, we found that the degree of variability in flower coloration for particular angiosperm species matched the range of reflectance colours that can only be discriminated by bees that have experienced differential conditioning. This observation suggests a requirement for plasticity in the nervous systems of pollinators to allow generalization of flowers of the same species while overcoming the possible presence of non-rewarding flower mimics

Temperatures used in this study (± s.d.).

<p>Temperatures used in this study (± s.d.).</p

Typical crop contents of <i>Trigona carbonaria</i> bees after visiting either a cool or warm feeder.

<p>The consistency in crop contents between the two feeders indicates that the bees completely imbibe warm sucrose in the range 38–39°C. Also shown is an anaesthetised bee.</p

Sucrose temperature preferences of <i>Trigona carbonaria</i> across a range of ambient temperatures.

<p>The preference for a feeder that is at ambient temperature compared with a feeder that is 6°C warmer is dependent upon the ambient temperature (mean +/− s.d.). *Preference for the ambient feeder is significantly lower than expected by chance (one sample t-test, P&lt;0.001), but the preferences do not differ significantly different from each other [one way ANOVA, F(2,33)  = 1.527, P = 0.232]. **Preference for the ambient feeder is significantly higher than expected from chance (one sample t-test, t = 2.635, DF = 11, P = 0.023).</p