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

Shades of red: birdpollinated flowers target the specific colour discrimination abilities of avian vision

Summary Colour signals are a major cue in putative pollination syndromes. There is evidence that the reflectance spectra of many flowers target the distinctive visual discrimination abilities of hymenopteran insects, but far less is known about bird-pollinated flowers. Birds are hypothesized to exert different selective pressures on floral colour compared with hymenopterans because of differences in their visual systems. We measured the floral reflectance spectra of 206 Australian angiosperm species whose floral visitors are known from direct observation rather than inferred from floral characteristics. We quantified the match between these spectra and the hue discrimination abilities of hymenopteran and avian vision, and analysed these metrics in a phylogenetically informed comparison of flowers in different pollination groups. We show that bird-visited flowers and insect-visited flowers differ significantly from each other in the chromatic cues they provide, and that the differences are concentrated near wavelengths of optimal colour discrimination by whichever class of pollinator visits the flowers. Our results indicate that angiosperms have evolved the spectral signals most likely to reinforce their pollinators' floral constancy (the tendency of individual pollinators to visit flowers of the same species) in communities of similarly coloured floral competitors

Data from: Shades of red: bird-pollinated flowers target the specific colour discrimination abilities of avian vision

Colour signals are a major cue in putative pollination syndromes. There is evidence that the reflectance spectra of many flowers target the distinctive visual discrimination abilities of hymenopteran insects, but far less is known about bird-pollinated flowers. Birds are hypothesized to exert different selective pressures on floral colour compared with hymenopterans because of differences in their visual systems. We measured the floral reflectance spectra of 206 Australian angiosperm species whose floral visitors are known from direct observation rather than inferred from floral characteristics. We quantified the match between these spectra and the hue discrimination abilities of hymenopteran and avian vision, and analysed these metrics in a phylogenetically informed comparison of flowers in different pollination groups. We show that bird-visited flowers and insect-visited flowers differ significantly from each other in the chromatic cues they provide, and that the differences are concentrated near wavelengths of optimal colour discrimination by whichever class of pollinator visits the flowers. Our results indicate that angiosperms have evolved the spectral signals most likely to reinforce their pollinators’ floral constancy (the tendency of individual pollinators to visit flowers of the same species) in communities of similarly coloured floral competitors

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

Shrestha et al_New Phytol 2013_Species and Data

Shrestha et al_New Phytol 2013_Species and Dat

Colour preferences of Tetragonula carbonaria Sm. stingless bees for colour morphs of the Australian native orchid Caladenia carnea

Innate colour preferences promote the capacity of pollinators to find flowers, although currently there is a paucity of data on how preferences apply to real flowers. The Australian sugarbag bee (Tetragonula carbonaria Sm.) has innate preferences for colours, including UV-absorbing white. Sugarbag bees are pollinators of the terrestrial orchid Caladenia carnea R.Br., which has both white and pink morphs. In laboratory conditions, we tested flower-naïve bees with the white and pink flower morphs revealing a significant preference for the white morph, consistent with experiments using artificial stimuli. In experiments to understand how bees may select food-deceptive orchids following habituation to a particular colour morph, we observed a significant increase in choices towards novel white flowers. We also observed that the presence of a UV-reflecting dorsal sepal signal significantly increased bee choices compared to flowers that had the UV signal blocked. Our findings demonstrate that innate preference testing of insect pollinators with artificial stimuli is replicated in a biologically significant scenario with flowers. The findings also underscore how food-deceptive orchids can receive sufficient pollinator visits to ensure pollination by having different morphs that draw on the innate preferences of bees and their ability to make decisions in a complex ecological setting

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

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

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