[OGD] Euglossine bees

I am in Sri Lanka, nursing extensive leech bites after largely abortive orchid 
hunting in elfin forest. I had brought my accumulated heap of journals to read, 
and found a paper that may be (!) of interest. This is Ramirez et al Science 
333 pp 1742-1746 (2011).
Ten percent of the neotropical orchids are pollinated by Euglossine bees. The 
bees get no nectar or other obvious reward for performing this service, and the 
paper looks into why they do continue to do this. 

The authors first established the relatedness of the various bee genera by DNA 
analysis. They then captured 7000-odd wild bees, looking for those  that had 
orchid pollinaria stuck to them. More DNA analysis told them the orchid genus 
from which these pollinaria had come. Yet further analysis showed the scents 
that the bees were carrying. These scents prove to be crucial in shaping 
important neotropical genera. 

I did not know that bees actively collected not merely food but also scents 
from flowers and other sources, such as fungi. They use these suites of scent 
to attract mates. Some 580 such scents were identified, usually held in clearly 
selected, complex combinations that pinpointed a particular point in bee "scent 
space", to which other bees are preternaturally sensitive and which, 
presumably, communicate information. "A suave, urbane little bee of middle 
years and adequate means seeks life partner. Good sense of humour required."

It turns out that orchids supply a small and partially unique subset of these - 
about 8% of the total observed. Bees go to the relevant flower to pick up the 
scent, thus answering the question of why they bother with orchids that offer 
no food reward and emit no pheromonal attractors.
 
It also turns out, from analysis of how DNA itself drifts randomly over time 
that these particular orchids had switched from offering fake food rewards to 
bees - artifices chiefly on the lip that look like pollen or meat - to offering 
collectible scents. This happened about 30 million years ago. 

As already indicated, the experiment was done in South America, The 
interactions between orchids and scent-collecting (and only incidentally 
pollinating) bees has produced three loose groups of Euglossines and three 
rather tighter groups of orchids. These are the Catesetinae (which split off 
from their parent stem, together with their corresponding bees, some 18-27 
million years before the present, or mybp), the Zygopetalinae (20-25 mybp) and 
the Stanhopeinae (21 to 26 mybp). 

The last common ancestor of the bee groups and of these orchids lived in the 
hot Miocene period, and the subsequent long cooling period may have triggered 
this new relationship. 

The three orchid groups independently came up with this strategy, as has 
happened so often in evolution. The authors use statistical methods to puncture 
the fashionable idea of co-evolution, which would insist that the bees formed 
the orchids and that the orchids gave shape to the bees. Instead, they say that 
pre-wired insect preferences were exploited by orchids. (You always really knew 
that your plants were manipulating you... So nothing new there!)

I, personally, would like to know where the elaborate floral shapes came from, 
if everything was driven by scent. The complexity and specificity of a 
Stanhopea species could be seen as being analogous to a brand - Dior for bees, 
buy from Stanhopea such and so - with flower shape serving as the brand 
identity? What a crass thought. 

...But there is a monkey scattering cups on the verandah, so I must cease. (In 
edit, only one saucer lost, but the tablecloth is beyond recovery.)
________

Oliver Sparrow (ex Blackberry)
Mobile 07778409536
Fixed line +44 (0)1628 823187_______________________________________________
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