SELECTION – 1
SMOUSE – SPRING 2011
One of the first things you notice about adaptations is that they are
usually complex. Futuyma spends a bit of time describing particular adaptations, just to give you
the idea. The orchid story is so beautiful that it can stand a bit of elaboration here,
. Recall that orchids, like other monocots, have a basic floral morphology in 3’s.
- The orchid has 3 petals. One of the petals, the labellum, is greatly modified. The
sexual organs are fused into a single structure, the column, usually involving a single anther
with two pollen masses (pollinia), with the stigmatic surface just below the anther. The
labellum is quite pretty and highly aromatic, basically luring the insects into the flower.
In some cases, the insects are after nectar, in some cases pollen. In other cases, male insects
are confused by the aromas, and attempt to copulate with the labellum (pseudocopulation).
The insects are physically challenged to move in a particular route through the flower.
They are so constrained that they first leave pollen on the stigmatic surface, and then are
forced to pass by the anther, where their movements trigger the application of a pollinium, on
a body part that is the point of contact with the stigmatic surface of the next flower visited.
The Orchidaceae is the largest family of plants, with between 18,000 – 25,000 species, and
they have several thousand variations on this theme. For most species, the insect gets what it
came for (food), but in some cases (sexual deception), it just gets faked out. If we didn’t
know better, we could read
into the system.
Futuyma – Figure 12.3