"Peeny wallies", also known as 'click beetles' are always a source of wonder to
visitors at Windsor as they noisily zoom around with their
bioluminescent "headlights" shining .
Click beetles are so called because they have a jumping mechanism composed of a
prothoracic projection that fits into a socket on the middle part of the
thorax, which when activated makes a clicking sound. When placed on its back or
held in one's hand, a click beetle will flex its prothorax against the socket
and catapult itself several inches into the air attempting to right itself and
escape, making its namesake sound.
But most people's interest is more aroused by the two dorsal light organs, which
resemble two automobile headlights (a reason why in Brazil these beetles are
called 'Automobile bugs') and a single ventral organ visible from below and
only when the beetle is on flight. Researchers suspect that this ventral organ
is in fact used by the males as a mating signal to attract females, which are
typically found on the ground with their dorsal lights on. Very interestingly,
this ventral light is located in the rear part of the abdomen, which is hinged
so that, in flight, the male can tip its abdomen upwards and display this
extraordinarily bright light.
We know of one research project currently being undertaken by Sebastian Velez
from the University of Notre Dame, who is looking at the evolutionary
genetics of these incredible bioluminescent click beetles. His study concerns
the evolution of polymorphism for light colour which is occurring in Jamaica.
While the colour of the light organs of Caribbean click beetles has diverged
(so that the Belize species has green dorsal and yellow ventral, Dominican
Republic has green dorsal and ventral and Trinidad has green dorsal and
yellow-orange ventral), Jamaican click beetles are the only organism known to
be polymorphic (i.e., several phenotypes occur within the same population) for
light organ colour. Here, the dorsal light may be green or yellow-green, while
the ventral may be yellow-green, yellow or orange. The orange-light beetles
are found in higher frequency at the eastern end of the island and seem to be
spreading both in space and frequency towards the West. Sebastian is studying
this distribution and the selection process which may be causing the alleles
coding for the orange color to spread.
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