Sunday, August 5, 2012

I just want ... a bee for dinner

Goldenrod Crab Spider curiously not yellow but hungry
Goldenrod (Solidago spp.), an unlikely looking relative of daisies, has been in bloom the last few weeks in central Alberta and hosting its usual surprising diversity of arthropods. The golden sprays are the perfect nectaring platform for wasps and bees and flies and butterflies and even the occasional moth. Yet danger lurks among even the most pastoral of golden fields.
Ménage à trois et d'une embuscade à trois
The bloom is off this goldenrod and our Goldenrod Crab Spider looks more than a bit out of place, but if she moves on to another in full bloom, then her colour will eventually catch-up with her and her hunting success increase. But other curiosities lurk among the golden sprays.
Male and female Phymata americana squared
In the case of the American Ambush Bug Phymata americana americana Melin, 1930 (Hemiptera: Reduviidae, Phymatinae), the females lurk much better than the males. Like the Goldenrod Crab Spider the ambush bugs can change colour from mostly white to mostly yellow. Additionally, the females have a light brown patterning that helps break-up their outline and blend them into the floral background so that they can carry out their nefarious designs with little chance of being noticed until they pounce.
Single-minded male spoiling a perfectly good camouflage
In contrast, male ambush bugs have much more extensive and darker coloration that rather ruins the illusion that they are not there. David Punzalan and his then colleagues Helen Rodd and Lock Rowe at the University of Toronto wondered why? Knowing that insects generally depend on the environment to regulate body temperature, that darker colours absorb more heat that lighter colours, and that males generally have one thing foremost on their minds, they devised and carried out a series of rather elegant experiments. They found that males with darker sides generally spent less time searching for females than males with lighter sides and that this difference was more pronounced during cool ambient temperatures. Similarly, when cooler temperatures prevailed, dark-sided males got the girls.
Darker sides = warmer males = more girl friends
 Interestingly, the variation in dorsal (top side) coloration had no detectable effect on male searching abilities or success rate. Perhaps the extra heat absorption isn't very important during the mid-day when the sun is more or less overhead or some other factor trumps dark dorsums.
Even ambush bugs sometimes get their colour-coordination wrong

Punzalan D, FH Rodd & L Rowe. 2008. Sexual selection mediated by the thermoregulatory effects of male colour pattern in the ambush bug Phymata Americana. Proc. R. Soc. B 275,:483–492 doi:10.1098/rspb.2007.1585
Punzalan D, M Cooray, FH Rodd & L Rowe. 2008. Condition dependence of sexually dimorphic colouration and longevity in the ambush bug Phymata americana. J. Evol. Biol. 21: 1297–1306 doi:10.1111/j.1420-9101.2008.01571.x

No comments:

Post a Comment