It has been waaaaay too long since I posted any photos. Funny how life can speed-up and suck all your timeóespecially over Christmas holidays when you have kids! Anyhow, Iím back and after a 2-week hiatus I have finally posted some photos on my blog of freshwater amphipods (that I took last summer). The photo above is of a very pretty specimen of Gammarus lacustris; apparently the only species of freshwater gammarid amphipod found in British Columbia.
Whenever (and wherever) I have collected freshwater Gammarus in the past, they have been coloured drab shades of brown and olive green. But as you can see, the specimensIcollectedfrom this particular stream showed some real diversity in colouration, including some really pretty specimens with bright red spots on a translucent yellowish body. Others had a single very obvious bright red spot on their side. I still donít know if the spot was on the critterís exoskeleton or was something inside the bodyÖ
The mystery of the amphipod with the red spot has been solved...it turns out that the red spot was actually an acanthocephalan (thorny-headed or spiny-headed worm) parasite called Polymorphus. Acanthocephalans are parasitic and donít have a digestive tract; they are basically a sack containing reproductive organs and musculature with a spiny proboscis that can stick out of one end. The proboscis is used to stab into and attach to the gut of its host (the animal in which it is living and feeding from). They ingest nutrients directly through their body surface.
The cool thing is how Polymorphus alters the behaviour of the host amphipod. Gammarus lacustris are preyed upon by ducks (amongst other predators). Needless to say they generally try to avoid being eaten and tend to avoid light and stay away from the surface (where ducks are). However, Polymorphus eventually causes its host to becomes attracted by light and swim towards the surface to increase the likelihood of being eaten by a duck. The bird then becomes infected by the parasite...
Below Iíve uploaded a tightly cropped version of the red-spot photo. Now Iím wondering what the little clump is that is growing on the back of the amphipod (in the upper right corner of the photo)?