Wednesday, June 20, 2018
Mutualism vs. Parasitoidism: Two interesting examples
I was there last weekend not primarily to photograph showboat mockingbirds, but to take part in a seminar on Ohio River sand terraces, put on by the Cincinnati Museum Center's Edge of Appalachia operation and held at the always interesting Edge of Appalachia Preserve. Big thanks to Chris Bedel, preserve director, for including me. My fellow presenter and trip leader was Matt Purtill, an archaeologist and geomorphologist. Matt is an expert on the formation of these "dunes", and full of insight about the Paleo-Indians who first colonized this region. I learned tons from Matt.
You can bet I turned my big lens to this interesting fellow, who can also mimic sounds but not nearly as well as a mockingbird. It is a yellow-breasted chat, and if you turn to any bird book it will be with the warblers. Time for updates, authors. Last year, the chat was moved from the warblers (Parulidae) to its own monotypic (only one species) family, the Icteriidae. Good move. The chat is quite unwarblerlike in nearly every way, and although the warblers are good company to keep, it was high time the odd chat got carved out and into its own niche.
On the way to and from the workshop, I traveled through Shawnee State Forest. This place is always a goldmine of flora and fauna, in spite of the current powers-that-be doing way too much timber cutting. Among the legions of plants that I saw was this, the black cohosh, Actaea (formerly Cimicifuga) racemosa. The plants weren't this far along yet - the shot above is from a few years ago, later in June - but were in full bud and still conspicuous. Budding black cohosh means the potential of finding one of our cooler caterpillars, so I paid them close mind.
At first initiation, one might think the ants were attacking the caterpillars. Nothing could be further from the case. Tending phalanxes of ants guard the caterpillars carefully, fending off small parasitoid flies, wasps and other would-be predators. The flies and wasps lay eggs on caterpillar hosts, and the hatchling grubs bore into the victim and ultimately eat it alive. But not with ferocious ants on hand, replete with powerful mandibles and strength far out of proportion to their elfin size.
In return for their protective services, the ants are rewarded with "honeydew" secreted by the caterpillar. This liquid is high in nutrients and for the ant, must be the equivalent of a rich protein shake. Such a relationship, where both parties benefit, is termed mutualism. Even more specifically in this case, the relationship is an example of myrmecophily, an alliance between ants and other insects.
Bit of a horrorshow here, but a very cool tale. The paralyzed wolf spider, Rabida rabidosa, in the foreground was extracted from the little mud jug in the backdrop. During the Sunday morning field trip, we found a number of the little adobe crypts under a sheet of metal on the ground. A spider-hunting wasp known as Phanagenia bombycina grabbed the spider, paralyzed it with a sting, flew and dragged it "home". Once there, it then packed the paralyzed spider into this little mud tomb which she had already created. The wasp is a parasitoid, not a parasite. The latter take from their hosts but do not give anything in return, such as mites, lice, ticks, etc., but normally do not kill their host. The parasitoids DO kill their hosts and often in very grisly fashion.
Once the spider was entombed, the wasp laid an egg in the chamber then sealed everything up. The wasp grub can be seen feeding on the spider's back. To add to the horror, the wasp amputated five of the spider's legs before bringing it to the nest. Remember, the spider is only paralyzed by the wasp's powerful neurotoxin, not dead. She probably chewed those legs off to make for easier transport, and perhaps to better fit the victim into its crypt. After our group gaped for a bit at the gruesome scene, we put the spider and wasp grub back in the chamber and returned it to where we found it. An awesome example of parasitoidism!
Nature, oftentimes, is not very Disneyesque.
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