Wednesday, April 5, 2017

Eat and be Eaten

Central newt with zits - parasitized by a trematode, Clinostomum
Linda Bower recently has been filming central newts in her incredible pond.  This particular newt had a bad case of zits, but these aren't like our teenage year's variety.  In this case, living creatures will crawl out..... remember "Alien?"

The central newt belongs to the amphibian family Salamandridae, a group of salamanders commonly referred to as newts. According to the Missouri Department of Conservation, it is the only species of newt found in Missouri. They are seldom numerous in ponds that harbor fish or that lack aquatic plants. Adult newts eat small aquatic invertebrates such as worms, small mollusks, insects, crayfish, salamander larvae, and small tadpoles.
Central newt larvae - Wikipedia

Red eft phase - Wikimedia
Breeding occurs in late March through early May. Females lay 200–375 eggs singly on aquatic plants in May and June. The eggs hatch after 3–5 weeks. The larvae live in water until late July or early August, lose their gills, and transform into land-dwelling red efts. After living 2–3 years on land, they return to a pond or swamp, change into adults, and spend the rest of their lives mostly in water.

I will leave the rest up to Linda below.

Eyeing an innocent pond snail - Linda Bower
The newt above is featured in this video.  It is infested with metacercariae of the trematode Clinostomum (a fluke commonly known as a “yellow grub"). The disease produces grossly visible yellowish lumps under the skin, and an experienced parasitologist makes a diagnosis by removing the encysted parasite. Dr. Thomas Raffel of Oakland University had posted a photograph showing similar lumps. He confirmed that a Clinostomum sp. is the likely cause, given the presence of Planorbella sp.  snails in the pond, of which the ramshorn snail is one that I have documented.

Yellow grubs - Clinostomum metacercariae - S.
But, it’s not that simple. This parasite has two intermediate hosts (snails and amphibians/fish) and one definitive host (wading birds). The parasite’s eggs hatch in the water and the miracidium (ciliated larval stage) invades the foot of the snails. The larva leaves the snail and encysts in the newt.

"This science gives me a headache"
According to Dr. Raffel, the newt needs to be eaten by a wading bird for the parasite to complete its life cycle. He states,
“At that point, the parasite can detect its host being eaten and it immediately excysts (emerges) through the newt's skin. It needs to do this quickly because this particular parasite prefers to live in the bird's gular pouch, so it doesn't want to go through the gut. This is one of the few trematodes I know of whose metacercariae grow within the amphibian host, presumably so they are mature enough to immediately infect the bird once eaten.”   
The birds must urinate or defecate in the water to pass the parasite’s eggs while the adult parasites remain in the gular (throat) pouch.
OK, Linda, enough is enough.....even for a retired gastroenterologist.