"So, naturalists observe, a flea has smaller fleas that on him prey; and these have smaller still to bite ’em; and so proceed ad infinitum."
- Jonathan Swift

October 7, 2015

Marsupiobdella africana

Leeches are not endearing animals and many are literal blood-suckers. As a result they often evoke a sense of disgust in most people, and the term "leech" is usually used in a derogatory way. But most people might not realise that leeches also has a warm, maternal side too, one which is amply demonstrated in the kangaroo leech, Marsupiobdella africana. But this leech does not parasitise the kangaroo - indeed, in southern Africa where M. africanus is found there are no kangaroos - the reason it has that name actually has more to do with how it reproduces

Left: A pair of mating leech.                                   Right: Leeches riding on the legs of  a crab      (from Fig. 1 of the paper)
Marsupiobdella africana makes a living sucking blood from Xenopus laevis - the African clawed frog which is commonly used as a laboratory model for developmental biology research. When it reach sexual maturity, the leech detaches from its frog host to find a suitable mate. Some do so by simply crawling around in the environment, but they are also known to hitch-hike on the legs on crabs as if they some kind of crustacean-based Uber, admittedly an armoured, multi-legged one.

Top: Leech with spermatophore attached
Middle: Leech with filled brood pouch
Bottom: Young leeches emerging
from brood pouch
From Fig. 2 of the paper
These leech are hermaphrodites, and each individual take turns being the sperm depositor and the recipient. Mating between kangaroo leech is a very different affair to how you might imagine it, and from our perspective it is not very romantic. Instead of bringing their respective genitalia together, the leech playing the sperm depositor role actually pulls out a spermatophore - which is something like a biological hypodermic syringe filled with sperm - and stabs it into the recipient, which may end up being tagged with one to three of those sperm packets.

If the prospect of being harpooned with a sperm-filled syringe is not daunting enough, the recipient also make a habit of collecting a bunch of spermatophores from a number of different depositors, probably to ensure they can have the cream of the crop (so to speak). Once the spermatophore has made its mark, the sperm it carries are able to make their own way to the egg, no matter where the spermatophore may have initially landed on the leech's body. At this point it is not entirely clear how they accomplish this.

Once the eggs are fertilised, the sperm recipient, now playing the role of mother leech, transfer the eggs (which can be as many as 50) to a brood pouch in her belly (which is where the name kangaroo leech came from). There they will be protected and nurtured. Once the eggs hatch, the baby leeches continue to receive nutrient from their mother through her body wall and into their posterior suckers. Those developing leeches will stay in the pouch for four weeks. As a final send-off, the mother leech will find an unsuspecting clawed frog, and the young leeches are "released explosively" over the surface of the frog, thus ensuring that those blood-suckers will get the best possible start to their own lives.

Marsupiobdella africana - a loving and nurturing blood-sucker which wants nothing but the best for its babies (see also another blood sucker which goes to great lengths to care for its brood here).

Kruger, N., & Du Preez, L. (2015). Reproductive strategies of the kangaroo leech, Marsupiobdella africana (Glossiphoniidae). International Journal for Parasitology: Parasites and Wildlife 4: 142-147.

No comments:

Post a Comment