Continuing with the theme from last Friday of wacky sperm in nature, I found this gem about an intestinal parasite (Gyliauchen sp.) of the dusky rabbitfish. The parasite is a type of flatworm. The authors of the paper wanted to see if there was anything special about their sperm (as part of a larger effort to describe the sperm of related parasites) so that it could be used to distinguish this species from similar-looking species. Sperm and male genitalia are often used to distinguish between related species (I know this mostly from working with flies), because boy bits are wacky and tend to change pretty dramatically over short evolutionary times, even when the rest of the animal does not.
The parasite’s sperm did end up having a number of interesting things that set it apart from the rest. Most of those things are too technical for me to really want to get into (but if you’re really interested, you can access the paper online–link below). But there was one major characteristic I’d like to focus on: spines.
The sperm are cool looking at first glance. The authors divide the sperm cell into 4 parts, each with its own unique bits. At the top, they have a modest little hook sticking out. In the next region down, there are several of what the authors call “external ornamentation”–little blebs on the sides of the sperm that I can only assume make them look fabulous to the eggs.
But region 3 is by far the best: along one side of the sperm, there are several giant, freaky spines sticking out (see drawing to the right, but check out Figure 11 of the paper for a more realistic view). It looks like the back of a stegosaurus. On a sperm. (I can’t post the image from the paper here, but you can find it by following this link. Check out the drawing in Figure 32).
What are the spines for? Who knows! But they sure do make human sperm look lame by comparison. In the interest of full disclosure, I should tell you that the spiny bits are not unique to the sperm of this species. They were first described in a different fish parasite in 2000. But, they are unique (in this family of parasites, at least) in that they aren’t at all associated with the “external ornamentation” blebs. Just imagine how much these guys have to know about sperm to know that that’s what makes these ones special.
The paper doesn’t mention anything at all about the mating system of these parasites, or the ecology of the fish. But I did find this article about a related parasite that also lives in the guts of fish. If our spiny sperm-having friends are similar, they are probably hermaphrodites that exchange both sperm and eggs with other worms.
I wonder if the sperm duke it out, using their spines as weapons? Probably not, but I’ll still imagine it that way anyway.
Quilichini Y, Foata J, Justine JL, Bray RA, & Marchand B (2011). Spermatozoon ultrastructure of Gyliauchen sp. (Digenea: Gyliauchenidae), an intestinal parasite of Siganus fuscescens (Pisces: Teleostei). The Biological bulletin, 221 (2), 197-205 PMID: 22042438