Unfeasibly large gonads…

This post isn’t about the famous Viz character, rather the mind-boggling diversity of nematodes, which I touched on in a previous post. One nematode that beautifully illustrates the bizarre life histories of these animals is Sphaerularia bombi, a parasite of queen bumblebees. Like so many other parasites this little nematode manipulates the behaviour of its host in order to increase its chances of continuing the freeloading tradition. In short, a queen bee afflicted with this nematode forages and feeds, but she makes no effort to found a nest of her own. Instead, she is compelled by the parasite to return to the place where she hibernated or a another suitable spot and it is here the nematode’s offspring find their way into the outside world in the faeces of their host where they wait to infect another queen bee that makes use of the hibernaculum.

Such a strategy is a long shot to say the least, so to offset the long odds huge numbers of offspring are required. With a body only a few millimetres long the nematode is rather limited in how many eggs it can produce, but to get around this problem something incredible happens to its gonads. Its entire reproductive system turns inside out and balloons to relatively enormous proportions, eventually dwarfing the nematode that dangles at the end of this structure like a vestigial appendage (see photo below). With unfeasibly large gonads the nematode can produce tens of thousands of eggs.