Dangerous Liaisons: Hermaphrodite Edition

Scanning electron micrograph of the love dart of Everettia corrugata

Scanning electron micrograph of the love dart of Everettia corrugata

Following on the heels of my Fruit Fly Sexy Time post, this paper caught my eye. The researchers used an electron microscope to look at the ‘love-dart’ of a species of land snail. The words ‘love-dart’ do not do justice to this weapon of reproduction (as pictured). Truly, it is a Battle of the Sexes here. You can read the original paper, published in the journal PLOS One.

✤ Sexual encounters typically involve a conflict of interest between partners; this is because something that is advantageous to one sex can be bad news to the other. Therefore such conflicts can lead to co-evolutionary arms races that involve truly strange, costly and cruel mating behaviors. These conflicts between the sexes can have important implications for the evolution of these sexual characteristics and behaviors.

✤ How does the battle of the sexes work when it comes to hermaphrodites? It actually makes the battle more ruthless. Within each mating, a simultaneous hermaphrodite can gain an evolutionary advantage through being a male, a female and the additional option of self-fertilization. This leads to the evolution of even more harmful reproductive behaviors when comparing hermaphrodite species vs. species with separate sexes.

✤ For example, tropical flatworms are hermaphrodites that mate with each other using a system known as ‘hypodermic insemination’ which is as romantic as it sounds. Sea slugs, on the other hand, are comparatively gentler by injecting their mate with a sedative prior to mating.

✤ A better understood mating strategy exists in land snails where a ‘love-dart’, made of calcium, is forcefully stabbed through the partner’s skin during mating, and a gland product is transferred into the partner’s blood. The gland product then goes on to cause changes to the female reproductive system that inhibits the entrance to an organ that otherwise digests the sperm, known as the bursa copulatrix. This sperm-digesting mechanism is in place to ensure that only the most active and healthiest sperm cells that survive will be used later for fertilization. Therefore there is clear support for the antagonistic co-evolution (aka battle-of-the-sexes) between love-darts and sperm-receiving organs.

✤ When it comes to the love-dart, you can have a reusable one which is used to stab the partner repeatedly, or you could have a disposable one-time-use love-dart! The love-dart in the snail Everettia corrugata appears to function as a true injection needle, with tiny channels inside the dart. It also has tiny side-perforations on the sides in order to prevent the clogging of the needle tip! Intriguingly, this same design for the prevention of clogging is also found in the venom machinery for poisonous sea snails as well.

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