There is not much to add to the whole story on disposable penises after Ed Yong wrote about it. So being a big fan of the Ten Hundred Most Used Words challenge (Can you explain a hard idea using only the ten hundred most used words?), I decided it was time I give it a go…
Animals that are both man and woman at the same time often have strange ways. In a crazy soft animal that lives in water, one will cut off its man parts after each love act. After one day it can do the fun dance again with a new man part. To have enough man part to do it three times, the man part is pressed and rolled up inside. Man parts that can be thrown away are only known from these soft animals that live in water.
Although it is often thought that sexual selection is weaker in simultaneous hermaphrodites than in gonochorists, some simultaneous hermaphrodites exhibit bizarre mating behaviour. In the simultaneously hermaphroditic nudibranch Chromodoris reticulata, we found a peculiar mating behaviour, wherein the nudibranch autotomized its penis after each copulation and was able to copulate again within 24 h. To have sufficient length to be replenished for three copulations, the penis is compressed and spiralled internally. No other animal is known to repeatedly copulate using such ‘dis- posable penes’. Entangled sperm masses were observed on the outer surface of the autotomized penis, which is equipped with many backward-pointed spines. There is a possibility that the nudibranch removes sperm already stored in a mating partner’s sperm storage organ(s).
Figure 1. Mating and morphology of the penis in Chromodoris reticulata. (a,b) Two individuals reciprocally insert their penis into the partner’s vagina. (c,d) Auto- tomized penes after copulation; the tip of the penis is swollen. A mass of sperm (sp) is attached to the thorny penis in (d ). (e) Surface of the penis is equipped with innumerable backward-pointed spines. (f) Sperm are entangled in the spines. Autotomized penis stained with haematoxylin after being air-dried on a glass slide. Arrows show the direction of penis insertion.
Ayami Sekizawa, Satoko Seki, Masakazu Tokuzato, Sakiko Shiga, and Yasuhiro Nakashima
Disposable penis and its replenishment in a simultaneous hermaphrodite
Biol. Lett. April 23, 2013 9 2 20121150; doi:10.1098/rsbl.2012.1150 1744-957X