Perhaps the most likely is that the formation of bundles is associated with the evolution of some form of postcoital sperm competition (Jones et al. Features of the echidna’s biology indeed suggest that sperm competition is likely. In WEIT, I describe several adaptations in other species that may have been favored by sperm competition (these include “copulatory plugs” in rodents and “penis scoops” in damselflies - features of a male’s penis that he uses to remove the sperm of a previously-mating male before he ejaculates himself). If females can be inseminated by more than one male, anything that gives a male’s sperm a leg up in the race to the egg will be favored by natural selection. For by working as a team, a group of sperm can swim faster than individual sperm, something that’s already been observed in the opposum, in which many sperm join with another to form pairs in the ejaculate. To the authors (and also me), this cooperation among sperm implies one thing: sperm competition. Semen samples contained bundles of up to 100 spermatozoa that were joined at their apical extremity and were observed to swim progressively forward in a vigorous and co‐ordinated pattern. What is going on here? Is there any explanation for this bizarre ejaculatory behavior? One possibility arises from examining the echidna’s sperm: During ejaculation, the semen pooled into the cups of the rosettes as a white viscous fluid ( fig. Erection and ejaculation typically lasted between 10 and 15 min. When erect, the penis was about one‐quarter of the echidna’s body length. Ejaculation commences approximately 20 s after the penis has become fully erect.

In this form, the engorged penis would appear to deliver the semen directly adjacent to the female’s oviductal ostia. The penile morphology of the erect echidna penis is therefore, at this point, completely compatible with the anatomy of the cranial portion of the female’s urogenital sinus. 1).īut the ejaculatory behavior of the generously-endowed male is unique:ĭuring the early stages of erection, the glans penis displays all four rosettes, but as the erection continues, two of the rosettes retract, leaving the remaining rosettes fully engorged and slightly rotated, to give the fully erect penis a symmetrical appearance ( figs. Using a closed fist, the zookeeper gently pushes his hand into the lower abdomen of the animal, at which time the echidna usually responds by pushing its cloaca up against the zookeeper’s fist and developing an erection ( fig. In preparation for semen collection, the echidna is placed in lateral recumbency on a clean surface of the floor of its enclosure. Over a period of 2 weeks, zookeepers at Currumbin Wildlife Sanctuary conditioned the echidna to develop an erection to the point where it would ejaculate. Zookeepers noted that, on handling, this animal would readily produce an erection. In 2005, Currumbin Wildlife Sanctuary (Gold Coast, Australia) came into possession of a 17‐year‐old captive male echidna that had become habituated to human presence as part of an interactive public display. The methods and materials section is interesting. This video derives from research described in a 1997 article in The American Naturalis t. (Doesn’t that penis resemble the alien bursting forth from the guy’s stomach in the eponymous movie?)

A platypus penis