Is spermatozoa retention in Tiliqua for long periods a possible reproductive strategy?
For captive blue-tongue skink breeding projects, and just a general understanding of Tiliqua reproduction in the wild, it would be important to discover if viable spermatozoa could be carried across breeding seasons. I’m not aware of any examples except for one anecdotal account reported by Australian herpetologist and reptile keeper, Raymond Hoser:
“Neil Simpson caught a gravid female T. scincoides at Milperra, NSW. He housed the lizard in the nearby suburb of Bankstown where 23 live young were produced. The adult was retained in a cage by itself and produced a second litter of 12 young the following summer. At no stage did the adult lizard have contact with others of it’s own species except for the young produced in 1986 (immediately after birth only). Thus there was no possibility of the female mating with young as in the case documented by Riches (1988). Simpson was unable to recall if unfertilised ova or similar material was passed by the female, although he noted that on both occasions there were no stillborn young (or none observed).
Sperm storage in snakes, and some small skink species, has been validated in numerous species. Hoser himself noted the storage over winter in the species Acanthophis antarcticus.
More recently Luke Allen, who curates a venom laboratory in South Australia, organized a major study to show how this is accomplished in Australia’s largest elapid, the coastal taipan (Oxyuranus scutellatus).
Allen was able to demonstrate that females were capable of storing sperm for at least six months, using the sperm from one mating, to fertilize eggs from three separate clutches.
“To do so he believes they use special cells in their bodies that secrete sugars and proteins to keep the sperm alive.
The sperm are kept in small pockets along a spongy tube that leads to the snakes’ ovaries.”
It turns out the trigger mechanism in his study was availability of food. Snakes kept on a moderate diet did not employ this sperm retention mechanism, using all the sperm for one clutch. Snakes gorged with food, however, reflecting a bountiful condition in the wild, used sperm retention to maximize their offspring. This can offer an evolutionary advantage by supercharging reproduction at optimal times.
So far this mechanism has not been established in the coastal taipan’s cousin, Oxyuranus microlepidotus, the inland taipan (drop for drop, the most deadly snake in the world), which experiences far more intense feast and famine feeding conditions in its desert environment. The snakes gorge on rodent populations in good years with abundant rainfall, but often survive years of drought and food deprivation.
The inland taipan, most likely, would be under far more intensive selection for sperm retention than its coastal cousin. However, this remains unstudied.
Among the Tiliqua, long term spermatozoa retention might occur in species that inhabit highly arid regions subject to long droughts, occasionally broken by heavy rains, such as Tiliqua multifasciata and Tiliqua occipitalus. Males in several species of Tiliqua are highly territorial, attempting to control access to females, and drive off rivals. For females, breeding can lead to serious injuries, and sperm retention to produce multiple litters could be advantageous.
Here is a remarkable photo of male to male combat in the Western Blue-tongue skink, taken by Colin Prickett and Chris Punter in spring 2014.
If anyone has encountered other examples of long term spermatozoa retention in Tiliqua, please contact me and I can add them to the post.