Whose Sperm Is It Anyway?


Who’s the daddy? And why do eggs fertilised at the same have different fathers? These are questions that some scientists have being trying to get to the bottom of when examining the reproduction of Hermann Tortoises.

Hermann Tortoises are native to Southern Europe in the region surrounding the Mediterranean Sea, where they are known to bask in the sunshine to warm their bodies up and eat plants found in Mediterranean meadows. Unfortunately the meadows are declining due to urbanisation, fragmenting the habitats, reducing the proximity of available mates. Accidental killings by humans, machinery and dogs are also reducing the wild population. As a result, several studies are being undertaken to understand and maintain wild population of this ancient reptile.

Female Hermann Tortoises mate with multiple males and can store their sperm for up to four years, a trait not uncommon within the reptile world with some species of geckos and turtles also exhibiting this behaviour. They can then use this sperm at the optimum time for their eggs to ensure successful fertilisation, maximising the number of offspring produced and often producing offspring with several different fathers in the same clutch of eggs.

Studies have shown that the last male to mate with the female was more successful at producing offspring of his own, a “last in, first out” policy. The more the female mates, the more sperm she garners and the older sperm gets pushed further up the tube and further away from the unfertilised egg.  When the egg needs to be fertilised the tube simply releases some of the stored sperm. This would suggest that the sperm closest the egg will be used first, hence the belief the last male will be the most successful.

Yet when the tortoise offspring underwent paternity tests in the most recent study, the results showed that the fathers were not necessarily the last acquainted males, suggesting that the sperm gets mixed when in storage or that the female actively uses older sperm first to prevent it becoming unviable.

Scientists believe that the lifestyle of the Hermann Tortoises could have provoked such an adaptation. With wild populations becoming increasingly low, it is a case of getting the sperm whilst they can and then using it when appropriate.

There you have it; to become the daddy a policy of “last in, first out” isn’t always true… in relation to Hermann Tortoises, of course!




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