Who’s The Daddy?

An academic paper was published last week by scientists S. Corrigan, D. Kacev & J. Werry on one of Sharktrooth’s favourite shark species – the Shortfin Mako (latin name Isurus oxyrinchus).

The title of this paper is “A case of genetic polyandry in the shortfin mako”.

This article documents a case of genetic polyandry in the oceanic and pelagic shortfin mako and comments on the implications of this finding.

Sharktrooth

The Mako is a very close relative of the Great White and is also the fastest shark in the ocean. The Shortfin Mako also has one of the largest brain:body ratios. From tests involving shape differentiation to electroreception tests and individual recognition, scientists have discovered that Makos are fast-learning sharks, able to determine whether or not the researchers were threatening.

In this particular study – genetic polyandry was discovered. Polyandry is defined as “the mating of one female with more than one male while each male mates with only one female.” Exclusive polyandry is very rare, occurring in only about 1% of animal populations. The basis of polyandry is a sex role reversal. The females compete for the males and can be larger and more colorful, while the males take on the parental role. With the sex role reversal, a natural selection against older males evolves. This is accomplished by the females tending to select the males with the best sperm in order to give the female the most offspring possible. Younger males will more likely have fertile sperm; therefore impregnating the female on more instances than an older male with less fertile sperm.

Sharktrooth
Diagram of a female Shortfin Mako

The comments on the implications of this discovery have not been made available to Sharktrooth, but we would speculate that this is of benefit to the species survival for a number of reasons:

  • Sharks usually take a long time to reach sexual maturity
  • Shortfin Mako are targeted for trophy fishing
  • All sharks are targeted for their fins
  • If the male Shortfin Mako is sought by the female to reproduce earlier – there is less chance he has been caught before he has a chance to impregnate

Of course, this only works if the males are sexually mature at a younger age.

Whatever the outcome, the only real way to help these animals is to deal with the biggest threat to their survival and that is us. Humans are killing millions of sharks every year and this is just not a sustainable figure. Please show your support for these amazing creatures (that survived millions of years before people came along), by visiting our Shark Friends page and getting involved with some or all of the groups there.

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