Sharks are among the few big species that can reproduce asexually or by storing sperm. But just how long are female sharks able to hold on to the male seed? To the surprise of biologists at Steinhart Aquarium, the bamboo female shark can stock the sperm for nearly four years.
Scholars from the California Academy of Sciences discovered a few years ago some shark egg case dropped by a grown-up bamboo shark. The scientists moved numerous egg cases which were found in the Shark Lagoon display of the aquarium into a different container which was accessible to the public. In 2012 one of the two eggs found by the scientists cracked and a healthy baby shark emerged. This determined the scientists to investigate how the unlikely reproduction took place.
With this recent case there were two possibilities. Either the female grown-up shark managed to reproduce without the help of a male in a process entitled parthenogenesis or it had kept some sperm from her last mating experience a few years before the egg showed up in the tidal pond.
The biologists removed a DNA sample from the young shark and its alleged mother which were analyzed in a laboratory. The DNA analysis revealed that if the mother had laid the egg without a male’s help the pup would have had less genetic diversity than the mother. However, this was not the case and the scientists concluded the female shark most have stored the sperm.
According to Luiz Rocha, custodian at the ichthyology office from California Academy of Sciences said that the females ability to store sperm over extended periods of time is unique adjustment that aides increasing genetic diversity. Sperm- storage means that the female sharks postpones the fertilization for months or years after matting with a male shark.
The discovery marks the first time when a brown banded bamboo shark has been known to stockpile sperm.
Following the mating ritual a few types of female sharks are able to stock sperm in the tubules close to their oviduct – conceptive area that helps create the jam- like substance encompassing fertilized eggs. This sort of genetic variety is very useful for wild sharks. Diversity is pivotal in preserving marine life’s health, especially for those species that are threatened by overfishing, ecological dangers, and an absence of potential mating partners. Low genetic diversity species are in danger of widespread extinction in face of environmental challenges.
Moises A. Bernal, a specialist in the institute’s ichthyology division noted that even if researchers are aware that few types of sharks have some special reproductive capacities, like sperm storage and parthenogenesis, they need to establish when and how these methods are activated.
Luiz Rocha added that investigating the bamboo shark’s capacity to stock sperm gives researchers hope. More exactly, they can assume that wild sharks can as well do that and thus defend the genetic diversity of their population when mates are rare and genuine threats emerge.
The Journal of Fish Biology published the results of the new findings.
Image Source: Eurek Alert