Sharks are apparently the luckiest creatures on earth. Why? Because they have two penises. What? Ya you read it right. Sharks do have two reproductive organs which are known as claspers which act as penises. The claspers are the main differentiating organ between a male and a female shark. This fact may be a known fact to biologists especially people studying marine biology but is off course a new information to many people. Now recently a study has been done on the biological evolution and molecular development of the copulatory organs of these fishes.
In the extreme past, most of the vertebrate animals had copulatory organs which are paired penises or double penises. Now with the evolution in nature, most of the vertebrates have shed off this paired up penises but the male chondrichthyans. The sharks, skates and rays fall in this category of species. The claspers of shark extend from their pelvic fins and they are associated with internal fertilization and viviparity in Devonian placoderms. These claspers is guided by a type of hormone secretion known as Sonic hedgehog (Shh). This hormone regulation helps to induce clasping motion in the cartilage in females.
The paper says:
“Androgen receptor (AR) controls the male-specific pattern of Shh in pelvic fins by regulation of Hand2. We identify an androgen response element (ARE) in the Hand2 locus and present biochemical evidence that AR can directly bind the Hand2 ARE. Together, our results suggest that the genetic circuit for appendage development evolved an androgen regulatory input, which prolonged signalling activity and drove clasper skeletogenesis in male fins.”
In simpler sentence, the male and the female sharks have a circuit appendage which has evolved owing to Androgen reception. This is nothing but a signalling activity of male fins to allure female sharks for reproduction.
Source: Nature Communications