14 DAY TRIAL // Many researches have revealed that the installation of sexual maturation can be triggered by chemical stimulants from other individuals in a lot of species, from insects and fish to even mammals, like rats and sheep.
Now, a team at the Universities of Exeter and Glasgow has revealed a visual mechanism of sexual timing: some females begin sexually maturation more quickly if they detect visually the presence of attractive males.
The study presents for the first time how the sight of physical sexual ornamentation on another individual of the opposite sex can determine when an individual is ready to reproduce. The study was made on green swordtail fishes, a small species native to Central America and popular in tropical aquariums, being easy to keep and breeding easily. Moreover, this species is viviparous (swordtail fishes and their relatives are an unusual case of viviparous reproduction amongst bony fishes).
The green swordtail receives its name after the striking sword-like growth, which males grow on the lower lobe of their tail-fin, so they look larger and more attractive to females, even if in reality the females more than double the males.
When the females in the group were presented males possessing long lobes, a sign of high sexual fitness, they speeded up with four months sexual maturity compared to those that did not see gorgeous males.
Moreover, young males that were exposed visually to mature males with huge "swords" delayed the moment of their maturation compared to those that had contact with lower quality competition.
In fact, this way, both sexes unconsciously rise their mating opportunities using visual clues. In the case of females, they increase their chances to mate with potential quality males while the males maturing later avoid competition with more successful males. "This is the first evidence that a species adjusts its rate of sexual maturation in response to visual cues. While our study focused on green swordtail fish, it seems unlikely that this attribute is limited to this one species," said Dr Craig Walling of the University of Exeter's School of Biosciences.
Because the fishes were kept in separate tanks, they could only see each other through the glass, without employing other senses. "It's well established that sexual maturation in swordtails is highly variable, occurring anywhere between four and 20 months of age even though they rarely live longer than two years. We were really surprised to find that visual cues can have such an effect on sexual maturation, which is so important to an individual's reproductive success", said Dr Walling.
Photo: A pair of green swordtail fish.
