With the intention of attracting the female?

2005/01/01 Leunda Urretabizkaia, Pedro M. Iturria: Elhuyar aldizkaria

• Biologia
• Zoologia

Photograph taken on the bank of the river with a digital camera at a fishmonger of 85 mm.

J. Martinez-Lage

The fish factor ( Phoxinus phoxinus ) is a small fish from the cypress family that inhabits almost all the rivers and lakes of the Eurasian continent. The northern river basin of the Iberian Peninsula has its southwest distribution limit. This small cypride barely measures 120 mm, but it seems that when it is 50 mm (1-2 years) it is sexually mature.

The fishmonger lives in large populations and develops a huge sexual dimorphism in the reproductive period, that is, from May to August. The male fishnet changes a lot: the fins, the belly and the lips are dyed red, the sides of the body are dressed in blue or metallic green and in the head grow the so-called reproductive tubercles.

The goal of these changes would be to have more success in reproduction. Winifred E. 1943 The researcher Frost described in detail these sexual characters in the already historical article.

During the summer season, the ezkailes migrate to well oxygenated fluvial sections and with pebbles on the substrate; they meet in groups to prepare the male ezkailes and the laying corners. Afterwards, they usually swim around these corners, until a female ready to spawn approaches.

The female tests with the head the proper size of the pebbles of the substrate of the laying corner. While doing so, he receives burukadas of the males, which allows him to know the size of the tubercles. In these courtship movements, the male is often placed face down to show the female the red color of their fins and belly. In addition, the males give heads between them, driven by competition. According to these behaviors, tubers appear to be, above all, a fighting weapon among males, but females can also serve to know what kind of attention to choose.

Winifred E. Frost made the drawing in 1943.

W.E. Frost frost frost

The device performs external fertilisation. Therefore, in this chaos of short movements and heads, the female waits for the moment closest to the selected male. When this male approaches quite a lot, the laying of the 200-1,000 eggs kept by the female thyme, and the fertile male, extending his sperm on the eggs. When investigating the keys to this reproductive behavior, it is observed that both redness and tubercles are, in addition to a dichotomy between aesthetics and competition, a sign of other factors.

Piscarotenoid is not able to synthesize carotenoids that produce redness, but it gets them from invertebrates that eat and accumulates them in surface erythroforums. Therefore, when the female chooses the most intense red male, she chooses the most skilled to hunt and better fed.

On the other hand, it seems that redness has some relationship with the heterocinity of some DNA sequences (having the two forms of the gene) that have been studied. And, therefore, the female seems to certify the genetic diversity of her descendants by choosing the red male.

In addition, studies show that the most reddening cracks usually have fewer parasites. It is not clear whether having fewer parasites is a consequence of a good diet or whether they are due to genetic properties. If it were genetic, it could be thought that the female, when choosing these males, would increase the chances that their descendants are more resistant to parasites.

In addition, the size of tubercles is positively related to the presence of cerebral and visceral parasites, that is, they usually develop larger tubercles in those with a higher degree of infection. Therefore, through the tubers we can know the degree of infection that the males have.

The fish factor has its southwest limit with the river basins of the north of the Iberian Peninsula.

J. Larrañaga

For all this, it can be affirmed that the sexual dimorphism of the piscardo has distinguished and specialized two functions. On the one hand, the redness of the lips, fins and belly of the male peel would be an indicator of the genetic quality and nutritional and health status that the female prefers when choosing an intense reddish color.

On the other hand, the tuber of the head of the male bell seems designed for the fight of males. In fact, healthy males with red belly do not develop large tubercles, since thanks to the color they have great possibilities to equip themselves with females. The less healthy males, on the other hand, are more difficult to select by females, which use more energy in the development of tubers. And tubers are used as weapons against others.

In short, in exhaustive research factors appear beyond aesthetics and competition between males when analyzing the reproductive behaviors of animals.