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Sharks are aquatic animals that present sexual dimorphism, that is, external characteristics observable at some stage of life that differentiate males from females. Some of these features are mentioned below.
copulatory organs
A feature common to all shark species that allows males to be identified is the presence of two external copulatory organs that function as penises called pterygopodia or claspers , located between the two ventral fins. Through the claspers , the male introduces the sperm into the female.
Size
Female sharks tend to be larger and heavier than males. These differences in body size may be related to the fact that females have a higher energy expenditure; this is due to the strong selection pressure, which causes the need to house many young within their reproductive systems.
Growth rate
In some shark species it has been shown that males reach sexual maturity earlier than females, who take longer to develop their reproductive organs and reach the size necessary to form their young. This represents a strong threat to such species, as they may become extinct faster than they can reproduce through activities such as fishing.
big heads
In species such as Scyliorhinus canicula, males have longer mouths, heads and teeth than females. As sharks typically engage in reproductive behavior in which the male has to bite into one of the female’s fins to allow copulation, differences in the size of their snouts and teeth may suggest adaptations of the head to reach the female. bite her and hold her.
thicker skin
The females of several shark species have thicker skin compared to that of the males. It has been suggested that this dimorphism is an adaptive mechanism to protect itself from bites during courtship or to facilitate the grasping of males during copulation and penetration by claspers . The thick scales are concentrated in areas of the body where males have been observed to bite and attach to the body of females, i.e. on the pectoral fin, in the area behind the pectoral fin, on the caudal fin and on the tail. pelvic girdle.
Differentiated sensory organs
All shark species have specialized sensory organs called Lorenzini’s blebs, which detect both electromagnetic fields and changes in temperature. Each ampulla is a canal filled with gelatinous substance at the bottom of which are groups of small bags filled with receptor cells, with an opening to the outside through a pore in the skin.
In species such as the catshark, males were found to have larger blisters and pouches, larger areas of the body occupied by Lorenzini’s blebs, and a greater number of receptor cells. Until now, these differences are thought to increase the ability of adult males to detect females in heat, an essential mechanism during the breeding season.
Sources
Barbosa, AP., Da Silva, E., Manir, L., Nunes e Silva LP, da Silva, Z., Silva, JL. Sexual dimorphism of sharks from the amazonian equatorial coast . Universitas Scientiarum , 20(3): 297-304. 2015.
Benavides, R., Brenes, C., Márquez, A. Sex ratio, length-weight relationship, and geographic-bathymetric distribution of Squalus cubensis (SQUALIFORMES: SQUALIDAE) on the Caribbean coast of Central America . Uniscience , 31(2): 69-82, 2017.
