When wondering if in nature only male and female individuals exist, the answer would seem obvious, but the natural world is incredibly varied for which there is never only “white or black”, but, as they say, many shades of gray. In fact, there is a series of adaptations that cannot always lead to the rigid distinction between “male” and “female”. In biology, the series of anatomical and behavioral differences that characterize individuals of opposite sex in the same species is called “sexual dwelling“And, even if widely widespread, it is not exclusive. The distinction in two sexes, in fact, is closely linked to the mechanism of the sexual reproductionand to the fact that reproductive cells (gametes) Male and female are in different individuals. But this is not always true in nature: first of all they can be present simultaneously in the same individual. Furthermore, the presence of one or the other gamete does not necessarily involve a clear separation also in anatomical structures, in the appearance and behavior of individuals: there are individuals with male gametes, but with appearances and female external characters.
Two sexes in one individual
Sometimes in a single animal we find two sexes: this phenomenon is known as simultaneous hermaphroditism and provides for the presence contemporary of the reproductive organs and male and female gametes in the same individual. It is more widespread than you can imagine in the animal kingdom and, in many cases, this mixed condition is very advantageous, even more than the division of reproductive tasks between two individuals of opposite sex. One could say, the maximum of the performance!
If, in fact, an organism presents both reproduce devices can self -reflect or try a double coupling With another individual of the same species, thus obtaining considerable saving of time and energy. The strategy is imposed above all by species that move very slowly Or who have few individuals distributed on very large areas and therefore with reduced probability of meeting a partner. Just to give some examples, in earthworms Each individual has both reproductive organs in such a way that two earthworms meeting can fertilize each other. Likewise the snail (Limax Maximus), considering the slowness of movement, is hermaphrodite and can also self -reflect.
Organisms that change sex
Some species they change sex over the life being born males and then becomes females later (Proterandial bodies), or being born females and then then becomes male (proteroginic bodies) based on specific needs. There are also alternating species, With individuals who change sex More than once during their life cycle. Sometimes, the male to female sequence is useful for the defense of a territory or a harem of other female individuals. Conversely, the transition from male to female can be linked to the increase in size: the growing individual becomes female and takes on dimensions suitable for producing a greater quantity of offspring.
Common examples of this phenomenon are observed in the oysters (Ostrea Edulis), in the grouper (Epinephelus marginatus) or in Napoleon fish (Cheilinus Undulatus). Also an animal very close to our daily life, the henin certain conditions it can change sex, at least a behavioral level. Sometimes, an old hen in a gallus -free chicken coil takes on some morphological characters and male character.
Males who prefer to look like females
Sometimes, among animals, males prefer to “disguise” to look like females. This phenomenon also has adaptive reasons in terms of reproductive strategy. For example, in Palude Falco (Circus Aeruginosus) young males present a female plumage that helps them to camouflage allowing them to avoid competition with other dominant males. Or the ruff (Philomachus Pugnax), a coastal bird, has male individuals who resemble females in order to approach and mate with real females without undergoing waste.
In many species there are also homosexual behaviors such as Evolutionary cooperation strategy within the group or pack. In the tursiopi (Tursiops Truncatus) Amorous relationships between individuals of the same sex in the youth phase can be established, and then subsequently facilitated the cooperation between males in the coupling phases with a female.
Females that reproduce without males
The females of some species they don’t always need males to reproduce. This is the phenomenon of parthenogenesisor that mechanism for which from a egg not fertilized However, a new individual was born from the male gamete. Many animals adopt this mixed strategy: for example, thequeen bee It produces a large number of eggs and then establishes how many must be fertilized by the male to produce workers and how many do not go fertilized to produce fires through partnership. Also the female of Komodic dragon (Varanus Komettiensis) adopts this reproductive strategy.
Individuals in part male and partly females
In some cases the birth of individuals that morphologically are a Mix of male and female characters. This phenomenon is said Ginandromorphismthe individual is a little male and a little female and depends on anomalies to the chromosomal level that manifest themselves at the morphological level. There are rare ginandromorphism phenomena between birdswhile it is much more frequent in arthropodsfor example in the small crustacean Daphnia Magnain the butterfly Periga CircumStans And in many hymenoptera.
