Hermaphroditism is a phenomenon in which one individual has characteristics of both female and male gender. Hermaphrodites in the animal kingdom are not as rare as you might think. Many invertebrates - worms, insects, mollusks, crustaceans - perform the functions of both male and female. Nature has developed different methods of reproduction that allow animals to continue their race in any living conditions.
Hermaphroditism among invertebrates
The phenomenon got its name from Greek mythology. According to legend, the son of Aphrodite and Hermes named Hermaphrodite was very handsome. One day the young man met a nymph, and both were inflamed with mutual passion. In order to never be separated, the lovers wished to unite in a single being. This is how the bisexual creature arose.
Natural hermaphrodites are devoid of any charm, since for the most part they are invertebrates:
- Sponges, polyps, jellyfish, ctenophores.
- Most of the worms are turbellaria, flukes, tapeworms, nemerteans, nematodes, leeches.
- Almost all crayfish and mollusks.
In earthworms, snails and perches, two types of fertilization occur: mutual (both individuals are both male and female) or sequential, when one individual takes on one role.
In worms (also in hydras and mollusks), self-fertilization most often occurs, while in fish this is most often impossible for physiological reasons.
Hermaphroditism also occurs among vertebrates. A striking example is sea bass.
More than 300 species of fish are capable of changing their sex during their lives. This depends on environmental factors - water temperature, alternation of time of day, and the number of males in the flock.
Other representatives of the fauna are also capable of changing sex:
- Sea corals.
- Holothurians (sea cucumbers).
- Shrimps.
Millions of dog mummies discovered in the sanctuary of the deity Anubis
Clown fish can arbitrarily turn into females, in which a clear hierarchy is observed in the school. If a female in a dominant pair dies, the male replaces her, and the leader is replaced by the largest member of the pack.
So the creators of the famous cartoon were mistaken - Nemo would have had a mother in any case.
Cleaner wrasses also live in small groups. They are engaged in eating parasites on predators, so neither sharks, nor moray eels or tunas touch them. The “brigade” is headed by one male, who strictly maintains order. But if he suddenly dies, one of his wives takes over as leader, changing gender in a matter of days.
Greek legends say that the beautiful nymph Salmacis fell madly in love with the unusually handsome young man Hermaphroditus, the son of Hermes and Aphrodite, raised by naiads. She asked the gods to make them inseparable forever, and the gods, heeding her request, merged them in one body. Naturally, this fantastic creature turned out to be bisexual.
Not only the Greek gods, but also nature loved to joke. There are many genuine hermaphrodites on Earth - true bisexual creatures.
Hermaphroditism can be natural or pathological, occurring as a congenital deformity. What are hermaphroditic creatures?
True hermaphrodites must necessarily have two gonads, one of which produces male and the other female reproductive cells. However, one should not think that each such animal, operating with the germ cells of both species, is able to give birth to a new creature on its own. Such animals are known, but they are few in number. For the reproduction of most hermaphroditic animals, it is necessary that at least two individuals participate in this process, as in dioecious organisms.
Self-fertilization often imitates the mating process. One of the ciliated worms, in order to meet gametes, must insert its own copulatory organ into a special hole on its body.
For many hermaphroditic organisms, self-fertilization is impossible. The reasons can be very different. Most often, male and female reproductive products mature at different times. But it also happens that female reproductive cells cannot be fertilized by sperm originating from the same organism. This phenomenon is observed in ascidians, its mechanism has not yet been solved.
Most hermaphroditic organisms, incapable of self-fertilization, during the reproduction period either simultaneously perform the functions of a male and a female, or at different periods of life act in one or another role.
A representative of the first group is the well-known earthworm. On the fifteenth segment of each worm there are two genital openings: one for excreting sperm, the other for receiving it. During mating, two worms press closely together so that the hole for excreting the sperm of each worm coincides with the hole for receiving it. Due to the secretion of sticky mucus, both specimens can remain in this position for a long time.
The group of hermaphrodites that change their sex depending on which sexual products are ripe in them is also numerous. This is how the frog round lungworm behaves. Isopods and some mollusks act as males at the beginning of their lives, and in the second half as females.
In synchronous hermaphroditism, an individual is capable of simultaneously producing both male and female gametes.
In the plant world, this situation often leads to self-fertilization, which occurs in many species of fungi, algae and flowering plants (self-fertilization in self-fertile plants).
In the animal world, self-fertilization during synchronous hermaphroditism occurs in helminths, hydras and mollusks, as well as some fish (Rivulus marmoratus), however, in most cases, autogamy is prevented by the structure of the genital organs, in which the transfer of one’s own sperm to the female genital organs of an individual is physically impossible (mollusks, in particular , Aplysia, ciliated worms), or the impossibility of fusion of their own differentiated gametes into a viable zygote (some ascidians).
Accordingly, with exogamous synchronous hermaphroditism, two types of copulatory behavior are observed:
Mutual fertilization, in which both copulating individuals act as both males and females (most often among invertebrates, examples include earthworms and grape snails)
- sequential fertilization - one of the individuals plays the role of a male, and the other plays the role of a female; mutual fertilization does not occur in this case (for example, in perch fish of the genera Hypoplectrus and Serranus).
In the case of sequential hermaphroditism (dichogamy), an individual sequentially produces male or female gametes, and either sequential activation of male and female gonads occurs, or a change in the phenotype associated with the entire sex. Dichogamy can manifest itself both within one reproductive cycle and throughout the life cycle of an individual, and the reproductive cycle can begin with either the male (protandry) or the female (protogyny).
In plants, as a rule, the first option is common - when flowers form, the anthers and stigmas do not ripen at the same time. Thus, on the one hand, self-pollination is prevented and, on the other hand, due to the non-simultaneous flowering time of various plants in the population, cross-pollination is ensured.
In the case of animals, a change in phenotype most often occurs, that is, a change in sex. A striking example is the many species of fish - representatives of the families wrasse (Labridae), grouper fish (Serranidae), pomacentridae (Pomacentridae), parrot fish (Scaridae), most of which are inhabitants of coral reefs.
Sometimes sex changes are observed in highly developed dioecious organisms. In amateur aquariums you can see fairly common viviparous fish - swordtails. Often, a young female swordtail, after bearing offspring, turns into a full-fledged male. Similar phenomena are known in frogs.
In the genital tract of female worms, Bonellia verdeum, Trichosoma and others, several males live. They bear little resemblance to a female and, based on their external features, could be classified as animals of a different species. Such confusion actually occurred. Naturally, the presence of males directly in the genital tract of females significantly increases the chances of successful fertilization.
Hermaphroditism is a common phenomenon for lower animals. Among the higher classes it occurs only as a rare deformity. Similar developmental anomalies are sometimes found in humans. Most often, the matter is limited to the fact that the patient has some external signs of the other sex. In men, a beard and mustache do not grow, the mammary glands develop strongly, and fat is deposited on the hips and other places, which gives the members a certain roundness. In women, on the contrary, hair develops on the face, legs or other parts of the body, the mammary glands can be very small, and the timbre of the voice can be masculine.
Less commonly, the external genitalia acquire features that make them resemble the genitals of the opposite sex. Sometimes they are so poorly developed that sex determination becomes impossible.
Such phenomena are called false hermaphroditism, since the matter is limited only to changes in external signs. The gonads in such subjects belong to one sex, although they may be underdeveloped.
True hermaphroditism, when one person has both ovaries and testes, is extremely rare. Only a few reliable cases are known, and in most of them the glands of only one sex had full functional activity.
Since it is difficult to correctly determine the sex of hermaphrodites at birth (and not only at birth), and the obstetrician must resolve this issue and register it in the relevant documents immediately, errors are possible. In the future, the wrong direction of upbringing can lead to the fact that the patient’s mental makeup and sexual inclinations will not correspond to the state of his gonads. In true hermaphrodites, the mental makeup and sexual orientation may change throughout life.
Now, thanks to the high development of surgical technology, this developmental defect can be eliminated without any particular risk to the patient. When deciding which gonads are to be removed, the doctor is guided not by their functional ability, but by the mental makeup of the patient and performs the operation in accordance with this. Only if the mental makeup is not clearly defined, the surgeon performs the operation, guided by the condition of the gonads.
Hermaphrodites are fish that have both male and female sexual characteristics. Hermaphroditism itself is the simultaneous (or sequential) presence in a living organism of female and male sexual characteristics, as well as organs for reproduction.
Instructions
Many fish species are characterized by a clear division of their sexes and, as a consequence, bisexual reproduction. It is curious that some fish are polygamous, while others are monogamous. But perhaps the most curious fish are hermaphrodites. It’s hard to believe, but some of these fish can even change sex several times throughout their lives. Such an individual can function as either a female or a male. Typically, fish exhibit consistent hermaphroditism, which can be influenced by both the state of the environment and some changes in their population.
There are also hermaphrodite fish, which at the beginning of their lives are males, and later undergo dramatic metamorphoses of their reproductive system, turning into fully functional females. Here we are already talking about protoandric hermaphroditism. For example, representatives of the grouper family exhibit this form of hermaphroditism. Sea wrasses can serve as a striking example of such transformations: all males transform into females with age.
However, in the wrasse family, the opposite process is also observed: if necessary, females can take the place of disappeared males. This happens if a male is removed from a group of wrasses. In this case, the strongest female will begin to demonstrate the behavior of the male, and after two weeks her reproductive system changes dramatically, beginning to produce male reproductive cells.
Hermaphroditism in fish can be not only natural, but also artificial, occurring under the influence of some chemicals. For example, American scientists from the US Geological Survey, who studied the basins of large US rivers, came to the conclusion that mutant fish, bisexual creatures, appeared in certain American rivers. It turned out that both smallmouth and largemouth bass are mutant hermaphrodites. Scientists have identified the main habitats of these fish: the Mississippi, Yampe, Columbia, Colorado, Pee Dee, Rio Grande, Colorado, and Apalachicole rivers.
Biologists from the US State Geological Research Center are confident that this phenomenon is not associated with the natural life activity of these fish. According to them, there is a suspicion that the hormonal changes in these creatures occurred under the influence of disorienting chemical signals in their bodies. It is worth noting that some scientists who previously claimed that these fish change their sex under the influence of various chemicals do not exclude the possibility that other factors influenced them, since some of these creatures were generally found in fairly clean bodies of water.
Hermaphroditism
Many fish have natural hermaphroditism. Currently, permanent hermaphrodites are known in representatives of four families: Serranidae, Sparidae, Maenidae and Centracanthidae; all marine fish, mainly from tropical and subtropical latitudes.
True hermaphrodites are divided into: a) functional, or synchronous, and b) non-functional. In fish of the first group, the gonads have different ovarian and testicular parts, and both mature eggs and sperm can be present at the same time. Self-fertilization, as a rule, does not occur in these fish, although it is possible in some species. Thus, Clark (Clark, 1959) notes that individuals isolated in an aquarium are functional hermaphrodites Serranellus subligarius lay fertilized eggs. L.P. Salekhova (1963) carried out fertilization of rock perch eggs Serranus scriba L. sperm from the same individual and showed that egg development proceeds normally, although better survival occurs with cross-fertilization. However, under natural conditions, self-fertilization probably does not occur, and each individual alternately performs the function of a female and then the function of a male.
Many species of the family belong to the group of synchronous hermaphrodites. Serraninae (family Serranidae), as Hypoplectrus unicolor(Walb.), Prionodes phoebe(Poey), P. tabacarius(Cuvier a. Valeric), P. tigrinus(Bloch) (Smith, 1959).
In fish belonging to the group of non-functional hermaphrodites, the ovarian and testicular parts of the gonad also differ, but unlike the functional parts in non-functional hermaphrodites, both parts do not function at the same time. In some fish species, the ovarian part reaches its greatest development at a young age, while the male part remains inactive. Such individuals function as females. After one or several spawns, the ovary undergoes reduction, the oocytes are resorbed, and the testis develops. This phenomenon of gender reversal is called protogyny. Protogyny is found in fish of the family. Serranidae subfamily. Epinephelinae - Epinephelus guttatus(L.), E. striatus(Bloch) Mycteroperca bonaci(Poey),M. tigris(Cuvier a. Valenc) (Smith, 1959),
family Maenidae - Pagellus erythrinus(Zei a. Zupanovic, 1961), fam. Sparidae - Diplodus annularis L., D. sargus (L.) and others (D "Ancona, 1950), Taius tumifrons (Aoyama, 1955), in a representative of the family Centracanthidae - Spicara maena (Reinboth, 1962).
In other species, a different pattern is observed. At younger ages they function as males, and at older ages as females. This change of sexes is called protandry. Protandry was observed in fish of the family. Sparidae - Diplodus sargus, Pagellus mormyrus(D"Ancona, 1950) Diplodus annularis(Salekhova, 1961; Reinboth, 1962).
According to L.P. Salekhova (1961), in the population of Diplodus annularis there are both dioecious individuals and hermaphrodites, and the percentage of hermaphrodite individuals decreases with age. Thus, among 4-year-old fish there are 60/6 females, 20% males and 20% hermaphrodites, and among 6-year-old fish there are only 3% hermaphrodites.
The third type of potential hermaphroditism is known in fish of the family. Labridae (Bacci a. Razzanti, 1957; Reinboth, 1961,1962; Okada, 1962; Sordi, 1961, 1962) and in one representative of the order Symbranchiformes (Lin, 1944; Liem, 1963). Fish of this group at younger ages have an ovary and function as females, then they undergo sex reversal, and at older ages the fish are represented only by males. Protogyny is also observed here, but unlike the protogyny of non-functional hermaphrodites, fish with potential hermaphroditism do not have a pronounced testicular part in the female gonad. Among the oocytes there are only undifferentiated germ cells - gonia, the further development of which forms the testis instead of the ovary.
U Coris julis Günth. there is a short phase of sex change and long periods of being female or male. Sex change in this species is associated with a change in color, causing young fish Coris julis, who were in the period of female development, were previously mistaken for another species - Coris giofredi Risso. Monopterus albus(Zuiev) lives in the rice fields of Southeast Asia and the Malay Archipelago. In this species, young individuals function like females, old ones function like males. General sex ratio: 3 females to 1 male.
The biological meaning of natural hermaphroditism is not always clear. Protogyny and the sex ratio shifted towards the predominance of females at younger ages are apparently an adaptation to increase the rate of reproduction in extremely unfavorable conditions. So, Monopterus albus has a short breeding season and has managed to adapt to the extremely unstable living conditions in the rice fields. After the dry period, the population recovers quickly due to the fact that all food resources are used primarily to support the life of individuals functioning as females; this leads to an increase in population size. Individuals that survive an unfavorable period become males. These fish are larger, produce more sperm, and are capable of spawning with multiple females.
Thus, protogyny is an adaptation that ensures an increase in population size through the use of food resources of a reservoir by individuals functioning as females. Protogyny is obviously characteristic of species living in water bodies or parts of water bodies where unstable conditions are observed and where the food supply is limited.
Protandry is somewhat less common. It is obviously due to the fact that smaller individuals, functioning as males, are able to ensure successful insemination of eggs, and larger individuals, becoming females, increase the fertility of the population.
In the case of synchronous hermaphrodites, it is possible to restore the population even with the preservation of single individuals.
A strict distribution of hermaphrodite species among the indicated hermaphrodite groups is not always possible. Detailed study of gonad development over several years on one generation of sea crucian Diplodus annularis conducted by L.P. Salekhova (1961), showed that in this species there are both dioecious individuals and functional hermaphrodites and protandry is observed. Thus, the range of sexual variation in this species is much wider than previously indicated by other researchers. In old fish, due to the decline of sexual function, sex reversal can also be observed, which was noted in female minnows, carp, and river flounder (Anisimova, 1956, 1956a; Bullough, 1940; Mikelsaar, 1958; observations by A.P. Makeeva).
Fish of almost all species are dioecious. Organic hermaphroditism is characteristic only of hagfishes. Among bony fish, only sea bass and sea crucian carp are usually hermaphrodites. Occasionally, hermaphrodites are found among herring, salmon, pike, carp and perch. At the same time, in chum salmon and mullet, sections of the ovaries and testes alternate in the gonads. Reports of hermaphroditism in carp are extremely rare. In one of these cases, a hermaphrodite described the release of both eggs and sperm. In this case, self-fertilization was accompanied by a significant waste of eggs (29% of the embryos developed), while when the eggs of another female were inseminated with the sperm of a hermaphrodite, 98% of the eggs developed. In fish, a change, transformation (reversion) of sex can occur. For example, juvenile rainbow trout in the early stages of development (at the age of 135-160 days), which has a mass of female germ cells in the gonads, subsequently develops into males. In most freshwater fish, the gonads during laying are indifferent with regard to gender, they are, as it were, potentially bisexual. The sex of such an intersex individual can only be determined during further development. Sex reversal can also occur in adults. There are known cases when, in the toothed carp Cyprinodontidae, sexually mature, previously spawned females suddenly turned into males and became capable of fertilizing eggs. In some fish, sex changes are observed more than once during their lives. Directed sex change is also possible: females and males of rainbow trout treated with steroid hormones (by feeding) changed their sex to the opposite and successfully spawned. This method may be important when breeding commercial fish. For example, in a salmon herd it is more profitable to have more females (they are larger), and in a tilapia herd - fewer, since they grow slowly and often spawn. In fish, fertilization selectivity takes place. Therefore, the use of sperm from two or more individuals when inseminating eggs increases its fertility.
Fish reproduce in a variety of conditions and on different substrates, therefore the following ecological groups are distinguished. Lithophiles
They breed on rocky soil (in rivers with currents or on the bottom of oligotrophic lakes or coastal areas of seas) in places rich in oxygen. These are sturgeon, salmon, podust, etc. Phytophiles
They reproduce among vegetation, laying eggs in stagnant or slow-flowing water on dead or vegetative plants. In this case, oxygen conditions may be different. This group includes pike, carp, bream, roach, perch, etc. Psammophiles
They lay their eggs on the sand, sometimes attaching them to the roots of plants. Often the egg shells are encrusted with sand. They usually develop in places rich in oxygen. This group includes minnows, some loaches, etc. Pelagophiles
They spawn eggs into the water column. Eggs and free embryos develop by floating freely in the water column, usually under conditions favorable for respiration. This group includes almost all types of herring, cod, flounder, and some carp (sichel fish, silver carp, grass carp, etc.). Ostracophiles
The eggs are laid inside the mantle cavity of mollusks and sometimes under the shells of crabs and other animals. Eggs can develop without sufficient oxygen. These are some gudgeons, bitterlings, etc. This classification does not cover all fish; there are intermediate forms: fishermen can spawn on vegetation and on stones, i.e., both as phytophilic and lithophilic fish. Most fish do not care about their offspring. There are often cases when parents even eat their own eggs and especially juveniles. Cannibalism occurs in gambusia, navaga, and even carp. Therefore, in order to preserve juveniles, it is advisable to catch spawners from spawning ponds. However, many species of fish take care of their offspring. In this case, the protection of offspring in most cases falls to the lot of males. Examples of caring for offspring are interesting and varied: a male stickleback builds a nest from pieces of grass blades glued together by kidney secretions (Fig. 4). The nest initially has two holes, and after filling it with eggs from several females, the male closes one hole and remains guarding it, aerating the water with the movements of his fins. After hatching the juveniles, the male makes sure that they are in the nest for several days and returns those that swim out there, capturing them with his mouth. Female tilapia carry eggs in their mouths and, for some time after hatching, take the young into their mouths when in danger. In pipefish and seahorses, the eggs are incubated in a fold or pouch on the abdomen of the male. Labyrinth fish build a nest of air bubbles and salivary secretions. Although the juveniles appear in the nest within a day, the male guards it until the fish are fully formed. The construction of nests of varying complexity is not uncommon among fish. Trout and salmon dig several holes in the ground, and the laid eggs are covered with sand and gravel with movements of the tail, creating so-called spawning mounds. Some gobies and catfish make nests from pebbles and pieces of plants. The lumpfish guards a lump of eggs deposited near the surf; during low tide, it pours water from its mouth on it. The pike perch builds a nest from pieces of roots or by clearing a rocky area: it bites the hand extended to the nest, and cannot be driven away. By moving the pectoral fins, it creates a current of water that washes away the silt from the eggs. The most perfect form of caring for offspring is viviparity. In this case, fertility is usually low - several dozen individuals. Essentially, this is ovoviviparity with retention of offspring in the female genital tract until the yolk sac is reabsorbed. It is inherent in many sharks, and among bony fish - eelpout, sea bass, gambusia, guppies and swordtails. In the individual development of fish, a number of large segments (periods) can be distinguished, each of which is characterized by properties common to different species. I. Embryonic period-