Mermaid

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Mermaid
Mermaid (Coris julis) Transitional form?

Mermaid ( Coris julis ) Transitional form Venus symbol (female) ?Mars symbol (male)

Systematics
Perch relatives (Percomorphaceae)
Order : Labriformes
Family : Wrasse (Labridae)
Subfamily : Junker Wrasse (Julidinae)
Genre : Coris
Type : Mermaid
Scientific name
Coris julis
( Linnaeus , 1758)

The mermaid ( Coris julis ) is a species of wrasse that occurs throughout the Mediterranean, as well as in the eastern Atlantic and the Black Sea. The fish are partly protogynous hermaphrodites .

Geographical distribution and habitat

The distribution of the mermaid ranges from the southern Black Sea across the entire Mediterranean to the eastern Atlantic . There it occurs from the Atlantic coast in front of Sweden over the Bay of Biscay to the central African coast in front of Gabon . There are also populations in the Azores , off the Canary Islands and Madeira Island . Mermaids often live in sympathy with the sister species Coris atlantica . Their habitat is close to the coast and is preferably rock littoral overgrown with algae or seagrass meadows ( Posidonia oceanica ). The latter are mainly used for rearing and offer protection to the juvenile mermaids. The animals usually stay in shallow water from one to 60 meters deep, in winter they tend to be deeper. Older males also prefer deeper waters. However, they occur to a depth of 120 meters.

Male phase

features

The mermaid has an elongated shape and is less high back than many representatives of the Labridae . It has a terminal mouth and is up to 25 cm long. The sideline is occupied by at least 70 sheds. The initial color of a mermaid is a brown-greenish back and a light yellowish belly, separated by a lighter longitudinal stripe below the lateral line organ and with a shiny black to dark blue spot on the edge of the gill cover. In females and primary males (i.e. all young animals) the initial color hardly changes. The more colorful dress of secondary males (i.e. males who emerged from females through sex reassignment ) is blue-green on the back and has an orange, zigzag-shaped band on the side and a dark blue spot that extends from the shoulder to the anal fin. The dorsal fin is dorsally provided with a red and ventrally with a dark blue spot. Of the eight to nine rays, the first three are elongated. However, there are intraspecific differences in secondary males as well. For example, the body of mermaids that are native to the Atlantic becomes darker and blackish-streaked caudally. The shape of the body in the populations of the Mediterranean also varies. Fruciano was able to show that the body shape of the mermaids off the Croatian coast near Split is the most elongated compared to other Mediterranean populations. Animals from more southerly populations, for example near Sicily , have more stocky bodies.

All juvenile mermaids are either females or "primary" males. Most females later develop into "secondary" males. Since mermaids can therefore have two very different colors, it was assumed in the first half of the 20th century that there were two Coris species. Small mermaids with a simple dress were assigned to the species Coris giofredi and the larger, more colorfully patterned ones to the species Coris julis . However, research in the 1960s showed that both forms are the same species, but different sexes. The smaller, more plainly colored animals are either females or primary males. In contrast, mermaids with more conspicuous colors are exclusively secondary males.

gender transformation

The natural gender distribution during the breeding season, i.e. mid-July to September, is approximately 68% females, 25% primary males and 7% secondary males. The high proportion of females ensures a high egg production. All females are smaller than 18 cm. At the end of the breeding season, around mid-September to the end of October (in some cases as early as mid-July), the sex change from females to secondary males takes place. Then the relationship with the secondary males shifts. In the process, morphological and anatomical changes take place in the mermaid . Externally, a pale red-blue-white color on the dorsal fin is gradually becoming visible. Then the brown flanks turn orange at the point where the characteristic zigzag band will later lie. The first three rays of the dorsal fin become longer, the lateral spot slowly becomes visible and the head becomes greener. Finally, the lateral stain takes on a dark blue, the jagged band a strong orange and the belly a green-whitish color. Anatomically, the transformation is limited to changing the gonads . In the females, male germ cells are already present at the edge of the ovaries. From this, several cell layers are initially formed, while the oocytes inside degenerate. The smaller the ovary, the thicker the cell layer on the edge of the male germ cells. Ultimately, this cell layer creates a male gonad, which is encapsulated from the rest of the degenerated ovary and becomes functional. The transformation of the gonads does not fully correlate with the change in habitus , but some events can be summarized: While the dorsal fin changes color, the ovary degenerates and the development of the male gonad takes place simultaneously with the maintenance of the secondary dress. In contrast to primary males, which have shorter and more voluminous gonads (20-24 mm length, 4-6 mm diameter), those of the secondary males are longer and narrower (10-20 mm length, 10-15 mm diameter). The conversion takes a few weeks.

The sex change is due to several factors. The interrelationships between individuals play a major role here. If there is a shortage of males, this induces a change of sex - even in smaller animals under 12 cm. However, the territorial behavior (which is only exercised by secondary males) leads to the opposite. That is why the sex change does not occur until the end of the breeding season, when the animals no longer behave territorially. No territorial behavior could be observed in areas where mermaids transformed very early in the year . In an experiment by Reinboth it was shown that females converted to secondary males after administration of testosterone isobutyrate and that, among other things, this hormone is the basis of the sex change.

In general, the reasons for successive hermaphroditism (asynchronous hermaphroditism ) lie in the fact that some habitats are not seasonally stable and the populations decline at certain times during the year. In the event that only two individuals of a species survive, the probability that it is a male and a female is 50%. Assuming that both individuals are of the same sex, future reproduction could still be ensured with asynchronous hermaphroditism.

nutrition

The mermaid eats an omnivorous diet, but has a preference for animal food. His menu includes snails ( Gastropoda ), crustaceans ( Crustacea ), mussels ( Bivalvia ), smaller fish, polychaeta , echinodermata ( Echinodermata ), woodlice ( Isopoda ), amphipods ( Amphipoda ) and benthic algae. Juvenile fish can also be optional cleaner fish .

Reproduction

The mermaid is sexually mature at one year. The mermaid breeding season begins in mid-July and lasts until September. First, the female adopts a courtship position, which is followed by circling by the secondary male. Then both swim in a spiral towards the surface of the water. After about three meters ascent, the female turns on her back for a brief moment and the germ cells are expelled from both sexes . The large but comparatively few eggs are fertilized pelagically. At the end of the breeding season there are less successful matings; the females seem to be losing interest. It has been observed that primary males often passively participate in an act of reproduction by observing the courtship between the female and the secondary male, but are subsequently driven away by the secondary male (which is why it can be assumed that these are in fact primary males and not females acts). The primary male may be trying to get to the female himself, although this does not happen often. Hence, this could explain the low proportion of primary males (25%). Newly hatched mermaids have a planktonic larval stage of four to six weeks and live in seagrass beds , where they have better hiding places.

behavior

Territorial behavior can be observed in some secondary males . These start with the search for a territory with the beginning of summer. As soon as a secondary male has found a suitable territory, it is marked by an imposing behavior. It stays in the center of the territory, where it can be seen from afar, or it swims around the boundaries of the territory with its dorsal fin upright, so that the red-blue-white color is recognizable. The size of the animal is not necessarily the decisive factor here; even smaller mermaids can show a successful territorial behavior towards larger ones, but the reason is unclear. Perhaps the impressive behavior is perceived more clearly than the size of the conspecific. However, defensive acts are only taken against males, suggesting that mermaids can distinguish between primary males and females. The territorial male also has to assert itself against other neighboring species. The rule is that the acceptance by the neighbors increases with the duration of territorial ownership. The intensity of the territorial behavior reaches its peak by mid-July, only to then appear again in a weaker form. In late September, territorial males will tolerate other males as well. A territory provides a feeding ground and a breeding place for a mermaid. Mermaids that are not territorial (i.e. primary males and females) live tied to one place for life. The mermaid sleeps in the sediment and digging into it depends on both the light conditions and the temperature. Not only through the darkness, but also through cold water, a sleeping behavior, i.e. burrowing in the sediment, can be induced in mermaids. In midsummer they are awake from 6 a.m. to 8 p.m., while the waking phase at the end of winter only lasts from 8:30 a.m. to 3:30 p.m. As an escape reaction, mermaids dig up to five centimeters into the sediment.

Chromosomal examinations

The number of chromosomes in mermaids is 48. Females and secondary males have 38 acrocentric and 10 metacentric and primary males 37 acrocentric and 11 metacentric chromosomes. The chromosomes can be grouped into 23 chromosome pairs of homologous chromosomes and a 24th chromosome pair, which can have three different possible combinations:

a) Two acrocentric chromosomes of identical size
b) One large and one small acrocentric chromosome
c) One large acrocentric and one larger metacentric chromosome

Duchac showed that the combination option a) occurs rarely and only in females, combination option b) with females and secondary males and combination option c) exclusively with primary males. It is very likely that females with combination options a) are lifelong functional females who keep their sex throughout their lives. However, these are rare and only make up one sixth of all females. In addition, the larger metacentric chromosome shows that only primary males can father the same and thus proves the fact that these also reproduce.

particularities

The optical ability of the mermaid is comparatively well developed. The diencephalon (which contains most of the optical switching stations in the brain) of the mermaid is larger than that of the monk fish Chromis chromis and the retina of the mermaid is of the "light" type - retina with many cones , which are important for a diurnal lifestyle. There is also a fovea , which is centrally located and has a clear pit. These properties testify to the good visual performance of this wrasse species. Since the mermaid is not as thermophilic as the sea ​​peacock ( Thalossoma pavo ), it is displaced by it in many warm and shallow water areas. In the Golfe du Lion (France), however, the population sizes are increasing; The reasons for this are the construction of dams in the Rhone to reduce the inflow of cold water, and probably climate change .

literature

  • A. Campbell: What lives in the Mediterranean? Plants and Animals d. Mediterranean coast in color . Franckh, Stuttgart 1983, ISBN 3-440-05138-2 .
  • P. Louisy: Marine fish. Western Europe Mediterranean . Eugen Ulmer Verlag, Stuttgart 2002, ISBN 3-8001-3844-1 .
  • R. Riedl: Fauna and flora of the Mediterranean. 3., rework. u. exp. Edition. Parey, Hamburg 1983, ISBN 3-490-23418-9 .
  • Andreas Vilcinskas: Fish. (= BLV regulations books ). 2nd Edition. BLV Verlagsgesellschaft, Munich 2000, ISBN 3-405-15848-6 , p. 138.

Web links

Commons : mermaid  album with pictures, videos and audio files

Individual evidence

  1. ↑ P. Parenti, J. Randall: An annotated checklist of the species of the labroid fish families Labridae and Scaridae. In: Ichthyological Bulletin. 68, 2000, pp. 1-97.
  2. ↑ a b c d e D. Pollard, P. Afonso: Coris julis . The IUCN Red List of Threatened Species 2010. December 2, 2016 2010.
  3. ^ A. Campbell: What lives in the Mediterranean? Plants and Animals d. Mediterranean coast in color. Franckh, Stuttgart 1983.
  4. ^ R. Riedl: Fauna and Flora of the Mediterranean Sea. Parey, Hamburg 1983.
  5. ^ A b P. Louisy: Marine fish: Western Europe and the Mediterranean. Ulmer, Stuttgart (Hohenheim) 2002.
  6. ↑ a b c d e f g h i B. Duchac: Ecological and cytogenetic aspects of sex change in 'Coris julis' L. (Labridae, Teleostei). University of Basel, Basel 1981.
  7. ↑ a b D. Aurelle et al .: Genetic study of 'Coris julis' (Osteichtyes, Perciformes, Labridae) evolutionary history and dispersal abilities. In: Elsevier CR Biologies. 326, 2003, pp. 771-785.
  8. ↑ a b C. Fruciano: Geographical and morphological variation within and between color phases in Coris julis (L. 1758), a protogynous marine fish. In: Biological Journal of the Linnean Society. 104, 2011, pp. 148-162.
  9. ^ A b E. Tortonese: Fauna d'Italia, Osteichthyes. Edizione Calderini, Bologna 1975.
  10. ↑ R. Reinboth: Natural sex reassignment in adult teleostars. In: Zool. Indicator. 24, 1961, pp. 259-262.
  11. ^ M. Roede: Notes on the labrid fish 'Coris julis' (Linnaeus, 1758) with emphasis on dichromatism and sex. In: Vie Milieu A. 17, 1966, pp. 1317-1333.
  12. ^ A b F. Bentivegna, P. Cirino: Sexual inversion in 'Coris julis' L. 1758. In: Cybium. 8, 1984, pp. 51-61.
  13. ↑ R. Reinboth: Experimentally induced sex change in fish. In: Verh. Dt. Zool. Ges. Munich 1963. pp. 67–73.
  14. ↑ P. Karachle, K. Stergiou: The effect of season and sex on trophic levels of marine fishes. In: Journal of Fish Biology. 72, 2008, pp. 1463-1487.
  15. ↑ J. Pinnegar, J. Polunin: Contributions of stableisotope data to elucidating food webs of Mediterranean rocky littoral fishes. In: Oecologia. 122, 2000, pp. 399-409.
  16. ↑ H. Kabasakal: Description of the feeding morphology and the food habits of four sympatric labrids (Perciformes Labridae) from south-eastern Aegean Sea, Turkey. In: Netherlands Journal of Zoology. 51, 2001, pp. 439-455.
  17. ^ D. Zander, J. Nieder: Interspecific associations in Mediterranean fishes: feeding communities, cleaning symbioses and cleaner mimics. In: Vie et Milieu. 47, 1997, pp. 203-212.
  18. ↑ a b c F. Huber: About the life and sex change of 'Coris julis' (L.). Zoological Institute Basel 1978.
  19. ^ W. Finck: To the optical system of 'Coris julis' (L.) (Labridae, Perciformes). A cytoarchitectonic-histological examination with the help of BODIAN and HRP technology. 1984