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Nuptial tubercles

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Sexual ornaments of fish "Pearl organ" redirects here. For the obscure organ of a deep-sea fish, see Pearleye.

Nuptial tubercles on stone-roller, Campostoma anomalum

Nuptial tubercles or breeding tubercles (also called pearl organs or nuptial efflorescence) are noticeable skin roughness or horny nodules that form on male fish during breeding. They are made of keratin, the same material as hair, hooves, and fingernails.

Use and description

These tubercles are dermal structures present in 15 families of fish belonging to 4 orders of Actinopterygii – Salmoniformes, Gonorhynchiformes, Cypriniformes and Perciformes are used in the courtship and reproduction process. They consist of partially or fully keratinised cells that form in certain regions, used to stimulate females during courtship. Their development is stimulated by hormones secreted by the pituitary and adrenal glands, and is induced shortly before the breeding season and discarded after. In some species, at least, there is a correlation between the level of androgens present in the endocrine system and the volume and complexity of tubercle growth.

Tubercles on the nose of Fathead minnow (Pimephales promelas)

They normally form on the heads of male fish, often covering the whole of the top part of the snout, but may also occur on fins, or anywhere else on the scaled integumentary system. The actual purpose of nuptial tubercles is not definitively known. There are many theories about their function, which include: use to stimulate females during courtship, in aggressive rituals performed by males during mate selection, to maintain contact between individuals during reproduction, or in defence of the nest from predators. There is definite proof that they grow mainly on areas with greater mechanical stress, which means that those species that head-butt females to stimulate them to release eggs will have more on the head, whereas those that dig nests in gravel substrates will develop them more on their fins. Nuptial tubercles occasionally develop on female fish also, but this is rare, and they are often barely visible to the naked eye.

Nuptial tubercles have been described as an honest signal of the general health of the male bearer, in common with other biological ornaments. Indeed, research has proven a correlation between tubercle density and parasite resistance, though it is not always a positive correlation.

In species that use lek mating, the females choose the males with the roughest skin, but were not confused by males that had papillomatosis (a skin disease resulting in rough skin).

The presence of nuptial tubercles has been used to distinguish speciation. The genus Leucos was described from similar Rutilus species in Europe as they do not develop them. Similarly, the description of Messinobarbus (now a synonym of Luciobarbus) in 1994 was an attempt to distinguish those species with them from Barbus that do not have them.

Similar structures in other fishes

Odontodes on male Loricariidae sp.

Visually similar structures to nuptial tubercles are produced by male loricariid catfishes during the mating season, in similar places to nuptial tubercles (snout and fins). These are actually hypertrophied odontodes, which are therefore dermal teeth, rather than keratin, and are covered by flesh containing taste buds. It has been proposed that these ornaments may assist breeding success by mimicking fry, tempting females to lay their eggs in the nest cave of a successful male, already guarding his own offspring.

Instead of tubercles, cichlid males produce nuchal humps (koks), where additional fat is laid under the skin over the skull forming a hump on the head. This trait has been developed to an extreme in the hybrid Flowerhorn cichlid, by selective breeding in the aquarist hobby.

Gallery

See also

Nuptial pad - a similar ornament of frogs

References

  1. "nuptial tubercle". Academic Dictionaries and Encyclopedias: Dictionary of ichthyology.
  2. Froese, Rainer; Pauly, Daniel (eds.). "Glossary Search for pearl organ". FishBase glossary.
  3. ^ Wiley, M. L. & Collette, B. B. (1970). "Breeding tubercles and contact organs in fishes: their occurrence, structure, and significance". Bulletin of the American Museum of Natural History. 143: 145–216.
  4. ^ Raine Kortet; Jouni Taskinen; Anssi Vainikka & Hannu Ylönen (August 2004). "Breeding Tubercles, Papillomatosis and Dominance Behaviour of Male Roach (Rutilus rutilus) During the Spawning Period". Ethology. 110 (8): 591–601. Bibcode:2004Ethol.110..591K. doi:10.1111/j.1439-0310.2004.01002.x.
  5. Poncin, P.; Matondo, B.N.; Termol, C.; et al. (2011). "Relationships between circulating androgens, aggressive behaviour and breeding tubercles in males of the common bream Abramis brama L. in an aquarium environment". Fish Physiol Biochem. 37 (3): 533–542. Bibcode:2011FPBio..37..533P. doi:10.1007/s10695-010-9455-y. PMID 21132526.
  6. Mary F. Willson (February 1997). "Variation in Salmonid Life Histories | Patterns and Perspectives" (PDF). Research Paper. USDA Forest Service: 11.
  7. Huuskonen, Hannu; Haakana, Helena; Kekäläinen, Jukka (October 2009). "Offspring performance is linked to parental identity and male breeding ornamentation in whitefish". Biological Journal of the Linnean Society. 98 (3): 532–539. doi:10.1111/j.1095-8312.2009.01315.x.
  8. Taskinen, J. & R. Kortet (2002). "Dead and alive parasites: sexual ornaments signal resistance in the male fish, Rutilus rutilus". Evolutionary Ecology Research. 4: 919–929.
  9. R. Kortet & J. Taskinen (7 May 2004). "Parasitism, condition and number of front head breeding tubercles in roach (Rutilus rutilus L.)". Ecology of Freshwater Fish. 13 (2): 119–124. Bibcode:2004EcoFF..13..119K. doi:10.1111/j.1600-0633.2004.00039.x.
  10. Bianco, P.G.; Ketmaier, V. (2014). "A revision of the Rutilus complex from Mediterranean Europe with description of a new genus, Sarmarutilus, and a new species, Rutilus stoumboudae (Teleostei: Cyprinidae)" (PDF). Zootaxa. 3841 (3): 379–402. doi:10.11646/zootaxa.3841.3.4. PMID 25082046.
  11. Bianco, P.G. (1998). "Diversity of Barbinae fishes in southern Europe with description of a new genus and a new species (Cyprinidae)". Italian Journal of Zoology. 65 (1): 125–136. doi:10.1080/11250009809386804.
  12. Sabaj, Mark H.; Armbruster, Jonathan W.; Page, Lawrence M. (1999). "Spawning in Ancistrus (Siluriformes: Loricariidae) with comments on the evolution of snout tentacles as a novel reproductive strategy: larval mimicry". Ichthyol. Explor. Freshwaters. 10 (3): 217–229. Retrieved 2009-06-23.
  13. Sina J. Rometsch; Julián Torres-Dowdall; Gonzalo Machado-Schiaffino; Nidal Karagic; Axel Meyer (23 November 2021). "Dual function and associated costs of a highly exaggerated trait in a cichlid fish". Ecology and Evolution. 11 (23): 17496–17508. Bibcode:2021EcoEv..1117496R. doi:10.1002/ece3.8383. PMC 8668731. PMID 34938524.

Further reading

Stephanie C. McMillan; Zhe T. Xu; Jing Zhang; Cathleen Teh; Vladimir Korzh; Vance L. Trudeau; Marie-Andrée Akimenko (2013). "Regeneration of breeding tubercles on zebrafish pectoral fins requires androgens and two waves of revascularization". Development. 140 (21): 4323–4334. doi:10.1242/dev.095992. hdl:10393/31649. PMID 24089472.

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