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Why Some Tropical Fish Are Getting More Colorful

Why Some Tropical Fish Are Getting More Colorful

They say that the new generations always improve their predecessors. At least this is what happens with different species ofPterophyllum scalare - better known as scalar fish or angelfish - that produce hybrid offspring even more colorful than their parents.

Some coral reef fish, such as several species of scalar or angelfish (Pterophyllum scalare), are capable of producing hybrid offspring with even more striking colors than their parents, since the eggs of one species and the sperm of another are combined.

A new study by Australian researchers has comprehensively documented all known naturally occurring hybrids of marine angelfish. The results are published in the journalProceedings of the Royal Society B.

After comparing the mitochondrial DNA of 37 hybrids with that of their parent species, the team found that 48% of marine angelfish can hybridize, more than any other group of coral reef fish. These data end the previous record achieved by butterflyfish (Chaetodontidae), a family in which more than a third of the species are capable of producing hybrids.

In the case of the butterflyfish, they do not stray too far from their own species as they could have trouble finding a mate. However, most angelfish hybrids occur between deeply divergent lineages.

In principle, this type of hybridization does not make evolutionary sense, and it even represents a threat to the diversity of species. For the experts, led by Yi-Kai Tea, a graduate student at the University of Sydney and the Australian Museum Research Institute (AMRI), one possible explanation is that angelfish ‘reject’ monogamy.

Unlike butterflyfish, which mate for life, angelfish live in 'harems' where multiple females mate with a single male. "When the male identifies a female, they rise up the water column and release her sperm and eggs," explains Tea. Once adrift, the egg is ready for fertilization by a sperm of any other species.

Many unknowns to solve

One of the most surprising findings of the work is that angelfish can produce hybrid offspring with species that have up to 11% difference in mitochondrial DNA, as occurs with a mix between emperor angelfish (Pomacanthus imperator) and the blue angelfishPomacanthus annularis). "This is extremely important," says Tea. “Reef fish rarely hybridize with a difference of more than6 %”.

Although the work reveals a surprising abundance of angelfish hybrids, the mechanism itself - how and why hybrids form - remains an enigma. For example, the researchers could not find a single example ofPygoplites diacanthus or hybrid royal angelfish, a tropical fish that swims almost anywhere there is a tropical ocean.

Reference:

Yi-Kai Tea, Jean-Paul A Hobbs, Federico Vitelli, Joseph D DiBattista, Simon Y W Ho, Nathan Lo. Angels in disguise: sympatric hybridization in the marine angelfishes is widespread and occurs between deeply divergent lineages!Proc Biol Sci. 2020 Aug 12; 287 (1932): 20201459. doi: 10.1098 / rspb.2020.1459. Epub 2020 Aug 5.

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