1. Introduction
Cichlid fishes are well-known among aquarists and biologists for their enormous colour diversity. The family comprises between 2000 and 3000 species that inhabit rivers and lakes in tropical and subtropical regions of Africa and the Americas, as well as India and Sri Lanka. Taxonomically, Cichlidae are divided into several tribes, among which for example the African Haplochromini are renowned as particularly species rich and colourful. It is not only their phenotypic diversity that makes cichlids so fascinating, but also the speed at which some of this diversity evolved. For example, the several hundred species of the East African Great Lakes emerged within tens of thousands to some million years. Closely related species often differ in little else but the colour of body and fins.
In many species, body colours are overlaid with dark vertical bars and/or horizontal stripes. Frequently, the differently coloured body regions are not defined by sharp boundaries but rather shade into one another—in contrast to the sharp-edged patterns of many well-known coral reef fishes.
Colour patterns vary not only between cichlid species, but also within and among populations of a species (sexual dichromatism, polychromatism and geographic variation), as well as within individuals, depending on their age and social status.
In this review, we aim to provide an overview of this variation, its underlying mechanisms and evolutionary consequences, and identify knowledge gaps and priorities for future research.
1. Introduction
Cichlid fishes are well-known among aquarists and biologists for their enormous colour diversity. The family comprises between 2000 and 3000 species that inhabit rivers and lakes in tropical and subtropical regions of Africa and the Americas, as well as India and Sri Lanka. Taxonomically, Cichlidae are divided into several tribes, among which for example the African Haplochromini are renowned as particularly species rich and colourful. It is not only their phenotypic diversity that makes cichlids so fascinating, but also the speed at which some of this diversity evolved. For example, the several hundred species of the East African Great Lakes emerged within tens of thousands to some million years. Closely related species often differ in little else but the colour of body and fins.
In many species, body colours are overlaid with dark vertical bars and/or horizontal stripes. Frequently, the differently coloured body regions are not defined by sharp boundaries but rather shade into one another—in contrast to the sharp-edged patterns of many well-known coral reef fishes.
Colour patterns vary not only between cichlid species, but also within and among populations of a species (sexual dichromatism, polychromatism and geographic variation), as well as within individuals, depending on their age and social status.
In this review, we aim to provide an overview of this variation, its underlying mechanisms and evolutionary consequences, and identify knowledge gaps and priorities for future research.
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