Cichlids - Taxonomy and evolution
Cichlids are known for mating rituals, territoriality, and parental care, which are hallmarks of cichlid behavioral ecology. Let's look at their classification to better understand it.
Just a small reminder:
- The major classifications in the tree of life: class -> order -> family -> genus -> species.
- Phylogenetics - is the systematic study of reconstructing the past evolutionary history of extant species or taxa, based on recent data.
Classification of Cichlids
Cichlids are classified within the order Cichliformes, which is part of the larger fish group known as Perciformes, the largest order of vertebrates.
The family Cichlidae is further divided into four subfamilies*:
Cichlinae (includes well-known genera such as Cichla, Geophagus, Apistogramma, and Discus (genus Symphysodon) )
Encompassing New World cichlids (from Central and South America), this subfamily includes tribes such as Cichlasomatini, Heroini, and Geophagini. Cichlinae species are equally diverse, occupying habitats ranging from fast-flowing rivers to still waters. They demonstrate a variety of parental care strategies, including some unique nesting and brood care behaviors not seen in their African counterparts.
Pseudocrenilabrinae (includes some of the most studied and well-known cichlid genera, such as Neolamprologus, Tropheus, and Mbuna),
This subfamily is primarily composed of African cichlids, including those from the explosive radiations in the African Great Lakes (e.g. Lakes Malawi, Victoria, and Tanganyika). Pseudocrenilabrinae are known for their incredible diversity in morphology, behavior, and reproductive strategies. They exhibit various breeding behaviors, such as mouthbrooding and substrate guarding, and show a wide range of dietary adaptations from herbivory to carnivory.
Etroplinae (comprises the genera Etroplus and Paretroplus)
Sometimes included, this smaller subfamily consists primarily of Indian and Sri Lankan cichlids. They are not as diverse as the African and American cichlids but are important for understanding the early evolutionary history of the Cichlidae family.
Ptychochrominae
Known as the Malagasy cichlids, are native to Madagascar and exhibit unique characteristics and evolutionary histories separate from their African and American counterparts.
These subfamilies encompass a diverse range of species found across South America, Africa, and parts of Asia.
Modern taxonomy relies heavily on both morphological and genetic data to classify cichlids, with a particular focus on their unique features such as the pharyngeal jaws—a second set of jaws in the throat used for processing food. Advances in DNA sequencing have refined our understanding of relationships within this group, highlighting the dynamic nature of cichlid phylogenetics, which continues to evolve as new species are discovered and existing classifications are challenged.
Evolutionary History and Speciation
Cichlids are a model group for studying rapid speciation and adaptive radiation. Their evolutionary history is marked by significant diversity that arose from a common ancestor shared with a group of saltwater fish species around 100 million years ago. The most spectacular examples of adaptive radiation are observed in the African Great Lakes—Victoria, Malawi, and Tanganyika—where cichlids have diversified into several hundred species within each lake.
This explosive speciation is attributed to several factors: sexual selection, niche differentiation, and geographic isolation. Cichlids have developed a wide array of mating preferences and territorial behaviors, which, coupled with their dietary versatility, allows them to exploit different ecological niches. The isolation of populations in distinct lake environments with varying ecological conditions has further encouraged divergence through allopatric speciation.
Geographic Distribution
Cichlids are primarily found in tropical and subtropical freshwater habitats across Africa, South America, and parts of Asia, including Madagascar and Sri Lanka. In Africa, cichlids are distributed throughout various river systems and lakes, most notably in the East African Rift Valley lakes, which are home to an incredible diversity of endemic species. South American cichlids are distributed across the Amazon Basin, exhibiting a different pattern of diversity focused more on riverine habitats.
The dispersal of cichlids across such diverse geographical areas is believed to have been influenced by continental drift and paleoclimatic changes, which provided bridges or barriers to movement at different times. This wide distribution makes them an excellent subject for biogeographical studies, providing insights into how environmental changes can drive evolutionary processes.
The study of cichlid taxonomy and evolution not only enriches our understanding of biodiversity but also offers valuable lessons on the mechanisms of evolution and adaptation. For aquarium enthusiasts and breeders, a deeper understanding of these processes is crucial for the successful care and breeding of cichlid species, ensuring the maintenance of genetic health and species integrity in captive populations.
*Artigas Azas, Juan Miguel. (Jul 08, 2024). "The Cichliformes". Cichlid Room Companion. Retrieved on Oct 06, 2024, from: https://cichlidae.com/section.php?id=345.
