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Juan Miguel Artigas Azas,
Cichlid Room Companion
Editorial

Two species of Labeotropheus

By , 2024. image
Last updated on 20-Feb-2024


Classification: Taxonomy and phylogeny, Lake Malawi.

" After the Lake Malawi cichlid genus Labeotropheus was split into eleven species in recent years, Ad Konings pushes back and explains why only two species should be recognized "

Male at Chimwalani Reef A male of Labeotropheus fuelleborni at Chimwalani Reef, Lake Malawi [Malawi]. Photo by Ad Konings. (2006-10-18). determiner Ad Konings

For many years since 1956, the genus Labeotropheus of rock-dwelling cichlid species from Lake Malawi was understood to be comprised of two usually sympatric species, one elongated (L. trewavasae), and one with a higher body (L. fuelleborni). Specialists in Lake Malawi cichlids came to terms with the fact that the populations of each one of those species show a large degree of variability in male breeding coloration and have small morphological differences. This derives from the fact that they inhabit isolated rocky reefs in the lake that they cannot abandon. So each population is reproductively isolated with some genes drifting or adjusting to particular conditions. The majority of those reefs host both L. fuelleborni and L. trewavasae, while some just L. fuelleborni.

Starting in 2016, some of the populations of the two hitherto recognized species were gradually proposed as new species by Michael J. Pauers, with nine of them recently proposed at the end of 2023 by Pauers and Titus B. Phiri. With this, the number of Labeotropheus species increased to eleven. The authors claimed as one of their arguments that geographically different forms of other mbuna had been described as distinct species before.

In the more recent number of Cichlid News Magazine, Ad Konings, quite likely the person who has spent more hours underwater observing Lake Malawi cichlids, and one of the top specialists in the world, published an article in which he reviews the situation in detail. Konings points out that variations of existing mbuna species have rarely been described as distinct species, pointing to many Lake Malawi mbuna species which great variations that have not been challenged.

Variations in isolated populations of Labeotropheus can be produced by many factors, which include light penetration — with its resulting amount or variability of algae, substrate, and competition. Discerning if a population is a geographical variant or a different species is sometimes difficult. Pauers & Phiri compare populations found far away from each other to generate a diagnosis, something that can be misleading.

In most cases, the new Labeotropheus species are mainly based on male breeding coloration since morphological differences are so small. Konings makes a strong case for why only two species of Labeotropheus exist, and proposes the synonymy of all nine new species to the long-accepted L. fuelleborni and L. trewavasae, treating each individual case.

One of Koning’s arguments is that Pauers & Phiri claim to adhere to the Evolutionary Species Concept in their descriptions. In this scenario, “a species is a single lineage of ancestor-descendant populations of organisms which maintains its identity from other such lineages and which has its own evolutionary tendencies and historical fate”. In Lake Malawi, the water level has experienced huge fluctuations over the years, with at least 15 drops of more than 400 m. With each major drop in lake level, all the geographical variants that had evolved since the last rise in lake level came together and recognized each other as conspecific. If they wouldn’t and these variants were different species we would have more than two species sharing a rocky reef nowadays.

Konings argues that there appear to be two strategies for two different species of Labeotropheus to coexist at the same locality without hybridizing: "either one species is visually much slenderer than the other or one species has a coloration different from the standard royal blue. Although both strategies may exist at a single locality, it is not necessary for a differently colored Labeotropheus to be slender or deep-bodied to distinguish itself from the sympatric other Labeotropheus species. Since variants interbreed during a drop in lake level, when various populations get mixed, the “prototype” in the greatly diminished paleo-lake, over the years, has acquired the genes for the various color schemes we see today among Labeotropheus. Of course, introgression, where a slender type crosses with a deep-bodied type, occurs when a suitable habitat becomes severely limited or is about to disappear. This is the reason that we see similar color schemes, either orange-ocher color on the body or orange/red in the dorsal fin, in both L. trewavasae as well as in L. fuelleborni".

For those of you interested in a full understanding of the situation and a detailed explanation of each species' synonymy, I highly recommend reading Konings' paper, which is offered by Aquatic Promotion through the Cichlid Room Companion: “Labeotropheus —A taxonomic nightmare”. You can also read the genus and species profiles by Ad Konings in the Cichlid Room Companion

Citation:

Artigas Azas, Juan Miguel. (Feb 20, 2024). "Two species of Labeotropheus". Cichlid Room Companion. Retrieved on Apr 17, 2024, from: https://cichlidae.com/section.php?id=340.