Abactochromis, new genus

[Michael Oliver]

Oliver, M.K., & M.E. Arnegard 2010. A new genus for Melanochromis labrosus, a problematic Lake Malawi cichlid with hypertrophied lips (Teleostei: Cichlidae). Ichthyol. Explor. Freshwaters, Vol. 21, No. 3, pp. 209-232. This is open-access and can be freely distributed - http://malawicichlids.com/oliver_arnegard_2010.pdf and should also be available in the CRC library soon.

Abstract: Melanochromis labrosus is the only one of the 800 or so endemic cichlid species in Lake Malawi whose placement with mbuna or non-mbuna has been disputed on morphological grounds. Here, we redescribe M. labrosus using all obtainable specimens collected since its original description. In addition, we extensively survey vertebral counts in the mbuna. To determine if M. labrosus belongs with the mbuna, we review the morphological traits often considered to define the mbuna as a natural group, concluding that none is a uniquely shared specialization. Two features of body coloration (a relatively small number of ocellate spots in the anal fin and a possible polychromatism in one population) suggest that M. labrosus is best considered a species of mbuna. Although its placement within the mbuna group remains somewhat equivocal, we unambiguously demonstrate that M. labrosus is not a Melanochromis, since it lacks the synapomorphic striped color pattern typical of that genus. Melanochromis labrosus also does not fit within any other described genus. Therefore, we designate it the type species of Abactochromis, new genus. Abactochromis is unique in the mbuna in having greatly enlarged, lobate lips and several other autapomorphies. Contrary to published opinion, the hypertrophied lips of A. labrosus express high densities of taste buds. We review the little that is known about the biology of A. labrosus and emphasize its noteworthy distribution within Lake Malawi, on rocky shores lakewide excepting the southern arms. We underscore the importance of including this problematic, and therefore potentially informative, species in future evolutionary genetic and genomic studies of the Lake Malawi cichlid species flock. Finally, we provide a key to the now thirteen genera of mbuna inhabiting Lake Malawi.

[Tachymarptis]

Congratulations for this work! At last, the labrosus got a name! By the way, not only I feel that you are right in including Abactochromis in the mbunas, but I think also that it is close to some Labidochromis such as those of the L.-caeruleus group, as it shows similar behavior and body shape (apart from the enlarged head and lips). Unless I missed something, you don't mention the strongly prognathous jaws, isn't it?

Patrick.

[Michael Oliver]

Hi Patrick,

Thank you for the kind remarks about our paper. As for the jaws, actually, most specimens we examined are not strongly prognathous - the lower jaw projects only a little, or not at all in some specimens, forward beyond the upper jaw. (Genyochromis mento -- now that's prognathous.)

We discuss the similarities to Labidochromis in detail (see the sections on Autapomorphies, and Comparisons with other mbuna genera). It's unclear if the similarities are convergent or homologous; as we discuss, A. labrosus is outside the range of variation of Labidochromis in several respects. I don't see its behavior as particularly Labido-like; the lack of a fixed territory, the wandering habits, are quite odd. Anyway, an intriguing fish!

Regards,
Michael

[Tachymarptis]

Hi, Michael,

As for the jaws, actually, most specimens we examined are not strongly prognathous - the lower jaw projects only a little, or not at all in some specimens, forward beyond the upper jaw. (Genyochromis mento -- now that's prognathous.)

I observed specimens where this feature is really strong. Maybe it depends on geographical location, and also on age and size.

We discuss the similarities to Labidochromis in detail (see the sections on Autapomorphies, and Comparisons with other mbuna genera). It's unclear if the similarities are convergent or homologous; as we discuss, A. labrosus is outside the range of variation of Labidochromis in several respects. I don't see its behavior as particularly Labido-like; the lack of a fixed territory, the wandering habits, are quite odd. Anyway, an intriguing fish!

Yes, I had read this section. According to my own aquarium observations (of course, these are "only" aquarium observations), A. labrosus and L. caeruleus behave similarly, they are not territorial and their aggressive behavior is similar. This is not the case in all Labidochromis, but I am convinced that Labidochromis sensu Lewis is a polyphyletic group. The labido-like jaws are likely to have evolved more than one time in mbunas.

But nowadays, this will require a lot of work to be established... Who wants to be applicant?

[Michael Oliver]

I observed specimens where this feature [prognathous lower jaw] is really strong. Maybe it depends on geographical location, and also on age and size.

Maybe, but we had specimens from 5 localities well distributed along the lake, and a wide range of fish lengths including all the wild-collected museum specimens we could find.

According to my own aquarium observations (of course, these are "only" aquarium observations), A. labrosus and L. caeruleus behave similarly, they are not territorial and their aggressive behavior is similar. This is not the case in all Labidochromis, but I am convinced that Labidochromis sensu Lewis is a polyphyletic group. The labido-like jaws are likely to have evolved more than one time in mbunas.

I'm not so sure it's polyphyletic - Labidochromis is one of the more distinctive genera of mbuna - but I certainly can agree there is a rather wide range of variation in it. Until there is a defensible cladogram of mbuna and other Malawi cichlids (one with character evidence, not just bootstrap statistics and such), questions like the monophyly or polyphyly of Labidochromis cannot be answered except by "feeling" (not science). As you saw, even though most of us "feel" confident that the mbuna are a real group, not a single adequate character to define them has been found yet.

[Tachymarptis]

Maybe, but we had specimens from 5 localities well distributed along the lake, and a wide range of fish lengths including all the wild-collected museum specimens we could find.

I'm sure you did, but I wonder if we could find a correlation with age or location or not.

I'm not so sure it's polyphyletic - Labidochromis is one of the more distinctive genera of mbuna - but I certainly can agree there is a rather wide range of variation in it. Until there is a defensible cladogram of mbuna and other Malawi cichlids (one with character evidence, not just bootstrap statistics and such), questions like the monophyly or polyphyly of Labidochromis cannot be answered except by "feeling" (not science). As you saw, even though most of us "feel" confident that the mbuna are a real group, not a single adequate character to define them has been found yet.

Perhaps because as long as we don't determine their sister group, you can define them only by a character combination, not a single apomorphy. By the way, we are already implying that the molecular phylogenies which includes the Aulonocara-Lethrinops group inside mbunas are probably wrong.

Concerning the phylogeny inside the mbunas, I also agree with you that we need more than mere bootstrap statistics. Nevertheless, I would be very surprised if someone ever succeeds in classifying them only by cladistic tools, as they very likely follow a reticulate pattern. We may rather end with an unsatisfactory status quo similar to that of Victoria haplochromines. IMHO, for obtaining some results, we should admit that especially in such cases, classification is not an exact science. So, as was made before the arising of the cladistic mood, we will have to admit "nebulas" inside our classifications, not only pure clades, as practically, these are only special cases, not the rule. Otherwise, most of them will remain "Pseudotropheus" or something else with brackets. By the way, we reach now such a theoretical cul-de-sac that even new species are decribed in genus between brackets (Haplochromis snoeksi)!

Concerning labidos, they are well-defined only by trophic-related features (denture and jaws apparatus), which are above all submitted to strong selective pressure (more than behavioral subtelties, for example), so are more likely to lead up to convergences. But of course, as they also probably follow a reticulate model, this may also open on endless contests.