Rhamphochromina Oliver 2024, new subtribe
Year: 2024
Type: article
Abstract: Rhamphochromina Oliver, 2024 new subtribe Description Sometimes called the Lake Malawi “ pelagic subradiation ”, this clade is distinguished most definitively by a large (> 3.5 million base pairs) inversion at astCal 1.2 coordinates 4,788,189 to 8,315,641 bp on chromosome 20 in at least Diplotaxodon and Rhamphochromis spp.; the single Pallidochromis species has not yet been studied (Blumer et al. 2024: p. 24 of supplementary text). This inversion is absent in the other Lake Malawi subtribes, with one exception (see Notes, below). The subtribe is also distinguishable from other Lake Malawi " haplochromines " by the following, in combination: pelagic, mid-water to deep-living species with predatory facies preying on fishes or zooplankton (versus demersal or epibenthic species found over sandy, muddy or rocky substrates or habitats intermediate between these and with widely varying diet, often fishes or zooplankton, but also specialists on benthic invertebrates, epilithic or epiphytic algae or even fish scales and fins); all jaw teeth simple, unicuspid, those of the outer row widely spaced in most species (versus jaw teeth unicuspid, bicuspid or tricuspid, the outer jaw teeth usually more closely spaced); absence (loss) of the plesiomorphic dark vertical bars and usually also absence of a mid-lateral horizontal stripe, resulting in the flanks of individuals being plain silver, grey, blackish or countershaded with no distinct melanic markings, except for a thin mid-lateral stripe in Rhamphochromis esox and R. sp. “ stripe ” (versus distinct melanic patterns present, visible at least in the " fright pattern " and in females and non-breeding males; vertical bars usually present, often in addition to darker markings such as spots, longitudinal stripe (s) or an oblique stripe). Vertebral and pterygiophore counts and most-frequent insertion patterns of the latter, are summarised in Tables 1, 2, but do not separate members of Rhamphochromina from those of Cyrtocarina. However, non-overlapping counts of vertebrae posterior to those bracketing the last occupied dorsal insertion space separate Rhamphochromina from Pseudotropheina (10–13 and 6–9, respectively). Total vertebrae are 33–40 in Rhamphochromina versus 28–33 in Pseudotropheina, 29–35 in Cyrtocarina. Type genus: Rhamphochromis Regan, 1922 Included genera: Diplotaxodon Trewavas, 1935; Pallidochromis Turner, 1994; Rhamphochromis Regan, 1922. Distribution Lakes Malawi, Malombe, Chilingali and Kingiri and the upper Shire River. Notes Turner et al. (2004) had already suggested, based on a mitochondrial phylogeny, that Rhamphochromis is monophyletic and that its sister group consists of Diplotaxodon plus Pallidochromis. The discovery by Blumer et al. (2024) of the shared chromosome 2 inversion largely confirms that suggestion, although Pallidochromis tokolosh has not yet been examined. Subsequent to the divergence of Rhamphochromis and Diplotaxodon from their common ancestor, this inversion was apparently passed to the ancestor of the “ benthic ” subradiation (a part of Cyrtocarina) through hybridisation with a Diplotaxodon (Blumer et al. 2024). Thus the chromosome 20 inversion does not define a strictly monophyletic group. The other characteristics listed in the diagnosis, however, will distinguish Rhamphochromina from “ benthic ” species.
Author: Oliver, Michael K.
Institution: Yale Peabody Museum
Language: English
Subfield: Aquatic Science
Domain: Life Sciences
Open Access status: green
OpenAlex ID: W6949690119
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