Reproductive isolation among deep‐water cichlid fishes of Lake Malawi differing in monochromatic male breeding dress

Abstract

Male nuptial colour hues are important for the maintenance of reproductive isolation among cichlid fish species, and environmental changes that lead to narrower light spectra can lead to hybridization. However, cichlid species can naturally co-occur in narrow light spectrum habitats, such as turbid shallow lakes and the deep benthic zones of African rift lakes. Closely related species from narrow light spectrum habitats tend to differ little in the palette of male nuptial colours, thus for these taxa differences in colour patterns may be more important than differences in colour hue for species recognition. To investigate this hypothesis we examined morphometric and genetic differentiation among males of four sympatric putative species within the deep-water genus Diplotaxodon. These taxa live in a narrow-light spectrum environment where only blue light is present, and males differ primarily in 'monochromatic' black, white and silver patterning of the body and fins. Significant genetic differentiation was present among taxa in both microsatellite DNA and mitochondrial DNA, including one pair with no significant morphometric differentiation. Thus, these taxa represent reproductively isolated biological species, a result consistent with male nuptial patterning being important for species recognition and assortative mating. As such, we suggest that narrow-light spectra need not always represent barriers to effective visually mediated mate recognition.

Morphometric variation of the Herichthys bartoni (Bean, 1892) species group (Teleostei: Cichlidae): How many species comprise H. labridens (Pellegrin, 1903)?

“…Similar results have been found in other cichlids due to the high levels of overlap between taxonomic characters (Genner et al, 2007;Schmitter-Soto, 2007;McMahan et al, 2011;Soria-Barreto et al, 2011). In recent years, geometric morphometrics have arisen as a useful tool for discriminating species.…”

“…For example, Maderbacher et al (2008), using 17 landmarks and 9 semi landmarks for the body, were able to discriminate among three morphs of Tropheus moorii from Lake Tanganyika, whereas traditional morphometrics failed to find significant differences because meristic counts and traditional measurements are very plastic and often overlap between species. Similar results were found by Genner et al (2007), who used geometric morphometrics of 25 landmarks from the body coupled with molecular markers and were able to discriminate between four putative sympatric species of the genus Diplotaxodon, which had previously been identified only by their nuptial coloration. However, geometric morphometrics could also have restrictions; for example, in a recent study of a flock species of the genus Crenicichla from Uruguay, Burress et al (2013) failed to find significant differences among shapes from the 25 landmarks of the body evaluated, although they found significant differences in the geometric morphometrics of the lower pharyngeal plate.…”

“…Each specimen was photographed in the left view, and 25 landmarks were digitized for the body, as was a subsample of 15 landmarks of the head, in accordance with Trapani (2003) and Genner et al (2007) in tpsdig (Rohlf, 2010) (Fig. 2).…”

Colour variation in cichlid fish: Developmental mechanisms, selective pressures and evolutionary consequences

“…Likewise, species-specific monochromatic patterning in the deeper waters of Lake Malawi, where the narrow light spectrum precludes hue discrimination, is consistent with predictions of sensory drive [103]. However, a systematic analysis of associations between light environments and male nuptial colouration, in haplochromines and other lineages, is lacking (but see, for Lake Malawi: [143–145]).…”

The genetic and evolutionary basis of colour variation in vertebrates

“…Interestingly, in cichlids, different light regimes or even bright colours are no prerequisite for sexual selection. For deep-water cichlids of the genus Diplotaxodon, living in Lake Malawi, it was found that males differ in colour patterns, which are detectable despite the narrow wave length spectrum in their habitat [64]. However, it is unknown whether these species evolved in sympatry or in allopatry.…”