Fig. 2

Morphological variation and morphospace partitioning between Lake Mweru radiations. a Morphological complementarity of the four intralacustrine cichlid radiations, the lacustrine members of the Orthochromis assemblage, the non-endemic Serranochromis altus and Se. angusticeps (Se. alt/ang), the nonendemic Se. robustus and Se. thumbergi (Se. rob/thumb) and Orthochromis stormsi (O. stormsi) in Lake Mweru. The first two principal components of all haplochromine cichlid species we found in Lake Mweru show nearly perfect complementarity in morphospace occupation among the radiations. Of the Orthochromis species, only the taxa occurring in Lake Mweru, O. polyacanthus and O. sp. “red-cheek” are shown, but not the seven riverine species of the Kalungwishi and Luongo Rivers. Sister taxa of each radiation are indicated with filled symbols. Their centroids or that of the radiations themselves (in the absence of sister taxa) are connected by thin lines to each phenotype of the corresponding radiation to visualize approximate trajectories of phenotypic divergence and diversification. The underlying data and the R script for all panels are provided at Zenodo with doi: 10.5281/zenodo.3435419. b Mweru taxa predicted onto morphospace of serranochromines of the radiation of ancient Lake Makgadikgadi. Makgadikgadi Sargochromis include Chetia and Pharyngochromis species which are nested in the genus Sargochromis⁴². In the presence of a diverse Pseudocrenilabrus radiation in Lake Mweru, the serranochromine radiations altogether are confined to a subset of the morphospace this lineage occupies elsewhere (such as in the Okavango region, the modern centre of Makgadikgadi-derived diversity). This is mostly due to much reduced morphological diversity in Sargochromis of Lake Mweru. Compared to Pseudocrenilabrus of Lake Bangweulu, the Pseudocrenilabrus radiation in Lake Mweru expanded into serranochromine morphospace. c In the presence of the Pseudocrenilabrus radiation in the lake, Orthochromis are confined to the epilithic algae and Aufwuchs scraper niche in the rocky wave washed littoral of the lake, an extreme feeding niche that the Pseudocrenilabrus radiation has not invaded. In the rivers, where Pseudocrenilabrus have not radiated and only the ancestral type P. philander is present, two species with partial Orthochromis and partial Pseudocrenilabrus ancestry evolved in lentic, i.e. lake-like, parts of the river. These “New Kalungwishi” species overlap in morphospace with littoral Pseudocrenilabrus from Lake Mweru.