Evolution of adaptive divergence: from repeated polymorphisms to ecological speciation
This study provides first genome-wide results on phylogeny and population genetic structure of Labeobarbus from East Africa (genome-wide data were previously obtained only for South AfricanLabeobarbus by Stobie et al., 2018). Our phylogenetic results are in agreement with previously obtained mtDNA phylogenies (Beshera, Harris, 2014; Levin et al., 2020) and confirmed that thick-lipped ecomorphs have evolved independently several times. The repeated origins of thick-lipped ecomorphs in the river systems of the Ethiopian Highlands suggests that this polymorphism in trophic morphology might be an old developmental and genetic system that might be facilitated by genetic assimilation (Schneider et al., 2014; Gunter et al. 2017). Although results on genetic population structure confirmed absence of genetic divergence between sympatric ecomorphs with and without hypertrophied lips in the most of populations, one sympatric pair was genetically divergent (in the Didessa River). To sort out the cases of the sympatric pairs in terms of polymorphism or divergent evolution, we analyzed data on trophic morphology, trophic niche segregation along with genetic data (Table 2).
Table 2. Heat-map of ranking the sympatric pairs of generalized and thick-lipped ecomorphs in different rivers based on divergence in trophic morphology, SI composition, and genetics: 0 – non-significant difference; 1 – significant difference (0.5 is given for SI composition if only one of two analyzed elements is different). The populations were placed from left to right according to their total ranking from lower value to higher. Cells in rows of variables are colored according to points: 0 – no color, 0.5 – blue, 1 – intense blue; ‘Total points’ row are marked by various intense of yellow color corresponded to number of cumulative points from 1 to 3. P – polymorphism (n – ecologically non-functional; sf – ecologically semi-functional; f - ecologically functional), S – speciation completed.