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.