Abstract:
Cichlid fishes are well known for the
ir
spectacular adaptive radiations in the Great East
African lakes. Yet, a number of reasons including their size, young age and recent
hybridizati
on render it to difficult
to
infer the evolutionary history of these huge species
assemblages. The Soda tilapia form a small radiation (Genus
Alcolapia
) that is endemic to an
extreme environment
-
Lakes
Magadi and
Natron in Kenya and Tanzania. It provides
an
excellent system in which to investigate ecological aspects during the early stages of
speciation. We used an integrated approach including population genomics based on RAD
-
seq data, geometric morphometrics, and stable isotope analyses to investigate th
e eco
-
morphological diversification of Lake Magadi tilapia. Based on coalescent simulations and
joint site frequency spectrum analyses we reconstructed their demographic history. The
population in the isolated satellite lake Little Magadi has a characteris
tically upturned mouth,
an adaptation associated with feeding on prey from the water surface. Ecomorphological
differences between geographically separated populations within Lake Magadi are more
subtle, but coincide with ecological differences. All popula
tions diverged simultaneously only
about 1
100 (95% CI: 846
-
1632) generations ago. Differences in the amount of gene flow
between populations and the effective population sizes have likely resulted in variable
patterns of genome
-
wide differentiation that w
as inferred from RAD
-
seq data.