Elucidating diversification dynamics in freshwater biota from the East African Rift System – divEARS

A central aim of modern evolutionary biology is to understand how new species arise and how they cope with environmental changes. At the microevolutionary scale, research has focused on the mechanisms driving trait evolution and progressive reproductive isolation up to speciation in living taxa. At the macroevolutionary scale, paleontologists have accrued data on how species diversity waxed and waned over time, while phylogenetic approaches have been developed to infer rates of trait evolution, speciation and extinction. To what extent and how the mechanisms that generate intraspecific variation and population differentiation contribute to macroevolution remain central questions, however. In the project divEARS, we will address these questions via integrative studies of three mollusk families from the East African Rift Systems (EARS) at both microevolutionary and macroevolutionary scales. We will generate data on ecology, life-history traits, reproductive strategies, phenotypes and single-copy orthologous genes to document intraspecific variation, dynamics of population differentiation up to speciation, as well as phylogenetic rates of diversification and phenotypic evolution, leveraging new advances in phylogenetics.

In WP1 we will study how differences in life-history strategies and ecology influence intraspecific variation, population differentiation, and ultimately dynamics of speciation in six clades of endemic mollusks from Lake Tanganyika. We will use phylogenetics to identify ~15-20 species pairs for subsequent comparative population genomic analyses. This approach will enable us to assess variation in genetic diversity and phenotypic disparity within populations, among populations and among species in the context of differences in life-history and ecology, providing insight into how intrinsic drivers of population differentiation contribute to the dynamics of speciation.

In WP2 we will take a phylogenetic approach on all continent-wide representatives of the three mollusk families studied in WP1 to examine how extrinsic (habitat heterogeneity, environmental stability) and intrinsic differences (life-history strategies and ecology) contribute to variation in macroevolutionary patterns as well as rates of diversification and trait change throughout the EARS. We will estimate lineage-specific diversification rates and apply time-, environment-, and trait-dependent diversification models to investigate dynamics of diversification and trait change, first in extant taxa alone, and then incorporating extinct, fossil species to assess how rates and dynamics change.

In WP3 we will synthesize data from WPs 1&2 to test whether features that enhance intraspecific genetic and phenotypic variation contribute to higher rates of speciation and phenotypic evolution at the macroevolutionary scale. We will take two complementary approaches: i) we will examine whether certain microevolutionary features or drivers of intraspecific differentiation systematically correlate with rates of speciation, extinction, species turnover and phenotypic change at the macroevolutionary scale; and ii) we will test quantitative theoretical predictions for speciation and extinction rates using empirical data from WPs 1&2.

By bridging micro- and macroevolution, divEARS will provide fundamental insights into how evolutionary processes shape biodiversity. This knowledge is crucial for predicting biological responses to global environmental change, as accelerating anthropogenic pressures transform ecosystems worldwide.