Date/Time
Date(s) - 02/04/2026
1:30 pm - 2:30 pm

Speaker: Amaury Lambert (Collège de France & École Normale Supérieure)

Location: Hamilton Hall, Room 217

Title: Geometry and stability of species complexes

Abstract: Species complexes are groups of closely related populations connected by migration. We speak of “gene flow” or “gene introgression” when migrants can interbreed with local individuals and leave descendants which carry part of their genes. We study by a modeling approach  the structure and stability of species complexes in a class of metapopulation models where $N$ demes see their gene pools homogenize as an effect of gene flow and diverge through the local accumulation of  neutral or selective mutations. Importantly, we model the feedback of differentiation on gene flow by assuming that the success of introgressions of foreign alleles increases with genomic similarity, through a specific function $h$. As the target of genomic differentiation gets large, pairwise genomic similarities approximately follow an autonomous system of $N(N-1)/2$ differential equations. We investigate the emergence of non-transitive species structures such as ring species and study the effect of temporary isolation on the species complex, depending on some mathematical characteristics of the feedback function $h$. We also show that in large, well-connected metapopulations, species form increasingly coherent, transitive and uniform entities, so that the initiation of speciation events requires the existence of idiosyncratic geographic or selective restrictions on gene flow.