RESUMO
Geographic barriers can come and go depending on natural conditions. These fluctuations cause population cycles of expansion and contraction, introducing intermittent migrations that may not hinder speciation but rather promote diversification. Here, we study a neutral 2-island speciation model with intermittent migration driven by sea-level fluctuations. Seabed depth modulates isolation and connection periods between the islands, with migration occurring during connection periods with a certain probability. Mating is restricted to genetically compatible individuals on the same island and offspring inherit genomes from both parents through recombination. We observe speciation pulses that would not occur under strict isolation or continuous migration, with infrequent, temporary increases in species richness happening at different times depending on the combination of geographic settings and migration probability. The resulting dynamic patterns of richness exhibit contrasting behavior between connected and isolated scenarios, often including species that do not persist. Prolonged isolation can reduce richness to 1 species per island, resembling patterns commonly associated with archipelagos under sea-level fluctuations. Together with other studies, our results in out-of-equilibrium populations support the relevance of investigating the impact of variable migration on diversification, particularly in regions of high diversity.
Assuntos
Especiação Genética , Humanos , Probabilidade , FilogeniaRESUMO
Geographic isolation is a central mechanism of speciation, but perfect isolation of populations is rare. Although speciation can be hindered if gene flow is large, intermediate levels of migration can enhance speciation by introducing genetic novelty in the semi-isolated populations or founding small communities of migrants. Here, we consider a two-island neutral model of speciation with continuous migration and study diversity patterns as a function of the migration probability, population size, and number of genes involved in reproductive isolation (dubbed as genome size). For small genomes, low levels of migration induce speciation on the islands that otherwise would not occur. Diversity, however, drops sharply to a single species inhabiting both islands as the migration probability increases. For large genomes, sympatric speciation occurs even when the islands are strictly isolated. Then species richness per island increases with the probability of migration, but the total number of species decreases as they become cosmopolitan. For each genome size, there is an optimal migration intensity for each population size that maximizes the number of species. We discuss the observed modes of speciation induced by migration and how they increase species richness in the insular system while promoting asymmetry between the islands and hindering endemism.