Effects of archipelago geo-environmental dynamics on phylogenetic tree shape

In archipelagic environments, the successive emergence and submergence of islands induces variations of area, spatial structure and isolation. Here, we aim to understand how such geo-environmental dynamics, by inducing variations in migration, speciation and extinction over time, may impact phylogenetic patterns. We use a neutral, stochastic, individual-based model which simulates a community evolving in an archipelago where four islands emerge and submerge consecutively. We record each birth, death and migration event, allowing us to build the complete phylogeny at any time, from which we extract the phylogeny of extant species. We show that the rate of lineage accumulation and tree imbalance vary according to a hump-shaped curve, and we show that this is mainly due to variations in area and inter-island connectivity. We highlight that past abrupt changes, such as island emergence, may leave persistent imprints in the rate of lineage accumulation. We show that the spatial configuration of an archipelago modulates these effects: (i) enhancing inter-island connectivity results in more frequent inter-island speciation events, thus a faster accumulation of lineages, and in larger evolutionary radiations, thus highly imbalanced phylogenies ; (ii) increase in mainland connectivity brings ancestral lineages to the islands which slows down the rate of lineage accumulation and increases the species turnover allowing for more balanced phylogenies. Taking into account variations in the geo-environmental configuration of an archipelago is important to understand the shape of contemporary phylogenies. However, these effects have to be interpreted in the context of the spatial configuration of an archipelago.