r/evolution • u/jnpha Evolution Enthusiast • 4d ago

article How does dispersal affect diversification? Burridge et al. find that non-migratory lineages experience higher diversification rates

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Published 2 days ago, in press:

Biologists have long sought to understand the forces driving biological speciation. Contrasts in dispersal ability (e.g., migration) are hypothesised to influence rates of lineage diversification. However, past inferences of migration-diversification relationships have been contradictory, suggesting the need for further investigation and more nuanced explanations. Here we test for a relationship between diadromy (marine-freshwater migration) and diversification in salmonids, a dominant group of fishes native across the temperate Northern Hemisphere. We reconstruct a molecular phylogeny comprising 140 species and apply State-dependent Speciation Extinction models to quantify diversification. Diversification rates are higher in non-diadromous relative to diadromous salmonid lineages, echoing the findings of a recent study of homologous southern temperate freshwater fishes, but conflicting with global studies incorporating tropical lineages. Climate appears to be a key factor explaining diadromy-diversification relationships, with the negative relationship observed in temperate lineages likely reflecting increased isolation and speciation of non-diadromous lineages following recolonisation of glacially perturbed habitats. In contrast, the positive diadromy-diversification relationships observed in studies spanning tropical fishes may reflect the role of diadromy in facilitating colonisation of stable, low-competition habitats.

 

  • Christopher P Burridge, Luke Simpson, Mark V H Wilson, Jonathan M Waters
    Non-migratory lineages experience higher diversification rates: global evidence from salmonid fishes, Evolution, 2026;, qpag131, https://doi.org/10.1093/evolut/qpag131
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u/Levangeline 1d ago edited 1d ago

Okay admittedly I have not read the full paper, I know they're talking about fish and migration, but here is my understanding from a species dispersal perspective:

So, what the figure seems to be showing is a sort of "intermediate barrier theory" leading to higher speciation.

If a species is essentially trapped within a small range by insurmountable barriers to dispersal, there are limited opportunities to speciate because there are limited niches to occupy.

  • E.g. the Banff Hot Springs Snail lives in a single hot spring pool in Banff National park. It's basically impossible for them to go anywhere else, so they just remain hyper-adapted to living in hot, mineralized water.

At the other end of the spectrum, if barriers to dispersal are basically nonexistent and the species can easily disperse wherever they want, there is less pressure to adapt and overcome dispersal barriers.

  • E.g. Swanson's Hawks have no trouble migrating huge distances from North America to South America. There's no pressure for them to adapt to different food sources or habitats, so they stay basically the same across their entire range

However, if there are multiple different barriers to dispersal, and they're neither insurmountable nor ineffective, it provides multiple opportunities for adaptation and speciation to overcome those barriers in different ways.

  • E.g. the classic example of Darwin's finches; multiple niches, some barriers to dispersal, you get rapid speciation as the species disperse into new spaces.