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, 281 (1784), 20140473

Settling Down of Seasonal Migrants Promotes Bird Diversification

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Settling Down of Seasonal Migrants Promotes Bird Diversification

Jonathan Rolland et al. Proc Biol Sci.

Abstract

How seasonal migration originated and impacted diversification in birds remains largely unknown. Although migratory behaviour is likely to affect bird diversification, previous studies have not detected any effect. Here, we infer ancestral migratory behaviour and the effect of seasonal migration on speciation and extinction dynamics using a complete bird tree of life. Our analyses infer that sedentary behaviour is ancestral, and that migratory behaviour evolved independently multiple times during the evolutionary history of birds. Speciation of a sedentary species into two sedentary daughter species is more frequent than speciation of a migratory species into two migratory daughter species. However, migratory species often diversify by generating a sedentary daughter species in addition to the ancestral migratory one. This leads to an overall higher migratory speciation rate. Migratory species also experience lower extinction rates. Hence, although migratory species represent a minority (18.5%) of all extant birds, they have a higher net diversification rate than sedentary species. These results suggest that the evolution of seasonal migration in birds has facilitated diversification through the divergence of migratory subpopulations that become sedentary, and illustrate asymmetrical diversification as a mechanism by which diversification rates are decoupled from species richness.

Keywords: ancestral character reconstruction; behavioural evolution; extinction rate; speciation rate.

Figures

Figure 1.
Figure 1.
Migration promotes bird diversification. In comparison with sedentary birds (green), migratory birds (red) have low symmetrical and high asymmetrical speciation rates (a), low extinction rates (b) and high net diversification rates (c). Anagenetic transition rates are very low (d). Posterior distributions not different between migratory and sedentary species are shown in grey. Posterior distributions estimates are from MCMC analyses on all birds, using the best-fitting model.
Figure 2.
Figure 2.
Migration promotes diversification in all species-rich orders. Posterior distributions of migratory (red) and sedentary (green) speciation—symmetrical and asymmetrical—, extinction, net diversification and anagenetic transition rates, computed using the best-fitting model. In the majority of groups, in comparison with sedentary birds, migratory birds have higher speciation rates and lower—or equal—extinction rates, resulting in higher net diversification rates. Anagenetic transition rates are very low. Posterior distributions not different between migratory and sedentary species are shown in grey. Posterior distributions estimates are from MCMC analyses on all birds, using the best-fitting model.
Figure 3.
Figure 3.
Ancestral bird lineages are reconstructed as sedentary (green), with repeated apparitions of the migratory behaviour (red). The ancestral state reconstruction is based on the best-fitting BiSSE model and is plotted on the dated consensus tree. The colour of a given branch is scaled from completely green (inferred probability of being migratory equals 0) to completely red (inferred probability of being migratory equals 1), based on the mean probability of the two adjacent nodes.

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