Range size heritability and diversification patterns in the liverwort genus Radula

Area of Science:

• Ecology and Evolutionary Biology
• Phylogenetics and Biogeography

Background:

• Understanding factors driving variation in species' geographical range sizes and their impact on diversification rates is a key ecological and evolutionary question.
• The liverwort genus Radula, originating in the Cretaceous period, provides a model system to investigate these relationships due to its diverse lineages and distributions.

Purpose of the Study:

• To investigate the mechanisms explaining differences in geographical range size and diversification rates among Radula lineages.
• To assess the roles of phylogenetic constraints, plate tectonics, dispersal, and niche conservatism in shaping current distribution patterns.

Main Methods:

• Phylogenetic comparative analyses were employed to study evolutionary relationships and traits.
• Ancestral area estimations were used to reconstruct the historical biogeography of Radula lineages.
• Analysis of dispersal life-history traits and macroecological niche traits was conducted.

Main Results:

• Range size was phylogenetically constrained, with two sub-genera showing strong Australasian and Neotropical endemicity, potentially linked to continental drift.
• Niche conservatism, rather than loss of dispersal ability, was identified as a primary factor limiting the geographic ranges of certain lineages (Amentuloradula, Volutoradula, Metaradula).
• Contrary to expectations, restricted lineages (Amentuloradula, Volutoradula) did not exhibit significantly lower diversification rates than widespread ones.

Conclusions:

• Both ancient vicariance events driven by plate tectonics and niche conservatism play significant roles in the current distribution of Radula species.
• Stochastic long-distance dispersal may homogenize genetic variation across wide ranges, potentially reducing diversification rates in widespread, highly mobile lineages.
• The study challenges the assumption that larger geographical ranges consistently promote higher speciation rates.