Ecological and Mutation-Order Speciation in Senecio.

Area of Science:

• Evolutionary Biology
• Speciation Research
• Ecology

Background:

• Reproductive barriers are key to speciation, but their formation mechanisms are debated.
• Ecological divergence and mutation-order processes are often considered separate speciation drivers.
• The Senecio lautus species complex provides a model for studying repeated ecotype evolution along coastlines.

Purpose of the Study:

• To investigate how divergent and uniform natural selection contribute to reproductive isolation in the Senecio lautus species complex.
• To explore the role of environmental heterogeneity and polygenic adaptation in driving speciation.
• To extend theoretical models of hybrid incompatibilities to incorporate environmental gradients.

Main Methods:

• Field studies and crossing experiments were conducted on Dune and Headland ecotypes of Senecio lautus.
• Theoretical models were extended to account for environmental gradients and polygenic adaptation.
• Analysis focused on the genetic architecture and selection coefficients of beneficial mutations.

Main Results:

• Divergent natural selection strongly isolates Dune and Headland ecotypes.
• Uniform selection maintains reproductive compatibility within ecologically similar Dune populations.
• Geographically distant Headland populations evolved reproductive barriers due to adaptation to local environmental differences, despite similar phenotypes.

Conclusions:

• Speciation mechanisms can operate as a continuum of selective pressures.
• Reproductive isolation probability depends on environmental similarity, genetic architecture complexity, and selection coefficient distribution.
• Multiple forms of selection acting jointly can drive speciation, as observed in the Senecio lautus system.