Reduced evolutionary constraint accompanies ongoing radiation in deep-sea anglerfishes

Area of Science:

• Evolutionary Biology
• Macroevolutionary Studies
• Ichthyology

Background:

• Colonization of new habitats often drives phenotypic diversification.
• Some environments pose significant constraints, limiting evolutionary solutions.
• Anglerfishes (Lophiiformes) provide a model for studying habitat transition impacts.

Purpose of the Study:

• To investigate macroevolutionary diversification following habitat transitions in anglerfishes.
• To examine the tempo and mode of phenotypic diversification in deep-sea pelagic anglerfishes.
• To understand how environmental constraints and opportunities shape evolutionary trajectories.

Main Methods:

• Phylogenetic reconstruction using 1,092 loci with extensive species sampling (~38%).
• Analysis of three-dimensional phenotypic data from museum specimens.
• Examination of lineage diversification rates and phenotypic disparity.

Main Results:

• Deep-sea pelagic anglerfishes, originating from benthic ancestors, rapidly diversified.
• This transition involved shifts to larger jaws, smaller eyes, and a laterally compressed body plan.
• High phenotypic disparity in body, skull, and jaw shapes was observed, with bathypelagic species showing greater body elongation variability than constrained benthic species.

Conclusions:

• Evolutionary radiations can be spectacular even in environments with few resources and high physiological challenges.
• Phenotypic evolution is concentrated in recently diverged lineages, particularly those deviating from ancestral body plans.
• Anglerfish diversification highlights the interplay between ecological opportunity and environmental constraints in shaping macroevolutionary patterns.