Lineage Identification Affects Estimates of Evolutionary Mode in Marine Snails.

Area of Science:

• Evolutionary biology
• Paleontology
• Marine biology

Background:

• Accurate species and lineage identification is crucial for understanding evolutionary patterns.
• Integrating genetic and morphological data, alongside fossil records, offers a robust method for lineage reconstruction.
• Marine snails of the genus Penion provide a valuable model for studying long-term evolutionary processes.

Purpose of the Study:

• To investigate the concordance between genetic and shell morphological variation in extant Penion snails.
• To extend this analysis to deep time by incorporating fossil specimens.
• To refine our understanding of evolutionary patterns and processes, including speciation and stasis, through improved lineage identification.

Main Methods:

• Genotyping by sequencing (GBS) was used to analyze genetic variation in extant populations.
• Geometric morphometrics was applied to quantify shell shape variation in both extant and fossil specimens.
• Phylogenetic analyses were conducted to infer evolutionary relationships and assess species delimitation.

Main Results:

• Genetic and morphological data largely agree on extant species boundaries, but shell size proved to be an unreliable trait for species delimitation, leading to potential over-splitting.
• Some fossil specimens were incorrectly assigned to existing species.
• A single evolutionary lineage, Penion sulcatus, was inferred to have persisted for 22 million years, with shell shape and size evolving primarily via a random walk model.
• Re-evaluation, excluding previously misclassified extinct species (P. marwicki), revealed morphological stasis along one axis of shell shape variation.

Conclusions:

• Combining genetic, morphological, and fossil data enhances the accuracy of species and lineage identification through time.
• Shell size is a poor indicator for species delimitation in Penion, necessitating careful taxonomic evaluation.
• The perception of evolutionary patterns, such as stasis versus continuous change, is sensitive to accurate lineage identification, highlighting the dynamic nature of evolutionary processes.