Lineage Identification Affects Estimates of Evolutionary Mode in Marine Snails

Abstract

In order to study evolutionary pattern and process, we need to be able to accurately identify species and the evolutionary lineages from which they are derived. Determining the concordance between genetic and morphological variation of living populations, and then directly comparing extant and fossil morphological data, provides a robust approach for improving our identification of lineages through time. We investigate genetic and shell morphological variation in extant species of Penion marine snails from New Zealand, and extend this analysis into deep time using fossils. We find that genetic and morphological variation identify similar patterns and support most currently recognized extant species. However, some taxonomic over-splitting is detected due to shell size being a poor trait for species delimitation, and we identify incorrect assignment of some fossil specimens. We infer that a single evolutionary lineage (Penion sulcatus) has existed for 22 myr, with most aspects of shell shape and shell size evolving under a random walk. However, by removing samples previously classified as the extinct species P. marwicki, we instead detect morphological stasis for one axis of shell shape variation. This result demonstrates how lineage identification can change our perception of evolutionary pattern and process. [Genotyping by sequencing; geometric morphometrics; morphological evolution; Neogastropoda; phenotype; speciation; stasis.]

When less is more and more is less: the impact of sampling effort on species delineation

“…This kind of investigation could also be done at a larger geographical and/or temporal scale by combining the use of morphological and genetic data, as Vaux et al . (2020) did with extinct and extant snails from New Zealand. Ultimately, our results imply that a representative portion of the observed variation should always be documented, that is, including unambiguously determined specimens and the most ambiguous specimens that are left in open nomenclature.…”