Geographic contingency, not species sorting, dominates macroevolutionary dynamics in an extinct clade of neogastropods (Volutospina; Volutidae)

Dana S Friend,Warren D Allmon,Brendan M Anderson

doi:10.1017/pab.2020.60

Abstract

AbstractRates of speciation and extinction are often linked to many ecological factors, traits (emergent and nonemergent) such as environmental tolerance, body size, feeding type, and geographic range. Marine gastropods in particular have been used to examine the role of larval dispersal in speciation. However, relatively few studies have been conducted placing larval modes in species-level phylogenetic context. Those that have, have not incorporated fossil data, while landmark macroevolutionary studies on fossil clades have not considered both phylogenetic context and net speciation (speciation–extinction) rates. This study utilizes Eocene volutid Volutospina species from the U.S. Gulf Coastal Plain and the Hampshire Basin, U.K., to explore the relationships among larval mode, geographic range, and duration. Based on the phylogeny of these Volutospina, we calculated speciation and extinction rates in order to compare the macroevolutionary effects of larval mode. Species with planktotrophic larvae had a median duration of 9.7 Myr, which compared significantly to 4.7 Myr for those with non-planktotrophic larvae. Larval mode did not significantly factor into geographic-range size, but U.S. and U.K. species do differ, indicating a locality-specific component to maximum geographic-range size. Non-planktotrophs (NPTs)were absent among the Volutospina species during the Paleocene–early Eocene. The relative proportions of NPTs increased in the early middle Eocene, and the late Eocene was characterized by disappearance of planktotrophs (PTs). The pattern of observed lineage diversity shows an increasing preponderance of NPTs; however, this is clearly driven by a dramatic extinction of PTs, rather than higher NPT speciation rates during the late Eocene. This study adds nuance to paleontology's understanding of the macroevolutionary consequences of larval mode.

Highlights

Many ecological factors have been suggested as influencing rates of speciation and extinction, including feeding type (Levinton 1974), population size (Boucot 1975), range of environmental tolerance (Jackson 1974), and dispersal ability (Lester et al 2007)
Following the method outlined by Shuto (1974), we used the ratio between maximum diameter (D) and number of volutions of the protoconch (Vol) to infer each species’ larval type (D/Vol)
Results of a Mann-Whitney U-test of geographic range between Gulf Coastal Plain (GCP) species and AngloParisian Basin (APB) species (Table 3) is consistent with the hypothesis that the size of the biogeographic province may control the geographic range of all APB Volutospina

Summary

Introduction

Many ecological factors have been suggested as influencing rates of speciation and extinction, including feeding type (Levinton 1974), population size (Boucot 1975), range of environmental tolerance (Jackson 1974), and dispersal ability (Lester et al 2007). Relatively few studies have been conducted placing larval modes in species-level phylogenetic context (Collin 2004; Krug et al 2015; Sang et al 2019). Those that have, have not incorporated fossil data, while landmark macroevolutionary studies on fossil clades (Jablonski and Lutz 1983; Jablonski 1986; Hansen 1997) have not considered both phylogenetic context and net speciation (speciation–extinction) rates (Krug et al 2015).

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