Evolutionary origins of novel conchologic growth patterns in tropical American corbulid bivalves

Abstract

We conducted a combined sclerochronologic and phylogenetic analysis to document patterns and rates of shell accretion in several subclades of related corbulids, and to explore the evolutionary origins of novel conchologic developmental patterns. We found three disparate patterns of valve development in Neogene tropical American corbulid genera. These patterns include growth through primarily radial accretion along the sagittal plane, and two derivative patterns: one characterized by initial deposition of a thin shell followed by valve thickening with little increase in valve height, and another producing a well-defined nepioconch through a marked change in the primary growth direction. We conducted a species-level phylogenetic analysis of the taxa surveyed for growth patterns, focusing on the ([Bothrocorbula+Hexacorbula]+Caryocorbula) clade. The phylogenetic distribution of shell growth patterns suggests that this clade is characterized by derivative patterns of growth. Oxygen-isotope calibrated ontogenetic age estimates of species in the derived Bothrocorbula subclade further suggest that transitions from the ancestral radial (sagittal) growth pattern to a derived pattern of growth are a function of heterochrony (peramorphosis by acceleration). These findings are significant because they link previously observed patterns of morphological constraint with a specific evolutionary process, demonstrate how morphologic constraint and innovation can be interrelated, and serve as a model for understanding the evolution of morphologic diversity in the clade as a whole. Furthermore, this study highlights the utility of sclerochronologic records as an important component of evolutionary developmental research on organisms with accretionary skeletal growth.

Spermatozoan ultrastructure and mitochondrial gene sequence ofCaryocorbula caribaea(d'Orbigny, 1853) (Corbulidae: Bivalvia), a species with plasticity in shell morphology

“…3A, 3B). Following Goodwin et al (2008), this development pattern, named 'Growth Form 2' (GF2) and observed in Caryocorbula amethystina Olsson, 1961, was also identified in C. caribaea. The existence of this growth pattern explains why tiny individuals, which are already sexually mature, exhibit quite unusual features.…”

A phylogenetic and morphologic context for the radiation of an endemic fauna in a long-lived lake: Corbulidae (Bivalvia; Myoida) in the Miocene Pebas Formation of western Amazonia

“…Often, these morphologic radiations are associated with modifications of highly plastic, preadaptive traits, such as the pharyngeal jaw apparatus and tooth structures of East Afri can cichlids (e.g., Salzburger and Meyer 2004), or the radula of Sulawesi pachychilid gastropods (Glaubrecht and von Rintelen 2008). Did the Corbulidae, whose marine members are generally considered to be morphologically conservative (although see Goodwin et al 2008), possess such preadap tations that allowed them to successfully invade freshwater in the Mesozoic and radiate with abandon in the Miocene Pebas system? On the basis of ecologic and paleoecologic information (cited below), the family possesses the means and opportunity, both physiologic and morphologic, to first success fully invade and then diversify in limnic habitats.…”

Fossil bivalves and the sclerochronological reawakening

“…A worthwhile effort would be to assemble phylogenies for taxa that show, for example, long life spans today, push them back in time using the rock record, and try to discern patterns in the heritability of life-history traits within genera, eventually working toward higher taxonomic levels. Several phylogenies already exist that can facilitate this effort (e.g., Anderson and Roopnarine 2003; Goodwin et al 2008; Bieler et al 2014; McClure and Lockwood 2015; Collins et al 2016; Alvarez and del Rio 2020). These analyses would have to be done in the context of climate, as temperature also plays a role in setting life-history traits, but the stable oxygen isotope data generated to verify the annual nature of growth increments can also yield that information.…”

“…from the Jurassic of the United Kingdom. Yet, despite some notable exceptions (e.g., Goodwin et al 2008; Geary et al 2012; Collins et al 2016), the tools of sclerochronology never quite gained wide usage in the paleobiological realm.…”