A cheilostome bryozoan story of fitness & phenotypes across 2 million years | Emanuela Di Martino

A cheilostome bryozoan story of fitness & phenotypes across 2 million years

Natural selection can be quantified and modelled as statistical associations between fitness and phenotypes. Although the fossil record offers unique insights into long-term phenotypic evolution, successfully operationalizing the study of selection on data from the fossil record is challenging. Estimating fitness components using fossil populations allows linking observed patterns of evolution and selective forces in the past, but these are not available for most groups of organisms. Cheilostome bryozoans, a group of calcified colonial marine invertebrates with an exceptional fossil record, offer a unique opportunity to overcome this barrier: either the measure of the density of skeletal brooding structures/ovicells within a colony of genetically identical feeding modules/autozooids) or outcomes of overgrowth competition can be used as proxies for fitness components (i.e. fecundity and partial mortality, respectively). Using multiple fossil populations of closely related cheilostome bryozoans (four species of the genus Microporella) and a non-related species (Antarctothoa tongima), this study investigates multivariate signals of trait-fitness associations over more than two million years of the Pleistocene in the Wanganui Basin, New Zealand. Three phenotypic traits—autozooid size, autozooid shape, and ovicell size—were analyzed to address the following questions: (i) How do trait-fitness associations vary across time and among species or lineages? (ii) How do these associations differ when fitness is measured using either fecundity or overgrowth competition? (iii) Can trait-fitness associations predict phenotypic evolutionary outcomes? Additionally, the study examines how paleotemperature and its variability influence the substantial variation observed in each of the three quantitative traits and fecundity across different time intervals.