Temporal trends in allometry of shell calcification in northeastern Pacific venerid bivalves: implications for...

Despite literature spanning almost a century, how allometric relationships of phenotypic traits behave over evolutionary time remains poorly known for most marine species. In particular, the fossil record is seriously underutilized in this context despite harbouring a rich archive of traits. Here we use the late Pleistocene fossil record in San Diego, California, in conjunction with archival and field collected specimens, to quantify temporal changes in allometric relationships between shell size and calcification, two important functional traits, in five different species of marine bivalves. Our results reject the traditional hypothesis that allometric relationships are invariant over time. They also show that temporal changes in allometric relationships are species-specific, with closely related species showing divergent trends. Finally, we argue that information about the nature of long-term changes in allometric relationships of functionally important traits can provide a powerful yet underappreciated tool for understanding species and population responses to climate change.