Donax variabilis Say, 1822
Family Donacidae (Wedge Clams and Coquinas)
Coquinas are found in great numbers in the surf zone of sandy beaches. Although these clams spend most of their time buried in the sand, they emerge several times per tidal cycle to migrate with the waves. This process is not merely the passive erosion of clams from the sand; rather the clams actively jump out of the sand, using sound to identify large waves. Activity is greatest during the rising tide, when the clams emerge to ride only the largest (loudest) 20% of waves, which move them furthest on the beach. Donax variabilis is renowned for its polychromism (many colors), believed to act as an anti-predator device, preventing shore birds from forming a single search image of the clam. The family Donacidae is known since the Cretaceous Period and is represented by ca. 5 living genera and ca. 60 species, distributed worldwide.
Evolution on the Half Shell...
The Assembling the Tree of Life: Bivalvia project (BivAToL) is a part of the Assembling the Tree of Life initiative, a large research effort sponsored by the National Science Foundation. Its goal is to reconstruct the evolutionary origins of all living things.
Jetsam & Flotsam
Some of the BivATOL team met in early May at the Mote Marine Laboratory’s Tropical Research Station at Summerland Key, FL for a combined collecting trip and coding workshop. Both activities are essential to our project’s goal of determining the phylogenetic relationships among the bivalve families.
After collection, many of the species’ visible and molecular characteristics must be compared and “coded,” after which the phylogenetic computer analyses will be run to produce the final “tree” from which a hypothesis of relationships can be made. Below is an example of a portion of such a phylogenetic tree. Families that are on nearby branches are more closely related to each other than those further away.