STATISTICAL TRENDS IN AMINO ACID COMPOSITION OF CHIONE ELEVATA FROM FLORIDA'S PLIO-PLEISTOCENE SHELL BEDS: A PRACTICAL APPLICATION OF CANONICAL DISCRIMINANT ANALYSIS (CDA)

Canonical discriminant analysis (CDA) is a statistical application that defines the maximum differences between multivariate observations from a priori defined classes within a large data set. Variation within the data set is accounted for by a set of canonical variables defined by linear equations composed of the original multivariate observations. This technique is applied to measurements of concentration and racemization (D/L ratios) of the amino acids aspartic acid, glutamic acid, valine, phenylalanine, and alloisoleucine/isoleucine, in the venerid bivalve, Chione elevata, with the intention of better interpreting the aminostratigraphy and chronology of Florida's Plio-Pleistocene shell beds. Samples (n=129) from 11 distinct locations in central and southern Florida represent the Tamiami (middle - upper Pliocene), Caloosahatchee (upper Pliocene - lower Pleistocene), Bermont (lower - middle Pleistocene), and Ft. Thompson (middle - upper Pleistocene) stratigraphic units. In this case, sets of amino acid measurements arranged by both locality and/or stratigraphic unit are statistically distinct. Linear functions defining the first two canonical variables (describing ≥ 90% of the total variation in the data set) have been calculated. Amino acid measurements that best describe differences between stratigraphic units are defined first by amino acid concentration and secondarily by D/L ratios. It should be noted that a majority of D/L ratios are near equilibrium values of 1.0 (1.3 for alloisoleucine/isoleucine) in samples from several of the units. Amino acids that rank highest within the first two canonical variables are aspartic acid, valine and phenylalanine. Validity test results performed with independent samples from known stratigraphic units in the study region are pending.

The implication that amino acid concentrations can be used to distinguish among stratigraphic units when D/L ratios are approaching equilibrium values suggests that transformations of amino acids that affect their relative abundances (e.g., deamination, deamidation) should be more closely scrutinized to properly assess internal controls on racemization and amino acid variability within the system.