Paper No. 10
Presentation Time: 10:15 AM
INTRASPECIES VARIATION BETWEEN TWO EXTANT POPULATIONS OF LAQUEUS CALIFORNIANUS AS MODELED BY ELLIPTICAL FOURIER ANALYSIS
The range of morphological variability within and among populations and species of living brachiopods is surprisingly poorly known. In order to evaluate the boundaries of morphological species in the fossil record, our knowledge of recent variation must be improved. We used Elliptical Fourier Analysis (EFA) to study intraspecific variation among dorsal valve commissural outlines of 90 Laqueus californianus specimens collected from Catalina Island, California and 19 specimens from Puget Sound, Washington. EFA uses outline data points to find harmonic coefficients which complete a series of sine and cosine curves which when summed together can reproduce the original outline, simplifying the outline into fewer shape variables. In order to capture actual morphological differences, every shell outline must be oriented similarly, invariant to size, start position, location, and rotation in coordinate space. If not oriented similarly, EFA harmonic coefficients will largely reflect different positions in coordinate space rather than actual shell morphology. Though the EFA program we used (Rohlf and Ferson, 1993) contains options to run the analysis invariant to size, location, rotation and start position, these options are set (pre-coded) arbitrarily. We created non-arbitrary invariant options that are able to orient shell outlines accurately and consistently, making the outlines invariant to size, start position, location, and rotation. Principal Component Analysis of the harmonic coefficients from both populations reveals that the pre-coded invariant options do not enable us to distinguish between populations, while our calculated invariance values clearly differentiate the two populations in morphometric shape space. Moreover, our calculated invariance values reveal that, while Puget Sound individuals are smaller, their shape is most closely comparable to the larger Catalina specimens, suggesting that growth rates and growth directions in these two populations of Laqueus californianus vary considerably along a latitudinal gradient. With the addition of age information, these differences in size and shape have the potential to suggest intriguing hypotheses about the role of heterochrony in the evolution of this lineage.