T255 Species and Speciation in the Fossil Record (Posters)

Wednesday, 12 October 2011
9:00 AM - 6:00 PM
Hall C

STABILITY AND INTENSITY OF CLINAL REGIMES OVER LONGER TIME INTERVALS: IMPLICATIONS FOR INTERPRETING STRATOPHENETIC PATTERNS IN THE FOSSIL RECORD

Paper number: T255-7
Program: Technical Sessions
Time: 9:00 AM – 6:00 PM

Authors

Abstract

Clines have long been documented in plants and animals and have been recognized as potentially important systems of speciation. Due to the heterogeneous nature of environmental conditions along a cline, interactions between environment and morphology can be described and modeled as the norm of reaction for a particular species. Nearly all traits will show some plasticity along a cline because phenotypes result from the interaction of genetics with environment, yet the response of phenotypic plasticity to variable environmental conditions requires further understanding. The power of the fossil record is that it allows us to measure the spatial and temporal dynamics of morphological change within a species over longer time scales. This gives us the opportunity to understand how these clinal systems operate over longer-term intervals thereby elucidating their potential contributions to microevolutionary patterns routinely documented in the fossil record.

The richly fossiliferous Kope Formation makes an excellent setting in which to conduct this analysis because these strata currently form the basis for ongoing, high-resolution correlation studies across a wide geographic area and because environmental gradients within this setting have been modeled in detail. This study has quantified the norm of reaction in the trilobite Flexicalymene granulosa through geographic analyses at a temporal resolution of 103 years, and then tracked this relationship between morphology and environment stratigraphically over an interval of 105 years. Results indicate that clines are persistent, dynamic and responsive to environmental shifts. Within this clinal regime novel morphologies do not appear and stratophenetic patterns mirror patterns of environmental change due to the dominant process of clinal translocation. Therefore, clines will not be the site of speciation unless environmental perturbation is severe enough to require adaptation rather than migration, or the steepness of the gradient changes sufficiently enough to reduce gene flow and promote isolation.