LIFE CYCLE-ASSOCIATED CHARACTER VARIATION IN AULACOSEIRA KRAMMERI SP. NOV., A NEW MIOCENE SPECIES FROM OREGON, U.S.A.

Abstract

A new freshwater species, Aulacoseira krammeri R.K. Edgar, Kociolek & S.M. Edgar, from Miocene deposits in Oregon is described. The variation within this species encompasses distinctive robust and gracile morphotypes, and is described emphasizing variation incontinuous characters of valve morphology over the entire vegetative life cycle, especially with respect to covariation of mantle height, interareolar distance (within striae), interstriae distance, ringleist depth and height, and number of ringleist rimoportular canals with size(i.e. valve diameter). The morphometric differentiation of A. krammeri, A. solida (Eulenstein in Van Heurck) Krammer and A. paucistriata Bradbury is examined with an emphasis on size-standardised comparisons and is shown to be largely quantitative. Differences among species in principal axis regression slopes of characters versus valve diameter or mantle height and the location of bivariate means (character and valve diameter or mantle height) were statistically assessed using confidence intervals and confidence ellipses, respectively. A. krammeri displays a unique, non-overlapping distribution of linking and separation spine morphologies with respect to valve diameter and intermediate spine morphologies in a narrow range of cell sizes closely associated with resting spore formation, reflecting a process of developmental conversion.