Intraspecific variability of pollen morphology as revealed by elliptic Fourier analysis

Pollen grains have long fascinated biologists who used their remarkable interspecific diversity as a marker to infer profiles of past and present vegetations and environment. This study addresses the question of the diversity of the morphology of pollen grains at the intraspecific level: how different are pollen grains of the same species sampled in different populations? Such differences are expected, and are actually well known to palynologists, but at the same time technically challenging to quantify. We used elliptic Fourier analysis, a powerful morphometric approach for the comparison of outlines, on equatorial and polar views of 30 pollen grains sampled in two different populations for each of five tropical species, thus yielding 600 outlines. Multivariate analysis of variance revealed intraspecific variation of shape of the pollen grains in three out of the five species studied. Our goal here was to test if there were differences in the shape of pollen. This, to our knowledge, would be the first such study of this particular aspect of palynology. We also discuss some relevant evolutionary hypotheses. Further studies using outline analysis, coupled with a choice of appropriate sampling strategies, to suit varying environmental conditions, would prove of great value in testing such hypotheses.