S‡NCHEZ-BARACALDO, PATRICIA* AND ROBERT P. GURALNICK. Department of Integrative Biology, University of California, Berkeley, CA 94720. - Multifaceted Heterochrony: Evolution, development, and ecological covariates of leaf morphology in Neotropical ferns.
Developmental shifts are the proximate causes of morphological
evolution, and these shifts themselves have been theorized to be
driven by ecological factors. Here we present a case study showing
the interplay between evolution, development, and environment using
Andean Neotropical ferns. Our focus is a comparison of the shape and
number of pinnae along a rachis for the Eriosorus-Jamesonia
complex with a known and well corroborated phylogeny. Species of
"eriosorus", a basal paraphyletic group, are
characteristically found at lower elevations in sheltered, shady, and
xeric environments. "Jamesonia", a polyphyletic collection
of derived clades, is found at high elevation environments ranging
from open, humid, xeric, exposed to grassy habitats, and has been
derived independently at least three times. "Jamesonia"
pinnae have a highly modified morphology compared to
"eriosorus". "Eriosorus" has relatively few
highly plicate leaves, and this "plicate-ness" increases
along the rachis from younger to older leaves. "Jamesonia"
has many simple, almost oval-shaped leaves that do not appear to
change shape along the rachis. We empirically document these
heuristic patterns using two methods: 1) eigenshape analysis, in
order to construct ontogenetic shape trajectories for the pinnae, and
2) Chi-square analysis to test whether pinnae number has increased or
decreased through phylogeny. Our preliminary results suggest a trend
of truncation of the shape trajectories, such that the older pinnae of
"jamesonia" resemble the youngest pinnae of
"eriosorus". Furthermore, based on our count data, there
has been an opposite, meristic trend towards greater number of leaves
in "jamesonia". Thus shape trajectories have been truncated
but leaf number increased possibly demonstrating peadomorphosis via
neotony. An obviously correlated and perhaps causal factor is the
environment. Although "jamesonia" is polyphyletic, in each
case a similar morphology has evolved, perhaps in response to high
levels of insolation, strong winds, and temperatures ranging from 12
¡C to -2 ¡C.
Key words: evolution, heterochrony, leaf morphology, Neotropical ferns, ontogeny