Biology Reference
In-Depth Information
echinulate pollen and pollination by flies. We think that the flaw of this study is
inherent to the fact that correlations were established without statistical analysis
and without taking into account the phylogenetic background of the family, mak-
ing it impossible to know whether the correlations observed between the pollen
and pollinator types result from adaptation or from common ancestry.
The processes underlying a relationship between two characters remain gener-
ally extremely difficult to determine [4,5]. A correlation may be the result of ad-
aptation, but also of developmental constraints. It may also be simply the result of
phylogenetic inertia i.e., that related species resemble each other more than they
resemble species drawn at random [6]. Various mathematical approaches, called
Phylogenetic Comparative Methods or PCM [4,7], have been proposed over the
last twenty years [8-10] and take into account the phylogenetic background of the
organisms studied.
Here we re-examine the correlation between pollen sculpturing and pollinator
type proposed by Grayum [3], in light of the phylogenetic framework available
for the Araceae family [11] using two PCM applied to discrete characters. In the
conclusion of his paper, Grayum suggested to investigate other groups of mono-
cotyledons, palms in particular. In this family a large amount of pollen data has
been recorded but rarely studied from an evolutionary point of view, except for
the number of apertures [12]. Moreover data on pollinators are available and a
detailed and well resolved phylogeny including almost all of the genera [13] now
exists. Consequently we also examine the correlation between pollen and pollina-
tor types in the palm family (Arecaceae).
Methods
Character optimization was carried out with the Maximum Parsimony method
implemented in the Mesquite software [14].
Two PCMs were used: the Concentrated Changes Test or CCT [9] and Dis-
crete [10].
Results and Discussion
Character Evolution in the Araceae
To our knowledge, there is little data in the literature concerning the evolution of
ornamentation of pollen grains in monocots [15]. Concerning the angiosperms,
a recent study showed that the ancestral exine structure had a continuous or mi-
croperforate surface [16]. However, foveolate-reticulate tectum would have arisen
