TITLE:
Modulations in seed micromorphology reveal signature of adaptive species-diversification in Dendrobium (Orchidaceae)
AUTHORS:
Bhupendra Chaudhary, Pritam Chattopadhyay, Nirmalya Banerjee
KEYWORDS:
Dendrobium; Seed Micromorphology; Phytogeography; Tropical; Subtropical; Temperate; Phylogeny
JOURNAL NAME:
Open Journal of Ecology,
Vol.4 No.2,
February
8,
2014
ABSTRACT: During speciation in flowering plants, many
morphological characters were evolved in response to continuous selection
pressure. Such characters are largely governed by genetic changes or get
modulated according to ecological adaptations. To explore the potential of
latter, a novel comparative analysis of seed micromorphology and ultrastructure
was performed in twenty species in the genus Dendrobium (Orchidaceae)
from well-defined altitude based phytogeographical realms i.e. temperate, subtropical and tropical regions. Seed
morphological characteristics from all collected species were examined using 13
quantitative traits descriptors. Comparative seed morphology revealed that the
species from temperate region have larger seed volumes and seed volume/embryo
volume ratio than species from subtropical or tropical regions irrespective of
their phylogenetic association. Hence, phylogenetically related species
emphasized their preference for a climatic region as their prime habitat.
Similar trends towards gradual increase of percentage free air space were
observed in the species of tropical to subtropical and subtropical to temperate
regions. The higher percentage of free air space may have an advantage for the
species from temperate region with relatively low atmospheric pressure that had
greater buoyancy for optimal seed dispersal. Also, phylogenetically distant
species from a particular climatic region, showed characteristic features of
the testa cell walls sculptured with bead-like orna-mentations or covered
with cottony white substances. Based on these observations, it may be concluded
that seed volume, % free air space and seed coat ornamentation in Dendrobium species are signatures of
adaptation according to climatic preferences rather than their selection during
speciation.