TABLE CONTENTS

Missing the Unseen: Morphological and Ultrastructural Characters in
Genomic Era
Mundo-Ocampo, M. & J.G. Baldwin
Department of Nematology, University of California-Riverside. Riverside, CA 92504. USA
Molecular phylogenetics are undoubtedly providing critical information to be incorporated in
diagnostics and phylogenetics of nematodes. In spite of this, comparative morphological
diversity remains crucial to understanding functional biology and phenotypic evolution.
Unfortunately, for most nematode taxonomists, morphological diversity and classical
morphological characters selected for diagnostics among nematodes (i.e. Tylenchomorpha)
often does not provide very reliable characters to support solid phylogenetic analyses. This
in part may be because many characters are at the limits of light microscope resolution and
are subject to misinterpretation. The ‘known’ diversity of nematodes (in particular free
living and marine taxa) when analyzed with the aid of modern light, electron microscopy
(SEM & TEM), 3D reconstruction and multi focal video imaging, usually provides new
character information never included in classical taxonomic systems. Moreover, new taxa are
discovered at a steady pace and often further expand the collective range of potentially
diagnostic features. Resulting observations increase the relevance and accuracy of
morphologically supported phylogenies, classification and identification. They further
provide a basis to establish hypotheses of character homology across taxa and to understand
specific functional adaptations. Case examples are presented and discussed.
Taxonomy and Systematics of Hirschmanniella
De Ley, I.T., O. Holovachov, P. De Ley & J. Baldwin
Department of Nematology, University of California, Riverside, CA 92521
Hirschmanniella species are versatile and taxonomically confounding nematodes. The genus
is composed of 36 nominal morphospecies distinguished mainly by a few phenotypic
characters that are oftentimes highly variable and difficult to resolve with light microscopy. A
case in point is the recently described cryptic species Hirschmanniella santarosae which is
morphologically very close to H. pomponiensis and only differs in excretory pore position
and shape of stylet knobs, even though both species showed 1% and 4% sequence
differences in small subunit (SSU) and partial (D2D3) large subunit (LSU) nuclear ribosomal
DNA (rDNA), respectively.
We have obtained six additional Hirschmanniella isolates from both sides of the Atlantic and
present their phenotypic and genetic character suites as well as phylogenetic analyses in order
to provide better resolution of the evolutionary relationships and species delimitation among
congeners. Combined analyses of these and other isolates suggest the likely discovery of
additional cryptic species and species complexes, including further evidence of extensive
radiation among Californian lineages. Morphological and molecular data must clearly be
analysed jointly in order to eventually produce a more reliable estimate of species diversity in
this problematic genus.
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