 |
|
Testing homologies in tylenchid nematodes relative to freeliving outgroups, with implications for phylogenetic congruence
Erik James Ragsdale
Paperback. ProQuest, UMI Dissertation Publishing 2011-09-08.
ISBN 9781243713742
|
|
|
|
Hitta bokens lägsta pris
|
Förlagets beskrivning
Molecular phylogenetics has often posed serious challenges to ideas of relationships based on morphology. A pressing case of incongruence is that of nematodes in the largely plant- and insect-parasitic Tylenchomorpha, which molecular phylogenies strongly support as a sister group to the freeliving Cephalobomorpha. Because of a sharp disjunction in taxonomically important feeding structures, this relationship has been uncorroborated by morphology. To understand feeding structure homologies and their evolutionary transformations, morphology is examined as individual cells using three-dimensional reconstruction based on serial thin sections for transmission electron microscopy. Reconstructions in a model tylenchid nematode, Aphelenchus avenae, are compared to those existing for Cephalobomorpha (Acrobeles complexus) and Rhabditomorpha (Caenorhabditis elegans). Reconstruction of the stomatostylet apparatus, including all associated epithelial and muscle cells, reveals a precise correlation of underlying epidermal and arcade syncytia with outgroups. Homologies are supported by spatial arrangement, numbers and positions of cell body processes, and connectivity to sensory cells. Evolution of the stylet from a freeliving stoma involved expansion or retraction of individual underlying cells, but fundamental connectivity is highly conserved. Novel morphological data from the anterior sensory system tests the phylogenetic framework for hypotheses of feeding structure evolution. A high degree of similarity with outgroups facilitates identification of sensory homologies. Several features are hypothesized as synapomorphic between tylenchid and cephalob representatives, constituting the first strong morphological evidence for a clade including these taxa but excluding Rhabditomorpha. Reconstruction of the pharyngeal corpus shows that numbers of cell classes, including with respect to dorsal gland orifice (DGO) position, and numbers of nuclei per class correspond exactly between A. avenae and C. elegans. Numbers of neuron cell bodies within the corpus are identical with outgroups and other Tylenchomorpha. Non-homology of the procorpus challenges homology of a metacorporal DGO position, the primary character circumscribing "Aphelenchoidea." Possible convergence of an "aphelenchid" pharynx in two separate lineages would be congruent with independent phylogeny. In general, dissertation results demonstrate that, despite superficial divergences between taxa, morphology shows a conserved modality of evolution at a cellular level. Resolution of apparent incongruence, by closer examination of morphology and reevaluation of primary homologies, has implications for modern systematics
Liknande böcker
Recensioner
Den här boken har tyvärr inte några recensioner ännu. Om du redan läst boken, skriv en recension!
Recensera boken
Skriv en recension och dela dina åsikter med andra. Försök att fokusera på bokens innehåll. Läs våra instruktioner för mer information.
Testing homologies in tylenchid nematodes relative to freeliving outgroups, with implications for phylogenetic congruence
Bokrecensioner » Testing homologies in tylenchid nematodes relative to freeliving outgroups, with implications for phylogenetic congruence
|
|
 |
|
|
|
|
