Chromatin diminution in copepods
Evolution of genome size
Zooplankton life history evolution
Molecular systematics of copepods
Heterochromatin and evolution of highly repetitive DNA
Chromatin diminution as a mechanism of speciation
My laboratory, in collaboration with the laboratory of Dr. Ellen M. Rasch at James H. Quillen College of Medicine, East Tennessee State University, is studying how genomic reorganization is changing how we think about evolutionary processes. Specifically, we are examining how genomes respond to DNA loss and massive intragenomic reorganizations and whether the highly repeated DNA sequences found in many organisms are functional or "junk" DNA. The genome sizes of copepods vary widely according to species (0.5 — 30 pg). The diminution of DNA during development may be a mechanism for controlling genome size. Planktonic crustaceans (copepods) excise major portions (35 — 95%) of their chromosomes during early development in a highly precise and regulated manner. This phenomenon is called chromatin diminution. Using cytological and molecular analyses of chromosomes in the process of fragmenting, we are determining the identity of the excised DNA. We are examining if there is a relationship between variation in genome size and ecological fitness traits. We are also constructing a phylogenetic tree of the Cyclopidae family, in order to make inferences about the evolution of this trait.
Adult female copepod carries embryos in external sacs. Chromatin diminution occurs during the 4th - 7th cleavage divisions, depending upon species
Feulgen-stained chromatin diminution figure of 5th cleavage division of Mesocyclops edax embryo. Note chromosomes at each anaphase pole which comprise presumptive somatic genomes. Large clumps of excised chromatin lie at equator. Image generated by confocal microscopy at 365 nm excitation (courtesy of Dr. Stanley L. Erlandsen, Univ. Minnesota).
Classic model of embryonic chromatin diminution using the example of Diacyclops navus. At 4th embryonic cleavage division DNA is excised from the presomatic line, resulting in dramatically reduced somatic nuclear DNA contents and a reorganized somatic genome. According to the model of Beermann (1977), the germ line is unaffected.
related to chromatin diminution
and cryptic species:
E.M. Rasch, S.I. Dodson, and
G.A. Wyngaard. 2006. Genetic architecture of the cryptic speices
complex of Acanthocyclops vernalis
(Crustacea: Copepoda) II. Crossbreeding experiments, cytogenetics and a
model of chromosomal evolution. Evolution, in press.
Rasch, E.M. and
G.A. Wyngaard. 2006. Changes in
nuclear morphology assoicated with elevated DNA levels during
gametogensis in cyclopoid copepod with chromatin diminution.
Invertebrate Biology, in press.
Rasch, E.M. and G.A. Wyngaard. 2006. Genome sizes of cyclopoid copepods (Crustacea): Evidence of evolutionary constraint. Biological Journal of the Linnean Society, in press.
Grishanin, A.K., E.M. Rasch, S.I. Dodson and G.A. Wyngaard 2005. Variability in genetic architecture of the cryptic species complex of Acanthocyclops vernalis (Copeoda) I. Evidence from karyotypes, genome size, and ribosomal DNA sequences. Journal of Crustacean Biology 25(3): 373 - 383.
Wyngaard, G.A., E.M. Rasch, N.M. Manning, K. Gasser and R. Domangue. 2005. The relationship between genome size, development rate, and body size in copepods. Hydrobiologia 532: 123-137.
Dodson, S.I., A.K. Grishanin, K. Gross, and G.A. Wyngaard 2003. Morphological analysis of some cryptic species in the Acanthocyclops vernalis species complex from North America. Hydrobiologia 500: 131-143.
Wyngaard, G.A. and R. Gregory 2001. Temporal control of DNA replication and the adaptive value of chromatin diminution in copepods. Molecular and Developmental Evolution - The Journal of Experimental Zoology 291: 310-316.
Rasch, E.M. and G.A. Wyngaard 2001. Evidence for Endoreduplication: Germ Cell DNA Levels Prior to Chromatin Diminution in Mesocyclops edax.Journal of Histochemistry and Cytochemistry 49: 1 - 1.
Wyngaard, G.A. 2000. Patterns of genome size in the Copepoda: in: Alekseev, V.,G.A. Wyngaard, and F. Ferrari (eds). Advances in Copepod Taxonomy: A Tribute to Ulrich Einsle. Kluwer, Hydrobiologia 417: 43-56.
Wyngaard, G.A. 2000. The contributions of Ulrich Enisle to copepod taxonomy. In: Alekseev, V. G.A. Wyngaard and F. Ferrari (eds.), Advances in Copepod Taxonomy: A Tribute to Ulrich Enisle. Kluwer, Hydrobiologia 417: 1 — 10.
Rasch, E.M. and G. A. Wyngaard. 1997. Analysis of DNA levels during gonomery in early cleavage divisions of the freshwater copepod Mesocyclops edax.Microscopy and Microanalysis 3, Suppl. 2: 191-192.
Dorward, H.M. and G.A. Wyngaard. 1997. Variability and pattern of chromatin diminution in the freshwater Cyclopidae (Crustacea: Copepoda). Archiv für Hydrobiologie, Suppl. 107(4): 447-465.
Leech, D.M. and G. A. Wyngaard. 1996. Timing of chromatin diminution in the free- living, freshwater Cyclopidae (Crustacea: Copepoda). Journal of Crustacean Biology. 16(3): 496-500.
Wyngaard, G.A., I.A. McLaren, M.M. White, and J.-M. Sévigny. 1995.;Unusually high numbers of ribosomal RNA genes in copepods(Arthropoda: Crustacea) and their relationship to genome size. Genome, 38: 97-104.
Wyngaard, G.A. 1989. Evidence of food limitation in a subtropical copepod population. Verh. Internat. Verein. Limnol. 24: 2839-2843.
Wyngaard, G.A. 1988. Geographical variation in dormancy of a copepod: evidence from population crosses. Hydrobiologia 167/168:367-374. in: Boxshall, G.A, and H.K. Schmicke, eds. Biology of Copepods. Kluwer Academic Publishers.
Wyngaard, G.A. and C.C. Chinnappa. 1982. General Biology and Cytology of Cyclopoids. In: Harrison, R.W. and R.C. Cowden (eds.), Developmental Biology of Freshwater Invertebrates. A.R. Liss, N.Y., N.Y., pp 495-533.