Genome sizes of cyclopoid copepods (Crustacea): evidence of evolutionary constraint

Abstract

Genome sizes for 36 species of cyclopoid copepods were determined by DNA-Feulgen cytophotometry of nuclei from adults collected from diverse habitats and locales in North America, South America, Europe, and Asia. Genome sizes are small, show a 20-fold range ( C = 0.10-2.02 pg DNA), and vary in a discontinuous fashion. The genomes of cyclopoid copepods are remarkably small and constant within each species, unlike the large and variable genomes of marine calanoid species. These differences may reflect the evolutionary antiquity of marine copepods in relation to marine, brackish, and freshwater copepods, as well as differences in mechanisms used to modulate genome size. The small genome sizes of contemporary cyclopoids provide substantive evidence of evolutionary constraint, possibly favouring small genomes, rapid replication rates and accelerated development as adaptive strategies for survival in often fragmented, stressful, and changing habitats.

Genetic Architecture of the Cryptic Species Complex of Acanthocyclops Vernalis (Crustacea: Copepoda). Ii. Crossbreeding Experiments, Cytogenetics, and a Model of Chromosomal Evoloution

“…Likewise, geographical distance was not a reliable predictor of degree of reproductive success, as some sympatric populations failed to produce viable, fertile offspring. The present study reinforces the emerging picture of a species complex for which morphology, genome size, 18S rDNA sequence, and chromosomal number fail to discriminate reproductively isolated species (Dodson et al 2003;Rasch and Wyngaard 2006). The reproductive isolation between forms that share certain characters and the reproductive compatibility between populations with apparent differences serves as an intriguing example of variability at the population level in nature.…”

“…Genome size within cyclopoid copepod species tends to be highly conserved (Rasch and Wyngaard 2006), but an exception is A. vernalis collected from an Ohio lake in a companion study (Grishanin et al 2005). One Ohio isofemale line possessed the genome size of the parental lines in the present study, while another Ohio isofemale possessed the genome size of the F 3 and F 15 hybrids, and a third Ohio isofemale line contained still less DNA in its genome.…”

“…Classical morphological characters once used to distinguish populations and species of A. vernalis and A. robustus (Dodson 1994) were revealed to be phenotypically plastic and useless for discrimination (Dodson et al 2003). Similarly, the nuclear DNA content shows little variation among populations in these forms (Grishanin et al 2005;Rasch and Wyngaard 2006). Species boundaries appear less clear with each new investigation.…”

Natural Pathways towards Polyploidy in Animals: The <b><i>Squalius alburnoides</i></b> Fish Complex as a Model System to Study Genome Size and Genome Reorganization in Polyploids

“…This is clearly insufficient to get a landscape perspective within and between the most abundant phyla, despite the existence of some tentative reviews [e.g. Hardie and Hebert, 2004;Gregory and Mable, 2005;Rasch and Wyngaard, 2006;Smith and Gregory, 2009;Mable et al, 2011].…”

“…Evidence is mainly obtained from animal populations facing environmental fluctuations [see e.g. Stöck et al, 2002;Jokela et al, 2003;Rasch and Wyngaard, 2006;Janko et al, 2007;Hall, 2009;Scali and Milani, 2009;Milani et al, 2010]. Furthermore, a positive correlation seems to exist between records of natural polyploids and the effort put into taxonomic surveys by animal cytogeneticists.…”