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Dev Genes Evol (2009) 219:207210 DOI 10.1007/s00427-009-0281-0
SEQUENCE CORNER
Extremely small genomes in two unrelated dipteran insects with shared early developmental traits
Urs Schmidt-Ott & Ab. Matteen Rafiqi & Klaus Sander &
J. Spencer Johnston
Received: 16 January 2009 /Accepted: 4 March 2009 /Published online: 24 March 2009 # The Author(s) 2009. This article is published with open access at Springerlink.com
Abstract We discovered extremely small genomes (1C ~100 Mb) in the dipteran insects Coboldia fuscipes (Scatopsidae) and Psychoda cinerea (Psychodidae). The small genomes of these species cannot be explained by a fast developmental rate, which has been shown to correlate with small genome sizes in animals and plants but might accommodate the combined effects of other developmental traits, including small egg size, thin blastoderm layer, and long-germ development.
Keywords Diptera . Genome size . Egg size . Blastoderm . Pair-rule patterning . Flow cytometry
Introduction
Genome size evolution is a complex multifactorial process.
However, in animals and plants, genome size often
correlates with cell size and the rate of cell division (Gregory 2001; Gregory 2002). The coding genome of animals seems to impose a lower threshold at about 100 Mb for the haploid (1C) genome; smaller genomes may require a substantive reduction of the coding genome (Lynch 2007). The 100-Mb threshold coincides for example with the genome size of Caenorhabdites elegans (Bennett et al. 2003), a very fast developing organism with about 19,000 protein-coding genes. The smallest insect genomes reported so far belong to highly specialized parasitic species including the louse Pediculus humanus (1C=105 Mb; Johnston et al. 2007) and the strepsipteran Caenocholax fenyesi texensis (1C=108 Mb; Johnston et al. 2004). The next to follow in size are the genomes of certain dipteran midges (Mayetiola destructor, Cecidomyidae; Prodiamesa olivacea, Chironomidae) with 1C>120 Mb (Zacharias 1979; Petitpierre 1996; Johnston et al. 2004), but genome size estimates of other dipterans are distinctly larger (1C> 140 Mb, Gregory et al. 2007).
A recent study surveying the genome sizes of 67 drosophilid species provided evidence for a significant positive correlation between genome size and developmental time, which suggests that, as a rule, species with smaller genome sizes develop more quickly than those with larger genomes (Gregory and Johnston 2008). Another developmental factor, egg size, might influence the genome...