On the Evolution of Genome Size of Birds

Abstract

We measured genome size (nuclear DNA content) by fluorescence flow cytometry in 55 species of birds representing 12 different orders. Similar studies were performed in approximately 100 species by laboratories using absorption cytophotometry of Feulgen-stained nuclei. Although there have been apparent discrepancies in the assigned values for the species used as a reference, the values obtained in the different laboratories are generally in agreement. When the data are standardized in relation to a diploid (2C) value of 2.5 picograms (pg) of DNA for the domestic chicken (Gallus gallus domesticus), the mean for DNA content in 135 species representing 17 orders is 2.82 +/- 0.33 (SD) pg with a range of 2.0-3.8 pg. Thus the genome size of birds is the most conservative of any vertebrate class and, all values considered, is smaller and more uniform in size than previous estimates would indicate. This could be explained by a previously unexplored hypothesis: that the genome of birds has evolved from a small ancestral genome that was reduced before emergence of the protoavian.

Genome size and wing parameters in passerine birds

“…The question of whether the small genomes of birds are ancestral or derived ( Tiersch & Wachtel 1991)-that is, 'whether they have jettisoned their genomic baggage or whether it was never loaded in the first place' (Gregory 2002a,b)-is central to determining whether small genomes represent an adaptation to flight per se. New light has been recently shed on this issue by Organ et al (2007) who analysed the sizes of fossil osteocytes in dinosaurs and concluded that birds inherited already diminutive genomes from ancestral theropod dinosaurs (see also Ellegren 2007;Zimmer 2007).…”

“…Bachmann et al 1972;Tiersch & Wachtel 1991). Available genome size estimates for roughly 200 species of birds reveal a range of only approximately twofold (approx.…”

“…1-2 pg in mass, where 1 pg equals 978 mbp) (Gregory 2008). Based on the positive association between genome size and red blood cell size observed across vertebrates (Olmo 1983;Gregory 2001a,b), a common explanation for the apparent constraint on genome size diversity among birds has been that small cells with high relative surface areas for gas exchange-and hence small genomes-are required to meet the metabolic demands of powered flight ( Tiersch & Wachtel 1991;Wachtel & Tiersch 1993;Hughes & Hughes 1995;Hughes 1999;Gregory 2002a,b).…”

A Draft Sequence of the Puerto Rican Parrot Genome (Amazona vittata) – a Genome Project funded by a Local Community Effort

“…Similarly to most birds, the A, vittata genome, is relatively small (1.59Gb), less than half the size of the human genome 5 . It is also highly invariable due to the recent population bottleneck 6 .…”

Genome size of three Brazilian flies from the Sciaridae family

“…Birds, reptiles and mammals display only a small variation in the DNA content within classes, with the genome size of birds being the most conserved (Tiersch and Wachtel, 1991). However, in amphibians, fish and insects there is a wide variation in C-values between species whose apparent complexity does not vary greatly.…”