The C-value enigma in plants and animals: a review of parallels and an appeal for partnership

Abstract

Aims: Plants and animals represent the first two kingdoms recognized, and remain the two best-studied groups in terms of nuclear DNA content variation. Unfortunately, the traditional chasm between botanists and zoologists has done much to prevent an integrated approach to resolving the C-value enigma, the long-standing puzzle surrounding the evolution of genome size. This grand division is both unnecessary and counterproductive, and the present review aims to illustrate the numerous links between the patterns and processes found in plants and animals so that a stronger unity can be developed in the future.

Scope: This review discusses the numerous parallels that exist in genome size evolution between plants and animals, including (i) the construction of large databases, (ii) the patterns of DNA content variation among taxa, (iii) the cytological, morphological, physiological and evolutionary impacts of genome size, (iv) the mechanisms by which genomes change in size, and (v) the development of new methodologies for estimating DNA contents.

Conclusions: The fundamental questions of the C-value enigma clearly transcend taxonomic boundaries, and increased communication is therefore urged among those who study genome size evolution, whether in plants, animals or other organisms.

Fig. 1.

Ranges in C-value (haploid nuclear DNA contents, in pg) for the major groups of plants and animals that have been studied to date. The number of species in each group for which data are available (as of November 2003) is given in parentheses. Mean C-value is indicated by the vertical line within the bars, and is obviously close to the low end of the distribution in most of these groups. This indicates that most C-values in both plant and animal taxa are small, with only a few subgroups extending to larger values. The monilophytes refers to the monophyletic clade of horsetails and ferns (see Pryer et al., 2001). Data are from the Plant DNA C-values Database (Bennett and Leitch, 2003), the Animal Genome Size Database (Gregory, 2001b), and Kapraun (2005).