Genome size evolution: towards new model systems for old questions

Abstract

Genome size (GS) variation is a fundamental biological characteristic; however, its evolutionary causes and consequences are the topic of ongoing debate. Whether GS is a neutral trait or one subject to selective pressures, and how strong these selective pressures are, may remain open questions. Fundamentally, the genomic sequences responsible for this variation directly impact the potential evolutionary outcomes and, equally, are the targets of different evolutionary pressures. For example, duplications and deletions of genic regions (large or small) can have immediate and drastic phenotypic effects, while an expansion or contraction of non-coding DNA is less likely to cause catastrophic phenotypic effects. However, in the long term, the accumulation or deletion of ncDNA is likely to have larger effects. Modern sequencing technologies are allowing for the dissection of these proximate causes, but a combination of these new technologies with more traditional evolutionary experiments and approaches could revolutionize this debate and potentially resolve many of these arguments. Here, I discuss an ambitious way forward for GS research, putting it in context of historical debates, theories and sometimes contradictory evidence, and highlighting the promise of combining new sequencing technologies and analytical developments with more traditional experimental evolution approaches.

Genome Size Covaries More Positively with Propagule Size than Adult Size: New Insights into an Old Problem

“…How nucleotypic effects work is not well understood and subject to considerable debate [ 7 , 8 ]. For further information, the reader should see the reviews in [ 7 , 8 , 16 , 174 , 176 , 183 , 194 , 241 , 242 , 243 ]. Suffice it to say here that, as a general rule, large cells appear to require larger genomes to support their greater structure and resource demands than do smaller cells.…”

“…In addition, because of spatial (body-volume) constraints (following assumption #8), organisms in these specific environments may produce larger, but fewer somatic cells and reproductive propagules than those with similar body sizes in other environments favoring smaller propagules (also see Figure 5 ). Other hypothetical possibilities involving selection on the sizes of somatic cells (or their correlates, such as rates of growth, development and metabolism [ 7 , 8 , 15 , 89 , 96 , 176 , 181 , 218 , 244 , 252 , 253 , 254 , 255 , 256 , 257 , 258 ]) with secondary effects on genome size and propagule size, or effects of spontaneous or environmentally induced duplication of DNA sequences or whole genomes [ 8 , 11 , 17 , 103 , 172 , 186 , 242 ] on the sizes of somatic cells and reproductive propagules ( Figure 6 ) should also be considered and evaluated. Mechanisms underlying relationships among genome size, cell size and propagule size are likely complex and multidirectional in cause-and-effect ( Figure 6 ; see also Section 4.7 ).…”

A high-quality carabid genome provides insights into beetle genome evolution and cold adaptation

“…Despite many attempts to find abiotic and biotic factors that contribute to the enormous natural variation in genome size, it remains an open question which evolutionary and ecological variables drive genome size changes (Blommaert 2020). The main challenges to resolving this question arise from the complexity of genome composition, decoupling the role of selection (if present) from many different environmental factors, and the dependence of genome size on phylogenetic relatedness (Alfsneset al 2017;Canapa et al 2020;Ritchie et al2017).…”

Robertsonian rearrangements in Neotropical Meliponini karyotype evolution (Hymenoptera: Apidae: Meliponini)

“…Besides the chromosome number, the nuclear genome size (1C value) provides valuable insights about genome and karyotype evolution (Blommaert, 2020; Gregory, 2005). Karyotype rearrangements involving duplication/amplification or deletion/reduction of chromosome portions (Schubert and Lysak, 2011) can result in nuclear genome size changes and consequently in reproductive isolation, which prevents gene flow, leading to diversification and speciation (Ferree and Prasad, 2012; Cardoso et al ., 2018).…”