Genome size in arthropods; different roles of phylogeny, habitat and life history in insects and crustaceans

Abstract

Despite the major role of genome size for physiology, ecology, and evolution, there is still mixed evidence with regard to proximate and ultimate drivers. The main causes of large genome size are proliferation of noncoding elements and/or duplication events. The relative role and interplay between these proximate causes and the evolutionary patterns shaped by phylogeny, life history traits or environment are largely unknown for the arthropods. Genome size shows a tremendous variability in this group, and it has a major impact on a range of fitness‐related parameters such as growth, metabolism, life history traits, and for many species also body size. In this study, we compared genome size in two major arthropod groups, insects and crustaceans, and related this to phylogenetic patterns and parameters affecting ambient temperature (latitude, depth, or altitude), insect developmental mode, as well as crustacean body size and habitat, for species where data were available. For the insects, the genome size is clearly phylogeny‐dependent, reflecting primarily their life history and mode of development, while for crustaceans there was a weaker association between genome size and phylogeny, suggesting life cycle strategies and habitat as more important determinants. Maximum observed latitude and depth, and their combined effect, showed positive, and possibly phylogenetic independent, correlations with genome size for crustaceans. This study illustrate the striking difference in genome sizes both between and within these two major groups of arthropods, and that while living in the cold with low developmental rates may promote large genomes in marine crustaceans, there is a multitude of proximate and ultimate drivers of genome size.

DraftAphaenogastergenomes expand our view of ant genome size variation across climate gradients

“…After controlling for both spatial autocorrelation and potential phylogenetic patterns, we found a marginally significant, positive correlation between ant genome size similarity and climate similarity (Mantel R = 0.14, p-value = 0.055). Although genome size similarity and MASH genome similarity were not significantly correlated (Mantel R = 0.08, p-value = 0.217), we included MASH as a covariate in addition to geodesic distance because previous research indicated that genome size is associated with phylogenetic relatedness (Alfsnes et al, 2017). We found that different spatial and climatic variables were associated with the size similarity of ant genomes.…”

“…We are cautious to offer possible mechanisms for this trend. In the general context of arthropods, genome size appears to be influenced by a complex array of selection pressures, as evidenced by the recent study by Alfsnes et al (2017), which found that genome size patterns varied greatly among major arthropod taxa with high potential for different mechanisms affecting genome size. For example, insects displayed clear phylogenetic correlations with genome size while genome size patterns in crustaceans were nearly independent of phylogeny but strongly related to biogeographic gradients (e.g.…”

“…Recent observational studies have reported biogeographic patterns in genome size in arthropod taxa, e.g. Crustacea (Hultgren et al, 2018), and patterns in insect genomes suggest that climate may constrain genome size with cold temperatures possibly selecting for larger genome sizes (Mousseau, 1997; Petrov, 2001; Alfsnes et al, 2017). Specific to ants, previous research into genome size variation using flow cytometry found that ants have small genomes relative to other insect taxa and that their genomes display large variation across subfamilies with patterns indicative of both gradual and rapid evolution in genome size (Tsutsui et al, 2008).…”

Population Genomics of Marine Zooplankton

“…Second, genome size has been associated with specific habitats and environmental conditions. Marine crustaceans are likely to have larger genomes than freshwater and terrestrial ones (Jeffery 2015;Alfsnes et al 2017); within the marine realm, polar species tend to have larger genomes compared to temperate species (Hessen and Persson 2009;Jeffery 2015;Leinaas et al 2016). Jeffery (Jeffery 2015) hypothesizes that such large genomes may result from the expansion of transposable elements and other repetitive elements, due to relaxed selection for rapid development or reduced constraints on body size in predictable and stable marine polar environments, compared to more fluctuating environments.…”

“…Nevertheless, evidence from insects and crustaceans suggest that accumulation of transposable and repetitive elements may be the primary contributor to their large genome sizes (Alfsnes et al 2017), while polyploidization is probably not the most common driver of genome evolution in zooplankton (Gregory and Hebert 1999). For example, species of the copepod genera Calanus and Pseudocalanus exhibit quantum shifts in genome size (C-values) within each genus, but share similar chromosome complements (McLaren et al 1989).…”