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.

Keywords: C‐value; crustaceans; ecology; evolution; insects; life history; temperature‐size‐rules.

Figure 1

Dendrogram of insects with known C‐values (n = 586). C‐values (maximum shown value 5 pg DNA/cell) shown in red gradient (minimum/light red = 0.10 pg DNA/cell, maximum/dark red = 5 pg DNA/cell). C‐values above the set threshold are marked with asterisk (*); specific C‐values may be retrieved from the Table S2. Branches colored according to mechanism of DEV (green = Ametabola, orange = Hemimetabola, and purple = Holometabola). Class (in bold), order, and other notable groups (Sc = subclass) shown next to branches

Figure 2

Dendrogram of crustaceans with known C‐values (n = 182). C‐values (maximum shown value 10 pg DNA/cell) shown in outer circle in red gradient (minimum/light red = 0.14 pg DNA/cell, maximum/dark red = 10 pg DNA/cell). C‐values above the set threshold are marked with asterisk (*); specific C‐values may be retrieved from the Table S1. Branches colored according to habitat (green = terrestrial, light blue = freshwater, and dark blue = marine). Subphylum (in bold), class, and other notable groups (Ic = infraclass, O = order) shown next to branches

Figure 3

C‐values by clades in crustaceans (a) (with representatives from the outgroup Subphylum Myriapoda as represented in Figure 2). The class Maxillopoda show the combined C‐values of the infraclasses Cirripedia and Copepoda, and the class Malacostraca show the combined C‐values of the orders Stomatopoda, Isopoda, Amphipoda, Euphausiacea, and Decapoda, and insects (b) (with representatives from the outgroup Class Entognatha as represented in Figure 1)