Johnston Part of Group Studying How Genome Size Affects Reproductive Fitness in Seed Beetles


Seed Beetle (Callosobruchus maculatus) female. Photo by Simon Hinkley & Ken Walker

Beetles can teach us a lot of things about genetics, especially with regard to differences in genome size within and between species. Professor Spencer Johnston worked with a team of scientists to test how the genome size affects reproductive fitness in seed beetles.

Led by Goran Arnqvist of the University of Uppsala in Sweden, the researchers have presented evidence suggesting that natural selection may be a more important determinant of genome size than chance events (genetic drift). In the study published in the September 2015 issue of the Proceedings of the Royal Society of London, they found no evidence that genome size is determined by random processes.

Johnston said they conducted a phylogenetic comparison of 12 species of seed beetles to describe the tempo and mode of the genome size evolution in the group, as well as to test if there was any correlation in evolution between the size of genome and body size at an interspecific scale.

The group also used a second group of 18 distinct genotypes of the main model species, Callosobruchus maculatus, to characterize interspecies variation in genome size and to ask whether genome size shows correlated evolution with life history and sex-specific fitness.

There was a reason to study this particular organism. These beetles are considered pests because their larvae infest seeds of legumes, such as soybeans and cow peas, doing considerable damage.

The researchers found that within the groups of seed beetles studied, the genome size was directly and positively related to successful reproduction in both males and females. The results suggest that variation in genome size may be much more important than previously believed.

Dr. Johnston said that novel analytic methods used in this study could be adapted to study other insects and could possibly help find new and improved methods of controlling the beetles and other pests.

“I have long sought evidence that genome size variation was adaptive.  This is of interest, because we often find genome size differences among populations, including mosquitos and other very serious pest insects,” Johnston said.  “Here we find that the populations with larger genomes have higher lifetime fecundity in females and greater competitive success as males.  What I find interesting is that we really do not know why this should be so.  It opens a whole new area for control efforts.”

The article can be found here:


Comments are closed.