Genetics and evolutionary dynamics of male-killer suppression in the lacewing, Mallada desjardinsi

Evolution has historically been thought of as a slow process, happening over geological time periods. However, we now know that contemporary evolution can in fact be very fast, with new genetic types (mutations) spreading rapidly through natural populations. One case where evolution is particularly quick is the response of insect populations to male-killing bacteria. Many insect species carry these microbes - which do exactly what their name suggests -kill only male carriers (and leave females unharmed). They pass from a female (mother) insect into sons and daughters - and kill the sons.

Natural selection, of course, promotes mutations in insects that rescues these males. These rescue mutations are known in four different cases now. In 2007, we were fortunate enough to observe one of these rescue genes spread in nature through a population of butterflies. Before the rescue mutation spread, male-killing bacteria were so common and effective there were 100 females to every male butterfly. After the spread of the rescue element, males and females equally common. The rescue mutation spread through the population in under a year - 10 butterfly generations. Further research has also told us how rescue works - the mutation makes male butterflies in a different way that stops them being killed.

Recent work by a Japanese group observed the same type of evolutionary event in a different bacteria/insect interaction in a different part of the world. Here, the insect was a lacewing, and the male rescue mutation took 4-5 years to establish - very fast even if not quite as quick. We call these independent but similar events cases of convergent evolution - and they allow us a wonderful opportunity into understanding whether natural selection takes the same route to 'solve' the same problem - and whether evolution in response to these parasites hits a single aspect of host biology - or many.

This study will examine this study system in order to determine if the outwardly similar event (evolution to rescue males) has the same target or whether these evolutionary events actually involve many different aspects of male/female development. We will use state of the art genomic technology to determine whether the gene changes that rescue male lacewings are of the same kind that rescue male butterflies.

Further, we can ask if the dynamics of these super fast evolutionary events is the same in different cases - or whether it depends on the properties of the particular symbiont. We predict it will be different in this case, as the symbionts affect on the host differ in some important ways.

Finally, we ask if the rescue mutation affects the fertility and fecundity of male and female adults. If it does, then this implies that how male and females are is not simply a product of sexual selection - of competition for mates or selection to produce offspring - but also selection to avoid sex specific parasitism.

The team brings together complementary skills. The Japanese group brings expertise of the study system, and vital historical samples and data that allow us to infer evolution directly. The UK group brings expertise in the genetic analysis of evolutionary change. Together, they can solve a long standing puzzle.

Biological control companies represent the principle non-academic group that will benefit from this research. Lacewings are voracious predators that are widely mass cultured and sold to help control aphid and lepidoptera pests. The genomic resources developed in this project will represent the first for a lacewing. In parallel with other systems, developing genomic understanding allows more targeted development and breeding of strains that will be more efficacious in biocontrol. For instance, the male-killing trait under study may be harnessed to improve mass culture, where the size of the female population is key for productivity. The genetic markers and genomic knowledge may additionally be used to develop more efficient strains in application in glass house and field settings.

Together, the resources would allow biocontrol to reduce the per unit cost of production of this agent, and the efficiency with which it supplies control.

UK competitiveness will also benefit from this research in terms of providing new collaborations with Japanese investigators, and training of early career scientists in next generation sequencing and bioinformatic skills that are becoming widely used in health and food science research.