Evolution of developmental plasticity and the potential of host shift in the seed beetle: Insights from laboratory evolution experiments

Expansion of the host range in phytophagous insects, followed by the specialisation on novel hosts, encompasses changes in many aspects of insects' behaviour, physiology, and the interaction between their life-history features. Here, we analyse the roles of insects' developmental plasticity in the process of host shift. Using laboratory populations of the seed beetle (Acanthoscelides obtectus), which have evolved on both optimal (common beans) and suboptimal (chickpea) plant hosts for more than 35 years, we experimentally replicated the process of host shift and analysed the patterns of short-term and long-term life-history responses to host variation. In order to test whether selection for increased plasticity has an effect on host shifting processes, we used existing bean and chickpea adapted populations to establish new populations in which the host plant offered for insect development was changed each generation (for 13 generations). To test the potential for a short-term plastic response, beetles from each laboratory population were raised on both hosts for one generation. Results showed that, in contrast to the populations that evolved on beans, which maintained high levels of developmental plasticity, long-term host switching to chickpeas was accompanied with specialisation of pre-adult viability with a simultaneous increase in fecundity. Populations evolved on alternate plant hosts that revealed similar plasticity patterns as their ancestral populations. These results suggest that short-term plastic responses could determine the paths of long-term evolution of life-history plasticity. However, more time could be needed for plasticity to evolve differently from the initial responses.