Print PageUnderstanding the circumstances which promote or hinder speciation is critical to the study of ecological diversity and niche utilization. The ecological speciation model describes how populations may become reproductively isolated by means of adaptation to different ecological niches. Many laboratory experiments have studied speciation by creating divergent strains of organisms, and then after some time, testing for reproductive isolation. Few, however, holistically observe the effects of divergent selection on multiple stages of reproductive isolation. We subjugated Tribolium castaneum to a novel food resource for 5 years (35-40 generations) and tested for pre-mating, post-copulatory, and post-zygotic isolation between beetles from the ancestral (wheat flour) and novel (corn flour) resource lineages.
Results/Conclusions
Our results indicate that pre-mating isolation is incomplete and assymetrical. Females adapted to the ancestral resource preferred conspecific males but females adapted to the novel resource did not show a significant preference for either male type. We did not find post-copulatory isolation: when virgin females were mated with either a conspecific or heterospecific male, those from the novel habitat laid more eggs when mated with heterospecifics, and those from the ancestral habitat showed no difference in egg laying rate. Survival rates of the offspring (a measure of post-zygotic isolation) was dependent on maternal lineage and was not affected by paternal lineage. Thus, females adapted to the novel resource did not have strong mate preference but laid more eggs when mated with ancestral males even though the male type did not affect offspring survival. Our study indicates adaptation to a novel resource does not necessarily promote reproductive isolation and that multiple stages of reproductive isolation may evolve independently, possibly resulting in complex and varied niche utilization.
