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Social evolution and genomic investigation of breeding adaptation in burying beetles
Tsai, Isheng Jason
Competition shapes the evolution of life and determines how organisms live now. Carcasses are nutritious but unpredictable and transient resources that drive intense competition among scavengers and microbiomes. Burying beetles (Coleoptera: Silphidae: Nicrophorus) are one of the unique scavenging insects which use small vertebrate carcasses as the sole resources to reproduce. To compete against the major interspecific competitor, blowflies, they formed cooperative groups on carcasses. This study used a series of field and laboratory experiments to clarify the mechanism of group formation in burying beetles and found that interspecific competition drove Nicrophorus nepalensis to use a sulfur-containing organic volatile compound, dimethyl disulfide (DMDS) as the cue to indicate interspecific competition and form social groups on carcasses. On the other hand, the interspecific competition also drove N. nepalensis to evolve two breeding types, i.e., continuous breeding (CB) and seasonal breeding (SB), among populations. To understand the transition in the molecular mechanism between two breeding types, I performed the genomic comparison among N. nepalensis and 14 Hexapoda species and the transcriptomic comparisons between two N. nepalensis populations. The results showed the insects of two breeding types had convergent evolution at gene levels, respectively, and N. nepalensis shared breeding-type specific genes with both breeding types. These two studies provide evidence to demonstrate how N. nepalensis adapt to interspecific competition in terms of cooperative behavior and also adjusting breeding seasons. When the pressure of interspecific competition increases, N. nepalensis shifts from intraspecific competition to cooperation to compete with interspecific competitors. Because N. nepalensis has both breeding-type specific gene features in its genome, N. nepalensis can adjust the breeding season to avoid interspecific competitors when the competitive pressure is too high. Differentiation in the length of breeding seasons implies N. nepalensis has local adaptation among populations. In future work, the study would be focused on the molecular evolution among populations using genomic data in order to further understand the local adaptation and its driving forces in N. nepalensis.
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