Description
The legume genus Astragalus contains some of the highest levels of morphological diversity in plants and has the highest diversity accumulation known. In addition, Astragalus lineages possess toxic secondary compounds which are predicted to deter herbivory. Although the reasons behind the rapid speciation of this genus are uncertain, it is predicted that the specialist seed beetles that oviposit their eggs on the seeds of Astragalus decrease the fitness of this plant. Despite rapid speciation in the plant, the specialist seed beetle Acanthoscelides pullus is able to successfully live on approximately 25 known species of Astragalus which are generally geographically isolated. If coevolution is driving speciation in the beetles and plants, one prediction is that host association will be a better predictor of barriers to gene flow (e.g. migration rates or reproductive isolation) than geography. On the other hand, geographic isolation alone would only promote allopatric speciation in association with geographic distance through the evolution of reproductive barriers between population attributed genetic drift. In order to measure the relative role of host plant and geography in lineage diversification within Ac. pullus, reproductive isolation experiments were performed to see if geographically isolated populations of beetle or beetles reared from different host plants in the field are able to mate and lay viable eggs that develop into hybrid offspring. Preliminary data suggest that both may play a role in the evolution of reproductive isolation, as Ac. pullus displays reproductive isolation between isolated populations and between different host plants.
Measuring genetic divergence of endemic seed beetles Acanthoscelides pullus through reproductive isolation
The legume genus Astragalus contains some of the highest levels of morphological diversity in plants and has the highest diversity accumulation known. In addition, Astragalus lineages possess toxic secondary compounds which are predicted to deter herbivory. Although the reasons behind the rapid speciation of this genus are uncertain, it is predicted that the specialist seed beetles that oviposit their eggs on the seeds of Astragalus decrease the fitness of this plant. Despite rapid speciation in the plant, the specialist seed beetle Acanthoscelides pullus is able to successfully live on approximately 25 known species of Astragalus which are generally geographically isolated. If coevolution is driving speciation in the beetles and plants, one prediction is that host association will be a better predictor of barriers to gene flow (e.g. migration rates or reproductive isolation) than geography. On the other hand, geographic isolation alone would only promote allopatric speciation in association with geographic distance through the evolution of reproductive barriers between population attributed genetic drift. In order to measure the relative role of host plant and geography in lineage diversification within Ac. pullus, reproductive isolation experiments were performed to see if geographically isolated populations of beetle or beetles reared from different host plants in the field are able to mate and lay viable eggs that develop into hybrid offspring. Preliminary data suggest that both may play a role in the evolution of reproductive isolation, as Ac. pullus displays reproductive isolation between isolated populations and between different host plants.