Forest fragmentation may endanger a plant-insect interaction: the case of the highly specialist native aphid Neuquenaphis staryi in Chile

The diversity and distribution of the genetic variation in forest phytophagous insect populations can be highly sensitive to forest fragmentation. This should be particularly evident for monophagous insects living on endangered host plants. The aphid Neuquenaphis staryi uses the tree Nothofagus alessandrii, commonly named Ruil, exclusively as a host. Nothofagus alessandrii is an endemic and endangered species whose distribution is highly fragmented in the unique Maulino temperate forests of the coastal range of Central Chile. Here, we provide proof of the specialist status of N. staryi and provide evidence on the genetic diversity and structure of their populations sampled on distinct remnant fragments of the Ruil forest. A sample representing 480 individuals collected from five fragments of Ruil forests revealed 147 distinct multilocus genotypes at six microsatellite loci. Clonal diversity and other genetic parameters were consistent with aphids reproducing by cyclic parthenogenesis and showed few signs of diversity loss. The genetic differentiation among populations was significant as evidenced by the presence of at least three genetic clusters, which are mostly explained by low migration due to geographic barriers that restrict aphid dispersion. Our results suggest that forest fragmentation imposes genetic discontinuities on a highly specialised phytophagous insect, which may have important implications for the conservation status of this ancient aphid-plant interaction.