Landscape heterogeneity and the reconfiguration of host plant
distributions as a consequence of Quaternary climate oscillations are
suggested to play a determinant role in shaping the evolutionary history
of herbivorous insects. The cactus moth, Cactoblastis cactorum, is a
southern South American phytophagous insect specialized in the use of
cacti as feeding and breeding resources. It can be found across broad
latitudinal and longitudinal gradients feeding on diverse native Opuntia
species as well as the exotic and cultivated species Opuntia
ficus-indica. Using high-throughput sequence data for the nuclear genome
and mitochondrial DNA sequencing, we investigated patterns of genomic
variation of C. cactorum across its native distribution. We integrated a
demographic modeling approach for inferring gene flow and divergence
times between C. cactorum populations, within a landscape genomic
framework, to test alternative spatially-explicit hypotheses of past and
current population connectivity based on climatically suitable areas for
the focal species and distributions of host plants. Regions currently
exhibiting high genomic diversity were evaluated for congruence with
areas where suitable climatic conditions remained stable from the last
glacial maximum to the present. Results revealed significant population
structure across the range of C. cactorum, that can be explained by the
spatial configuration of persistently suitable environmental conditions
and host plant ranges during interglacial and glacial periods. Moreover,
genomic data supported a hypothesis of long-term habitat stability in
the northern regions of the distribution that served as a refuge for C.
cactorum, enabling the accumulation and maintenance of high levels of
genetic diversity over time.