Does the genome of a putatively specialist moth (Schinia gracilenta) contain a signal of the indigenous cultivation of its host plant (Iva annua)

Does the genome of a putatively specialist moth (Schinia gracilenta) contain a signal of the indigenous cultivation of its host plant (Iva annua)

When one species depends on one another for survival, they may have shared demographic histories. Further, when symbionts have shorter life spans, their rate of evolution may be quicker than that of their hosts. For this reason, detecting a recent demographic signal in a symbiont’s genome may often be easier than directly studying the host.

Here I study the slender flower moth (Schinia gracilenta) and its host plant, sumpweed (Iva annua). Sumpweed is thought to have been cultivated in North American ca. 5000 BC - AD 1700 and its range may have been expanded during this time. I collected S. gracilenta, Schinia rivulosa and Schinia thoreaui feeding on I. annua, Iva frutescens, Ambrosia trifida and Ambrosia artemisiifolia. I used Restriction-site Associated DNA sequencing (RAD-seq) to test whether S. gracilenta genomes contain signatures of a possible human-mediated I. annua range expansion. Using the RAD-seq results, I inferred a phylogenetic tree, generated population summary statistics, and estimated population structure.

I found no evidence that S. gracilenta has undergone a recent range expansion. This could be because its host I. annua was cultivated without a range expansion, or because its range expanded but S. gracilenta’s did not. However, I also found some S. gracilenta feeding on Ambrosia species and detected alleles that had introgressed into S. gracilenta from other Schinia species. It is possible, therefore, that S. gracilenta and I. annua do not have the strictly obligate symbiotic relationship required for detection of a host’s demographic histories.