Spatial and host related genomic variation in partially sympatric cactophagous moth species

Abstract

Surveys of patterns of genetic variation in natural sympatric and allopatric populations of recently diverged species are necessary to understand the processes driving intra‐ and interspecific diversification. The South American moths Cactoblastis cactorum, Cactoblastis doddi and Cactoblastis bucyrus are specialized in the use of cacti as host plants. These species have partially different geographic ranges and differ in patterns of host plant use. However, there are areas that overlap, particularly, in northwestern Argentina, where they are sympatric. Using a combination of genome‐wide SNPs and mitochondrial data we assessed intra and interspecific genetic variation and investigated the relative roles of geography and host plants on genetic divergence. We also searched for genetic footprints of hybridization between species. We identified three well delimited species and detected signs of hybridization in the area of sympatry. Our results supported a hypothetical scenario of allopatric speciation in the generalist C. cactorum and genetic interchange during secondary geographic contact with the pair of specialists C. bucyrus and C. doddi that probably speciated sympatrically. In both cases, adaptation to new host plants probably played an important role in speciation. The results also suggested the interplay of geography and host plant use as drivers of divergence and limiting gene flow at intra and interspecific levels.

Geography, climate and shifts in host plants distribution explain the genomic variation in the cactus moth

“…Climatic changes during the Quaternary also promoted complex phylogeographic patterns in others southern South American herbivorous insects, such as the grasshopper Dichroplus vittatus Bruner (Rosetti et al, 2022) Maps of environmental suitability estimated using ecological modeling suggested that the Chaco and northern Pampean regions harbored larger climatically suitable areas than other biogeographic regions such as the Yungas, Monte, Puna and Prepuna (Figure 1). Both C. doddi and C. bucyrus are found in the Prepuna and Monte regions where C. cactorum is absent, supporting the idea that disparate environmental/habitat conditions and disjunct host plant distributions played a role in divergence within C. cactorum and closely related species (Poveda-Martıńez et al, 2022). Overall, these findings suggest that intraspecific diversification within this group of closely related herbivorous insects have been strongly influenced by shifts in the distribution of host species in response to Quaternary climate dynamics.…”

“…SNPs under selection were identified using Bayescan v.2.1 (Foll and Gaggiotti, 2008) (COI) (mtDNA) was amplified using primers C1-J-2183 and PatII. Amplifications, PCR-product purification and sequencing were performed as detailed in Poveda-Martıńez et al (2022).…”

Genomic and ecological evidence shed light on the recent demographic history of two related invasive insects

“…Although there is a certain degree of overlap in the distributions of host cacti across sampling sites, host plant preferences and divergent selection may be an additional ecological factor promoting genetic differentiation as shown in the native range of the H. pungens species complex 25 . Host plant use and geographic isolation seem to be the main forces promoting intraspecific divergence in herbivorous insects 49 – 51 . Rapid genetic differentiation among invasive insect populations has recently been reported in the cotton mealybug Phenacoccus solenopsis Tinsley (Hemiptera: Pseudococcidae).…”

“…Although niche modeling analyses indicated that current climatic niches do not overlap between both invasive species, the models also depict a very plausible scenario in which both Hyp-C and Hyp-AP would spread to new areas and become sympatric under ongoing trends of climate change. Such range overlap may negatively affect management strategies since sympatry could facilitate hybridization, a frequent event documented in closely related species 51 , 54 , 55 . This hypothetical scenario would bring about a potential source of new genetic variation prompting adaptive changes in the recipient species 56 , triggering adaptive radiation in the cactus pest.…”

Genomic evidence for contrasting patterns of host‐associated genetic differentiation across shared host‐plant species in leaf‐ and bud‐galling sawflies

“…Unfortunately, comparative analyses of HAD are still rare and have been constrained by a lack of efficient genetic marker systems, as such comparisons necessarily must target groups containing multiple very closely related taxa (Dorchin et al, 2015; Forbes et al, 2017; Mlynarek & Heard, 2018). This obstacle has only recently been removed by rapid developments in high‐throughput sequencing methods and computation‐intensive bioinformatics, which in combination provide unprecedented possibilities for studying HAD in nonmodel organisms for which genomic resources have hitherto not been available (Cerca et al, 2021; Johnson, 2019; Poveda‐Martínez et al, 2020, 2022; Wachi et al, 2018).…”