Population genetic structure and genetic diversity of the threatened White Mountain arctic butterfly (Oeneis melissa semidea)

Moths passing in the night: Phenological and genomic divergences within a forest pest complex

Temporal separation of reproductive timing can contribute to species diversification both through allochronic speciation and later reinforcement of species boundaries. Such phenological differences are an enigmatic component of evolutionary divergence between two major forest defoliator species of the spruce budworm complex: Choristoneura fumiferana and C. occidentalis. While these species interbreed freely in laboratory settings, natural hybridization rates have not been reliably quantified due to their indistinguishable morphology. To assess whether temporal isolation is contributing to reproductive isolation, we collected adult individuals throughout their expected zone of sympatry in western Canada at 10-day intervals over two successive years, assigning taxonomic identities using thousands of single nucleotide polymorphisms. We found unexpectedly broad sympatry between C. fumiferana and C. occidentalis biennis and substantial overlap of regional flight periods. However, flight period divergence was much more apparent on a location-by-location basis, highlighting the importance of considering spatial scale in these analyses. Phenological comparisons were further complicated by the biennial life cycle of C. o. biennis, the main subspecies of C. occidentalis in the region, and the occasional occurrence of the annually breeding subspecies C. o. occidentalis. Nonetheless, we demonstrate that biennialism is not a likely contributor to reproductive isolation within the species complex. Overall, interspecific F1 hybrids comprised 2.9% of sequenced individuals, confirming the genomic distinctiveness of C. fumiferana and C. occidentalis, while also showing incomplete reproductive isolation of lineages. Finally, we used F ST-based outlier and genotype-environment association analyses to identify several genomic regions under putative divergent selection. These regions were disproportionately located on the Z linkage region of C. fumiferana, and contained genes, particularly antifreeze proteins, that are likely to be associated with overwintering success and diapause. In addition to temporal isolation, we conclude that other mechanisms, including ecologically mediated selection, are contributing to evolutionary divergence within the spruce budworm species complex.

Comparison of Genetic Structure between Endangered and Common Butterflies, Ypthima multistriata and Y. argus (Lepidoptera; Nymphalidae), Inhabiting Japan

Genetic structures of two closely related butterflies, Ypthima multistriata and Y. argus, inhabiting Japan were compared based on the mitochondrial cytochrome c oxidase subunit I (COI) sequences. The former species is classified as a vulnerable species and exhibits a characteristic pattern of voltinism: univoltine and bivoltine populations are distributed in a scattered manner. The latter species is common and has a normal geographical pattern of voltinism: the number of annual generations is correlated with latitude. Our genetic analyses of these two species yielded contrasting results: a spatial analysis of molecular variance (SAMOVA) and F_ST between each pair of populations revealed a locally fragmented genetic structure for Y. multistriata, compared to three distinct geographic groups of Y. argus within which range-wide gene flow occurs. Although Y. argus is a common species, only the southernmost populations in Japan had higher genetic diversity, while the other populations had the same or lower levels of genetic diversity, compared to Y. multistriata. These results indicate that: 1) the degree of fragmentation of Y. multistriata populations was higher; however, markedly lower genetic diversity was not found, and 2) although Y. argus is a common species, its populations may not be genetically robust. In addition, AMOVA revealed a relationship between voltinism and genetic variation in Y. multistriata. This result suggests a phylogenetic constraint of voltinism in this butterfly.

Population genetic structure and assessment of allochronic divergence in the Macoun’s Arctic (Oeneis macounii) butterfly

Patterns in the genetic variation of species can be used to infer their specific demographic and evolutionary history and provide insight into the general mechanisms underlying population divergence and speciation. The Macoun’s Arctic (Oeneis macounii (W.H. Edwards, 1885); MA) butterfly occurs across Canada and parts of the northern United States in association with jack pine (Pinus banksiana Lamb.) and lodgepole pine (Pinus contorta Douglas ex Loudon). MA’s current distribution is highly fragmented, and the extent of reproductive isolation among allopatric populations is unknown. Furthermore, although MA is biennial, adults emerge every year in some populations. These populations presumably consist of two alternate-year cohorts, providing the opportunity for sympatric divergence via allochronic isolation. Using mitochondrial DNA (mtDNA) and amplified fragment length polymorphism (AFLP) markers, we analyzed MA’s genetic structure to determine the current and historical role of allopatric and allochronic isolation in MA population divergence. Both markers revealed high diversity and a low, but significant, degree of spatial structure and pattern of isolation by distance. Phylogeographic structure was generally absent, with low divergence among mtDNA haplotypes. MA likely exhibits low dispersal and gene flow among most allopatric populations; however, there was no evidence of differentiation resulting from allochronic isolation for sympatric cohorts.

Effect of Climatic Conditions and Land Cover on Genetic Structure and Diversity of Eunica tatila (Lepidoptera) in the Yucatan Peninsula, Mexico

Fragmentation is the third cause of the biodiversity declination. Population genetic studies using Lepidoptera as the model species in the context of loss of habitat are scarce, particularly for tropical areas. We chose a widespread butterfly from Mexico as the model species to explore how changes of habitat characteristics (undisturbed forest, anthropogenic disturbances, and coastal areas), and climatic conditions affect genetic diversity and population structure. The Nymphalidae Eunica tatila is a common species in the Yucatan Peninsula considered to be a bio-indicator of undisturbed tropical forest, with migratory potential and a possible sex-biased dispersal. We genotyped 323 individuals collected in eight undisturbed areas, using four Inter Simple Sequence Repeats primers. Results show a high genetic diversity and no population structure. Temperature and shrub density present a positive and significant relationship with polymorphism values. Furthermore, our results show the positive effect of surrounding forest habitat on genetic diversity, confirming that E. tatila is a bio-indicator of undisturbed tropical forest. We found evidence of sex-biased dispersal. This paper represents one of the few studies on population genetics of tropical butterfly in a fragmented landscape and is, therefore, an important step in understanding the impact of habitat fragmentation on the risk of a butterflies’ decline.

Genetic divergence of isolated populations of the native micromoth Bucculatrix mirnae (Lepidoptera: Bucculatricidae) in the arid environments of Northern Chile

Analysis of maternally inherited genes is especially helpful in population studies of host-specialized insects, as female dispersal is key to find an adequate host plant to ensure larval survival. Bucculatrix mirnae (Lepidoptera: Bucculatricidae) is a little-known Neotropical micromoth native to the arid environments of northern Chile whose hypermetamorphic larvae are miners and skeletonizers on leaves of two species of Baccharis (Asteraceae) shrubs. This micromoth has been detected in three isolated locations embracing a narrow geographic range: two from the coastal valleys of the Atacama Desert near sea level and one from the western slopes of the Andes at about 3000 m elevation. As the dispersal of B. mirnae is mostly restricted to the small adult stage, the altitudinal gradient and desert areas among the three localities could be effective barriers, triggering genetic differentiation among populations. Sequences of the DNA barcode fragment of the cytocrome oxidase subunit I mitochondrial gene were analyzed to assess for the first time the patterns of genetic variation of B. mirnae. Fifteen haplotypes, each exclusive to one locality, were found in the 71 specimens analyzed. Genetic divergence (K2P) between haplotypes of different localities was at least 2.0%. A Bayesian analysis with sequences of congeneric species grouped all the B. mirnae haplotypes in a clade, in which three well-supported locality-specific haplogroups were found. In concordance with this pattern, an analysis of molecular variance showed that the highest genetic variation was found among populations. Furthermore, all the population pairwise comparisons (F_ST) were significant. These results suggest that female migration between isolated populations of B. mirnae is absent. This pattern must be considered in the current scenario of habitat destruction and modification in the arid environments of northern Chile.