Unraveling the diversification history of grasshoppers belonging to the "Trimerotropis pallidipennis" (Oedipodinae: Acrididae) species group: a hotspot of biodiversity in the Central Andes

Stable inversion clines in a grasshopper species group despite complex geographical history

Chromosomal inversions are known to play roles in adaptation and differentiation in many species. They involve clusters of correlated genes (i.e., loci in linkage disequilibrium, LD) possibly associated with environmental variables. The grasshopper "species complex" Trimerotropis pallidipennis comprises several genetic lineages distributed from North to South America in arid and semi-arid high-altitude environments. The southernmost lineage, Trimerotropis sp., segregates for four to seven putative inversions that display clinal variation, possibly through adaptation to temperate environments. We analysed chromosomal, mitochondrial and genome-wide single nucleotide polymorphism data in 19 Trimerotropis sp. populations mainly distributed along two altitudinal gradients (MS and Ju). Populations across Argentina comprise two main chromosomally and genetically differentiated lineages: one distributed across the southernmost border of the "Andes Centrales," adding evidence for a differentiation hotspot in this area; and the other widely distributed in Argentina. Within the latter, network analytical approaches to LD found three clusters of correlated loci (LD-clusters), with inversion karyotypes explaining >79% of the genetic variation. Outlier loci associated with environmental variables mapped to two of these LD-clusters. Furthermore, despite the complex geographical history indicated by population genetic analyses, the clines in inversion karyotypes have remained stable for more than 20 generations, implicating their role in adaptation and differentiation within this lineage. We hypothesize that these clines could be the consequence of a coupling between extrinsic postzygotic barriers and spatially varying selection along environmental gradients resulting in a hybrid zone. These results provide a framework for future investigations about candidate genes implicated in rapid adaptation to new environments.

Molecular phylogeny and species delimitation of the genus Tonkinacris (Orthoptera, Acrididae, Melanoplinae) from China

Tonkinacris is a small group in Acrididae. While a few species were occasionally sampled in some previous molecular studies, there is no revisionary research devoted to the genus. In this study, we explored the phylogeny of and the relationships among Chinese species of the genus Tonkinacris using the mitochondrial COI barcode and the complete sequences of ITS1 and ITS2 of the nuclear ribosomal DNA. The phylogeny was reconstructed in maximum likelihood and Bayesian inference frameworks, respectively. The overlap range between intraspecific variation and interspecific divergence was assessed via K2P distances. Species boundaries were delimitated using phylogenetic species concept, NJ tree, K2P distance, the statistical parsimony network as well as the GMYC model. The results demonstrate that the Chinese Tonkinacris species is a monophyletic group and the phylogenetic relationship among them is (T. sinensis, (T. meridionalis, (T. decoratus, T. damingshanus))). While T. sinensis, T. meridionalis and T. decoratus were confirmed being good independent species strongly supported by both morphological and molecular evidences, the validity of T. damingshanus was not perfectly supported by molecular evidence in this study.

The Galápagos Islands: biogeographic patterns and geology

In the traditional biogeographic model, the Galápagos Islands appeared a few million years ago in a sea where no other islands existed and were colonized from areas outside the region. However, recent work has shown that the Galápagos hotspot is 139 million years old (Early Cretaceous), and so groups are likely to have survived at the hotspot by dispersal of populations onto new islands from older ones. This process of metapopulation dynamics means that species can persist indefinitely in an oceanic region, as long as new islands are being produced. Metapopulations can also undergo vicariance into two metapopulations, for example at active island arcs that are rifted by transform faults. We reviewed the geographic relationships of Galápagos groups and found 10 biogeographic patterns that are shared by at least two groups. Each of the patterns coincides spatially with a major tectonic structure; these structures include: the East Pacific Rise; west Pacific and American subduction zones; large igneous plateaus in the Pacific; Alisitos terrane (Baja California), Guerrero terrane (western Mexico); rifting of North and South America; formation of the Caribbean Plateau by the Galápagos hotspot, and its eastward movement; accretion of Galápagos hotspot tracks; Andean uplift; and displacement on the Romeral fault system. All these geological features were active in the Cretaceous, suggesting that geological change at that time caused vicariance in widespread ancestors. The present distributions are explicable if ancestors survived as metapopulations occupying both the Galápagos hotspot and other regions before differentiating, more or less in situ.

Phylogeny and species delimitation of the genus Longgenacris and Fruhstorferiola viridifemorata species group (Orthoptera: Acrididae: Melanoplinae) based on molecular evidence

Phylogenetic positions of the genus Longgenacris and one of its members, i.e. L. rufiantennus are controversial. The species boundaries within both of L. rufiantennus+Fruhstorferiola tonkinensis and F. viridifemorata species groups are unclear. In this study, we explored the phylogenetic positions of the genus Longgenacris and the species L. rufiantennus and the relationships among F. viridifemorata group based on the 658-base fragment of the mitochondrial gene cytochrome c oxidase subunit I (COI) barcode and the complete sequences of the internal transcribed spacer regions (ITS1 and ITS2) of the nuclear ribosomal DNA. The phylogenies were reconstructed in maximum likelihood framework using IQ-TREE. K2P distances were used to assess the overlap range between intraspecific variation and interspecific divergence. Phylogenetic species concept and NJ tree, K2P distance, the statistical parsimony network as well as the generalized mixed Yule coalescent model (GMYC) were employed to delimitate the species boundaries in L. rufiantennus+F. tonkinensis and F. viridifemorata species groups. The results demonstrated that the genus Longgenacris should be placed in the subfamily Melanoplinae but not Catantopinae, and L. rufiantennus should be a member of the genus Fruhstorferiola but not Longgenacris. Species boundary delimitation confirmed the presence of oversplitting in L. rufiantennus+F. tonkinensis and F. viridifemorata species groups and suggested that each group should be treated as a single species.

Biogeographical patterns and processes in the genus group Scotussae (Acrididae: Melanoplinae): an integrative approach

A biogeographical study of the genus group Scotussae, a clade of grasshoppers endemic to the subtropical temperate region of the La Plata Basin, South America, was performed within a phylogenetic context to test whether wing reduction reflects evolutionary and ecological processes within the clade. We used an integrative biogeographical approach to determine the role of geohistorical events, geography, ecology and phylogenetic niche conservatism on the distribution and diversification processes of the group. We performed a total evidence phylogenetic analysis and tested the phylogenetic signal of ecological niche traits (niche optimum and niche breadth). We also assessed the degree to which phylogenetic distance is correlated with geographical and ecological niche traits and we used BioGeoBEARS to estimate ancestral ranges. The results provided evidence for phylogenetic niche conservatism as well as a significant association between phylogeny and both geographical and, more strongly, ecological traits. Two main clades were clearly associated with wing development, and evidence points to the evolutionary and ecological processes within these two groups being different. The Brachypterous clade shows evidence that allopatric speciation was the main source of diversification, while for the Macropterous clade sympatric speciation seems more likely.