How the Aridification of Australia Structured the Biogeography and Influenced the Diversification of a Large Lineage of Australian Cicadas

Genetic Structure of Monochamus alternatus (Hope) in Qinling-Daba Mountains and Expansion Trend: Implications for Pest Prevention and Management

Pine wilt disease (PWD), caused by Bursaphelenchus xylophilus, severely threatens global pine forests. Monochamus alternatus is the primary vector of B. xylophilus in East Asia. Understanding the population structure and evolutionary forces of vector insects is critical for establishing effective PWD management strategies. The present work explores the genetic structure and phylogenetic relationships of 20 populations of M. alternatus from the Qinling-Daba Mountains (QDM) in China using the mitochondria DNA dataset, supplemented by ecological niche modeling (ENM). All M. alternatus populations were categorized into three phylogeographic clusters (Clade A, Clade B, and Clade C), with Clade A and Clade B corresponding to the western and eastern QDM, respectively. The results of divergence time estimation concur with environmental changes induced by Quaternary glacial climate oscillations in QDM of China. M. alternatus populations exhibited significant genetic differentiation, with expansion in their population size. Ecological niche modeling (ENM) demonstrated that precipitation and temperature significantly influence the distribution of M. alternatus and the species is anticipated to grow into higher latitude and higher altitude regions in the future. In a nutshell, exploring the genetic structure and evolutionary dynamics of M. alternatus can provide valuable insights into the prevention and occurrence of B. xylophilus. These findings also serve as a reference for research on population differentiation and phylogeography of other species in QDM and adjacent areas.

Genetic divergence, population differentiation and phylogeography of the cicada Subpsaltria yangi based on molecular and acoustic data: an example of the early stage of speciation?

Background

Geographical isolation combined with historical climatic fluctuations have been identified as two major factors that contribute to the formation of new species. On the other hand, biotic factors such as competition and predation are also able to drive the evolution and diversification of organisms. To determine whether geographical barriers contributed to population divergence or speciation in the rare endemic cicada Subpsaltria yangi the population differentiation, genetic structure and phylogeography of the species were investigated in the Loess Plateau and adjacent areas of northwestern China by analysing mitochondrial and nuclear DNA and comparing the calling song structure of 161 male individuals.

Results

The results reveal a low level of genetic differentiation and relatively simple phylogeographic structure for this species, but two independent clades corresponding to geographically isolated populations were recognised. Genetic and geographical distances were significantly correlated among lineages. Results of divergence-time estimation are consistent with a scenario of isolation due to glacial refugia and interglacial climate oscillation in northwestern China. Significant genetic divergence was found between the population occurring in the Helan Mountains and other populations, and recent population expansion has occurred in the Helan Mountains and/or adjacent areas. This population is also significantly different in calling song structure from other populations.

Conclusions

Geographical barriers (i.e., the deserts and semi-deserts surrounding the Helan Mountains), possibly coupled with related ecological differences, may have driven population divergence and allopatric speciation. This provides a possible example of incipient speciation in Cicadidae, improves understanding of population differentiation, acoustic signal diversification and phylogeographic relationships of this rare cicada species of conservation concern, and informs future studies on population differentiation, speciation and phylogeography of other insects with a high degree of endemism in the Helan Mountains and adjacent areas.

Electronic supplementary material

The online version of this article (10.1186/s12862-018-1317-8) contains supplementary material, which is available to authorized users.

Miocene biome turnover drove conservative body size evolution across Australian vertebrates

On deep time scales, changing climatic trends can have a predictable influence on macroevolution. From evidence of mass extinctions, we know that rapid climatic oscillations can indirectly open niche space and precipitate adaptive radiation, changing the course of ecological diversification. These dramatic shifts in the global climate, however, are rare events relative to extended periods of protracted climate change and biome turnover. It remains unclear whether during gradually changing periods, shifting habitats may instead promote non-adaptive speciation by facilitating allopatry and phenotypic conservatism. Using fossil-calibrated, species-level phylogenies for five Australian radiations comprising more than 800 species, we investigated temporal trends in biogeography and body size evolution. Here, we demonstrate that gradual Miocene cooling and aridification correlates with the restricted phenotypic diversification of multiple ecologically diverse vertebrate groups. This probably occurred as species ranges became fractured and isolated during continental biome restructuring, encouraging a shift towards conservatism in body size evolution. Our results provide further evidence that abiotic changes, not only biotic interactions, may act as selective forces influencing phenotypic macroevolution.