Conflict and complementarity of paleontological and molecular chronologies?

Evolutionary history studies depend on having reliable chronologies of macroevolutionary processes. Construction of such chronologies often yields discrepancies between paleontological and molecular dates, which are sometimes viewed as conflicting. Nevertheless, each macroevolutionary process is composed of two main phases: emergence of a trait or clade and success of that trait or clade, which differ in mechanisms, drivers, and types of evidence. Moreover, emergence may be observed as gene divergence (which may be trait-coding or trait-unrelated genes), trait emergence, and clade emergence; whereas success can be observed as increase in abundance, diffusion, and/or diversity or as overall persistence over geologic time. Therefore, to fully and correctly understand any macroevolutionary process, it is of paramount importance to understand what event each date refers to, and how dates of various events and their integration reveal the complexity of macroevolutionary processes. I demonstrate this through three examples: the chronological gap between oxygenic photosynthesis emergence and the Great Oxidation Event, the chronological gap between paleontological and molecular dates of angiosperm emergence, and the evolution of plant silicon accumulation.

Genetic constraints on microevolutionary divergence of sex-biased gene expression

The evolution of sex-specific phenotypes is an important dimension of diversification and local adaptation. The sex-dependent regulation of gene expression is considered a key genomic mechanism facilitating sex-dependent adaptation. In many species, genes with male-biased expression evolve faster in DNA sequence and expression level than genes with female-biased or sexually monomorphic expression. While positive selection may be responsible for rapid DNA sequence evolution, why expression of male-biased genes also evolves rapidly remains unclear. Beyond sex differences in selection, some aspects of the genetic architecture of gene expression could contribute to the rapid evolution of male-biased gene expression. First, male-biased genes might simply have greater standing genetic variance than female-biased genes. Second, male-biased genes could be less constrained by pleiotropy, either within or between sexes. Here, we evaluate these alternative explanations on an intraspecific scale using a series of quantitative genetic experiments conducted on natural variation in male and female gene expression in the fly Drosophila serrata . Male-biased genes had significantly higher genetic variance than female-biased genes and were generally more narrowly expressed across tissues, suggesting lower within-individual pleiotropy. However, consistent with stronger constraints due to between-sex pleiotropy, their between-sex genetic correlations, r MF , were higher than for female-biased genes and more strongly negatively associated with sex bias. Using an extensive clinal dataset, we tested whether sex differences in gene expression divergence among populations have been shaped by pleiotropy . Here too, male-biased gene divergence was more strongly associated with between-sex pleiotropy than was female-biased gene divergence. Systematic differences in genetic variance and pleiotropy may be important factors influencing sex-specific adaptation arising through changes in gene expression. This article is part of the theme issue ‘Linking local adaptation with the evolution of sex differences’.

Morphology and mitochondrial gene divergence in Hipposideros armiger armiger occurs only in China

In China, the status of

Chromosome Stability and Gene Loss in Cockroach Endosymbionts

ABSTRACT Insect endosymbiont genomes reflect massive gene loss. Two Blattabacterium genomes display colinearity and similar gene contents, despite high orthologous gene divergence, reflecting over 140 million years of independent evolution in separate cockroach lineages. We speculate that distant homologs may replace the functions of some eliminated genes through broadened substrate specificity.