Evolution across the adaptive landscape in a hyperdiverse beetle radiation.

The extraordinary diversification of beetles on Earth is a textbook example of adaptive evolution. Yet, the tempo and drivers of this super-radiation remain largely unclear. Here, we address this problem by investigating macroevolutionary dynamics in darkling beetles (Coleoptera: Tenebrionidae), one of the most ecomorphologically diverse beetle families (with over 30,000 species). Using multiple genomic datasets and analytical approaches, we resolve the long-standing inconsistency over deep relationships in the family. In conjunction with a landmark-based dataset of body shape morphology, we show that the evolutionary history of darkling beetles is marked by ancient rapid radiations, frequent ecological transitions, and rapid bursts of morphological diversification. On a global scale, our analyses uncovered a significant pulse of phenotypic diversification proximal to the Cretaceous-Palaeogene (K/Pg) mass extinction and convergence of body shape associated with recurrent ecological specializations. On a regional scale, two major Australasian radiations, the Adeliini and the Heleine clade, exhibited contrasting patterns of ecomorphological diversification, representing phylogenetic niche conservatism versus adaptive radiation. Our findings align with the Simpsonian model of adaptive evolution across the macroevolutionary landscape and highlight a significant role of ecological opportunity in driving the immense ecomorphological diversity in a hyperdiverse beetle group.

Century-old chromatin architecture revealed in formalin-fixed vertebrates.

Gene expression is regulated by changes in chromatin architecture intrinsic to cellular differentiation and as an active response to environmental stimuli. Chromatin dynamics are a major driver of phenotypic diversity, regulation of development, and manifestation of disease. Remarkably, we know little about the evolutionary dynamics of chromatin reorganisation through time, data essential to characterise the impact of environmental stress during the ongoing biodiversity extinction crisis (20th-21st century). Linking the disparate fields of chromatin biology and museum science through their common use of the preservative formaldehyde (a constituent of formalin), we have generated historical chromatin profiles in museum specimens up to 117 years old. Historical chromatin profiles are reproducible, tissue-specific, sex-specific, and environmental condition-dependent in vertebrate specimens. Additionally, we show that over-fixation modulates differential chromatin accessibility to enable semi-quantitative estimates of relative gene expression in vertebrates and a yeast model. Our approach transforms formalin-fixed biological collections into an accurate, comprehensive, and global record of environmental impact on gene expression and phenotype.