Cretaceous origin of giant rhinoceros beetles (Dynastini; Coleoptera) and correlation of their evolution with the Pangean breakup

Abstract

The giant rhinoceros beetles (Dynastini, Scarabaeidae, Coleoptera) are distributed in tropical and temperate regions in Asia, America and Africa. Recent molecular phylogenetic studies have revealed that the giant rhinoceros beetles can be divided into three clades representing Asia, America and Africa. Although a correlation between their evolution and the continental drift during the Pangean breakup was suggested, there is no accurate divergence time estimation among the three clades based on molecular data. Moreover, there is a long chronological gap between the timing of the Pangean breakup (Cretaceous: 110-148 Ma) and the emergence of the oldest fossil record (Oligocene: 33 Ma). In this study, we estimated their divergence times based on molecular data, using several combinations of fossil calibration sets, and obtained robust estimates. The inter-continental divergence events among the clades were estimated to have occurred about 99 Ma (Asian clade and others) and 78 Ma (American clade and African clade), both of which are after the Pangean breakup. These estimates suggest their inter-continental divergences occurred by overseas sweepstakes dispersal, rather than by vicariances of the population caused by the Pangean breakup.

Synopsis of the cyclocephaline scarab beetles (Coleoptera, Scarabaeidae, Dynastinae)

“…Rowland and Miller (2012) performed a four-gene phylogenetic analysis of Dynastini (Dynastinae) that included one Cyclocephala exemplar. This analysis was useful for recovering subtribal relationships within Dynastini, but the relationship of Dynastini to Cyclocephalini ( Cyclocephala ) and Pentodontini ( Orizabus ) was unresolved (Rowland and Miller 2012, see also Jin et al 2016). …”

Demographic analysis of cyanobacteria based on the mutation rates estimated from an ancient ice core

“…The possibility of contamination from modern DNA samples was also evaluated using a molecular evolutionary approach. Jin et al (2016) demonstrated that the Fig. 5 Bayesian skyline plots that show the Ne×t, where Ne stands for the effective population size and t stands for the generation intervals over time in cyanobacterial OTU4 and OTU9.…”

Evolution of horn length and lifting strength in the Japanese rhinoceros beetleTrypoxylus dichotomus

“…Males have a short, curved horn extending from the dorsal prothorax and a much longer, four-tined “pitchfork” shaped horn extending from the top of the head (Figure 2). Males of the two closest sister species, Xyloscaptes davidis and Allomyrina pfeifferi (Rowland and Miller 2021; Dutrillaux et al, 2013; Jin et al, 2016; Yang et al, 2020), have a much smaller, two-tined forked horn extending from the center of the head. Both X. davidis and A. pfeifferi are rare and very poorly understood outside of systematics.…”