Least speciose among the most speciose: Natural history correlates of monospecific and bispecific genera of Rodentia and Soricomorpha.

Monospecific and bispecific genera are of special concern as they represent unique phylogenetic/evolutionary trajectories within larger clades. In addition, as phylogenetically older taxa are supposed to be exposed to higher rarity and extinction risk, monospecific and bispecific genera may be intrinsically more prone to extinction risks than multispecies genera, although extinction risks also depend on the ecological and biological strategy of the species. Here, the distribution across biogeographical zones and the levels of threat to 2 speciose orders of mammals (monospecific and bispecific genera of Rodentia and Soricomorpha) are investigated in order to highlight major patterns at the worldwide scale. In Rodentia, 39.7% of the genera (n = 490) were monospecific and 17.9% were bispecific. In Soricomorpha, 44.4% of the total genera (n = 45) were monospecific and 15% were bispecific. There was a positive correlation between the number of monospecific genera and the total number of genera per family. Peaks of monospecific and bispecific genera richness were observed in Neotropical, Oriental and Afrotropical regions in rodents and in the Palearctic region in soricomorphs. Range size was significantly uneven across biogeographic region in rodents (with larger ranges in Nearctic and Oriental regions and smaller ranges in the Australian region), but there was no difference across biogeographic regions in terms of range size in soricomorphs. Most of the monospecific and bispecific genera occurred in forest habitat in both taxa. The frequency distribution of the monospecific and bispecific genera across IUCN categories did not differ significantly from the expected pattern using the total rodent genera and the multispecies genera.

On monospecific genera in prokaryotic taxonomy.

A monospecific genus contains a single species ever since it was proposed. Though formally more than half of the known prokaryotic genera are monospecific, we pick up those which actually raise taxonomic problems by violating monophyly of the taxon within which it resides. Taking monophyly as a guiding principle, our arguments are based on simultaneous support from 16S rRNA sequence analysis and whole-genome phylogeny of prokaryotes, as provided by the LVTree Viewer and CVTree Web Server, respectively. The main purpose of this study consists in calling attention to this specific way of global taxonomic analysis. Therefore, we refrain from making formal emendations for the time being.