Systematics of southern African Anostostomatidae (Orthoptera) based on morphological and molecular data

Abstract

The eight southern African King Cricket genera, namely Bochus, Borborothis, Henicus, Libanasa, Libanasidus, Nasidius, Onosandridus, and Onosandrus are redescribed from type and museum material and a key to the genera is provided. Additionally, the status of Libanasidus impicta is investigated and species characteristics confirmed. A key to the two Libanasidus species is also provided. No morphological support for these eight southern African anostostomatid genera was attained with cladistic analysis, despite the incorporation of taxonomically important characters. High levels of homoplasy and possible incorrect species placement, resulting in character ambiguity within genera, renders many of the diagnostic characters of this group ineffective for resolving generic relationships. Genetic data based on the large ribosomal subunit (16S) did provide phylogenetic resolution between six of the genera with good bootstrap support. This confirmed speculation by previous authors as to the ancestral nature of Bochus and Borborothis to other genera within the Anostostomatini tribe, as well as the placement of Libanasa within a separate tribe, the Lutosini. The recent merge of the genus Platysiagon with Libanasa is also provisionally supported. Close association was obtained between Libanasidus and Nasidius with Onosandrus being more related to Bochus and Borborothis, supported by the lack of sexual dimorphism in Onosandrus and Borborothis. The phylogenetic position of the genera Henicus and Onosandridus remains unresolved. It is suggested that the designation of the eight anostostomatid genera in southern Africa are valid, but that species placement within these genera need to be revised to resolve character conflict. Focusing on the genetic and morphometric structuring within the famous Parktown Prawn, Libanasidus vittatus from southern Africa consistently suggests two main population assemblages. These correspond to a large North-South ranging population including individuals west of the prominent escarpment, and a smaller population including individuals from the eastern side of the escarpment. COI sequence data recovers two clades representing these two populations with good bootstrap support in likelihood, parsimony, Bayesian and distance analyses. Genetic divergence between the two clades averaged 3.3%, while population parameters estimated using maximum likelihood methods show low migration rates corresponding to less that one female migration per generation. A priori morphometric analyses including PCA&clustering methods show no biologically meaningful variation, suggesting that the two clades recovered represent cryptic sibling species. Inferring a molecular clock of 2% divergence per million years used for sister taxa, signifies isolation of the eastern population at 1.65 mya. A posteriori morphometric analyses confirmed the genetic results, based on 11 size-related measurements. This study provides a starting point for further work on the taxonomy, behaviour and ecology of these fascinating insects. Cytogenetics, multiple genetic loci and geometric morphometrics will provide useful insight into the taxonomic status of the 51 anostostomatid species in southern Africa and is promoted for further studies.