Genetic variation corroborates subspecific delimitation in the Namib fog-basking beetle, Onymacris unguicularis (Haag) (Tenebrionidae, Coleoptera)

Trip Lamb,Jason Bond,Rachel Pollard

doi:10.3897/zookeys.353.6228

Abstract

The fog-basking beetle, Onymacris unguicularis (Haag, 1875), is currently listed as a polytypic form comprising two subspecies. A flightless substrate specialist, the beetleis endemic to vegetationless dunes in the Namib, where southern populations constitute the nominate subspecies, O. u. unguicularis, and populations some 300 km to the north compose O. u. schulzeae Penrith, 1984. Their taxonomic descriptions are based on minor differences in pronotal and prosternal shape, and the phylogenetic validity of these subspecies has yet to be ascertained. Here we reassess the polytypic status of O. unguicularis by (1) examining diagnostic phenotypic characters in conjunction with a geometric morphometric analysis, and (2) conducting phylogenetic analysis of mitochondrial DNA sequences. Our results confirm pronotal and prosternal differences, which are complemented by geometric morphometric resolution of the subspecies. Phylogenetic analysis recovered two reciprocally monophyletic lineages that exhibit perfect phylogeographic congruence with phenotypic variation. Our genetic data identify southern and northern populations as distinct lineages, corroborate morphometric data regarding subspecific delimitation, and therefore support the recognition of O. u. unguicularis and O. u. schulzeae as valid taxa under the general lineage concept.

Highlights

Darkling beetles figure prominently in the arthropod fauna of Africa’s Namib Desert, where they compose ~80% of all coleopterans (Louw 1983)
Penrith’s (1984) view of subspecies reflects the classic use of this taxonomic category in recognizing “geographic forms which cannot rank as full species” by noting that her morphological diagnosis could not “on the present evidence, separate the northern population more than subspecifically from southern populations.”
In the geometric morphometric analysis, the first two principal components based on the non-uniform components of dorsal shape account for 78.54% of the variation between subspecies

Summary

Introduction

Darkling beetles (family Tenebrionidae) figure prominently in the arthropod fauna of Africa’s Namib Desert, where they compose ~80% of all coleopterans (Louw 1983). Onymacris unguicularis has been the subject of taxonomic investigation; Penrith (1984) examined morphological variation throughout the species’ range, which is apportioned south to north in a patchy network along the Namib’s coastal segment (Fig. 1). These flightless beetles exhibit further restriction, being habitually if not exclusively confined to vegetationless dunes within the desert’s major sand seas. Penrith (1984) identified phenotypic distinctions between northern vs southern populations, which are separated by ~300 km of duneless plains Based on their morphological differentiation and apparent absence of gene flow, she proposed northern and southern populations be recognized as subspecies (Figs 2–3). Penrith (1984) designated southern populations as the nominate subspecies and named the northern populations Onymacris unguicularis schulzeae—honoring Lieselotte Prozesky-Schulze, who first reported differences between northern/southern populations on the basis of larval characteristics (Schulze 1964). Penrith’s (1984) view of subspecies reflects the classic use of this taxonomic category in recognizing “geographic forms which cannot rank as full species” by noting that her morphological diagnosis could not “on the present evidence, separate the northern population more than subspecifically from southern populations.”

Methods

Results

Conclusion