Research Article |
Corresponding author: Trip Lamb ( lamba@ecu.edu ) Academic editor: Aaron Smith
© 2017 Trip Lamb, Eugene Marais, Jason Bond.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Lamb T, Marais E, Bond JE (2017) A second locality for the Namib darkling beetle Onymacris brainei (Tenebrionidae, Coleoptera) and first report on its molecular phylogenetic placement. ZooKeys 687: 63-72. https://doi.org/10.3897/zookeys.687.13660
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Onymacris brainei Penrith, 1984 – the most recent species of Onymacris to be described – is known only from its type locality in the Namib Desert, adjacent to the Cunene River in northern Namibia. No additional specimens are known to have been collected beyond the type series. Herein, we report on eight specimens discovered at a second site near the original locality. DNA from four beetles was used to determine the phylogenetic placement of O. brainei among congeners, based on sequence data from one nuclear (histone III) and two mitochondrial (cox1, cox2) genes. Maximum likelihood analysis identifies O. brainei as a member of the ‘white’ Onymacris clade, in which it forms a strongly supported subclade with O. bicolor and O. marginipennis. More broadly, its phylogenetic placement augments previous molecular results that revealed a sister taxon relationship between the ‘white’ Onymacris and a second genus, Physadesmia. The paraphyly of Onymacris with respect to Physadesmia highlights a need for nomenclatural change, but revision should await acquisition of genetic data for the few species outstanding in both genera.
Adesmiini , Namib Desert, Onymacris , Tenebrionidae
The darkling beetle genus Onymacris is a diverse assemblage of fast-running diurnal species endemic to Africa’s Namib Desert and adjacent southwestern edges of the Kalahari. As substrate specialists, these beetles are restricted to loose sand that characterizes hummocks, dry riverbeds, and dune fields, where they occur in abundance and assume key ecological roles as detritivores (
‘White’ Onymacris are restricted to the northern Namib, where they are patchily distributed, often with limited geographic ranges. Onymacris brainei–the most recent member of the genus to be described (
To our knowledge, no other specimens or localities for O. brainei have been documented since its description. In 2015, some 30 years after Penrith and Müller’s expedition, we searched the general vicinity of the type locality in an attempt to update the status of O. brainei. Herein, we report on eight additional specimens taken from a second site. Importantly, these beetles provided a source of fresh tissue for DNA extraction, gene sequencing, and phylogenetic analysis. Hence we also offer the first report on the molecular phylogenetic placement of O. brainei among its congeners.
Rear legs from four of the eight beetles were preserved in RNAlater for subsequent DNA isolation using Qiagen’s DNeasy kit. The mitochondrial genes cytochrome oxidase I (cox1) and cytochrome oxidase II (cox2) and a nuclear gene (histone III, H3) were amplified using the primers and PCR conditions listed in Table
Gene | Primer | Annealing | Cycles | Reference |
---|---|---|---|---|
cox1 | TY-J-1460 | 50°C | 35 |
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TL2-N-3014 | ||||
C1-J-2183 | sequencing only | |||
cox2 | TL2-J-3037 | 50°C | 35 | |
TK-N-3785 | ||||
H3 | Hex AF | 61.5°C | 45 | Odgen and Whiting (2003) |
Hex AR |
DNA sequences for O. brainei were combined with sequence data previously generated for Onymacris (Table
GenBank accession numbers for adesmiine sequences used in the ML analysis.
Species | GenBank | GenBank | GenBank |
---|---|---|---|
cox1 | cox2 | H3 | |
Onymacris brainei | MF459686 | MF459688 | MF459690 |
Onymacris brainei | MF459687 | MF459689 | — |
O. bicolor | JX448896 | JX448934 | JX448972 |
O. marginipennis | JX448907 | JX448945 | JX448983 |
O. langi cornelii | JX448900 | JX448938 | JX448976 |
O. langi meridionalis | JX448909 | JX448947 | JX448985 |
O. langi visseri | JX448921 | JX448959 | JX448997 |
O. boschimana | JX448897 | JX448935 | JX448973 |
O. multistriata | JX448912 | JX448950 | JX448988 |
O. hottentota | JX448901 | JX448939 | JX448977 |
O. plana | JX448915 | JX448953 | JX448991 |
O. lobicollis | JX448906 | JX448944 | JX448982 |
O paiva | JX448913 | JX448951 | JX448989 |
O. rugatipennis | JX448917 | JX448955 | JX448993 |
O. laeviceps | JX448904 | JX448942 | JX448980 |
O. u. unguicularis | JX448919 | JX448957 | JX448995 |
O. u. schulzeae | JX448920 | JX448958 | JX448996 |
Physadesmia globosa | JX448887 | JX448925 | JX448963 |
Eustolopus octoseriatus | JX448886 | JX448924 | JX448962 |
Adesmia cribripes | JX448889 | JX448927 | JX448965 |
We used maximum likelihood (ML) to analyze the concatenated gene dataset. The ML analysis, executed in RAxML ver. 7.2.8 (
The second locality for Onymacris brainei was discovered on 22 May 2015. Based on the general geographic information provided in
As noted, Onymacris brainei is diagnosed by the presence of three broad yellow to tan stripes on white elytra. Specifically, this patterning involves a prominent dorsal stripe that is bisected by the elytral suture and flanked by a slightly narrower lateral stripe on either side. All three stripes bear diffuse edges that coalesce anteriorly near the pronotum, taper posteriorly, and terminate at (or just before) the apical declivity. White elytral coloration is not due to any pigment product but rather a function of reflectivity involving microscopic “bubbles” within the cuticle (
DNA sequences were invariant for the nuclear gene H3 but did exhibit variation for both mitochondrial genes (two haplotypes for each gene); mean sequence divergence for the cox1 and cox2 was 1.49 % and 0.05%, respectively.
ML analysis of the concatenated dataset identified O. brainei as sister to O. marginipennis + O. bicolor in a highly supported clade (BS = 100%) that is sister to a second ‘white’ clade comprising the three subspecies of O. langi represented in our dataset (Fig.
In her paper originally describing Onymacris brainei,
Our ML phylogeny corroborates bicolor-brainei-marginipennis monophyly but differs by depicting O. bicolor and O. marginipennis as sister species. To this end, we note a preliminary aspect of the molecular results–our somewhat limited geographic representation for O. bicolor and O. marginipennis. Relative to the other ‘white’ taxa, both these species have extended ranges and were recognized historically as being polytypic (
The molecular phylogenetic placement of O. brainei with other ‘white’ Onymacris not only offers incremental support for the ‘white’ clade but, more broadly, augments a diphyletic Onymacris relative to Physadesmia (
“Rediscovery” is a beguiling catchword, conveying equal parts accomplishment and optimism upon finding species thought to be rare or possibly extinct. We were indeed relieved to locate new specimens of O. brainei–a species gone unreported for 33 years. However, a claim of rediscovery might be overstated: the hiatus is attributable in large degree to the northern Namib’s remote setting and limited accessibility. A more telling discovery may be the genetic divergence (1.49%, cox1) observed among individuals at the new locality, which could possibly indicate a historically larger geographic distribution. It is worth noting that O. candidipennis, once thought to be restricted to the Namib’s northern terminus in Angola, has been reported from Namibia at the Cunene River, near the type locality for O. brainei (
We thank Patrice Bouchard, Edie Jeffreys, and Mike Wooten for their assistance in the field. Michael Brewer graciously provided access to his laboratory’s composite imaging system. Specimens were processed under Research/Collecting Permit # 2015/2015 provided by Namibia’s Ministry of Environment and Tourism. Funding for this project was provided by Research and Exploration grant # 9582-14 from the National Geographic Society.