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Mitt. Münch. Ent. Ges. 97 17-21 München, 15.10.2007 ISSN 0340-4943
Rhantus elisabethae sp. n. - a new diving beetle from
Papua New Guinean highlands
(Coleoptera: Dytiscidae)
Michael BALKE, Andrew KINIBEL, and Katayo SAGATA
Abstract
We describe Rhantus elisabethae sp.n. from Papua New Guinea's central highlands. The new species is close
to R. bacchusi and R. papuanus, but well characterized by its different male genital structure. Comparative
analysis of the cytochrome c oxidase 1 gene suggests recent speciation in this group of Rhantus species.
Introduction
Papua New Guinea's (PNG) extensive highlands are home to diverse endemic fauna, in many parts still
awaiting discovery and scientific documentation. However, this fauna is increasingly threatened by
intensifying gardening and deforestation (BALKE et al. 2005). As part of a UK Darwin Initiative Project, we
conduct biotic surveys to remedy the lack of knowledge in selected groups of insects, train Papua New
Guinean conservation biologists, and prepare information materials for local communities. Our focus are
aquatic insects, and here we report the discovery of a conspicuous new species of the genus Rhantus DEJEAN.
These comparably large diving beetles are a characteristic part of the highland water beetle fauna. Known
PNG species include the widespread R. suturalis (MAC LEAY, 1833), R. bacchusi BALKE, 2001 only known
from the Eastern Highlands Province and R. papuanus BALFOUR-BROWNE, 1939 (BALKE 1993, 2001) only
recorded from the Eastern Huon Peninsula and thought to be extinct (GROOMBRIDGE 1994). We now
conducted surveys in the Eastern parts of PNG's central highlands, between Tari and Mount Hagen, and
discovered a new species of Rhantus described herein.
We used DNA sequencing to phylogenetically place the new species and to characterise its infraspecific
haplotype diversity. Methods applied are standard procedure explained elsewhere (BALKE et al. 2007).
BMNH - Natural History Museum, London, UK
NMW - Naturhistorisches Museum Wien, Austria
PNGNIC - PNG National Insect Collection, Port Moresby, Papua New Guinea
ZSM - Zoologische Staatssammlung, Munich, Germany
Rhantus elisabethae sp.n.
(Figs 1-3)
Types: Holotype male: Papua New Guinea: Enga, Kumul Lodge at foot of Mt. Hagen, 2700 m, 5.xii.2006,
05.47.548S 143.58.761E, BALKE & KINIBEL (PNG 124) (BMNH).
Paratypes: 7 inds. same as holotype (PNGNIC, NMW, ZSM); 1 female, Papua New Guinea: Southern
Highlands, Sopulkul, 30-35 km NE Mendi, 2680 m, 16.vi.2006, 06.02.944S 143.46.485E, John (PNG 79)
(PNGNIC); 11 inds., Papua New Guinea: Southern Highlands, Tari, Mt. Ambua, 2500 m, 14.v.2006,
05.58.169S 143.06.749E, BALKE (PNG 63) (PNGNIC, ZSM). The PNG numbers refer to M. BALKE's locality
numbers.
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Fig. 1. Habitus, male genital structures, and last ventrite of Rhantus spp. For the latter, the curvature of the hind margin
as seen in one specimen is depicted above the hind margin of the fully drawn ventrite.(scale 2.00 mm).
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Fig. 2. Distribution of Rhantus elisabethae (red dots), R. bacchusi (blue squares) and R. papuanus / R. sp. Huon (yellow
polygon).
Fig. 3. Neighbour joining diagram illustrating cox1 sequence similarities between Rhantus spp.
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Descriptive notes
Size: Length 10.9 - 11.1 mm, greatest width 5.3 - 5.5 mm.
Species similar to R. bacchusi and R. papuanus sharing a slightly more parallel-sided body outline
compared to e.g. R. suturalis; pronotum with marginal bead broad and extending to anterior angle, pronotum
slightly narrower between hind angles than immediately in front of hind angles; dark ventral side, as well as
male fore and middle claws simply curved, of subequal length and c. ¾ length of fifth tarsomere.
Rhantus elisabethae is however readily characterised by (1) its laterally strongly rugose last ventrite
(Fig. 1), a character less apparent in R. papuanus and much less apparent in R. bacchusi; (2) and the different
shape of the median lobe of the aedeagus (Fig. 1), which is larger than in R. papuanus and R. bacchusi, and
of different curvature. The parameres of Rhantus elisabethae (Fig. 1) resemble in shape the other species, and
also bear some trumpet-shaped setae in the fringe of long golden setae.
Etymology: For Mrs Elisabeth HINTELMANN (Munich), celebrating her outstanding, long-term contributions
in support of systematic zoology.
Distribution: So far known from the mountain area between Mountain Hagen and Mount Ambua, including
Mount Giluwe (Fig. 2).
Habitat: At Ambua gap, the new species was collected from among grasses in the shallow to c. 50 cm deep
water at the edge of a roadside irrigation pool, associated with R. suturalis. At Mount Giluwe, the single
beetle was taken out of a small waterhole in Sphagnum bog, with Limbodessus sp., R. suturalis and
Carabdytes upin. Finally, close to the foot of Mt. Hagen on the Kumul Lodge ground, we collected R.
elisabethae from a small swampy spot (2 m x 40 cm, max. depth ca. 5 cm only) on peaty ground, feeding into
a first order stream, in disturbed Pandanus moss forest; one specimen was collected from a roadside ditch
nearby, with R. suturalis and Limbodessus sp.
Molecular Biology
Seven specimens were used to sequence the 3' end of the cytochrome c oxidase subunit 1 gene. Infraspecific
uncorrected p-distances were 0 - 3.7 %, distributed as follows: 0% (4 matches), 1.0 - 1.5% (2 matches), 2.5
- 3.0% (8 matches), 3.0 - 3.5% (7 matches), which is a comparably high infraspecific diversity, considering
the small overall range of the species. Specimens cluster according to geographical locality (Mt. Giluwe only
one specimen available), suggesting interrupted or restricted genetic exchange between localities.
Remarkably, the single individual of R. bacchusi included was subordinated withing R. elisabethae in the
distance-based neighbour joining analysis. We found similar scenarios in other New Guinean Rhantus
species, indicative of recent speciation and incomplete lineage sorting. In other words, in such recently
diversified groups, DNA sequence data from mitochondrial genes alone can not be considered useful for
rapid species discovery. We found another genetically very similar morphospecies of Rhantus on the Huon
Peninsula of PNG, in Fig. 3 marked as "1317 R. sp. Huon" which we first identified as R. papuanus, but
which appears to represent another narrowly endemic, undescribed species. We will address this issue later
after more material becomes available from that region.
We also included one specimen of R. elisabethae in a phylogenetic analysis of New Guinean and
Australian Colymbetini, based on ca. 4 kb DNA sequence data from mitochondrial and nuclear genes (BALKE
et al. in preparation). Rhantus elisabethae unambiguously forms a clade with R. bacchusi, as intuitively
suggested based on morphology.
Acknowledgements
Drs L. HENDRICH (Munich), E.-G. BURMEISTER (Munich), H. FERY (Berlin) and Mr. E. DILLER (Munich)
kindly read earlier versions of the manuscript. We thank Dr. L. ZERCHE (DEI, Eberswalde) for the loan of the
holotype of Rhantus papuanus.
We thank the PNG Department of Environment and Conservation for permission to conduct research
in PNG and for permission to export specimens for study. It is our pleasure to convey a "tenkyu tru" to the
countless people and particularly landowners we met, who helped in many ways, and granted permission to
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stay and look around on their land and more often than not had a "buai" (betel nut) when it was needed most.
We thank the UK Darwin Initiative, German Science Foundation (BA2152/3-2), Linnean Society of London
and the Percy Sladen Memorial Fund for financial support. MB acknowledges the support of SYNTHESYS
grants GB-TAF 2211 and AT-TAF 223.
References
BALKE, M. 1993: Taxonomische Revision der pazifischen, australischen und indonesischen Arten der
Gattung Rhantus DEJEAN, 1833 (Coleoptera: Dytiscidae). – Koleopterol. Rundsch. 63, 39-84.
BALKE, M. 2001: Biogeography and classification of New Guinea Colymbetini (Coleoptera: Dytiscidae). –
Invertebr. Taxon. 15 (2), 259-275.
BALKE, M., ALARIE, Y., RIBERA, I. & G. WEWALKA 2007: Molecular Phylogeny of Pacific Island
Colymbetini: radiation of New Caledonian and Fijian species. – Zool. Scr. 36, 173-200.
BALKE, M., HENDRICH, L., SAGATA, K. & G. WEWALKA 2005: Hydaticus dintelmanni sp.n. from Papua New
Guinea highlands (Coleoptera: Dytiscidae). – Linzer biol. Beitr. 37 (2), 1251-1255.
GROOMBRIDGE, B. (ed.) 1994: 1994 IUCN Red List of Threatened Animals. IUCN, Gland, Switzerland.
Author's addresses:
Dr. Michael BALKE
Zoologische Staatssammlung
Münchhausenstr. 21
D-81247 München, Germany
michael_balke@yahoo.de
Andrew KINIBEL
PNG Binatang Research Center
Nagada, Madang
Papua New Guinea
akinibel@yahoo.com.au
Katayo SAGATA
Wildlife Conservation Society
Papua New Guinea Program
Goroka, EHP
Papua New Guinea
