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A subterranean species of Exocelina diving beetle from the Malay Peninsula filling a 4,000 km distribution gap between Melanesia and southern China


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We describe a new subterranean species of the genus Exocelina Broun, 1886 (Coleoptera: Dytiscidae) from the Malay Peninsula. Almost all of the 196 species of that genus are epigean and distributed mainly in New Guinea, Australia, Oceania and New Caledonia. One epigean species is, however, known from China. The discovery of a species on the Malay Peninsula fills that distribution gap to some degree.
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New subterranean diving beetle 25
A subterranean species of Exocelina diving beetle from
the Malay Peninsula filling a 4,000 km distribution gap
between Melanesia and southern China
Michael Balke1, Ignacio Ribera2
1 SNSB-Zoologische Staatssammlung, Münchhausenstrasse 21, D-81247 München, Germany 2 Institute of
Evolutionary Biology (CSIC-Universitat Pompeu Fabra), Barcelona, Spain
Corresponding author: Michael Balke (
Academic editor: Oana Moldovan | Received 15 January 2020 | Accepted 22 February 2020 | Published 10 March2020
Citation: Balke M, Ribera I (2020) A subterranean species of Exocelina diving beetle from the Malay Peninsula lling a
4,000 km distribution gap between Melanesia and southern China. Title. Subterranean Biology 34: 25–37. https://doi.
We describe a new subterranean species of the genus Exocelina Broun, 1886 (Coleoptera: Dytiscidae)
from the Malay Peninsula. Almost all of the 196 species of that genus are epigean and distributed mainly
in New Guinea, Australia, Oceania and New Caledonia. One epigean species is, however, known from
China. e discovery of a species on the Malay Peninsula lls that distribution gap to some degree.
Beetles, blind subterranean species, disjunct distribution, new species
Here we report the discovery of a new subterranean diving beetle from the Malay
Peninsula. is species was placed in the Dytiscidae, subfamily Copelatinae based on
morphological characters using the key of Miller and Bergsten (2016). It was then
unambiguously assigned to the genus Exocelina Broun, 1886 in a phylogenetic analysis
using molecular systematic data of Toussaint et al. (2014, 2015, 2020 in preparation).
Subterranean Biology 34: 25–37 (2020)
doi: 10.3897/subtbiol.34.50148
Copyright Michael Balke, Ignacio Ribera. 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 origina author and source are credited.
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Michael Balke & Ignacio Ribera / Subterranean Biology 34: 25–37 (2020)
e 196 described species of Exocelina are mostly from New Guinea (141 species, see
e.g. Balke 1998; Shaverdo et al. 2018, 2019; Shaverdo and Balke 2019), followed by
New Caledonia (37 species) and Australia (16 species, two of them subterranean),
with single species each in Hawaii and Vanuatu (Balke et al. 2007; Nilsson and Hájek
2019). All of these localities lie east of the Lydekkers line. A single species was discov-
ered in Shizong, Yunnan, China (Balke and Bergsten 2003), leaving a gap of around
4,000 km in the distributional range of Exocelina, essentially the entire Indonesian
Archipelago and mainland Southeast Asia. e present nding partly lls this gap and
suggests that more discoveries are to be expected, for example from the little sampled
mountain regions of Vietnam and Laos. A synopsis of the subterranean diving beetles
of the World was provided by Miller and Bergsten (2016), who provide an identica-
tion key as well as habitus photographs.
Material and methods
Specimens were studied with a Leica M205C stereo microscope at 10–160x. Images
were taken with a Canon EOS 5DS camera tted with a Mitutoyo 10x ELWD Plan
Apo objective attached to a Carl Zeiss Jena Sonnar 3.5 / 135 MC as focus lens. Illu-
mination was with two to four LED segments SN-1 from Stonemaster (https://www. Image stacks were generated using the Stackmaster macro
rail (Stonemaster), and images were then assembled with the computer software Heli-
con Focus 4.77TM.
Drawings were produced with a camera lucida, rst sketched with pencil on paper,
then photographed and digitally inked using an iPad Pro and the Concepts as well as
MediBang Paint APPs.
One paratype male of the new species (voucher number IBE-AN1160) was used
for a non-destructive DNA extraction using a commercial kit (Qiagen DNeasy Tissue
Kit). We successfully amplied six mitochondrial and nuclear genes in ve sequencing
reactions, two cytochrome c oxidase subunit I fragments (COI-5’ -the "barcode"- and
COI-3’), 5’ end of rrnL RNA plus leucine tRNA transfer (tRNA-L1) plus 5’ end of
NADH dehydrogenase subunit I (NAD1), and one internal fragment of both small
ribosomal unit (18S RNA) and Histone 3 (H3) (see Villastrigo et al. 2018, for de-
tails of the primers and sequencing conditions). ese are fragments routinely used
for Dytiscidae systematics. Sequences were edited using Geneious v10.1 (Kearse et al.
2012). Here, we combined the newly obtained sequences of COI-3', 18S and H3 (ENA
database with accession numbers LR759936 H3, LR759937 18S, LR759938 3'COI,
LR760127 5'COI) with the data of Toussaint et al. (2014, 2015 as well as 2020 in
preparation). Other markers used by the latter authors (such as Carbomoylphosphate
synthase (CAD) and Alpha-Spectrin (Asp)) could not be amplied here.
e combined dataset was analysed with a fast maximum likelihood search as im-
plemented in IQ-TREE v1.6 (Nguyen et al. 2015), with a partition by gene fragment
and the best evolutionary model as selected by Modelnder (Kalyaanamoorthy et al.
2017) using the AIC (Akaike Information Criterion). We assessed topological stability
New subterranean diving beetle 27
with 1000 ultrafast bootstraps and tested tree branches by SH-like aLRT with 1000
replicates (Nguyen et al. 2015).
IBE Institute of Evolutionary Biology, Barcelona, Spain
KSc Kazuki Sugaya collection, Zama, Japan
NMW Naturhistorisches Museum Wien, Austria
ZSM Zoologische Staatssammlung München, München, Germany
Family Dytiscidae Leach, 1815
Genus Exocelina Broun, 1886
Exocelina sugayai sp. nov.
Type locality. Malaysia, Pahang, Cameron Highlands, Tanah Rata, 4.474705,
Material examined. Holotype male (ZSM): Malaysia, Pahang, Cameron High-
lands, Tanah Rata, Mount Berembun, 4.474705, 101.384043, 1,500m, 27.–29.ii.2012,
K. Sugaya leg.
Paratypes: 4 males (1 used for DNA extraction and sequencing, voucher No. IBE-
AN1160) and 2 females, same label data as holotype (IBE, KSc, NMW, ZSM).
Description of holotype. Size and shape: Smallest Exocelina known (length of
holotype including head 2.7 mm, length without head 2.4 mm, greatest width 1.0
mm). Abdomen comparably parallel sided; pronotum also comparably parallel sided,
slightly constricted before base, hind angles produced backwards (Fig. 1A).
Coloration. Testaceous and slightly translucent (Figs 1A, B, 2A–F).
Surface sculpture. Head and pronotum with distinct microreticulation formed
by small regular cells and ne moderately dense punctation. Elytra with distinct mi-
croreticulation formed by small regular cells and dense, coarse, setiferous punctation
(Fig. 1A, D). Ventral side with distinct microreticulation formed by small regular cells,
including distinct microreticulation on metacoxal processes (Figs 3A, 4A–C).
Structures. Eyes fully reduced, with only small black scars remaining on surface
of head (Figs 1A, B, 2A, B). Male antennomeres strongly modied: 2 and 3 monili-
form, 4 slightly broadened in dorsal view, 5–11 strongly expanded, 11 at and blade
like (Fig. 1A). Fore tarsus dilated, fore angle of tarsomere 4 ventrally produced (Fig.
1C) and with two thicker setae (but no hook as in other Exocelina), on tarsomere
5 ventrally without obvious setation; pro and mesotarsomeres 1–3 with 4 rows of
stalked suction discs (2 per row). Pronotum with faint lateral bead not reaching an-
Michael Balke & Ignacio Ribera / Subterranean Biology 34: 25–37 (2020)
Figure 1. Exocelina sugayai sp. nov. A habitus dorsal of male B same of female C foretarsus of male, ar-
row pointing at expanded anterior ventral angle of tarsomere IV D surface sculpture on male elytral disc,
cropped from A. Length of left beetle: 2.7 mm.
terior nor posterior corners (Fig. 2B, D, F). Prosternal process short, lanceolate, de-
exed, gently rounded ventrally (Figs 3A, 4A); metaventrite broadly triangular, its
lateral “wings” very narrow (Fig. 4B, C). Membranous wings strongly reduced, with
only very short stubs visible at the wing base. Metacoxal “lines” broadly diverging,
fainting well before hind margin of metaventrite (Figs 3A, 4B). Metacoxal processes
small, more elongate oval, with wide gap in middle (to possibly enable higher mobil-
ity of hindlegs) (Figs 3A, 4B). Last ventrite apically rounded. Median lobe of aedea-
gus simply curved in lateral view, parameres of simple, Copelatinae-type triangular
shape (Fig. 5A, B).
Female. Antennomeres liform to slightly moniliform (Fig. 1B). Pro and mesotar-
someres 1–3 not bearing stalked suction discs and protarsomere 4 not modied.
New subterranean diving beetle 29
Figure 2. Exocelina sugayai sp. nov. male A eye in lateral view B detail of head and pronotum C surface
sculpture on base of head and anterior margin of pronotum D detail of posterior angle of pronotum E
detail of surface sculpture on base of elytron F detail of lateral view of elytral and pronotal base and head.
Michael Balke & Ignacio Ribera / Subterranean Biology 34: 25–37 (2020)
Figure 3. Ventral view of A Exocelina sugayai sp. nov. male and B Exocelina abdita.
Variation. Length of beetle including head 2.4–2.8 mm. Two paratypes are darker
orange (see Fig. 1B). According to the collector, this is due to subsequent darkening in
alcohol storage.
Etymology. Named after Kazuki Sugaya, the discoverer of this species.
Dierential diagnosis. is species diers from all other Dytiscidae by: Copelati-
nae with reduced eyes; beetle length < 3 mm; body with well visible microreticulation;
prosternal process short and deexed; metacoxal processes small, more elongate oval
(in other Copelatinae, including the groundwater species Exocelina abdita Balke et al.
2004, this structure is more rounded, and the metacoxal “lines” can be more parallel
sided, Figs 3B, 4D); male with strongly modied antennomeres.
New subterranean diving beetle 31
Figure 4. Exocelina sugayai sp. nov. male, ventral side A prosternal process and mesocoxal area B meta-
coxa and metacoxal processes C metaventrite and metaxoca D Exocelina abdita, metacoxa and metacoxal
processes. Lines in B and D inserted to highlight outline of metacoxal processes.
Habitat. Collected from two helocrenes on a slope in forested area. e beetles
were observed creeping around and were not swimming when observed (K. Sugaya
personal communication 2019) (Fig. 6A, B).
Phylogenetic anities. e best evolutionary model tting the data according to
Modelnder was a GTR+F for all partitions. Exocelina sugayai sp. nov. was recovered
deeply subordinated within Exocelina, as the sister of the Chinese E. shizong Balke &
Michael Balke & Ignacio Ribera / Subterranean Biology 34: 25–37 (2020)
Figure 5. Exocelina sugayai sp. nov. male genital, A median lobe of aedeagus in lateral view B paramere
lateral inner view.
Bergsten, 2003 and the New Caledonian E. nehoue Balke et al., 2014. ese three spe-
cies are part of a clade (“C4” in Toussaint et al. 2015) otherwise containing E. parvula
(Boisduval, 1835) from Hawaii as well as a clade of New Caledonian and one Vanuatu
species (Fig. 7). e other two subterranean species of Exocelina are E. abdita Balke et al.,
2004 and E. rasjadi Watts & Humphreys, 2009 from Australia. e former was included
in our phylogenetic analysis and placed in a dierent clade than Exocelina sugayai sp.
nov. (Fig. 7, included subterranean species in red). Data for E. rasjadi were not available.
Most species of Exocelina inhabit stream associated (lotic) habitats, specically areas
of stagnant water at the edge of streams and creeks, the interstitial and tiniest of water
holes on riverbanks, as well as small puddles in intermittent creeks including the source
area that might only have occasional water ow after rainfalls (see habitat photos in
Shaverdo et al. 2012). is is the likely ancestral habitat type in Exocelina, with four
subsequent shifts to lentic habitats (and only a few species in the lentic clades) (Tous-
saint et al. 2015). Most species have limited geographic ranges; in one widespread
epigean species population genomic studies revealed strong geographic structure even
in populations as close to each other as 40 km straight line (Lam et al. 2018).
New subterranean diving beetle 33
Figure 6. Habitat of Exocelina sugayai sp. nov. A overview B detailed, with a beetle crawling about in
the center of the image.
Michael Balke & Ignacio Ribera / Subterranean Biology 34: 25–37 (2020)
Figure 7. Simplied phylogenetic tree obtained with IQ-TREE using the DNA sequence dataset of
Toussaint et al. (2014, 2015 as well as 2020 in preparation ) plus the newly obtained sequences of Ex-
ocelina sugayai sp. nov. Non-relevant clades are collapsed to genus or other major clades. Numbers in
nodes, ultrafast bootstrap / SH-like aLRT support.
e lotic beetles often hide in the gravel when disturbed, and observations of M.
Balke in New Guinea suggest that the interstitial of riverbanks is often utilized by these
beetles, possibly to avoid downstream drift. e beetles seem to avoid habitat with ne,
dense substrates, which we suggest make it hard to hide as such substrate clogs the
space between stones and pebbles (see also Balke 2001).
New subterranean diving beetle 35
is lifestyle could be interpreted as a preadaptation for interstitial or stygobitic
life. In fact, some Australian species seem to mainly inhabit the interstitial, and have
been suggested to provide a scenario for the transition from epigean to stygobitic life
(Watts et al. 2016). To date, two species have been described from groundwater habi-
tats in Australia. ey exhibit a strongly modied morphology typical of stygobitic
species, such as wing and eye reduction and depigmentation (Balke et al. 2004; Watts
and Humphreys 2009, see also Watts et al. 2016). e discovery of the new species
described here suggests that many more such stygobitic Exocelina could be found in
the future. Our phylogenetic analysis also suggests that the evolution of subterranean
Exocelina occurred at least two times independently (Fig. 7). In Copelatinae, one species
of the genus Copelatus Erichson, 1832 from Brazil has been described from the subter-
ranean habitat (Caetano et al. 2013).
Biogeographically, the occurrence of Southeast Asian and a Chinese species of Ex-
ocelina remains enigmatic. e origin of the clade containing these species was es-
timated as at least 10 million years ago (“C4” Toussaint et al. 2015). Based on the
information currently available, we can not state with condence whether the Asian
species are “relics” of a previously diverse and widespread Exocelina fauna, or the result
of rare dispersal events without apparent subsequent diversication.
We express our sincere thanks to Kazuki Sugaya for sending the specimens studied here
to the senior author, and Anabela Cardoso for laboratory work. Helena Shaverdo and
Günther Wewalka (Vienna) provided very valuable reviews of the submitted manu-
script. is research was supported by DFG Ba2152/4-1, 7-1, 11-1, 11-2 and 24-1.
Michael Balke acknowledges support from the EU SYNTHESYS program projects
FR-TAF-6972 and GB-TAF-6776.
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... To date, 152 species have been described from New Guinea and its satellite islands (e.g., [61,62]), 151 of which form a monophyletic group (see [41,46]. The majority of species outside New Guinea occur in Australia and New Caledonia, with single species e.g., in Hawaii, China, Peninsula Malaysia [63] and Vanuatu. Most species are found in a variety of running water associated habitats (but avoiding water current), only a few Australian and only one New Guinea and New Caledonian species, respectively, inhabit pools or swamps [46]. ...
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Background The New Guinean archipelago has been shaped by millions of years of plate tectonic activity combined with long-term fluctuations in climate and sea level. These processes combined with New Guinea’s location at the tectonic junction between the Australian and Pacific plates are inherently linked to the evolution of its rich endemic biota. With the advent of molecular phylogenetics and an increasing amount of geological data, the field of New Guinean biogeography begins to be reinvigorated. Results We inferred a comprehensive dated molecular phylogeny of endemic diving beetles to test historical hypotheses pertaining to the evolution of the New Guinean biota. We used geospatial analysis techniques to compare our phylogenetic results with a newly developed geological terrane map of New Guinea as well as the altitudinal and geographic range of species ( ). Our divergence time estimations indicate a crown age (early diversification) for New Guinea Exocelina beetles in the mid-Miocene ca. 17 Ma, when the New Guinean orogeny was at an early stage. Geographic and geological ancestral state reconstructions suggest an origin of Exocelina ancestors on the eastern part of the New Guinean central range on basement rocks (with a shared affinity with the Australian Plate). Our results do not support the hypothesis of ancestors migrating to the northern margin of the Australian Plate from Pacific terranes that incrementally accreted to New Guinea over time. However, our analyses support to some extent a scenario in which Exocelina ancestors would have been able to colonize back and forth between the amalgamated Australian and Pacific terranes from the Miocene onwards. Our reconstructions also do not support an origin on ultramafic or ophiolite rocks that have been colonized much later in the evolution of the radiation. Macroevolutionary analyses do not support the hypothesis of heterogeneous diversification rates throughout the evolution of this radiation, suggesting instead a continuous slowdown in speciation. Conclusions Overall, our geospatial analysis approach to investigate the links between the location and evolution of New Guinea’s biota with the underlying geology sheds a new light on the patterns and processes of lineage diversification in this exceedingly diverse region of the planet.
... Morphological and ecological features are highly specialized among subterranean insects [1]. These features have been the subject of many taxonomic and evolutionary studies [2][3][4]. Studies of subterranean insects can provide insights into the mechanisms underlying interspecific relationships [5], which are considerably influenced by various abiotic and biotic factors in aboveground systems, complicating the interpretation of results. In contrast, subterranean systems generally comprise a limited range of environments [5][6][7]. ...
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An endemic subterranean Japanese carabid beetle lineage, the Pterostichus macrogenys species group, was recently revealed to have marked regional differentiation. Studies of such features reveal insect species diversity and provide insight into the mechanisms driving species diversity. We examined specimens of this species group collected from the southern Tohoku District of Honshu, Japan, where its diversity has not yet been fully elucidated, using fine-scale field sampling and detailed comparative morphological analysis of male genitalia. In total, 103 specimens from 13 localities were classified into one new (P. monolineatus sp. n.) and eight known species. In four of the known species, we observed disjunct distributions, which have not previously been reported in this species group and may be more common than previously recognized. Species coexistence was observed at four sites, with two species of different body sizes coexisting at three sites and three species coexisting at the remaining site. The three coexisting species included one large and two small species, the latter of which have male genitalia of a different size. This newly discovered coexistence pattern implies separate effects of differential body and genital size in species coexistence, which has rarely been reported in insects.
... To date, this group contains 54 species (including the two new species) endemic to New Guinea (Balke 1998;Shaverdo and Balke 2019;Shaverdo et al. 2005Shaverdo et al. , 2012Shaverdo et al. , 2016. Including the results of this paper, 142 species of Exocelina are now described from New Guinea and 199 species worldwide (Shaverdo and Balke 2019;Shaverdo et al. 2019;Balke and Ribera 2020;Nilsson and Hájek 2020). As in most of our previous papers on the genus, all species data will be presented on the ...
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Two new species of the genus Exocelina Broun, 1886: E. athesphatos sp. nov. and E. tsinga sp. nov. are described from New Guinea and placed into the E. ekari group based on the structure of their male genitalia. The two species are very similar with respect to their external morphology and characterised by almost identical, strongly modified male antennae. However, they can easily be separated by the shape and setation of the median lobe and paramere. Based on morphological similarity and results of a molecular phylogenetic analysis, we suggest these are sister species. Both of them have been collected on the southern slopes of the Central Range (the spine of New Guinea), with a distance of ca. 380 km straight line between the collecting localities.
Predaceous diving beetles (Dytiscidae) are a highly speciose group of insects occurring in a large variety of habitat types, where they often form multispecies assemblages, due to their high diversity and large variation in the degree of habitat specificity. While most species have broad habitat preferences, some are specialized for life under extreme habitat conditions. In this chapter, we provide an overview of the main habitats in which dytiscids occur and summarize some of the habitat variables that contribute most to shaping the distribution of dytiscids across habitats and landscapes. These include a range of abiotic conditions and plant–beetle relationships, which act as major habitat selection factors. We discuss how a variety of habitats in agricultural and urban landscapes can contribute to maintain high dytiscid diversity. We then describe some of the most peculiar habitats where dytiscids occur, including phytotelmata, subterranean and interstitial habitats, rock pools, and terrestrial habitats. Over the past couple of decades, examination of habitats that had been typically underexplored for dytiscids has led to the discovery of new species and even new genera. These studies suggest that further exploration of these habitats and the increasing availability of phylogenetic data will provide important insights into the ecology and evolutionary history of species colonizing extreme habitats. This is in turn critical to improve our understanding of the vulnerability of dytiscids to global environmental changes associated with changes in habitat characteristics and availability.
The phylogenetics and higher (family-group) classification of extant members of the beetle family Dytiscidae (Coleoptera), or predaceous diving beetles, is reviewed and reassessed. A phylogenetic analysis of the family is presented based on 168 species of diving beetles and 9 outgroup taxa from Gyrinidae, Noteridae, Amphizoidae, and Paelobiidae. All currently recognized dytiscid subfamilies and tribes are represented, most by multiple genera and species. Data include 104 morphological characters and approximately 6700 aligned bases from 9 DNA sequence fragments from cytochrome c oxidase I (COI) and II (COII), histone III (H3), 16S rRNA (16S), 12S rRNA (12S), arginine kinase (argkin), RNA polymerase II (RNA pol II), elongation factor 1 alpha (Ef1α), and wingless (wnt). Parsimony and Bayesian analyses were conducted. The topology of the parsimony tree (consensus of 13 equally-parsimonious solutions) exhibits numerous anomalies inconsistent with convincing morphological features and the Bayesian results and has, generally, relatively poor bootstrap support for major clades. The Bayesian topology is more consistent with major morphological features and has strong support for most clades, and conclusions are based primarily on this estimate. Major higher-level phylogenetic relationships with strong support include: (1) monophyly of Dytiscidae Leach, (2) Matinae Branden sister to the rest of Dytiscidae, (3) Agabinae Thomson + Colymbetinae Erichson, (4) Hydrodytinae Miller + Hydroporinae Aubé, (5) Dytiscinae Leach + Laccophilinae Gistel + Cybistrini Sharp + Copelatinae Branden, (6) monophyly of the subfamilies Matinae, Colymbetinae, Copelatinae, Coptotominae Branden, Lancetinae Branden, Laccophilinae (including Agabetes Crotch), Agabinae (support weaker than in other subfamilies) and Hydroporinae (monophyly of Hydrodytinae not tested), (7) paraphyly of Dytiscinae with Cybistrini sister to Laccophilinae (with strong support) and this clade sister to other Dytiscinae, and (8) monophyly of both Agabini (Agabus-group of genera) and Hydrotrupini Roughley (Hydrotrupes Sharp and the Platynectes-group of genera). Major conclusions regarding tribes within Hydroporinae include: (1) monophyly of the tribes Vatellini Sharp, Methlini Branden, Hydrovatini Sharp, Hygrotini Portevin, Hyphydrini Gistel (without Pachydrus Sharp) and Bidessini Sharp (including Peschetius Guignot, Hydrodessus J. Balfour-Browne and Amarodytes Régimbart) (monophyly of Laccornini Wolfe and Roughley and Pachydrini Biström, Nilsson and Wewalka not tested), (2) Pachydrini is a problematic, long-branched taxa resolved here as sister to Hydrovatini but with weak support, (3) Hydroporini monophyletic except for Laccornellus Roughley and Wolfe and Canthyporus Zimmermann, (4) Laccornellus and Canthyporus together monophyletic and sister to Hydroporinae except Laccornini. Four groups are resolved within Hydroporini exclusive of Laccornellus + Canthyporus corresponding to the Deronectes-, the Graptodytes-, the Necterosoma- and the Hydroporus-groups of genera. The classification of Dytiscidae is revised with the following taxonomic changes [2014]: (1) Hydrotrupini is recognized as a tribe of Agabinae including the genus Hydrotrupes and the Platynectes-group of genera, (2) the genus Rugosus García is moved from Colymbetinae to Copelatinae, (3) Cybistrini is elevated from tribe rank within Dytiscinae to subfamily of Dytiscidae, (4) Hyderodini Miller is placed as a junior synonym of Dytiscini, (5) Laccornellus and Canthyporus are removed from Hydroporini and placed in their own tribe, Laccornellini, (6) the following family-group names are resurrected from synonymy with Hydroporini and placed as subtribes within Hydroporini, Deronectina Galewski (for the Deronectes-group of genera), Siettitiina Smrž (for the Graptodytes-group of genera), Sternopriscina Branden (for the Necterosoma-group of genera), and Hydroporina (for the Hydroporus-group of genera), (7) Carabhydrini Watts is placed as a junior synonym of Sternopriscina, and (8) Hydrodessus, formerly incerta sedis with respect to tribe, is placed in Bidessini. Each subfamily, tribe and subtribe is diagnosed and its taxonomic history discussed.
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Detailed information about the known species groups of Exocelina Broun, 1886 from New Guinea is presented, including species numbers, distribution, and references of species-group diagnoses, keys to the species, and species descriptions. An identification key to all species groups is provided. Phylogeny and morphological character evolution are discussed.
The subterranean environment comprises voids of any size in which life can develop in aphotic, aseasonal and largely oligotrophic conditions. A small proportion of living organisms have been able to evolve and adapt to such conditions. Some of them have become strictly dependent on this harsh environment, at the price of a set of profound biological adaptations. Key new discoveries shed light on ancient biogeographical patterns but challenge our views regarding the origin and history of the extant fauna, as illustrated by the recently discovered monospecific genus Iberotrechodes in a cave in Cantabria, Spain. Vicariance by plate tectonics remains the main explanatory factor for the amphi‐Atlantic distribution displayed by many groups of subterranean Crustacea. An accurate knowledge of subterranean diversity at the species level, combined with a comprehensive overview of the geological and paleoclimatic histories of the areas of interest, is a prerequisite to the understanding of biogeographic patterns.
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The first stygobiontic diving beetle known from Laos, Laodytes lapiei n. gen., n. sp., is described from a cave located in the Vientiane province. Its morphological characters lead to its placement, among Hydroporinae, in Hydroporini. Inside these, the new species could not be assigned to an existing genus. As a result, a new genus has been defined without it being possible, at the present stage, to assign it to one of the currently recognized subtribes. Résumé.-Nouveaux genre et espèce de Coléoptère aquatique souterrain du Laos (Coleoptera, Dytiscidae, Hydroporinae, Hydroporini). Le premier Dytiscidae stygobie connu du Laos, Laodytes lapiei n. gen., n. sp., est décrit d'une grotte de la province de Vientiane. Ses caractères morphologiques conduisent à le placer, parmi les Hydroporinae, dans les Hydroporini. À l'intérieur de ceux-ci, la nouvelle espèce n'a pu trouver place dans aucun genre existant. En conséquence, un nouveau genre a été défini, sans qu'il soit possible, à ce stade, de le rattacher à l'une des sous-tribus actuellement reconnues.
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Exocelina kowalskii sp.n. (Coleoptera: Dytiscidae) is described from Papua New Guinea (Morobe Province) and placed in the E. ekari group based on the structure of the male genitalia. Affinities with morphologically similar species of the group are discussed. The new species is characterized by its male antennae and the shape of the male genitalia. Important diagnostic characters of the new species (habitus, colour, male antenna and protarsomeres 4-5, male genitalia) are illustrated. New faunistic data of 12 other species of Exocelina BROUN, 1886 are provided.
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Nine new species groups of Exocelina Broun, 1886 from New Guinea are introduced with keys to their representatives. Four groups are monotypic and include three new species: the E. aipomek group, the E. koroba group: E. korobasp. nov. , the E. mekilensis group: E. mekilensissp. nov. , and the E. morobensis group: E. morobensissp. nov. The remaining five species groups include 18 species with 12 new species and one new subspecies: the E. bacchusi group: E. akamekusp. nov. , E. oiwasp. nov. , E. oksibilensissp. nov. , and E. bacchusi herzogensisssp. nov. ; the E. jaseminae group: E. asekisp. nov. , E. kailakisp. nov. , and E. pseudojaseminaesp. nov. ; the E. larsoni group: E. warahulenensissp. nov. ; the E. takime group: E. mianminensissp. nov. ; and the E. warasera group: E. haiasp. nov. , E. kobausp. nov. , E. pulchellasp. nov. , and E. waraserasp. nov. Diagnoses of five already described species of these groups are provided, as well as comparatives notes on all species. Exocelina santimontis (Balke, 1998) syn. nov. is a junior synonym of E. aipomek (Balke, 1998). Data on the distribution of the species are given, showing that most of the species of these groups occur in the Papua New Guinea.
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Nineteen new species of Exocelina Broun, 1886 from New Guinea are described herein: E.adelbertensissp. n. , E.ambuasp. n. , E.bewanisp. n. , E.cyclopssp. n. , E.ibalimisp. n. , E.kekisp. n. , E.kumulensissp. n. , E.mendiensissp. n. , E.menyamyasp. n. , E.okapasp. n. , E.piusisp. n. , E.pseudofumesp. n. , E.pseudopusillasp. n. , E.pusillasp. n. , E.simasp. n. , E.simbaiensissp. n. , E.simbaijimisp. n. , E.sumokedisp. n. , and E.yoginofisp. n . All of them, together with five already described species, have been united into the newly defined casuarina -group, a polyphyletic complex of related species with similar shape of the median lobe and paramere setation. An identification key to all known species of the group is provided, and important diagnostic characters (habitus, color, male protarsomeres 4–5, median lobes, and parameres) are illustrated. Data on the distribution of the species are given, showing that most of the species occur in the central, mountain part of Papua New Guinea.
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The Habitat Template Concept applied to a freshwater system indicates that lotic species, or those which occupy permanent habitats along stream courses, are less dispersive than lentic species, or those that occur in more ephemeral aquatic habitats. Thus, populations of lotic species will be more structured than those of lentic species. Stream courses include both flowing water and small, stagnant microhabitats that can provide refuge when streams are low. Many species occur in these microhabitats but remain poorly studied. Here we present population genetic data for one such species, the tropical diving beetle Exocelina manokwariensis (Dytiscidae), sampled from six localities along a ~300 km transect across the Birds Head Peninsula of New Guinea. Molecular data from both mitochondrial (CO1sequences) and nuclear (ddRAD loci) regions document fine‐scale population structure across populations that are ~ 45 km apart. Our results are concordant with previous phylogenetic and macroecological studies that applied the Habitat Template Concept to aquatic systems. This study also illustrates that these diverse but mostly overlooked microhabitats are promising study systems in freshwater ecology and evolutionary biology. With the advent of next generation sequencing, fine‐scale population genomic studies are feasible for small non‐model organisms to help illuminate the effect of habitat stability on species’ natural history, population structure, and geographic distribution. This article is protected by copyright. All rights reserved.
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Exocelina saltusholmesensis sp. n. is described from a single female collected in Holmes Jungle Reserve near Darwin in the Northern Territory, Australia. Phylogenetically, the new species is sister to a clade containing the epigean E. ferruginea (Sharp, 1882) and E. punctipennis (Lea, 1899) but well characterized by its smaller size, the much smaller eyes, vestigial wings and paler surface. Exocelina saltusholmesensis sp. n. was collected from a small pool in an intermittent and temporary small creek. The collecting circumstances suggest that this is an interstitial species, with morphological characters interpreted as adaptations to a strongly hidden if not mostly subterranean lifestyle.
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The fate of newly settled dispersers on freshly colonized oceanic islands is a central theme of island biogeography. The emergence of increasingly sophisticated methods of macroevolutionary pattern inference paves the way for a deeper understanding of the mechanisms governing these diversification patterns on lineages following their colonization of oceanic islands. Here we infer a comprehensive molecular phylogeny for Melanesian Exocelina diving beetles. Recent methods in historical biogeography and diversification rate inference were then used to investigate the evolution of these insects in space and time. An Australian origin in the mid-Miocene was followed by independent colonization events towards New Guinea and New Caledonia in the late Miocene. One colonization of New Guinea led to a large radiation of >150 species and 3 independent colonizations of New Caledonia gave rise to about 40 species. The comparably late colonizations of Vanuatu, Hawaii and China left only one or two species in each region. The contrasting diversification trajectories of these insects on Melanesian islands are likely accounted for by island size, age and availability of ecological opportunities during the colonization stage.
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Large phylogenomics data sets require fast tree inference methods, especially for maximum-likelihood (ML) phylogenies. Fast programs exist, but due to inherent heuristics to find optimal trees, it is not clear whether the best tree is found. Thus, there is need for additional approaches that employ different search strategies to find ML trees and that are at the same time as fast as currently available ML programs. We show that a combination of hill-climbing approaches and a stochastic perturbation method can be time-efficiently implemented. If we allow the same CPU time as RAxML and PhyML, then our software IQ-TREE found higher likelihoods between 62.2% and 87.1% of the studied alignments, thus efficiently exploring the tree-space. If we use the IQ-TREE stopping rule, RAxML and PhyML are faster in 75.7% and 47.1% of the DNA alignments and 42.2% and 100% of the protein alignments, respectively. However, the range of obtaining higher likelihoods with IQ-TREE improves to 73.3–97.1%. IQ-TREE is freely available at
Some species of the diving beetle tribe Hygrotini (subfamily Hydroporinae) are among the few insects able to tolerate saline concentrations more than twice that of seawater. However, the phylogenetic relationships of the species of Hygrotini, and the origin and evolution of tolerance to salinity in this lineage, are unknown. In this work, we aim to reconstruct how many times salinity tolerance did evolve in Hygrotini, whether this evolution was gradual or if tolerance to hypersalinity could evolve directly from strictly freshwater (FW) species, and to estimate the probabilities of transition between habitats. We build a phylogeny with ca. 45% of the 137 species of Hygrotini, including all major lineages and almost all of the known halophile or tolerant species. We used sequence data of four mitochondrial (COI-5′, COI-3′, 16S + tRNA and NADH1) and three nuclear (28S, 18S and H3) gene fragments, plus ecological data to reconstruct the history of the salinity tolerance using Bayesian inference. Our results demonstrate multiple origins of the tolerance to salinity, although most saline and hypersaline species were concentrated in two lineages. The evolution of salinity was gradual, with no direct transitions from FW to hypersaline habitats, but with some reversals from tolerant to FW species. The oldest transition to saline tolerance, at the base of the clade with the highest number of saline species, was dated in the late Eocene-early Oligocene, a period with decreasing temperature and precipitation. This temporal coincidence suggests a link between increased aridity and the development of tolerance to saline waters, in agreement with recent research in other groups of aquatic Coleoptera.
Among the hundreds of thousands of species of beetles, there is one family, containing some 4,300 species, that stands out as one of the most diverse and important groups of aquatic predatory insects. This is the Dytiscidae, whose species are commonly known as diving beetles. No comprehensive treatment of this group has been compiled in over 130 years, a period during which a great many changes in classification and a near quadrupling of known species has occurred. In Diving Beetles of the World, Kelly B. Miller and Johannes Bergsten provide the only full treatments of all 186 Dytiscid genera ever assembled. Entomologists, systematists, limnologists, ecologists, and others with an interest in aquatic systems or insect diversity will find these extensively illustrated keys and taxon accounts immensely helpful. The keys make it possible to identify all taxa from subfamily to genera, and each key and taxon treatment is accompanied by both photographs and detailed pen-and-ink drawings of diagnostic features. Every genus account covers body length, diagnostic characters, classification, species diversity, a review of known natural history, and world distribution. Each account is also accompanied by a range map and at least one high-resolution habitus image of a specimen. Diving beetles are fast becoming important models for aquatic ecology, world biogeography, population ecology, and animal sexual evolution and, with this book, the diversity of the group is finally accessible.
Model-based molecular phylogenetics plays an important role in comparisons of genomic data, and model selection is a key step in all such analyses. We present ModelFinder, a fast model-selection method that greatly improves the accuracy of phylogenetic estimates by incorporating a model of rate heterogeneity across sites not previously considered in this context and by allowing concurrent searches of model space and tree space.