Revision of Australian Matini diving beetles based on morphological and molecular data (Coleoptera, Dytiscidae, Matinae), with description of a new species

Abstract Morphological characters and mitochondrial DNA sequence data were used to revise the Australian diving beetles in the genera Allomatus Mouchamps, 1964 and Batrachomatus Clark, 1863. As a result of these studies Allomatus syn. n. is synonymised with Batrachomatus, and Allomatus nannup Watts, 1978 from SW Australia and Allomatus wilsoni Mouchamps, 1964 from SE Victoria are transferred to Batrachomatus. The four Australian Matini species knownso far are re-described, and Batrachomatus larsoni sp. n. from the Windsor Tableland in NE Queensland is described. After more than 40 years Batrachomatus wilsoni has been re-discovered in two rivers in Victoria. We delineate the species using traditionally employed morphological structures such as in the male genitalia and body size, shape and colour pattern, as well as mitochondrial cox1 sequence data for 20 individuals. Important species characters (median lobes, parameres and colour patterns) were illustrated. We provide an identification key and outline distribution and habitat preferences of each species. All Australian Matini are lotic, inhabiting permanent and intermittent streams, creeks and rivers.


introduction
The Matini, the single tribe of the subfamily Matinae, is thus far known to contain eight species in three genera. Their current distribution is highly disjunct. Matus Aubé, 1836 is distributed in the Nearctic region with four species and one subspecies. In Australia there are two species so far assigned to Allomatus Mouchamps, 1964 and two assigned to Batrachomatus Clark, 1863. The American species were revised by Larson et al. (2000), and the Australian ones by Mouchamps (1964) and Watts (1978). The larvae of A. nannup, B. daemeli, M. bicarinatus (Say, 1823) and M. leechi Young, 1953 have been described and phylogenetic relationships within the Matini based on larval characters have been discussed by Wolfe and Roughley (1985), Alarie et al. (2001) and Alarie and Butera (2003).
Despite their disjunct distribution, members of the Matinae are postulated to share a monophyletic origin and to be relicts of a once more extensively distributed taxon (Alarie et al. 2001, Alarie andButera 2003).
The aim of this paper is to revise the Australian Matini taxonomically, combining morphology and mitochondrial DNA sequence data. Allomatus syn. n. is synonymized with Batrachomatus, we describe one new species from the Atherton Tableland in Queensland and provide a key to the five Australian species known so far. All DNA sequence data and digital images of morphological structures were also made available online in Wiki format for faster dissemination of taxonomic knowledge and the option of future edits and additions to the species pages in a fully versioned framework.
The two species of the genus Batrachomatus are widespread in tropical northern Australia (B. wingii) and in south-eastern Australia (B. daemeli), whereas all species of the former genus Allomatus are restricted to one or two river systems in the southwest (A. nannup), or the southeast (A. wilsoni). Except for A. nannup and B. daemeli, all other species are very rarely collected and are mainly known from only a few specimens from their type localities. One undescribed species from northern Queensland was found among the Dytiscidae donated by D.J. Larson (Maple Creek, Canada) to the Australian National Insect Collection (ANIC) in Canberra.

Material:
We examined 401 specimens, including the type material of all species.
Descriptions: Beetles were studied with a Leica MZ 12.5 microscope at 10-100x. Photos of the male genitalia, used for the drawings, were made using a digital photo imaging system, composed of a Leica DM 2500 M microscope and a Tucsen 5.0 MP camera. This microscope was fitted with Leica HCX PL "Fluotar" 5x and 10x metallurgical grade lenses (Buffington and Gates 2008). Image stacks were aligned and assembled with the computer software Helicon Focus 4.77 TM . The drawings were scanned and edited, using the software Adobe Illustrator CS5.1. Label data of type material were cited in quotation marks. All type specimens of the herein described species were provided with red labels.
The terminology to denote the orientation of the genitalia follows Miller and Nilsson (2003). The following abbreviations were used: TL (total length), TL-H (total length without head), and MW (maximum width).
Coordinates are given in decimal notation unless cited verbatim from labels. Beside various Australian road maps, we also used Google Earth (http://earth.google. com) to locate localities.
Submerged roots and vegetation, stones and rotten logs were swept heavily; the material obtained was then placed on a white nylon sheet (1 m²) or in a white plastic box. Specimens were collected with forceps or by hand. Remarks. Medium-sized (TL = 6.9-9.6 mm), elongate, shiny and flattened mainly black diving beetles, unicolorous or with testaceous or ferruginous markings on elytra. Epipleuron in apical half more than twice as wide as base of longer spur of metatibia. Both parameres abruptly narrowed near middle. Outer metatarsal claw curved, prosternum with median furrow. Body covered with dense fine punctures and/or very fine microreticulation, meshes irregular, polygonal.
Allomatus was justified as a genus based only on the presence of a reticulated pronotum and elytra without any punctuation in contrast to Batrachomatus which has a non-reticulate but densely and finely punctate pronotum and elytra (Mouchamps 1964, Watts 1978. Brachomatus larsoni sp. n. has characters from both genera: a polygonal double reticulation with punctures at the intersections of all meshes. The cox1 sequence data show ( Fig. 15) that Allomatus wilsoni is sister to Batrachomatus daemeli, B. wingi sister to these two, and A. nannup sister to all of these. We use Matus bicarinatus (Say, 1823) from North America as well as Hygrobia maculata Britton, 1981 andH. wattsi Hendrich, 2001 as outgroups (Hygrobia were pruned for Fig. 15). Consequently Allomatus Mouchamps, 1964 is here synonymised with Batrachomatus Clark, 1863.
Type locality. Sydney, New South Wales, Australia.
Structure and sculpture. Body outline oblong oval. Dorsal surface densely and evenly covered with small punctures, and with a very fine, almost subobsolete close reticulation with large meshes. Serial punctures on elytron distinct, large and shallow. Ventral surface finely and densely punctate. Prothoracic process broad, flat, apex pointed, broadly grooved in middle for whole length, sides strongly margined. Metacoxal lines raised, well separated, reaching almost to hind margin of metaventrite, diverging a little anteriorly.
Male. Pro-and mesotarsi dilated and stouter than in female, furnished beneath with dense, short, stout setae arranged in groups, many of the setae ending in minute Variability. A very variable species in size and colour. Specimens having reddish shoulders of various form and extension were named B. burnsi Mouchamps, 1964 (Fig. 2, large red patch on the shoulder) and B. burnsi var. obscurior (smaller and interrupted reddish patch on shoulder). Such specimens can be found all over the species distributional range.
According to our study of the complete material of B. daemeli two different forms can be recognized: larger specimens (see measurements above) with larger median lobes and smaller specimens [Measurements: TL = 7.3-8.0 mm, TL-H = 6.5-7.05 mm; MW = 3.6-3.9 mm] (Fig. 3) with smaller and less elongated median lobes. The latter have been collected at several places in New South Wales and Victoria, sometimes syntopic with the larger form. Despite the fact that intergrades between the typical B. daemeli and the "smaller form" have been found, for some time we even have been strongly tempted to describe those smaller specimens as another new species. On the other hand we have not been able to find any constant extern morphological character-except of the size-and also the shapes of the male genitalia are more or less the same. In addition, in our cox1 tree (Fig. 15) specimens of both forms are grouped in the same clade.
Affinities. B. daemeli differs from the northern Australian B. larsoni sp. n. and B. wingii in the broader, more oblong shape, the lack of colour pattern on upper surface in most specimens, the weakly diverging metacoxal lines and the shape of the median lobe.
Distribution. The most widespread and common species of the genus in Australia (Fig. 13). From the Atherton Tableland in Queensland along the east coast of New South Wales, Canberra area, to western Victoria and north-eastern Tasmania (Watts 1978).
Habitat. Batrachomatus daemeli inhabits permanent streams, creeks and slow flowing larger rivers at an altitude from about sea level to almost 1000 m, from more or less open country in cultivated areas to closed-canopy forest sites (Figs 20-23). Most specimens were found in low-gradient stream or river sections where the substrate was enriched with rotten leaves, wood and larger stones. In this habitat the beetles were found in areas of medium, laminar flow, generally in deeper water (50 cm depth and more) under larger logs and stones. When disturbed the adults can be observed swimming around and coming to the surface. In dryer periods the species can be found in the deepest parts of the remaining rest pools of a creek or river. All the mentioned smaller specimens from Coffs Harbour, Flaggy Creek were collected in a peaty and intermittent creek, with muddy bottom, shaded by wet eucalypt forest. The adults were mainly being located in a mixture of water and mud under a larger rotten tree trunk (Fig. 20 Description. Measurements. Holotype: TL = 7.9 mm, TL-H = 7.1 mm; MW = 3.85 mm. Paratype: TL = 7.7 mm, TL-H = 7.0 mm; MW = 3.8 mm. Colour. Dorsal surface shiny, black, appendages reddish. Head black with epistome and labrum lighter. Pronotum with reddish broad lateral margin. Elytron with narrow reddish band along 2/3 of length of elytron (Fig. 4).
Structure and sculpture. Body outline oblong oval, only slightly convex. Head, pronotal and elytral surface covered by polygonal double reticulation, smaller superficial meshes inside larger and more visible meshes, with punctures at intersections of all the larger meshes. Sides of pronotum moderately curved and convergent anteriorly. Sculpture on elytra as in pronotum but punctures at the intersections of all larger meshes smaller. Serial punctures on elytron distinct, large and shallow. On ventral side, metacoxal plate with very fine microreticulation, meshes very elongate, inside minutely and sparsely punctate. Lateral wings of metaventrite very narrow. Prosternal process flat, broad, broadly carinate in midline, parallel-sided, weakly pointed apically, weakly margined. Metacoxal lines well separated, strongly diverging anteriorly. Area between metacoxal lines with many small punctures.
Etymology. This species is dedicated to our Canadian colleague David Larson (Maple Creek, Canada) who collected the only known specimens and recognized the species as new. The specific epithet is a substantive in the genitive case.
Affinities. Batrachomatus larsoni sp. n. differs from B. wilsoni by its smaller size (B. larsoni TL = 7.9 mm and B. wilsoni TL = 8.4-8.5 mm), in the lack of any reddish humeral angles on elytra, the more flattened and narrowly formed body, and in having the reticulation on the elytra weak without punctuation, instead of moderately strong and punctate. Both species can be separated by the shape of their median lobes.
Distribution. Only known from the type locality in NE Queensland (Fig. 14).
Habitat. The Windsor Tableland is a granite plateau at about 1100 m, near to but further inland from Mt. Spurgeon and Mt. Lewis, in north-east Queensland. Because of its altitude, it receives enough rainfall to sustain mountain rainforest over much of the plateau surface, although it is surrounded by tropical eucalypt savannah at lower altitudes. Access to the Windsor Tableland is now for scientific study only, the public are permanently barred. A very detailed habitat description is given by Larson (1993): "Two specimens were collected from a low gradient section of a small, permanent, closed forest stream. The stream was largely shaded by a tall, more or less closed tree canopy. The stream bed was coarse sand and consisted of shallow, gentle riffles which separated pools formed where sand had been scoured from around and behind logs and from under tree roots to produce pools under overhanging roots-mats. The specimens were found swimming in a pool after the trailing roots on an overhanging bank on one side of the pool had been vigorously swept with a net. It is assumed the beetles came from under the bank but similar habitat, which was common along the stream, was searched without yielding additional specimens". (Watts, 1978)   Colour. Dorsal surface shiny, black; appendages reddish. Head black with epistome and labrum lighter (Fig. 5).

Batrachomatus nannup
Structure and sculpture. Body outline narrowly oval, flattened and only slightly convex, pointed apically. Head with strongly impressed reticulation, meshes moderately large and irregular, some scattered small punctures; reticulation and punctures in pronotum rather weak. Elytron with fine reticulation, with transversely elongate small meshes, virtually impunctate apart from serial punctures, being comparatively large and well marked.
Ventral side with metacoxal plate covered by very fine microreticulation, meshes very elongate, inside minutely and sparsely provided with small punctures. Prosternal process flat, broad, broadly carinate in midline, parallel-sided, weakly pointed apically, weakly margined. Metacoxal lines well separated, subparallel in anterior 2/3, moderately diverging posteriad, area between lines with many small punctures.
Affinities. Batrachomatus nannup differs from most specimens of B. wilsoni and B. larsoni sp. n. in the lack of any reddish humeral angles to elytra, the more flattened and narrowly formed body, and in having the reticulation on the elytra weak without punctuation, instead of moderately strong and punctuate. All three species can be easily separated by the shape of their median lobes and their distribution.
Distribution. An endemic species of the Blackwood River in south-western Australia. All records between Bridgetown and Nannup but probably more widespread in the Blackwood River and its larger tributaries (Fig. 13).
Habitat. The Blackwood River is the largest river in south-western Australia. The river begins near Quelarup and runs in a south-western direction through the town of Bridgetown then through Nannup until it discharges into the Southern Ocean at Hardy Inlet near the town of Augusta. The river has 41 tributaries and the upper or larger catchment area of the river is in agricultural areas, while the middle catchment area passes through forested areas, and the lower portion of the river passes into mixed forest, agricultural and residential lands (Wikipedia).
At the sampling localities the Blackwood is partly shaded by old River gum trees. In late spring the adults of B. nannup can be either found in larger (6-10 m²) and deeper (40-80 cm depth) sandy pools in the floodzone of the river or among floating roots, rotten twigs and logs in shallow water of protected embayments of the slow flowing river (Fig. 16). In summer and in dryer periods the adults were collected only in the deepest parts of the almost standing river, under larger logs, stones and rotten debris (Fig. 17). When disturbed the beetles can be observed swimming around and coming to the surface. (Mouchamps, 1964) comb. n. by its larger size (B. wilsoni TL = 8.4-8.5 mm and B. larsoni TL = 7.9 mm), the different elytral coloration, and the more oblong and less narrowly formed body. Furthermore, all three species can be separated by the shape of their median lobes.

Batrachomatus wilsoni
Distribution. South-eastern Australia (Fig. 13). A rarely collected species with a very limited distribution. Only known from four sites from southern New South Wales (Wallagaraugh River) to southern and south-eastern Victoria (Macalister River, King Parrot Creek, Thurra River).  Habitat. Batrachomatus wilsoni inhabits permanent slow flowing larger rivers, at an altitude from about sea level to almost 170 m, in closed-canopy old growth forest sites. The type locality King Parrot Creek, near Kerrisdale, is in many parts a low gradient river, similar to the south-western Australian Blackwood River. The two recently collected specimens from Victoria and New South Wales were found in low-gradient river sections where the substrate was enriched with rotten leaves, wood and larger stones (Figs 18, 19). In this habitat the beetles were found in areas of medium, laminar flow, generally in deeper water (50 cm and more) under larger logs and stones, always together with numerous B. daemeli.  Description. Measurements. TL = 6.9-7.8 mm, TL-H = 6.2-7.2 mm; MW = 3.2-3.7 mm.

Batrachomatus wingii
Colour. Black, anterior part of head reddish brown, pronotum with broad yellow lateral margins, elytron with a narrow yellow band of which apical 1/3 close to side and basal 2/3 some distance from side (Fig. 7). Underside and parts of head reddish brown, appendages reddish brown.
Structure and sculpture. Body outline elongate oval, flattened, pointed apically. Dorsal surface shiny, head, pronotum and elytral surface densely and evenly covered with small punctures, reticulation absent. Serial punctures on elytron sparse, weakly impressed, indistinct. Sides of pronotum moderately curved and convergent anteriorly. Ventral surface very densely and minutely punctured. Prosternal process flat, broad, parallel-sided, weakly and narrowly grooved in midline, and weakly margined at side, tip bluntly pointed, apex pointed. Metacoxal lines well separated, subparallel, reaching almost to hind margin of metaventrite. Male. Pro-and mesotarsi stouter than in female, furnished beneath with dense, short, stout setae arranged in groups, many of the setae ending in minute suction cups. Aedeagus: median lobe (Fig. 12 a, b); paramere (Fig. 12 c).
Affinities. A very characteristic species and one of the most beautiful dytiscids in Australia (Fig. 7). B. wingii differs from all other species of the genus in the narrower and more flattened shape of body, the dorsal yellowish longitudinal stripes on the elytra, the subparallel metacoxal lines and the shape of the median lobe.
Distribution. Tropical northern Australia. Occurring from the northern Pilbara and the Kimberley region in the northwest, the Daly River, Darwin area and Kakadu National Park in the north, to the Atherton Tableland in northern Queensland, and along the east coast south to Rockhampton (Fig. 14).
Habitat. Batrachomatus wingii occurs in seasonal and permanent lowland streams, creeks and slow flowing smaller rivers at an altitude from about 20 to almost 150 m, at least partly shaded by eucalypt woodland or monsoonal forest. Most specimens were found in low-gradient stream sections where the substratum was entirely coarse sand and smaller pebbles yet the current was strong enough to clear the bottom of silt and leaves (Figs 24,25,27). In this habitat the beetles were found in areas of medium, laminar flow, generally in deeper water (50 cm depth and more), along the outside curve of stream bend, among floating gum roots, under larger logs and stones. In the Northern Territory, at the end of the dry season, a larger series of the species was collected in the deepest, coldest and most oxygen rich part (50-80 cm depths) of a rest pool (10 m²), situated in a broad and almost dry and sandy creek bed. The pool was without any vegetation but rich in rotten leaves and partly shaded (Fig. 26). As mentioned by Larson (1993), who collected the species in northern Queensland at three different sites, the sub-surface seepage and local water temperatures could also be factors responsible for the local aggregation of beetles. In the Northern Territory larvae have been collected after the rainy season in February by Watts (Alarie et al. 2001).

Habitats and faunistics
All Australian Batrachomatus species are strongly lotic and restricted to streams, creeks and rivers with sand, pebble and cobble beds, often situated in woodland or closedcanopy forest sites (Figs 16-27). It is probable that at least the larvae are sensitive to low levels of dissolved oxygen and require cooler temperatures. If this is so the occurrence of any Batrachomatus species can be considered a good indicator of a running water´s health, habitat and water quality.
The currently known altitudinal distribution and ecology of Batrachomatus species is shown in Table 1 of the south-eastern B. wilsoni might be the result of human impacts (irrigation, increasing of salinity, clearing of riverine forests) on almost all river systems in Victoria in the last five decades. All species seem to be capable of flight but none was ever obtained by operating light traps. The larvae of B. daemeli and B. nannup were recently described by Alarie et al. (2001). The larvae of B. wilsoni, B. larsoni sp. n. and B. wingii remain unknown. When in a net and out of the water specimens of Batrachomatus move very rapidly and are easily to recognise and to collect. In contrast, Larson et al. (2000) noted that the related Nearctic Matus are all lentic and occur along the margins of rather eutrophic ponds, often amongst Typha or decaying deciduous leaves. They are often slow to move and with their brownish colour are easily overlooked and consequently are not well collected. Despite the fact that all Australian species are capable of flight, none was obtained by operating light traps. Body outline oval, slightly convex. Humeral angle of elytron reddish. Punctures at the intersections of a very few larger meshes. Metacoxal lines separating metacoxal plate into three unequal parts; the median sparsely punctured, the lateral almost smooth with an extremely sparse and scarcely visible microreticulation. Aedeagus: median lobe (Fig. 11 a, b)  Body outline narrowly oval, flattened and only slightly convex, pointed apically. Elytron uniformly black, reticulation virtually impunctate. Metacoxal lines well separated, subparallel in anterior 2/3, moderately diverging posteriad, area between lines with many small punctures. Aedeagus: median lobe (Fig. 10 a, b)  Pronotum totally black. Elytra with or without a red humeral angle. Body outline oblong oval. Dorsal surface with a very fine almost obsolete close reticulation with larger meshes. Metacoxal lines raised, well separated, reaching almost to hind margin of metaventrite, diverging a little anteriorly. Aedeagus: median lobe (Fig. 8 a, b)  Pronotum with broad yellow lateral margins, elytron with a narrow yellow band of which apical 1/3 is close to side and basal 2/3 some distance from side. Body outline elongate oval, flattened, pointed apically. Reticulation on dorsal surface absent. Metacoxal lines subparallel. Aedeagus: median lobe (Fig. 12 a, b)