Dexoris chome, Bocak, Ladislav & Masek, Michal, 2013

Bocak, Ladislav & Masek, Michal, 2013, A new species of Dexoris (Coleoptera: Lycidae) and parallel evolution of brachyptery in the soft-bodied elateroid beetles, Zootaxa 3721 (5), pp. 495-500 : 496-497

Dexoris (s. str.) chome sp. nov.

( Figs 1–8 , 10–13 )

Type material. Holotype. Male, “ Tanzania, South Pare Mts., Chome For., S4.27064° E37.92595°, 2159 m, 3.i.2013, sift38, V. Grebennikov leg.” The holotype is deposited in the Canadian National Collection of Insects, Arachnids and Nematodes, Ottawa.

Type locality. Tanzania, South Pare, Chome Forest, S4.27064° E37.92595°, 2159 m.

Diagnosis. Dexoris chome sp. nov. is the only species in the genus with a brachelytrous male. The only known male of the new species differs from other fully winged Dexoris males in having shorter elytra, nonfunctional and vestigial hind wings, short robust antennae and the pronotum widest in the anterior third ( Fig. 1 ). Additionally, D. chome sp. nov. differs in having 3-segmented maxillary palpi (4-segmented in other Dexoris ) and 2-segmented labial palpi (a single free palpomere in other Dexoris species). Male genitalia have a well sclerotized asymmetrical phallobase, unlike other Dexoris ( Figs 10–12 ).

Description. Male. Body small, light testaceous, wings partly infuscate, eyes black ( Figs 1–2 ). Head small, hypognathous, partly covered by pronotum; cranium with slightly prominent frontal part, surface roughly punctured, very sparsely pubescent. Antennae 11-segmented, inserted fronto-laterally, below frontal tubercles, short, reaching slightly behind posterior angles of pronotum, rounded in cross section; scapus robust and pear-like, pedicel small and slightly shorter than wide, antennomere 3 1.5x longer than antennomere 2, subsequent antennomeres gradually shorter, antennomere 11 parallel-sided and long, all antennomeres with short dense pubescence ( Fig. 6 ). Eyes small, hemispherically prominent, eye diameter 0.29x interocular distance. Mouthparts with slender and short mandibles ( Fig. 4 ). Labrum transverse, with shallowly emarginate apex ( Fig. 5 ). Hypopharynx forming simple oblong plate, much narrower than labrum. Maxillae with plate-like stipes, cardo inconspicuous and partly membranous; mala reduced and with sparse setae; maxillary palpi 3-segmented, basal palpomere short, transverse, ring-like, palpomere 2 twice longer, palpomere 3 robust, apex pointed. Labium small, single weakly sclerotized plate present, ligula inconspicuous, palpi 2-segmented, basal palpomere short, apical palpomere 3 times longer ( Fig. 3 ). Pronotum slightly wider than long, parallel-sided at base, widening anterad, basal angles slightly obtuse, not prominent, frontal angles obtuse, anterior margin almost straight, deeply and narrowly emarginate in middle; pronotum with robust longitudinal carinae forming well marked areola attached to posterior margin, middle of longitudinal carinae with attached vestiges of lateral keels, surface with deep irregular punctures ( Fig. 1 ), disc covered with sparse pubescence. Scutellum bilobed apically, distal processes slender ( Fig. 1 ). Elytra shortened, tapering towards apex, without longitudinal or transverse costae, with small papillae each bearing single tiny seta ( Fig. 1 ), elytra completely covered with dense microsetae. Wings vestigial, about 0.4x elytral length, longitudinal costae present, transverse costae absent, fused costal veins at base of wing robust, radia and media inconspicuous at base, gradually becoming visible distad, other longitudinal veins absent ( Fig. 2 ). Legs short, robust, femora with emarginate posterior part, basal interconnecting membrane reaching in posterior part to middle of femoral length, tarsomeres slender, similar in width ( Fig. 8 ). Abdomen wide, terminal sternite parallelsided, shallowly emarginate at apex ( Figs 7 , 13 ). Male genitalia with phallus and asymmetrical phallobase, parameres absent. Phallus about 7.5x longer than wide in middle, gradually tapering and pointed apically, internal sac membranous, without sclerotized structures ( Figs 10–12 ).

Measurements. Body length 6.15 mm, pronotal length at midline 1.0 mm, maximum pronotal width 1.25 mm, length of elytra 2.18 mm, length of hind wings 0.94 mm, length of abdomen (ventrally) 3.88 mm, maximum width of abdomen 1.88 mm, minimum frontal distance between eyes 0.83 mm, maximum eye diameter in the lateral view 0.24 mm.

Distribution. Dexoris chome sp. nov. is known only from the type locality. It is the only Dexoris recorded from Tanzania. The distribution of all 11 known Dexoris species ( Fig. 14 ) closely corresponds to the hypothesized distribution of the stable forests during the arid periods (Fjeldså & Lovett 1997), also currently matching the diversity hotspots in Africa (Myers et al. 2000). The very limited dispersal capacity of Dexoris species, all having wingless females, limits these beetles to regions with uninterrupted, relatively wet forest.

Etymology. The specific epithet refers to the Chome Forest in the North Pare mountains in Tanzania, the geographic origin of the holotype; noun in apposition.

Biology. A single male was extracted using a Winkler funnel, from the fine fraction of the forest floor leaf litter sifted through a seven millimetre mesh in almost undisturbed mountain rainforest. Females of the species remain unknown and we hypothesise them to be completely larviform and resembling in this respect other neotenics Lycidae (Wong 1996) . Detecting only a single specimen of the new species is rather remarkable considering that a relatively large sifting effort has been conducted.

Figures

FIGURE 14. The distribution of Dexoris and centres for evolution of new species defined by Fjeldså & Lovett (1997).

FIGURES 1 – 8. Dexoris chome sp. nov. 1 general appearance, 2 hind wing, 3 maxillae and labium, 4 mandible, 5 labrum, 6 antenna, 7 abdomen, 8 hind leg. Scales 1 mm (Figs 1, 7), 0.5 mm (Figs 6, 8), 0.25 mm (Figs 2 – 5).

FIGURES 9 – 13. 9 Omalisus fontisbellaquaei, general appearance; 10 – 12 Dexoris chome sp. nov., male genitalia; 13 ditto, terminal abdominal segments. Scale 1 mm (Fig. 9), 0.2 mm (Figs 10 – 13).