Sympetrum nantouensis, Tang, Hsin-Chieh, Yeh, Wen-Chi & Chen, Szu-Lung, 2013

Tang, Hsin-Chieh, Yeh, Wen-Chi & Chen, Szu-Lung, 2013, Description of an endemic and endangered new Sympetrum species (Odonata: Libellulidae) from the subtropical area of Taiwan, Zootaxa 3693 (3), pp. 351-357 : 352-356

Sympetrum nantouensis sp. nov.

( Figs. 1–11 )

Etymology. The specific name purports to the limited occurrence of this species, currently known only from Nantou County of Central Taiwan.

Male holotype. Labium dirty whitish, narrowly black at inner margins of lateral lobes; face cream-white, pale brown at middle of labrum and antefrons, moderately adorned with short black hairs; black basal band of postfrons narrow, medially produced triangularly; vertex bulging and black; compound eyes dark reddish dorsally and grayish ventrally; occiput deep brown; posterior margin of head black without pale marking and fringed with short brown hairs.

Prothorax black, hind lobe deep brown and fringed with long brown hairs at upper margin. Pterothorax with anterior side deep brown at upper part, including antealar sinuses, and black at lower part, pale yellowish dorsal stripes directed outwards at lower ends; sides of pterothorax pale yellow with broad black stripes on humeral and 1st and 2nd lateral sutures ( Fig. 2 ); black stripes of humeral and 1st lateral sutures connected to each other ventrally behind mesinfraepisternum; black stripes of 2nd lateral sutures on both sides extending downwards across ventral side of pterothorax and connected to each other; anterior side of pterothorax sparsely adorned with long brown hairs. Legs dark brown, ventral sides of fore femora pale yellowish. Wings transparent, faintly colored with amber basal to 1st antenodal vein in both wing pairs; pterostigma dark reddish brown. Crossveins 9-9-8- 8 in forewings and 9-7- 7-9 in hindwings.

Abdomen slim, weakly broadened on S2 and S3 ( Fig. 1 ); S1 dark brown, remaining segments vividly red with black apico-lateral spots on S4–7 and black lower stripes on sides of S8–9; ventral sides of S5–9 black. Cerci pale reddish and as long as S9–10; in dorsal view straight and parallel-sided with apex bent slightly inwards; in lateral view beak-like, apex obliquely truncate and ending in a downcurved tooth, ventral margin with triangular process at middle. Epiproct yellowish brown, 3/4 as long as cerci ( Fig. 7 ).

Hamules of secondary genitalia with inner hooks strongly curved and directed outward in lateral view, closely adjoining and as high as elongate outer lobes ( Fig. 8 ); genital lobes erect, directing posteroventrally and with round apex. Segment 4 of penis spoon-shaped ( Fig. 9 ), cornua mostly covered by two broad, flat and closely adjoining medial lobes ( Fig. 10 ) with exposed apices twisted and upcurved ( Fig. 11 ); Ventral margin of segment 4 with crestlike protuberances (medial nodules of Pilgrim & von Dohlen 2012).

Female (paratype). General appearance of female similar to holotype male, sexual differences noted as follows. Labrum entirely pale brown, black basal band on postfrons broader and without clearly defined anterior margin. Pterothorax with anterior side darker. Abdomen deep brown dorsally and black laterally ( Fig. 3 ); S1 black dorsally and with diffused small pale spots laterally; S2 black at anterior margin, rectangular yellow mark on lateral side concave on both ends along posterior margin; lateral sides of S3–7 black, with spots both before and behind transverse carina adjoining each other on S3–5, lateral spots of S6 and S7 connected to dorsal deep brown areas; S8–10 black with paired deep brown baso-dorsal spots, spots of S8 elongate, three times as large as on S9, spots of S10 tiny and obscure ( Fig. 4 ); cerci brownish, shorter than S9, straight and pointed at apex; sternum of S8 truncate at apex, valvula vulvae aberrant and indiscernible; sternum of S9 with apex smoothly rounded and reaching middle of S10.

Variation in paratypes. Color pattern on anterior side of pterothorax a little variable in this species ( Fig. 5 ). Dorsal stripe may change to deep brown, confluent with upper deep brown area, forming broad 7-shaped marking, or anterior side of pterothorax may become darker entirely, leaving only a pair of narrow deep brown dorsal stripes and two spots below antealar sinuses. Red-form female with dorsum of abdomen dull red.

Measurements (mm). Holotype: ♂ abd. + cerci 25, hindwing 28, pterostigma 2.5; Paratypes: ♂ abd. + cerci 24–27, hindwing 27–30, pterostigma 3.0; ♀ abd. + cerci 24–26, hindwing 27–30, pterostigma 3.0.

Material examined. Holotype: ♂, Yuchih Lienhuachih, Nantou County, Central Taiwan, 11/XI/2009, leg. SLC; Paratypes: 9 ♂ & 6 ♀, with same data as holotype. All type specimens will be deposited in the Insect Collection of TFRI.

Diagnosis. Sides of pterothorax in both sexes are well striped with broad black and pale yellow. In both sexes, all wings are almost entirely hyaline. Males have abdomen vividly red and slender; cerci beak-like, obliquely truncate apically and ending in a downcurved tooth, with a ventral triangular process at middle; apical segment of penis with broad medial lobes adjoining each other and cornua twisted and upcurved at apex.

Remarks. S. nantouensis has a limited range, currently known only from the low mountainous area of Central Taiwan. So far, this species has been recorded from only four townships in Nantou County, i.e. Yuchih, Puli, Jiji and Shueili, with elevation varying from 300- 800 m. The records from Jiji and Shueili consist of single individuals and do not prove the existence of a sustainable population. The main habitat in Yuchih is a small grassy marsh ( Fig. 6 ) surrounded for the most part by secondary broad-leaved forests and conifer plantations. According to local people, this marsh has been paddy field in the past and was abandoned two decades ago. The vegetation of the marsh is mainly composed of grasses and sedges of Gramineae and Cyperaceae , dominated by Leersia hexandra Sw., Isachne globosa (Thunb.) Kuntze , Eleocharis dulcis (Burm. f.) Trin. ex Hensch. var. tuberosa (Roxb.) T. Koyama , Murdannia keisak (Hassk.) Hand. -Mazz., and Ischaemum indicum (Houtt.) Merr. The water depth is usually low and invisible below the coverage of grassy vegetation but can reach up to 20–30 cm deep from September to November.

The dragonfly community of this marsh is poor and dominated by S. nantouensis . Other species recorded, usually in low numbers, are Ceriagrion fallax fallax Ris , Gynacantha japonica Bartenef , Crocothemis servilia servilia (Drury) , Orthetrum triangulare (Selys) and Pantala flavescens (Fabricius) .

This species has a long flight season, extending mainly from mid August to January, with a few individuals observed as early as July. During the breeding season the mating of adults could be seen from 11:00 to 13:00, with copulations lasting from several minutes to more than ten minutes if not disturbed. Females usually performed noncontact and egg-dropping ovipostion in tandem with their mates while they hovered low above the marsh. On one occasion, a female was observed to make contact oviposition directly into the water.

Discussion

Pilgrim & von Dohlen (2012), in their phylogenetic analysis of the genus Sympetrum based on both molecular and morphological characters, have recognized six species-groups worldwide. They show that male penile morphology is a good clue to allocate species to these groups. Judging from penile morphology, S. nantouensis clearly belongs to the infuscatum -group. Five species have been put in this group by Pilgrim & von Dohlen, included S. darwinianum , S. gracile Oguma, S. infuscatum (Selys), S. maculatum Oguma and S. risi . Other species that should be transferred to this group include S. hypomelas (Selys) ( Fig. 13 ), S. orientale (Selys) ( Fig. 14 ) and S. xiaoi Han & Zhu (present authors, unpublished). S. daliensis , which is probably conspecific with S. risi , should also belong to this group. The members of this group are better characterized by a combination of the following features on segment 4 of male penis: medial lobes well-developed and elongate, not covered at least basally by lateral lobes or apical extensions of segment 4 (cf. Figs. 15 and 16 for S. b. baccha , whose medial lobes are concealed basally), hence exposed and clearly visible ventrally; medial lobe hides from below most of cornu, which is more or less curved apically; and the presence of ventral protuberances on segment 4 (weak in S. darwinianum , S. maculatum and S. orientale ).

In the infuscatum -group, S. nantouensis is most similar to S. risi in general appearance and structure of the male secondary genitalia. S. risi is distributed only in East Asia, with an insular endemic subspecies, S. r. yosico Asahina, in Hokkaido, Japan (Sugimura et al. 2001). S. nantouensis and S. risi have in common broad medial lobes adjoining each other on penile segment 4 and partly covered ventrally by a narrow extension branched off from the apical margin of the segment. However, S. nantouensis is easily separated from S. risi by its beak-like male cerci. The penile segment 4 of S. risi differs from that of S. nantouensis in having posterior and inner lobes well developed and easily recognizable, medial lobes shorter, and cornua completely covered by medial lobes ( Fig. 12 ). In outer appearance S. nantouensis has a more contrasting body pattern than S. risi , with lateral black stripes of pterothorax broader, nearly as wide as or wider than the pale stripes on the pleura.

S. nantouensis is unique among the known Sympetrum both morphologically and biogeographically. The beaklike cerci are among the strangest in its genus and very different from those of S. risi . This suggests it is only remotely related to S. risi despite the general similarities between them. This argument is supported by unpublished molecular data from Dr. Lin Sue-Cheng (pers. comm.). Hence it is possible that there could be one or more closer relatives of S. nantouensis waiting to be discovered somewhere in Indochina and/or Mainland China. The known geographic range of S. nantouensis is very small when compared to those of most of its congeners. It is probably the only known Sympetrum endemic to an island such as Taiwan, which began to emerge above sea level only about 5-10 million years ago (Liu et al. 2000; Huang 2011) and is relatively young in geology. So far, no other Sympetrum has such a limited distribution confined to a small subtropical area. The insular and peripheral existence of S. nantouensis in the entire range of the infuscatum -group, which is mainly East Asian, deserves further research on its biogeography and speciation, and the results in turn will throw some light on the evolution of its group and genus.

All localities where S. nantouensis was recorded are near cultivated lands or orchards, and none is situated in a protected region. The main habitat in Yuchih belonged to a private estate and was vulnerable to human disturbance. The clearing of the understory for recreational development in neighboring forests has already been undertaken in 2012. In view of its uniqueness in terms of evolution and biogeography, and considering the environmental pressures of the near future, a proper conservation act for this species is strongly recommended. We suggest listing this species both locally and globally as “Endangered” [(EN, B1ab(ii,iv)] following The IUCN Red List Categories and Criteria (IUCN, 2001).

Figures

FIGURES 1 – 6. Sympetrum nantouensis. 1, holotype, male, lateral; 2, holotype, male, dorsal; 3, paratype female, dorsal; 4, paratype female, lateral; 5, Color patterns on the anterior side of pterothorax; 6, The main habitat of S. nantouensis in Yuchih, Nantou County, Taiwan.

FIGURES 7 – 12. Male reproductive structures in Sympetrum. 7 – 11, S. nantouensis, 12, S. risi. 7, cerci, lateral; 8, male hamule, lateral, upside down; 9, penis, lateral, upside down; 10, penis, ventral; 11, penis, posterolateroventral; 12, penis, lateral.

FIGURES 13 – 16. Penes of Sympetrum. 13 – 15, lateral, upside down, 16 ventral. 13, S. hypomelas; 14, S. orientale; 15 – 16, S. b. baccha.