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The exuviae of the Urothemistinae of the Arabian Peninsula including the first description of the exuvia and final instar larva of Urothemis thomasi Longfield 1932 (Odonata: Libellulidae).

Key words: Odonata, dragonfly, larval description, Urothemistinae, Urothemis thomasi

Abstract

The exuviae of all four species of Urothemistinae known from the Arabian Peninsula (Macrodiplax cora, Selysiothemis nigra, Urothemis edwardsii and U. thomasi) were collected on recent surveys in UAE and Oman. The exuvia of Urothemis thomasi, first discovered in 2013, is described here for the first time. This paper, when used in conjunction with Suhling et al. (2014), provides sufficient information for all species of Libellulidae currently known from Arabia to be identified from final instar larvae and/or exuviae. It is hoped that this will encourage local naturalists to collect and identify specimens, which will improve knowledge of this region of which large areas remain little known.

Introduction and Discovery

On 7 June 2013 Urothemis thomasi was recorded for the first time in the United Arab Emirates (UAE), from Wadi Wurayah National Park (WWNP) (Feulner & Judas 2013). Present on that occasion as a visiting naturalist was one of the authors, DGC, who during his visit collected exuviae from WWNP. In the autumn of 2013, DGC examined the collected material and found a large libellulid exuvia that he was unable to identify. Photographs were circulated to a number of authorities with no success. Eventually, CB took more and better photographs and then sent the material on to RS, who examined it in detail. RS listed the following features as being those unique to the genus Urothemis within the Urothemistinae, which is one of the few subfamilies still recognised in the Libellulidae, along with the Libellulinae and the Leucorrhiniinae (Ware et al. 2007; Dijkstra et al., 2013):

* eyes strongly directed and elongated backwards;

* well expressed body setulation;

* long, slender and tapering antennal segment 7;

* triangular shaped poststernum which is present in very few genera of Libellulidae and illustrated in Figure 3 below;

* wide and flat-notched distal frons (wider than submental width);

* crenulated distal border of palp;

* softly curved connection between arch and lobe; and

* short epiproct and short anal pyramid.

Having concluded that the specimen was a member of the genus Urothemis and knowing that U. thomasi had recently been recorded from the same site, RS proposed that the exuviae was that of U. thomasi, which is the only species of this genus known from the UAE.

In a subsequent trip to Wadi Wurayah in April 2014, DGC collected a late instar larva and an additional exuvia of this species. This material was augmented on a trip to Oman in Autumn 2014, where Christian Monnerat, a Swiss researcher, collected larvae. These specimens were passed to CB for photographing and breeding out. Unfortunately, all these specimens died immediately prior to emergence.

In October 2014 and thanks to funding from the Mohamed bin Zayed Species Conservation Fund, a field trip into the UAE and Northern Oman took place with the prime purpose of establishing the status and distribution of U. thomasi in the region. This trip again found adults and exuviae of U. thomasi in Wadi Wurayah in the UAE, but not yet in Northern Oman. A second field trip took place in April 2015, which included the Dhofar province of southern Oman, and was successful in finding exuviae of U. thomasi, together with exuviae of three other species pertaining to the regional Urothemistinae. Most importantly, Anthony Stoquert, a member of the second field trip, collected a live larva of U. thomasi from Dhofar This latter was first reared in the field station at WWNP by Patricia Cabrera, then by Philippe Lambret who took it to the Tour du Valat research station (Camargue, France) and various other locations during further displacements up to its emergence in August 2015. The emergence confirms the original RS identification.

DGC was not present during the second trip but was charged with the identification of the collected exuviae material. The Urothemistinae exuviae examined for purposes of this paper are set out below and were collected by DGC from UAE and Oman and by Anthony Stoquert during the first and second field trips to Oman, respectively:

* Macrodiplax cora--4 ex.

* Selysiothemis nigra--9 ex.

* Urothemis edwardsii--9 ex.

* Urothemis thomasi--8 ex.

RS has provided additional expertise and was able to correct some of the original assumptions made by DGC. This paper summarises the identification of all the Urothemistinae found in the Arabian Peninsula and provides a detailed description of the exuvia /final instar larva of U. thomasi for the first time. Details of the biology and ecology of U. thomasi have not been included here but are to be found in Lambret et al. (2015).

The Urothemistinae of Arabia

The Arabian Peninsula, hereinafter referred to as Arabia, consists of the Kingdom of Saudi Arabia, Kuwait, the Republic of Yemen, the Sultanate of Oman, the United Arab Emirates, Qatar and the Kingdom of Bahrain. At the time of writing (early 2015), a total of 66 species of Odonata have been recorded from the region, including 38 species of Libellulidae. The larvae of all but three of these Arabian Libellulidae species are described and illustrated in Suhling et al. (2014). This latter work covers the region of Namibia in southern Africa and none of the three excluded species occurs in that region. Those three species together with Urothemis edwardsii (which is included in Suhling et al. (2014)) are all of the Arabian members of the Urothemistinae.

The contribution made by this paper is presented in two parts:

I. Key and general description of the Urothemistinae of Arabia--Taking features described in Suhling et al. (2014) to highlight the identification features of the Urothemistinae of Arabia. Macrodiplax cora and Selysiothemis nigra are illustrated and described in general terms.

II. The genus Urothemis in Arabia--The two remaining species are of the genus Urothemis. Urothemis thomasi is described for the first time. Its congener U. edwardsii has been described in detail by Seidenbusch (1995) and Khelifa et al. (2013) and is illustrated here. In the interest of brevity, the description of U. thomasi provided here concentrates only upon the differences between the two species.

This paper, when used in conjunction with Suhling et al. (2014), provides sufficient information for all species of Libellulidae currently known from Arabia to be identified based on final instar larvae and/or exuviae.

I. Key and general description of the Urothemistinae in Arabia

Figure 1 shows headshapes (viewed from above and not to scale) for Libellulidae encountered in the Middle east and North Africa. The features have been emphasised for effect.

[FIGURE 1 OMITTED]

* Headshape 1 is unique to the Libellulinae subfamily. The very small eyes (highlighted in red) and parallel head margins (blue)are diagnostic.

* Headshape 2 typical of the other members of the family Libellulidae not featured here with large eyes and rounded margins (blue)

* Headshape 3, with its strong round eyes and strongly incurved head margins, is unique and diagnostic to Zygonyx.

Headshape 4, with almost triangular profile and strongly backward pointing eyes, is found in three groups identifiable in Arabia with the following key:

1. Abdomen without dorsal spines................Tramea and Pantala (footnote 1)

1'. Abdomen with dorsal spines often very small............................ 2

2. Dorsal spines not present on abdominal segment (ab. seg.) 9 .......... Urothemistinae (Urothemis, Selysiothemis and Macrodiplax)

2'. Dorsal spines present on ab. seg. 9.......................3

3. Larvae/exuviae <17.0 mm long; distinctive egg shaped abdomen with very compressed anal pyramid ........................... Rhyothemis (footnote 2)

3'. Larvae/exuviae 20.0 mm long; rounded abdomen with prominent anal pyramid Tholymis (footnote 2)

Footnote 1: Pantala does have small dorsal spines, but only on ab. segs. 2-4; the overall appearance is very similar to Tramea although the uniformly black tarsi of Pantala are diagnostic. Other features separating Pantala from Tramea are the very short moveable hook and deep palpal crenations of the former species.

The features above are illustrated in Suhling et al. (2014). In addition, Rhyothemis exuvia is described in Samways et al. (1998).

Footnote 2: The eyes in Tramea, Pantala and the Urothemistinae are greater than half head length, eyes in Rhyothemis and Tholymis are small and less than half head length.

The Urothemistinae can therefore be separated by:

* Headshape type 4)

* Dorsal spines present but absent from ab. seg. 9

* Eyes greater than half the length of the head

* Large size, always in excess of 17.0 mm long

Figure 2 shows all four species of Urothemistinae that have currently been recorded from the Arabian Peninsula. The most striking feature is how distinct Urothemis thomasi is from the other three species, with its distinctive colour patterning very strong dark markings on head, thorax and abdomen and minute dorsal and lateral abdominal spines.

[FIGURE 2 OMITTED]

The regional members of the genus Urothemis can be separated from the remaining two genera by the presence of conspicuous and long setae which are best seen on the live larvae but persist on the exuviae (Figure 3).

[FIGURE 3 OMITTED]

The presence of setae in exuviae can be difficult to detect as they can easily be broken. In such cases the triangular or sub-triangular shape of the poststernum is diagnostic within the Urothemistinae (Figure 4).

Figure 4. Poststernum in Urothemistinae--for emphasis shown in black--viewed from the underside.

[FIGURE 4 OMITTED]

Macrodiplax and Selysiothemis are both very mobile, vagrant and migrant, species and are highly salt-tolerant. The former is known from the Dhofar coast and inland desert oases as well as from northern Oman in coastal lagoons. It has even been recorded in a resort swimming pool. Selysiothemis nigra has been widely recorded from a variety of habitats over much of Arabia. Both species are known from neighbouring coastal lagoons in northern Oman and probably will be found syntopically in the future. Their exuviae are quite distinct, as shown below.

According to de Fonseka (2000), the larvae of Macrodiplax cora had never been described. It was, however, subsequently figured and/or keyed in several publications (e.g. Theischinger & Hawking, 2006; Theischinger & Endersby, 2009, 2014) and appears to be a large exuvia (20.2 mm) with very distinctive straight lateral spines extending at least to the end of the anal pyramid. In the photo provided by Ozono et al. (2012), the lateral spines on ab. seg. 9 do not quite reach the apex of the anal pyramid, however, showing that the variability of this feature remains open to study. The sharply pointed nature of the lateral spines on ab. seg. 9 is used in Theischinger & Endersby (2009) (p. 180) to separate Macrodiplax from Urothemis. Besides, this lateral spine is described as having a slightly S-curved outer edge, whereas the latter is straight in Urothemis. Both features match our specimens, which we can therefore ascribe to Macrodiplax cora (Figure 5a). The larva of this taxon is also illustrated, without description, by Lieftinck (1962). However, on p. 83, the figure of M. cora looks rather different from both that of Theischinger & Endersby (2009) and our specimens. Lieftinck's illustration has convergent lateral spines and a very short anal pyramid (Figure 5c).

In order to support our identification with further evidence, we have compared the exuviae of Macrodiplax cora and Macrodiplax balteatus, the only other species of this genus, which is found in the southern parts of the USA. The two species are shown in Figure 5 together with Lieftinck's illustration. The specimen of M. balteatus shown here was collected in southern Florida and has been identified using Needham et al. (2000). The only obvious difference between the two species is that M. balteatus is very heavily marked whilst M. cora shows a quite uniform light brown. All 17 specimens of M. balteatus in DGC's collection show these very strong markings which are not present in M. cora. However, the absence of markings cannot be regarded as a diagnostic feature as the M. cora specimens may simply have been bleached by the sun. The principal point is that the whole genus is characterised by a large anal pyramid and straight and sharply pointed lateral spines on ab. seg. 9. The identity of the Lieftinck specimen (Figure 5c) is open to speculation.

[FIGURE 5 OMITTED]

Selysiothemis nigra has an appearance closer to the genus Urothemis with its inward pointing lateral spines and thinner dorsal spines, and can be separated from M. cora as shown in Figure 6. The dorsal spines are also quite different (Figures 6c & 6d). S. nigra and M. cora lack the long setae present in Urothemis and both genera have a trapezoidal poststernum. S. nigra is a very variable exuvia, with some having strong dark brown markings (Figure 6b) and others suffused with small and poorly defined light brown areas (Figure 7a). Lateral spines may or may not reach the end of the anal pyramid (Figures 6b and 7b). Their size also shows considerable variation, with some specimens exceeding 20 mm in length in, for example, Turkey. Great care should, therefore, be taken in their identification.

The three genera of Urothemistinae in Arabia can be keyed as follows:

1. Abdomen with triangular poststernum (Figure 4b) and long setae on both tergites and sternites, found in the larvae and persisting in the exuviae (Figure 3a) ........................... Urothemis

1'. Abdomen with trapezoidal poststernum (Figure 4a) and without setae as above ........................ 2

2. Abdomen with wide-based angulated dorsal spines and long straight parallel lateral spines on ab. seg. 8 & 9 ......................................... Macrodiplax

2'. Abdomen with narrow-based curved dorsal spines and incurved lateral spines on ab. seg. 8 & 9. Those on ab. seg. 9 convergent ..................................... Selysiothemis

II. The genus Urothemis in Arabia: comparison of the exuviae of U. thomasi and U. edwardsii

Two species of Urothemis are currently known from Arabia. Whereas the exuvia of U. edwardsii has been described in detail by Seidenbusch (1995) and Khelifa et al. (2013), the exuvia of U. thomasi will be described here for the first time. Figures will highlight the differences between the two species.

General comparison

Figure 8 shows both species of Urothemis. The most important difference between U. edwardsii and U. thomasi is the greatly reduced abdominal spines in U. thomasi, both dorsal and lateral. A secondary difference, although perhaps not always reliable (see Macrodiplax and Selysiothemis descriptions above), is the strength of the colour patterning of U. thomasi. In two of the eight specimens of U. thomasi, the contrasting dark markings are almost black, as shown on the right of figure 8a and on Figure 8c. In contrast, all 9 specimens of U. edwardsii are a uniform brown (Figure 8b). The extensive setae, characteristic of the genus, are clearly seen in Figure 8d.

[FIGURE 8 OMITTED]

Overall size

Table 1 shows the comparative sizes of the larvae of the two Urothemis species found in Arabia. Based upon the material available, U. edwardsii in southern Oman is significantly shorter (23.0%) than those from the Mediterranean coast of Algeria. Even larger specimens (27.0 mm) have been recorded from Lake Bleu, Algeria (B. Samraoui leg.) (Seidenbusch, 1995). Suhling et al. (2014) described U. edwardsii (p. 74) but did not give any overall size information.

The head of U. thomasi is much more strongly marked than U. edwardsii and shows a large and well-defined pale spot in the middle in dorsal view (Figure 9). See also Figures 2b and 2c, and 8a and 8b.

Labium

[FIGURE 9 OMITTED]

The labium of the two Urothemis species is very similar (Figure10: dorsal view; Figure11: ventral view). The most significant difference is that U. edwardsii has more extensive dark spotting on both the labial palps and the underside of the prementum. This dark spotting can be seen as well in figure 12, which also shows the long antennae with slender tapering segment 7, identified by RS as an additional important feature for the genus.

[FIGURE 10 OMITTED]

[FIGURE 11 OMITTED]

[FIGURE 12 OMITTED]

Thorax

The thorax is identical for both species, except for the extensive brown/black markings in U. thomasi as shown in Figure 8.

Abdomen

All specimens of U. edwardsii have a uniformly brown abdomen with faint and indistinct brown markings only visible after the abdomens have been cleaned (Figure13a). Contrarily, U. thomasi has very extensive dark brown to black markings on the upper surface of the abdomen (Figure13b). The markings are similar to but much stronger and more extensive than those on Sympetrum fonscolombii, to which the abdomen bears a striking resemblance (Figure13c). However, the S. fonscolombii larva or exuvia can easily be separated from Urothemis by its smaller size, the head shape and the absence of long setae. In addition the dark markings are only present on ab.seg. 6-10 on S. fonscolombii whereas they occur on ab.seg. 5-10 on U. thomasi.

[FIGURE 13 OMITTED]

As mentioned above, markings can be very unreliable in exuviae and structural features should always be relied upon for identification as follows:

Dorsal spines. Present on abdominal segments 3 to 8 in both species, but well defined in U. edwardsii and quite residual in U. thomasi (Figure14a, b).

[FIGURE 14a OMITTED]

Lateral spines. Present on abdominal segments 8 & 9 in both species, but well defined in U. edwardsii and quite residual on S8 and small on S9 in U. thomasi (Figure 15a, b).

[FIGURE 14b OMITTED]

* Anal pyramid. The cerci ratios are similar in both species, so we can add little to the information provided by Khelifa et al. (2013).

[FIGURE 15 OMITTED]

Conclusion

The initial features which drew the attention of DGC and RS to the separation of U. thomasi from other exuviae collected from the region have proved to be correct. The residual abdominal spines combined with the large size and the very distinctive dark markings clearly separate the species. As for the genus Urothemis, the long setae found on all parts of the larva and which persist in the exuvia appear to be diagnostic and the triangular shaped poststernum is diagnostic within the Urothemistinae.

Acknowledgements

We are indebted to the management of WWNP for access to the park and for permission to collect material, and particularly to Jacky Judas, Research Manager at WWNP, for his support, and to his team for all their help and assistance. We are also very grateful to the Mohamed bin Zayed Species Conservation Fund for funding field work and enabling research into U. thomasi and other dragonflies in the region.

We would like to thank Philippe Lambret for his dedication in rearing to emergence a live larva of U. thomasi, which confirmed the identification of the species. Our thanks also to Christian Monnerat for supplying the live larvae from Oman and sending these to CB. Finally, thanks to Anthony Stoquert who replaced DGC at short notice on the second field trip and was responsible for collecting the exuviae and the larva of U. thomasi that was subsequently bred out.

Finally we would like to thank Gary Feulner for his extremely helpful comments and amendments which have been incorporated.

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by David Chelmick (DGC), Richard Seidenbusch (RS), Jean-Pierre Boudot (JPB) and Christophe Brochard (CB)

David Chelmick

Macromia Scientific

31 High Beech Lane, Haywards Heath

West Sussex, RH16 1SQ, UK

Email: dgc@davidchelmick.com

Richard Seidenbusch

Klenze Str 5, D-92237

Sulzbach-Rosenberg, Germany

Email: rich@vodafone.de

Jean-Pierre Boudot

Immeuble Orphee, Apt 703, 78 rue de la Justice,

F-54710 Ludres, France

Christophe Brochard

Marsstraat 77, 9742EL Groningen

The Netherlands

Email: info@cbrochard.com
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Author:Chelmick, David; Seidenbusch, Richard; Boudot, Jean-Pierre; Brochard, Christophe
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Date:Jan 1, 2016
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