Thesilea mallicolensis Kulzer, 1951

Soldati, Laurent, Kergoat, Gael J. & Condamine, Fabien L., 2012, Preliminary report on the Tenebrionidae (Insecta, Coleoptera) collected during the SANTO 2006 expedition to Vanuatu, with description of a new species of the genus Uloma Dejean, 1821, Zoosystema 34 (2), pp. 305-317 : 313-315

Thesilea mallicolensis Kulzer, 1951

Thesilea mallicolensis Kulzer, 1951: 148 .

MATERIAL EXAMINED. — Vanuatu. Espiritu Santo Isl., Luganville, CETRAV in Saraoutou, ecotone between dense rainforest and coffee tree plantation, beating shrubs, 2-10.X.2006, leg. L. Soldati, 2 ♂♂ and 15 other ex. ( MNHN), 5 ex. (coll. LS) (sex unknown). — Espiritu Santo Isl., Butmas, in rainforest, 21.X.2006, leg. L. Soldati, 1 ♂ ( MNHN), 1 ♂ (coll. LS).

DISTRIBUTION. — Originally described from Mallicolo (Malekula Island) in the French New Hebrides (now Vanuatu), this species also occurs in the neighbouring island of Espiritu Santo.

BIOGEOGRAPHY OF VANUATU

AND ASSUMPTIONS ON THE ORIGIN OF THE TENEBRIONIDAE

IN THE ARCHIPELAGO.

The Vanuatu islands and that of Santo in particular are known to be recently emerged volcanic islands (about 4 million years), and can thus be qualified oceanic islands ( Gillespie & Roderick 2002). This geological evidence suggests that the local fauna most likely originated by dispersal and not by vicariance. After their arrival, some of the species may have then evolved to endemic species. This leads us to raise the following question: which is (are) the origin(s) of this fauna? In other words, what were the borrowed colonisation routes to reach the archipelago of the Vanuatu?

With reference to the Tenebrionidae , one can say that there were nearly (because of the humanmediated introduction of species like Tribolium castaneum ) as many colonisation events as different genera existing in Vanuatu, which are not considered as sister clades. Note that if a genus is represented by more than one species, we cannot exclude the hypothesis of multiple colonisation events as well (e.g., Balke et al. 2007). If we replace Vanuatu in a geographical context, one can put forth biogeographic hypotheses as for the source of these dispersions. Indeed, these events can come from several areas around the archipelago.

First of all, several genera of Tenebrionidae could originate from New Guinea, which probably holds the greatest diversity of Tenebrionidae of the Australasian region ( Gebien 1920). Its geographical position makes it obvious that its fauna is part of the Melanesian arch. In particular, dispersals to the Vanuatu could be facilitated by the Solomon Islands, as they are themselves strongly influenced by New Guinean fauna ( Merkl 1989; Bremer 1993). This assumption is corroborated by the presence of the genus Amarygmus in the Vanuatu, whose centre of diversity is located in New Guinea and certain representatives in the Solomon Islands ( Gebien 1920). Species of Amarygmus are also known from the Fiji Islands ( Kaszab 1955), which attests of a colonisation front going towards southeast. In the same way, if Uloma of the area and the presently described Vanuatu species are examined, morphological affinities show that U. vanuatensis L. Soldati n. sp. is closely related to a species group of Uloma from New Guinea (i.e. the U. bituberosa group; Gebien 1920). New Caledonia, the nearest insular territory to Vanuatu (400 km), has the greatest Uloma diversity with respect to its surface ( Kaszab 1982b, 1986). However, no New Caledonian species are morphologically related to U. vanuatensis L. Soldati n. sp. On the contrary, the Fijian species, Uloma cavicollis Fairmaire, 1849 , shows several morphological features bringing it closer to U. vanuatensis L. Soldati n. sp. As in the case of Amarygmus , it seems that the presence of Uloma in Vanuatu is the result of a southeastern oriented dispersal using Solomon Islands as stepping-stones. It is interesting to note that this dispersal has not yet reach New Caledonia whose Uloma representatives seem to originate from Australia ( Matthews and Bouchard 2005). Consequently, it appears clearly that New Guinea played a crucial role in the species assemblage of Tenebrionidae in Vanuatu via a dispersal that followed the Melanesian arch. The genera Bradymerus ( B. lobicollis ), Platydema ( P. novaeguineense ), Promethis ( P. sulcigera ) and Toxicum ( T. quadricorne ) are most probably originating from New Guinea, too.

Then, other genera can come from the Fiji Islands, a wide archipelago including approximately 80 species of Tenebrionidae ( Kaszab 1955) . Its proximity to Vanuatu suggests that faunal exchange could have been frequent and that resulted in several genera occurring in both archipelagoes. For example, a Melanesian connection was probably established concerning the genus Chariotheca with two species ( C. striata and C. cuprina ) occuring both in the Fiji Islands and in Vanuatu. These dispersals pursued westward to reach New Caledonia ( Kaszab 1982b, 1986), but also northward to the Solomon Islands, where the genus is also present.

Lastly, New Caledonia could have also influenced the fauna of Vanuatu. Emerged approximately 34- 37 million years ago ( Pelletier 2006), it has some genera in common with the Vanuatu archipelago. Even though New Caledonia and Vanuatu exhibit many affinities for the plants for instance ( Pillon 2011), most tenebrionid species from the two areas are different ( Kaszab 1955, 1982b, 1986). Moreover, several widespread Australasian genera ( Amarygmus , Promethis and Toxicum ) are found in Vanuatu but not in New Caledonia ( Matthews & Bouchard 2005). In the same way, many New Caledonian genera do not occur in Vanuatu. This low level of affinity demonstrates the scarcity of the past exchanges between these two areas in spite of their proximity. This can be explained by two major hypotheses:First, one can imagine that competition or poor adaptation prevented some tenebrionid genera from colonising one or the other archipelago. New Caledonia, for example, is covered by ultramafic soils that have strongly constrained the diversification of plants ( Pillon et al. 2010). Second, it can be thought that dispersal opportunities between the two archipelagoes were limited for poor dispersers (wingless species), or that abiotic (e.g., marine currents) or biotic factors prevented these dispersal events. Testing these assumptions would require a more thorough knowledge of the biodiversity of the region, as well as an estimate of their phylogenetic relationships among species existing between the distinct areas through a historical biogeography approach (interspecific level) or phylogeography (intraspecific level).

In conclusion, the tenebrionid fauna of Vanuatu represents a reserve of species, which provides an interesting and still incompletely known biogeographic history with questions about its origin and evolution. Thanks to this first inventory, we highlight multiple and independent origins to explain the colonisation of the archipelago. However, understanding of the evolutionary and ecological processes, which have contributed to the community assemblage, remains a fascinating challenge that requires a more thorough sampling over the entire Australasian region. Even if it appears that New Guinea is the major source of this biodiversity, it would be very interesting to test these biogeographic hypotheses within a phylogenetic perspective including dense taxon sampling for each genus. Phylogenetic and dating analyses would then provide additional evidence for better apprehending when and how appeared the Tenebrionidae of Vanuatu.