Gabusibius, Hugel & Desutter-Grandcolas, 2021

Hugel, Sylvain & Desutter-Grandcolas, Laure, 2021, New intertidal crickets from Comoros and Mascarene islands (Orthoptera Trigonidiidae: Nemobiinae: Burcini), Zootaxa 4995 (1), pp. 1-26 : 23

Distribution of Burcini and endemism in coastal Orthoptera in SWIO islands

Two genera of Burcini are now recorded on SWIO islands, all species here described being single island endemics ( Fig. 77 ). The genus Gabusibius n. gen. occurs on all Comoros with the remarkable exception of Grande Comore whereas the genus Makalapobius n. gen. occurs on both Grande Comore and Mauritius. This distribution with species from Grande Comore and Mauritius morphologically closer to other species from Comoros may appear surprising since on SWIO islands, several genera of Orthoptera are endemic at the level of archipelagoes (see for example Hugel, 2012a; Hugel et al., 2021). It is nevertheless not a unique case since similar situation occurs for birds ( Foudia and Zosterops ) as well as for plants ( Begonia ) (see discussion in Warren et al. 2013). Various scenarios may account for that peculiar distribution, including multiple dispersal events and even extinctions. The occurrence of Gabusibius n. gen. on Comoros islands of older volcanic origin ( Mayotte, Mohéli, Anjouan) and not on Grande Comore may speculatively suggest that ancestors of Gabusibius n. gen. reached Comoros before the emergence of Grande Comore (volcanic origin estimates: 0.5 MYA). Alternatively, an extinction event might have occurred on Grande Comore, the surface of which is made of quite recent lavas (oldest exposed lavas 0.13 MYA) and harbors an active volcano (see discussion and references for dating in Warren et al. 2013). The lack of Burcini on Grande Comore would speculatively have left a vacant niche for subsequent colonization by ancestors of Malakapobius masihu n. gen. n. sp. . Such highly speculative scenarios will be examined by molecular approaches.

All species described in the present manuscript are single-island endemics. This is remarkable for lowland Orthoptera on SWIO islands since most species occurring on coastal SWIO habitats are widespread and not endemic (Hugel, in press). This is for example the case for the crickets Myrmecophilus americanus Saussure, 1877 and Myrmecophilus quadrispina Perkins, 1899 , ( Hugel and Blard, 2005; Hsu et al. 2020) T rigonidium cicindeloides Rambur, 1839, Natula longipennis (Serville, 1839) ( Hugel, 2012b) and Gryllodes sigillatus (Walker, 1869) (Hugel, in press) as well as for the Caelifera Aiolopus thalassinus rodericensis (Butler, 1876) ( Parnaudeau et al. 2013; Hugel, 2014) and Xya minor (Chopard, 1920) (Hugel, 2021) among others. Only very few coastal Orthoptera species are single-island-endemics, such as species belonging to the genus Microlandreva Chopard, 1958 on Comoros and Mayotte (SH-LDG, unpublished observations), Mogoplistidae species on Comoros (SH-LDG, unpublished observations) and Mascarene islands ( Warren et al. 2016), and the Grasshopper Odontomelus ancestrus Hugel, 2014 on Round Island, an islet North to Mauritius ( Hugel, 2014). It has been suggested that this low level of endemism of Orthoptera in SWIO coastal habitats may be a consequence of habitat destruction at low altitude rather than a naturally occurring phenomenon (Hugel, in press).

Importantly, since intertidal habitats are not frequently examined by entomologists, and particularly by Orthopterists, the occurrence of more species of Burcini on SWIO islands is expected, and would deserve targeted surveys.

Figures

FIGURE 77. Distribution of Makalapobius n. gen. and Gabusibius n. gen. in South Western Indian Ocean.