Cerrorchestia taboukeli sp. nov., a new terrestrial amphipod (Amphipoda, Talitridae) from Martinique Island

During recent investigations on the terrestrial invertebrates of the tropical rainforest on Martinique Island (Pitons du Carbet), specimens of a new species of the terrestrial amphipod genus Cerrorchestia Lindeman, 1990, C. taboukeli sp. nov., were collected by means of different quantitative and non-quantitative methods (hand collection and Tullgren extraction) in the forest fl oor. The new species can be easily distinguished from the only other species of the genus, C. hyloraina Lindeman, 1990, by gnathopod 2 (carpus short, palm longer than wide), pereopod 4 dactylus with a denticulate patch, pereopod 5 basis ovate with a deep posterodistal lobe reaching the distal end of the ischium, pleopod 3 ramus with more than six articles. Cerrorchestia tabouleki sp. nov. is the fi rst forest-hopper discovered in the Lesser Antilles, raising the question of island colonization by terrestrial amphipods. Ecological data and a key to terrestrial Talitridae of Central America and the Caribbean islands are provided.


Introduction
and could be pooled into three different ecological groups (i.e., beach-hoppers, fi eld-hoppers and forest-hoppers) according to their environmental distribution and morphological adaptations (Lowry & Myers 2019). Almost half of the Caribbean species belong to beach-hopper and fi eld-hopper groups of species (Bousfi eld 1984;Ciavatti 1989) and 11 species could be considered as forest-hoppers (i.e., terrestrial species), which are known to inhabit the rain and cloud forests of the Greater Antilles islands and Central America (Lindeman 1990, Ortiz & Lalana 2009).
In the Lesser Antilles, six amphipod species are known (Floresorchestia guadalupensis Ciavatti, 1989, Hyalella caribbeana Bousfi eld, 1996, Platorchestia platensis (Krøyer, 1845, Amphiatlantica sulensoni (Stebbing, 1899), Tethorchestia antillensis Bousfi eld, 1984 and Tethorchestia karukarae Ciavatti, 1989), all from sandy beaches, lakes and ponds and only on Guadeloupe. No terrestrial species are known to date. Moreover, there is no knowledge on the distribution of amphipods on Martinique Island, so the exploration of Pitons du Carbet carried out in 2017 and 2018 could therefore be considered as the fi rst contribution to the description of the amphipod fauna of the island, notwithstanding the fact that these samplings were focused on soil arthropods of the tropical sub-mountain rainforest.
The present paper provides the description of a new terrestrial amphipod, attributed to the genus Cerrorchestia Lindeman, 1990 and collected above 1000 m of altitude in Pitons du Carbet Mountain Range. A few ecological comments about this new species and a key to the terrestrial species of the region are provided.

Study sites
Amphipods were sampled in the mountain range of Pitons du Carbet on Martinique Island where they occur above 1000 m in small forest patches distributed around the summits and high plateaus. The vegetation has the characteristic of a cloud forest, i.e., it is subjected to high precipitation (mean annual rainfall above 6000 mm), high nebulosity and epiphytic plants are very abundant. The species was found in the litter layer of Clusia mangle Rich. ex Planch. & Triana and Scheffl era attenuate (Sw.) Frodin, which are the two dominant tree species of the area. Amphipods were found at two localities -the pass between the Piton Alma and Piton Dumauzé (alt. 1045 m, 14°41′56.6″ N, 61°06′08.0″ W) and on the top of the Piton Boucher (alt. 1059 m, 14°42′52.6″ N, 61°06′18.0″ W).

Amphipod sampling
Specimens were collected on the forest fl oor by means of different quantitative and non-quantitative methods (hand collection and Tullgren extraction). After separation from the remaining material, the specimens of Cerrorchestia were transferred to 96° alcohol vials and dissected under a stereo microscope SZX16 (Olympus © ). Amphipod slides were prepared using Faure's media after maceration of material in lactic acid and KOH (10%) and coloration with pink lignin (Ayati et al. 2018). Digital pictures were realized with a microscope equipped with a CCD microscopy camera infi nity 3-1 (Luminera©) and the stacking software CombineZP in order to create a composite image with an extended depth of fi eld. Body parts were digitally drawn using a Wacom tablet and the Illustrator CC software package (AdobeTM) following the method proposed by Coleman 2003.

Etymology
The epithet taboukeli refers to 'Taboukéli oüébo' in the Kalinago language, the pre-Columbian inhabitants of Martinique Island. This term means 'summit of the mountain' and refers to the extremely narrow distribution area of the species that is currently known to be restricted to peaks and high plateaus of Pitons du Carbet Mountain Range.

Male
Description based on holotype male 11.3 mm. BODY (Fig. 1A). Medium and smooth.

Female
Description based on paratype female 9.6 mm.
HEAD. Antenna 1 and 2 similar to those of male.

Ecology and distribution
Cerrorchestia taboukeli sp. nov. was found in very wet conditions of the Pitons du Carbet Mountain Range (annual precipitation higher than 6000 mm per year) always at an altitude higher than 1000 m. At this altitude, the cloud forest is sparse, alternating with mountain grassland (Fig. 6A). It is worth noting that C. taboukeli sp. nov. was found only under tree patches in a shaded environment where leaves of Clusia mangle and Scheffl era attenuate create a thick litter layer on the soil. During daylight, the animals rest almost motionless under the leaf litter unless disturbed, in which cases they actively jump in search for shelter. Live C. taboukeli sp. nov. are very dark brownish red (Fig. 6A). Using a quadrat of 25 × 25 cm, the population density was estimated to be, on average, 196 ± 112 ind/m 2 (n = 9). The sex ratio of adults was biased toward females, and juveniles represented more than 75% of the population during the sampling period. The other species of the genus, C. hyloraina, is known from Panama to Costa Rica in similar environmental conditions (Lindeman 1990). The species live in leaf litter of cloud forest with an andosol developed on volcanic rocks (andesite). The main soil characteristics are given in Table 1.

Discussion
Classifi cation of the members within the highly diverse family Talitridae is very complex with 116 genera for only 358 species (WORMS 2019), among which 68 have been described over the last 20 years (Lowry & Myers 2019). Bousfi eld (1984) proposed to organize Talitridae in four systematic-ecological groups according to their ecological preferences. Those groups are polyphyletic and overlapping, but are pragmatically useful (Bousfi eld 1984). The fi rst group harbors palustrine semi-aquatic species living in estuarine and some freshwater habitats of tropical and antipodean continental areas. The second group pools together the semi-terrestrial and terrestrial (but non-substrate-modifying) beach fl ea species living in supralittoral and coastal rain forests of tropical to boreal marine coastlines. The third group harbors specialized (substrate-modifying) semi-terrestrial, supralittoral sand hoppers living on sandy beaches of tropical and temperate marine shores. Finally, the fourth group contains specialized terrestrial (but seldom substrate-modifying) land hoppers, living in coastal continental and high-island angiosperm rain forests, mainly of tropical Indo-Pacifi c and antipodean temperate regions. In their recent revision of Talitridae, Lowry & Myers (2019) proposed to divide the terrestrial land-hopper group into six groups to  account for the wide variety of ecotypes occupied by terrestrial talitrids. Cerrorchestia taboukeli sp. nov. described in this study confi rms the characteristic terrestrial specialization of the genus Cerrorchestia (Lindeman 1990), considered as one of the 75 genera with terrestrial species belonging to the foresthoppers (Lowry & Myers 2019).
In a morphological study, Lindeman (1991) discovered that the genera Caribitroides and Cerrorchestia from Central America and Jamaica evolved from a palustrine ancestor close to the Chelorchestia. Smith (1998) rejected this hypothesis by describing the genus Cariborchestia from a small island of Puerto Rico, which differs substantially from both Caribitroides and Cerrorchestia, and proposed another hypothesis with a proto-antillean beach fl ea close to Tethorchesta (Bousfi eld, 1984) as the ancestor of Cariborchestia. In accordance with Smith's hypothesis, Bousfi eld & Poinard (1995) described a fossil amphipod belonging to the genus Tethorchesta. Moreover, Lowry & Myers (2019) confi rm that the mascupod (i.e., enlarged male gnathopod 2) is an important morphological trait that tends to confi rm that Cerrorchestia (with mascupod) is probably not closely related neither to Cariborchestia nor to Mexitroides, both genera having femipods (gnathopod 2 not enlarged). Moreover, a vicariant event is not favored as the explanation for most patterns of biogeographical distribution in the Lesser Antilles because most of islands were under water until the end of the Oligocene (23 Ma). Indeed, a proto-Antillean vicariant event cannot be invoked to explain the presence of many plant species from South America (Buck 1990). Consequently, the vicariance hypothesis is apparently not a good explanation of the presence of Cerrorchestia in both Panama and on the Lesser Antilles. The presence of the genus Cerrorchestia on the Lesser Antilles and in Panama is more congruent with the mid-Cenozoic Greater Antilles Aves Ridge land bridge (GAARlandia) hypothesis at a time when ocean levels were lower and land masses were closer to each other (Iturralde-Vinent & MacPhee 1999). The most likely explanation is a colonization of the Lesser Antilles by a South American ancestor at the Eo-Oligocene boundary (34 Ma), followed by the colonization of Panama when the Panamanian Isthmus arose between 2.3 and 9.0 Ma ago (Iturralde-Vinent 2006). Unfortunately, the knowledge on talitrids of this region remains very scarce and does not allow us to formulate sustainable hypotheses concerning the colonization of Caribbean Islands by amphipods. Further research including phylogeographical studies may help us to disentangle the evolutionary history of Talitridae in the region.