An enigma: the lack of Siphonaptera on wild rats and mice on densely populated tropical islands

摘要

The Siphonaptera of the present and past mammalian terrestrial fauna (bats excepted; 11 species among which only 8 alien species remain today, the 3 endemics having disappeared) of Martinique and Guadeloupe Islands (French West Indies) has barely been studied. Between 1996 and 2002, we collected fleas on 125 small Indian mongooses (Herpestes javanicus auropunctatus) and 4219 specimens of the three rodent species (Rattus rattus, R. norvegicus and Mus musculus) collected throughout the year from 4 crop habitats, 3 "natural" ones, and one rural settlement. The survey resulted in the discovery of only two Siphonaptera taxa among the six known from the Caribbean archipelago, Ctenocephalides felis felis and Xenopsylla cheopis, both alien. The former was found in the wild in low abundance and prevalence only on the mongoose and on goats and dogs living in or near human settlements. The latter was discovered on two R. rattus trapped in rural settlements of Martinique and was totally absent from all 4215 rodents collected in crop and natural ecosystems. We conclude that such a paucity of Siphonaptera in the wild in the French West Indies is not caused by potential invaders' having missed the boat, nor by high local extinction rates. This paucity probably is related to the inability of these species to persist in the wild on these islands. Nevertheless, several species persist in French West Indies human settlements, perhaps owing to a permanent flux from mainland, and 5 species reported from the Caribbean remain absent from the French West Indies. These facts lead to the question of the original habitat for these 5 species: human settlements or the wild? Having posed this question, we note the necessity of stratified host samples that are currently lacking. These facts raise a second question: what aspects of human and wild habitats differ that may explain the presence of some Siphonaptera species in the former and none in the latter?