Population Dynamics and Coevolution of Adult Siphonapteran Parasites of the Southern Flying Squirrel (Glaucomys volans volans)

Abstract

One possible outcome of the competitive interaction of two or more species for a limited resource is the development of one or more strategies which allow all of the species involved to use the resource that is limiting. This study suggests that four species of fleas which inhabit the nest of the southern flying squirrel (Glaucomys volans volans) have coevolved life history strategies which allow them to cycle asynchronously. By being in the adult stage during different months of the year the four flea species apparently do not place undue parasitic pressure on the host squirrels. INTRODUCTION Whenever two or more sympatric species require the same habitat, the same food source, and the resource is in short supply competition will result. As a group, fleas have three major mechanisms to avoid interspecific competition. Some species sEparate spatially while feeding on the host. Prasad (1972) showed that two rat fleas, Xenopsylla cheopis and Xenopsylla astia, prefer different feeding sites on the host rats with X. astia feeding only on the anterior half of the host, mainly on the neck, and X. cheopis feeding only on the posterior portions. A second mechanism is extremely sensitive microhabitat selection. Benton (1972) noted several species in which the external environment surrounding the host and its nest is as important as the host itself. George (1959) found that the microenvironment within the nest of the pied flycatcher, Muscicapa hypoleuca, as determined by the compass direction in which the nest hole faced, determined the overall numbers of the different species of fleas present in any given nest. Third, fleas may separate temporally. Abreu (in press) has shown this in fleas of the European rabbit, Oryctolagus cuniculus, in Portugal. We suggest that this mechanism has been developed by nest fleas which infest the southern flying squirrel Glaucomys volans volans (Linnaeus). Preliminary studies (K. Baker and M. Prusak, pers. comm.) indicated the existence of a temporal separating mechanism used by four species of siphonapteran nest parasites infesting the nest of the southern flying squirrel. Glaucomys v. volans acts as a primary host for four species of fleas in the northeastern United States (Benton and Cerwonka, 1960; Main, 1970; Miller and Benton, 1973; Benton and Kelly, 1975; Conorhinopsylla stanfordi Stewart, Epitedia faceta (Rothschild), Opisodasys pseudarctomys (Baker), and Orchopeas howardii howardii (Baker). All four are primarily nest fleas but can also be taken from the host. Nest fleas are extremely specialized in terms of habitat use. They usually require a blood meal from a mammal present in the nest in order to lay fertile eggs and they are very often quite host-specific. The fleas also require a suitable nest in which to complete the four stages of their development. It is therefore possible that different species of fleas infesting the same host and host nest would come under intense interspecific competition in both the larval and adult stages, and this competition could lead to temporal species separation. 1 Parts of this material were presented at the First International Conference on Fleas, Ashton, England, June, 1977. 2 Present address: Department of Entomology, University of Massachusetts, Amherst, MA 01003.