Researches On Prevalent Distribution And Community Characteristics Of Medical Gamasid Mites In Yunnan

Objectives:To provide the guideline for the surveillance and control of vector mites and some mite born diseases, the prevalent distribution and community characteristics of medical gamasid mites on the body surface of small mammals were investigated in Yunnan Province of China, which covered the species composition and species diversity of gamasid mite community, the basic structure of the community, spatial patterns of the communities in different geographical areas, the determination of minimum host (small mammal) samples and the estimation of total mite species on the basis of illustrating the prevalent distribution patterns of gamasid mites.Materials and Methods:(1) The original data came from the field investigation in 28 counties of Yunnan Province from 1990 to 2008. The 28 investigated counties belong to the five microsubregions of two subregions (Southwestern Mountainous Subregion and South Mountainous Subregion of Yunnan) within two regions (Southwestern Region of China and South Region of China) in Sino-Indian Subrealm of Oriental Realm in zoogeography. These five microsubregions are namelyⅠMiddle Microregion of Hengduan Mountains,ⅡSouthern Microregion of Hengduan Mountains,ⅢEastern Plateau Microregion of Yunnan, IV Western Plateau Microregion of Yunnan and V Southern Mountainous Microregion of Yunnan. (2) The Principal Component Analysis (PC A) was used to analyze the main factors that influenced the prevalent distribution of medical gamasid mites. (3) The constituent ratio (Cr), species richness (S), Simpson's dominance index (D), Shannon diversity index (H), Pielou evenness (E), prevalence (P) and mean abundance (MA) were used to measure the community structure. (4) The community characteristics and the spatial distribution of gamasid mites along the geographical gradients (longitudes, latitudes and altitudes) were described by using species richness, Shannon diversity index and mean abundance. (5) The gamasid mites on 18 main species of small mammal hosts were defined as 18 gamasid mite communities. Based on hierarchical clustering analysis, the similarity of 18 mite communities was compared with SPSS 16.0 software. (6) Based on the "species-area" relationship theory in ecology, the small mammal species captured with large number was selected as the object and a "species-sampling" curve of gamasid mites and their hosts was fitted to determine the minimum sampling small mammal hosts. (7) Chao 1 richness estimator (Chao 1984) was used to estimate the total species richness of gamasid mite community. (8) All the 67 species of small mammals captured from 28 counties were regarded as 67 series of host resources and the individuals of each species of gamasid mites on 67 species of small mammals were calculated into constituent ratios in 67 host resource series. Levins' and Colwell-Futuyma's methods were used to measure the niche breadth and niche overlap respectively. The hierachical analysis in SPSS 16.0 statistical software was used to classify the mite communies into different niche overlaping groups to evaluate the ecological coevolution between the gamasid mites and their corresponding hosts.Results:(1) A total of 14 544 individuals of small mammals were captured and identified as 10 families,35 genera and 67 species in five orders (Rodentia, Insectivora, Scandentia, Lagomorpha and Carnivora). From the body surface of captured small mammal hosts,80 791 individuals of gamasid mites were collected and they were identified as 10 families,33 genera and 112 species. The results indicated that the dominant host species were Rattus tanezumi, Apodemus chevrieri, and Eothenomys miletus, while the dominant gamasid mite species were Laelaps nuttalli, L. echidninus and L. guizhouensis. (2) The results showed that the mites and small mammals are higher in species richness and diversity indices in the Middle Micro-region of Hengduan Mountains than in other geographical micro-regions. (3) The spatial density distribution of 15 dominant gamasid mite species along latitudinal and altitudinal gradients showed a similar pattern. (4) The species richness and diversity patterns of gamasid mites and their small mammal hosts presented a similar trend of single-peak curves, which increased and then decreased gradually with the increase of latitude and elevation, peaking at the latitude 26°N to 27°N and the elevation of 2000 m to 2500 m. (5) The similarity of most gamasid mite communities were in accordance with the taxonomic relationship and the habitats of their corresponding small mammal hosts. The gamasid mite communities are clustered into the same group when their hosts are similar in zoological taxonomy and habitat selection. (6) A species-plot relation curve of gamasid mites and their hosts was successfully made, and the median of the curve which representing 2050 individuals of R. tanezumi was determined as the minimum rat samples. (7) According to the estimation of species richness, the total species of gamasid mites on R. tanezumi were estimated to be 66 species. (8) Most of the mites can parasitize a wide range of host species (2～31), but they usually achieve more individual abundant on certain dominant host species, their niche breadths ranged from 0.0154 to 0.1646. Most species of gamasid mites showed a relatively low niche overlaps between every two of them. Based on the hierachical clustering analysis, the 30 species of gamasid mites studied were classified into 15 niche overlapping groups whenλ= 5.0 in the clustering dendrogram.Conclusions:(1) The species of medical gamasid mites are very rich in Yunnan Province with high biodiversity. The distribution of gamasid mites are closely related to the unique topography, ecological landscape and climate features and the distribution and diversity of small mammal hosts. Among the species recorded during the investigations, Laelaps echidninus, L. nuttalli, L. traubi, Ornithonyssus bacoti,Hirstionyssus sunc, L turkestanicus are wide-distributed and multi-host mite species; L. liui, L.paucisetosa, Lguizhouensis, L.xingyiensis, Dipolaelaps anourosorecis, Lalgericus, Eulaelaps dremomydis and E. shanghaiensis are narrow-distributed and narrow-host mite species; L. jingdongensis and Haemogamasus sanxiaensis are endemic species of Middle Microregion of Hengduan Mountains. The wide-distributed and multi-host mite species are potential vectors in the transmission of mite-borne diseases, which may play a key role in rat-human and rat-rat transmission and the maintenance of foci of HFRS. (2) The community structure of gamasid mites on small mammals in Yunnan is extremely complicated with high biodiversity. The similarity of gamasid mite communities are influenced by both the taxonomy status and the habitats of their hosts. (3) The diversity spatial distribution patterns of gamasid mites and their small mammal hosts showed the similar trends of single-peak curves which gradually increased and then decreased with increasing of latitude and elevation, peaking at latitude 26°N to 27°N and the elevation of 2000 m to 2500 m. The spatial distribution patterns of gamasid mites in Yunnan Province may be the results of the "edge effect" between the Oriental and Palaearctic realms. The horizontal and vertical distribution patterns of gamasid mites are similar. (4) The species composition and community structures of gamasid mite on small mammals in Yunnan varied with the variation of the regions and the habitat types of their hosts. To reach the plateau phase of "species-sampling" curve of gamasid mites and their hosts, a larger samples of small mammals is needed. (5) Except for a few mite species which have high host specificity, the majority of the mite species have low host specificity. Although most of the mites can parasitize a wide range of host species, they usually have some relatively fixed dominant hosts, which suggest that some coevolutionary relationship may exsist between gamasid mites and their small mammal hosts, but the degree is not very high.