Distribution And Ecology Of Ectoparasitic Insects On Small Mammals In Yunnan Province

Objective:(1) To investigate the species composition, distribution, community structure and species diversity of ectoparasitic insects (fleas and sucking lice) on the body surface of small mammals in Yunnan Province. (2) To search the ecological adaptation of ectoparasitic insects to their small animal hosts and environment on the basis of analyzing the community similarity and the ecological niche of main insect species in different environmental gradients (or geographical subregions).(3) To investigate the geographical distribution and and to study the mutual selection relation between the flea and it's hosts.Material and Methods:(1) All the original data of fleas were accumulated from 12 years'field investigation in 22 counties of Yunnan Province from 1997 to 2008. Since we did not collect sucking lice in the field investigation before 2000. the original data of sucking lice only came from 20 counties (no collection of sucking lice in Jinghong and Mojiang). (2) Infestation rate(Rf) and infestation index(If), the richness (S). eveness (J'), diversity index (H'). dominance index (C') and constituent ratios (Cr) were used to analyze the community structure. (3) According to the geographical division of China. Yunnan Province is divided into five zoogeographic microregions, namely Middle Microregion of Hengduan Mountains, Southern Microregion of Hengduan Mountains. Eastern Plateau Microregion of Yunnan, Western Plateau Microregion of Yunnan. Southern Mountainous Microregion of Yunnan and Western Plateau Microregion of Yunnan. Western Plateau Microregion of Yunnan is not involved in this paper. On the basis of comparing the species diversity and the faunal distribution of the ectoparasitic insects (fleas and sucking lice) in every zoogeographical microregion. the adaptation of the insects to their hosts and environment was then analyzed and discussed. (4) For analyzing the fluctuation of species diversity along the environmental gradients, the species richness(S), Shannon-Wiener diversity index (H') and dominance index (C') were used to analyze the horizontal and vertical distribution pattern of the richness and fauna of the ectoparasitic insects. (5) Levin's methods were used to measure the ecological niche breadth of 24 species of ectoparasitic insects (12 species of fleas and 12 species of sucking lice) in different altitudes, latitudes and hosts. Niche proportional similarity and niche overlap of 12 species of fleas were measured,by repectively using Cowell-Futuyma's methods and Pearson correlation. The above results were analysed to research the adaptation between ectoparasitic insects and the differet environment and to study similarity among flea species along altitudes.Results:(1)13769 mammals were captured, which belong to 11 families,33 genera and 60 species in six orders.10330 individuals of fleas(belonging to 6 families,26 genera and 51 species) and a total of 36170 sucking lice (identified into 7 families,9 genera and 31 species) were collected from the mammal hosts. Four dominant small mammals are Rattus flavipectus (27.95%). Apodemus chevrieri (13.54%), Eothenomys miletus (12.67%) and Rattus norvegicus (8.29%) while the dominant fleas are Ctenophthalmus quadratus (23.46%), Xenopsylla cheopis (22.70%) and Leptopsylla segnis (12.92%), the dominant sucking lice are Polyplax spinulosa (22.62%), Hoplopleura pacifica (14.77%), Polyplax serrata (10.95%) and Hoplopleura edentula (10.72%). To contrast with other provinces, however, the plentiful species of fleas and sucking lice were found in Yunnan Province with a high biodiversity, which may be related to the specific geographical position and ecological landscape of Yunnan Province. (2) The geographical distribution of two kinds of ectoparasitic insects was of imbalance in Yunnan's different zoogeographical microregions. Species are relatively abundant in Middle microregion of Hengduan Mountains in comparison with the rest three ones' in Yunnan's four zoogeographical microregions. Community stability of fleas and sucking lice have the same trend, followed by Middle Microregion of Hengduan Mountains> Eastern Plateau Microregion of Yunnan> Southern Mountainous Microregion of Yunnan> Southern Microregion of Hengduan Mountains. The flea fauna in Yunnan Province had the following characteristics:Oriental compositions (31 species) was most abundant while Palaearctic compositions (only 3 species) was less abundant; Of 31 sucking lice, there were 19 species of Oriental compositions, only one Palaearctic composition and 11 species of Palaearctic and Oriental common compositions. Most dominant species were the common components in both Palaearctic and Oriental regions such as Xenopsylla cheopis, Leptopsylla segnis in fleas and Polyplox spinulosa, Hoplopleura pacifica in sucking lice. (3) The fluctuation of community diversity of fleas and sucking lice showed the similar tendency along the latitudinal gradients. The fluctuation curve of both insects had the same peak between 25°N and 28°N, in which there were 69.66% flea individuals (43 species) and 86.94% individuals of sucking lice.36 species of fleas (59.48% of the total) distributed between 2000m and 3500m and all 31 species of sucking lice (90.47% of the total) distributed between 1000～3500m. This might be considered as a result of long-term adaptation between the surrounding habitat and fleas and sucking lice on small mammals. (4) The results from the niche breadths of the 12 flea species and 12 species of sucking lice indicated that Aviostivalius klossi and Polyplax spinulosa had the widest trophic niche breadths (0.066 and 0.074 repectively); Monopsyllus anisus and Hoplopleura akanezumi had the widest vertical niche breadths (0.393 and 0.510 repectively); Leptopsylla segnis and Hoplopleura akanezumi had the widest horizontal niche breadths (0.390 and 0.435 repectively). The above niche breadths of fleas and sucking lice were relatively narrow and the trophic niche breadths and host ranges of fleas were slightly higher than those of sucking lice. The vertical and horizontal niche breadths of two sorts of insects were of no significant difference. The indices of niche proportional similarity of most fleas were also relatively high and the different species of fleas showed the apparent niche divergence phenomenon in selecting resources. The overlap indices are also low among different flea species in selecting different altitudes, and 12 species of fleas just showed the aggregate phenomenon whenλ=23 through the analysis of niche overlap with hierarchical clustering analysis. The clustering process of most fleas was relatively early. The above results also indicated that the selective of fleas is strong along the different altitudes. (5) Most individuals of Ctenophthalmus quadratus (98.40%) were found in the "Middle Microregion of Hengduan Mountains" in the zoogeographical regions.96.73% of Ctenophthalmus quadratus were collected from 5 species of small mammals. Eothenomys miletus, Eothenomys custos, Mus pahari, Apodemus chevrieri and Anourosorex Squamipes. Of the five main hosts, Eothenomys miletus is the most important host with 85.97% of the total fleas collected from its body surface.Conclusions:(1) The species of fleas and sucking lice were very abundant in Yunnan Province while the distribution of insects was of imbalance in the different environment. Oriental compositions of fleas and sucking lice hold a leading post, but most dominant species were the common components in both Palaearctic and Oriental regions (2) The adaptation between fleas and small mammal hosts or the environment was low, and the adaptation of fleas on small mammals, in the host selection, was slightly higher than sucking lice. (3) Ctenophthalmus quadratus mainly distributes in the Middle Microregion of Hengduan Mountains and its main host is Eothenomys miletus with a relatively high host-specificity.