寄生蟲對宿主生理、行為與生活史的影響可產生複雜生態演化效應。除了對宿主生存與繁殖的直接影響，寄生蟲也可能改變宿主在生存與繁殖間的權衡，且這些影響皆可能隨宿主性別而異。本研究檢測腸胃道寄生蟲（helminths）對不同性別之台灣森鼠（Apodemus semotus）在生存、繁殖以及身體狀況上的影響。實驗方式為隨機給予一半宿主個體寄生蟲移除藥劑（ivermectin），並持續追蹤宿主的生存、繁殖及身體狀況達9個月（2011年8月至2012年5月）。我利用重複捕捉標放的記錄來量化宿主的生存，並藉由雌性陰道口開、乳頭呈哺乳狀態、懷孕，以及雄性睪丸下降等性徵量化宿主繁殖表現。宿主身體狀況則是利用體重改變量進行量化。結果顯示，宿主繁殖隨寄生蟲量增加而提升，且移除寄生蟲降低雌性宿主的生存。同時，我發現雌性宿主在當下繁殖與未來生存間有權衡的現象（trade-offs between current reproduction and future survival），顯示寄生蟲移除可能促使雌性宿主提升對當下繁殖的投資，導致未來生存機率的降低。寄生蟲移除對宿主身體狀況沒有影響。此外，我並沒有發現文獻中常提及的雄性宿主寄生蟲量較高的現象（male-biased parasitism）。這個研究提供了一個寄生蟲對不同性別宿主會有不同影響的實證，且幫助我們了解寄生蟲在宿主生活史權衡上可能扮演的複雜角色。

Parasites can influence host physiology, behavior and life history, leading to complex ecological and evolutionary consequences. In addition to directly influencing host survival and reproduction, parasites can also alter the trade-offs between host survival and reproduction. For sexual host species, many parasitism effects are sex-specific. In this study, I tested sex differences in parasitism effects from intestinal helminths on the survival, reproduction and body condition of a rodent host, Apodemus semotus. I conducted a field experiment where I randomly assigned parasite removal treatment (ivermectin) to half of the rodents and tracked their survival, reproduction and body condition for 9 months from August 2011 to May 2012. I quantified host survival with capture-recapture data, their reproduction by physical signs of perforated vagina, lactation or pregnancy in females and descended testicles in males, and their body condition with body mass changes. My results showed that host reproduction generally increases with parasite loads, and parasite removal treatment reduced female A. semotus survival. In the meantime, A. semotus exhibit female-only trade-offs between current reproduction and future survival, suggesting that parasite removal might increase female hosts’ investment in current reproduction at the expense of their future survival. I did not find parasite removal effects on host body condition. Contrary to the male-biased parasitism commonly reported in mammalian hosts, I did not find sex-biased parasitism in A. semotus. This study provided an empirical case of sex-specific parasitism effects in a common rodent host, and highlighted the complex role of parasitism in host life-history trade-offs.

Allan, B.F., Varns, T.S. & Chase, J.M. (2010). Fear of parasites: lone star ticks increase giving-up densities in white-tailed deer. Israel Journal of Ecology and Evolution, 56, 313-324.
Baker, R.J., Makova, K.D. & Chesser, R.K. (1999). Microsatellites indicate a high frequency of multiple paternity in Apodemus (Rodentia). Molecular Ecology, 8, 107-111.
Barger, I.A. (1993). Influence of sex and reproductive status on susceptibility of ruminants to nematode parasitism. International journal for parasitology, 23, 463-469.
Bordes, F., Ponlet, N., de Bellocq, J.G., Ribas, A., Krasnov, B.R. & Morand, S. (2012). Is there sex-biased resistance and tolerance in Mediterranean wood mouse (Apodemus sylvaticus) populations facing multiple helminth infections? Oecologia, 170, 123-135.
Butterworth, M., McClellan, B. & Aklansmith, M. (1967). Influence of sex on immunoglobulin levels. Nature, 214, 1224-1225.
Christe, P., Glaizot, O., Evanno, G., Bruyndonckx, N., Devevey, G., Yannic, G., Patthey, P., Maeder, A., Vogel, P. & Arlettaz, R. (2007). Host sex and ectoparasites choice: preference for, and higher survival on female hosts. Journal of Animal Ecology, 76, 703-710.
Coop, R.L., Sykes, A.R. & Angus, K.W. (1982). The effect of three levels of intake of Ostertagia circumcincta larvae on growth rate, food intake and body composition of growing lambs. Journal of Agricultural Science, 98, 247-255.
Derting, T.L. & Virk, M.K. (2005). Positive effects of testosterone and immunochallenge on energy allocation to reproductive organs. Journal of Comparative Physiology, 175, 543-556.
Duneau, D. & Ebert, D. (2012). Host sexual dimorphism and parasite adaptation. PLoS Biology, 10, 1-9.
Folstad, I. & Karter, A.J. (1992). Parasites, bright males, and the immunocompetence handicap. American Naturalist, 139, 603-622.
Forbes, M.R. (1993). Parasitism and host reproductive effort. Oikos, 67, 444-450.
Forbes, T. & Hodgson, J. (1985). The reaction of grazing sheep and cattle to the presence of dung from the same or the other species. Grass and Forage Science, 40, 177-182.
Foreyt, W.J. (2001). Veterinary parasitology reference manual. Iowa State University Press. Iowa City, IA, USA.
Gooderham, K. & Schulte-Hostedde, A. (2011). Macroparasitism influences reproductive success in red squirrels (Tamiasciurus hudsonicus). Behavioral Ecology, 22, 1195-1200.
Hart, B.L. (1990). Behavioral adaptations to pathogens and parasites: five strategies. Neuroscience and Biobehavioral Reviews, 14, 273-294.
Hawlena, H., Abramsky, Z. & Krasnov, B.R. (2006). Ectoparasites and age-dependent survival in a desert rodent. Oecologia, 148, 30-39.
Hou, J. & Wu, F.Z. (1988). Effect of sex hormones on NK and ADDC activity of mice. International Journal of Immunopharmacology, 10, 15-22.
Huang, B.M., Lin, L.K. & Alexander, P.S. (1997). Annual reproductive cycle of the Formosan wood mouse, Apodemus semotus. Zoological Studies, 36, 17-25.
Hutchings, M., Kyriazakis, I., Anderson, D., Gordon, I. & Coop, R. (1998). Behavioural strategies used by parasitized and non-parasitized sheep to avoid ingestion of gastro-intestinal nematodes associated with faeces. Animal Science, 67, 97-106.
Jorgenson, J.T., Festa-Bianchet, M., Gaillard, J.M. & Wishart, W.D. (1997). Effects of age, sex, disease, and density on survival of bighorn sheep. Ecology, 78, 1019-1032.
Kallio, E.R., Voutilainen, L., Vapalahti, O., Vaheri, A., Henttonen, H., Koskela, E. & Mappes, T. (2007). Endemic hantavirus infection impairs the winter survival of its rodent host. Ecology, 88, 1911-1916.
Khokhlova, I.S., Serobyan, V., Degen, A.A. & Krasnov, B.R. (2010). Host gender and offspring quality in a flea parasitic on a rodent. Journal of Experimental Biology, 213, 3299-3304.
Klein, S.L. (2000). Hormones and mating system affect sex and species differences in immune function among vertebrates. Behavioural Processes, 51, 149-166.
Klein, S.L. (2004). Hormonal and immunological mechanisms mediating sex differences in parasite infection. Parasite Immunology, 26, 247-264.
Krasnov, B.R., Khokhlova, I.S., Arakelyan, M.S. & Degen, A.A. (2005). Is a starving host tastier? Reproduction in fleas parasitizing food-limited rodents. Functional Ecology, 19, 625-631.
Lin, L.K. & Shiraishi, S. (1992a). Reproductive biology of the Formosan wood mouse, Apodemus semotus. Journal of the Faculty of Agriculture, Kyushu University, 36, 183-200.
Lin, L.K. & Shiraishi, S. (1992b). Home Range and microhabitat utilization in the Formosan wood mouse, Apodemus semotus. Journal of the Faculty of Agriculture, Kyushu University, 37, 13-27.
Lozano, G.A. (1991). Optimal foraging theory: a possible role for parasites. Oikos, 60, 391-395.
MacIntosh, A.J., Hernandez, A.D. & Huffman, M.A. (2010). Host age, sex, and reproductive seasonality affect nematode parasitism in wild Japanese macaques. Primates, 51, 353-364.
Myer-Lucht, Y. & Sommer, S. (2005). MHC diversity and the association to nematode parasitism in the yellow-neched mouse (Apodemus flavicollis). Molecular Ecology, 14, 2233-2243.
Mills, S.C., Grapputo, A., Jokinen, I., Koskela, E., Mappes, T. & Poikonen T. (2010). Fitness trade-offs mediated by immunosuppression costs in a small mammal. Evolution, 64, 166-179.
Moore, S.L. & Wilson, K. (2002). Parasites as a viability cost of sexual selection in natural populations of mammals. Science, 297, 2015-2018.
Neuhaus, P. (2003). Parasite removal and its impact on litter size and body condition in Columbian ground squirrels (Spermophilus columbianus). Proceedings of the Royal Society of Biological Sciences, 270, 213-215.
Pedersen, A.B. & Greives, T.J. (2008). The interaction of parasites and resources cause crashes in a wild mouse population. Journal of Animal Ecology, 77, 370-377.
Perrin, N., Christe, P. & Richner, H. (1996). On host life-history response to parasitism. Oikos, 75, 317-320.
Pianka, E.R. & Parker, W.S. (1975). Age-specific reproductive tactics. American Naturalist, 109, 453-464.
Poulin, R. (1996). Sexual inequalities in helminth infections: a cost of being a male? American Naturalist, 147, 287-295.
Quesenberry, K. & Carpenter, J.W. (2011). Ferrets, rabbits and rodents: Clinical medicine and surgery. Saunders.
Råberg, L., Graham, A.L. & Read, A.F. (2009). Decomposing health: tolerance and resistance to parasites in animals. Philosophical Transactions of the Royal Society B: Biological Sciences, 364, 37-49.
Schuurs, A.H.W.M. & Verheul, H.A.M. (1990). Effects of gender and sex steroids on the immune response. Journal of Steroid Biochemistry, 35, 157-172.
Schwanz, L.E. (2006). Schistosome infection in deer mice (Peromyscus maniculatus): impacts on host physiology, behavior and energetics. Journal of Experimental Biology, 209, 5029-5037.
Schwanz, L.E. (2008). Persistent effects of maternal parasitic infection on offspring fitness: implications for adaptive reproductive strategies when parasitized. Functional Ecology, 22, 691-698.
Simon, A., Thomas, D., Blondel, J., Perret, P. & Lambrechts, M.M. (2004). Physiological ecology of Mediterranean blue tits (Parus caeruleus L.): effects of ectoparasites (Protocalliphora spp.) and food abundance on metabolic capacity of nestlings. Physiological and Biochemical Zoology, 77, 492-501.
Smith, L., White, P. & Hutchings, M. (2006). Effect of the nutritional environment and reproductive investment on herbivore–parasite interactions in grazing environments. Behavioral Ecology, 17, 591-596.
Stanford, K.M. & King, R.B. (2004). Growth, survival, and reproduction in a northern Illinois population of the plains gartersnake, Thamnophis radix. Journal Information, 3, 465-478.
Stearns, S.C. & Koella, J.C. (1986). The evolution of phenotypic plasticity in life-history traits: predictions of reaction norms for age and size at maturity. Evolution, 40, 893-913.
Tavecchia, G., Pradel, R., Boy, V., Johnson, A.R. & Cézilly, F. (2001). Sex-and age-related variation in survival and cost of first reproduction in greater flamingos. Ecology, 82, 165-174.
Telfer, S., Bennett, M., Bown, K., Carslake, D., Cavanagh, R., Hazel, S., Jones, T. & Begon, M. (2005). Infection with cowpox virus decreases female maturation rates in wild populations of woodland rodents. Oikos, 109, 317-322.
Vandegrift, K.J., Raffel, T.R. & Hudson, P.J. (2008). Parasites prevent summer breeding in white-footed mice, Peromyscus leucopus. Ecology, 89, 2251-2258.
Victoria, J. & Trujillo, R. (2001). Topical ivermectin: a new successful treatment for scabies. Pediatric Dermatology, 18, 63-65.
Williams, G.C. (1966). Natural selection, the costs of reproduction, and a refinement of Lack's principle. American Naturalist, 100, 687-690.
Zuk, M. & McKean, K.A. (1996). Sex differences in parasite infections: patterns and processes. International Journal for Parasitology, 26, 1009-1024.
Zuk, M. & Stoehr ,A.M. (2002). Immune defense and host life history. American Naturalist, 160, 9-22.
Yu, H.T. (1993). Natural history of small mammals of subtropical montane areas in central Taiwan. Journal of Zoology, 231, 403-422.
Yu, H.T. (1994). Distribution and abundance of small mammals along a subtropical elevational gradient in central Taiwan. Journal of Zoology, 234, 577-600.