根據生活史理論，在有限的資源下，自然選擇可優化(optimize)生物在生存與繁殖間的資源分配，而最大化(maximize)其子代數或子代品質(此即生活史權衡，life history trade-off)。一般認為，寄生蟲與食物資源皆會影響生物的能量分配與獲得，進而影響宿主的繁殖表現；同時，由於雌雄兩性往往有不同的生活史，在面對寄生蟲與食物資源的影響時，可能有不同的權衡方式。本研究檢測內寄生蟲與種子食物資源對台灣森鼠(Apodemus semotus)繁殖表現(子代數與子代品質)的影響。2013年我在雪霸國家公園內一處針闊混林進行野外操控實驗，包括有系統地挑選樣點給予種子添加，以及將所有捕捉之 A. semotus隨機分配給予移除內寄生蟲藥物Ivermectin或水(控制組)。接著我利用10個微衛星基因座進行親子鑑定，並用捕捉標放資料計算子代的平均體重(子代品質的指標)。結果顯示，內寄生蟲移除對A. semotus子代數沒有影響，而食物資源可提高個體子代數；同時，內寄生蟲與食物資源並不影響A. semotus子代品質。本研究顯示，相較於內寄生蟲，食物資源對A. semotus的繁殖表現更為重要。此結果有助於我們了解外在因子如何影響宿主生活史策略與族群動態。由於本研究所估算的子代數與子代品質相當接近A. semotus的適存度，而非前人研究常使用的短期或單次的繁殖表現，因此本研究可作為內寄生蟲對宿主適存度無負面影響的一個重要案例。

Life history theory predicts that organisms allocate resources to survival and reproduction such that they maximize number or quality of their offspring. Parasites and food resources can both influence host energy budget, thereby affecting their reproductive performance. Furthermore, the influence of parasites and food resources on host reproduction may be different for males and females given their differences in life history trade-offs. Here I tested the effects of intestinal parasites and seed resources on the reproductive success (number and quality of offspring) of Apodemus semotus. I conducted a manipulated field experiment in 2013 at a mixed conifer-deciduous forest in the Shei-pa National Park, which included (1) seed addition to a set of systematically selected locations, and (2) parasite removal by randomly assigning adult A. semotus to either Ivermectin (i.e. parasite removal) or water treatment (i.e. control). I used 10 microsatellite markers for parentage assignment, and mark-capture data for assessing offspring body mass (the proxy for offspring quality). My results indicate that seed addition had a positive effect on the number of offspring, which is independent from parasite removal. Parasite removal did not influence the number of offspring. In addition, neither parasite removal nor seed addition affects offspring quality. The results suggest that food resource is more important than parasitism to the mice’s reproductive performance, which helps us better understand how extrinsic factors may shape life history strategy and population dynamics. Because the number and quality of offspring estimated in this study are more closely linked to the host fitness compared to many previous studies using short-term or single-season reproduction data, my findings provide a solid case supporting non-negative effect of endoparasites on host fitness.

Altizer, S., Nunn, C.L., Thrall, P.H., Gittleman, J.L., Antonovics, J., Cunningham, A.A., Dobson, A.P., Ezenwa, V., Jones, K.E., Pedersen, A.B., Poss, M. & Pullian, J.R.C. (2003). Social organization and parasite risk in mammals: integrating theory and empirical studies. Annual Review of Ecology, Evolutionary and Systematics, 34, 517-547.
Bize, P., Jeanneret, C., Klopfenstein, A., & Roulin, A. (2008). What makes a host profitable? Parasites balance host nutritive resources against immunity. American Naturalist, 171,107-118.
Bloomer, S.E.M., Willebrand, T., Keith, I.M. & Keith, L.B. (1995). Impact of helminth parasitism on a snowshoe hare population in central Wisconsin: a field experiment. Canadian Journal of Zoology, 73, 1891-1898.
Boutin, S. (1990). Food supplementation experiments with terrestrial vertebrates: patterns, problems, and the future. Canadian Journal of Zoology, 68, 203-220.
Charnov, E.L. (1991). Evolution of life history variation among female mammals. Proceeding of the National Academy of Sciences, 88, 1134-1137.
Davis, J.A., Paylor, R., McDonalod, M.P., Libbey, M., Ligler, A., Bryant, K. & Crawley, J.N. (1999). Behavior effect of ivermectin in mice. Laboratory Animal Science, 49, 288-296.
Degen, A.A. (2006). Effect of macroparasites on the energy budget of small mammals. In: Morand, S., Krasnov, B.R., Poulin, R. editors.Micromammals and macroparasites: from evolutionary ecology to management. Tokyo (Japan): Springer, p. 371-399
Díaz, M. & Alonso, C.L. (2003). Wood mouse Apodemus sylvaticus winter food supply: density, condition, breeding, and parasites. Ecology, 84, 2680-2691.
Faircloth, B.C. (2008). msatcommander: detection of microsatellite repeat arrays and automated, locus‐specific primer design. Molecular Ecology Resources, 8, 92-94.
Geer, L.Y., Marchler-Bauer, A., Geer, R.C., Han, L., He, J., He, S., Liu, C., Shi, W. & Bryant, S.H. (2010). The NCBI biosystems database. Nucleic Acids Research, 38, D492-D496.
Gemmell, N.J. & Akiyama, S. (1996). An efficient method for the extraction of DNA from vertebrate tissues. Trends in Genetics, 12, 338-339.
Gilbert, B.S. & Krebs, C.J. (1981). Effect of extra food on Peromyscus and Clethrionomys populations in southern Yukon. Oecologia, 51, 326-331.
Grear, D.A., Perkins, S.E & Hudson, P.J. (2009). Does elevated testosterone result in increased exposure and transmission of parasites? Ecology Letters, 12, 528-537.
Gooderham, K. & Schulte-Hostedde, A. (2011). Macroparasitism influences reproductive success in red squirrels (Tamiasciurus hudsonicus). Behavioral Ecology, 22, 1195-1200.
Gourbal, B.E.F. & Gabrion, C. (2004). A study of mate choice in mice with experimental Teania crassiceps cysticercosis: can males choose. Canadian Journal of Zoology, 82: 635-643.
Hudson, P.J., Dobson, A.P. & Newborn, D. (1998). Prevention of population cycles by parasite removal. Science, 282, 2256-2258.
Kalinowski, S.T., Taper, M.L. & Marshall, T.C. (2007). Revising how the computer program CERVUS accommodates genotyping error increases success in paternity assignment. Molecular Ecology, 16, 1099-1106.
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.
Lin, J.W., Lo, H.Y., Wang, H.C. & Shaner, P.L. (2014). The effects of mite parasitism on the reproduction and survival of the Taiwan field mice (Apodemus semotus). Zoological Studies, 53, 79.
Lin, L.K. & Shiraishi, S. (1992). Reproductive biology of the Formosan wood mouse, Apodemus semotus. Journal of the Faculty of Agriculture, Kyushu University, 36-3, 183-200.
Lin, L.K., Nishino, T. & Shiraishi, S. (1993). Postnatal Growth and Development of the Formosan Wood Mouse Apodemus semotus. Journal of the Mammalogical Society of Japan, 18, 1-18.
Lo, H.Y. & Shaner, P.L. (2015). Sex-specific effect of parasitism on survival and reproduction of a rodent host in a subtropical montane region. Oecalogia, 177, 657-667.
Lochmiller, R.L. & Deerenberg, C. (2000). Trade‐offs in evolutionary immunology: just what is the cost of immunity?. Oikos, 88, 87-98.
Martin, G.B., Blache, D., Miller, D.W. & Vercoe, P.E. (2010). Interaction between nutrition and reproduction in the management of the mature male ruminant. Animal, 4 ,1214-1226.
McAdam, A.G., Boutin, S., Sykes, A.K. & Humphries, M.M. (2007). Life histories of female red squirrels and their contributions to population growth and lifetime fitness. Ecoscience, 14, 362-369.
Michalakis, Y. & Hochberg, M.E. (1994). Parasite effects on host life-history traits: a review of recent studies. Parasite, 1, 291-297.
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 London. Series B: Biological Sciences, 270, S213-S215.
Patterson, J.E., Neuhaus, P., Kutz, S. J. & Ruckstuhl, K.E. (2013). Parasite removal improves reproductive success of female North American red squirrels (Tamiasciurus hudsonicus). PLoS One, 8, e55779.
Patterson, L.D. & Schulte-Hostedde, A.I. (2011). Behavioral correlates to parasitism and reproductive success in male eastern chipmunks, Tamias striatus. Animal Behaviour, 81, 1129-1137.
Pedersen, A.B. & Antonvics, J. (2013). Anthelmintic treatment alters the parasite community in a wild mouse host. Biology letters, 9, 20130205.
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.
Penn, D. & Potts, W.K. (1998). Chemical signals and parasite-mediated sexual selection. Trends in Ecology and Evolution, 13, 391-396
Poul, J.M. (1988). Effect of perinatal ivermectin exposure on behavioral development of rat. Neurotoxicology and Teratology, 10, 267-272.
Poulin, R & Forbes, M.R. (2012). Meta-analysis and research on host-parasite interaction: past and future. Evolutionary Ecology, 26, 1169-1185.
Prevedello, J.A., Dickman, C.R., Vieira, M.V. & Vieira, E.M. (2013). Population responses of small mammals to food supply and predators: a global meta-analysis. Journal of Animal Ecology, 82, 927-936.
Promislow, D.E.L. & Harvey, P.H. (1990). Living fast and dying young: a comparative analysis of life history among mammal. Journal of Zoology, 220, 417-437.
Raveh, S., Heg, D., Dobson, F.S., Coltman, D.W., Gorrell, J.C., Balmer, A., Röösli, S. & Neuhaus, P. (2011). No experimental effects of parasite load on male mating behaviour and reproductive success. Animal Behaviour, 82, 673-682.
Resssl, S. & Schall, J.J. (1989). Parasites and showy males: malarial infection and color variation in fencen lizard. Oecologia, 78, 185-164.
Rozen, S. & Skaletsky, H. (1999). Primer3 on the WWW for general users and for biologist programmers. In Bioinformatics methods and protocols: method in molecular biology. S. Misener and S.A. Krawetz, editors. Humana Press. Totowa, New Jersey, USA. Pp. 365-386.
Ruffino, L., Salo, P., Koivisto, E., Banks, P.B. & Korpimäki, E. (2014). Reproductive responses of birds to experimental food supplementation: a meta-analysis. Frontiers in Zoology, 11, 80.
Salvador, A., Veiga,J.P., Martin, J., Lopez, P., Abelenda, M. & Puerta, M. (1996). The cost of producing sexual signal: testosterone increases the susceptibility of male lizards to ectoparasitic infestation. Behavioral Ecology, 7, 145-150.
Scantlebury, M., Waterman, J.M., Hillegass, M., Speakman, J.R. & Bennett, N.C. (2007). Energetic costs of parasitism in the Cape ground squirrel Xerus inauris. Proceedings of the Royal Society B: Biological Sciences, 274, 2169-2177.
Schuelke, M. (2000). An economic method for the fluorescent labeling of PCR fragments. Nature Biotechnology, 18, 233-234.
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.
Shaner, P.L., Wu, S.H., Ke, L. & Kao, S.J. (2013). Tropic niche divergence reduces survival in an omnivorous rodent. Evolutionary Ecology Research, 15, 1-14.
Sheldon, B.C. & Verhulst, S. (1996). Ecological immunology: costly parasite defences and trade-offs in evolutionary ecology. Trends in Ecology and Evolution, 11, 317-321.
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.
Stearns, S.C. (1976). Life-history tactics: a review of idea. The Quarterly Review of Biology, 51, 3-47.
Stien, A., Irvine, R.J., Ropstad, E., Halvorsen, O., Langvatn, R. & Albon, S.D. (2002). The impact of gastrointestinal nematodes on wild reindeer: Experimental and cross‐sectional studies. Journal of Animal Ecology, 71, 937-945.
Taitt, M.J. (1981). The effect of extra food on small rodent population: I. deermice (Peromyscus maniculatus). Journal of Animal Ecology, 50, 111-124.
Vandegrift, K.J., Raffel, T.R. & Hudson, P.J. (2008). Parasites prevent summer breeding in white-footed mice, Peromyscus leucopus. Ecology, 89, 2251-2258.
Vergara, P., Mougeot, F., Martínez-Padilla, J., Leckie, F. & Redpath, S.M. (2012). The condition dependence of secondary sexual trait stronger under high parasite infection level. Behavioral Ecology, 23, 502-511.
Walsh, P.T., McCreless, E. & Pedersen, A.B. (2013). Faecal avoidance and selective foraging: do wild mice have the luxury to avoid feaces? Animal Behavior, 86, 558-566.
Weatherhead, P.J., Metz, K.J., Bennett, G.F. & Irwin, R.F. (1993). Parasite faunas, testosterone and secondary sexual traits in male red-winged blackbirds. Behavioral Ecology and Sociobiology, 33,13-23.
Wolff, J.O. & Sherman, P.W. (Eds.) (2007). Rodent societies: An ecological and evolutionary perspective. Chicago: University of Chicago Press.
Watson, M.J. (2013). What drives population-level effects of parasites? Meta-analysis meets life-history. International Journal for Parasitology: Parasites and Wildlife, 2, 190-196.
Yu, H.T. (1994). Distribution and abundance of small mammals along a subtropical elevational gradient in central Taiwan. Journal of Zoology, 234, 577-600.
Zahavi, A. (1975). Mate selection – a selection for a handicap. Journal of Theoretical Biology, 53, 205-214.