寄生蟲與食物資源對台灣森鼠繁殖表現的影響
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2016
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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.
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.
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生活史, 適存度, 親子鑑定, 齧齒目, fitness, life history, parentage assignment, rodentia