寄生蟲移除改變台灣森鼠的覓食行為

Abstract

動物的覓食行為受到許多因子影響，例如外在風險以及個體狀況。過去研究主要關注在掠食風險如何影響動物的覓食行為，對於其他風險種類，例如被寄生的風險則研究相對較少。近期研究指出，動物的確有可能藉由避免利用被糞便污染的區塊覓食，來降低被寄生的風險。本研究利用野外與室內實驗，檢測是否經由驅蟲藥（ivermectin）減少寄生蟲的台灣森鼠（Apodemus semotus）在覓食行為上會有改變。在野外實驗部分，我先於捕捉到的野生森鼠身上植入晶片，再於野外放置三種處理的食物站，包含：（1）高寄生蟲卵糞便污染的食物；（2）低寄生蟲卵糞便污染的食物；（3）無糞便污染的食物。最後以晶片掃描器來記錄前來食物站的老鼠晶片號碼與所待的時間。經由驅蟲藥處理過的老鼠在放置糞便處理的食物站待的時間較控制組短。在室內實驗部分，我比較有無驅蟲藥之森鼠，在能量攝取、生物量與血液生化值上的差異。經驅蟲藥處理過的雄性能量攝取較高，雌性則是相反。驅蟲藥處理對於森鼠的生物量與血液生化值皆沒有影響。本研究證實寄生蟲移除可以改變宿主對風險的敏感度。因此，寄生蟲在宿主覓食行為上不但可能扮演一個重要的角色，寄生蟲本身也可能因此獲得提升傳播率的好處。

Foraging behavior can be influenced by many factors, including risk and individual condition. While predation risk has been shown to influence a forager’s patch use, the effects of other types of risk, such as parasitism risk, are rarely explored. Recent evidence suggests that hosts may reduce the amount of time spent foraging in a patch contaminated with feces, potentially to avoid parasite infection. In this study, I examined whether wild Formosan field mice, Apodemus semotus, alter their foraging behavior in response to parasite removal treatment using both field and laboratory experiments. I used ivermectin to remove helminth parasites from A. semotus. In the field experiment, I live-trapped the rodents and marked them with passive integrated transponder (PIT) tags. I set up food stations, each consisting of 3 food trays: (1) food contaminated with feces that have high numbers of parasite eggs (high risk patch); (2) food contaminated with feces that have low numbers of parasite eggs (low risk patch); and (3) food not contaminated with feces (no risk patch). A data logger and a PIT antenna were attached to each food tray to record the time an individual spent in that patch. I found that A. semotus treated with ivermectin spent less time in risky patches (high- and low-risk patches) than no-risk patches. In the laboratory experiment, I measured and compared energy intake, body mass, hematological and serum biochemical parameters of ivermectin-treated and control groups. Ivermectin-treated males had higher energy intake than the control whereas ivermectin-treated females showed the opposite pattern. However, I did not find parasite removal effects on body mass, immune function (hematological parameters) or nutritional status (serum biochemical parameters). This study provided empirical evidence that parasite removal can influence risk sensitivity in a wild rodent. Thus, parasites may play a role in hosts’ foraging behavior and by doing so, benefit from improved transmission.