性別差異感染普遍存在於寄主類群中。雌性與雄性宿主受寄生蟲感染程度不同的現象可能源於其行為或生理上的差異，大多數以脊椎動物為宿主的情況下，雄性宿主的寄生蟲感染程度會高於雌性宿主。此現象通常被歸因至雄性激素引起之免疫抑制反應，或是為了交配而採取的高風險行為。先前文獻對於哺乳動物宿主間性別差異感染的現象已有大量之探討，但鮮少有人探討兩棲類動物寄生蟲的相關現象。本研究聚焦於台灣地區太田樹蛙與恙螨的寄生關係，探討其潛在的性別差異感染現象及其背後的生理與環境因子。我們在2023年5月至2024年5月進行每月一次的調查，研究地點為台東知本溪及花蓮美崙溪。我們發現恙螨感染率與宿主體型呈正相關，GLMM也顯示宿主體型是影響恙螨感染程度的重要因子，我們因而推測恙螨可能偏好較大的宿主。恙螨感染率與宿主身體健康狀態呈負相關，但我們無法得知其因果關係。分析結果顯示微棲地類型及濕度是影響恙螨感染程度的主要環境因子，該結果可能與恙螨的生活史相關。我們原先預期公蛙會在雄性激素和繁殖季節群聚鳴叫的影響下具有較高恙螨感染程度，研究結果卻顯示知本地區全年間雌蛙的感染強度顯著高於雄蛙且盛行率在大多數月份略高於雄蛙。知本溪與美崙溪相比之下明顯具有全年較高的恙螨盛行率，該差異可能源自於其他環境因子（例如溫泉）以及恙螨與宿主族群間的交互作用。雖然太田樹蛙的雌雄二型性可能是形塑雌性偏好感染現象的原因，但我們仍需要進一步驗證雌性偏好寄生現象背後的機制假說（例如：雌性宿主體型較大，能提供恙螨豐富的食物來源；雌性生殖與免疫投資之間具有拮抗效應；宿主性別間行為具有顯著差異）以及探討恙螨感染部位分布明顯不均的原因。

Sex-biased parasitism has been observed across a wide range of taxa. Different infection levels between host sexes can be attributed to behavioral or physiological differences. Majority of cases in vertebrate hosts show higher level of infection on males. This phenomenon has been explained by immunosuppression due to sex hormone or risky mating behaviors. Although sex-biased parasitism in mammal hosts was well documented in previous studies, there has been limited research exploring this pattern in amphibians. In this study, we focus on the sex-biased pattern of a chigger mite, Endotrombicula sp., associated with its anuran host Buergeria otai in Taiwan. We also attend to figure out the correlation among chigger infestation, host condition and environmental factors. Monthly surveys were taken from May 2023 to May 2024 on two localities, Zhiben River and Meilun River. We found positive correlation between infection probability and host body size. Chigger intensity also positively correlates with body size, which may results from chigger preference. Infection probability has negative correlation with body condition, but the causation of the relationship needs further investigation. GLMM shows that microhabitat and relative humidity are main factors influencing chigger infestation, which may be associated with the chigger life cycle. We predicted that chigger infestation will be male-biased due to both androgen-induced immunosuppression and lekking behavior during the mating season. Conversely, intensity of chigger infection is significantly higher on females than males in Zhiben River in a few months. Monthly prevalence of chiggers on females was also slightly higher than males, although it did not reach statistic significance. We found a consistently high-level prevalence of mite infestation in Zhiben River compared to Meilun River, which can be explained by favor environmental factors (e.g., existence of hotspring) and biotic interactions such as population density. Although the sexual size dimorphism of Buergeria otai may explain the female-biased parastism, further studies are needed to determine the mechanism behind it (e.g., female frogs serving as great resources for chiggers, trade-offs between reproduction and immunity, and the behavioral differences between sexes) and the body distribution pattern of chigger infestation.

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