鵠沼枝額蟲交配行為與配偶辨識

Abstract

生存於不穩定且不可預期的暫時性水域環境，豐年蟲需要擁有有效率之交配系統，以便能迅速產下休眠卵，然而過去對於牠們交配行為所知不多。本研究目的為測試(1)光照對其交配行為之影響，(2)交配成功是否受配偶對雄蟲求偶的反應所影響。首先觀察與描述鵠沼枝額蟲 (Branchinella kugenumaensis (Ishikawa, 1895)) 之交配行為，之後紀錄主角雄蟲 (focal male) 與配偶配對所展現之交配行為頻率。實驗控制因子包含兩不同照度、以及三種配偶(可孕雌蟲 (receptive female)、不可孕雌蟲 (non-receptive female)、雄蟲 (male))。另外以錄影方式記錄不同配偶所展現之移動行為。結果顯示鵠沼枝額蟲雄蟲之交配行為分成朝向 (orientation)、維持配對體位 (station taking)、抱握 (amplexus)、插入 (intromission)、交尾 (copulation) 與分開 (disengagement) 六個階段，且光線對所有交配行為皆有顯著影響。主角雄蟲在朝向時期雖然無法辨識配偶;在維持配對體位與抱握時期卻顯著偏好可孕雌蟲。雖然三類配偶個體的移動速度並無顯著差異，在被雄蟲求偶時其速度皆有顯著提升。此外，雄蟲只會對具有速度較慢之配偶展現抱握行為。本研究證明視覺對鵠沼枝額蟲交配行為有關鍵影響，並於第一個行為階段便發生，而雄蟲之配偶辨識發生於朝向階段。配偶有可能藉主動降低移動速度使雄蟲交配成功，因此配偶選擇 (mate choice) 機制可能存在。總結，推測鵠沼枝額蟲符合一般豐年蟲之交配系統 (scramble-competition polygyny)，其交配系統與視覺利用是高族群密度與短暫繁殖期壓力下之適應。

Anostracas face stress of reproduction within transient time period. Efficient mating system is necessary to prevent abortive hatching. Previous studies on anostracan mating behavior were few. In this study, I aim to estimate effect of 1) light and 2) mate swimming velocity on anostracan mating behavior. Hence, mating behavior of Branchinella kugenumaensis (Ishikawa, 1895) was observed and described. Mating behavior exhibited by focal males was compared between light and dark conditions, and among different type potential mates (receptive females, non-receptive females, and other males). I also measured swimming speeds of potential mates by videotaping and horizontal velocity measuring. The results demonstrated that mating behavior of B. kugenumaensis was consistent to general anostracan mating behavior. It was divided into orientation, station taking, amplexus, intromission, copulation, and disengagement. Light effect was significant in orientation, station taking, and amplexus, regardless of potential mate type. Focal males did not prefer any type mate in orientation but preferred receptive females in station taking and amplexus. All different type potential mates behaved similar swimming speed, wherein velocity significantly increasing during courtship than before courtship. In addition, amplexus occurred with significantly low potential mate velocities. Therefore, light does affect male B. kugenumaensis mating behavior. They may orient to every potential mates in orientation phase. Mate discrimination occurs in orientation phase. Amplexus was affected by velocities of potential mates, thus mate choice might exist in this mating system. I suggest that B. kugenumaensis fits general anostracan mating system, scramble-competition polygyny. Visual utilization and its mating system are adaptations to high population densities and transient reproduction durations.