Data from: The consequences of co-infections for parasite transmission in the mosquito Aedes aegypti

1)Co-infections may modify parasite transmission opportunities directly as a consequence of interactions in the within host environment, but also indirectly through changes in host life-history. Furthermore, host and parasite traits are sensitive to the abiotic environment with variable consequences for parasite transmission in co-infections. (2)We investigate how co-infection of the mosquito Aedes aegypti with two microsporidian parasites (Vavraia culicis and Edhazardia aedis) at two levels of larval food availability affects parasite transmission directly, and indirectly through effects on host traits (3)In a laboratory infection experiment we compared how co-infection, at low and high larval food availability, affected the probability of infection, within-host growth and the transmission potential of each parasite, compared to single infections. Horizontal transmission was deemed possible for both parasites when infected hosts died harbouring horizontally-transmitting spores. Vertical transmission was judged possible for E. aedis when infected females emerged as adults. We also compared the total input number of spores used to seed infections with output number, in single and co-infections for each parasite. (4)The effects of co-infection on parasite fitness were complex, especially for V. culicis. In low larval food conditions, co-infection increased the chances of mosquitoes dying as larvae or pupae, thus increasing opportunities for V. culicis’ horizontal transmission. However, co-infection reduced larval longevity and hence time available for V. culicis spore production. Overall there was a negative net effect of co-infection on V. culicis whereby the number of spores produced was less than the number used to seed infection. Co-infections also negatively affected horizontal transmission of the more virulent parasite, E. aedis, through reduced longevity of pre-adult hosts. However, its potential transmission suffered less relative to V. culicis. (5)Our results show that co-infection can negatively affect parasite transmission opportunities, both directly as well as indirectly via effects on host life-history. We also find that transmission is contingent on the combined effect of the abiotic environment.

1) 共感染（co-infection）可经由宿主内环境中的相互作用直接改变寄生虫的传播机会，亦可通过调控宿主生活史（host life-history）间接产生影响。此外，宿主与寄生虫的性状对非生物环境（abiotic environment）敏感，这会为共感染情境下的寄生虫传播带来可变的结局。(2) 本研究旨在探讨：当埃及伊蚊（Aedes aegypti）在两种幼虫食物供应量水平下，同时感染两种微孢子虫（microsporidian）寄生虫——库氏瓦拉微孢子虫（Vavraia culicis）与伊蚊爱德哈微孢子虫（Edhazardia aedis）时，共感染如何直接影响寄生虫的传播，以及通过作用于宿主性状间接引发的传播效应。(3) 在实验室感染实验中，相较于单一感染，我们对比了在低、高幼虫食物供应条件下的共感染对两种寄生虫的感染概率、宿主体内增殖情况以及传播潜力的影响。当受感染宿主死亡时仍携带可水平传播（horizontal transmission）的孢子，则判定该寄生虫可发生水平传播；当受感染雌蚊羽化至成虫阶段，则判定伊蚊爱德哈微孢子虫可发生垂直传播（vertical transmission）。此外，我们还对比了每种寄生虫在单一感染与共感染条件下，用于启动感染的孢子总输入量与最终产出孢子量。(4) 共感染对寄生虫适合度（parasite fitness）的影响较为复杂，对库氏瓦拉微孢子虫而言尤为显著。在低幼虫食物条件下，共感染会提升蚊子以幼虫或蛹阶段死亡的概率，从而增加库氏瓦拉微孢子虫的水平传播机会。但共感染同时会缩短幼虫的寿命，进而压缩库氏瓦拉微孢子虫的孢子生产时长。总体而言，共感染对库氏瓦拉微孢子虫存在净负效应：其产出的孢子数量少于启动感染的输入孢子量。共感染还会通过缩短宿主幼体的寿命，对致病力更强的伊蚊爱德哈微孢子虫的水平传播产生负面影响，不过相较于库氏瓦拉微孢子虫，其传播潜力受到的损害相对更轻。(5) 本研究结果表明，共感染可通过直接途径以及作用于宿主生活史的间接途径，对寄生虫的传播机会产生负向影响。同时我们还发现，寄生虫的传播事件取决于非生物环境的综合作用。