曼氏血吸虫中间宿主光滑双脐螺的生物学特性：生殖与生存

Study on biological characteristics: reproduction and viability of Biomphalaria glabrata as an intermediate host of Schistosoma mansoni

目的比较光滑双脐螺自体受精和异体受精的繁殖力差异,观察昼夜和光照对产卵的影响,以及成螺对缺水缺食的耐受性,旨在为现场控制该螺提供依据。方法采用实验室条件下培育的光滑双脐螺,分成自体受精组和自然受精组,比较两组受精螺的产卵能力、所产卵的发育和孵化、幼螺生长发育等状况。将成螺分成全天光照组、全天避光组、日间光照和夜间避光(自然环境状态)组、日间避光和夜间光照组等4种饲养环境,比较各组螺的产卵情况。将光滑双脐螺成螺分别暴露在相对湿度为0、65%、87%和100%的不同环境中,观察其生存情况。采用快速烘干法去除光滑双脐螺成螺软体内水分,观察螺体重分别减轻10%、20%、30%、40%、50%、52%、55%、57%、60%和70%后的存活率。结果在25℃环境条件下,自体受精组和自然受精组螺15 d的产卵数分别为(8.77±16.92)枚/螺和(149.71±142.28)枚/螺,两组间差异有统计学意义(t=0.999 999,P <0.01);所产螺卵的孵化率分别为50.1%和78.9%(χ^2=18.18,P <0.01),生殖成熟率分别为19.3%和3.8%(χ^2=11.83,P <0.01),两组间差异均有统计学意义。全天光照组、全天避光组、日间光照和夜间避光组、日间避光和夜间光照组等4种饲养环境下产卵量分别为(999.07±444.00)、(602.93±510.68)、(944.07±392.53)、(577.07±279.76)枚/d;其中日间光照和夜间避光组的日间和夜间产卵量分别占10.1%和89.9%,提示该螺产卵以夜间为主;但光照可改变其昼夜节律性。光滑双脐螺成螺在相对湿度分别为0、65%、87%和100%的25℃环境中的最长生存时间分别为7、70、150 d及100 d,而缺食对照组为50 d。光滑双脐螺成螺软体脱水率为10%、20%、30%、40%、50%、52%、55%、57%、60%和70%时,存活率分别为100%、100%、100%、100%、70%、30%、0、0、0、0。结论光滑双脐螺可通过异体受精或自体受精完成生殖过程;自体受精螺的繁殖力弱于异体受精螺,但其生殖成熟率高于异体受精螺。光滑双脐螺对缺水缺食具有一定的耐受性,提示光滑双脐螺孳生区旱季后仍存活的螺对当地螺种群的维持及曼氏血吸虫病传播具有重要意义。

Objective To compare the difference of fertility of Biomphalaria glabrata snails between self-fertilization and cross-fertilization and to observe the circadian rhythm of laying eggs, the effect of light on laying eggs and the tolerance of the snail to water and food deficiency, so as to provide the evidence for control and elimination of B. glabrata snails in the field.Methods Under laboratory conditions, a single B. glabrata egg for self-fertilization was separated and hatched individually, and young snails were raised in different plastic boxes individually. The eggs for cross-fertilization were hatched and the young snails were fed in the same plastic box. The ability of spawn, the development of the eggs, and the number of snails growing from young to adult snails were compared between the self-fertilization and cross-fertilization. The snails were in the water under four environments, all day illumination, all day without illumination, daytime lighting and night without illumination, and daytime without illumination but night lighting. The eggs were collected and counted daily. The circadian rhythm of spawn and the effect of illumination on spawn were observed. The adult snails were divided into 6 groups and exposed to the environments with relative humidity of 0, 65%, 87% and 100%, respectively. The survival rates of the adult snails exposed to the different environments after different time were observed. The adult snails were placed at 25 ℃ in the oven to remove water content from the soft body of snails.When the dehydration rates of the soft bodies achieved 10%, 20%, 30%, 40%, 50%, 52%, 55%, 57%, 60%, and 70% respectively, the survival rates of the adult snails exposed to the oven were observed. Results In the 25 ℃ water, the average laying egg number for 15 days per snail was(8.77 ± 16.92) eggs/snail in the self-fertilization snail. The average laying egg number for 15 days per snail was(149.71 ± 142.28) eggs/snail in the cross-fertilization snails. There was a significant difference between the self-fertilization snail and cross-fertilization snail(t = 0.999 999,P < 0.01). The hatching rate and reproductive maturation rate of the self-fertilization snails and cross-fertilization snails were 50.1% and 78.9%, and 19.3% and 3.8%, respectively, There was a significant difference(the hatching rate:χ^2= 18.18,P < 0.01, the reproductive maturation rate:χ^2= 11.83,P < 0.01). In the natural environment of daytime with illumination and nighttime with darkness, the amount of laying 20 eggs of B. glabrata snail was(944.07 ± 392.53) eggs/day during a whole day, among them the amount of laying eggs during daytime account for 10.1% and the amount of laying eggs during nighttime account for 89.9%, and the laying egg was given priority to with the night. The above results suggested that the dark environment was conducive to B. glabrata snails to lay eggs. The above results suggested that light can promote the increase of spawning of B. glabrata. When B. glabrata was exposed to the environments with the relative humidity of 0, 65%, 87% and 100% at 25 ℃, respectively, and the longest survival times of snails were 7, 70, 150 d and 100 d, respectively. In the 25 ℃ water, the snails could survive for 50 days without food. The adult snails were placed at 25 ℃ in the oven to remove water content from the soft body of snails. When the dehydration rates of the soft bodies achieved 10%, 20%, 30%, 40%,50%, 52%, 55%, 57%, 60%, and 70% respectively, the survival rates of the adult snails exposed to the oven were 100%, 100%,100%, 100%, 70%, 30%, 0, 0, 0 and 0, respectively. Conclusions B. glabrata can achieve the reproductive process by crossfertilization or self-fertilization. There is a significant difference in reproductive ability between the cross-fertilization snail and self-fertilization snail, cross-fertilization is stronger than self-fertilization, but the rate of reproduction in the self-fertilization is higher than that in the cross-fertilization. It is indicated that B. glabrata that survive after the dry season plays an important role in the maintenance of local snail populations and transmission of schistosomiasis mansoni.