Biomphalaria tenagophila, a snail host of human schistosomiasis, is a simultaneous hermaphrodite with the ability of self-fertilization. However, in the presence of partners, cross-fertilization is prefered Paraense It has been observed that self-fertilizing isolated snails kept under the same conditions in the laboratory have different reproductive rates.
Before starting studies about the reproductive biology of these molluscans, it is important to know such differences. During the course of studies on the reproductive biology of B. It was also observed that many individuals with reproductive problems in self-fertilization had, in general, a satisfactory peformance in cross-fertilization. However, it was observed that in B. Bulinus cernicus specimens of similar ages and development stages, evaluated by the ability of self-fertilization, showed differences in their roles' performance Rollinson et al.
The probable individual variation in the ability of snails to adopt different sexual roles requires more attention. It may be wrong to assume that all the snails in a population are equally well-balanced for tendencies to perform the female or male role. Rudolph and Bailey , for example, observed that male sexual role is more frequent in populations of Bulinus. Moreover, the performance of this role is not dependent on previous sexual experience as male or female.
The objective of the present study is to verify the influence of self-fertilization performance and copulation behaviour in the production of embryos by cross-fertilization in groups of B. The following hypotheses were tested: a snails that have low reproductive success during the process of self-fertilization do not increase their reproductive success after the end of grouping, b the copulation behaviour and the presence of one snail whose eggs have a low viability rate influence the partner's reproductive success by cross-fertilization.
They came from Joinville southern Brazil , and were reared and kept at the laboratory for approximately 10 years. The snails were kept in isolation since the period of sexual immaturity and used in the experiments upon reaching a diameter of 10 to 12 mm and the age of 2 to 3 months. Albinism, determined by a pair of recessive genes Newton , was used as a genetic marker.
The water was refilled periodically to compensate evaporation. The individuals were isolated in a glass container of ml, previously prepared with one tablespoon of earth the same used in the ration and 80 ml of water without chlorine. About five days later, albino and pigmented embryos could be identified.
The eggs were counted, under a steroscopic microscope, every two days, and classified into the following categories: pigmented, albino or sterile embryos, eggs with a hole and empty or small less than half size of normal egg. The snails were marked individually with one piece of spangle glued in the right side of the shell. The water volume per snail was ml. The copulation behaviour was observed over a 12 hr period after the snails had been placed in groups.
The duration of each copulation and the sexual role performed by each partner were noted. The snails were subsequently isolated and the reproductive performance monitored over a 30 day period. The results were analyzed statistically by using nonparametric tests. During the observation period, 55 copulations were recorded. The average frequency of copulation per snail, over 12 hr period, was 3. The two albino categories and the pigmented snails performed the sexual roles Fig.
According to Rollinson et al. The model consists of giving and receiving gametes in alternate and successive parcels. The male or female gamete may be exchanged. However, an association exists between the gamete which will be traded and that which has more risk of loss during the fertilization process.
In the case of Biomphalaria , the gametes are subject to an assymetrical risk of damage. The spermatozoa can be considered gametes of risk, and likewise the gamete which will be traded. In our study, the grouping period of 12 hr, may not be long enough to observe greater differences between sexual performance among the partners.
On average, the copulation lasted In molluscans, copulation can last from a few minutes to 12 hr, but usually lasts from 30 to 90 min.
Simultaneous reciprocal copulations of up to 4 hr were observed in pairs of Helisoma trivolvis Duncan and in pairs of B. A positive relationship between reproductive performance before and after mating was also observed in groups Freitas and in pairs of B. To relate the copulation behaviour with the reproductive success, we considered only the copulation in which the pigmented snails performed male or male and female roles simultaneously SRC in relation to their albino partners Table III.
Of the twelve pigmented snails, eight were observed in copulation behaviour with their albino partners. Of these eight, three snails Table III , repetitions no. The other five pigmented snails Table III , repetitions no.
Thus, "bad reproducers" might have caused a decrease in the cross-reproduction performance by "good reproducers". There is an absence of sperm transference sterile copulation in the great majority of unilateral copulations and there is sperm transference fertile copulation in the great majority of reciprocal copulations in pairs of B. In addition, 64 to min of copulation are necessary for sperm transference to occur in unilateral copulations.
Explanation: The act of bringing the genital organs closer together to enhance the chances of fertilization occurring is called copulation. Related questions How do gametes affect genetic variation? How is a zygote formed in humans?
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