PATTERNS OF SEXUAL ROLES ADOPTED BY THE SCHISTOSOME-VECTOR SNAIL BIOMPHALARIA GLABRATA (PLANORBIDAE)

Abstract

Relatively little u known about the mating behaviour of hermaphrodite freshwater snails, many of which transmit the Schistosoma trematodes among humans in developing countries. Knowledge of the breeding biology of these snails could help in the design of schistosome control programmes, as well as possibly contributing to our understanding of the evolution of simultaneous hermaphroditism in animaLv Here we describe an experiment investigating the patterns of sexual roles adopted by the Schistosoma mansoni-veclot snail, Bwmphalana glabrata. During observations on groups of freely interacting snails, no individuals copulated significantly more often in the male than in the female role, or vice versa. Only one individual showed a pattern of alternating sexual roles over successive matings that differed significantly from a random sequence of roles. There was no evidence for reciprocal copulation with one particular partner, either between consecutive matings (unless they were temporarily isolated from other snails) or between non-consecutive matings (separated by copulations with other conspecifics). We discuss these results in the context of sex allocation and ESS mating strategy theories.

Parasite infection, host resistance and mate choice: battle of the genders in a simultaneous hermaphrodite

“…The position (side of arena), time of initiation, duration and identity of snail initiating and/or terminating each interaction were individually recorded, producing a total of 13 600 lines of data. Mating duration was recorded as the duration that a snail's penis was visibly inserted into the other snail's genital pore (Vernon 1993;Vernon & Taylor 1996;Trigwell et al 1997). Nineteen triplets containing uninfected free-moving snails and 10 triplets containing patently infected free-moving snails were analysed (proc GLM in SAS/STAT v. 81999) using infection status, genotype and gender as the independent variables.…”

“…Although data are limited, some evidence of differential mating has been detected among unselected and uninfected B. glabrata lines, relating to inbreeding avoidance (Vernon et al 1995;Vernon & Taylor 1996) and geographical origin (Rupp & Woolhouse 1999). No gender biases, where individuals preferentially mate as male or female, were reported (Vernon et al 1995;Vernon & Taylor 1996;Trigwell et al 1997;Rupp & Woolhouse 1999). We investigated here whether an interplay of potential infection status (host resistance versus susceptibility genotypes) and current infection status (infected versus uninfected) influenced the reproductive strategy of B. glabrata snails.…”

“…Genetic variability for both susceptibility and resistance is maintained within natural snail metapopulations through, in part, trade-offs between the high fitness costs resulting from parasitism and those associated with resistance: susceptible snails suffer from significantly increased mortality when infected, whereas resistant individuals suffer reduced egg viability (despite equal egg mass and embryo production, significantly fewer offspring hatch from resistant lines, potentially owing to deficiencies in internal factors that, although primarily associated with host reproduction, are also essential for normal parasite development; Woolhouse 1989;Cooper et al 1994;Cousin et al 1995;Webster & Woolhouse 1999). Laboratorial behavioural and molecular studies have revealed that B. glabrata preferentially outcross (Vernon et al 1995;Vernon & Taylor 1996;Webster 2001). Although data are limited, some evidence of differential mating has been detected among unselected and uninfected B. glabrata lines, relating to inbreeding avoidance (Vernon et al 1995;Vernon & Taylor 1996) and geographical origin (Rupp & Woolhouse 1999).…”

Neuro-endocrine control of reproduction in hermaphroditic freshwater snails: mechanisms and evolution

“…In such a chain, the frontmost individual acts only as a female, the last individual only as a male, and each individual in between acts as male to the partner directly in front of it and female to the partner directly in its back. In a few species simultaneously reciprocal matings may occasionally take place (reviewed in Jordaens et al, 2007 [ Biomphalaria glabrata : Brumpt, 1941; Vernon and Taylor, 1996; Trigwell et al, 1997; Vianey-Liaud, 1998; B. tenogophila : Springer de Freitas et al, 1997; Helisoma trivolvis : Duncan, 1975]). In a standard unilateral copulation, the sperm recipient seems to be more or less inactive when mounted by a partner.…”

Establishment of the dominant lethal test in the freshwater mollusk Biomphalaria glabrata (Say, 1818)

“…It is known that, in spite of the highly developed ability of B. glabrata to self-fertilize, it shows an absolute preference to cross-fertilization [23]. Besides, in a pairing of two snails, both act as male and female without preference to any role [27]. Thus, assuming that the rates of cross-fertilization in the wild-type snails have been of the same order of the high rates observed in the albino snails, we may conclude that a minority of self-fertilized embryos has been produced.…”