Mate Choice and Mechanical Constraint on Size‐Assortative Paring Success in a Simultaneous Hermaphroditic Pond Snail Radix lagotis (Gastropoda: Pulmonata) on the Tibetan Plateau

Abstract

Body size is expected to affect the mating behaviour and mating patterns of simultaneous hermaphrodites, because it can influence fecundity, mate choice and mechanical constraints to mating. However, there is a lack of detailed research on size‐dependent mating patterns in hermaphroditic species, including aquatic pulmonates. We investigated mating patterns and mating success in the simultaneous hermaphroditic pond snail Radix lagotis (Gastropoda: Pulmonata). We found that fecundity increased with body size and we observed a strong pattern of size‐assortative mating across two breeding seasons. Sperm donors were more likely to inseminate large snails than small snails, and pairings between two large individuals were more likely to result in successful copulations than pairings of two small individuals or two individuals of differing sizes. Other possible explanations (mechanical constraint) for these patterns are also discussed.

Size‐Dependent Male Mate Preference and its Association with Size‐Assortative Mating in a Mangrove Snail, Littoraria ardouiniana

“…). Mechanical constraints can, for example, be a result of small individuals with short copulatory organs not being able to inseminate large mating partners and vice versa (Yu & Wang ). Such mechanical constraints do not, however, seem to be relevant in littorinids including L. ardouiniana, as active mating partners found in the field can vary greatly in size and copulation can last for a considerable duration in these pairs (Erlandsson & Johannesson ; Cardoso et al.…”

“…Apart from sexual selection, two other prevailing explanations for size-assortative mating are mechanical constraints on copulation between unequally sized mates, and the non-random distribution of differentsized individuals (Crespi 1989;Arnqvist et al 1996). Mechanical constraints can, for example, be a result of small individuals with short copulatory organs not being able to inseminate large mating partners and vice versa (Yu & Wang 2013). Such mechanical constraints do not, however, seem to be relevant in littorinids including L. ardouiniana, as active mating partners found in the field can vary greatly in size and copulation can last for a considerable duration in these pairs (Erlandsson & Johannesson 1994;Cardoso et al 2007;Ng & Williams 2012).…”

“…In both hermaphroditic and dioecious snails, sexual selection has been widely proposed as a major driver of size‐assortative mating (Erlandsson & Johannesson ; Angeloni ; Zahradnik et al. ; Yu & Wang ) as males or sperm donors (in hermaphroditic snails) often prefer to mate with larger, more fecund, partners (Erlandsson & Johannesson ; Zahradnik et al. ; Yu & Wang ).…”

“…; Yu & Wang ) as males or sperm donors (in hermaphroditic snails) often prefer to mate with larger, more fecund, partners (Erlandsson & Johannesson ; Zahradnik et al. ; Yu & Wang ). A size advantage of large males/sperm donors over small rivals in mating competitions, along with male mate preference for large females, are necessary to generate size‐assortative mating, but male–male competition has rarely been observed in snails (but see Gibson ; Bradshaw‐Hawkins & Sander ; Zahradnik et al.…”

“…In both hermaphroditic and dioecious snails, sexual selection has been widely proposed as a major driver of size-assortative mating (Erlandsson & Johannesson 1994;Angeloni 2003;Zahradnik et al 2008;Yu & Wang 2013) as males or sperm donors (in hermaphroditic snails) often prefer to mate with larger, more fecund, partners (Erlandsson & Johannesson 1994;Zahradnik et al 2008;Yu & Wang 2013). A size advantage of large males/sperm donors over small rivals in mating competitions, along with male mate preference for large females, are necessary to generate size-assortative mating, but male-male competition has rarely been observed in snails (but see Gibson 1965;Bradshaw-Hawkins & Sander 1981;Zahradnik et al 2008).…”