Social facilitation affects longevity and lifetime reproductive success in a self‐fertilizing land snail

Abstract

Factors that reduce the reproductive output of self‐fertilizing hermaphrodites are receiving increasing attention. The combined effects of reduced fecundity of selfing parents and inbreeding depression of the progeny have been referred to as self‐fertilization depression. In isolated freshwater snails the reproductive output of selfing individuals also decreases due to the lack of social facilitation (absence of a conspecific). We examined the effect of social facilitation on lifetime reproductive success (number of young produced and longevity) over two generations in the simultaneously hermaphroditic land snail Balea perversa. In a parallel study we showed that B. perversa kept singly and in pairs reproduced exclusively by self‐fertilization. In the parent generation, snails kept singly produced less offspring than snails kept in pairs. The difference in lifetime number of young was mainly due to differences in adult life span. Snails of the two groups did not differ in reproductive rate (number of young produced per 100 d of reproductive life) and hatchling size. In the offspring generation, snails kept singly did not differ from individuals kept in pairs in the lifetime number of young and hatchling survival. As in the parent generation, snails kept singly reproduced during a shorter period than snails kept in pairs. However, the shorter reproductive life span of snails kept singly was compensated for by a slightly (but not significantly) higher reproductive rate which resulted in a similar number of offspring produced for both groups. In both generations, snails of the two groups did not differ in size at first reproduction, adult growth rate and size at death. These findings suggest that social facilitation may affect longevity in selfing B. perversa.

Effects of mating, breeding system and parasites on reproduction in hermaphrodites: pulmonate gastropods (Mollusca)

“…In the offspring generation, snails kept singly did not differ from individuals kept in pairs in the lifetime number of young and hatchling survival but (as in the parent generation) snails kept singly reproduced during a shorter period than snails kept in pairs. Since the species reproduces exclusively by self-fertilisation (Wirth et al, 1997;Baur and Baur, 2000), this result may not be attributed to inbreeding depression but suggests that social facilitation may affect longevity in selfing B. perversa.…”

“…Studies that investigate life history variation or evaluate the effects of inbreeding or outbreeding depression may be partly confounded with the snail's social environment (isolated versus paired/grouped) (Vernon, 1995) and the relevant controls have not been performed to disentangle these two possible effects on reproductive output (see Breeding system). Baur and Baur (2000) kept individuals of Balea perversa singly or in pairs for two generations. In the parent generation, snails kept singly produced less offspring than snails kept in pairs which was mainly due to their shorter adult life span .…”

Selfing and brooding in Alinda biplicata (Gastropoda: Pulmonata: Clausiliidae) – life history traits of a good coloniser

“…Among Clausiliidae it has only been recorded for Balea perversa (Wirth et al, 1997;Baur & Baur, 2000). Alinda biplicata is thus the second species of the family reported to be capable of selfing.…”

“…On the other hand, the many unhatched eggs provide excellent food to the few juveniles, ensuring their faster growth and greater survivorship (Baur, 1994). Probably in A. biplicata the selfing is only an alternative and not the main mode of reproduction, as opposed to B. perversa, in which selfing prevails irrespective of whether the snails are kept in isolation or in groups (Wirth et al, 1997;Baur & Baur, 2000). B. perversa starts reproducing 1-2 months after growth completion (Baur & Baur, 1992), A. biplicata that are kept in pairs after 5-7 months (Maltz & SulikowskaDrozd, 2012), and kept in isolation after ca.…”

“…If brooding increases offspring survivorsbip and colonisation success, especially for low-fecundity snails, and selfing also increases cbances of species' survival and its colonising abilities, tbe combination of brooding and selfing will make it easier for tbe species to occupy new sites. Great colonising abilities bave been demonstrated for B. perversa (brooding and selfing) in tbe Great Alvar (Sweden) (Wirtb et al, 1997;Baur & Baur, 2000). Tbe common ancestor (probably brooding and selfing) of tbat snail and tbe genus Tristania (now Balea; Preece & Gittenberger, 2003) colonised -probably transported by birds (Gittenberger et al, 2006) -islands in tbe Tristan da CunbaGougb group in tbe Soutb Atlantic (islands very remote from tbe natural, Palaearctic range of Clausiliidae).…”