Acquisition of Ca2+ and HCO3 −/CO3 2− for shell formation in embryos of the common pond snail Lymnaea stagnalis

Abstract

Embryos of the freshwater common pond snail Lymnaea stagnalis develop to hatch within 10 days under control conditions (22°C, Miami-Dade tap water) and this development is impaired by removal of ambient calcium. In contrast, embryos did not exhibit dependence upon an ambient HCO 3 -/CO 3 2-source, developing and hatching in HCO 3 -/CO 3 2--free water at rates comparable to controls. Post-metamorphic, shell-laying embryos exhibited a significant saturation-type calcium uptake as a function of increasing ambient calcium concentration. However, changes in ambient bicarbonate concentration did not influence calcium or apparent titratable alkalinity uptake. There was a distinct shift from no significant flux in premetamorphic embryos to net uptake of calcium in postmetamorphic stages as indicated by an increased uptake from the micro-environment surrounding the egg mass and increased net uptake in 24-h, whole egg mass flux measurements. Furthermore, HCO 3 -/CO 3 2-acquisition as measured by titratable alkalinity flux is at least partially attributable to an endogenous carbonate source that is associated with acid extrusion. Thus, calcium requirements for embryonic shell formation are met via uptake but HCO 3 -/ CO 3 2-, which is also necessary for shell formation is acquired in part from endogenous sources with no detectable correlation to ambient HCO 3 -/CO 3 2-availability.

Characterization of mechanisms for Ca2+ and HCO3–/CO32– acquisition for shell formation in embryos of the freshwater common pond snail Lymnaea stagnalis

“…We found that the onset of apparent net titratable alkalinity uptake/acid extrusion was concurrent with metamorphosis, the onset of Ca 2+ uptake and shell formation. Also, Ca 2+ uptake was significantly greater and apparent net titratable alkalinity uptake/acid extrusion was significantly reduced, but not inhibited, under HCO 3 --free conditions (Ebanks et al, 2010). These findings motivated the series of experiments to determine the possible sources of carbonate for shell formation that are described in this paper.…”

“…In the absence of ambient total calcium (Ca), they tend to develop at a retarded rate relative to controls but grow and hatch at least as well as controls when reared in carbonate-free water (Ebanks et al, 2010). Although they are provided with maternal stores of calcium and carbonate in the perivitelline fluid and within the gelatinous matrix (tunica interna) of the egg mass, they begin to rely on Ca 2+ from the surrounding medium as maternal stores in the perivitelline fluid and tunica capsulis become depleted, at approximately day5 post-oviposition (Ebanks et al, 2010). At this point in embryonic development, embryos increase oxygen consumption and total CO 2 retention (Baldwin, 1935).…”

“…At this point in embryonic development, embryos increase oxygen consumption and total CO 2 retention (Baldwin, 1935). Metamorphosis and shell formation have been observed for Lymnaea palustris (Morrill, 1982), L. stagnalis (Ebanks et al, 2010) and another freshwater pulmonate snail Biomphalaria glabrata (Bielefeld and Becker, 1991;Marxen et al, 2003). The post-metamorphic Ca 2+ requirements seem to be met entirely by active uptake, but the carbonate requirements can apparently be accommodated through both uptake and endogenous sources or by endogenous sources exclusively (Ebanks et al, 2010).…”

“…Considering that carbonic anhydrase-mediated CO 2 hydration produces HCO 3 been studied until recently (Ebanks et al, 2010). Also, the possible role of the proton, resulting from CO 2 hydration and CaCO 3 formation, in the acquisition of the essential shell-forming ions by these embryos remains to be evaluated.…”

Social snails: the effect of social isolation on cognition is dependent on environmental context

“…Performing primarily as a male during copulation (De Boer et al, 1997;Koene and Ter Maat, 2007) and reducing egg-laying behaviour (Koene and Ter Maat, 2004) following isolation for 8days will potentially significantly reduce the calcium requirements of an individual snail. Although there is evidence that embryonic snails require external calcium availability for normal growth and development, they are still able to undergo partial development in the absence of environmental calcium (Ebanks et al, 2010), which, alongside [Ca 2+ ] ions being found to be at a greater concentration in recently laid egg capsules compared with ambient conditions (Taylor, 1973), indicates maternal provision of calcium to embryos. Therefore, switching energy investment primarily towards male reproductive output when isolated (De Boer et al, 1997;Koene and Ter Maat, 2007) may significantly reduce calcium requirements of L. stagnalis, thereby reducing the stress associated with being held in low calcium conditions.…”