Reproductive Tactics in Relation to Life‐Cycle Bioenergetics in Three Naturla populations of the Freshwater Snail, Leptoxis Carinata

Abstract

Regular sampling of three populations of the riverine prosobranch snail, Leptoxis carinata, revealed it to be a slow—growing, semelparous biennial. Copulation and egg laying are restricted to 23—mo—old individuals. Growth is restricted to two 3—mo periods during their 25—mo life cycle. Mean numerical fecundity at the three sites (170—330 eggs per female life—span) is inversely correlated with adult density. Experimental evidence indicates that differences in adult density (over moderate levels) have no direct effect on numerical fecundity whereas increasing egg density has a marked negative effect. Egg C:N ratio decline (less nonprotein stores) as numerical fecundity increases. Survivorship of eggs and young is very low but improves after 8 mo of age. Female reproductive effort (reproductive biomass as a percentage of growth) is relatively low in Leptoxis. The mean reproductive effort values range from 12 to 19% for carbon and 6 to 11% for nitrogen. The life—cycle traits of Leptoxis (semelparity after long prereproductive life; and low reproductive effort combined with relatively low numerical fecundity) reflect a compromise strategy imposed by severe environmental periodicities and concomitant physiological constraints (including low growth rates).