The effect of temperature on the development of encapsulated embryos of Concholepas concholepas along a latitudinal cline

Abstract

Encapsulating species face more constraints than active brooders in adjusting oxygen supply to the needs of the embryos. Therefore, the packing of embryos in gelatinous egg masses or egg capsules is expected to be adjusted to the temperature and oxygen conditions that the embryos are likely to experience. We studied the patterns of embryo packing (number of embryos per unit area) of the gastropod, Concholepas concholepas, from 14 sites over an extended geographic area spanning 22° of latitude off the coast of Chile. A clear break in the patterns of embryo packing was found at approximately 29 to 30° S. Capsules collected at the sites located north of this break exhib- ited significantly fewer embryos per unit area than capsules from southern sites. Embryo packing is correlated with mean temperature shortly before egg deposition. A set of laboratory experiments were conducted to determine if the effects of temperature reside in females (incubating females col- lected in 2 different sites at a common temperature) or in embryos (incubating capsules at different temperatures). Laboratory experiments showed that temperature does not affect the number of embryos that successfully develop in the capsules within the tolerated range of temperatures, but does influence developmental success at temperatures that are extreme for the sites of the sample population. Our results suggest that packing and protection of embryos in marine invertebrates might be linked to the capacity to supply oxygen to the brood, which can have important conse- quences for the distribution of brooding and encapsulating species across temperature gradients.