Sex differences in reproductive investment: maternal care reduces escape response capacity in the whelk Buccinum undatum

Abstract

We evaluated the effect of reproductive state and biochemical status of male and female whelks Buccinum undatum on their escape responses (foot contortions) when touched by their major predator, the sea star Leptasterias polaris. Gonad growth in males was not associated with a decrease in their general energetic and metabolic capacity, nor in their capacity for escape responses, but did reduce the rate of foot contortions during recuperation from exhaustive exercise. Similarly, the energetic status of females was good when the ovary was mature, suggesting that oogenesis did not require somatic reserves. On the other hand, the energetic status and muscle metabolic capacities of females dropped with egg laying. This decrease was associated with a reduced capacity for escape responses. Thus, egg laying resulted in (1) major drops in the carbohydrate and protein contents of the foot, (2) decreased activities of several glycolytic enzymes (LDH, ADH and APK) in the foot muscle, (3) a sharp drop in the digestive gland index, (4) a decrease in the number of foot contortions and (5) a decreased ability to recover from exhaustive escape exercise. Reproductive costs are much greater for females than males (as females must produce protective egg capsules, search for egg-laying sites and lay the capsules). Females have greater escape capacities than males, except directly after egg laying when their energetic reserves are virtually depleted. The greater capacity of females for escape responses may attenuate the risks associated with their greater boldness in stealing food from their predator L. polaris, particularly prior to egg laying.