Detection of cross-mating between two generations of the cuttlefish Sepia officinalis by sperm reservoir analysis

Abstract

This study concerns the reproductive cycle of Sepia officinalis living in southern Brittany and about mating between the two-year classes of breeders living there. The reproductive cycle is partly similar to that proposed by Mesnil (1977). The less important Sepia officinalis group, which realised its cycle in one year, come, in all likelihood, from the early broods of the large group II breeder (GIIB) females. The group I breeder (GIB) females, which arrive later in the breeding area, would generate the long life cycle individuals. But, considering that GIB females are in minority and less fecund than larger GIIB females, it is not possible that they generate, on their own, all the long life cycle recruits. Obviously, part of GIIB offspring reproduce also during the second year. The year class of some males can be determined using some of the sperm reservoir (SR) found in the buccal pouch of the wild females. We estimate that under a size of 2.6 mm, the SR found in the buccal pouch of a female, would be deposited by GIB male and above 4.7 mm it would be deposited by GIIB. In this way, cross-mating between GIB males and GlIB females has been detected during the breeding season. The opposite situation (i.e. GIIB males with GIB females) is rather rare. In conclusion, the two year classes of breeding cuttlefish living in southern Brittany are not reproductively separated. There is gene flow between GIB and GIIB, due to mating between GIB males and GIIB females and also between GIB offspring and part of GlIB offspring going through a long life cycle.