Kauffman, M.R., Y. Ikeda, C.Patton, G. Van Dykhuizen and D. Epple. 1998. Bacterial symbionts colonize the accessory nidamental gland of the squid Loligo opalescens via horizontal transmission. Biological Bulletin 194: 36-43.
This study sought to determine the source and method of bacterial colonization of the accessory nidamental gland (AN) in Loligo. Kauffman et al. proposed two ways in which bacteria could migrate into the accessory gland: vertical and horizontal migration. The vertical migration hypothesis suggests that the bacteria migrate from the egg sheath surrounding the embryo upon emergence of the juvenile from the egg case. Horizontal migration on the other hand, proposes that bacteria colonize the AN gland via the water column post-partum.
In the study, several Loligo were raised under laboratory conditions and the AN gland was fixed and sectioned at various stages of development. It was found that the AN gland is undifferentiated at birth and the first emergence of a single-layered epithelium was 87 days after birth. However, at the 87 day stage, no bacteria were present in the AN gland suggesting that bacterial colonization of the AN gland must occur via the water column by Kauffman's horizontal transmission theory. In addition a multi-layered complex gland was observed by the 129-day stage. At this stage, some protozoa and a very small amount of bacteria were detected.
Although unlikely, Kauffman also points out that if vertical transmission did occur, bacteria upon parturition may be stored in a reserve gland outside the AN gland until they are required to invade the AN gland upon sexual maturity.
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