Environmental Enrichment Accelerates the Ontogeny of Cryptic Behavior in Pharaoh Cuttlefish (Sepia pharaonis)

We examined effect of environmental enrichment on cuttlefish, the most neutrally advanced invertebrate, to compare species variation of genetic and environmental influences. Cuttlefish were reared from seven to 117 days in one of three environments, namely, "poor" (artificial bottom without objects), "standard" (sandy bottom), and "enriched" (sandy bottom with objects). In Experiment 1, we explored whether enrichment affects the exhibition of crypsis in the cuttlefish. The cuttlefish in the standard and enriched environments spent most of their time at the bottom, exhibiting the mottled or disruptive pattern starting at 27 days of age. On the contrary, those in the poor environment exhibited uniform pattern starting at 87 days of age. Additionally, they repeatedly attempted to dig from 27 to 87 days of age, and moved around by hovering from 77 to 117 days of age. In Experiment 2, we exposed the cuttlefish to six novel substrates every other month after 53 days of age to verify whether enrichment actually affected the maturation of cryptic ability. Cuttlefish from the poor environment tended not to dig into white sandy bottom at 53-55 days of age. Additionally, they did not clearly exhibit appropriate body patterns in response to the six substrates compared to those from the other two environments at 81-83 days of age. However, at 113-115 days of age, most cuttlefish from the three environments exhibited similar cryptic behaviors in response to novel substrates. We conclude that physical enrichment promotes crypsis and accelerates the maturation of this ability in cuttlefish.