NISHIGUCHI, M.K.*: Reverse physiological patterns between sepiolid squids and their luminous bacterial symbionts: Host specificity examined from down under.

Mutualistic associations between bacteria and their eukaryotic hosts have a variety of mechanisms that determine patterns of host specificity among symbionts during infection and colonization. Although most symbiotic bacteria are only capable of infecting their particular host partner, closely related strains with similar host species have been shown to colonize and persist in other host species. Sepiolid squids (Cephalopoda: Family Sepiolidae) and their bioluminescent bacteria (Genus Vibrio) are one example where symbiotic bacterial strains are capable of infecting similar host species. These different symbiotic strains have the same infection and colonization behavior as do native strains, but when placed in direct competition with one another, the native strain is always dominant. This study examined how symbiotically competent Vibrio fischeri strains isolated from Australian Euprymna tasmanica display dominance for native squid hosts over other equally competent V. fischeri strains isolated from other sepiolid squids. Infection by bacterial symbionts from the monocentrid fish Cleidopus gloriamaris and the loliginid squid Photololigo noctiluca produced a lesser degree of infection, despite their presence in the same geographical location. Since previous studies have shown that a similar phenomenon occurs in the sister species E. scolopes (Hawaii), this comparision of both host species exemplifies the importance of host-symbiont recognition in habitats where symbiont composition is dictated by a specific host and not the environment.