Wei, S.L. and R.E. Young. 1989. Marine Biology 103: 541-546.
The squid Euprymna scolopes can bioluminesce due to symbiotic, luminous bacteria Vibrio fischeri. How is this relationship initiated? Are bacteria transferred to the egg during embryonic development or do E. scolopes obtain the bacteria after hatching?
E. scolopes contain V. fischeri in a pair of bilobed organs called light organs. These organs have an opening to the external environment. Bioluminescence occurs when light organs are fully developed an bacteria initiate luminescence.
Experiments included the monitoring of bioluminescence, using a photometer, of eggs and juveniles from three hatching conditions: 1) unfiltered water without adults, which were removed at two different intervals, 2) unfiltered water with adults, and 3) filtered water without adults. Unfiltered water had high concentrations of bacteria; filtered water had none. Bioluminescence was not detected in eggs, newly hatched juveniles or individuals raised in filtered, adultless water. It was also not detected in squids from water in which adults had been removed ten days before hatching, but it was detected when adults were removed only two days prior. Bioluminescence was detected, usually ten to twenty hours after hatching, in cephalopods in water containing adults.
Since bioluminescence was only detected in squid hatched in water containing V. fischeri, this experiment demonstrated that inoculation of bacteria after hatching is required for development of bioluminescence, although the selection mechanism is unknown. Also, the water containing adults had a higher concentration of bacteria suggesting that adults release V. fischeri and these bacteria are obtained by juveniles. Bacteria are not transferred to the eggs.
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