Embryonic motility and hatching success of Ambystoma maculatum are influenced by a symbiotic alga

To augment O2 supply through the jelly mass and egg capsule, embryonic yellow-spotted salamanders ( Ambystoma maculatum (Shaw, 1802)) take advantage of a unicellular alga, Oophila ambystomatis . Convective currents from surface cilia, however, may also enhance O2 transport, whereas muscular contractions could either enhance delivery or contribute to O2 consumption. Embryonic motion is, therefore, potentially vital to salamander development. We examined embryonic motility across multiple developmental stages, survivorship, and hatching timing in response to different algal levels by rearing salamander egg masses under three different diel light cycles: 24 h dark, 12 h light, and 24 h light per day. Embryos raised in continuous light hatched synchronously and at slightly earlier developmental stages than embryos raised in the dark or in 12 h light per day. We removed eggs at multiple stages to examine embryonic rotation and muscular contraction rates under 180 min periods of both light and dark. Rotational movements occurred more frequently in alga-free than in algae-inhabited eggs, and more frequently in algae-inhabited eggs in the dark than in light. At later developmental stages, muscular contractions were more frequent in embryos from algae-inhabited egg masses in light than those in the dark; thus embryos with less O2 reduced muscular activity, thereby reducing energy consumption when O2 availability was compromised.