Developmental arrest in vent worm embryos

Temperature is a key factor in controlling the distribution of marine organisms and is particularly important at hydrothermal vents, where steep thermal gradients are present over a scale of centimetres. The thermophilic worm Alvinella pompejana, which is found at the vents of the East Pacific Rise (2,500-m depth), has an unusually broad thermotolerance (20-28 degree C) as an adult, but we show here that the temperature range required by the developing embryo is very different from that tolerated by adults. Our results indicate that early embryos may disperse through cold abyssal water in a state of developmental arrest, completing their development only when they encounter water that is warm enough for their growth and survival. We obtained early embryos of A. pompejana by in vitro fertilization, and reared them at temperatures ranging from 2 degree C to 20 degree C under atmospheric and deep-sea pressures. We monitored mortality (diagnosed by the breakdown of the plasma membrane or by production of irregular cytoplasmic blebs) and zygotic cleavage during early development.