Amphioxus (Branchiostoma floridae) Spawning and Embryo Collection

INTRODUCTION

This protocol describes how to obtain and collect embryos from the amphioxus Branchiostoma floridae. Currently, it is only possible to obtain fertilizable gametes from this species on the days in summer when ripe animals would normally spawn in the field once about every 2 wk. Sexes are separate, and in the natural environment, mature oocytes undergo meiotic maturation and arrest at the second meiotic metaphase in the early afternoon, while sperm gain the ability to become motile upon exposure to seawater. In the evening, animals with mature gametes emerge from the sand to spawn ~30 min after sunset, that is, ~9:00 p.m. Animals collected in the afternoon of the day of spawning can be brought into the laboratory and prevented from spawning by the normal room light in the laboratory, allowing the investigator to obtain freshly spawned eggs and sperm throughout the night either by placing adults in the dark or by applying a mild electric shock (50 V DC). Unfortunately, toward dawn of the next day, the quality of gametes begins to drop, and the animals stop spawning. Therefore, investigators need to work during the night to fertilize eggs and perform experiments on early embryos.