Sea Squirt Sex

I f you spend a minute observing behaviour at your next party, it is easy to grasp the basics of sexual selection theory females are choosy and males compete. But how do you choose or compete for the best partner when you are permanently stuck to a rock? Most marine organisms reproduce by releasing their eggs and sperm into the ocean. This mode of reproduction is called broadcast spawning. You've probably seen an example of broadcast spawning on nature documentaries: the coral spawning on the Great Barrier Reef every October/November is one of the best-known examples. Because fertilisation in broadcast spawners occurs externally, competition among males and mate choice by females occurs at the gamete level. Therefore we decided to test whether broadcast spawners change their gametes to suit local conditions. Before we can answer this question we must understand a little more about what types of problems a broadcast spawner faces when trying to mate. First let us examine mothers. Assuming there is a fixed energy budget for reproduction, mothers can either invest a lot of energy in a few large eggs or less energy in many small eggs. The advantage of producing small eggs is that you can make lots of them. However, the advantage of producing large eggs is that these offspring are more likely to survive, particularly in poor conditions. Therefore, the first reproductive challenge facing any mother is what size offspring to make.