The evolution of sociality in a coral reef associated fish
Have you ever wondered why some fish school together while others seem perfectly happy living a solitary existence? No? Well what about birds? Why do Corellas, for example, form huge flocks while eagles prefer to fly solo? Mammals (including ourselves), insects, reptiles. I’m sure you can think of hundreds of examples of species you have seen forming groups. I am interested in why animals form these groups (I wonder if plants do too….). Particularly coral gobies.
Why coral gobies? Wait. What is a coral goby?
Coral gobies are fishes of the genus Gobiodon and Paragobiodon (and a couple of others which I’m ignoring for the time being). They are small fish, the largest species (G. citrinus) grows to a whopping 6.6 cm. Most species grow to around the 3 cm range. They live within the branches of Acroporid corals and eat algae which….
Acroporid. Corals of the genus Acropora
Not these ones….
No that’s a clam…
Branching corals. So the coral gobies live within the branches of these Acroporid corals and eat the algae which tries to invade the coral. In turn the coral structure provides the gobies with protection from predators. Isn’t that nice 🙂
So why coral gobies?
Well because they’re an excellent study species. They are everywhere! Once you start looking for them, they start appearing everywhere (even in your dreams!). They are highly site attached which makes them relatively easy to capture and easy to find again if we want to observe a particular group on multiple occasions. They are also very species diverse, which means that there are lots of species to look at. During my first round of field work we found 13 different species of Gobiodon and 3 species of Paragobiodon at Lizard Island. These species also display a variety of social structures from strictly pair forming species to groups of 10 or more individuals. This variety allows me to investigate whether pair forming species differ in some ecological, life history or social factor from group forming species.
Well, revealing the factors, whether they be ecological, life history, social or a combination, that led to the evolution of sociality in these fish will help us to understand sociality in other organisms. The framework we are using to study sociality is called “Cooperative Breeding Theory”.
Ok, let’s look at the world from the point of view of our genes. Wouldn’t the best way to ensure that our genetic material survives through time be to start reproducing as soon as possible and as many times as possible (i.e. getting us much of our genetic material out there as possible)? In a perfect world, this may very well be the best strategy, but it is not what we observe in the real world. I bet you can think of 3 animals right now, off the top of your head, which form groups. Now, let’s look a little closer at those groups. Often the group will contain some dominant members and some subordinate members. Often the subordinate members contain mature individuals who have delayed pursuing their own breeding opportunities in order to remain within a group and help with raising the offspring of the dominant breeders. We call this cooperative breeding.
Ok, got it. So back to the point of this research.
So, if our genes just want to keep spawning copies of themselves all over the place, why would an individual make the decision to delay or completely forgo their own breeding opportunities to remain within a group? While a lot of excellent research has been carried out on terrestrial organisms, a general explanation for the reasons that non-breeders choose to forego their own reproductive opportunities and remain within a group is still lacking. One hindrance to the resolution of this problem is that there have been relatively few studies examining social group living in animals besides birds, mammals and insects. So by studying Coral Gobies, I hope to build on this knowledge base and bring us a step closer to understanding how this behaviour has evolved.
Understanding the role that ecological, life history and social factors have played in the evolution of sociality is valuable as it may provide insights into how animal societies will react to varying environmental conditions in the future. Interesting huh?
Can we go to the beach now?
If you’d like to learn more about what this research is about, fill out the form below and I’d be happy to discuss in more/less detail.