Early in his academic work, Hurd's study organism was birds where he began working on mathematical models, which he eventually parlayed into doctoral studies at Stockholm University in Sweden. It was there he was introduced to cichlids. He went on to do his post-doc work at the University of Texas at Austin where he worked with lizards and also did some experiments with acoustic signaling during fights between firemouth cichlids (Thorichthys meeki).
I reached out to Dr. Hurd to inquire about his interest in doing an interview for the blog. He enthusiastically agreed and here we are.
The cichlid stage: Please tell the readers a bit about your research using cichlids.
I'm interested in the biological basis of personality - why are there consistent behavioural differences between members of the same species. Originally, I was specifically focused on differences in aggressiveness - what are the costs and benefits of being more or less aggressive - but have become interested in the more general question of why different individuals play different strategies in life. Currently in my lab we're doing some work on how stresses during early development shape adult personality using convict cichlids (Amatitlania nigrofasciata), and then with Kribensis cichlids (Pelvicachromis pulcher) we're examining how environmental sex determination might relate to variation in brain and behaviour. We're also examining how some of the gene regulation behind that may be involved in variation in human brain and behaviour also.
TCS: What is so intriguing to you about cichlids to make them a study animal?
Well, the really amazing thing about cichlids is how rich of a social life comes from such a small nervous system. Compared to the rodents favoured by many neuroscientists, so many species of cichlids show much more involved parental care, and a far larger repertoire of social behaviours. And then there are the stand-out cases, for example, the socially breeding cichlids of Lake Tanganyika. Not only do these animals pair up and parent, but they also have extended family structures of unrelated helpers at the nest. Biologists might awe at the complexity of social life in a lion pride, but all the same stuff is going on among really small fish. This blows me away!
This evolutionary transition from pair breeding to breeding within a society, complete with multiple social relationships, has happened many times over evolutionary time. The brain has to manage classes of mates, versus friends and allies, and others that are not friends. The brain has to change the way that it works, from a solitary life to life in a society, and not go extinct while making the transition. The degree of similarity between humans’ brains and fish brains, at least in this part of the social behaviour network, is very very strong. These are not the fancy cortical structures that we associate with abstract thought. These are the evolutionarily conserved brain areas where our motivating emotions seem to come from. The emotions Darwin argued so convincingly that we share with other animals, love and anger, urge us to protect our offspring and our friends. For all the differences between human and fish society, the same bits of brain are working with basically the same chemicals to produce the same emotions.
TCS: What’s your favorite species to work with and why?
My favourite research species is the Kribensis, because of the different male morphs. The yellow males tend toward monogamous breeding, while the reds to polygynous breeding. The blue and green males also seem to have their own quirks. I've also kept many of the Tanganyikan shell dwellers and I'm super-fond of them. I havn't done research with them but I have a few projects that I think would be perfect to do with Lamprolus ocellatus or meleagris.
TCS: Cichlids are known for possessing individual personalities, which sets them apart from most community fish (e.g., tetras, barbs). For those hobbyists who breed cichlids, are there environmental factors that can be manipulated to influence personality development of fry?
I think so. I suspect that manipulating temperature and pH that Kribensis fry are exposed to in their first month of life, or giving convict cichlids cues to lead them to believe that predators are either more or less prevalent, does shape their personality a bit. On the other hand though, these changes are subtle enough that you would need to measure and compare the behaviour of many individuals to see the effect, on average, between the treatments. There would still be a lot of personality variation within each group, and the range of individual personalities would overlap considerably between the two groups. However, I don't think there's really a way to totally change a fish's personality completely dramatically, so that it is far outside the typical range for its species.
TCS: What has your research shown are some of the most influential environmental factors affecting social behavior, in general?
Well, we're looking at the effects of water temperature and pH in the first month of life. This influences what sex kribensis become when they mature. We're also exposing the convicts to environmental cues (damage pheromone) suggesting that the presence of predators is very high over that same early life period for them. Another important environmental variable is biotic, the social environment, such as where a fish is in the size heirarchy of its brothers and sisters. That is another one we come back to, whether being chased around is traumatizing - whether stunting your growth to avoid being a threat to bigger siblings has lasting personality consequences or whether being the biggest fish in the tank for the first few months of life program a bold personality for the rest of life.
TCS: With respect to Kribensis and convict cichlids, if there are a couple of main strategies for reducing con-specific aggression with these species in aquaria, what would they be?
Density is key. We either have them in a situation where we expect them to breed or we have them in stock tanks crowded enough to swamp all their territorial ambitions. Most of our tanks are at the sort of densities you would see in a well-run store, rather than a hobbyist's tank. If the tank has a defendable territory, there's going to be sex and violence, you know, biology happens.
TCS: In summary, what are some of the most surprising behavioral findings that you have discovered (in any cichlid species)?
I think the most surprising thing was the very first work I did on cichlids, looking at threat display use in Nannacara anomala. There's some colour pattern changes they go through during territorial interactions that function to facilitate figuring out who would win a physical fight without actually having one, sometimes. If a fight gets really nastily escalated, it will be won by the bigger fish, but many of the less escalated behaviours, such as tail beating, seem to serve the function of giving information about the size of a fish to its opponent. In tail beating, the fish don't actually touch each other. They just shoot a jet of water at the other fish. If that's going to convince the other fish that you are bigger, then it is of benefit to you that the other fish expects you to do this, so they can be well placed and paying attention. I think one of the colour patterns they use, the horizontal line, does exactly that. The idea that some "threats" are actually more like cooperative behaviours, which settle a fight without it turning into a big dangerous physical fight, was really kind of perspective shifting.
TCS: What do you consider the most effective and humane methods for euthanizing a sick or dying fish?
Well, I think the key to humane euthanasia is to stop the brain working as quickly as possible. The ethics authorities require anesthetizing fish before decapitation, so that's what we do. I can imagine slightly more humane techniques, ones that would be faster, but we follow the rules. Anesthetic dose, then decapitation.
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