December 20, 2017

Some clownfish lack personality, scientists find

Researchers measured behavioural traits of boldness, aggression and sociability in two subtropical species

A study analysing personality traits among individuals of two species of clownfish (also known as anemonefish) found that one species lacked personality.

Researchers studied the behaviour of two species of subtropical clownfish, Amphiprion mccullochi, endemic to Lord Howe Island, and Amphiprion latezonatus, which is found in subtropical eastern Australia, including at North Solitary Island.

Most species of anemonefish (including Amphiprion ocellaris, made famous by the movie Finding Nemo) live in tropical waters and in previous laboratory studies have been shown to exhibit personality traits. The scientists wanted to see whether their southern cousins showed similar behavioural traits.

To determine personality, biologists look for consistency in an individual’s behaviour (for example in their levels of boldness, aggression and sociability) and variation within a population in the levels of those traits. If an individual is inconsistent in its behaviour, or if all the individuals in a population display similar levels of those personality traits, then they can be said to lack personality.

While the anemonefish from Lord Howe Island, which live in a shallow, sheltered lagoon, were found to have distinct personalities, those from the deeper, more exposed waters at North Solitary Island lacked personality.

The paper’s lead author, marine biologist Dr Marian Wong from the University of Wollongong’s Centre for Sustainable Ecosystems Solutions, said there wasn’t enough variation between the A. latezonatus at North Solitary Island anemonefish to say the species exhibits personality traits.

“To say that a species exhibits personality traits we need a combination of within-individual consistency and between-individual variation. With A. latezonatus, the species we found that doesn't exhibit strong personality traits, there wasn't much between-individual variation; individuals were quite consistent but they were all on the same level of boldness and shyness,” Dr Wong said.

Dr Marian Wong from UOW's Centre for Sustainable Ecosystems Solutions says personality traits have a big impact on an individual's evolutionary fitness.

Personality is believed to contribute to an individual’s and a species’ resilience and ability to adapt to environmental change. Bolder and more aggressive individuals are likely to get greater access to food and are more likely to reproduce, however, they are also more likely to get eaten by a predator than are more timid individuals.

“Personality traits have a big impact on our overall fitness as individuals – how well we survive, whether we reproduce, and whether or not we can find food – and it's the same for animals. Ultimately, all behaviour contributes to your ability to survive and reproduce,” Dr Wong said.

“It could also affect how well a species responds to future environmental challenges, including climate change.

“As this paper suggests, there are some species that don't appear to show personalities, which surprised us. A lot of other studies, not just of fish but birds and mammals as well, are reporting that individual animals do have personality traits, so it really intrigued us as to why one of these species didn't.

“It may be something to do with their environment, which is a lot more variable than the environment in which the other species lives. Perhaps when the environment is so variable there’s no advantage in having individuals that vary in their behaviour, they may need to be at similar levels to cope with the environmental fluctuations.”

The team, which included Dr Anna Scott and students from Southern Cross University, plus volunteer scuba divers, set up underwater cameras to observe the fish in their natural habitat. The video was then analysed to quantify how consistent individuals were in their behaviours.

“One of the key behaviours we looked at was how individuals measured on the boldness-shyness continuum. Because anemonefish rely so heavily on the protection of their anemone, what we quantified for a fish being bold was the amount of time spent away from the anemone; how much time they’re up in the water column, and how much time they’re hunkered down in the tentacles, safe from predators.

“The second was how aggressive they are to other individuals of the same species, so the number of times that they would bite or chase or show an aggressive posture towards another fish in that group. “The third was sociability; the amount of time an individual followed another individual or met up with another individual.”

“Some anemonefish lack personality: a comparative assessment of behavioural variation and repeatability in relation to environmental and social factors”, is published in Coral Reefs.

The research was funded by the Sea World Research and Rescue Foundation, the Australian Geographic Society, and was a collaboration between Southern Cross University’s Marine Ecology Research Centre and the Centre for Sustainable Ecosystems Solutions at the University of Wollongong.

Researchers found that Amphiprion latezonatus (left) lacked personality, while Amphiprion mccullochi (centre and right) did have personalities.