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Balancing act

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Dr Jenni Donelson, Chancellor’s Post Doctoral Fellow in the School of Life Sciences at the University of Technology Sydney, explores the effects of climate change on coral reef fish. Dr Donelson has been working with coral reef fish for a few years, with an interest in understanding their capacity to cope with climate change and global warming over multiple years and multiple generations. The aquarium facilities at UTS are a good place to conduct tests on fish under future ocean conditions.

Parents can make many types of non-genetic contributions to their offspring, including the amount and type of provisioning, which can affect traits like growth rates. Parental effects are interesting to look at in relation to climate change to see whether offspring perform better or worse in different climate conditions depending on their parents’ environment. The research involves well-structured experiments in the aquarium using different parental conditions crossed with different offspring conditions, teasing out the contributions of the parents. Like birds, fish alter how much nutritional provisions are given to their offspring. Some eggs are larger than others and some may be programmed for faster growth and some may be programmed to reach maximum sizes faster.


Like many animals the gender of offspring is not pre-determined at birth in fish, something which is also the case for turtles and lizards. Some reef fish will transition between genders at different life or size stages, while for others their gender is affected by the temperatures they develop in during the first few weeks of life. For fish, warmer environments means that more juveniles will become male but parents can change this gender ratio. When the juveniles maintained in warmer conditions become adults and produce their own juveniles, they produce an appropriate gender ratio again, overcoming the effects of temperature in a kind of parental mediation process of gender balance. This process is likely to be occurring through either epigenetic mechanisms or as a direct result of providing juveniles with more female hormones.

In other work, fish such as cardinalfish, damselfish and tropical wrasses are brought back from the reef and developed in the aquarium under different water temperatures. The various groups can then be tested on things like swimming ability, escape performance along with physiological traits like aerobic capacity.
Juveniles that are developed under warmer conditions do far better when tested against those that are not, showing that they have acclimatised to those warmer conditions. Oxygen ability is important as warmer waters carry less oxygen, meaning there is more of a cost in extracting it. When the juveniles become adults, they will breed a new generation which can then be compared as to how their parents performed under varying conditions. For now, some traits like oxygen transport physiology seem to quickly respond to temperature changes whereas others, like reproduction, struggle to achieve the same level of flexibility.

The research is also looking at how many eggs are produced, the size of those eggs and what the offspring look like when they hatch. Generally, as temperatures get warmer, breeding individuals produce less eggs and smaller eggs. Future generations, however, improve on the number and size of those eggs. This is the case when those temperature changes are small. Fish struggle when the temperature changes are larger, which is what is predicted by the end of this century.
Just like their gender, it seems the future of reef fish is a balancing act.


Dr Jennifer Donelson was interviewed by Ruby Vincent for A Question of Balance. Images from Dr Donelson. Summary text by Victor Barry March 2015

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