Individual Variation Determines A Species’ Fate in Changing Times

30 November 2019 - By: Jonathan Smith

Individual Variation Determines A Species’ Fate in Changing Times

It goes without saying that every person is unique. They can be tall or small, quiet or loud, and many other traits besides. For a long time in biology research, this wide variation in creatures of the same species was seen as little more than a nuisance that makes biological data ‘noisy’.

In the last twenty years or so, however, things have started to change. According to Dr Tommy Norin, ecological physiologist at the Technical University of Denmark, the study of variation between individuals has gained traction in biological and ecological research because “both natural and human-induced selection (e.g. fishing) will favour individuals with certain traits that are advantageous in a given environment or context. If the trait in question is heritable, this will lead to evolution.”

In his work, Tommy has focused on how good fish are at readjusting their metabolism in response to shifting environments. The adaptation of one's metabolism is a form of phenotypic plasticity -- an often crucial survival tool for organisms living in changeable environments.

One example of Tommy’s experiments was in the barramundi1 (Lates calcarifer), a tropical fish that is found in places where the environment fluctuates a lot, such as river estuaries. Since it is a cold-blooded animal, external temperatures are particularly important for determining the fish’s metabolism.

Tommy and his colleagues measured the oxygen consumption of the fish by holding the animals in special tubes with a flow of water going through them -- a technique called respirometry. He did this to work out what the metabolic rates of the fish were. He first calculated their standard metabolic rate -- the minimum metabolic rate needed to keep the fish alive -- and then chased them briefly to measure their maximum metabolic rate. By using these measures, he calculated how well they could cope with increasing demands on metabolism.

He discovered -- by briefly exposing the barramundi to low salinity, high temperatures or low oxygen at different time points -- that the metabolic rate of the individual fish in control conditions strongly influenced how their metabolism reacted to the different conditions.

“Individual barramundi with a relatively high metabolic rate are less affected by warming than their low-metabolic rate counterparts,” explained Tommy. This resistance to warming came at the cost of being more vulnerable to low oxygen than individual fish with low metabolic rates.

“Trade-offs like this are common in biology and are what maintains among-individual variation within animal populations, as different strategies work best in different environments,” Tommy said.

As well as the barramundi, Tommy is lately studying a species that could have importance in the aquaculture industry. The cleaning fish Tautogolabrus adspersus eats sea lice and could help to control these pests in salmon farms. In addition, Tommy is studying individual variation in salinity tolerance of round goby, which is a potentially invasive species in the salty North Sea.

The study of individual variations in metabolism in aquatic life has other real-world implications too. Specifically, it will be instrumental in understanding the effects of global climate change on these animals.

“The benefits associated with a high degree of phenotypic plasticity will be context-dependent, as climate warming is likely to also cause cascading effects on food availability,” he said.

The link between individual variation and the population in evolution is a very complex one. Therefore, a lot more research is needed to improve our ecological predictions and potential countermeasures to blunt the effects of climate change on aquatic animals. In particular, Tommy believes that this will require a wide range of techniques and approaches.

“I think it is my multifaceted and meticulous approach to research that has allowed me to continue being successful in my field,” he noted.

Tommy will feature his ongoing projects at the session ‘The physiology behind phenotypic plasticity in rapidly changing environments’ at the SEB Conference later this year.