Assume we could see twenty generations of whales or sharks reacting to climate change, tracking how they develop and how their biology changes as temperatures and CO2 levels increase. That might tell us a lot about how adaptable life in the seas is to a warmer planet. However, it would take hundreds of years, which is inconvenient for scientists and politicians seeking to comprehend our warming planet now.
Consider the life of the copepod Acartia tonsa, a little and modest water organism on the bottom of the food chain. In around twenty days, it reproduces, develops, and generates a new generation. In roughly a year, twenty copepod generations pass.
A group of six scientists, led by University of Vermont biologist Melissa Pespeni and postdoctoral scientist Reid Brennan, did just that in a first-of-its-kind laboratory experiment in which they exposed thousands of copepods to the high temperatures and high carbon dioxide levels predicted for the future of the oceans. And sat back and observed as twenty generations passed. They then removed some of the copepods and returned them to the baseline settings — the temperature and CO2 levels that the first generation began in, which are similar to current ocean conditions. They then sat back and watched as three more generations passed.
The findings, published in the journal Nature Communications, “suggest that there is optimism, but also complexity in how life adapts to climate change,” according to Pespeni.
The cost of plasticity
Her optimism stems from the team’s finding that the copepods did not perish as a result of the climatic change. They, on the other hand, endured and even prospered. The researchers from UVM, the University of Connecticut, the GEOMAR Helmholtz Center for Ocean Research in Germany, and the University of Colorado, Boulder, observed numerous changes in the genes of copepods related to how they manage heat stress, grow their skeletons in more acidic waters, produce energy, and other cellular processes affected by climate change. This demonstrates that these species have the genetic make-up to adapt across twenty generations, evolving to preserve their fitness in a dramatically changing environment by using the variance seen in wild populations. The findings support the concept that copepods, a worldwide dispersed group of crustaceans consumed by many economically significant fish species, may be resistant to the unusually fast warming and acidification caused by human fossil-fuel consumption in the seas.
The intricacy stems from the team’s observation of what occurred to the copepods that were returned to baseline settings. “It’s definitely a warning,” Pespeni adds. These organisms exposed the unintended consequences of the previous twenty generations of adaptation. The flexibility that allowed copepods to adapt over twenty generations – what scientists term “phenotypic plasticity” – was diminished when they attempted to return to previously favorable surroundings. Copepods brought “home” were less healthy and formed smaller populations. They were able to re-evolve back to their ancestral circumstances after three generations, but they had lost the capacity to endure low food supplies and exhibited diminished tolerance to various new types of stress.
“Will copepods or other organisms be able to handle some other environmental stressor, some other change in the environment if they have to travel down this adaptation road — and invest part of their genetic variety to deal with climate change?” Pespeni is perplexed. Copepods are one of several species projected to be adaptable to fast climate change, according to a new research funded by the National Science Foundation.
“However, we must be cautious of overly simple models that look at just one variable to predict how well species will do and which will survive in the future,” said Reid Brennan, who completed this study in Melissa Pespeni’s lab at the University of Vermont and is now at the GEOMAR Helmholtz Centre for Ocean Research in Kiel, Germany. And the scientists’ latest research of copepods hints to a greater fact about the complex economics of evolution: there may be unintended consequences to rapidly developing in a suddenly heated environment.