A new study indicates that parental environment can influence adaptation to projected increases in sea level temperatures, not only by altering the fitness of offspring but also by altering the genetic variance available to increase fitness.
Evatt Chirgwin, along with his PhD supervisors Dustin Marshall, Carla Sgro and Keyne Monro, were interested in how, in the face of global change, populations can maintain or recover fitness. Evatt used a small, marine tubeworm Galeolaria caespitosa to examine how parental exposure to projected ocean warming affects adaptive potential for survival during the most vulnerable early life stage.
Individuals faced with environmental stress can respond through ‘plastic’ changes to morphology, physiology and/or behaviour and these changes can persist in their offspring. But in order for populations to persist in the longer term, they will often require adaptive evolution, which rests on the availability of adequate genetic variation.
Galeolaria is an external fertiliser which allowed Evatt to manipulate fertilisation across different males and females as well as exposing parents and embryos to different temperatures. Evatt took sperm from each male parent and crossed it with eggs from multiple females and vice versa; a design that allowed him to estimate genetic variance and therefore adaptive potential to ocean warming.
Embryos and larvae are the life stages most sensitive to stress in marine invertebrates, and are key to assessing vulnerability to ocean warming. Evatt measured survival of 20,000 Galeolaria offspring as a measure of fitness where parents were exposed to two temperatures prior to spawning and offspring were then reared in the same two temperatures.
The team found that mean offspring survival was higher when offspring were reared at the same temperatures as their parents, but also that parental exposure to warming altered genetic variance. This means that parental environments may have broader ranging effects on adaptive capacity to global warming than is currently appreciated.
While effects were subtle, even this modest buffering may help natural populations to persist under rising ocean temperatures. This study is an important step towards understanding how plasticity and adaptation jointly shape population dynamics and extinction risks under global change.