Rhythm of Antarctic life
‘Clock genes’ that regulate the daily and seasonal internal rhythms of krill are the target of new research by Antarctic scientists seeking a better understanding of what makes these important crustaceans tick.
Australian Antarctic Division krill biologist, Dr So Kawaguchi, and molecular biologist, Dr Simon Jarman, are part of an international collaboration searching for genes that control how krill respond to changing day length and other environmental cues, such as sea ice extent and ocean temperature.
The study is based on decades of research on the circadian rhythms of the fruit fly (Drosophila) by collaborating scientists at the University of Padova in Italy.
‘There are about a dozen key genes in fruit flies that regulate their daily and seasonal biorhythms, and we’re trying to identify the equivalent genes in krill,’ Dr Jarman says.
‘Insects and crustaceans share similar systems but we’ll also be looking for other genes that interact with these clock genes or that are specific to krill. It’s likely that an organism like krill, which has evolved in the changeable Antarctic environment, will have extra genes that also contribute to regulating their biorhythms’
The research is expected to provide clues to how krill will fare in a changing environment. Krill have 11 larval developmental stages before they become juveniles and, finally, adults. These developmental stages need to be timed to make the most of the food (sea ice algae) that’s on offer.
‘When winter ends and there’s spring growth of algae, if the krill aren’t developing at the right time, then they could starve, or miss out on critical feeding opportunities as other organisms eat the algae before them,’ Dr Jarman says.
This could happen if a disconnect forms between changing day length (from complete darkness in winter to all-day sunlight in summer) and sea ice conditions that may be affected by a warming ocean and changing wind patterns.
‘If krill have evolved a physiology or behaviour that changes with day length rather than sea ice conditions, and changing sea ice conditions lead to earlier or later algal blooms, then there could be a desynchronisation of food availability and larval development, or adult breeding,’ Dr Jarman says.
The research team has formed the Helmholtz Virtual Institute for 'Polar Time', centred on the Alfred-Wegener Institute of Polar and Marine Research* in Germany and led by krill physiologist Dr Bettina Meyer.
During the recent Sea Ice Physics and Ecosystem eXperiment (SIPEX-II) Dr Meyer and her colleague Dr Ulrich Freier collected live larval and juvenile Antarctic krill for the Polar Time project. They will now look to see if, or how strongly, the clock genes are expressed in the cells of late-stage larval krill and juveniles, compared to adults.
‘From previous investigations we know that the clock gene machinery is active in adult krill, but it has not yet been observed in the larvae stages. We don’t know in which of the developmental stages the genes become active. So we need to collect krill at different life stages to identify when the transition occurs,’ Dr Meyer says.
‘With the animals collected on the SIPEX-II voyage we’ll also be able to compare clock gene expression in krill during spring – a time of year when the day length increases daily – to those we’ve already collected during autumn, summer and mid-winter.’
Gene expression will be assessed by measuring the amount of clock-gene-specific mRNA (messenger ribonucleic acid) in krill cells. This molecule is the direct result of genes (DNA) being switched on in response to various triggers. Immediately after capture on the SIPEX-II voyage the krill were prepared by Dr Freier for RNA extraction. The extraction process will be completed by Dr Freier and Dr Jarman back at the Australian Antarctic Division.
This work will provide a baseline against which to compare future experiments on captive krill in the Australian Antarctic Division’s krill aquarium.
‘We have the only facility in the world where we can conduct experiments on captive krill under simulated Antarctic conditions,’ Dr Jarman says.
‘We’ll set up light regimes similar to those that wild krill experience, but we’ll also set up different light regimes to look at the effect on clock gene expression.’
The research team also includes ecosystem modellers, who will combine gene expression data with sea ice and other environmental data to see how changes in sea ice extent, day length, algal growth and the internal biorhythm of krill, interact.
‘This work is fundamental biology, so we don’t know necessarily where it will end up. It will have links into sustainable fisheries policy, but it will also turn up things that have not been thought of yet,’ Dr Jarman says.
*The Helmholtz Virtual Institute partners are the Australian Antarctic Division, Alfred-Wegener Institute, University of Padova, the University of Oldenburg and the Charité Berlin.
Australian Antarctic Division