This Monday Professor Tracy Lawson from the University of Essex talked to students and academic staff in Bristol about her last findings in the survey of stomata behaviour as a response to different environmental stimuli.

This Monday, Professor Tracy Lawson from the School of Biological Sciences of the University of Essex talked to students and academic staff of the LSB in Bristol about her last findings in the survey of stomatal behaviour as a response to different environmental stimuli. During the last 6 years, she and the members of her lab have been working on stomata, water assimilation rates and CO2 gain, the speed of response of stomata in different light conditions, and the importance of studying this topic according to current and future global environmental conditions such as increases in temperatures worldwide, more food production using less land, changing rainfall patterns and lack of water sources for demanding irrigation crops.

During the first part of her talk, Professor Lawson talked about how different plants have different patterns of stomatal behaviour and how these respond differently according to plant phenotype and environmental conditions. Just to mention an example, rice can get a maximum carbon assimilation rate of 95% in only 10 minutes in comparison to Ginkgo biloba that takes one hour to reach a similar rate.

To know more about how plants respond to light fluctuations and climate, Professor Lawson mimicked natural fluctuations in light over a diurnal period to examine the effect on the photosynthetic processes and growth of Arabidopsis (Arabidopsis thaliana). She compared the plant’s behaviour under square wave light and fluctuating light conditions. Under the first treatment, plants responded with thicker leaves, more photosynthetic efficiency, better leaf structure and more proteins associated with electron transport. Plants under the second treatment produced thinner leaves, lower light absorption and slower growth. Under both conditions, plants maintained similar photosynthetic rates.

However, these results highlight that there is a negative feedback control of photosynthesis resulting in a decrease of diurnal carbon assimilation under fluctuating light conditions and that plants under square wave light fail as predictors of performance under realistic light regimes.

The following part of her talk was about the impact of dynamic growth light on stomatal acclimation and behaviour. Professor Lawson assessed the impact of growth light regime on stomatal acclimation and gas exchange growing Arabidopsis plants in three different lighting regimes:

1. with the same average daily intensity,
2. fluctuating with a fixed pattern of light, fluctuating with a randomized pattern of light (sinusoidal), and non-fluctuating (square wave).

With this experiment she and her research team demonstrated that g_s (stomatal conductance to water vapour) acclimation is influenced by pattern and intensity of light, modifying the stomatal kinetics at different times of the day and resulting in differences in the rapidity and magnitude of the g_s response. They quantified the response to a signal that uncouples variation in CO2 assimilation and g_s over most of the diurnal period. This can be translated as 25% water loss during the day without CO2 assimilation. The g_s response can be characterized by a Gaussian element when incorporated into the Ball-Berry model to predict the g_s in a dynamic environment.

Professor Lawson concluded that acclimation of g_s to light could be an important strategy for maintaining carbon fixation and overall plant water status and should be considered to infer responses of crops under field conditions.

Written by Carlos Gracida Juarez (Biological Sciences PhD)

What killed over 200,000 saiga antelopes in Kazakhstan in 2015 and should it change how we think of wildlife disease?

As a species that inhabits vast regions of the Kazakhstan steppe and maintains one of the most magnificent migratory patterns in the world, it is no wonder that the mass mortality event of 2015 that killed over 200,000 saiga antelope became a global cause for concern.

In his seminar, Eric Morgan, a Professor at the School of Biological Sciences at Queen’s University Belfast, outlined the scientific response to such a mass mortality event, placing particular emphasis on the challenges he and his research team faced in the identification of the causal agent.

Saiga antelope, distinct due to their bulbous nose, roam the planes of Kazakhstan, migrating vast distances from winter to summer to aid survival in harsh environmental conditions. Once abundant, the species has experienced a series of population crashes since the collapse of communism due to a corresponding crash in livestock numbers, resulting in an increase in hunting.

Due to their complex migratory patterns, the saiga antelope is difficult to conserve, therefore mobile nature reserves were constructed by local authorities in response to their decline. This resulted in significant population growth, making the initiative “a great conservation success story”, as described by Eric.

However, the story doesn’t end there. In 2015 Richard Kock, Professor of wildlife health and emerging diseases at the Royal Veterinary College in London, discovered a vast graveyard of saiga antelope that had aggregated in central Kazakhstan to calve.

As a keystone species, this mass mortality event attracted a flurry of media attention and demanded urgent answers as to what had caused so many saiga antelope to die over a minute timescale. A meeting hosted by the UN resulted in the construction of a core research team, of which Eric Morgan was a key member.

Having never seen anything of this nature before, Eric went on to explain some of the atypical features of the scene that stumped researchers, such as even spacing of carcases, indicating an almost synchronised death of antelopes at the time of calving. Additionally, dead calves were found with their stomachs full, which is unusual as orphaned calves typically die of starvation. Therefore, this indicated to the research team that whatever had killed the adults had been passed to the offspring during feeding.

Symptoms included weakness, diarrhoea, respiratory difficulties and internal haemorrhages. Eric described the project as uncomfortable and difficult to be involved in not only due to the tragedy but due to the lack of time to respond, stating that “it was so up in the air”. The research team, therefore, were denied the time to generate and develop full hypotheses, finding themselves testing hunches, not factors. A working hypothesis table was constructed, detailing circumstantial causes rated from high to low probability. This table can be found supplementary to Eric’s paper.

The team ruled out many bacteria and viruses along with heavy metals as causal factors. A laugh was shared as Eric displayed a picture of his arm covered in mosquitoes, explaining how he had to let day-feeding mosquitoes land on him so that they could be picked off and sampled to rule out a vector-borne disease.

Finally, a diagnosis of Pasturella multocida was made, again puzzling the research team in that the bacteria is very common in the tonsils of carrier animals, so why doesn’t it cause a mortality every year? A factor within the saiga population must have been changing for bacteria carried in the tonsils to suddenly begin to invade the rest of the body. So far, further research does not show any differences between bacteria that breach the intestinal mucosa and that carried on the tonsils.

Eric continued by highlighting other interacting factors that may form additional pieces of the puzzle such as climate and parasite invasion. Climatic data at the time of past die-offs was collected and a principal component analysis developed. It was concluded that past die-offs had climatic factors in common, such as above 80% humidity and greater precipitation. Eric described this as a ‘climatic

signature’ but, highlighted that the link is weak as it is difficult to associate something out of the ordinary, a mass mortality event, with a variable factor such as climate.
But how do parasites enter the picture? “Humble gut-worms” stated Eric. Parasites invade the intestinal mucosa having dramatic effects on protein metabolism, and the effects may be accelerated during pregnancy. During late pregnancy and early-lactation, the mother directs proteins towards the developing calve, therefore is immunosuppressed and subsequently more vulnerable to bacterial infection.

Eric concluded by stating the team have only got so far in making definitive conclusions and that research is still ongoing. He commented that he is very pleased to have been involved in “a real conundrum” and described the experience as “most satisfying”.
It is possible that nothing can be done to prevent mass mortality events like this from affecting the saiga antelopes in the future. Therefore, research must focus on ways to develop populations large enough to “survive the hit”. However, it is important to acknowledge that this is relevant beyond the saiga system. Climate change is having a profound effect on host susceptibility and virulence. Adaptation to new conditions may be possible however room for manoeuvre is required. Eric stated “Leave parasites alone as they are part of the natural system? Maybe we cannot think like that anymore”.

The lecture was rounded off with a couple of questions, with one audience member enquiring as to whether the research team sought to treat any of the antelopes to try and increase the population back up to a sustainable level. Eric replied by stating “there is no time to intervene in something of this scale and would you want to?” He explained that the knee-jerk reaction may be to start feeding the saiga population hay and pasture, but that may lead to population aggregation around the food source and disease spread. “You have to think very carefully before you intervene in natural systems”.

Written by Beth Harris (year 3 Biology MSci)