Research fellow position: ecologist specialising in life history theory

  • Level A, research-only academic
  • $66,706 to $90,532 pa + 9.5% superannuation
  • Full-time, starting late 2018
  • Two-year, fixed-term
  • Monash University Clayton campus

The Centre for Geometric Biology is currently seeking to recruit an experienced ecologist who specialises in life history theory. This position will be with Professor Dustin Marshall and based within the School of Biological Sciences at Clayton Campus.

As the successful candidate, you will be expected to use existing datasets to investigate evolutionary patterns both within and across species, but more importantly demonstrate a strong conceptual understanding of relevant life history theory and have a demonstrated track record in producing high quality publications. 

Key selection criteria

  1. The appointee will have a doctoral qualification in life history theory or evolutionary ecology
  2. Demonstrated analytical and manuscript preparation skills; including an excellent track record of refereed research publications in high impact journals
  3. Demonstrated experience in asking questions about life history theory using cutting-edge quantitative approaches
  4. Ability to solve complex problems by using discretion, innovation and the exercise of diagnostic skills and/or expertise
  5. Well-developed planning and organisational skills, with the ability to prioritise multiple tasks and set and meet deadlines
  6. Excellent written communication and verbal communication skills with proven ability to produce clear, succinct reports and documents
  7. A demonstrated awareness of the principles of confidentiality, privacy and information handling
  8. A demonstrated capacity to work in a collegiate manner with other staff in the workplace
  9. Demonstrated computer literacy and proficiency in the production of high level work using software such as Microsoft Office applications and specified University software programs, with the capability and willingness to learn new packages as appropriate

Enquiries to Professor Dustin Marshall on +61 3 9902 4449

For more information, or to apply, refer to the Monash University website

Bigger is better when it comes to female fish and feeding the planet

An international study led by the Centre for Geometric Biology has found that larger fish are much more important to feeding the planet than previously thought.

The research confirmed what field biologists have long suggested: that larger mothers reproduced disproportionately much more than smaller ones. Furthermore, larger mothers may produce offspring that perform better and are more likely to survive to adulthood.

The findings clash with current theories. And the results have major implications for fisheries, the value placed on marine protected areas, the impacts of climate change and the 20% of people globally who rely on fish for protein.

The Centre’s Diego Barneche, Craig White, and Dustin Marshall, with Ross Robertson from The Smithsonian Tropical Research Institute, collated and analysed data from 342 species of fish across 14 orders gathered from studies undertaken over a 100-year time span. The team were particularly interested in understanding the relationships between female size and the number of eggs produced, egg volume and egg energy content.

Most life-history theories assume that reproductive output increases proportionately with female size; for every unit increase in female size, there is a proportional increase in reproductive output.  That is, the combined reproductive output of two one-kilogram fish is assumed to be the same as a single two-kilogram fish. But for the overwhelming majority of species, the research team found that overall reproductive output increased disproportionately with female body size. Bigger is much, much better.

The consequences for fisheries cannot be understated. Reproductive output drives population replenishment, and larger fish are much more important for the replenishment of marine fish populations than previously assumed. Outdated models for sustainable harvesting of fish populations are fundamentally flawed.

Our models of how organisms grow and reproduce are based on the wrong assumptions, and as a consequence we are overharvesting wild populations with calamitous consequences.Dustin Marshall

The costs of global change make the study findings even more stark. Climate change is predicted to cause fish body sizes to decrease. Warmer oceans will likely have fewer (and smaller) fish, and drastically reproductive output.

But the research also points to some good news, suggesting that current conservation strategies are more potent than previously thought.  Marine protected areas have been shown to increase fish size by 28% on average. That means that the per-capita reproductive output of fish inside these areas will be much higher than is generally appreciated.

Our discovery means that the benefits of marine protected areas have been massively underestimated, they produce far more new fish than unprotected areas of the same size.Dustin Marshall

This research is published in the Journal Science.

Download high-resolution infographic (PNG 2.4 MB)

Request a copy of the paper

How does parental environment influence the potential for adaptation to global change?

Authors: Evatt Chirgwin, Dustin J Marshall, Carla M Sgrò, and Keyne Monro

Published in: Proceedings of the Royal Society B

Abstract

Parental environments are regularly shown to alter the mean fitness of offspring, but their impacts on the genetic variation for fitness, which predicts adaptive capacity and is also measured on offspring, are unclear. Consequently, how parental environments mediate adaptation to environmental stressors, like those accompanying global change, is largely unknown.

Here, using an ecologically important marine tubeworm in a quantitative-genetic breeding design, we tested how parental exposure to projected ocean warming alters the mean survival, and genetic variation for survival, of offspring during their most vulnerable life stage under current and projected temperatures.

Offspring survival was higher when parent and offspring temperatures matched. Across offspring temperatures, parental exposure to warming altered the distribution of additive genetic variance for survival, making it covary across current and projected temperatures in a way that may aid adaptation to future warming. Parental exposure to warming also amplified nonadditive genetic variance for survival, suggesting that compatibilities between parental genomes may grow increasingly important under future warming.

Our study shows that parental environments potentially have broader-ranging effects on adaptive capacity than currently appreciated, not only mitigating the negative impacts of global change but also reshaping the raw fuel for evolutionary responses to it.

Chirgwin E, Marshall DJ, Sgrò CM, Monro K (2018) How does parental environment influence the potential for adaptation to global change?, Proceedings of the Royal Society B PDF DOI

Death is not the end, especially if you are a colonial organism

Colonial, or modular, organisms are fascinating because each module can experience its own life history while the colony as a whole shares resources. This means that when a module dies it can actually be beneficial to the whole colony. The death of an older module can mean resources are allocated to younger, more vital modules which, in turn, can increase colony reproduction and hence colony fitness. 

Most of our knowledge about these types of organisms comes from plants and although there are many marine examples of colonial organisms, there has been little testing of ideas about module mortality and its effects on colony fitness in these animals.

Karin Svanfeldt and her PhD supervisors Keyne Monro and Dustin Marshall have been working to redress the balance. Karin has been studying the colonial bryozoan Watersipora subtorquata as part of her PhD and she was interested in testing some ideas about selection on module longevity in this species and seeing how it compared with what we know about plants.

Karin used un-analysed data from a field experiment where she had manipulated food availability and flow rate. Karin also used data from another experiment where competition between different species was manipulated by settling Watersipora on either bare PVC plates or on plates where other animals were already growing.

Modules in colonial animals are called zooids and in the bryozoan Watersipora, growth and new zooids appear at the edge of the colony. Over time, the zooids in the centre of the colony lose colour and irreversibly senesce. Zooid senescence is visible as the appearance of a grey inner circle of older, dead zooids that expands as the colony grows. This meant that Karin was able to track individual zooids over time to provide measures of zooid longevity and also get data on the reproductive output of colonies to use as a measure of colony fitness. Karin measured reproductive output as either the number of new zooids or the number of ovicells per colony.

This data enabled Karin and her supervisors to ask the question: “does having a shorter zooid lifespan mean increased fitness for the colony as a whole?” Or, put another way: “is module longevity under selection?”

They found that, ‘Yes’ module longevity is under selection and that the strength of selection varies with environmental conditions, which is what has been found in numerous studies looking at modular plant species. 

This research has been published in the Journal of Evolutionary Biology.

Can we predict egg size of marine fish by looking at the predictability of the environment?

The size of eggs in marine fish has been observed to decrease with increasing temperatures and results from a new study support this finding but, more interestingly, suggest that the predictability of the environment is also important in shaping patterns in egg size.

Diego Barneche and Dustin Marshall from the Centre for Geometric Biology have collaborated with Scott Burgess of Florida State University to compile a dataset of 1078 observations of fish egg size taken from 192 studies that took place between 1880 and 2015 and which include 288 species. This enabled them to test multiple life history theories, including the prediction that in environments with stable food regimes the most effective strategy to maximise reproductive rates is to produce many small eggs.

When compiling this data, Diego and colleagues only included geo-located data so that they could use other existing datasets to estimate means and predictability of sea surface temperatures and chlorophyll a concentrations for the different locations.

The research team were interested, not only in testing how egg size responds to changes in average temperature, but how environmental productivity or food supply (using chlorophyll a as a proxy measure) will affect egg size. The team also formally tested how different components of environmental predictability would affect egg size; they looked at seasonality as well as temporal autocorrelation (how similar conditions at any one point in time are likely to be with previous conditions) to provide indices of environmental predictability.

Diego and colleagues found that egg size decreased as temperatures or chlorophyll a concentrations increased. In contrast, environments that were more seasonal in respect to temperature had larger eggs, but so did environments that were not seasonal in respect to chlorophyll a but were temporally autocorrelated.

These graphs show data from 192 studies and 1,078 observations of fish egg size where egg size decreased as both (a) temperature and (b) chlorophyll-a concentrations increased.

The findings from this study are consistent with a theory that suggests that in an unpredictable environment mothers employ a ‘bet-hedging’ strategy whereby they insulate their offspring from poor conditions through better provisioning, that is, they produce larger eggs.

Importantly this study demonstrated that different components of environmental variation – not just changes in the mean environmental state – contribute to observed patterns in egg size. As future changes to the ocean are expected to impact not only the average state but the degree of predictability, there may be profound effects on the distribution of marine life history traits.

This research is published in the journal Global Ecology and Biogeography

Global environmental drivers of marine fish egg size

Authors: Diego R Barneche, Scott C Burgess, and Dustin J Marshall

Published in: Global Ecology and Biogeography

Abstract

Aim: To test long‐standing theory on the role of environmental conditions (both mean and predictability) in shaping global patterns in the egg sizes of marine fishes.

Location: Global (50° S to 50° N).

Time period: 1880 to 2015.

Major taxa studied: Marine fish.

Methods: We compiled the largest geo‐located dataset of marine fish egg size (diameter) to date (n = 1,078 observations; 192 studies; 288 species; 242 localities). We decomposed sea surface temperature (SST) and chlorophyll‐a time series into mean and predictability (seasonality and colour of environmental noise – i.e. how predictable the environment is between consecutive time steps), and used these as predictors of egg size in a Bayesian phylogenetic hierarchical model. We test four specific hypotheses based on the classic discussion by Rass (1941), as well as contemporary life‐history theory, and the conceptual model of Winemiller and Rose (1992).

Results: Both environmental mean and predictability correlated with egg size. Our parsimonious model indicated that egg size decreases by c. 2.0‐fold moving from 1 to 30 °C. Environments that were more seasonal with respect to temperature were associated with larger eggs. Increasing mean chlorophyll‐a, from 0.1 to 1 mg/m3, was associated with a c. 1.3‐fold decrease in egg size. Lower chlorophyll‐a seasonality and reddened noise were also associated with larger egg sizes – aseasonal but more temporally autocorrelated resource regimes favoured larger eggs.

Main conclusions: Our findings support results from Rass (1941) and some predictions from Winemiller and Rose (1992). The effects of environmental means and predictability on marine fish egg size are largely consistent with those observed in marine invertebrates with feeding larvae, suggesting that there are important commonalities in how ectotherm egg size responds to environmental change. Our results further suggest that anthropogenically mediated changes in the environment will have profound effects on the distribution of marine life histories.

Barneche DR, Burgess SC, Marshall DJ (2018) Global environmental drivers of marine fish egg size, Global Ecology and Biogeography PDF DOI 

How does size affect the maintenance of a constant body temperature?

Staying warm is a subject close to many of our hearts during winter and we probably wouldn’t be surprised to hear that animals from colder climes have higher rates of energy expenditure.  But is this true for all species, or is it more complicated than that?

Researchers from Uruguay, Daniel Naya and Hugo Naya, have joined forces with Craig White from the Centre for Geometric Biology to investigate how body mass in mammals affects the relationship between energy expenditure and climate. They found that, yes, energy expenditure was greater for species that live in colder regions but only in mammals smaller than 100 g. The effect became less marked as the animals got bigger. 

The Basal Metabolic Rate (BMR) is a measure that represents the minimum amount of energy needed to maintain a relatively constant body temperature through active heat production.  It has been repeatedly demonstrated that there is a negative correlation between temperature and residual BMR in mammals and birds.

So where does body mass come into all this?  Over half of all mammals weigh less than 100 g although the range in body mass for mammals scales over 8 orders of magnitude. Also, smaller animals are generally easier to work with in the laboratory and so it is likely that much of our data on BMR in mammals comes from smaller species.

In order to untangle the effects of size on the ‘Temperature – BMR’ relationship, Daniel, Hugo and Craig looked at existing data on 458 mammal species. They compiled data on body mass, BMR and temperature from each collection site.  Their data set, as expected, included many more small species than big ones. What is more, their prediction that smaller species would be more dependent on adjustments in BMR to cope with lower temperatures, was confirmed.

There are other ways to maintain constant body temperatures apart from exerting more energy or increasing the Basal Metabolic Rate. Some examples include physiological adjustments, such as the separation of core and outer temperatures through peripheral vasoconstriction.  Behavioural adjustments, such as building / using shelters or changing activity levels can also help maintain body temperatures. Body shapes (surface to volume ratio), body colour, and the properties of body fat and skin can all affect heat retention, absorbance and loss.

Smaller species may have less scope for accessing these alternative solutions. This is because their smaller size may place restrictions on their adoption; including both physical restrictions (fur thickness is limited by body size) and biological restrictions (colour change or activity changes can increase predation risk). Such factors may mean that smaller mammals are more dependent on basal heat generation as a means of maintaining a constant temperature than are larger mammals.

The research team are keen to see if the same pattern of strong Temperature – BMR relationships at smaller body mass but not at bigger body mass, hold true with birds as well.

This research was published in The American Naturalist.

Student session: Applying for a postdoc

Not all PhD students want to pursue a career in academia; some definitely do, while others feel that they would like to further their academic training through doing a postdoctoral fellowship before moving into industry or other fields.

But how do you go about getting a postdoc? 

Professors Dustin Marshall and Craig White will be speaking about their experiences as academics looking for postdocs, and we invite students and interested early career researchers to join us armed with questions about how to go about getting a postdoc, what to expect from a postdoc and ‘conversations you should have’ when starting a postdoc.

When: 2 pm, Thursday 23 August 2018

Where: Sanson Room (22 G01/02) Rainforest Walk, Monash University Clayton