Have we outgrown the existing models of growth?

Authors: Dustin J Marshall and Craig R White

Published in: Trends in Ecology & Evolution

Theories of growth have a long history in biology. Two major branches of theory (mechanistic and phenomenological) describe the dynamics of growth and explain variation in the size of organisms. Both theory branches usually assume that reproductive output scales proportionately with body size, in other words that reproductive output is isometric.

A meta-analysis of hundreds of marine fishes contradicts this assumption, larger mothers reproduce disproportion- ately more in 95% of species studied, and patterns in other taxa suggest that reproductive hyperallometry is widespread.

We argue here that reproductive hyperallometry represents a profound challenge to mechanistic theories of growth in particular, and that they should be revised accordingly. We suspect that hyperallometric reproduction drives growth trajectories in ways that are largely unanticipated by current theories.

Marshall DJ, White CR (2018) Have we outgrown the existing models of growth? Trends in Ecology & Evolution PDF DOI

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


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

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


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 

Research fellow position: ecologist specialising in life history theory

Update: this position has now been filled.

  • 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

Resources mediate selection on module longevity in the field

Authors: Karin Svanfeldt, Keyne Monro, and Dustin J Marshall

Published in: Evolutionary Biology


The life histories of modular organisms are complicated, where selection and optimization can occur at both organismal and modular levels.

At a modular level, growth, reproduction and death can occur in one module, independently of others. Across modular groups, there are no formal investigations of selection on module longevity.

We used two field experiments to test whether selection acts on module longevity in a sessile marine invertebrate and whether selection varies across successional gradients and resource regimes.

We found that selection does act on module longevity and that the strength of selection varies with environmental conditions. In environments where interspecific competition is high, selection favours colonies with longer zooid (module) longevity for colonies that initially received high levels of maternal investment. In environments where food availability is high and flow rate is low, selection also favours colonies with longer zooid longevity.

These patterns of selection provide partial support for module longevity theory developed for plants. Nevertheless, that selection on module longevity is so context‐dependent suggests that variation in module longevity is likely to be maintained in this system.

Svanfeldt K, Monro K, Marshall DJ (2018) Resources mediate selection on module longevity in the field, Journal of Evolutionary Biology PDF DOI 

Do larger individuals cope with resource fluctuations better? An artificial selection approach

Authors: Martino E Malerba, Maria M Palacios, and Dustin J Marshall

Published in: Proceedings of the Royal Society B


Size determines the rate at which organisms acquire and use resources but it is unclear what size should be favoured under unpredictable resource regimes.

Some theories claim smaller organisms can grow faster following a resource pulse, whereas others argue larger species can accumulate more resources and maintain growth for longer periods between resource pulses. Testing these theories has relied on interspecific comparisons, which tend to confound body size with other life-history traits.

As a more direct approach, we used 280 generations of artificial selection to evolve a 10-fold difference in mean body size between small- and large-selected phytoplankton lineages of Dunaliella tertiolecta, while controlling for biotic and abiotic variables. We then quantified how body size affected the ability of this species to grow at nutrient-replete conditions and following periods of nitrogen or phosphorous deprivation.

Overall, smaller cells showed slower growth, lower storage capacity and poorer recovery from phosphorous depletion, as predicted by the ‘fasting endurance hypothesis’. However, recovery from nitrogen limitation was independent of size—a finding unanticipated by current theories.

Phytoplankton species are responsible for much of the global carbon fixation and projected trends of cell size decline could reduce primary productivity by lowering the ability of a cell to store resources.

Malerba ME, Palacios MM, Marshall DJ (2018) Do larger individuals cope with resource fluctuations better? An artificial selection approach, Proceedings of the Royal Society B, PDF DOI 

A global synthesis of offspring size variation, its eco‐evolutionary causes and consequences

Authors: Dustin J Marshall, Amanda K Pettersen, and Hayley Cameron

Published in: Functional Ecology, volume 32, issue 6 (June 2018)


Offspring size is a key functional trait that can affect all phases of the life history, from birth to reproduction, and is common to all the Metazoa. Despite its ubiquity, reviews of this trait tend to be taxon‐specific. We explored the causes and consequences of offspring size variation across plants, invertebrates and vertebrates.

We find that offspring size shows clear latitudinal patterns among species: fish, amphibians, invertebrates and birds show a positive covariation in offspring size with latitude; plants and turtles show a negative covariation with latitude. We highlight the developmental window hypothesis as an explanation for why plants and turtles show negative covariance with latitude. Meanwhile, we find evidence for stronger, positive selection on offspring size at higher latitudes for most animals.

Offspring size also varies at all scales of organization, from populations through to broods from the same female. We explore the reasons for this variation and suspect that much of this variation is adaptive, but in many cases, there are too few tests to generalize.

We show that larger offspring lose relatively less energy during development to independence such that larger offspring may have greater net energy budgets than smaller offspring. Larger offspring therefore enter the independent phase with relatively more energy reserves than smaller offspring. This may explain why larger offspring tend to outperform smaller offspring but more work on how offspring size affects energy acquisition is needed.

While life‐history theorists have been fascinated by offspring size for over a century, key knowledge gaps remain. One important next step is to estimate the true energy costs of producing offspring of different sizes and numbers.

Marshall DJ, Pettersen AK, Cameron H (2018) A global synthesis of offspring size variation, its eco-evolutionary causes and consequences, Functional Ecology, PDF DOI