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Mapping the correlations and gaps in studies of complex life histories

Authors: Emily L Richardson and Dustin J Marshall

Published in: Ecology and Evolution

Abstract

For species with complex life histories, phenotypic correlations between life-history stages constrain both ecological and evolutionary trajectories.

Studies that seek to understand correlations across the life history differ greatly in their experimental approach: some follow individuals (“individual longitudinal”), while others follow cohorts (“cohort longitudinal”). Cohort longitudinal studies risk confounding results through Simpson’s Paradox, where correlations observed at the cohort level do not match that of the individual level. Individual longitudinal studies are laborious in comparison, but provide a more reliable test of correlations across life-history stages.

Our understanding of the prevalence, strength, and direction of phenotypic correlations depends on the approaches that we use, but the relative representation of different approaches remains unknown.

Using marine invertebrates as a model group, we used a formal, systematic literature map to screen 17,000+ papers studying complex life histories, and characterized the study type (i.e., cohort longitudinal, individual longitudinal, or single stage), as well as other factors.

For 3315 experiments from 1716 articles, 67% focused on a single stage, 31% were cohort longitudinal and just 1.7% used an individual longitudinal approach.

While life-history stages have been studied extensively, we suggest that the field prioritize individual longitudinal studies to understand the phenotypic correlations among stages.

Richardson EL, Marshall DJ (2023) Mapping the correlations and gaps in studies of complex life histories. Ecology and Evolution PDF DOI

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How does spawning frequency scale with body size in marine fishes?

Authors: Dustin J Marshall, Diego R Barneche, and Craig R White

Published in: Fish and Fisheries

Abstract

How does fecundity scale with female size? Female size not only affects the number and size of offspring released in any one reproductive bout (i.e. batch fecundity) but also affects frequency of bouts that occur within a given spawning season (i.e. spawning frequency).

Previous studies have noted contrasting effects of female size on spawning frequency such that the effect of female size on reproductive output and total egg production of a population remains unclear. If smaller females spawn more frequently, this could effectively nullify hyperallometry—the disproportionate contribution of larger females to batch fecundity.

Here, we explore the relationship between female size and spawning frequency in marine fishes and test this relationship while controlling for phylogeny.

Within all of the species considered, spawning frequency scaled positively with body size. Comparing across species, the smallest species showed steeper scaling than the largest.

Considering only batch fecundity scaling probably underestimates the relationship between body size and absolute fecundity for many species; reproduction is likely to be more hyperallometric than is currently appreciated based on batch fecundity estimates. Second, an understanding of fecundity scaling depends on estimates of batch fecundity, spawning frequency and spawning duration—we have far more estimates of the first parameter than we do the others, and more studies are required.

Marshall DJ, Barneche DR, White CR (2021) How does spawning frequency scale with body size in marine fishes? Fish and Fisheries PDF DOI 

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Fish reproductive-energy output increases disproportionately with body size

Authors: Diego R Barneche, D Ross Robertson, Craig R White, and Dustin J Marshall

Published in: Science, volume 360, issue 6389 (11 May 2018)

Abstract

Body size determines total reproductive-energy output.

Most theories assume reproductive output is a fixed proportion of size, with respect to mass, but formal macroecological tests are lacking. Management based on that assumption risks underestimating the contribution of larger mothers to replenishment, hindering sustainable harvesting.

We test this assumption in marine fishes with a phylogenetically controlled meta-analysis of the intraspecific mass scaling of reproductive-energy output.

We show that larger mothers reproduce disproportionately more than smaller mothers in not only fecundity but also total reproductive energy.

Our results reset much of the theory on how reproduction scales with size and suggest that larger mothers contribute disproportionately to population replenishment.

Global change and overharvesting cause fish sizes to decline; our results provide quantitative estimates of how these declines affect fisheries and ecosystem-level productivity.

Barneche DR, Robertson DR, White CR, Marshall DJ (2018) Fish reproductive-energy output increases disproportionately with body size. Science PDF DOI

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Biofilm history and oxygen availability interact to affect habitat selection in a marine invertebrate

Authors: Marcelo E Lagos, Craig R White and Dustin J Marshall

Published in: Biofouling, volume 32, issue 6

Abstract

In marine systems, oxygen availability varies at small temporal and spatial scales, such that current oxygen levels may not reflect conditions of the past.

Different studies have shown that marine invertebrate larvae can select settlement sites based on local oxygen levels and oxygenation history of the biofilm, but no study has examined the interaction of both.

The influence of normoxic and hypoxic water and oxygenation history of biofilms on pre-settlement behavior and settlement of the bryozoan Bugula neritina was tested. Larvae used cues in a hierarchical way: the oxygen levels in the water prime larvae to respond, the response to different biofilms is contingent on oxygen levels in the water. When oxygen levels varied throughout biofilm formation, larvae responded differently depending on the history of the biofilm.

It appears that B. neritina larvae integrate cues about current and historical oxygen levels to select the appropriate microhabitat and maximize their fitness.

Citation

Lagos ME, White CR, Marshall DJ (2016) Biofilm history and oxygen availability interact to affect habitat selection in a marine invertebrate, Biofouling, 32:6 645–655 PDF 1.6 MB doi: 10.1080/08927014.2016.1178725

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Propagule size and dispersal costs mediate establishment success of an invasive species

Authors: Rolanda Lange and Dustin J Marshall

Published in: Ecology, volume 97, issue 3 (March 2016)

Abstract

Bio-invasions depend on the number and frequency of invaders arriving in new habitats. Yet, as is often the case, it is not only quantity that counts, but also quality.

The process of dispersal can change disperser quality and establishment success. Invasions are a form of extra-range dispersal, so that invaders often experience changes in quality through dispersal.

To study effects of dispersal on invader quality, and its interactions with quantity on invasion success, we manipulated both in a field experiment using an invasive marine invertebrate.

Establishment success increased with the number of individuals arriving in a new habitat. Prolonged larval durations – our manipulation of prolonged dispersal – decreased individual quality and establishment success. Groups of invaders with prolonged larval durations contributed only a third of the offspring relative to invaders that settled immediately.

We also found an interaction between the quality and quantity of invaders on individual growth: only within high-quality cohorts did individuals experience density-dependent effects on growth.

Our findings highlight that dispersal not only affects the quantity of invaders arriving in a new habitat but also their quality, and both mediate establishment success.

Citation

Lange R , Marshall DJ (2016) Propagule size and dispersal costs mediate establishment success of an invasive species. Ecology, 97(3), 2016, pp. 569–575
DOI: 10.1890/15-1573 PDF 238 KB

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PhD position open: the evolutionary ecology of sessile marine invertebrates

A PhD position is open to students interested in working on the evolutionary ecology of sessile marine invertebrates in Professor Dustin Marshall’s group.

The Marine Evolutionary Ecology Group’s research ranges from quantitative genetics to community ecology. Most projects are field-based with a heavy empirical component. The specifics of the project will be determined by joint collaboration between student and supervisor.

After an expression of interest, approved applicants would be required to apply for a scholarship and tuition waiver through Monash University by 15 April 2014.

The success of such applications is not assured and the application process is extremely competitive, students without at least one first-author publication in an international journal (in the topic of ecology or evolution) will not be considered.

The stipends include all course fees plus approximately $25,000 AUD per annum, tax-free (the equivalent of approximately $33,000 before tax) with no teaching requirements for 3.5 years (the length of a PhD in Australia).

Should the applicant be successful, the funding of project costs and research support including the costs of attending at least one conference per year will be provided by the research group.

Project start dates must be before 30 June 2014.

Interested applicants should send an expression of interest, their CVs, a brief statement of a potential research project and the contact details of two referees to dustin.marshall@monash.edu.

To be eligible, applicants must have completed at least one year of post-graduate research in ecology or evolution.

Preference will be given to those with strong quantitative skills and publications in international journals.

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The maintenance of sperm variability: context-dependent selection on sperm morphology in a broadcast spawning invertebrate

Authors: Darren W Johnson, Keyne Monro, and Dustin J Marshall

Published in: Evolution, volume 67, issue 5 (May 2013)

Abstract

Why are sperm so variable despite having a singular, critical function and an intimate relationship with fitness?

A key to under-standing the evolution of sperm morphology is identifying which traits enable sperm to be successful fertilizers. Several sperm traits (e.g., tail length, overall size) are implicated in sperm performance, but the benefits of these traits are likely to be highly con- text dependent.

Here, we examined phenotypic selection on sperm morphology of a broadcast spawning tube worm (Galeolaria gemineoa). We conducted laboratory experiments to measure the relationship between average sperm morphology and relative fertilization success across a range of sperm environments that were designed to approximate the range of sperm concentrations and ages encountered by eggs in nature.

We found that the strength and form of multivariate selection varied substantially across our environmental gradients. Sperm with long tails and small heads were favored in high-concentration environments, whereas sperm with long heads were favored at low concentrations and old ages.

We suggest variation in the local fertilization environment and resulting differences in selection can preserve variability in sperm morphology both within and among males.

Full paper

Johnson D, Monro K, Marshall DJ (2013) The maintenance of sperm variability: context-dependent selection on sperm morphology in a broadcast spawning invertebrate. Evolution, 67-5: 1383–1395 PDF PDF 889 KB doi:10.1111/evo.12022

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Revisiting the classic biogeographical patterns in marine invertebrate reproduction

After four years of data collection and over 4,000 papers, our paper revisiting the classic biogeographical patterns in marine invertebrate reproduction has been published here.

 Published paper: The biogeography of marine invertebrate life histories

Heat map of the distribution of studies used in the review to examine geographical variation in marine invertebrate life histories. The vast majority of the marine environment remains unstudied, and our view of marine life histories comes from only a small fraction of those studies that exist.