Non-contact competition in a sessile marine invertebrate: causes and consequences

Authors: Matthew L Thompson, Dustin J Marshall and Keyne Monro

Published in: Marine Ecology Progress Series, volume 522 (March 2015)

Abstract

In marine benthic communities, phenotypic responses to contact competition are
well resolved, but the causes and consequences of non-contact competition remain unclear.

Here, we used the arborescent bryozoan Bugula neritina to firstly identify whether colonies change their phenotype as a result of non-contact competition, and then understand the mechanism behind the changes. Secondly, we determined the phenotypes that change in response to non-contact competition, with focus on changes in the feeding structure, viz. the lophophore. Lastly, we used a reciprocal transplant design to test whether phenotypic responses to non-contact competition reduce its negative effects.

We found that phenotypic responses to non-contact competition were mediated by the biological effects of conspecific neighbours, but were also determined by the physical effects associated with increased density. Further, we found that colonies grown in high
conspecific density environments were smaller (though more elongated for their size) and had smaller lophophores than colonies from low conspecific density treatments. However, we found no evidence that such phenotypic responses constituted adaptive plasticity; instead, individuals that experienced non-contact competition always performed worse than individuals that had not, and the effects of exposure to non-contact competition were additive.

Our study suggests that noncontact competition is an important and persistent process in benthic marine communities, but that phenotypic plasticity, though present, does not buffer individuals from the negative effects of this process.

Citation:

Thompson ML, Marshall DJ, Monro K (2015) Non-contact competition in a sessile marine invertebrate: causes and consequences. Marine Ecology Progress Series, 522:115–125 doi: 10.3354/meps11178

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.

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

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.