Authors: Marcelo E Lagos, Craig R White and Dustin J Marshall
Published in: Marine Ecology Progress Series, volume 540 (November 2015)
Oxygen-poor habitats are increasingly common in aquatic environments. Human activities are accelerating the spread of oxygen-poor environments, yet the way in which larvae avoid low-oxygen conditions remains poorly resolved.
For organisms with a sessile or sedentary adult phase, habitat selection is crucial, and many organisms show sophisticated responses to various habitat cues during colonization.
Whether oxygen availability serves as such a cue is unknown, yet increasingly, it seems that oxygen is an essential limiting resource in some systems.
In a series of experiments, we manipulated oxygen levels during dispersal and colonization in larvae of the model marine invertebrate Bugula neritina in the laboratory.
We found that, in the presence of lower oxygen levels, larvae reduce the time spent in habitat exploration and that they delay settlement. We also found that larvae avoid hypoxic water (positive oxytaxis) — the first such demonstration for marine larvae. All of these behaviors may decrease the likelihood of colonizing low-oxygen habitats in nature.
Our results suggest that marine invertebrate larvae, in this species at least, can use oxygen availability as an initial cue for habitat selection but that additional factors (e.g. biofilms) determine settlement patterns.
Lagos ME, White CR, Marshall DJ (2015) voiding low-oxygen environments: oxytaxis as a mechanism of habitat selection in a marine invertebrate, Marine Ecology Progress Series, 540 99–107 PDF (332 KB) doi:10.3354/meps11509
Authors: Scott C Burgess, Michael Bode and Dustin J Marshall
Published in: Functional Ecology doi: 10.1111/1365-2435.12080
Much of the theory on offspring size focuses on the effects of habitat quality on the relationship between offspring size and fitness. Habitat spacing may be another important factor that affects selection on offspring size when offspring disperse prior to colonization and accrue deferred costs that are mediated by offspring size.
We developed a theoretical model, based on a well-known optimality model, of how selection on offspring size changes with dispersal distance. The model assumes that offspring fitness depends on both offspring size and dispersal duration and that dispersal time and distance are positively related. Such assumptions are based on thousands of marine invertebrate species with non-feeding larvae, but our model also applies more generally to any organism where offspring size modifies the energetic costs of dispersal, and there is a positive relationship between dispersal duration and distance.
Our model predicts that, even when habitat quality does not vary, more isolated habitats may favour the production of fewer, larger offspring if smaller offspring incur greater deferred costs of dispersal. We then empirically demonstrate that offspring size and dispersal duration have interactive effects on post-settlement survival in a marine invertebrate (Bugula neritina), and such size-dependent deferred costs of dispersal are of a magnitude sufficient enough to potentially favour larger offspring in isolated habitats.
Together, our results indicate that the spatial pattern of suitable habitat could impose very different selective regimes on offspring size compared with the effects of habitat quality. Furthermore, our predictions contrast to those predicted for seed size and dispersal in plants, where the production of smaller, more numerous seeds is often a more efficient way for mothers to access distant, suitable habitat.
Burgess SC, Bode M, Marshall DJ (2013) Costs of dispersal alter optimal offspring size in patchy habitats: combining theory and data for a marine invertebrate. Functional Ecology PDF 329 KB doi: 10.1111/1365-2435.12080