Variation in rates of early development in Haliotis asinina generate competent larvae of different ages.

Daniel J Jackson,Bernard M Degnan,Sandie M Degnan

doi:10.1186/1742-9994-9-2

Daniel J Jackson, Bernard M Degnan + Show 1 more

Open Access

https://doi.org/10.1186/1742-9994-9-2

Copy DOI

Abstract

IntroductionInter-specific comparisons of metazoan developmental mechanisms have provided a wealth of data concerning the evolution of body form and the generation of morphological novelty. Conversely, studies of intra-specific variation in developmental programs are far fewer. Variation in the rate of development may be an advantage to the many marine invertebrates that posses a biphasic life cycle, where fitness commonly requires the recruitment of planktonically dispersing larvae to patchily distributed benthic environments.ResultsWe have characterised differences in the rate of development between individuals originating from a synchronised fertilisation event in the tropical abalone Haliotis asinina, a broadcast spawning lecithotrophic vetigastropod. We observed significant differences in the time taken to complete early developmental events (time taken to complete third cleavage and to hatch from the vitelline envelope), mid-larval events (variation in larval shell development) and late larval events (the acquisition of competence to respond to a metamorphosis inducing cue). We also provide estimates of the variation in maternally provided energy reserves that suggest maternal provisioning is unlikely to explain the majority of the variation in developmental rate we report here.ConclusionsSignificant differences in the rates of development exist both within and between cohorts of synchronously fertilised H. asinina gametes. These differences can be detected shortly after fertilisation and generate larvae of increasingly divergent development states. We discuss the significance of our results within an ecological context, the adaptive significance of mechanisms that might maintain this variation, and potential sources of this variation.

Highlights

Inter-specific comparisons of metazoan developmental mechanisms have provided a wealth of data concerning the evolution of body form and the generation of morphological novelty
Variation in the rate of embryonic and larval development during the dispersal phase, and in the time to acquire competence, has the potential to affect the likelihood of encountering a suitable metamorphosis inducing cue in a patchy environment
Variation in the time to hatching Observing the time taken for every individual larva to hatch from the vitelline envelope revealed a larger degree of chronological variation

Summary

Introduction

Inter-specific comparisons of metazoan developmental mechanisms have provided a wealth of data concerning the evolution of body form and the generation of morphological novelty. Variation in dispersal and larval recruitment are in turn well known to be mechanisms that can structure adult populations [18,19] Related to these observations is the fact that many marine invertebrate larvae must be exposed to specific and ‘patchily’ distributed chemical or physical cues in order for the processes of settlement and metamorphosis to be initiated [20,21,22]. Variation in the rate of embryonic and larval development during the dispersal phase, and in the time to acquire competence, has the potential to affect the likelihood of encountering a suitable metamorphosis inducing cue in a patchy environment It has long been known for some species that the rate of development is under genetic control. Due to the paucity of data, cross species comparisons of the molecular mechanisms that underlie developmental timing are not yet possible, it is clear that environmental factors can directly affect developmental rate, with temperature perhaps being the best studied and understood for the widest variety of taxa [33,34,35,36]

Methods

Results

Discussion

Conclusion