No outbreeding depression at a regional scale for a habitat-forming intertidal alga with limited dispersal
P. F. McKenzie A and Alecia Bellgrove A BA School of Life and Environmental Sciences, Deakin University, PO Box 423, Warrnambool, Victoria 3280, Australia.
B Corresponding author. Email: alecia@deakin.edu.au
Marine and Freshwater Research 57(6) 655-663 https://doi.org/10.1071/MF05078
Submitted: 29 April 2005 Accepted: 19 July 2006 Published: 31 August 2006
Abstract
Hormosira banksii is distributed throughout southern Australasia, but dispersal of propagules is thought to be limited. In the present study, the hypothesis that outbreeding depression occurs in H. banksii was tested by assessing fertilisation success and early development of embryos in crosses between populations at local to regional spatial scales. Hierarchical experiments were conducted at three spatial scales with nesting present within each scale: small scale (within a rocky shore population), intermediate scale (regions separated by 70 km) and large scale (450-km separation between two states: Victoria and Tasmania). In each experiment, eggs and sperm were crossed within and between each population located in the spatial scale of interest. There were no consistent patterns of variable fertilisation success and subsequent development within a population or at different spatial scales. It was concluded that outbreeding depression is not detected in analyses of fertilisation success or early development processes in H. banksii. The results suggest one of the following to be likely: (1) H. banksii is capable of longer distance dispersal than previously considered, thus maintaining gene flow between distant populations, (2) gene flow is restricted by limited dispersal, but populations have not been isolated for a sufficient length of time to cause genetic divergence or (3) outbreeding depression is manifested as effects on later life-history stages.
Extra keywords: cross-fertilisation, dispersal, fucoid, gametes, Hormosira banksii.
Acknowledgments
This research was funded by Deakin University grants to P. F. McKenzie and A. Bellgrove. Thanks to volunteers who assisted with field and laboratory work. Thanks also to the Deakin University Aquatic Ecology group and Prof. Chris Austin for critically reviewing drafts of this manuscript. We are grateful for comments and advice from Prof. Margaret Clayton. This manuscript was greatly improved following comments from three anonymous referees and Dr. Dugald McGlashan.
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