Aisha O’ Connor wrote this post as part of Dr. Stacy Krueger-Hadfield’s Science Communication course at the University of Alabama at Birmingham. Currently a MS student in the Krueger-Hadfield lab, she is interested in algae and conservation. Aisha tweets @Aisha_MOC.
We can all think of barriers to dispersal, such as mountains, rivers, or even urban sprawl. Other barriers may be less visible, but can be just as important for gene flow.
For example, what about currents? In the ocean, they can form strong barriers!
Hargarten et al. (2019) investigated how propagule dispersal affects genetic differentiation in two species of kelp: Pterygophora californica and Macrocystis pyrifera (Fig.1,2). Both species live in the subtidal, Macrocystis forms the canopy layer and P. californicais more of an understory species (Reed et al., 1996).
Macrocystis spores can disperse up to 5m (Anderson & North 1966), but its sporophytes can form floating rafts, whereby reproductive individuals can disperse spores over much greater distances. P. californica’s spores can travel several kilometers, but it doesn’t raft as far as Macrocystis (Reed et al., 1988). These differences might manifest at the population level with different patterns in connectivity between these two species.
Hargarten et al. (2019), using seven microsatellite loci, found Macrocystis to be slightly more genetically diverse than P. californica, but there was no significant difference in genetic differentiation between the two species. Are there similar patterns of connectivity between these two kelps in the Santa Barbara Channel? Perhaps!
But, there are other factors to consider when estimating gene flow and genetic connectivity of kelp populations. The lifespan and age limits of kelp sporophytes and gametophytes can affect connectivity. Considering the lifespan of P. californica and Macrocystis sporophytes, a study over a longer time period including these additional factors, would provide a more robust estimate of the connectivity of these two kelps, and the impact of long distance spore dispersal in Macrocystis.
In the ocean ecosystem barriers exist in many forms. They may take the shape of salinity gradients, lack of suitable substrate or even the presence of competitors. Nevertheless, in future studies, we may need to give more credit to barriers, such as currents and water movement, which appear to greatly influence sporophyte dispersal of ecologically important ecosystem engineers.
Anderson, E. K. and North, W. J. (1966). In situstudies of spore induction and dispersal in the giant kelp Macrocystis. In Proceedings of the Fifth International Seaweed Symposium, Halifaxpp. 73-86
Hargarten, H. L., Johansson, M. L., Reed, D. C., Coelho, N. C., Siegel, D. A., & Alberto, F. (2019). Seascape genetics of the stalked kelp Pterygophora californica and comparative population genetics in the Santa Barbara Channel. Journal of Phycology 56: 110-120.
Reed, D. C., Laur, D. R. & Ebeung, A. W. (1988). Variation in algal dispersal and recruitment; the importance of episodic events. Ecological Monographs58: 321-335
Reed, D., Ebeling, A., Anderson, T. & Anghera, M. (1996). Differential reproductive responses to fluctuating resources in two seaweeds with different reproductive strategies. Ecology 77: 300–316