Species replacement along a linear coastal habitat: phylogeography and speciation in the red alga Mazzaella laminarioides along the south east pacific
1 Instituto de Ciencias Ambientales y Evolutivas, Universidad Austral de Chile, Campus Isla Teja, Casilla 567, Valdivia, Chile
2 Departamento de Biología Marina, Facultad de Ciencias del Mar & Centro de Estudios Avanzados en Zonas Áridas (CEAZA), Universidad Católica del Norte, Larrondo 1281, Coquimbo, Chile
3 Departamento de Ecología, Facultad de Ciencias Biológicas, Pontificia Universidad Católica de Chile, Alameda 340, Santiago, Chile
4 Departamento de Ecología, Facultad de Ciencias, Universidad Católica de la Santísima Concepción, Casilla 297, Concepción, Chile
BMC Evolutionary Biology 2012, 12:97 doi:10.1186/1471-2148-12-97Published: 25 June 2012
The Chilean shoreline, a nearly strait line of coast expanding across 35 latitudinal degrees, represents an interesting region to assess historical processes using phylogeographic analyses. Stretching along the temperate section of the East Pacific margin, the region is characterized by intense geologic activity and has experienced drastic geomorphological transformations linked to eustatic and isostatic changes during the Quaternary. In this study, we used two molecular markers to evaluate the existence of phylogeographic discontinuities and detect the genetic footprints of Pleistocene glaciations among Patagonian populations of Mazzaella laminarioides, a low-dispersal benthic intertidal red seaweed that inhabits along ~3,700 km of the Chilean coastal rocky shore.
Three main genetic lineages were found within M. laminarioides. They are distributed along the Chilean coast in strict parapatry. The deep divergence among lineages suggests that they could be considered putative genetic sibling species. Unexpectedly, genetic breaks were not strictly concordant with the biogeographic breaks described in the region. A Northern lineage was restricted to a broad transition zone located between 30°S and 33°S and showed signals of a recent bottleneck. The reduction of population size could be related to warm events linked to El Niño Southern Oscillation, which is known to cause massive seaweed mortality in this region. To the south, we propose that transient habitat discontinuities driven by episodic tectonic uplifting of the shoreline around the Arauco region (37°S-38°S); one of the most active forearc-basins in the South East Pacific; could be at the origin of the Central/South genetic break. The large beaches, located around 38°S, are likely to contribute to the lineages’ integrity by limiting present gene flow. Finally, the Southern lineage, occupies an area affected by ice-cover during the last glaciations. Phylogeny suggested it is a derived clade and demographic analyses showed the lineage has a typical signature of postglacial recolonization from a northern glacial refugium area.
Even if environmental adaptation could have strengthened divergence among lineages in M. laminarioides, low dispersal capacity and small population size are sufficient to generate phylogeographic discontinuities determined by genetic drift alone. Interestingly, our results confirm that seaweed population connectivity over large geographic scales does not rely only on dispersal capacity but also seem to depend highly on substratum availability and population density of the receiving locality.