Polyploidy and the rise of invasiveness in marine seaweeds

A good part of research suggests that only a limited number of species within algal orders or just a single genetically distinct lineage from within the same morpho-species complex, becomes suddenly invasive. In plants, the switch to invasiveness has been recently related with differences in ploidy levels, meaning that genetic attributes such as polyploidy and high chromosome counts may be the drivers for the phenomenon (Pandit et al. 2011).

 

In their elegant study, Pandit and co-authors (2011) prove that endangered plants exhibit disproportionally low levels of ploidy and chromosome numbers compared to invasive plant species. Similar to hybridization therefore, polyploidy may lead to the production of novel and greater numbers of genetic variants, which increases the probability of a successful invasion. But what is happening in invasive marine seaweeds?

An association between polyploidy and invasiveness has been initially reported for the Indo-Pacific Mediterranean lineage 2 of the red seaweed Asparagopsis taxiformis on the basis of nuclear microsatellite patterns (Andreakis et al. 2007, 2009). At that time, it has been additionally recommended that more cases of association between invasiveness and polyploidy should be explored, particularly in notoriously legendary invasive marine algae, given the general propensity for polyploidy in seaweeds (based on nuclear genome size estimates; Kapraun 2005). Green algae of the genus Caulerpa have the potential to propagate clonally by fragmentation or sexually and they will often become invasive outside their native range of distribution. In a recent paper, Varela-Alvarez  et al. (2012) were able to resolve the life history and ploidy levels in three species of Caulerpa from the Mediterranean Sea. Varela-Alvarez and co-authors showed that ploidy levels and genome size vary in these species, with a reduction in genome size for the invasive ones. Furthermore, the Mediterranean Caulerpa species (C. prolifera, C. racemosa var. cylindracea, C. taxifolia) were recovered as to be polyploid in different life history phases.

PS & Disclaimer: I suspect that an invasion process must have dominated the dawn of any adaptive radiation event in this planet, that is, the occupation of an empty niche, eventually located in a disturbed area…..

Relevant literature

N Andreakis, WHCF Kooistra, and G Procaccini. Microsatellite markers in an invasive strain of Asparagopsis taxiformis (Bonnemaisoniales, Rhodophyta): Insights in ploidy level and sexual reproduction. Gene. 406: 144-151.

N Adreakis, WHCF Kooistra and G Procaccini. High genetic diversity and connectivity in the polyploid invasive seaweed Asparagopsis taxiformis (Bonnemaisoniales) in the Mediterranean, explored with microsatellite alleles and multilocus genotypes. Molecular Ecology. 18: 212-226.

Kapraun DF (2005) Nuclear DNA content estimates in multicellular green, red and brown algae: phylogenetic considerations. Ann Bot 95:7-44.

Pandit MK, Pocock MJO, Kunin WE (2011) Ploidy influences rarity and invasiveness in plants. J Ecol doi: 10.1111/j.1365-2745.2011.01838.x.

Varela-Alvarez E, Gomez Garreta A, Rull Lluch J, Salvador Soler N, Serrao EA, et al. (2012) Mediterranean Species of Caulerpa Are Polyploid with Smaller Genomes in the Invasive Ones. PLoS ONE 7(10): e47728. doi:10.1371/journal.pone.0047728.