Stranded alone: The first reported Peruvian population of Agarophyton chilensis is a single-male's clone

Abstract

Gracilariales, a red macroalgal order, is considered one of the top ten most invasive algal taxa. While Agarophyton vermiculophyllum is a well known example of an algal invader worldwide, its congeneric species A. chilensis has mainly remained within its original distribution range for thousands of years, and was only engaged in a few dispersal journeys to arrive from New Zealand to Chile over 19,000 years ago. Nowadays, A. chilensis is intensively farmed along the Chilean coast and the establishment of new populations has mostly been due to intentional/planned cultivation practices. No other source of range expansion has ever been reported, since its first description. However, in 2014 it was sighted for the first time at the docking of a small artisanal port in Peru, which nowadays represents its northernmost population. We genetically assessed 60 specimens taken from Peru in 2015 and 2017, using two different types of molecular markers (the ribosomal Internal Transcribed Spacer 2, ITS2 and six nuclear microsatellites). Altogether, our results suggest the population in Perú to be an unattached, vegetative, single male's clonal population. This population has sustained itself successfully, reproducing asexually through fragmentation, for at least four consecutive years and seems to have expanded in the area. The ITS2 sequences from these individuals corresponds all to one haplotype, the one ubiquitous among populations from Chile, the eastern coast of New Zealand and the Chatham Islands, not allowing to narrow down the potential area of origin of the Peruvian population. Based on first the allelic frequencies of six microsatellite loci estimated for 28 Chilean and five loci for seven New Zealander populations and second the analyses of Bayesian clustering, we propose the natural or unintentional anthropogenic introduction of a single male's thallus from Chile to be the source of the Peruvian population.