Origin and evolution of a new tetraploid mangrove species in an intertidal zone

Polyploidy is a major factor in the evolution of plants,yet we know little about the origin and evolution of polyploidy in intertidal species.This study aimed to identify the evolutionary transitions in three truemangrove species of the genus Acanthus distributed in the Indo-West Pacific region.For this purpose,we took an integrative approach that combined data on morphology,cytology,climatic niche,phylogeny,and biogeography of 493 samples from 42 geographic sites.Our results show that the Acanthus ilicifolius lineage distributed east of the Thai-Malay Peninsula possesses a tetraploid karyotype,which is morphologically distinct from that of the lineage on the west side.The haplotype networks and phylogenetic trees for the chloroplast genome and eight nuclear genes reveal that the tetraploid species has two sub-genomes,one each from A.ilicifolius and A.ebracteatus,the paternal and maternal parents,respectively.Population structure analysis also supports the hybrid speciation history of the new tetraploid species.The two sub-genomes of the tetraploid species diverged from their diploid progenitors during the Pleistocene.Environmental niche models revealed that the tetraploid species not only occupied the near-entire niche space of the diploids,but also expanded into novel environments.Our findings suggest that A.ilicifolius species distributed on the east side of the Thai-Malay Peninsula should be regarded as a new species,A.tetraploideus,which originated from hybridization between A.ilicifolius and A.ebracteatus,followed by chromosome doubling.This is the first report of a true-mangrove allopolyploid species that can reproduce sexually and clonally reproduction,which explains the long-term adaptive potential of the species.

Prominent genetic structure across native and introduced ranges of Pluchea indica, a mangrove associate, as revealed by microsatellite markers

Aims Pluchea indica is a mangrove-associate species,known for its medicinal properties in its native range and being invasive in part of its introduced range.This study aimed to assess geographic distribution of genetic variation of this species across its distribution range,identify the factors influencing its genetic structure and use this information to suggest conservation and management strategies in its native and introduced ranges,respectively.Methods We assessed the genetic diversity and population structure of 348 individuals from 31 populations across its native(Asia)and introduced(USA)ranges for 15 nuclear microsatellite loci.The spatial pattern of genetic variation was investigated at both large and regional spatial scales with the hypothesis that geographic distance and natural geographic barriers would influence the population structure with varying levels of differentiation across spatial scales.Important Findings We found relatively high genetic diversity at the population level and pronounced genetic differentiation in P.indica,as compared with the genetic diversity parameters of mangroves and mangrove associates in this region.Most of the populations showed heterozygote deficiency,primarily due to inbreeding and impediment of gene flow.Analysis of population structures at large spatial scale revealed the presence of two major clusters across the species’natural range separating populations in China from those in Indonesia,Malaysia,Singapore,Thailand,Cambodia and Philippines,and that the USA population might have been introduced from the population cluster in China.Genetic differentiation between populations was also observed at the regional scale.A large number of populations showed evidence of genetic bottleneck,thereby emphasizing the risk of local extinction.Based on these findings,our study recommends in situ conservation strategies,such as to prioritize populations for conservation actions and to maintain genetic diversity.