J Syst Evol

• Research Articles •    

Genomic variation patterns of subspecies defined by phenotypic criteria:Analyses of the mangrove species complex, Avicennia marina

Zhengzhen Wang1,4, Zixiao Guo1,*, Cairong Zhong2, Haomin Lyu1, Xinnian Li1, Norman C. Duke3, Suhua Shi1,*   

  1. 1 State Key Laboratory of Biocontrol, Guangdong Key Lab of Plant Resources, School of Life Sciences, Sun Yat-sen University, Guangzhou, 510275, China

    2 Hainan Dongzhai Harbor National Nature Reserve, Haikou, 571129, China

    3 Centre for Tropical Water and Aquatic Ecosystem Research, James Cook University, Townsville, 4811, Australia

    4 Guangdong Key Laboratory of Animal Conservation and Resource Utilization, Guangdong Public Laboratory of Wild Animal Conservation and Utilization, Institute of Zoology, Guangdong Academy of Sciences.

  • Received:2020-10-31 Accepted:2020-11-18

Abstract: Subspecies is used to designate taxa below species but above geographical populations. What patterns of genomic variation is expected if taxa are designated as subspecies? In this study, we carry out such a survey on the mangrove tree Avicennia marina of the Indo-West Pacific coasts. This species has three subspecies, distinguished by morphological traits and geographical distribution. We collected samples from 16 populations (577 individuals) covering all three subspecies and sequenced 94 nuclear genes. We reveal comprehensive genetic divergence among subspecies, generally higher than among geographical populations within subspecies. The level of genetic diversity differs among the three subspecies, possibly hinting at a degree of separation among their gene pools. We observed that divergence varies from locus to locus across the genome. A small portion of the genome is most informative about subspecies delineation while the rest is undifferentiated or slightly differentiated, hinting at uneven gene flow and incomplete isolation. The three subspecies likely split simultaneously with gene flow among lineages. This reticulate evolution results in some discordance between morphology and genetics in areas of population contact. In short, A. marina subspecies show species-like patterns in some respects and population-like patterns in others. We propose that the subspecies designated in A. marina are informative in predicting genetic divergences and useful in making conservation decisions.

Key words: Avicennia marina, Mangrove, Population genetics, Speciation, Subspecies, gene flow