Abstract
Mangrove plants comprise plants with similar ecological features that have enabled them to adapt to life between the sea and the land. Within a geographic region, different mangrove species share not only similar adaptations but also similar genetic structure patterns. Along the eastern coast of South America, there is a subdivision between the populations north and south of the continent's northeastern extremity. Here, we aimed to test for this north‐south genetic structure in Rhizophora mangle, a dominant mangrove plant in the Western Hemisphere. Additionally, we aimed to study the relationships between R. mangle, R. racemosa, and R. × harrisonii and to test for evidence of hybridization and introgression. Our results confirmed the north‐south genetic structure pattern in R. mangle and revealed a less abrupt genetic break in the northern population than those observed in Avicennia species, another dominant and widespread mangrove genus in the Western Hemisphere. These results are consistent with the role of oceanic currents influencing sea‐dispersed plants and differences between Avicennia and Rhizophora propagules in longevity and establishment time. We also observed that introgression and hybridization are relevant biological processes in the northeastern coast of South America and that they are likely asymmetric toward R. mangle, suggesting that adaptation might be a process maintaining this hybrid zone.
Highlights
Mangrove species are plants that grow in the intertidal zone along rivers, estuaries, and shores between latitudes of approximately 30°N and 30°S (Hamilton & Casey, 2016)
Our independent sampling and use of a new set of molecular markers enabled us to build on previous studies on the genetic diversity of Rhizophora mangle along the Atlantic coast of South America (Pil et al, 2011; Takayama et al, 2013)
This pattern has been observed in two species of Avicennia (Mori, Zucchi, & Souza, 2015), which is a true mangrove genus (Tomlinson, 1986), and H. pernambucensis (Takayama et al, 2008), a mangrove associate (Tomlinson, 1986)
Summary
Mangrove species are plants that grow in the intertidal zone along rivers, estuaries, and shores between latitudes of approximately 30°N and 30°S (Hamilton & Casey, 2016). Different species share similar genetic structure patterns at a wide range of geographic scales in many mangrove forest regions. Along the eastern coast of South America, there is a pattern of genetic subdivision between populations north and south of the northeastern extremity of the South America continent (NEESA) This divergence pattern is shared by the sea-dispersed plants Rhizophora mangle L. We sampled plants from four and seven mangrove forest regions north and south of the NEESA, respectively, to improve the representation of the northern “population.” because AEP Rhizophora species exhibit semipermeable species boundaries (Cerón-Souza et al, 2010, 2014; Takayama et al, 2013), it is possible that ancient and ongoing interspecific hybridization is a relevant evolutionary process in the northern population (Pil et al, 2011). To the best of our knowledge, R. racemosa and R. × harrisonii have not been recorded south to the NEESA
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