Geographical and environmental contributions to genomic divergence in mangrove forests

Abstract

<jats:title>ABSTRACT</jats:title><jats:p>Assessing the relative importance of geographic and environmental factors to the spatial distribution of genetic variation may provide relevant information about the processes that maintain genetic variation in natural populations. With a globally wide but very restricted habitat distribution, mangrove trees are an interesting model for studies aiming to understand the contributions of these factors. Mangroves occur along the continent-ocean interface of tropical and subtropical latitudes, regions considered inhospitable to many other plant types. Here, we used landscape genomics approaches to investigate the relative contributions of geographic and environmental variables to the genetic variation of two black mangrove species, <jats:italic>Avicennia schaueriana</jats:italic> and <jats:italic>Avicennia germinans</jats:italic>, along the South American coast. Using single nucleotide polymorphisms, our results revealed an important role of ocean currents in the gene flow of <jats:italic>A. schaueriana</jats:italic> and isolation by environment as the pattern that best explains the genetic differentiation of <jats:italic>A. germinans.</jats:italic> Additionally, for both species, we observed significant correlations between genetic variation with evidence of selection and precipitation regimes, tidal variation, solar radiation and temperature patterns. These discoveries expand our knowledge about the evolution of mangrove trees and provide important information to predict future responses of coastal species to the expected global changes for this century.</jats:p>

Distinguishing the Brazilian mangrove species Avicennia germinans and A. schaueriana (Acanthaceae) by elliptic Fourier analysis of leaf shape

“…Both species are recorded for the northern coast of Brazil, but A. schaueriana is not abundant in the main mangrove forests of Pará and Maranhão states (Menezes et al 2008) and there is no reliable published record of A. schaueriana from the mangrove forest of the Rio Parnaíba delta. Avicennia germinans , on the other hand, has been reported for the Parnaíba delta by various authors (Deus et al 2003, Andrade et al 2012, Meireles 2012, Mori 2013, Andrade et al 2014, Mori et al 2015a, Mori et al 2015b, Santos‐Filho et al 2015, Meireles 2016, Araújo et al 2018, Meireles et al 2018, Silva et al 2020).…”

Differential adaptive potential and vulnerability to climate-driven habitat loss in Brazilian mangroves

“…While populations from the northern coast of the country inhabit equatorial environments with a high annual rainfall and warmer temperatures, southern populations reach latitudes as low as 28°S and occupy subtropical areas with lower temperatures and less annual precipitation. This climatic variability has been associated with differentiation in the adaptive genetic composition of the mangrove populations, especially in loci related to temperature, solar radiation, and water stress (Bajay et al 2018, Cruz et al 2020, da Silva et al 2021). As a result, temperature rise and changes in precipitation patterns may differentially affect the persistence and survival of populations due to local adaptations, such as those reported for the dominant species Avicennia germinans and A. schaueriana ( Acanthaceae ) (Cruz et al 2020, da Silva et al 2021).…”

“…2 million hectares, mostly along the Brazilian coast (FAO 2007), with estimated impacts on the regional economy between US $33,000 and 57,000 per hectare per year (UNEP, 2014). In Brazil, due to the country’s wide geographic extent that ranges from 33.75°S to 5.27°N and the variety of environmental conditions found along the coastal latitudinal gradient, mangrove forests are naturally exposed to widely variable adaptive pressures (Cruz et al 2020, da Silva et al 2021). While populations from the northern coast of the country inhabit equatorial environments with a high annual rainfall and warmer temperatures, southern populations reach latitudes as low as 28°S and occupy subtropical areas with lower temperatures and less annual precipitation.…”

“…This climatic variability has been associated with differentiation in the adaptive genetic composition of the mangrove populations, especially in loci related to temperature, solar radiation, and water stress (Bajay et al 2018, Cruz et al 2020, da Silva et al 2021). As a result, temperature rise and changes in precipitation patterns may differentially affect the persistence and survival of populations due to local adaptations, such as those reported for the dominant species Avicennia germinans and A. schaueriana ( Acanthaceae ) (Cruz et al 2020, da Silva et al 2021).…”

“…Mangrove trees have high dispersal potential due to their waterborne propagules (fruits or seeds), but long-distance dispersal events are rare, which causes limited connectivity among populations (Van der Stocken et al 2019). At regional and biogeographic scales, abiotic factors such as coastal geomorphology (e.g., Triest et al 2020), landmasses (e.g., Cerón-Souza et al 2015, Ochoa-Zavala et al 2019, Mori et al 2021), and ocean currents and eddies (e.g., Mori et al 2015, Cerón-Souza et al 2015, Kennedy et al 2016, Triest et al 2021, da Silva et al 2021) influence how propagules move across geographical space. As these factors shape propagule dispersal, they may lead to the differentiation of populations and, consequently, their genetic divergence.…”