Genetic Diversity of the Black Mangrove Avicennia germinans (L.) Stearn in Northwestern Mexico

Abstract

Mangrove forests of Mexico have been threatened by the effects of anthropogenic activities during the last decades, mostly related to aquaculture, agriculture, livestock and urban development. Genetic diversity and fine-scale genetic structure of two generations of the black mangrove Avicennia germinans (L.) Stearn were investigated in perturbed and preserved sites from three lagoon systems in Sinaloa, Mexico. Genetic diversity and overall genetic structure were similar between perturbed and preserved sites. However, lower levels of fine-scale spatial genetic structure were observed in two of the younger (sapling) generations. We attribute this to differences in local dynamics of each lagoon system, their status of conservation and levels of fragmentation. Also, low connectivity and the effects of disturbance could restrict the movement of pollinators and seed dispersal capabilities, resulting in low levels of genetic diversity and signs of inbreeding. Perturbed populations of A. germinans may play an important role in in situ conservation of this complex ecosystem.

Channel network structure determines genetic connectivity of landward–seaward Avicennia marina populations in a tropical bay

“…0.028; see Table 3 in Vekemans & Hardy, 2004) referring to local conditions of retention, whereas results for all other sites suggest open systems with ample dispersal, certainly beyond neighboring trees (on average further away than 21 m). The obtained Sp values for A. marina in Gazi Bay are comparable to Sp values previously reported for A. germinans populations from estuaries in Northwestern Mexico (Millán‐Aquilar et al., 2016), which ranged from 0.002 to 0.015 in adult trees, and could increase for saplings up to 0.035. An overall estimate of Sp = 0.0186 was obtained for the same species in Caribbean and Pacific estuaries of Panama (Céron‐Souza et al., 2012).…”

“…Previous studies found correlations between genetic differentiation and geographic distance (e.g., Binks et al., 2018; Cerón‐Souza et al, 2015; Mori et al., 2015), a correlation known as "isolation by distance" (Rousset, 1997; Wright, 1943). However, aspects such as founding history, variations in dispersal traits, and interactions with spatially heterogeneous landscapes (i.e., spatial variation in transport resistance) have challenged the explanatory power of this model (e.g., Dodd et al., 2002; Maguire, Saenger, et al., 2000; Millán‐Aguillar et al, 2016; Wee et al., 2014). As a result, alternative hypotheses have been proposed that account for dispersal limitation (isolation‐by‐dispersal limitation; Orsini et al., 2013), the effect of ecological and geographical barriers (isolation‐by‐barrier; Ricketts, 2001), or incorporate resistance surfaces that reflect landscape properties (“roughness”) (isolation by resistance; McRae, 2006).…”

Coastal Landform Constrains Dispersal in Mangroves

“…FSGS detectable up to distances of 30 m (or 60 m) corresponded to more sheltered environmental settings that are void of large rivers. The Sp-values that we obtained for A. marina in sheltered sites (Sp = 0.010-0.098, average Sp = 0.053) are mostly higher than the Sp-values previously reported for Avicennia germinans (L.) Stearn populations from Northwestern Mexico, which ranged from Sp = 0.002 to 0.015 in adult trees, although these could increase for saplings up to Sp = 0.035 (Millán-Aquilar et al, 2016).…”

“…An overall estimate of Sp = 0.019 was obtained for A. germinans in Caribbean and Pacific estuaries of Panama (Céron-Souza et al, 2012). The first distance classes considered in each of these studies and our study are comparable, being 0-30 or 0-60 m (this study), 0-50 m (Millán-Aquilar et al, 2016), and 0-100 m (Céron-Souza et al, 2012). However, despite comparable minimal distances, the range of Sp-values for these Avicennia species is only comparable for the non-sheltered systems considered in this study, whereas Sp-values for our "bay" systems are among the highest and correspond to gravity dispersal (hence a very restricted/short-distance dispersal).…”

“…Similarly, evidence for genetic differentiation between estuarine and open-coast ecotypes of the seaweed Hormosira banksii has been found (Coleman et al, 2018). Despite the importance of identifying the influence of environmental settings on a species' dispersal characteristics and the genetic structure of populations, only recently did a few studies consider potential differences in genetic structure and diversity between mangrove populations that occupy different environmental settings (Hasan et al, 2018;Chablé Iuit et al, 2020;Triest et al, 2020), whereas several fine-scale genetic structure (FSGS) analyses delivered relevant information and revealed patterns at the within-site level (Céron-Souza et al, 2012;Mori et al, 2015;Millán-Aquilar et al, 2016;Do et al, 2019).…”