Reduction of Genetic Variation When Far From the Niche Centroid: Prediction for Mangrove Species

Abstract

The niche-centroid hypothesis states that populations that are distributed near the centroid of the species' ecological niche will have higher fitness-related attributes, such as population abundance and genetic diversity than populations near the edges of the niche. Empirical evidence based on abundance and, more recently, genetic diversity data support this hypothesis. However, there are few studies that test this hypothesis in coastal species, such as mangroves. Here, we focused on the black mangrove Avicennia germinans. We combined ecological, heterozygosity, and allelic richness information from 1,419 individuals distributed in 40 populations with three main goals: (1) test the relationship between distance to the niche centroid and genetic diversity, (2) determine the set of environmental variables that best explain heterozygosity and allelic richness, and (3) predict the spatial variation in genetic diversity throughout most of the species' natural geographic range. We found a strong correlation between the distance to the niche centroid and both observed heterozygosity (Ho; ρ2 = 0.67 P < 0.05) and expected heterozygosity (He; ρ2 = 0.65, P < 0.05). The niche variables that best explained geographic variation in genetic diversity were soil type and precipitation seasonality. This suggests that these environmental variables influence mangrove growth and establishment, indirectly impacting standing genetic variation. We also predicted the spatial heterozygosity of A. germinans across its natural geographic range in the Americas using regression model coefficients. They showed significant power in predicting the observed data (R2 = 0.65 for Ho; R2 = 0.60 for He), even when we considered independent data sets (R2= 0.28 for Ho; R2 = 0.25 for He). Using this approach, several genetic diversity estimates can be implemented and may take advantage of population genomics to improve genetic diversity predictions. We conclude that the level of genetic diversity in A. germinans is in agreement with expectations of the niche-centroid hypothesis, namely that the highest heterozygosity and allelic richness (the basic genetic units for adaptation) are higher at locations of high environmental suitability. This shows that this approach is a potentially powerful tool in the conservation and management of this species, including for modelling changes in the face of climate change.

The role of niche breadth in oak phylogeography: Quercus glaucoides as a study case

“…This region was amplified using three pairs of primers (trnC-ycf6R, ycf6-psbMR, psbMF-trnD) (Shaw et al, 2005). Sequences obtained were assembled and aligned with the software PhyDE® v0.9971 (Müller et al, 2008).…”

“…Several studies have demonstrated a decrease in intraspecific genetic diversity with distance from the niche centroid (e.g. Ochoa‐Zavala et al, 2022), but a potential relationship between niche breadth and phylogeographic patterns across species still requires evaluation.…”

Can upwelling regions be potential thermal refugia for marine species during climate warming? The case of Mexico

“…This study found spatial patterns of changes in suitability, ecological richness, and turnover through the climate change scenarios; however, their magnitude was related to the warming degree. Even though a direct measurement of abundance was not considered in our work, evidence has shown that estimations via ENMs may reflect important fitness parameters of the population, such as abundance and genetic diversity [59][60][61][73][74][75]. In this sense, the results of ENMs can be useful in identifying areas where species abundance may either increase or decrease.…”

“…The minimum volume ellipsoid (MVE) algorithm was used as an ENMs tool to represent the species fundamental niche. The election of this algorithm is because empirical and theoretical works assume that fundamental niches have convex shapes, such as ellipsoids [57]; moreover, the distance to the center of an ellipsoid has been shown to be negatively related to fitness attributes, such as population abundance and genetic variation [58][59][60][61]. The MVE is a multivariate estimator that builds ellipsoids spanning a predetermined percentage of observations, predicting a centroid and scattering of the data [62].…”

Oceanographic connectivity explains the intra-specific diversity of mangrove forests at global scales

“…The sea-level fluctuations during glacial-interglacial cycles of the Quaternary might have repeatedly shifted mangroves’ distribution, also influencing genetic diversity ( 2 ). More recently, ongoing climate changes ( 24 , 46 ) and human-induced disturbance ( 47 , 48 ) may have also impacted genetic levels owing to population size reductions in the face of unfavorable niche conditions or by founder effects at the leading edge of new colonizations ( 49 ). Alternative means of dispersal, such as wind and insect-driven pollination ( 21 , 50 ), and human-induced reforestation ( 51 ), can also shape the distribution of genetic diversity in ways (i.e., distance and direction) that may contrast with those from the prevalent oceanographic currents.…”