How ancient forest fragmentation and riparian connectivity generate high levels of genetic diversity in a microendemic Malagasy tree

Abstract

Understanding landscape changes is central to predicting evolutionary trajectories and defining conservation practices. While human-driven deforestation is intense throughout Madagascar, exception in areas like the Loky-Manambato region (North) raises questions. This region also harbors a rich and endemic flora, whose evolutionary origin remains poorly understood.We assessed the genetic diversity of an endangered micro-endemic Malagasy olive species (Noronhia spinifolia) to better understand the vegetation dynamic in the Loky-Manambato region and its influence on past evolutionary processes. We characterized 72 individuals sampled across eight forests through nuclear and mitochondrial restriction associated sequencing data (RADseq) and chloroplast microsatellites (cpSSR).Extremely high genetic diversity was revealed in the three genomic compartments (chloroplast h = 0.99, mitochondrial h = 0.85, and nuclear HO = 0.07-0.20). Combined population and landscape genetics analyses indicate that N. spinifolia diversity is best explained by the current forest cover (R2 = 0.90), highlighting a long-standing forest fragmentation in the region. Our results further suggest a predominant role of forestdwelling organisms in mediating pollen and seed dispersals.This sustains a major and long-term role of riparian corridors in maintaining connectivity across those antique mosaic-habitats, calling for the study of organismal interactions that promote gene flow.

An ancient age of open-canopy landscapes in northern Madagascar? Evidence from the population genetic structure of a forest tree

“…The results presented by Jordi Salmona and collaborators [4] contribute to the understanding of the history and ecology of understudied Madagascar ecosystems. Previous population genetic studies in some forest-dwelling mammals have been interpreted as supporting an old age for the fragmented landscapes in northern Madagascar [e.g.…”

“…Despite the small distribution of the species, Jordi Salmona and collaborators [4] found remarkable levels of genetic diversity. The spatial structure of this diversity was found to be mainly explained by the forest cover of the landscape, suggesting that the landscape has been composed by patches of forests and grasslands for a long time.…”

“…The work by Jordi Salmona and collaborators [4] studies the factors determining the population genetic structure of the Malagasy spiny olive (Noronhia spinifolia). This narrow endemic species is distributed in the…”

The antique genetic plight of the Mediterranean monk seal (Monachus monachus)

“…Additionally, we investigated patterns of genetic variance with a principal component analysis (PCA) of allele frequencies, with a discriminant analysis of principal components (DAPC, considering sampling regions as groups), and using the SnapClust clustering approach [47] for K = 1-15. To assess how the geographic distance alone explains the genetic diversity [48,49], we investigated individual- and population-based patterns of isolation by distance (IBD) using Mantel tests [50], and assessed which genetic distance metric and spatial scale best fitted the data [51,52]. To assess how dispersal is distributed geographically we used Mantel correlograms [53,54].…”

Genomic signatures of past megafrugivore-mediated dispersal in Malagasy palms

“…), and both isolation by distance and isolation by environment were inferred to affect genetic differentiation between orchid populations (Andriamihaja et al, 2021). Current forest cover has also been shown to be important for driving genetic diversity and genetic structure of endemic plants in Madagascar (Salmona et al, 2022). Finally, besides frugivores and the abiotic environment, humans have been a major determinant of present-day genetic diversity and genetic structure of plants (Arredondo et al, 2018; Smith et al, 2020).…”