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, exceptions in areas like the Loky-Manambato region (North) raise questions. Such regions also harbor a rich and endemic flora, whose evolutionary origin remains poorly understood. We assessed the genetic diversity of an endangered microendemic Malagasy olive species (Noronhia spinifolia Hong-Wa) 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). Combined population and landscape genetics analyses indicate that N. spinifolia diversity is largely explained by the current forest cover, highlighting a long-standing habitat mosaic in the region. 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.

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 DAPC (considering sampling regions as groups), and using the SnapClust clustering approach [47] for K = 1−15. To assess how the geographical 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].…”

The grassy ecosystems of Madagascar in context: Ecology, evolution, and conservation

“…The spread of open grassy systems in Madagascar and the radiation of C4 grass lineages were mirrored in the spread and niche adaptation of savanna woody species about the same time in Madagascar (Choo et al, 2020; Salmona et al, 2020, 2021; Veranso‐Libalah et al, 2018). In addition to the role of fire, we know from paleontological studies elsewhere that large mammalian browsers were important in the spread of open, grassy systems during the Miocene (Janis et al, 2000).…”

“…This process fostered genetic divergence among isolated populations, eventually leading to genetic divergence and allopatric speciation. Those published studies consistent with this hypothesis include the following: (1) the genetic structure of widespread, endemic bat species Macronycteris commersoni (Rakotoarivelo et al, 2019); (2) several studies of cryptic variation in several mouse lemur species populations (Poelstra et al, 2021; Tiley et al, 2022; Sgarlata et al, 2018, and of course Yoder et al, 2016); (3) micro‐endemism in 26 new species of microhylid frogs (Rakotoarison et al, 2017); (4) bird species in the genus Newtonia (Family Vangidae) (Younger et al, 2018); (5) tenrec species (Everson et al, 2020); (6) Salmona et al (2017) on two species of lemurs; (7) dwarf lemurs (Williams et al, 2020); (8) noctuid moths in the Central Highlands (Wiorek et al, 2021); (9) Quéméré et al (2012 on the golden‐crowned sifaka in northern Madagascar; and (10) Salmona et al (2021) on the diversification of some 60 forest and savanna species of Noronhia across Madagascar. It is noteworthy that mosaiced landscapes may not only have promoted evolution of various faunal clades but also may promote higher landscape biodiversity today (cf.…”

“…There is growing evidence that well‐functioning and biodiverse grassy ecosystems are under threat in Madagascar. See Salmona et al (2021), Waeber et al (2015), Virah‐Sawmy (2009), and Bardgett et al (2021) on conservation issues related to grassy systems including open woodlands of Madagascar. See also Rakotoarimanana et al (2001); Alvarado, Buisson, Rabarison, Rajeriarison, Birkinshaw, Lowry, and Morellato (2014b); Bloesch et al (2019); and Pareliussen (2004) and Pareliussen et al (2006) on how to manage these ecosystems sustainably with varying fire regimes.…”

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).…”