Late Miocene origin and recent population collapse of the Malagasy savanna olive tree (Noronhia lowryi)

Abstract

Debates regarding the origin of tropical savannas have attempted to disentangle the role of human, biotic and abiotic factors. Understanding the origins of savanna remains essential to identifying processes that gave rise to habitat mosaics, particularly those found in the Central Plateau of Madagascar. Documenting the evolutionary history and demography of native trees occurring in open habitats may reveal footprints left by past and recent environmental changes. We conducted a population genetic analysis of an endangered Malagasy shrub (Noronhia lowryi, Oleaceae) of the Central Plateau. Seventy-seven individuals were sampled from three sites and genotyped at 14 nuclear and 24 chloroplast microsatellites. We found a highly contrasting nuclear and plastid genetic structure, suggesting that pollen-mediated gene flow allows panmixia, while seed-based dispersal may rarely exceed tens of metres. From a phylogeny based on full plastomes, we dated the surprisingly old crown age of maternal lineages back to ~6.2 Mya, perhaps co-occurring with the global expansion of savanna. In contrast, recent demographic history inferred from nuclear data shows a bottleneck signature ~350 generations ago, probably reflecting an environmental shift during the Late Pleistocene or the Holocene. Ancient in situ adaptation and recent demographic collapse of an endangered woody plant highlight the unique value and vulnerability of the Malagasy savannas.

Paternity tests support a diallelic self‐incompatibility system in a wild olive (Olea europaea subsp. laperrinei, Oleaceae)

“…Sixteen microsatellite loci (Arbeiter, Hladnik, Jakše, & Bandelj, ; Carriero, Fontanazza, Cellini, & Giorio, ; Salmona et al, ; Sefc et al, ; Table ; Data ) were used to characterize 71 mature diploid/triploid individuals of the CEFE collection (subspp. europaea , laperrinei , cuspidata, and hybrids) plus 32 embryos of Laperrine's olive and the 46 embryos of Mediterranean olive.…”

“…europaea , laperrinei , cuspidata, and hybrids) plus 32 embryos of Laperrine's olive and the 46 embryos of Mediterranean olive. We used PCR conditions described by Salmona et al (). PCR products were diluted and multiplexed together with GenScan‐600 Liz (Applied Biosystems) in formamide.…”

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

“…We first tested whether its restricted geographic distribution resulted in a low genetic diversity, as expected under a neutral model (Kimura, 1983), or remained relatively high as for co-distributed primates [P. tattersalli and Microcebus tavaratra (Quéméré et al, 2010;Aleixo-Pais et al, 2019)]. We then inferred the effect of landscape components on maternally and biparentally inherited genetic diversity, to investigate patterns of seed and pollen dispersals, and assessed their congruence with those of a congeneric species from the High Plateau [N. lowryi (Salmona et al, 2020)], and of co-distributed taxa (abovementioned). We also examined whether the relative stability of the forest cover in the past 70 years (Quéméré et al, 2012;Salmona et al, 2017b) is reflected in N. spinifolia genetic makeup, comparing the effect of recent and historical forest covers on gene flow, as a proxy for the temporality of its habitat fragmentation.…”

“…Furthermore, the Miocene expansion of the Malagasy savannas (Vorontsova et al, 2016;Hackel et al, 2018;Solofondranohatra et al, 2018;Salmona et al, 2020) evidenced the antiquity of open-canopy environments. In some regions, it therefore remains crucial to confirm the questionable antiquity of landscapes and to identify their related change-inducing factors [e.g.…”

“…In some regions, it therefore remains crucial to confirm the questionable antiquity of landscapes and to identify their related change-inducing factors [e.g. (Quéméré et al, 2010;Yoder et al, 2016;Salmona et al, 2017bSalmona et al, , 2020].…”