Population genetic structure in Fraxinus excelsior L. Left: genepools inferred from nuclear SSR markers; right: plastid DNA lineages. From Heuertz, Hausman, et al. (2004); Heuertz, Fineschi, et al. (2004).

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... my PhD on population genetics of common ash, Fraxinus excelsior L. (Oleaceae), supervised by Dr. Xavier Vekemans at the Université Libre de Bruxelles (1999)(2000)(2001)(2002)(2003) (Figure 1), my research has been characterized by a high degree of internationalization. A first postdoc at the University of Uppsala in Sweden (2003Sweden ( -2004) familiarized me with molecular techniques to identify and sequence candidate genes in Norway spruce, Picea abies (L.) Karst, and with coalescent demographic modelling. ...

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... tree species -In collaboration with Dr. Giovanni Vendramin (CNR, Italy), I described the geographically widespread sharing of plastid DNA haplotypes between common ash, Fraxinus excelsior L. (Oleaceae), and the closely related narrow-leaved ash, F. angustifolia Vahl, showing that both species experienced extensive historical gene flow during glacial isolation in refuge populations or during postglacial recolonization leading to near-complete haplotype sharing in sympatric regions ( Figure 10; Heuertz, Carnevale, et al. 2006). In the sympatric distribution, higher genetic diversity in F. excelsior than in F. angustifolia reflected the more cold-tolerant temperament of the first species. ...

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... the sympatric distribution, higher genetic diversity in F. excelsior than in F. angustifolia reflected the more cold-tolerant temperament of the first species. We also discovered that the three southern European peninsulas as well as Turkey harboured glacial refuge populations for F. angustifolia, whereas F. ornus survived glaciations in the Appennine and Balkan peninsulas and Turkey without exchanging genes with the other two species ( Figure 10). My subsequent work on Fraxinus focussed on the colonization of the northern range margin of the species in Norway in a collaboration with Mari Mette Tollefsrud (NIBIO, Norway). ...

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... maternally transmitted plastid DNA markers to trace historical seed dispersal, we showed that the Norwegian coast was colonized by the main eastern European plastid DNA lineage ( Tollefsrud et al. 2016). Nuclear genetic diversity declined towards the north, suggesting successive colonization bottlenecks ( Figure 11; Tollefsrud et al. 2016). With the spread since the 1990s of ash dieback, an ascomycete pest causing large-scale mortality in European ash across Europe ( Pautasso et al. 2013), this phylogeographic work of the Fraxinus host is of interest to many researchers. ...

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... within the Pyrenees (Pinus uncinata Ram.) and the Alps Pyrenees (P. uncinata and P. mugo s.s.) were well-connected through pollenmediated gene flow since the last glaciation, and Alpine populations of P. uncinata exhibited a common gene pool with P. mugo s.s., so that geography was a better predictor of genetic structure in the complex than botanical species membership ( Figure 12) ). ...

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... Ma) than in the presentday Sahara (ca. 7 Ma, Figure 13) (Senut et al. 2009). Plant lineages in the south of the continent thus had time to adapt to a changing climate. ...

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... Flora -The Rand Flora is a well-known floristic pattern in which unrelated plant lineages show similar disjunct distributions in the continental margins of Africa and adjacent islands -Macaronesianorthwest Africa, Horn of Africa-Southern Arabia, Eastern Africa, and Southern Africa. These lineages are now separated by environmental barriers such as the arid regions of the Sahara and Kalahari deserts or the tropical lowlands of Central Africa ( Figure 13, right panel). To provide a temporal framework for the Rand Flora pattern, I collaborated with Isabel Sanmartín's team to date the age of geographic disjunctions using published plastid DNA sequence data from 17 lineages in 12 angiosperm families ( Figure 14). ...

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... lineages are now separated by environmental barriers such as the arid regions of the Sahara and Kalahari deserts or the tropical lowlands of Central Africa ( Figure 13, right panel). To provide a temporal framework for the Rand Flora pattern, I collaborated with Isabel Sanmartín's team to date the age of geographic disjunctions using published plastid DNA sequence data from 17 lineages in 12 angiosperm families ( Figure 14). Most disjunctions were dated to the Miocene and Pliocene, coinciding with the onset of a major aridification trend, with sub-humid taxa (e.g., Sideroxylon, Sapotaceae) diverging earlier and those with more xeric affinities (e.g., Campylanthus, Plantaginaceae) diverging later ( Pokorny et al. 2015). ...

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... results revealed that also locally widespread endemics may be alarmingly threatened, calling for urgent conservation action on the threatened ecosystems they inhabit. Tropical rainforests -West and Central African tropical rainforests, known as Guineo-Congolian rainforests ( Figure 13), constitute the second largest rainforest block in the world after the Amazon. These rainforests comprise ca. ...

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... et al. 2018). Similarly, in Santiria trimera (Burseraceae), we found that morphotypes with or without stilt roots corresponded to at least two species following the biological species concept in Central Africa (Figure 15; Koffi et al. 2010;Koffi 2010); this was later revised to be three species ( Ikabanga et al. 2017). In the Erythrophleum (Fabaceae) species complex, two species were suspected, E. suaveolens (Guill. ...

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... we were unable to identify any association between level of diversity and species life history traits nor any common phylogeographic pattern in most of these species ). However, a common pattern of North-South genetic discontinuity was observed in Lower Guinea in four tree species for which larger sample sizes were available (n>100), pointing to limited gene flow across the climatic hinge (meteorological equator) (Figure 16; Heuertz et al. 2014). The same North-South genetic discontinuity was observed in a review paper on nuclear and plastid DNA-based phylogeographic patterns of 13 rainforest tree species in Lower Guinea (Figure 17; Hardy et al. 2013). ...

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... a common pattern of North-South genetic discontinuity was observed in Lower Guinea in four tree species for which larger sample sizes were available (n>100), pointing to limited gene flow across the climatic hinge (meteorological equator) (Figure 16; Heuertz et al. 2014). The same North-South genetic discontinuity was observed in a review paper on nuclear and plastid DNA-based phylogeographic patterns of 13 rainforest tree species in Lower Guinea (Figure 17; Hardy et al. 2013). We observed several congruent genetic discontinuities in the study region, which supported the theory of PlioPleistocene rainforest refugia, however the location of these discontinuities challenged the classically proposed refuge locations by Maley (Hardy et al. 2013). ...

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... another study, we examined high-resolution plastid DNA patterns in eight tree species in Lower Guinea and detected significant congruence in genetic distinctiveness patterns mostly among five of the eight species, with strong congruence in the north of the study region ( Figure 18) ( Dauby et al. 2014). High distinctiveness in coastal Cameroon vs. low distinctiveness further east is compatible with a scenario of past climate-related fragmentation affecting primarily the forests in eastern Cameroon and northeastern Gabon, whereas in western Cameroon forests would have persisted in one or several refugia. ...

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... Ma ago. Very strong population genetic structure at SSRs with FST=0.73 among all populations, higher than the FCT=0.17 between the Yungas and Cerrado lineages, suggested signatures of repeated dispersal and local persistence in small isolated populations (Figure 19; Leal et al. submitted). ...

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... within a single population at a much narrower scale (ca. 150 m), we identified pronounced spatial genetic structure, which was best described by geography and altitude, i.e., by the population topography, comprising a central valley subpopulation as well as subpopulations dwelling on surrounding rocky outcrops, but not by corolla colour variation or the associated vegetation of individual plants ( Figure 21; Heuertz et al., in preparation). Through simulations, we inferred that the central valley of the population was mostly a source of gene flow, whereas individuals installed on the surrounding rocky outcrops were mostly recipients of gene flow. ...

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... inferred population splits and mixtures from the genome-wide allele frequency data and discovered more ancient divergence events in Africa vs. the Neotropics in a full coalescent analysis (Torroba-Balmori et al. unpublished). The French Guiana terra firme ecotype, Symphonia sp1, potentially a different species ( Baraloto et al. 2007b), was inferred to have a Neotropical origin ( Figure 31). Differentiation outlier loci associated to climate and soil data were identified, however, effects of geography and environment may be confounded due to the strong population genetic structure in this ancient tree species. ...