title: Nuclear microsatellite variation in Malagasy baobabs (Adansonia, Bombacoideae, Malvaceae) reveals past hybridization and introgression.
abstract: OBJECTIVE
  Adansonia comprises nine species, six of which are endemic to Madagascar. Genetic relationships between the Malagasy species remain unresolved due to conflicting results between nuclear and plastid DNA variation. Morphologically intermediate individuals between distinct species have been identified, indicative of interspecific hybridization. In this paper, microsatellite data are used to identify potential cases of hybridization and to provide insights into the evolutionary history of the genus on Madagascar.
  
  
  METHODS
  Eleven microsatellites amplified with new primers developed for Adansonia rubrostipa were used to analyse 672 individuals collected at 27 sites for the six Malagasy species and morphologically intermediate individuals. Rates of individual admixture were examined using three Bayesian clustering programs, STRUCTURE, BAPS and NewHybrids, with no a priori species assignment.
  
  
  RESULTS
  Population differentiation was coherent, with recognized species boundaries. In the four Malagasy species of section Longitubae, 8·0, 9·0 and 9·5 % of individuals with mixed genotypes were identified by BAPS, NewHybrids and STRUCTURE, respectively. At sites with sympatric populations of A. rubrostipa and A. za, NewHybrids indicated these individuals to be F2 and, predominantly, backcrosses with both parental species. In northern Madagascar, two populations of trees combining A. za and A. perrieri morphology and microsatellite alleles were identified in the current absence of the parental species.
  
  
  CONCLUSIONS
  The clear genetic differentiation observed between the six species may reflect their adaptation to different assortments of climate regimes and habitats during the colonization of the island. Microsatellite variation reveals that hybridization probably occurred in secondary contact between species of section Longitubae. This type of hybridization may also have been involved in the differentiation of a local new stabilized entity showing specific microsatellite alleles and morphological characters, suggesting a potential role of hybridization in the recent history of diversification on Madagascar.
authors.affiliation: DP Forêts et Biodiversité Madagascar (CIRAD, Université d'Antananarivo, FOFIFA), BP 853, Antananarivo 101, Madagascar.
authors.forename: Jean-Michel
authors.initials: JM
authors.lastname: Leong Pock Tsy
authors.forename: Roselyne
authors.initials: R
authors.lastname: Lumaret
authors.forename: Elodie
authors.initials: E
authors.lastname: Flaven-Noguier
authors.forename: Mathieu
authors.initials: M
authors.lastname: Sauve
authors.forename: Marie-Pierre
authors.initials: MP
authors.lastname: Dubois
authors.forename: Pascal
authors.initials: P
authors.lastname: Danthu
mesh_terms: D000483:Alleles; D014644:Genetic Variation; D006824:Hybridization, Genetic; D008270:Madagascar; D019660:Malvaceae / Q000235:genetics*; D018895:Microsatellite Repeats; D058974:Phylogeography
keywords: Adansonia; Madagascar; Nuclear microsatellite (nSSR) variation; baobab; genetic structure; hybridization; introgression