• PNAS Teaching Resources Portal
  • Science Sessions: The PNAS Podcast Program

Genetic data suggest a natural prehuman origin of open habitats in northern Madagascar and question the deforestation narrative in this region

  1. Lounès Chikhia,b,e,1
  1. aCentre National de la Recherche Scientifique, Université Paul Sabatier, Ecole Nationale de Formation Agronomique, and Unité Mixte de Recherche 5174 EDB (Laboratoire Évolution & Diversité Biologique), F-31062 Toulouse, France;
  2. bUniversité de Toulouse, Unité Mixte de Recherche 5174 EDB (Laboratoire Évolution & Diversité Biologique), F-31062 Toulouse, France;
  3. cUnité de Recherche 035 CEFS (Comportement et Écologie de la Faune Sauvage), Institut National de la Recherche Agronomique, F-31326 Castanet Tolosan Cedex, France;
  4. dUnité Mixte de Recherche 5185, Centre National de la Recherche Scientifique, Université Bordeaux “Aménagement, Développement Environnement, Santé, et Sociétés,” 33607 Pessac Cedex, France; and
  5. eInstituto Gulbenkian de Ciência, 2780-156 Oeiras, Portugal

  1. Edited by Karen B. Strier, University of Wisconsin, Madison, WI, and approved May 16, 2012 (received for review January 5, 2012)

  1. Fig. 1.
    View larger version:
    Fig. 1.

    Trends in forest cover change in the Daraina region between 1949 and 2002. (A) Circled letters on the satellite imagery of the north of Madagascar indicate the locations of the four places named in the main text and in Fig. 4: Ankarana massif (A), Irodo (B), Vohémar (C), and Andavakoaera (D). (B) Black dots on the map of the Daraina region show the sampling locations of the 105 P. tattersalli social groups genotyped. This figure shows that trends in forest cover change radically in the northwestern (deforestation) and southeastern (forest regeneration) parts of the region as exemplified by the two focus zones [detail (a) and detail (b)] for the periods 1949–1972, 1972–1994, and 1994–2002. The two focus zones are detailed in Fig. S1.

  2. Fig. 2.
    View larger version:
    Fig. 2.

    BF values for the four tested scenarios under the different sampling schemes. H1 corresponds to a contraction attributable to anthropogenic effects following the arrival of Europeans (0–500 Cal. YBP); H2 (500–1,000 Cal. YBP) corresponds to a contraction attributable to anthropogenic effects during the period for which first cities appeared in far northern Madagascar; H3 (1,000–2,000 Cal. YBP) corresponds to the first millennium of human presence, during which human densities were probably very low; and H4 (2,000–10,000 Cal. YBP) corresponds to a contraction caused by environmental factors before the arrival of humans in Madagascar. In the “global sample” analyses (green), samples were taken across the whole sampled area, ignoring any substructure identified in a previous study. In the KA (red) and KB (blue) analyses, the samples were taken only considering the KA and KB genetic clusters identified in a previous study (details are provided in Materials and Methods).

  3. Fig. 3.
    View larger version:
    Fig. 3.

    Most likely period for the start of the population decrease. This figure shows the value of the BF for fixed-length intervals of 500 y between 0 and 50,000 y ago and between 0 and 10,000 y ago (i.e., the Holocene period). The BF measures the weight of evidence for the hypothesis that the population started to decrease in a given interval (Ha) vs. any other time period (Hb). The different solid lines correspond to different sampling strategies described in Materials and Methods: red (genetic unit KA), blue (genetic unit KB), and green (global sample). BF = 1 indicates that Ha and Hb are equally likely. BF values greater (or smaller) than 1 support Ha (or Hb). We considered BF values >7 as significant evidence for Ha. We indicated, along the time frame, the intervals corresponding to the four tested scenarios (H1–H4) and the historical, palynologicial, and paleontological evidence discussed in the main text.

Online Impact