title: Elevation as a barrier: genetic structure for an Atlantic rain forest tree (Bathysa australis) in the Serra do Mar mountain range, SE Brazil.
abstract: Distance and discrete geographic barriers play a role in isolating populations, as seed and pollen dispersal become limited. Nearby populations without any geographic barrier between them may also suffer from ecological isolation driven by habitat heterogeneity, which may promote divergence by local adaptation and drift. Likewise, elevation gradients may influence the genetic structure and diversity of populations, particularly those marginally distributed. Bathysa australis (Rubiaceae) is a widespread tree along the elevation gradient of the Serra do Mar, SE Brazil. This self-compatible species is pollinated by bees and wasps and has autochoric seeds, suggesting restricted gene dispersal. We investigated the distribution of genetic diversity in six B. australis populations at two extreme sites along an elevation gradient: a lowland site (80-216 m) and an upland site (1010-1100 m.a.s.l.). Nine microsatellite loci were used to test for genetic structure and to verify differences in genetic diversity between sites. We found a marked genetic structure on a scale as small as 6 km (F ST = 0.21), and two distinct clusters were identified, each corresponding to a site. Although B. australis is continuously distributed along the elevation gradient, we have not observed a gene flow between the extreme populations. This might be related to B. australis biological features and creates a potential scenario for adaptation to the different conditions imposed by the elevation gradient. We failed to find an isolation-by-distance pattern; although on the fine scale, all populations showed spatial autocorrelation until ∼10-20 m. Elevation difference was a relevant factor though, but we need further sampling effort to check its correlation with genetic distance. The lowland populations had a higher allelic richness and showed higher rare allele counts than the upland ones. The upland site may be more selective, eliminating rare alleles, as we did not find any evidence for bottleneck.
authors.affiliation: Departamento de Biologia Vegetal, Instituto de Biologia, Universidade Estadual de Campinas - UNICAMP CP 6109, 13083-970, Campinas, SP, Brazil.
authors.forename: Talita Soares
authors.initials: TS
authors.lastname: Reis
authors.affiliation: Centro de Biologia Molecular e Engenharia Genética, Universidade Estadual de Campinas - UNICAMP CP 6010, 13083-970, Campinas, SP, Brazil.
authors.forename: Maísa
authors.initials: M
authors.lastname: Ciampi-Guillardi
authors.affiliation: Departamento de Genética, ESALQ/Universidade de São Paulo - USP 12418-900, Piracicaba, SP, Brazil.
authors.forename: Miklos Maximiliano
authors.initials: MM
authors.lastname: Bajay
authors.affiliation: Departamento de Biologia Vegetal, Instituto de Biologia, Universidade Estadual de Campinas - UNICAMP CP 6109, 13083-970, Campinas, SP, Brazil ; Centro de Biologia Molecular e Engenharia Genética, Universidade Estadual de Campinas - UNICAMP CP 6010, 13083-970, Campinas, SP, Brazil.
authors.forename: Anete Pereira
authors.initials: AP
authors.lastname: de Souza
authors.affiliation: Departamento de Biologia Vegetal, Instituto de Biologia, Universidade Estadual de Campinas - UNICAMP CP 6109, 13083-970, Campinas, SP, Brazil.
authors.forename: Flavio Antonio Maës
authors.initials: FA
authors.lastname: Dos Santos
keywords: Altitude; Rubiaceae; gene flow; genetic diversity; microsatellites