Spatial genetic structure and mating system in forest tree populations from seasonally dry tropical forests: a review

Gene dispersal processes shape demographic and microevolutionary dynamics of tree species. Gene dispersal patterns can be studied by spatially explicit methods. Spatial genetic structure (SGS), summarized in the Sp statistic, provides indirect estimates of gene dispersal across generations for a known or assumed population effective density. Sp is modulated by exogenous and endogenous factors including the mating system that can be assessed using outcrossing rates ( t m ). Knowledge on t m and Sp are particularly important for the conservation of species in fragmented biomes such as seasonally dry tropical forests (SDTF). The main aim of this review was to evaluate putative drivers of Sp and t m , and their consequences for gene dispersal in tree species from SDTF. We reviewed 59 genetic studies on SDTF tree species published between 2000 and 2020 and extracted data on propagule dispersal, successional stages, seasonality, mating system, population density, landscape features, type of molecular markers, pairwise kinship in the first distance class ( F 1 ), Sp statistic, mean gene dispersal distance ( σ g ), and multilocus outcrossing rates ( t m ) . Sp was significantly associated with the mating system where Sp (outcrossing) > Sp (mixed-mating), and population density where Sp was higher in high-density populations. Outcrossing rate was significantly associated with the type of propagule dispersal, where t m was higher in populations of plants pollinated by wind, and in those with animal-mediated seed dispersal, t m (zoochory) > t m (anemochory) > t m (autochory), and with successional stage where t m (late-successional) > t m (pioneer). These factors are relevant to inform management actions in conservation and restoration projects. Thus, the knowledge on the determinants of gene dispersal processes can help to rescue SDTF through sustainable management.