Diversidade genética neutra e variabilidade genética quantitativa de Tabebuia aurea (Silva Manso) Benth. & Hook.f. ex S. Moore (Bignoniaceae) em escala de paisagem

Abstract

Because of the rapid conversion of the Cerrado for agricultural expansion, this study evaluated the effects of landscape metrics on neutral genetic diversity, adaptive variation, and the evolutionary potential of Tabebuia aurea. We used a multi-scale geographic approach and two levels of analysis to select five landscapes, each with two sampling sites located in the central and southern regions of Goiás state. Three landscapes were located in legal reserve areas (ARL) on rural properties, with sampling sites in different habitat fragments; the other two landscapes were in located conservation units (UC), with sampling sites in the same habitat fragment. To estimate neutral genetic diversity indices (He, AR, and FST), we used genotypes from 10 microsatellite loci obtained from approximately 60 adult individuals at each sampling site. To assess adaptive variation and evolutionary potential, we measured seed size and mass and then planted the seeds in a greenhouse experiment with completely randomized blocks. We also measured several seedling traits related to initial growth and biomass. Neutral genetic diversity was higher (He and AR) at sites with less habitat, while neutral genetic differentiation (FST) was lower in landscapes with less habitat. The clustered distribution and synchronous flowering of T. aurea may cause pollinators to remain on the same plant or among nearby individuals because of the high availability of resources. These processes may promote self-fertilization and/or short-distance pollen dispersal, reducing genetic diversity within sampling sites and increasing genetic differentiation in landscapes with more habitat. Regarding adaptive variation in seeds and seedlings of T. aurea, seed size (DLS) was greater at sites with more habitat. Because seeds are wind-dispersed, larger seeds may disperse over shorter distances, increasing genetic differentiation and reducing genetic diversity. The evolutionary potential (CVg%) for root length (CR) and number of leaves (NF) increased as habitat amount decreased. Seedlings with more leaves can use sunlight more efficiently, while seedlings with longer roots can access water in deeper water tables. The evolutionary potential (CVg%) for transverse seed diameter (DTS) decreased with greater compositional heterogeneity, whereas the evolutionary potential (CVg%) for root dry mass (MSR) increased with greater compositional heterogeneity. Larger seeds may disperse shorter distances by wind, reducing genetic diversity, but they may also germinate more successfully; seedlings that allocate more biomass to roots may store more water 15 during the dry season. The evolutionary potential shown by these adaptive quantitative traits indicates that populations still have sufficient variation to respond to selection and environmental change. Landscapes with less habitat may be more stressful for plant species because of lower plant density, edge effects, and the negative impacts of agroecosystems. In these landscapes, longer roots may improve water uptake, increase survival, and reduce mortality caused by fire. Despite the recent expansion of agriculture in Central Brazil, landscape changes are already affecting the neutral and adaptive variation of T. aurea. Several populations showed low adaptive genetic variation for some traits and may therefore have limited evolutionary capacity, which could compromise the long-term persistence of the species. Because legal reserves on rural properties (ARL) showed the highest neutral genetic diversity, they should be maintained to support biodiversity conservation.