Abstract
Changes in landscape structure can affect essential population ecological features, such as dispersal and recruitment, and thus genetic processes. Here, we analyze the effects of landscape metrics on adaptive quantitative traits variation, evolutionary potential, and on neutral genetic diversity in populations of the Neotropical savanna tree Tabebuia aurea. Using a multi-scale approach, we sampled five landscapes with two sites of savanna in each. To obtain neutral genetic variation, we genotyped 60 adult individuals from each site using 10 microsatellite loci. We measured seed size and mass. Seeds were grown in nursery in completely randomized experimental design and 17 traits were measured in seedlings to obtain the average, additive genetic variance (Va) and coefficient of variation (CVa%), which measures evolvability, for each trait. We found that habitat loss increased genetic diversity (He) and allelic richness (AR), and decreased genetic differentiation among populations (FST), most likely due to longer dispersal distance of pollen in landscapes with lower density of flowering individuals. Habitat amount positively influenced seed size. Seeds of T. aurea are wind-dispersed and larger seeds may be dispersed to short distance, increasing genetic differentiation and decreasing genetic diversity and allelic richness. Evolvability (CVa%) in root length decreased with habitat amount. Savanna trees have higher root than shoot growth rate in the initial stages, allowing seedlings to obtain water from water tables. Landscapes with lower habitat amount may be more stressful for plant species, due to the lower plant density, edge effects and the negative impacts of agroecosystems. In these landscapes, larger roots may provide higher ability to obtain water, increasing survival and avoiding dying back because of fire. Despite the very recent agriculture expansion in Central Brazil, landscape changes are affecting neutral and adaptive variation in T. aurea. Several populations have low additive genetic variation for some traits and thus, may have limited evolvability, which may jeopardize species long-term persistence. The effect of habitat loss on highly variable neutral loci may only be detected after a certain threshold of population size is attained, that could become dangerously small masking important losses of heterozygosity endangering species conservation.
Highlights
Agricultural landscapes are occupying most of Neotropical savannas
Because genetic variability may be affected by effective population size (Ne), we modeled genetic parameters using both landscape metrics and Ne (Table 1)
Our findings show that contemporary changes in landscape affect genetic diversity and differentiation at neutral microsatellite loci among populations of T. aurea from the Cerrado biome
Summary
Agricultural landscapes are occupying most of Neotropical savannas. The Brazilian Cerrado biome is the largest Neotropical savanna and one of the world’s biodiversity hotspots because of its high level of endemism and threatening (Myers et al, 2000). Landscape changes may affect population connectivity and genetic diversity in different taxa (e.g., Dixo et al, 2009; Carvalho et al, 2015; Jackson and Fahrig, 2016; Moraes et al, 2018; GonzálezFernández et al, 2019). This occurs mainly due to reduction in population effective size and isolation (Gilpin and Soulé, 1986; Frankham et al, 1999). In this way, understanding how the still-ongoing landscape change affects savanna species may help designing sound conservation and management strategies
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