# Phenotypic Quantitative Divergence Across Heterogeneous Environments in a Widespread Southern South American Tree

## TL;DR

This study explores how a widespread South American tree adapts to different environments through genetic and phenotypic changes.

## Contribution

The study provides new evidence of adaptive phenotypic divergence in Vachellia caven shaped by environmental and geographic factors.

## Key findings

- FST estimates showed significant genetic divergence among Vachellia caven populations.
- PST–FST comparisons indicated all traits were under diversifying selection.
- Fruit dimensions correlated with environmental variables like precipitation and temperature.

## Abstract

Phenotypic and genetic divergence along environmental gradients often reflects local adaptation in broadly distributed species. The Fabaceae family is one of the largest and most ecologically important angiosperm groups; it has a centre of diversity in South America and shows high versatility in arid and disturbed environments. Here, we selected Vachellia
caven, a native tree with ecological breadth and taxonomic complexity, to investigate whether phenotypic trait variation among populations reflects adaptive divergence. We examined neutral genetic differentiation in six varieties among populations from Argentina, quantified the phenotypic differentiation of quantitative traits by an ANOVA, and performed PST—FST comparisons. We also assessed correlations between phenotypic variation, environmental variables, genotypic variation, and geographic distances. FST estimates revealed significant genetic divergence (0.329), in line with isolation by distance and environmental heterogeneity. PST—FST comparisons showed that all traits were under diversifying selection, supporting the hypothesis of adaptive phenotypic variation. We further detected that fruit width and length were significantly correlated with specific environmental variables like precipitation and temperature. These findings confirm that phenotypic divergence in V. caven is shaped by both geographic and environmental factors. This study offers a preliminary insight into the local adaptation of the examined traits, highlighting how morphological and genetic differentiation has enabled V. caven to thrive in diverse environments and contributing information as to how to face climate change scenarios.