Mating patterns of an ambophilous dioecious dominant tree in fragmented Chaco Serrano forests

Abstract

Lithraea molleoides is a dominant dioecious tree native to the Chaco Serrano Forest, a highly fragmented and threatened ecoregion in central Argentina. The species has ambophily and is able to set seeds via apomixis, traits that may confer resilience to genetic erosion in fragmented forests. We analyzed the genetic diversity of adults and progeny from both continuous and fragmented forests of the Chaco Serrano ecoregion, and conducted paternity assignment and pollen flow analyses. Adult tree populations showed no differences in genetic diversity and structure between continuous and fragmented forests, suggesting they precede the events of habitat loss and fragmentation. In contrast, only the progeny from fragmented forests showed lower genetic diversity and increased inbreeding. Changes in pollinator assemblages in fragmented forests and a higher incidence of apomixis (i.e., only genotypes from female trees reflected in the progeny) may have contributed to reduced genetic diversity in the progeny. Contemporary pollen flow was more restricted in fragmented environments, probably due to changes in pollinator composition and limited wind pollination. While ambophily and apomixis provide reproductive assurance for L. molleoides, our study highlights they cannot prevent the genetic erosion observed in the progeny generated in fragmented forests. These findings have significant implications for conservation strategies aimed at preserving the genetic diversity and viability of L. molleoides populations in the last tracts of Chaco Serrano Forests.