Seed dispersal of the mistletoe Tristerix corymbosus: a comparative study in two biomes with different animal assemblages

Abstract

The dispersal process in plants links adults and their offspring. Mistletoes are shrubby stem-parasitic plants for which seed dispersal is a critical link in their life cycle. The mistletoe Tristerix corymbosus has a wide latitudinal distribution spanning two different biomes: the Chilean Matorral in the north, and the Temperate Forest of South America in the south. The assemblage of seed dispersers is different in these biomes. Tristerix corymbosus is dispersed by three bird species in the Chilean Matorral, but in the Temperate Forest it is dispersed only by arboreal marsupials of the genus Dromiciops. We aimed to assess the effectiveness of T. corymbosus seed dispersal by these disperser groups in terms of deposition of seeds in suitable sites (host plant species and branch size) and the effect of seed passage through the digestive tract. For this, we selected 22 localities throughout the distributional range of T. corymbosus, 8 in the Chilean Matorral and 14 in the Temperate Forest. In each locality, we recorded the cover percentage of different substrates (host plants, non-host plants, and bare soil) and the patterns of deposition of faeces. Also, we conducted seed germination trials using control seeds, hand-cleaned seeds, and seeds defecated by each disperser group. We found that both groups of animals are efficient dispersers of T. corymbosus seeds within each biome, because they deposit seeds in suitable sites and improve seed germination. However, the spatial segregation and the different behavior displayed by these groups may be contributing to a gradual process of genetic differentiation between mistletoes inhabiting these two biomes.