Seed Trait Changes in Dispersers' Guts and Consequences for Germination and Seedling Growth

Abstract

The effectiveness of a frugivore as a disperser of a plant is greatly determined by how fruits and seeds are handled in its mouth and its digestive tract. Although a number of studies have investigated the effect of avian ingestion on germination, we still know very little about the modifications to seeds during ingestion and the specific consequences on plant fitness. Here we investigate for the first time the different mechanisms by which germination patterns of seeds are modified following ingestion by frugivores. Specifically, we examine changes in seed mass, water content, permeability, seed coat thickness, texture, and resistance in two common Mediterranean fleshy-fruited plants, Phillyrea angustifolia and Myrtus communis, after ingestion by Eurasian Blackbirds, Turdus merula. We found a number of differences between the plant species: Phillyrea seeds lost mass, mainly due to water loss, and had thinner coats after gut passage, but Myrtus seeds did not. Seeds of both species showed increased permeability, while Myrtus seeds in particular became less resistant to breakage. No quantifiable changes in seed coat texture were detected in either species, although this trait was partly associated with differences in germination rate in Phillyrea. High intraspecific plant variation was found for most seed traits measured. Seed passage through birds' guts sped up germination in both species, especially in Myrtus. Increased permeability in seeds of both species following ingestion resulted in a higher germination rate. Moreover, seeds with thick coats (and in the case of Phillyrea, harder coats) germinated at a slower rate and produced seedlings that also grew more slowly, indicating a cost of coat thickness and/or hardness for seedling emergence. Results obtained here contribute to explaining the great heterogeneity in germination responses among and within plant species and the large variety of factors, both intrinsic and extrinsic to the plants, that influence such responses.

Seed germination of Phillyrea angustifolia L., a species of difficult propagation

“…In field experiments, few seeds were recovered after being eaten by animals (Grande et al, 2013), supporting our finding of a deleterious effect of acid. However, while seed germination increased when eaten by goats (Grande et al, 2013), as seen in our data when compared to seeds with an endocarp, germination decreased when eaten by birds (Traveset et al, 2008). These apparently contradictory results may be explained on the basis of inter-population variability in endocarp permeability and hardness, as previously suggested for other Mediterranean species (Correia et al, 2014).…”

A reassessment of the role of simple seed traits in mortality following herbivore ingestion

“…Until this date, we still lack knowledge on the effect of suchlike attributes for dry-fruited herbs, whereas for fleshy-fruited shrubs and trees they are more often dealt with (e.g. in ornithochory; Traveset 1998;Traveset et al 2008).…”

High-quality seed dispersal by fruit-eating fishes in Amazonian floodplain habitats

“…Since frugivores can improve the germination success of seeds by removing fruit pulp and/or by scarifying seeds (Traveset et al 2008), we compared seeds consumed by Wsh with uningested seeds encased within entire fruits and uningested seeds manually extracted from their fruit pulp (Samuels and Levey 2005). In the Wrst set of experiments, we used seeds dissected out of the digestive systems of wild-caught Colossoma and Piaractus.…”