Fruit Laxatives and Seed Passage Rates in Frugivores: Consequences for Plant Reproductive Success

Abstract

To explore how plants may influence dispersal of their own seeds by manipulating the behavior and physiology of their dispersers, we studied the effect of a soluble chemical (or chemicals) in the fruits of Witheringia solanacea (Solanaceae), a Costa Rican cloud forest shrub, on passage of its seeds through the guts of one of its major dispersers, the Black—faced Solitaire, Myadestes melanops (Muscicapidae: Turdinae). Using artificial fruits containing natural seeds, we found that the presence of a crude pulp extract reduced the median seed retention time by nearly 50%. Estimation of seed dispersal distance as a function of retention time suggested that more rapid seed passage results in shorter average dispersal distances, especially for seeds retained <20 min. At the same time, germination trials revealed that seeds voided rapidly were far more likely to germinate than those remaining longer in Myadestes guts. We propose that “laxative” chemical(s) in Witheringia fruits balance these positive and negative consequences of ingestion by Myadestes.

Potential seed dispersal by Didelphis albiventris (Marsupialia, Didelphidae) in highly disturbed environment

“…Izhaki et al 1995). Seed germination success decreases as retention time increases (Murray et al 1994), which may explain low germination frequency of small consumed seeds (Traveset & Verdú 2002) in this study. Germination tests conducted in Petri dishes (used in this study) are also intermediate to detect differences between natural habitats and greenhouses.…”

Relationship between seed retention time in bird's gut and fruit characteristics

“…How quickly and how thoroughly seeds are processed has important evolutionary consequences for both fruiting plants and frugivores (Herrera 1995;Murray et al 1994). Fruits are generally considered to be a food resource high in bulk (Herrera 1987), and bulk overloads the gut thereby reducing ingestion rate.…”

“…There are, however, various conflicts between fruiting plants and frugivorous birds, for example, fruit pulp production is costly for plants, but provides frugivores with energy (Sorensen 1984;Fukui 1996). Fruiting plants and frugivorous birds are also in conflict over seed retention time (SRT), which is defined here as: the time from ingesting a fruit to the time when its seed(s) are eliminated, corresponding to the time spent passing through the bird's digestive system.Several studies have suggested that seed dispersal distance is a function of SRT, however, small seeds tend to be dispersed further (Hoppes 1988;Murray et al 1994), indicating a relationship between seed size and SRT. Small seeds tend to remain in the gut longer than large seeds.…”

“…Several studies have suggested that seed dispersal distance is a function of SRT, however, small seeds tend to be dispersed further (Hoppes 1988;Murray et al 1994), indicating a relationship between seed size and SRT. Small seeds tend to remain in the gut longer than large seeds.…”

Effects of gut passage on the germination of seeds ingested by didelphid marsupials in a neotropical savanna

“…However, considering the relationship between seed size and disperser size (Casella & Cáceres 2006;Lessa & Costa 2010), it has been observed that smaller seeds remain trapped in the digestive system for a longer period of time than do larger seeds (Jordano 1992). A longer seed retention period reduces germinability (Murray 1994) or germination time, which may explain differences in germinability and germination time of very small seeds, such as C. urceolata (~ 1.0 mm) and P. crassifolium (~ 0.6 mm) eaten by larger species, such as D. albiventris. Therefore, the simple passage through the digestive tract of the disperser is not a prerequisite for increasing the germination of gut-passed seeds (Cantor et al 2010).…”