The effects of seed detectability and seed traits on hoarding preference of two rodent species

Plant hormones mediate the interaction between oak acorn germination and rodent hoarding behaviour

The interaction between animals and plants for seed dispersal and predation has received much attention; however, the underlying physiological mechanisms driving the responses of both seeds and animals remain unclear. We conducted a series of behaviour and physiology experiments to examine the role of plant hormones in regulating seed germination and rodent hoarding behaviour in the Quercus variabilis and Leopoldamys edwardsi systems. We found that acorns that were partially consumed by rodents had increased gibberellin (GA) levels and shortened germination time. Rodents preferred scatter-hoarded abscisic acid (ABA)-treated and intact acorns but consumed germinated and GA-treated acorns; such treatment differences disappeared for inactivated acorns by boiling water. Moreover, we found that seven potential compounds may be linked to seed germination and rodent hoarding behaviour. Our results indicate that acorns of oak showed rapid germination when facing predation risk, while rodents could identify the germination status of seeds for hoarding; GA and ABA may play an important role in regulating seed germination of oak and hoarding behaviour of rodents.

Phylogeny more than plant height and leaf area explains variance in seed mass

Although variation in seed mass can be attributed to other plant functional traits such as plant height, leaf size, genome size, growth form, leaf N and phylogeny, until now, there has been little information on the relative contributions of these factors to variation in seed mass. We compiled data consisting of 1071 vascular plant species from the literature to quantify the relationships between seed mass, explanatory variables and phylogeny. Strong phylogenetic signals of these explanatory variables reflected inherited ancestral traits of the plant species. Without controlling phylogeny, growth form and leaf N are associated with seed mass. However, this association disappeared when accounting for phylogeny. Plant height, leaf area, and genome size showed consistent positive relationship with seed mass irrespective of phylogeny. Using phylogenetic partial R2s model, phylogeny explained 50.89% of the variance in seed mass, much more than plant height, leaf area, genome size, leaf N, and growth form explaining only 7.39%, 0.58%, 1.85%, 0.06% and 0.09%, respectively. Therefore, future ecological work investigating the evolution of seed size should be cautious given that phylogeny is the best overall predictor for seed mass. Our study provides a novel avenue for clarifying variation in functional traits across plant species, improving our better understanding of global patterns in plant traits.

Gut microbiota is associated with spatial memory and seed-hoarding behavior of South China field mice (Apodemus draco)

Background

Scatter-hoarding animals store food in multiple locations within their home range and rely on spatial memory for subsequent localization and retrieval. The relationship between memory and scatter-hoarding behavior has been widely demonstrated, but the association of gut microbiota with spatial memory and seed-hoarding behavior of animals remains unclear.

Methods

In this study, by using enclosure behavior tests, memory tests including an object location test (OLT) and a novel object recognition test (NORT), and fecal microbiota transplantation (FMT) experiment, we evaluated the role of gut microbiota in affecting the memory and seed-hoarding behavior of rodents. According to their scatter-hoarding intensity, South China field mice (Apodemus draco) were divided into scatter-hoarding group (SG) and non-scatter-hoarding group (NG).

Results

We found that the SG performed better than the NG in the NORT. FMT from SG donor mice altered the NG recipient mice's gut microbiota structure. Further tests demonstrated FMT from SG donor mice increased memory of NG recipient mice in laboratory tests and seed larder hoarding intensity of NG recipient mice in enclosures.

Conclusion

Our results suggest gut microbiota could modulate the memory and seed-hoarding behavior of animals.

Conflicting selection pressures on seed size and germination caused by carnivorous seed dispersers

Plants produce nutritious, fleshy fruits that attract various animals to facilitate seed dispersal and recruitment dynamic. Species-specific differential selection of seed size by multiple frugivorous disperser assemblages may affect the subsequent germination of the ingested seeds. However, there is little empirical evidence supporting this association. In the present study, we documented conflicting selection pressures exerted on seed size and germination by five frugivorous carnivores on a mammal-dispersed pioneer tree, the date-plum persimmon (Diospyros lotus), in a subtropical forest. Fecal analyses revealed that these carnivores acted as primary seed dispersers of D. lotus. We also observed that seed sizes were selected based on body mass and were species-specific, confirming the "gape limitation" hypothesis; three small carnivores (the masked palm civet Paguma larvata, yellow-throated marten Martes flavigula, and Chinese ferret-badger Melogale moschata) significantly preferred to disperse smaller seeds in comparison with control seeds obtained directly from wild plants whereas the largest Asiatic black bears (Ursus thibetanus) ingested larger seeds. Seeds dispersed by medium-sized hog badgers (Arctonyx albogularis) were not significantly different from control seeds. However, regarding the influence of gut passage on seed germination, three arboreal dispersal agents (martens, civets, and bears) enhanced germination success whereas terrestrial species (ferret-badgers and hog badgers) inhibited the germination process compared with undigested control seeds. These conflicting selection pressures on seed size and germination may enhance the heterogeneity of germination dynamics and thus increase species fitness through diversification of the regeneration niche. Our results advance our understanding of seed dispersal mechanisms and have important implications for forest recruitment and ecosystem dynamics.

Density-Dependent Seed Predation of Quercus wutaishanica by Rodents in Response to Different Seed States

The predation and/or dispersal of Quercus seeds by rodents play an important role in the creation of the tree species. The present study examined the effects of community habitats on the predation and dispersal of Quercus wutaishanica seeds by rodents. We released seeds with densities set at 2, 4, 8, 16, and 32 seed square meter with litter cover, soil burial, and bare ground in the Liupan Mountains National Nature Reserve in the Ningxia Hui Autonomous Region, northwest China. The results showed that (1) the litter cover and soil burial significantly increased the seed survival probability compared with bare ground treatments, especially the predation in situ (PIS) (p < 0.05). Both the scatter hoarding (SH) and larder hoarding (LH) for litter cover and soil burial were significantly increased compared with bare ground (p < 0.05). (2) The large seeds are preferentially predated after dispersal and their long-distance dispersal (>5 m) was significantly greater than that of small seeds (p < 0.05), while small seeds are more likely to be preyed on in situ or during short-distance dispersal (<3 m). (3) The Q. wutaishanica seed predation by rodents increased at a high density rather than at a low density, indicating a negative density-dependent predation. These findings provide insights into the ecological characteristics of Quercus tree regeneration and shed light on the coexistence between rodents and different-sized seeds.