Maternal Gut Dysbiosis Alters Offspring Microbiota and Social Interactions.

Increasing application of antibiotics changes the gut microbiota composition, leading to dysbiosis of the gut microbiota. Although growing evidence suggests the potential role of gut dysbiosis as the cause of neurodevelopmental disorders and behavioral defects, a broad gap of knowledge remains to be narrowed to better understand the exact mechanisms by which maternal gut dysbiosis alters microbiota development and social interactions of offspring. Here, we showed that maternal gut dysbiosis during gestation is a critical determinant of gut microbiota and social interactions off mouse offspring. Gut microbiota of 2-week-old offspring showed significant changes in response to maternal antibiotic treatment. We even detected distinct effects of maternal oral antibiotics on gut microbiota of 14-week-old offspring. Compared to controls, offspring born to antibiotics-treated mothers displayed reduction in sociability and preference for social novelty, suggesting that the altered offspring social behavior was closely linked to dysbiosis of maternal gut microbiota. Our study opens the possibility to better understand the mechanism of how maternal gut microbiota vertically impairs social interactions of offspring in animal models, providing support to the maternal gut microbiota as a potential mediator between offspring microbiota and behaviors.

Tracking Animal-Dispersed Seedlings Using 15N Xylem Injection Method.

Although various seed-marking methods have been developed for seed dispersal, it remains difficult to track the actual patterns of seed dispersal and seedling recruitment. Thus, new labeling methods that accurately track seedling establishment along with seed movement would help us better understand seed dispersal. Here, we developed a new nondestructive method using 15N xylem injection to track seed dispersal and seedling recruitment based on the enriched isotopic signals in the mature seeds. Our results first showed that xylem injection of 15N successfully enriched 15N both in the acorns and seedlings of Quercus variabilis. By marking acorns and seedlings with 15N stable isotopes, we successfully tracked seedlings established from acorns dispersed by seed-eating animals in the field. Our xylem 15N injection caused little alteration to seeds and showed no significant effects on seed selection by seed-eating animals as well as seed germination and seedling establishment, verifying the validity of the 15N xylem injection method to track seedling establishment. Our xylem 15N injection method is expected to be a powerful tool for tracking seed dispersal and seedling recruitment mediated by seed-eating animals in seed dispersal ecology.

Radicle pruning by seed-eating animals helps oak seedlings absorb more soil nutrient.

Although radicle pruning has well been observed in plant-animal interactions, research has not been conducted to determine how radicle pruning by seed-eating animals regulates nutrition mobilization of cotyledonary reserves and absorption of soil nutrients. We used stable nitrogen isotopes to test how acorns of early-germinating oak species (Quercus variabilis, Q. aliena, and Q. mogolica) trade off nutrients in the cotyledons and those in the soil in response to radicle pruning by seed-eating rodents. Radicle pruning by rodents resulted in root branching in the 3 early-germinating oak species. Moreover, radicle pruning increased shoot dry weight and substantially reduced the root-to-shoot ratio of oak species. Corresponding to the decreased dry weight of roots and root-to-shoot ratio, the dry weight of the remnant cotyledons was higher after radicle pruning in the 3 oak species. We provided first evidence that radicle pruning by seed-eating animals improved seedling performance of early-germinating oaks by increasing absorption of nutrients from soil. The results indicate that early-germinating oak seedlings trade off nutrition budget by altering nutrient absorption from soil and reserve mobilization from cotyledons in response to radicle pruning by seed-eating animals. Our study provided new insight into the nutrition allocation mechanism of young seedlings in response to radicle pruning by seed-eating animals, reflecting a mutualistic interaction between early-germinating oak and food-hoarding animals.

Olfaction alters spatial memory strategy of scatter-hoarding animals.

Although it has been suggested that olfaction is closely interconnected with hippocampal systems, whether olfaction regulates spatial memory strategy remains never known. Furthermore, no study has examined how olfaction mediates spatial memory established on the external objects, for example, caches made by scatter-hoarding animals. Here, we experimentally induced nondestructive and reversible olfaction loss of a scatter-hoarding animal Leopoldamys edwardsi, to test whether and how olfaction regulates spatial memory to mediate cache recovery and pilferage. Our results showed that the normal L. edwardsi preferred to pilfer caches of others rather than to recover their own using accurate spatial memory (35.7% vs. 18.6%). Anosmic L. edwardsi preferred to recover the caches they made prior to olfaction loss rather than to pilfer from others relied on spatial memory (54.2% vs. 36.0%). However, L. edwardsi with anosmia showed no preference either to the caches they established after olfaction loss or caches made by others (25.8% vs. 29.1%). These collectively indicate that olfaction loss has a potential to affect new memory formation but not previously established spatial memory on caches. Our study first showed that olfaction modified spatial memory strategy in cache recovery and pilferage behaviors of scatter-hoarding animals. We suggest that future studies pay more attention to the evolution of olfaction and its relationship with spatial memory strategy.

Inter-trophic Interaction of Gut Microbiota in a Tripartite System.

Gut microbiota can be transmitted either environmentally or socially and vertically at intraspecific level; however, whether gut microbiota interact along trophic levels has been largely overlooked. Here, we characterized the gut bacterial communities of weevil larvae of Curculio arakawai that infest acorns of Mongolian oak (Quercus mongolica) as well as acorn-eating mammals, Siberian chipmunk (Tamias sibiricus), to test whether consumption of seed-borne larvae remodels the gut bacterial communities of T. sibiricus. Ingestion of weevil larvae of C. arakawai significantly altered the gut bacterial communities of T. sibiricus. Consequently, T. sibiricus fed larvae of C. arakawai showed higher capability to counter the negative effects of tannins, in terms of body weight maintenance, acorn consumption, N content in feces, urine pH, and blood ALT activity. Our results may first show that seed-borne insects as hidden players have a potential to alter the gut microbiota of seed predators in the tripartite system.

Exclusion of interspecific competition reduces scatter-hoarding of Siberian chipmunk Tamias sibiricus: A field study.

Although food availability and the abundance of seed predators have been postulated to affect seed dispersal, it is not clear how seed-eating animals modify their scatter-hoarding strategies in response to different levels of interspecific competition. We placed paired germinated and ungerminated acorns of Quercus mongolica on 30-cm high platforms to exclude potential interspecific competition of the predominant larder hoarders Apodemus peninsulae and Myodes rufocanus, to investigate seed dispersal by a predominant scatter-hoarder, Tamias sibiricus, in the field in north-eastern China. Our results showed that T. sibiricus ate more acorns in situ in the absence of interspecific competition. In the presence of interspecific competition of A. peninsulae and C. rufocanus, however, more acorns were scatter-hoarded by T. sibiricus. Regardless of interspecific competition, germination of acorns showed no significant effects on seed dispersal patterns, inconsistent with the "seed perishability hypothesis" that animals avoid hoarding seeds with high perishability. Exclusion of interspecific competition, though relatively increasing the per capita seed abundance, appears to reduce seed dispersal, scatter-hoarding and seedling establishment. Therefore, we propose that moderate interspecific competition rather than competition exclusion may benefit seed scatter-hoarding and seedling establishment.