A multi-study analysis of gut microbiome data from the blue mussel (Mytilus edulis) emphasises the impact of depuration on biological interpretation.

The blue mussel (Mytilus edulis) is a suspension feeder which has been used in gut-microbiome surveys. Although raw 16S sequence data are often publicly available, unifying secondary analyses are lacking. The present work analysed raw data from seven projects conducted by one group over 7 years. Although each project had different motivations, experimental designs and conclusions, all selected samples were from the guts of M. edulis collected from a single location in Long Island Sound. The goal of this analysis was to determine which independent factors (e.g., collection date, depuration status) were responsible for governing composition and diversity in the gut microbiomes. Results indicated that whether mussels had undergone depuration, defined here as voidance of faeces in a controlled, no-food period, was the primary factor that governed gut microbiome composition. Gut microbiomes from non-depurated mussels were mixtures of resident and transient communities and were influenced by temporal factors. Resident communities from depurated mussels were influenced by the final food source and length of time host mussels were held under laboratory conditions. These findings reinforce the paradigm that gut microbiota are divided into resident and transient components and suggest that depuration status should be taken into consideration when designing and interpreting future experiments.

Nylon microfibers develop a distinct plastisphere but have no apparent effects on the gut microbiome or gut tissue status in the blue mussel, Mytilus edulis.

Ingestion of microplastics (MP) by suspension-feeding bivalves has been well-documented. However, it is unclear whether exposure to MP could damage the stomach and digestive gland (gut) of these animals, causing ramifications for organism and ecosystem health. Here, we show no apparent effects of nylon microfiber (MF) ingestion on the gut microbiome or digestive tissues of the blue mussel, Mytilus edulis. We exposed mussels to two low concentrations (50 and 100 particles/L) of either nylon MF or Spartina spp. particles (dried, ground marsh grass), ca. 250-500 µm in length, or a no particle control laboratory treatment for 21 days. Results showed that nylon MF, when aged in coarsely filtered seawater, developed a different microbial community than Spartina spp. particles and seawater, however, even after exposure to this different community, mussel gut microbial communities resisted disturbance from nylon MF. The microbial communities of experimental mussels clustered together in ordination and were similar in taxonomic composition and measures of alpha diversity. Additionally, there was no evidence of damage to gut tissues after ingestion of nylon MF or Spartina spp. Post-ingestive particle processing likely mediated a short gut retention time of these relatively large particles, contributing to the negligible treatment effects.

Beyond sound: bimodal acoustic calls used in mate-choice and aggression by red-eyed treefrogs.

Airborne sound signals function as key mediators of mate-choice, aggression and other social interactions in a wide range of vertebrate and invertebrate animals. Calling animals produce more than sound, however. When displaying on or near a solid substrate, such as vegetation or soil, they also unavoidably excite substrate vibrations because of the physics of sound production and of acoustic propagation, and these vibrations can propagate to receivers. Despite their near ubiquity, these vibrational signal components have received very little research attention and in vertebrates it is unknown whether they are relevant to mate-choice, an important driver of evolutionary divergence. Here, we show that female red-eyed treefrogs are more than twice as likely to choose a male mating call when airborne sound is paired with its corresponding substrate vibrations. Furthermore, males of the same species are more aggressive towards and display a greater range of aggressive behaviors in response to bimodal (sound and vibration) versus unimodal (sound or vibration alone) calls. In aggressive contexts, at least, air- and substrate-borne signal components function non-redundantly. These results are a clear demonstration that vibrations produced by a calling animal can function together with airborne sound to markedly enhance the function of a signal. If this phenomenon proves widespread, this finding has the potential to substantially influence our understanding of the function and evolution of acoustic signals.