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ABSTRACT Diet and host identity play fundamental roles in digestive physiology and the assembly of gut microbial communities. Research shows that microbial communities are plastic, with abundances of taxa and community interactions exhibiting changes in response to diet. Few studies considering the influence of diet on host and microbial plasticity disentangle the unique roles of specific nutrients, such as protein and fiber. Additionally, in the context of host–microbiome interactions, few studies have explored how host dietary strategies shape the plastic responses of microbial communities within the host digestive tract. To address these current gaps, we fed rodents with distinct dietary strategies (Peromyscus leucopus, Microtus montanus and Onychomys torridus) diets varying in fiber and protein content. Species varied in the degree of cecum size plasticity, with the carnivore showing no significant changes and the omnivore responding to both fiber and protein manipulation. There were also differences in the diversity indices of bacterial and fungal communities across hosts, and the microbes driving those differences were largely unique across rodent species. Additionally, community network interactions varied across treatments, and hub taxa that play a role in regulating network properties were identified. For example, bacteria in the Eubacterium groups, which are known to aid in fiber fermentation, were identified as hub taxa in all three species, but no group shared the same Eubacterium as a hub taxa. Overall, our data suggest that hosts with unique dietary strategies and their microbiomes respond uniquely to changes in the nutrient composition of their diets. 

ABSTRACT To efficiently digest food resources that may vary spatially and temporally, animals maintain physiological flexibility across levels of organization. For example, in response to dietary shifts, animals may exhibit changes in the expression of digestive enzymes, the size of digestive organs or the structure of their gut microbiome. A ‘Grand Challenge’ in comparative physiology is to understand how components of flexibility across organizational levels may scale to cumulatively determine organismal performance. Here, we conducted feeding trials on three rodent species with disparate feeding strategies: herbivorous montane voles (Microtus montanus), omnivorous white-footed mice (Peromyscus leucopus) and carnivorous grasshopper mice (Onychomys torridus). For each species, four groups of individuals were presented with diets that varied in carbohydrate, fiber and protein content. After 4–5 weeks, we measured organismal performance in the form of nutrient digestibility (dry matter, nitrogen, fiber). We also measured gut anatomy and organ size, and conducted enzyme assays on various tissues to measure activities of carbohydrases and peptidases. We found some shared physiological responses, e.g. fiber generally increased gut size across species. However, the specifics of these responses were distinct across species, suggesting different capacities for flexibility. Thus, in the context of digestion, we still lack an understanding of how flexibility across organizational levels may scale to determine whole-animal performance. 

Abstract Mice in the diverse genus Peromyscus are emerging as important models in the study of acoustic communication. However, reports on vocal repertoires exist for only 8 of the 56 currently recognized species. Descriptions of acoustic content and context are necessary to facilitate comparative studies. In this study, we present the first recordings of wild-captured pinyon mice (Peromyscus truei) in the laboratory in different social contexts. Similar to other Peromyscus species, pinyon mice produced four general types of vocalizations, including sustained vocalizations (SVs), barks, simple sweeps, and complex sweeps. SVs were produced primarily by females in social isolation, highlighting the potential significance of SVs in female advertisement behavior. While agonistic barks were rare, simple and complex sweeps were reliably produced in response to olfactory cues from same- and opposite-sex mice, and in paired contexts. Opposite-sex pairs produced significantly more complex sweeps than same-sex pairs, consistent with the well-supported function of sweeps in coordinating close-distance interactions. In addition, females produced sweeps with lower peak frequencies following separation from their social partner, indicative of a sex-specific mechanism to facilitate advertisement to potential mates and competitors. Together, our findings highlight the importance of social context in rodent vocal production, the significance of female vocal behavior, and the continued need to sample understudied species to better understand similarities and differences in rodent communication systems. 

Elaborate animal communication displays are often accompanied by morphological and physiological innovations. In rodents, acoustic signals used in reproductive contexts are produced by two distinct mechanisms, but the underlying anatomy that facilitates such divergence is poorly understood. ‘Audible’ vocalizations with spectral properties between 500 Hz and 16 kHz are thought to be produced by flow-induced vocal fold vibrations, whereas ‘ultrasonic’ vocalizations with fundamental frequencies above 19 kHz are produced by an aerodynamic whistle mechanism. Baiomyine mice (genus Baiomys and Scotinomys) produce complex frequency modulated songs that span these traditional distinctions and represent important models to understand the evolution of signal elaboration. We combined acoustic analyses of spontaneously vocalizing northern pygmy mice (B. taylori) mice in air and light gas atmosphere with morphometric analyses of their vocal apparatus to infer the mechanism of vocal production. Increased fundamental frequencies in heliox indicated that pygmy mouse songs are produced by an aerodynamic whistle mechanism supported by the presence of a ventral pouch and alar cartilage. Comparative analyses of the larynx and ventral pouch size among four additional ultrasonic whistle-producing rodents indicate that the unusually low ‘ultrasonic’ frequencies (relative to body size) of pygmy mice songs are associated with an enlarged ventral pouch. Additionally, mice produced shorter syllables while maintaining intersyllable interval duration, thereby increasing syllable repetition rates. We conclude that while laryngeal anatomy sets the foundation for vocal frequency range, variation and adjustment of central vocal motor control programs fine tunes spectral and temporal characters to promote acoustic diversity within and between species. 

Abstract The efficacy of animal acoustic communication depends on signal transmission through an oft-cluttered environment. Anthropogenic-induced changes in vegetation may affect sound propagation and thus habitat quality, but few studies have explored this hypothesis. In the southwestern United States, fire suppression and cattle grazing have facilitated displacement of grasslands by pinyon-juniper woodlands. Northern grasshopper mice ( Onychomys leucogaster ) inhabit regions impacted by juniper encroachment and produce long-distance vocalizations to advertise their presence to conspecifics. In this study, we coupled acoustic recordings and electrophysiological measurements of hearing sensitivity from wild mice in the laboratory with sound transmission experiments of synthesized calls in the field to estimate the active space (maximum distance that stimuli are detected) of grasshopper mouse vocalizations. We found that mice can detect loud (85 dB SPL at 1 m) 11.6 kHz vocalizations at 28 dB SPL. Sound transmission experiments revealed that signal active space is approximately 50 m. However, we found no effect of woody plant encroachment on call propagation because juniper and woody plant density were inversely associated and both present barriers to a 9 cm mouse advertising at ground level. Our data indicate that woody plant encroachment does not directly impact the efficacy of grasshopper mouse communication, but vegetation shifts may negatively impact mice via alternative mechanisms. Identifying the maximum distance that vocalizations function provides an important metric to understand the ecological context of species-specific signalling and potential responses to environmental change. 

Abstract Measurements of fecal pellet size can provide important information about wild mammals, such as body size and demographic information. Previous studies have not rigorously tested whether diet can confound these measurements. Furthermore, it is unknown whether diet might alter fecal dimensions directly or through changes in animal physiology. Here, we studied three closely related rodent species that differ in natural feeding strategies. Individuals were fed diets that varied in protein and fiber content for 5 weeks. We then measured body size, fecal widths and lengths, and the radius of the large intestine. Diet composition significantly changed fecal widths in all species. High-fiber content significantly increased fecal widths and would cause overestimations of body size if applied to wild feces. Using path analysis, we found that fiber can increase fecal widths both directly and indirectly through increasing the large intestine radius. Protein affected each species differently, suggesting that protein effects vary by species feeding strategy and existing physiology. Overall, diet and large intestine morphology can alter fecal pellet measurements. Studies using fecal measurements therefore must consider these effects in their conclusions. 

Diversification of animal vocalizations plays a key role in behavioral evolution and speciation. Vocal organ morphology represents an important source of acoustic variation, yet its small size, complex shape, and absence of homologous landmarks pose major challenges to comparative analyses. Here, we use a geometric morphometric approach based on geometrically homologous landmarks to quantify shape variation of laryngeal cartilages of four rodent genera representing three families. Reconstructed cartilages of the larynx from contrast-enhanced micro-CT images were quantified by variable numbers of three-dimensional landmarks placed on structural margins and major surfaces. Landmark sets were superimposed using generalized Procrustes analysis prior to statistical analysis. Correlations among pairwise Procrustes distances were used to identify the minimum number of landmarks necessary to fully characterize shape variation. We found that the five species occupy distinct positions in morphospace, with variation explained in part by phylogeny, body size, and differences in vocal production mechanisms. Our findings provide a foundation for quantifying the contribution of vocal organ morphology to acoustic diversification. 

Acoustic communication is a fundamental component of mate and competitor recognition in a variety of taxa and requires animals to detect and differentiate among acoustic stimuli (Bradbury and Vehrencamp 2011). The matched filter hypothesis predicts a correspondence between peripheral auditory tuning of receivers and properties of species-specific acoustic signals, but few studies have assessed this relationship in rodents. We recorded vocalizations and measured auditory brainstem responses (ABRs) in northern grasshopper mice (Onychomys leucogaster), a species that produces long-distance calls to advertise their presence to rivals and potential mates. ABR data indicate the highest sensitivity (28.33 9.07 dB SPL re: 20 Pa) at 10 kHz, roughly corresponding to the fundamental frequency (11.6 ± 0.63 kHz) of longdistance calls produced by conspecifics. However, the frequency range of peripheral auditory sensitivity was broad (8-24 kHz), indicating the potential to detect both the harmonics of conspecific calls and vocalizations of sympatric heterospecifics. Our findings provide support for the matched filter hypothesis extended to include other ecologically relevant stimuli. Our study contributes important baseline information about the sensory ecology of a unique rodent to the study of sound perception.