Digestive challenges for vertebrate animals: microbial diversity, cardiorespiratory coupling, and dietary specialization

Diverse diets and low-fiber, low-tannin foraging preferences: Foraging criteria of Tibetan macaques (Macaca thibetana) at low altitude in Huangshan

Nutrient composition and food availability determine food choices and foraging strategies of animals, while altitude and geographical location affect species distribution and food availability. Tibetan macaques (Macaca thibetana) have sophisticated foraging strategies as the largest species in Macaca. They are important in understanding the ecological evolution of the entire genus. However, the mechanism of food selection in Tibetan macaques at low altitudes remains unclear. In this study, we researched a wild Tibetan macaques group (Tianhu Mountain Group, 29 individuals) living in a low‐altitude area around Mt. Huangshan, Anhui Province, China. We used instantaneous scan sampling to observe these macaques' foraging behavior from September 2020 to August 2021. We recorded the dietary composition and food availability, compared the nutrient content of staple food and non‐food items, and analyzed the role of key nutrients in food selection. We found that Tibetan macaques forage on 111 plants belonging to 93 genera and 55 families. The food types included fruits (52.5%), mature leaves (17.0%), bamboo shoots (14.4%), young leaves (6.3%), flowers (4.5%), others (2.1%), stems (1.9%), and tender shoots (1.3%). Tibetan macaques forage for a maximum of 76 plant species during spring. However, dietary diversity was highest during summer (H′ = 3.052). Monthly fruit consumption was positively correlated with food availability. Staple foods are lower in fiber, tannin, and water than non‐foods. In addition, the time spent foraging for specific foods was negatively correlated with the fiber and tannin content of the food. The results showed that Tibetan macaques' foraging plant species and food types were diverse, and their foraging strategies varied seasonally. Our findings confirmed the effect of nutrients on food choice in Tibetan macaques. We highlighted the important role of fiber and tannin in their food choices and suggested that the foraging behavior of Tibetan macaques is highly flexible and adaptive.

Comparative analysis of the fecal bacterial communities of hawksbill sea turtles (Eretmochelys imbricata) and green sea turtles (Chelonia mydas)

Hawksbill sea turtles (Eretmochelys imbricata) are important for maintaining healthy coral reef ecosystems currently qualify as 'critically endangered' by the IUCN. Their gut microbiota is closely linked to host nutrition and health, however, the gut microbiota of hawksbill sea turtles from a natural reserve remains unclear. Therefore, exploring their microbial community structure in a natural reserve may provide valuable information on strategies for protecting this species. In this study, we investigated hawksbill sea turtle fecal microbial communities from a natural reserve using 16S metagenomics and compared the gut microbiota from fecal samples of hawksbill and green sea turtles (Chelonia mydas). The results indicated that the structure of fecal microbial communities was significantly different between hawksbill and green sea turtles. In hawksbill sea turtles, the three dominant phyla were Bacteroidetes, Firmicutes, and Fusobacteria, whereas the fecal microbial communities of green sea turtles were mainly composed of Firmicutes, Bacteroidetes, and Proteobacteria. Among the hawksbill sea turtle fecal microbes, the predominant genera were Cetobacterium and Rikenell, whereas in green sea turtles, the predominant genera were Bacteroides and Paludibacter. In addition, predictive metagenomic analysis indicated that sugar catabolism was enriched in green sea turtle fecal microbiota, whereas pathways related to secondary metabolite production were enriched in hawksbill sea turtle fecal microbiota. Our study provides preliminary data on the fecal microbiota features of sea turtles from the natural reserve which may contribute to the management of the food requirements and long-term conservation of hawksbill sea turtles.

Metagenomic comparison of gut communities between hawksbills (Eretmochelys imbricata) and green sea turtles (Chelonia mydas)

The gut microbiota is closely linked to host nutrition, immunity, and health. Here, metagenomic analysis was conducted to elucidate the taxonomic and functional diversity of gut communities from hawksbills and green sea turtles. In terms of diversity and abundance, the gut microbiota of herbivorous green sea turtles showed a higher bacterial diversity and richness than that of hawksbills. Firmicutes dominated in all groups; however, the phylum Proteobacteria showed a higher relative abundance in hawksbills. Several metabolic pathways displayed broad prevalence and high relative abundances in the two sea turtle populations. Antibiotic resistance genes (ARGs) responsible for resistance to glycopeptide and tetracycline were the most abundant in all samples. In ARGs, the subtype macB was the most abundant in the two different sea turtle populations; however, evgS, bcrA, and efrA were more abundant in the green sea turtles, while in the hawksbills, tetT and tetB(P) were more abundant. Among mobile genetic elements (MGEs), the abundance of 16 MGE types showed a significant difference between the two sea turtle populations. MGE type transposase and plasmid were the most abundant in the two sea turtle populations. Additionally, gene functions were enriched in carbohydrate esterases, glycoside hydrolases, and polysaccharide lyases in the green sea turtles, whereas genes related to glycosyltransferases and auxiliary activities were highly abundant in hawksbills. These metagenomic profiles provide further insights into the microbial diversities of the two types of sea turtles and provide valuable information for future conservation efforts.

Isolation and characterization of anaerobic bacteria with fiber degradation potential from faeces of Boselaphus tragocamelus grazing on semi arid Indian conditions

Hindgut of wild ruminants harbours diversified anaerobic bacteria with promising fiber degrading ability. Fibrolytic enzyme activity is strongly influenced by diet and host species which till date remains unexplored for harnessing their optimum benefits. The present study was conducted to isolate and characterize fiber degrading anaerobic bacteria from faeces of wild blue bull (Boselaphus tragocamelus) inhabiting in semiarid regions. A total of 167 isolates were obtained from 85 faecal samples using M-10 medium, on the basis of clear zones formed on Congo red plates 20 isolates were selected and designated as NLG1-20 for microscopic and biochemical characterization. Further, molecular confirmation was done by PCR analysis with universal 16S rDNA primers. All isolates were obligatory anaerobes except, NLG4, NLG19 and NLG20. Majority of the sugars tested were utilized by most of the isolates except arabinose. Fibrolytic enzyme activities revealed that NLG1 had highest endoglucanase activity, NLG13 had highest exoglucanase activity while NLG8 showed maximum xylanase activity. In case of FPase assay, highest and lowest values were observed in isolate NLG11 (8.96 U/mL) and NLG8 (5.58 U/mL), respectively. Phylogenetic analysis of the isolates revealed a highly diverse group of microbes mainly belonging to the family Paenibacillaceae which have not been previously characterized in ruminants for fiber degradation. Therefore, results obtained in the present study indicated that the screened isolates showed promising fiber degrading potential in terms of filter paper assay and fibrolytic enzyme activity which can be explored further for improving lignocellulose digestibility in ruminants as an additive.

A test of the Niche Variation Hypothesis in a ruminant herbivore

Despite the shared prediction that the width of a population's dietary niche expands as food becomes limiting, the Niche Variation Hypothesis (NVH) and Optimal Foraging Theory (OFT) offer contrasting views about how individuals alter diet selection when food is limited. Classical OFT predicts that dietary preferences do not change as food becomes limiting, so individuals expand their diets as they compensate for a lack of preferred foods. In contrast, the NVH predicts that among-individual variation in cognition, physiology or morphology create functional trade-offs in foraging efficiency, thereby causing individuals to specialize on different subsets of food as food becomes limiting. To evaluate (a) the predictions of the NVH and OFT and (b) evidence for physiological and cognitive-based functional trade-offs, we used DNA microsatellites and metabarcoding to quantify the diet, microbiome and genetic relatedness (a proxy for social learning) of 218 moose Alces alces across six populations that varied in their degree of food limitation. Consistent with both the NVH and OFT, dietary niche breadth increased with food limitation. Increased diet breadth of individuals-rather than increased diet specialization-was strongly correlated with both food limitation and dietary niche breadth of populations, indicating that moose foraged in accordance with OFT. Diets were not constrained by inheritance of the microbiome or inheritance of diet selection, offering support for the little-tested hypothesis that functional trade-offs in food use (or lack thereof) determine whether populations adhere to the predictions of the NVH or OFT. Our results indicate that both the absence of strong functional trade-offs and the digestive physiology of ruminants provide contexts under which populations should forage in accordance with OFT rather than the NVH. Also, because dietary niche width increased with increased food limitation, OFT and the NVH provide theoretical support for the notion that plant-herbivore interaction networks are plastic rather than static, which has important implications for understanding interspecific niche partitioning. Lastly, because population-level dietary niche breadth and calf recruitment are correlated, and because calf recruitment can be a proxy for food limitation, our work demonstrates how diet data can be employed to understand a populations' proximity to carrying capacity.

Nutrient contents predict the bamboo-leaf-based diet of Assamese macaques living in limestone forests of southwest Guangxi, China

Determining the nutrient factors influencing food choice provides important insight into the feeding strategy of animals, which is crucial for understanding their behavioral response to environmental changes. A bamboo-leaf-based diet is rare among mammals. Animals' food choice and nutritional goals have been explained by several frameworks; however, the influence of nutrients on food choice in bamboo-leaf-based macaques is not yet available. Assamese macaques (Macaca assamensis) inhabiting limestone forests are characterized by such a bamboo-leaf-based diet, predominantly consuming young leaves of Bonia saxatilis, a shrubby, karst-endemic bamboo. We studied the feeding behavior of one group of Assamese macaques using instantaneous scan sampling in limestone forests of the Guangxi Nonggang National Nature Reserve in southwest Guangxi, China. We compared the nutrient content of staple food and nonfood items and examine the role of key nutrients in the food selection of macaques. Our results showed that young leaves of bamboo B. saxatilis contained more water, crude protein, phosphorus, and less tannin than nonfood items. Furthermore, staple foods contained a higher content of water and less content of calcium than nonfood items. More specifically, quantities of water, crude protein, calcium, and phosphorus in food items were critical factors affecting feeding time on a specific plant item. Our results suggest that young bamboo leaves could meet macaques' required protein and water intake, while enabling them to maintain their mineral balance, consequently facilitating to maintain the primates' bamboo-leaf-diet in the limestone forest. Our findings confirm the effects of nutrient contents in food choice of Assamese macaques, highlighting the importance of the nutrient contents in maintaining their bamboo-based diet and the need to increase the knowledge on their nutritional strategy adapted to the bamboo-dominated diet inhabiting the unique limestone habitat.

Biofilm Improves Isopod Growth Independent of the Dietary Cellulose Content

Cellulose is an abundant source of carbon, accounting for more than 50% of foliage and 90% of woody tissues of plants. Despite the diversity of species that include living or dead plant tissue in their diets, the ability to digest cellulose through self-produced enzymatic machinery is considered rare in the animal kingdom. The majority of animals studied to date rely on the cellulolytic activity of symbiotic microorganisms in their digestive tract, with some evidence for a complementary action of endogenous cellulases. Terrestrial isopods have evolved a lifestyle including feeding on a lignocellulose diet. Whether isopods utilize both external and internal cellulases for digestion of a diet is still not understood. We experimentally manipulated the content of cellulose (30%, 60%, or 90%) and the amount of biofilm (small or large) in the offered food source and quantified growth and cellulolytic activity in the gut of the isopod Porcellio scaber. The presence of a visible biofilm significantly promoted isopod growth, regardless of the cellulose content in the diet. The activity of gut cellulases was not significantly affected by the amount of biofilm or the cellulose content. Our results do not support a significant contribution of either ingested or host enzymes to cellulose utilization in P. scaber. Cellulose might not represent a key nutrient for isopods and does not seem to affect the nutritional value of the diet-associated biofilm. We propose that it is the biofilm community that determines the quality of plant diet in terrestrial isopods and potentially also in other detrital plant feeders.

Hunters or farmers? Microbiome characteristics help elucidate the diet composition in an aquatic carnivorous plant

BACKGROUND

Utricularia are rootless aquatic carnivorous plants which have recently attracted the attention of researchers due to the peculiarities of their miniaturized genomes. Here, we focus on a novel aspect of Utricularia ecophysiology-the interactions with and within the complex communities of microorganisms colonizing their traps and external surfaces.

RESULTS

Bacteria, fungi, algae, and protozoa inhabit the miniature ecosystem of the Utricularia trap lumen and are involved in the regeneration of nutrients from complex organic matter. By combining molecular methods, microscopy, and other approaches to assess the trap-associated microbial community structure, diversity, function, as well as the nutrient turn-over potential of bacterivory, we gained insight into the nutrient acquisition strategies of the Utricularia hosts.

CONCLUSIONS

We conclude that Utricularia traps can, in terms of their ecophysiological function, be compared to microbial cultivators or farms, which center around complex microbial consortia acting synergistically to convert complex organic matter, often of algal origin, into a source of utilizable nutrients for the plants.

Influence of Season and Diet on Fiber Digestion and Bacterial Community Structure in the Rumen of Muskoxen (Ovibos moschatus)

We studied the relationship between fiber digestion and the composition of the bacterial community in the rumen of muskoxen at the start and the end of the annual window of plant growth from spring to fall. Eight ruminally cannulated castrated males were fed brome hay or triticale straw (69.6% vs. 84.6% neutral detergent fiber, respectively) that were similar in fiber content to the sedges consumed by wild muskoxen (64.5 to 71.7% neutral detergent fiber). Muskoxen digested fiber from both forages faster and to a greater extent when straw rather than hay was consumed. Fiber digestion was therefore inducible by diet 4 in each season. We used 16S rRNA sequences from ruminal contents to study how season and diet affected the bacterial community and how the latter related to fiber digestion. We found that Bacteroidetes and Firmicutes accounted for 90% of the sequences at the level of Phylum, which is typical for the mammal gut microbiome. Using partial least square regressions, it was found that between 48% and 72% of the variation in fiber digestion was associated with 36–43 genera of bacteria. The main fibrolytic bacteria typical of domestic ruminants were generally not among the most important bacteria associated with fiber digestion in muskoxen. This reveals that muskoxen rely upon on a large suite of bacterial genera that are largely distinct from those used by other ruminants to digest the cell walls of plants that vary widely in both abundance and nutritional quality through the year.

Fast acquisition of a polysaccharide fermenting gut microbiome by juvenile green turtles Chelonia mydas after settlement in coastal habitats

BACKGROUND

Tetrapods do not express hydrolases for cellulose and hemicellulose assimilation, and hence, the independent acquisition of herbivory required the establishment of new endosymbiotic relationships between tetrapods and microbes. Green turtles (Chelonia mydas) are one of the three groups of marine tetrapods with an herbivorous diet and which acquire it after several years consuming pelagic animals. We characterized the microbiota present in the feces and rectum of 24 young wild and captive green turtles from the coastal waters of Brazil, with curved carapace length ranging from 31.1 to 64.7 cm, to test the hypotheses that (1) the ontogenetic dietary shift after settlement is followed by a gradual change in the composition and diversity of the gut microbiome, (2) differences exist between the composition and diversity of the gut microbiome of green turtles from tropical and subtropical regions, and (3) the consumption of omnivorous diets modifies the gut microbiota of green turtles.

RESULTS

A genomic library of 2,186,596 valid bacterial 16S rRNA reads was obtained and these sequences were grouped into 6321 different operational taxonomic units (at 97% sequence homology cutoff). The results indicated that most of the juvenile green turtles less than 45 cm of curved carapace length exhibited a fecal microbiota co-dominated by representatives of the phyla Bacteroidetes and Firmicutes and high levels of Clostridiaceae, Prophyromonas, Ruminococaceae, and Lachnospiraceae within the latter phylum. Furthermore, this was the only microbiota profile found in wild green turtles > 45 cm CCL and in most of the captive green turtles of any size feeding on a macroalgae/fish mixed diet. Nevertheless, microbial diversity increased with turtle size and was higher in turtles from tropical than from subtropical regions.

CONCLUSIONS

These results indicate that juvenile green turtles from the coastal waters of Brazil had the same general microbiota, regardless of body size and origin, and suggest a fast acquisition of a polysaccharide fermenting gut microbiota by juvenile green turtles after settlement into coastal habitats.

Primate energy input and the evolutionary transition to energy-dense diets in humans

Humans and other large-brained hominins have been proposed to increase energy turnover during their evolutionary history. Such increased energy turnover is plausible, given the evolution of energy-rich diets, but requires empirical confirmation. Framing human energetics in a phylogenetic context, our meta-analysis of 17 wild non-human primate species shows that daily metabolizable energy input follows an allometric relationship with body mass where the allometric exponent for mass is 0.75 ± 0.04, close to that reported for daily energy expenditure measured with doubly labelled water in primates. Human populations at subsistence level (n = 6) largely fall within the variation of primate species in the scaling of energy intake and therefore do not consume significantly more energy than predicted for a non-human primate of equivalent mass. By contrast, humans ingest a conspicuously lower mass of food (-64 ± 6%) compared with primates and maintain their energy intake relatively more constantly across the year. We conclude that our hominin hunter-gatherer ancestors did not increase their energy turnover beyond the allometric relationship characterizing all primate species. The reduction in digestive costs due to consumption of a lower mass of high-quality food, as well as stabilization of energy supply, may have been important evolutionary steps enabling encephalization in the absence of significantly raised energy intakes.

Phytochemicals in animal health: diet selection and trade-offs between costs and benefits

Many plant tissues contain plant secondary compounds (PSC), which have long been recognised as defensive chemicals that deter herbivory via their toxic effects. However, herbivores may also benefit from including PSC into their diets. Plant-derived phenolics, terpenes and alkaloids have antiparasitic properties and sesquiterpene lactones have antibacterial, antifungal and antiparasitic properties. These actions are in part a consequence of the negative actions that PSC exert across several trophic levels, including the bacteria, parasites and fungi that inhabit herbivores' bodies. Given the dual action, toxin and medicine, it is possible to hypothesise that self-selection of PSC by herbivores should occur when the benefits outweigh the costs of PSC ingestion. Recent research suggests that sheep and goats self-medicate against parasitic infections. They increase preference for condensed tannin-containing foods when experiencing a parasitic burden. This behaviour improves health; it is triggered by parasitism and weakens when parasitism subsides. However, the causes underlying these responses are not straightforward when viewed under a unidimensional cost-benefit analysis. This is because the intensity of antinutritional/toxic and medicinal effects of PSC is not static or just dependent upon the isolated post-ingestive effects of single PSC. Nutrient-PSC and PSC-PSC interactions, social models, as well as feeding patterns, all influence the perceived net benefit of incorporating medicines into a diet. A better understanding of the net benefit of self-medication in complex feeding environments will allow for the development of innovative managing strategies aimed at providing the food alternatives and conditions for improving the nutrition, health and welfare of grazing animals.

Flexibility in metabolic rate and activity level determines individual variation in overwinter performance

Energy stores are essential for the overwinter survival of many temperate and polar animals, but individuals within a species often differ in how quickly they deplete their reserves. These disparities in overwinter performance may be explained by differences in their physiological and behavioral flexibility in response to food scarcity. However, little is known about whether individuals exhibit correlated or independent changes in these traits, and how these phenotypic changes collectively affect their winter energy use. We examined individual flexibility in both standard metabolic rate and activity level in response to food scarcity and their combined consequences for depletion of lipid stores among overwintering brown trout (Salmo trutta). Metabolism and activity tended to decrease, yet individuals exhibited striking differences in their physiological and behavioral flexibility. The rate of lipid depletion was negatively related to decreases in both metabolic and activity rates, with the smallest lipid loss over the simulated winter period occurring in individuals that had the greatest reductions in metabolism and/or activity. However, changes in metabolism and activity were negatively correlated; those individuals that decreased their SMR to a greater extent tended to increase their activity rates, and vice versa, suggesting among-individual variation in strategies for coping with food scarcity.

Plasticity of immunity in response to eating

Following a meal, an animal can exhibit dramatic shifts in physiology and morphology, as well as a substantial increase in metabolic rate associated with the energetic costs of processing a meal (i.e. specific dynamic action, SDA). However, little is known about the effects of digestion on another important physiological and energetically costly trait: immune function. Thus, we tested two competing hypotheses. (1) Digesting animals up-regulate their immune systems (putatively in response to the increased microbial exposure associated with ingested food). (2) Digesting animals down-regulate their immune systems (presumably to allocate energy to the breakdown of food). We assayed innate immunity (lytic capacity and agglutination) in cornsnakes (Pantherophis guttatus) during and after meal digestion. Lytic capacity was higher in females, and (in support of our first hypothesis) agglutination was higher during absorption. Given its potential energetic cost, immune up-regulation may contribute to SDA.

Contrasting Population and Diet Influences on Gut Length of an Omnivorous Tropical Fish, the Trinidadian Guppy (Poecilia reticulata)

Phenotypic plasticity is advantageous for organisms that live in variable environments. The digestive system is particularly plastic, responding to changes in diet. Gut length is the result of a trade-off between maximum nutrient absorption and minimum cost for its maintenance and it can be influenced by diet and by evolutionary history. We assessed variation in gut length of Trinidadian guppies (Poecilia reticulata) as a function of diet, season, ontogeny, and local adaptation. Populations of guppies adapted to different predation levels have evolved different life history traits and have different diets. We sampled guppies from sites with low (LP) and high predation (HP) pressure in the Aripo and Guanapo Rivers in Trinidad. We collected fish during both the dry and wet season and assessed their diet and gut length. During the dry season, guppies from HP sites fed mostly on invertebrates, while guppies in the LP sites fed mainly on detritus. During the wet season, the diet of LP and HP populations became very similar. We did not find strong evidence of an ontogenetic diet shift. Gut length was negatively correlated with the proportion of invertebrates in diet across fish from all sites, supporting the hypothesis that guppy digestive systems adapt in length to changes in diet. Population of origin also had an effect on gut length, as HP and LP fish maintained different gut lengths even in the wet season, when their diets were very similar and individuals in both types of populations fed mostly on detritus. Thus, both environment and population of origin influenced guppies gut length, but population of origin seemed to have a stronger effect. Our study also showed that, even in omnivorous fish, gut length adapted to different diets, being more evident when the magnitude of difference between animal and plant material in the diet was very large.

The gastrointestinal tract of the white-throated Woodrat (Neotoma albigula) harbors distinct consortia of oxalate-degrading bacteria

The microbiota inhabiting the mammalian gut is a functional organ that provides a number of services for the host. One factor that may regulate the composition and function of gut microbial communities is dietary toxins. Oxalate is a toxic plant secondary compound (PSC) produced in all major taxa of vascular plants and is consumed by a variety of animals. The mammalian herbivore Neotoma albigula is capable of consuming and degrading large quantities of dietary oxalate. We isolated and characterized oxalate-degrading bacteria from the gut contents of wild-caught animals and used high-throughput sequencing to determine the distribution of potential oxalate-degrading taxa along the gastrointestinal tract. Isolates spanned three genera: Lactobacillus, Clostridium, and Enterococcus. Over half of the isolates exhibited significant oxalate degradation in vitro, and all Lactobacillus isolates contained the oxc gene, one of the genes responsible for oxalate degradation. Although diverse potential oxalate-degrading genera were distributed throughout the gastrointestinal tract, they were most concentrated in the foregut, where dietary oxalate first enters the gastrointestinal tract. We hypothesize that unique environmental conditions present in each gut region provide diverse niches that select for particular functional taxa and communities.

The alligator gut microbiome and implications for archosaur symbioses

Among vertebrate gastrointestinal microbiome studies, complete representation of taxa is limited, particularly among reptiles. Here, we provide evidence for previously unrecognized host-microbiome associations along the gastrointestinal tract from the American alligator, a crown archosaur with shared ancestry to extinct taxa, including dinosaurs. Microbiome compositional variations reveal that the digestive system consists of multiple, longitudinally heterogeneous microbiomes that strongly correlate to specific gastrointestinal tract organs, regardless of rearing histories or feeding status. A core alligator gut microbiome comprised of Fusobacteria, but depleted in Bacteroidetes and Proteobacteria common to mammalians, is compositionally unique from other vertebrate gut microbiomes, including other reptiles, fish, and herbivorous and carnivorous mammals. As such, modern alligator gut microbiomes advance our understanding of archosaur gut microbiome evolution, particularly if conserved host ecology has retained archosaur-specific symbioses over geologic time.

Experience matters: prior exposure to plant toxins enhances diversity of gut microbes in herbivores

For decades, ecologists have hypothesised that exposure to plant secondary compounds (PSCs) modifies herbivore-associated microbial community composition. This notion has not been critically evaluated in wild mammalian herbivores on evolutionary timescales. We investigated responses of the microbial communities of two woodrat species (Neotoma bryanti and N. lepida). For each species, we compared experienced populations that independently converged to feed on the same toxic plant (creosote bush, Larrea tridentata) to naïve populations with no exposure to creosote toxins. The addition of dietary PSCs significantly altered gut microbial community structure, and the response was dependent on previous experience. Microbial diversity and relative abundances of several dominant phyla increased in experienced woodrats in response to PSCs; however, opposite effects were observed in naïve woodrats. These differential responses were convergent in experienced populations of both species. We hypothesise that adaptation of the foregut microbiota to creosote PSCs in experienced woodrats drives this differential response.

Molecules to migration: pressures of life

The highly successful Fourth International Conference in Africa for Comparative Physiology and Biochemistry (ICA-CPB) was held in the Maasai Mara National Reserve in July 2008. The theme of the meeting was "Molecules to Migration: Pressures of Life." To enhance the theme, the venue and timing of the meeting were chosen to coincide with the arrival of approximately 1.4 million wildebeest on their annual migration from the Serengeti National Park in Tanzania. Like the three previous ICA-CPB meetings, the discussion topics and the resulting collection of synthesia presented here were very diverse. The articles in this special collection reflect the authors' interest in broadening our understanding of the field of comparative physiology and biochemistry and their commitment to engaging in global research with international colleagues. These articles are brief, synthetic reviews integrating information presented at and inspired by the meeting. From seasonal migration and reproduction in birds, to cardiovascular system development in vertebrates, to strategies for hypoxia survival, papers range from specific to broad interactions. What they all have in common: they increase our understanding of how animals are affected by and respond to the pressures of life.