Gut microbial diversity increases with social rank in the African cichlid fish, Astatotilapia burtoni

East African cichlid fishes

Cichlid fishes are a very diverse and species-rich family of teleost fishes that inhabit lakes and rivers of India, Africa, and South and Central America. Research has largely focused on East African cichlids of the Rift Lakes Tanganyika, Malawi, and Victoria that constitute the biodiversity hotspots of cichlid fishes. Here, we give an overview of the study system, research questions, and methodologies. Research on cichlid fishes spans many disciplines including ecology, evolution, physiology, genetics, development, and behavioral biology. In this review, we focus on a range of organismal traits, including coloration phenotypes, trophic adaptations, appendages like fins and scales, sensory systems, sex, brains, and behaviors. Moreover, we discuss studies on cichlid phylogenies, plasticity, and general evolutionary patterns, ranging from convergence to speciation rates and the proximate and ultimate mechanisms underlying these processes. From a methodological viewpoint, the last decade has brought great advances in cichlid fish research, particularly through the advent of affordable deep sequencing and advances in genetic manipulations. The ability to integrate across traits and research disciplines, ranging from developmental biology to ecology and evolution, makes cichlid fishes a fascinating research system.

Enriching captivity conditions with natural elements does not prevent the loss of wild‐like gut microbiota but shapes its compositional variation in two small mammals

As continued growth in gut microbiota studies in captive and model animals elucidates the importance of their role in host biology, further pursuit of how to retain a wild‐like microbial community is becoming increasingly important to obtain representative results from captive animals. In this study, we assessed how the gut microbiota of two wild‐caught small mammals, namely Crocidura russula (Eulipotyphla, insectivore) and Apodemus sylvaticus (Rodentia, omnivore), changed when bringing them into captivity. We analyzed fecal samples of 15 A. sylvaticus and 21 C. russula, immediately after bringing them into captivity and 5 weeks later, spread over two housing treatments: a “natural” setup enriched with elements freshly collected from nature and a “laboratory” setup with sterile artificial elements. Through sequencing of the V3–V4 region of the 16S recombinant RNA gene, we found that the initial microbial diversity dropped during captivity in both species, regardless of treatment. Community composition underwent a change of similar magnitude in both species and under both treatments. However, we did observe that the temporal development of the gut microbiome took different trajectories (i.e., changed in different directions) under different treatments, particularly in C. russula, suggesting that C. russula may be more susceptible to environmental change. The results of this experiment do not support the use of microbially enriched environments to retain wild‐like microbial diversities and compositions, yet show that specific housing conditions can significantly affect the drift of microbial communities under captivity.

Effects of increasing dietary level of organic acids and nature-identical compounds on growth, intestinal cytokine gene expression and gut microbiota of rainbow trout (Oncorhynchus mykiss) reared at normal and high temperature

Organic acids (OA) and nature-identical compounds (NIC) such as monoterpenes and aldehydes are well-known growth and health promoters in terrestrial livestock while their application for fish production is recent and their mechanisms of action require further study. Hence, this study tested the increasing dietary level (D0, D250, D500, D1000; 0, 250, 500 and 1000 mg kg feed^-1 respectively) of a microencapsulated blend containing citric and sorbic acid, thymol and vanillin over 82 days on rainbow trout to assess the effects on growth, feed utilization, intestine cytokine gene expression and gut microbiota (GM). Furthermore, the effects on intestinal cytokine gene expression and GM were also explored after one week at high water temperature (23 °C). OA and NIC improved specific growth rate (SGR) and feed conversion rate (FCR) during the second half (day 40-82) of the feeding trial, while at the end of the trial protein (PER) and lipid efficiency (LER) increased with increasing dietary level. GM diversity and composition and cytokine gene expression analysis showed no significant differences in fish fed with increasing doses of OA and NIC (82 days) demonstrating the absence of inflammatory activity in the intestinal mucosa. Although there were no statistical differences, GM structure showed a tendency in clustering D0 group separately from the other dietary groups and a trend towards reduction of Streptococcus spp. was observed in the D250 and D1000 groups. After exposure to high water temperature, lower GM diversity and increased gene expression of inflammatory intestinal cytokines were observed for both inclusions (D0 vs. D1000) compared to groups in standard condition. However, the gene up-regulation involved a limited number of cytokines showing the absence of a substantial inflammation process able to compromise the functional activity of the intestine. Despite further study should be conducted to fully clarify this mechanism, cytokines up-regulation seems to be concomitant to the reduction of the GM diversity and, particularly, to the reduction of specific lactic acid bacteria such as Leuconostoc. The application of the microencapsulate blend tested can be a useful strategy to improve growth and feed utilization in rainbow trout under normal temperature conditions. According to the results organic acids and nature-identical compounds did not revert the effects triggered by the increased temperature of water.

Transitions and transmission: behavior and physiology as drivers of honey bee-associated microbial communities

Microbial communities have considerable impacts on animal health. However, only in recent years have the host factors impacting microbiome composition been explored. An increasing wealth of microbiome data in combination with decades of research on behavior, physiology, and development have resulted in the European honey bee (Apis mellifera) as a burgeoning model system for studying the influence of host behavior on the microbiota. Honey bees are eusocial insects which exhibit striking behavioral and physiological differences between castes and life stages. These include changes in social contact, environmental exposure, diet, and physiology: all factors which can affect microbial composition and function. The honey bee system offers an opportunity to tease apart the interactive effects of all these factors on microbiota composition, abundance, and diversity.