Cycles of heat exposure elevate metabolic enzyme genes and alters digestion in mussels

The intertidal sea mussel Mytilus californianus inhabits the Pacific coastline of North America. As a sessile organism it must cope with daily fluctuations of the marine and terrestrial environments. Organisms in stressful environments are commonly faced with energetic trade-offs between somatic and reproductive growth and stress management. Although, this energetic theory is generally accepted for mussels as well, the spectrum of mechanisms underlying this framework have not been widely investigated. In the current study we hypothesized that mussels acclimated to a cyclical moderately warm aerial environment would display enhanced transcript abundance of genes related to metabolism and exhibit resilient digestive enzyme activity (energy acquisition). Following acclimation to simulated tidal regimes in the laboratory we observed higher gene-expression of citrate synthase (CS), citrate lyase (ACLY), and mammalian target of rapamycin (MTOR) in heat stressed mussels. The expression of CS and MTOR was not elevated under acute thermal stress, suggestive that repeated stress is required for robust expression of these genes given that all other environmental variables are constant. We also observed reduced activity of the digestive enzyme, amylase in heat-shocked acclimated mussels (a proxy for energy acquisition). Our results suggest that mussels that settle high on shore not only face the challenge of thermal stress repair and limited access to food but may also be compromised by reduced digestive performance. Mussels may have adapted to cyclical energetic stress by overexpressing particular energy-related genes that can mitigate the disturbance to energy balance once the abundant transcripts are translated into functional proteins

A communal catalogue reveals Earth's multiscale microbial diversity

Our growing awareness of the microbial world's importance and diversity contrasts starkly with our limited understanding of its fundamental structure. Despite recent advances in DNA sequencing, a lack of standardized protocols and common analytical frameworks impedes comparisons among studies, hindering the development of global inferences about microbial life on Earth. Here we present a meta-analysis of microbial community samples collected by hundreds of researchers for the Earth Microbiome Project. Coordinated protocols and new analytical methods, particularly the use of exact sequences instead of clustered operational taxonomic units, enable bacterial and archaeal ribosomal RNA gene sequences to be followed across multiple studies and allow us to explore patterns of diversity at an unprecedented scale. The result is both a reference database giving global context to DNA sequence data and a framework for incorporating data from future studies, fostering increasingly complete characterization of Earth's microbial diversity.Peer reviewe

A communal catalogue reveals Earth’s multiscale microbial diversity

Our growing awareness of the microbial world’s importance and diversity contrasts starkly with our limited understanding of its fundamental structure. Despite recent advances in DNA sequencing, a lack of standardized protocols and common analytical frameworks impedes comparisons among studies, hindering the development of global inferences about microbial life on Earth. Here we present a meta-analysis of microbial community samples collected by hundreds of researchers for the Earth Microbiome Project. Coordinated protocols and new analytical methods, particularly the use of exact sequences instead of clustered operational taxonomic units, enable bacterial and archaeal ribosomal RNA gene sequences to be followed across multiple studies and allow us to explore patterns of diversity at an unprecedented scale. The result is both a reference database giving global context to DNA sequence data and a framework for incorporating data from future studies, fostering increasingly complete characterization of Earth’s microbial diversity

Who, When, and How Much? The Context Dependency of Rapid Evolution in Response to a Dietary Shift

A population of Italian Wall Lizards (Podarcis sicula) on a small island in Croatia has become primarily herbivorous and morphologically distinct from its source population on a nearby island in ~30 generations, making it a compelling example of rapid evolution. What changes in digestive physiology and morphology have facilitated this switch to a novel diet? How does this dietary shift affect digestive performance? Do these accommodations for plant eating vary through time or with aspects of the lizards’ life history? I compared gut size and histology, eight digestive enzyme activities, and products of microbial fermentation across the two island populations, with selected comparisons to a mainland outgroup of P. sicula. The newly omnivorous population had several targeted biochemical differences in their hindguts compared to their source population, but no large-scale changes in physiology or gut morphology to match the scale and direction of divergence in their diets. In fact, island-mainland effects were far more prominent, even between insectivorous populations.To test digestive performance, in the lab I fed lizards insect, mixed, or plant diets daily (high frequency, island males only) or on alternating days (low frequency, island and mainland males and females). When fed with high frequency, the newly omnivorous population was better at digesting plant proteins than their source population counterparts. However, when feed a low frequency, the males did not differ by population on any diet type. The females from the insectivorous source population, however, digested insect diets less efficiently than the other two populations.To better elucidate dietary differences between the new and source populations lizards, I used stable isotope analyses to track 13C and 15N enrichment in their livers in concert with measurements of body and gut size over time and in males and females. Isotopic enrichment and gut length vary considerably by both year and season and suggest that the diet these lizards actually digest is not as different between the populations as stomach contents have suggested. Measurements of six digestive enzymes show differing patterns between populations depending on season and sex. The lizards’ responses to this dietary shift are dependent on multiple contexts

Who, When, and How Much? The Context Dependency of Rapid Evolution in Response to a Dietary Shift

A population of Italian Wall Lizards (Podarcis sicula) on a small island in Croatia has become primarily herbivorous and morphologically distinct from its source population on a nearby island in ~30 generations, making it a compelling example of rapid evolution. What changes in digestive physiology and morphology have facilitated this switch to a novel diet? How does this dietary shift affect digestive performance? Do these accommodations for plant eating vary through time or with aspects of the lizards’ life history? I compared gut size and histology, eight digestive enzyme activities, and products of microbial fermentation across the two island populations, with selected comparisons to a mainland outgroup of P. sicula. The newly omnivorous population had several targeted biochemical differences in their hindguts compared to their source population, but no large-scale changes in physiology or gut morphology to match the scale and direction of divergence in their diets. In fact, island-mainland effects were far more prominent, even between insectivorous populations.To test digestive performance, in the lab I fed lizards insect, mixed, or plant diets daily (high frequency, island males only) or on alternating days (low frequency, island and mainland males and females). When fed with high frequency, the newly omnivorous population was better at digesting plant proteins than their source population counterparts. However, when feed a low frequency, the males did not differ by population on any diet type. The females from the insectivorous source population, however, digested insect diets less efficiently than the other two populations.To better elucidate dietary differences between the new and source populations lizards, I used stable isotope analyses to track 13C and 15N enrichment in their livers in concert with measurements of body and gut size over time and in males and females. Isotopic enrichment and gut length vary considerably by both year and season and suggest that the diet these lizards actually digest is not as different between the populations as stomach contents have suggested. Measurements of six digestive enzymes show differing patterns between populations depending on season and sex. The lizards’ responses to this dietary shift are dependent on multiple contexts

Proximate Drivers of Population-Level Lizard Gut Microbial Diversity: Impacts of Diet, Insularity, and Local Environment

Diet has been suggested to be an important driver of variation in microbiota composition in mammals. However, whether this is a more general phenomenon and how fast changes in gut microbiota occur with changes in diet remains poorly understood. Forty-nine years ago, ten lizards of the species Podarcis siculus were taken from the island of Pod Kopište and introduced onto the island of Pod Mrčaru (Croatia). The introduced population underwent a significant dietary shift, and their descendants became omnivorous (consuming up to 80% plant material during summer). Variation in their gut microbiota has never been investigated. To elucidate the possible impact on the gut microbiota of this rapid change in diet, we compared the microbiota (V4 region of the 16S rRNA gene) of P. siculus from Pod Mrčaru, Pod Kopište, and the mainland. In addition, we explored other drivers of variation in gut microbiota including insularity, the population of origin, and the year of sampling. Alpha-diversity analyses showed that the microbial diversity of omnivorous lizards was higher than the microbial diversity of insectivorous lizards. Moreover, omnivorous individuals harbored significantly more Methanobrevibacter. The gut microbial diversity of insectivorous lizards was nonetheless more heterogeneous. Insectivorous lizards on the mainland had different gut microbial communities than their counterparts on the island of Pod Kopište. Bacillus and Desulfovibrio were more abundant in the gut microbiota from insular lizards compared to mainland lizards. Finally, we showed that the population of origin was also an important driver of the composition of the gut microbiota. The dietary shift that occurred in the introduced population of P. siculus has had a detectable impact on the gut microbiota, but other factors such as insularity and the population of origin also contributed to differences in the gut microbial composition of these lizards, illustrating the multifactorial nature of the drivers of variation in gut microbiota. Overall, our data show that changes in gut microbiota may take place on ecological timescales. Yet, diet is only one of many factors driving variation in gut microbiota across populations

Diet variability among insular populations of Podarcis lizards reveals diverse strategies to face resource‐limited environments

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