Evolutionary Biology

eLife assessment

The authors re-analyzed a previously published dataset and identify patterns suggestive of increased bacterial biodiversity in the gut may creating new niches that lead to gene loss in a focal species and promote generation of more diversity. Two limitations are (i) that sequencing depth may not be sufficient to analyze strain-level diversity and (ii) that the evidence is exclusively based on correlations, and the observed patterns could also be explained by other eco-evolutionary processes. The claims should be supported by a more detailed analysis, and alternative hypotheses that the results do not fully exclude should be discussed. Understanding drivers of diversity in natural microbial communities is an important question that is of central interest to biomedically oriented microbiome scientists, microbial ecologists and evolutionary biologists.

eLife assessment

The authors investigate the cost and benefits of maintaining seemingly redundant multiple copies of the translation machinery components. The authors demonstrate that while redundant multiple copies are beneficial in a nutrient-rich environment, maintaining these extra copies is costly and deleterious in a nutrient-poor environment. This explains why copy numbers of translation machinery genes are under selection according to the environmental niche an organism occupies. The work is very important and the findings exciting and supported by compelling evidence. In particular, the fitness gain upon deletion of translation genes in poor conditions is an insightful observation.

eLife assessment

This study reports an interesting analysis of evolutionary variation in forelimb/hand bone shapes in relation to functional and developmental variation along the proximo-distal axis. The authors found expected and compelling patterns of evolutionary shape variation along the proximo-distal axis but less expected, yet equally compelling, patterns of shape integration. This paper will be of interest to researchers working on macroevolutionary patterns and sources of morphological diversity.

eLife assessment

The manuscript makes a fundamental contribution to our understanding of sugar release by symbiotic dinoflagellates, and is of broad interest for the fields of ecology, marine biology, and cell biology. The experiments, which combine algal culture with targeted metabolomics, transcriptomics and the application of inhibitors, provide substantial, though not entirely complete evidence for an acidic environment mimicking conditions reported for the intracellular organelle that hosts the symbiotic algae, leading to upregulation of algal cellulases, which in turn degrade the algal cell wall and thereby releasing glucose and galactose that can be used as a source of food by the coral host. This is a new idea and could significantly contribute to our understanding of photosymbiosis.

eLife assessment

This study addresses a fundamental question about the origin and evolution of selfish genetic elements, focusing on the paradoxical abundance of toxin-antidote elements in selfing Caenorhabditis species. The authors propose for the C. elegans peel-1 zeel-1 locus fitness advantages; if these the findings can be supported with additional data, they will be of considerable interest to the field due to their wider implications for the evolution of such systems.

eLife assessment

This manuscript provides an improved version of the little skate genome, which will be of great interest to the field of comparative genomics and evolutionary biology. The authors use the genome to compare gene expression and chromatin accessibility profiles in motor neurons of the little skate and other species (mouse, chicken), aiming to predict conserved and divergent gene regulatory mechanisms underlying motor neuron development. While the manuscript contributes a valuable resource to the field, more rigorous analyses and experimental validation are needed to support the major claims of this study.

eLife assessment

This study investigates factors that control egg size plasticity in a social insect, the honey bee Apis mellifera. It finds that honey bee queens vary egg size in response to size of their colony, and that the gene Rho1 is involved in egg-size determination. These findings inform our understanding of maternal control over egg size, a key form of maternal investment. The work is relevant to colleagues studying reproduction and social insects.

eLife assessment

Several mammal species, including dolphins, have evolved to be relatively "hairless". Kowalczyk and colleagues scan the genomes of multiple species to identify genomic regions that appear to have evolved at a faster or slower evolutionary rate along hairless lineages. They identify a number of protein-coding genes as well as noncoding regions that might explain how hairlessness evolved in mammals. This study is of interest to those investigating the development of the skin and its appendages as well as evolutionary biologists, especially those investigating instances of convergent evolution and those developing phylogenomic methods for genome comparisons.

eLife assessment

This work examines the evolutionary origins of acid-sensing ion channels (ASICs), a class of pH-sensing receptors expressed throughout the brain and body. By combining analysis of sequences, functional measurements, and measures of tissue distribution, the authors provide solid evidence that ASICs existed far earlier than previously believed. The present data indicate that ASICs emerged after the split between bilaterians (organisms with two-fold symmetry) and Cnidaria (jellyfish, anemones, corals, etc.), approximately 680 million years ago. This evolutionary and functional analysis of ASIC channels across bilaterian lineages provides relevant information about the evolution of nervous and sensory systems.

eLife Assessment:

This study is a useful extension of previous work on the relationship between body size and cancer risk and the mechanisms by which large-bodied mammals reduce their cancer risk. Through solid analyses of the genomes and several aspects of the cell biology of sloths, armadillos and their relatives, the study explores whether the evolution of large body size in their relatives (some extinct) was correlated with genomic changes such as the duplication of tumor suppressor genes, experimentally demonstrating that cells of Xenarthrans (sloths, armadillos, anteaters) are exceptionally sensitive to DNA damage. The study concerns a topic of great interest and contributes to our understanding of how cancer risk has evolved in mammals.

(This preprint has been reviewed by eLife. We include the public reviews from the reviewers here; the authors also receive private feedback with suggested changes to the manuscript. Reviewer #1 agreed to share their name with the authors.)