The evolution of plasticity of dauer larva developmental arrest in the nematode Caenorhabditis elegans.

Organisms can end up in unfavourable conditions and to survive this they have evolved various strategies. Some organisms, including nematodes, survive unfavourable conditions by undergoing developmental arrest. The model nematode Caenorhabditis elegans has a developmental choice between two larval forms, and it chooses to develop into the arrested dauer larva form in unfavourable conditions (specifically, a lack of food and high population density, indicated by the concentration of a pheromone). Wild C. elegans isolates vary extensively in their dauer larva arrest phenotypes, and this prompts the question of what selective pressures maintain such phenotypic diversity? To investigate this we grew C. elegans in four different environments, consisting of different combinations of cues that can induce dauer larva development: two combinations of food concentration (high and low) in the presence or absence of a dauer larva-inducing pheromone. Five generations of artificial selection of dauer larvae resulted in an overall increase in dauer larva formation in most selection regimes. The presence of pheromone in the environment selected for twice the number of dauer larvae, compared with environments not containing pheromone. Further, only a high food concentration environment containing pheromone increased the plasticity of dauer larva formation. These evolutionary responses also affected the timing of the worms' reproduction. Overall, these results give an insight into the environments that can select for different plasticities of C. elegans dauer larva arrest phenotypes, suggesting that different combinations of environmental cues can select for the diversity of phenotypically plastic responses seen in C. elegans.We would like to thank Henrique Teotonio for the gift of the G140.A population, Louise Hughes and Laura Weldon for technical help, two anonymous reviewers for their comments, and NERC for funding.This is the final published version of the article. It was originally published in Ecology and Evolution (Diaz SA, Viney M, Ecology and Evolution 2015, 5(6), 1343–1353, doi:10.1002/ece3.1436) http://dx.doi.org/10.1002/ece3.143

Climate change, adaptation, and phenotypic plasticity: the problem and the evidence

Peer reviewe

Queen Dominance May Reduce Worker Mushroom Body Size in a Social Bee

The mushroom body (MB) is an area of the insect brain involved in learning, memory, and sensory integration. Here, we used the sweat bee Megalopta genalis (Halictidae) to test for differences between queens and workers in the volume of the MB calyces. We used confocal microscopy to measure the volume of the whole brain, MB calyces, optic lobes, and antennal lobes of queens and workers. Queens had larger brains, larger MB calyces, and a larger MB calyces:whole brain ratio than workers, suggesting an effect of social dominance in brain development. This could result from social interactions leading to smaller worker MBs, or larger queen MBs. It could also result from other factors, such as differences in age or sensory experience. To test these explanations, we next compared queens and workers to other groups. We compared newly emerged bees, bees reared in isolation for 10 days, bees initiating new observation nests, and bees initiating new natural nests collected from the field to queens and workers. Queens did not differ from these other groups. We suggest that the effects of queen dominance over workers, rather than differences in age, experience, or reproductive status, are responsible for the queen–worker differences we observed. Worker MB development may be affected by queen aggression directly and/or manipulation of larval nutrition, which is provisioned by the queen. We found no consistent differences in the size of antennal lobes or optic lobes associated with differences in age, experience, reproductive status, or social caste.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/150573/1/dneu22705_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/150573/2/dneu22705.pd

The Origins of Cooperative Bacterial Communities

Bacteria live in complex multispecies communities. Intimately interacting bacterial cells are ubiquitous on biological and mineral surfaces in all habitats. Molecular and cellular biologists have unraveled some key mechanisms that modulate bacterial interactions, but the ecology and evolution of these associations remain poorly understood. One debate has focused on the relative importance of cooperation among cells in bacterial communities. Some researchers suggest that communication and cooperation, both within and among bacterial species, have produced emergent properties that give such groups a selective advantage. Evolutionary biologists have countered that the appearance of group-level traits should be viewed with caution, as natural selection almost invariably favors selfishness. A recent theory by Morris, Lenski, and Zinser, called the Black Queen Hypothesis, gives a new perspective on this debate (J. J. Morris, R. E. Lenski, and E. R. Zinser, mBio 3(2):e00036-12, 2012). These authors present a model that reshapes a decades-old idea: cooperation among species can be automatic and based upon purely selfish traits. Moreover, this hypothesis stands in contrast to the Red Queen Hypothesis, which states that species are in constant evolutionary conflict. Two assumptions serve as the core of the Black Queen model. First, bacterial functions are often leaky, such that cells unavoidably produce resources that benefit others. Second, the receivers of such by-products will tend to delete their own costly pathways for those products, thus building dependency into the interactions. Although not explicitly required in their model, an emergent prediction is that the initiation of such dependency can favor the spread of more obligate coevolved partnerships. This new paradigm suggests that bacteria might often form interdependent cooperative interactions in communities and moreover that bacterial cooperation should leave a clear genomic signature via complementary loss of shared diffusible functions

Shaping Robust System through Evolution

Biological functions are generated as a result of developmental dynamics that form phenotypes governed by genotypes. The dynamical system for development is shaped through genetic evolution following natural selection based on the fitness of the phenotype. Here we study how this dynamical system is robust to noise during development and to genetic change by mutation. We adopt a simplified transcription regulation network model to govern gene expression, which gives a fitness function. Through simulations of the network that undergoes mutation and selection, we show that a certain level of noise in gene expression is required for the network to acquire both types of robustness. The results reveal how the noise that cells encounter during development shapes any network's robustness, not only to noise but also to mutations. We also establish a relationship between developmental and mutational robustness through phenotypic variances caused by genetic variation and epigenetic noise. A universal relationship between the two variances is derived, akin to the fluctuation-dissipation relationship known in physics

Extreme Behavioral Adjustments by an Orb‐Web Spider to Restricted Spaces

Adaptive flexibility in response to environmental variation is often advantageous and occurs in many types of traits in many species. Although the basic designs of the orb webs of a given species are relatively uniform, spiders can adjust their webs to some types of environmental variation. This study of adult female Leucauge argyra tests the extremes to which they can adjust with respect to reduced area in which to build, and documents probably the most pronounced flexibility in orb design ever recorded. These adjustments revealed several behavioral rules that guide orb construction behavior. Spiders adjusted at least seven probably independent aspects of orb design when confined in tiny spaces that spanned about 7% of the maximum distance normally spanned by webs in the field and that had diameters that were only about three times the length of the spider itself. Webs in intermediate sized containers had intermediate designs, and many of the adjustments appear to result from extensions of the behavioral rules guiding orb construction in less severely restricted spaces in the field.The Smithsonian Tropical Research InstituteMciSmithsonian Tropical Research Institute, Panama, USAUCR::Vicerrectoría de Docencia::Ciencias Básicas::Facultad de Ciencias::Escuela de Biologí