Selection for brain size impairs innate, but not adaptive immune responses

Both the brain and the immune system are energetically demanding organs, and when natural selection favours increased investment into one, then the size or performance of the other should be reduced. While comparative analyses have attempted to test this potential evolutionary trade-off, the results remain inconclusive. To test this hypothesis, we compared the tissue graft rejection (an assay for measuring innate and acquired immune responses) in guppies ( Poecilia reticulata ) artificially selected for large and small relative brain size. Individual scales were transplanted between pairs of fish, creating reciprocal allografts, and the rejection reaction was scored over 8 days (before acquired immunity develops). Acquired immune responses were tested two weeks later, when the same pairs of fish received a second set of allografts and were scored again. Compared with large-brained animals, small-brained animals of both sexes mounted a significantly stronger rejection response to the first allograft. The rejection response to the second set of allografts did not differ between large- and small-brained fish. Our results show that selection for large brain size reduced innate immune responses to an allograft, which supports the hypothesis that there is a selective trade-off between investing into brain size and innate immunity.

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Brain enlargement and dental reduction were not linked in hominin evolution

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1608798114 ◽

2017 ◽

Vol 114 (3) ◽

pp. 468-473 ◽

Cited By ~ 24

Author(s):

Aida Gómez-Robles ◽

Jeroen B. Smaers ◽

Ralph L. Holloway ◽

P. David Polly ◽

Bernard A. Wood

Keyword(s):

Brain Size ◽

Behavioral Changes ◽

Modern Humans ◽

Distinctive Features ◽

Hominin Evolution ◽

Large Brain ◽

Dental Reduction ◽

Selection For ◽

Brain Reorganization ◽

Evolutionary Simulations

The large brain and small postcanine teeth of modern humans are among our most distinctive features, and trends in their evolution are well studied within the hominin clade. Classic accounts hypothesize that larger brains and smaller teeth coevolved because behavioral changes associated with increased brain size allowed a subsequent dental reduction. However, recent studies have found mismatches between trends in brain enlargement and posterior tooth size reduction in some hominin species. We use a multiple-variance Brownian motion approach in association with evolutionary simulations to measure the tempo and mode of the evolution of endocranial and dental size and shape within the hominin clade. We show that hominin postcanine teeth have evolved at a relatively consistent neutral rate, whereas brain size evolved at comparatively more heterogeneous rates that cannot be explained by a neutral model, with rapid pulses in the branches leading to later Homo species. Brain reorganization shows evidence of elevated rates only much later in hominin evolution, suggesting that fast-evolving traits such as the acquisition of a globular shape may be the result of direct or indirect selection for functional or structural traits typical of modern humans.

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Selection for improved resistance to Aeromonas hydrophila in Indian major carp Labeo rohita: Survival and innate immune responses in first generation of resistant and susceptible lines

Fish & Shellfish Immunology ◽

10.1016/j.fsi.2011.06.014 ◽

2011 ◽

Vol 31 (3) ◽

pp. 432-438 ◽

Cited By ~ 34

Author(s):

P.K. Sahoo ◽

P.R. Rauta ◽

B.R. Mohanty ◽

K.D. Mahapatra ◽

J.N. Saha ◽

...

Keyword(s):

Immune Responses ◽

Aeromonas Hydrophila ◽

First Generation ◽

Labeo Rohita ◽

Innate Immune ◽

Innate Immune Responses ◽

Indian Major Carp ◽

Selection For

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Dolphin social intelligence: complex alliance relationships in bottlenose dolphins and a consideration of selective environments for extreme brain size evolution in mammals

Philosophical Transactions of the Royal Society B Biological Sciences ◽

10.1098/rstb.2006.1997 ◽

2007 ◽

Vol 362 (1480) ◽

pp. 587-602 ◽

Cited By ~ 135

Author(s):

Richard C Connor

Keyword(s):

Cognitive Abilities ◽

Social Intelligence ◽

Brain Size ◽

Bottlenose Dolphins ◽

Sperm Whale ◽

Shark Bay ◽

External Threats ◽

Size Evolution ◽

Large Brain ◽

Selection For

Bottlenose dolphins in Shark Bay, Australia, live in a large, unbounded society with a fission–fusion grouping pattern. Potential cognitive demands include the need to develop social strategies involving the recognition of a large number of individuals and their relationships with others. Patterns of alliance affiliation among males may be more complex than are currently known for any non-human, with individuals participating in 2–3 levels of shifting alliances. Males mediate alliance relationships with gentle contact behaviours such as petting, but synchrony also plays an important role in affiliative interactions. In general, selection for social intelligence in the context of shifting alliances will depend on the extent to which there are strategic options and risk. Extreme brain size evolution may have occurred more than once in the toothed whales, reaching peaks in the dolphin family and the sperm whale. All three ‘peaks’ of large brain size evolution in mammals (odontocetes, humans and elephants) shared a common selective environment: extreme mutual dependence based on external threats from predators or conspecific groups. In this context, social competition, and consequently selection for greater cognitive abilities and large brain size, was intense.

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Effects of hibernation on bone marrow transcriptome in thirteen-lined ground squirrels

Physiological Genomics ◽

10.1152/physiolgenomics.00120.2015 ◽

2016 ◽

Vol 48 (7) ◽

pp. 513-525 ◽

Cited By ~ 17

Author(s):

Scott T. Cooper ◽

Shawn S. Sell ◽

Molly Fahrenkrog ◽

Kory Wilkinson ◽

David R. Howard ◽

...

Keyword(s):

Bone Marrow ◽

Immune Responses ◽

Ground Squirrels ◽

Innate Immune Responses ◽

Cold Response ◽

Expression Of Genes ◽

Acquired Immune Responses ◽

Shock Proteins ◽

Collagen Genes

Mammalian hibernators adapt to prolonged periods of immobility, hypometabolism, hypothermia, and oxidative stress, each capable of reducing bone marrow activity. In this study bone marrow transcriptomes were compared among thirteen-lined ground squirrels collected in July, winter torpor, and winter interbout arousal (IBA). The results were consistent with a suppression of acquired immune responses, and a shift to innate immune responses during hibernation through higher complement expression. Consistent with the increase in adipocytes found in bone marrow of hibernators, expression of genes associated with white adipose tissue are higher during hibernation. Genes that should strengthen the bone by increasing extracellular matrix were higher during hibernation, especially the collagen genes. Finally, expression of heat shock proteins were lower, and cold-response genes were higher, during hibernation. No differential expression of hematopoietic genes involved in erythrocyte or megakaryocyte production was observed. This global view of the changes in the bone marrow transcriptome over both short term (torpor vs. IBA) and long term (torpor vs. July) hypothermia can explain several observations made about circulating blood cells and the structure and strength of the bone during hibernation.

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Oral Immune Activation by Disgust and Disease-Related Pictures

Journal of Psychophysiology ◽

10.1027/0269-8803/a000143 ◽

2015 ◽

Vol 29 (3) ◽

pp. 119-129 ◽

Cited By ~ 4

Author(s):

Richard J. Stevenson ◽

Deborah Hodgson ◽

Megan J. Oaten ◽

Luba Sominsky ◽

Mehmet Mahmut ◽

...

Keyword(s):

Immune Response ◽

Immune Responses ◽

Innate Immune Response ◽

Negative Control ◽

Innate Immune ◽

Innate Immune Responses ◽

Immune Markers ◽

Before And After ◽

Secondary Analyses ◽

Image Set

Abstract. Both disgust and disease-related images appear able to induce an innate immune response but it is unclear whether these effects are independent or rely upon a common shared factor (e.g., disgust or disease-related cognitions). In this study we directly compared these two inductions using specifically generated sets of images. One set was disease-related but evoked little disgust, while the other set was disgust evoking but with less disease-relatedness. These two image sets were then compared to a third set, a negative control condition. Using a wholly within-subject design, participants viewed one image set per week, and provided saliva samples, before and after each viewing occasion, which were later analyzed for innate immune markers. We found that both the disease related and disgust images, relative to the negative control images, were not able to generate an innate immune response. However, secondary analyses revealed innate immune responses in participants with greater propensity to feel disgust following exposure to disease-related and disgusting images. These findings suggest that disgust images relatively free of disease-related themes, and disease-related images relatively free of disgust may be suboptimal cues for generating an innate immune response. Not only may this explain why disgust propensity mediates these effects, it may also imply a common pathway.

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