So far in this course we have dealt entirely with the evolution of characters that are controlled by simple Mendelian inheritance at a single locus. There are notes on the course website about gametic disequilibrium and how allele frequencies change at two loci simultaneously, but we didn’t discuss them. In every example we’ve considered we’ve imagined that we could understand something about evolution by examining the evolution of a single gene. That’s the domain of classical population genetics. For the next few weeks we’re going to be exploring a field that’s actually older than classical population genetics, although the approach we’ll be taking to it involves the use of population genetic machinery. If you know a little about the history of evolutionary biology, you may know that after the rediscovery of Mendel’s work in 1900 there was a heated debate between the “biometricians” (e.g., Galton and Pearson) and the “Mendelians” (e.g., de Vries, Correns, Bateson, and Morgan). Biometricians asserted that the really important variation in evolution didn’t follow Mendelian rules. Height, weight, skin color, and similar traits seemed to

Human biochemical genetics

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Modern Applied Statistics With S

Genetics and analysis of quantitative traits

In the face of continuous threats from parasites, hosts have evolved an elaborate series of preventative and controlling measures - the immune system - in order to reduce the fitness costs of parasitism. However, these measures do have associated costs. Viewing an individual's immune response to parasites as being subject to optimization in the face of other demands offers potential insights into mechanisms of life history trade-offs, sexual selection, parasite-mediated selection and population dynamics. We discuss some recent results that have been obtained by practitioners of this approach in natural and semi-natural populations, and suggest some ways in which this field may progress in the near future.

Ecological immunology: costly parasite defences and trade-offs in evolutionary ecology

Sexual Behavior in the Human Male

The battle of the sexes takes a sinister turn in the bean weevil. Because the costs and benefits of polygamy differ for males and females, copulation is not always a cooperative venture between the sexes1. Sperm competition2 can build on this asymmetry, producing male traits that harm females3,4 thereby generating coevolutionary arms races between the sexes5. We have found that the male genitalia of the bean weevil Callosobruchus maculatus damage the female genitalia, and that females act to reduce the extent of this damage. We propose that these functionally diametric sexual traits form the basis of reproductive conflict.

Genital damage, kicking and early death

Ecological immunology is a rapidly expanding field that examines the causes and consequences of variation in immune function in the context of evolution and of ecology. Millions of invertebrate species rely solely on innate immunity, compared with only 45,000 vertebrate species that rely additionally on an acquired immune system. Despite this difference in diversity, most studies of ecological immunology focus on vertebrates. Here we review recent progress derived largely from the mechanistic analysis of invertebrate innate immunity. Using this empirical base, we pose general questions in areas that are of central importance for the development of ecological immunology.

https://science.sciencemag.org/content/sci/301/5632/472.full.pdf

Invertebrate ecological immunology.

The cimicids, or bed bugs, belong to a highly specialized hematophagous taxon that parasitizes primarily humans, birds, and bats. Their best-known member is the bed bug, Cimex lectularius. This group demonstrates some bizarre but evolutionarily important biology. All members of the family Cimicidae show traumatic insemination and a suite of female adaptations to this male trait. Cimicids therefore constitute an ideal model system for examining the extreme causes and consequences of sexual selection. Our dual goal in re-examining the extensive literature on this group is to identify issues relevant to pest control, such as dispersal ecology and the recent global spread, and to understand the selective forces that have shaped the unique aspects of this insect's biology.

/pdf/biology-of-the-bed-bugs-cimicidae-eu4965avmw.pdf

Biology of the Bed Bugs (Cimicidae)

We review recent advances in our understanding of the mechanisms of insect immune defence, but do so in a framework defined by the ecological and evolutionary forces that shape insect immune defence. Recent advances in genetics and molecular biology have greatly expanded our understanding of the details of the immune mechanisms that enable insects to defend themselves against parasites and pathogens. However, these studies are primarily concerned with discovering and describing how resistance mechanisms work. They rarely address the question of why they are shaped the way they are. Partly because we know so much about the mechanisms that it is now becoming possible to ask such ultimate questions about insect immunity, and they are currently emerging from the developing field of ‘ecological immunology’. In this review we first present an overview of insect immune mechanisms and their coordination before examining the key ecological/evolutionary issues associated with ecological immunity. Finally, we identify important areas for future study in insect immunity that we feel can now be approached because of the insight provided by combining mechanistic and ecological approaches.

/pdf/insect-immunity-an-evolutionary-ecology-perspective-5a9fp7mvxg.pdf

Insect Immunity: An Evolutionary Ecology Perspective

There are well documented costs of mating in insects but little evidence for underlying mechanisms. Here, we provide experimental evidence for a hormone-based mechanism that reduces immunity as a result of mating. We examined the mealworm beetle Tenebrio molitor and show that (i) mating reduces a major humoral immune effector-system (phenoloxidase) in both sexes, and (ii) that this down-regulation is mediated by juvenile hormone. Because both juvenile hormone and phenoloxidase have highly conserved functions across all insects, the identified mechanism is similarly likely to be highly conserved. The positive physiological function of mating-induced juvenile hormone secretion is gamete and accessory gland production: we propose that its negative effects on immune function are the consequence of physiological antagonism. Therefore, we have identified a physiological tradeoff between mating and immunity. Our results suggest that increasing mating success can result in increasing periods of immune suppression, which in turn implies that reproductively successful individuals may be more vulnerable to infection by, and the negative fitness effects of, pathogens.

https://www.pnas.org/content/pnas/99/15/9916.full.pdf

Michael T. Siva-Jothy

Papers

Genital damage, kicking and early death

Invertebrate ecological immunology.

Biology of the Bed Bugs (Cimicidae)

Insect Immunity: An Evolutionary Ecology Perspective

Copulation corrupts immunity: a mechanism for a cost of mating in insects.