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

In the Hamadryas baboon, males are substantially larger than females. A troop of baboons is subdivided into a number of ‘one-male groups’, consisting of one adult male and one or more females with their young. The male prevents any of ‘his’ females from moving too far from him. Kummer (1971) performed the following experiment. Two males, A and B, previously unknown to each other, were placed in a large enclosure. Male A was free to move about the enclosure, but male B was shut in a small cage, from which he could observe A but not interfere. A female, unknown to both males, was then placed in the enclosure. Within 20 minutes male A had persuaded the female to accept his ownership. Male B was then released into the open enclosure. Instead of challenging male A , B avoided any contact, accepting A’s ownership.

Evolution and the Theory of Games

Plant hormones have pivotal roles in the regulation of plant growth, development, and reproduction. Additionally, they emerged as cellular signal molecules with key functions in the regulation of immune responses to microbial pathogens, insect herbivores, and beneficial microbes. Their signaling pathways are interconnected in a complex network, which provides plants with an enormous regulatory potential to rapidly adapt to their biotic environment and to utilize their limited resources for growth and survival in a cost-efficient manner. Plants activate their immune system to counteract attack by pathogens or herbivorous insects. Intriguingly, successful plant enemies evolved ingenious mechanisms to rewire the plant’s hormone signaling circuitry to suppress or evade host immunity. Evidence is emerging that beneficial root-inhabiting microbes also hijack the hormone-regulated immune signaling network to establish a prolonged mutualistic association, highlighting the central role of plant hormones in the regulation of plant growth and survival.

/pdf/hormonal-modulation-of-plant-immunity-na0dumzzdp.pdf

Hormonal Modulation of Plant Immunity

Parasitoids and predators of herbivores have evolved and function within a multitrophic context. Consequently, their physiology and behavior are in­ fluenced by elements from other trophic levels such as their herbivore victim (second trophic level) and its plant food (first trophic level) (126) . Natural enemies base their foraging decisions on information from these different trophic levels, and chemical information plays an important role. This review is restricted to the ecology of chemical information from the first and second trophic levels. The importance of so-called infochemicals, a subcategory of semiochemicals, in foraging by parasitoids and predators has been well documented (e.g. reviewed in 31, 78, Il l , 183, 185) , and we do not intend to repeat the details. But because of a lack of testable hypotheses, all this research is conducted rather haphazardly: the total puzzle of infochemical use has not been solved for any natural enemy species. Here we approach the use of infochemicals by natural enemies from an evolutionary and ecological standpoint. Our basic concept is that information from the first and second trophic levels differs in availability and in reliability, a difference that shapes the way infochemicals are used by a species. We generate hypotheses on (a)

/pdf/ecology-of-infochemical-use-by-natural-enemies-in-a-klyl2klq7j.pdf

Ecology of infochemical use by natural enemies in a tritrophic context.

In this paper we review the empirical studies documenting trait-mediated indirect interactions (TMIIs) in food webs. Basic models and empirical approaches that form the foundation of our conceptualization of species interactions generally assume that interactions are an intrinsic property of the two interacting species and therefore are governed by their respective densities. However, if a species reacts to the presence of a second species by altering its phenotype, then the trait changes in the reacting species can alter the per capita effect of the reacting species on other species and, consequently, population density or fitness of the other species. Such trait-mediated indirect interactions can reinforce or oppose density-mediated effects and have been largely overlooked by community ecologists. We first briefly develop the case for the broad mechanistic basis for TMIIs and then review the direct evidence for TMIIs in various permutations of simple three- to four-species food webs. We find strong evid...

A review of trait-mediated indirect interactions in ecological communities

Intraguild predation is thought to be ubiquitous in natural food webs. Yet, theory on intraguild predation predicts the intraguild prey to persist only under limited conditions. This gap between theory and empirical observations needs scrutiny. One reason might be that theory has focused on equilibrium dynamics and a limited set of species (usually three) that interact in well-mixed populations in unstructured habitats, and these assumptions will often not hold in natural systems. In this review, we focus on the effects of habitat structure on intraguild predation. Habitat structure could reduce encounter rates between predators and prey and could create refuges for prey. In both cases, habitat structure could reduce the strength of intraguild interactions, thereby facilitating species coexistence. A meta-analysis of studies on manipulation of habitat structure shows that intraguild prey indeed suffer less from intraguild predation in structured habitats. This was further confirmed by a meta-analysis in which studies on intraguild predation were classified according to habitat structure. Intraguild predation reduced densities of the intraguild prey significantly more in habitats with little structure than in habitats rich in structure. The effect of intraguild predation on the shared prey was negative, and not significantly affected by habitat structure. We conclude that habitat structure may increase persistence of the intraguild prey by decreasing the strength of the interaction between intraguild predator and intraguild prey.

https://www.jstor.org/stable/info/27651427

Habitat structure affects intraguild predation

Mites of the family Phytoseiidae are known to be predators of whiteflies in several agroecosystems, especially of Bemisia tabaci Gennadius, a pest with high resistance to chemical insecticides that occurs in greenhouses in temperate regions. We collected predatory mites that were found to co-occur with whiteflies in the Middle East for control of B. tabaci: Typhlodromus athiasae (Porath and Swirski), Neoseiulus barkeri Hughes, Typhlodromips swirskii (Athias-Henriot), Euseius scutalis (Athias-Henriot), Phytoseius finitimus Ribaga. As a first step in the evaluation of these species as biological control agents, we measured their life-history traits when feeding on whiteflies. The intrinsic rates of increase (rm) of the predatory mite species ranged between 0.131 and 0.215 per day and E. scutalis had the highest rm estimated. Comparisons with the rm of B. tabaci indicate that some of the species should be capable of suppressing local populations of whitefly. The ability of predators to use alternative food was also tested, since it facilitates the setup of mass cultures and it can promote their persistence in the crop, even if the prey is scarce. All predatory mite species tested were able to survive and reproduce on a diet of broad bean pollen.

Phytoseiid predators as potential biological control agents for Bemisia tabaci.

Mitess of the family Phytoseiidae are known to be predators of whiteflies inn several agroecosystems, especially of Bemisia tabaci (Gennadius), a pestt with high resistance to chemical insecticides that occurs in greenhousess in temperate regions. We collected predatory mites that weree found to co-occur with whiteflies in the Middle East for control of B.B. tabaci: Typhlodromus athiasae (Porath 6t Swirski), Neoseiulus barkeri Hughes,, Typhlodromips swirskii (Athias-Henriot), Euseius scutalis (Athias-Henriot),, Phytoseius finitimus Ribaga. As a first step in the evaluationn of these species as biological control agents, we measured theirr life-history traits when feeding on whiteflies. The intrinsic rates of increasee (rm) of the predatory mite species ranged between 0.131 and 0.2155 days' 1 and E. scutalis had the highest estimated. Comparisons withh the rm of B. tabaci indicate that some of the species should be capablee of suppressing local populations of whitefly. The ability of predatorss to use alternative food was also tested, since it facilitates the set-upp of mass cultures and it can promote their persistence in the crop,, even if the prey is scarce. All predatory mite species tested were ablee to survive and reproduce on a diet of broad bean pollen.

Phytoseii dd predators as potential biological controll agents for Bemisia tabaci

https://pure.uva.nl/ws/files/2536370/163075_Mechanisms_and_ecological_consequences_of_plant_defence.pdf

Mechanisms and ecological consequences of plant defence induction and suppression in herbivore communities.

Plants infected with pathogens often attract the pathogens' vectors, but it is not clear if this is advantageous to the vectors. We therefore quantified the direct and indirect (through the host plant) effects of a pathogen on its vector. A positive direct effect of the plant-pathogenic Tomato spotted wilt virus on its thrips vector (Frankliniella occidentalis) was found, but the main effect was indirect; juvenile survival and developmental rate of thrips was lower on pepper plants that were damaged by virus-free thrips than on unattacked plants, but such negative effects were absent on plants that were damaged and inoculated by infected thrips or were mechanically inoculated with the virus. Hence, potential vectors benefit from attacking plants with virus because virus-infected plants are of higher quality for the vector's offspring. We propose that plant pathogens in general have evolved mechanisms to overcome plant defences against their vectors, thus promoting pathogen spread

Arne Janssen

Papers

Habitat structure affects intraguild predation

Phytoseiid predators as potential biological control agents for Bemisia tabaci.

Phytoseii dd predators as potential biological controll agents for Bemisia tabaci

Mechanisms and ecological consequences of plant defence induction and suppression in herbivore communities.

Herbivore arthropods benefit from vectoring plant-viruses