ESSAY BUGS QUESTIONS 1. Outline the basic principles behind sexual selection. Describe why males are so commonly in competition over females and why females are so commonly choosy. One form of mating behavior that has evolved in insects is gift giving. Describe the mating system of one insect in which gift giving is important. What role does gift giving play in insect mating? Who gives the gift (male or female?) and who receives it? Explain gift giving in light of what you know about sexual selection. Sexual Selection- A type of natural selection where members of the sexes acquire distinct forms either because the members of one sex choose mates with particular features or because in the competition for mates among the members of one sex only those with certain traits succeed. Males and females have different goals for mating. o Males are in intense competition with each other to fertilize a limited number of extremely choosy receptive females. This leads to intense competition among males and the outcome is a remarkable diversity of mating strategies, tactics, and morphologies. o The optimal strategy for males is to fertilize the maximum number of eggs. The optimal strategy for females is to fertilize their eggs with the best sperm. As a result, females are very choosy. Gift giving- Mating is preceded by the presentation of an edible gift from male to female. Females are choosy based on the quality of the gift. o Male reproductive success is correlated with the size of the gift and the duration of feeding by the female. o Females generally re-mate when presented with a small gift. o Males are under strong sexual selection to procure large gifts. Scorpion Flies- Scorpion flies consume living and dead insects. Males collect dead insects that they present to females during mating. The larger the gift, the longer the mating, and the more sperm are transferred. Females offered short gifts generally re-mate afterwards.
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2. Compare and contrast holometabolous and hemimetabolous development. Name three orders that are holometabolous and three orders that are hemimetabolous. When in the fossil record did holometabolous development (metamorphosis) appear? Why is metamorphosis considered a "major adaptation" in insects? Hemimetabolous development- Undergoing development which is gradual and lacks a sharp separation into larval, pupal, and adult stages. Also known as incomplete metamorphosis. The nymph often resemble the adult o Order Orthoptera (grasshoppers and crickets) o Order Mantodea (praying mantises) o Order Blattaria (cockroaches) Holometabolous development- This is also known as complete metamorphosis. The term is applied to insect groups to describe the specific kind of insect development which includes four life stages - as an embryo, a larva, a pupa, and an imago. o Order Coleoptera (Beetles) o Order Diptera (Flies) o Order Hymenoptera (Ants and Bees) Fossil Record- Holometaboly is suspected to appear in the carboniferous period Major Adaptation- Metamorphosis is one of the key elements that explains why insects are so successful. Many insects have immature stages with completely different habitats from the adults. This means that insects can often exploit valuable food resources while still being able to disperse into new habitats as winged adults. The potential for adaptation and evolution is greatly enhanced by metamorphosis.
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3. Describe the dance language of the honey bee. How do honey bees convey distance, direction and quality in the dance? Why can honey bees be said to have different dance "dialects." How can the dance language be viewed as an adaptation? Dance Language of Honey Bee- When an experienced forager returns to the colony with a load of nectar or pollen that is sufficiently nutritious to warrant a return to the source, she performs a dance on the surface of the honey comb to tell other foragers where the food is. The dancer spells out two items of informationdistance and directionto the target food patch. Recruits then leave the hive to find the nectar or pollen. Direction of Food- The direction of the tail-wagging run conveys the direction to the goal. The direction to food is the angle of waggle run relative to vertical. For example, if the food is in the direction of the sun, the dance is directed upward. If it is opposite the sun the dance is aimed down. When the food is 80 degrees left of the sun, the corresponding dance is 80 degrees left of vertical. Distance to Food- To determine the distance of the food, pay attention to the duration of the waggle run and sounds. The rhythm of the dance, or the number of tail-wagging runs per unit of time, communicates the distance. Quality- The intensity of the dance and the number of workers dancing communicates the food quality. Dance Dialects- Not all bees speak the same language. The race of the bee plays large a role in the dialect. Racial differences can be noted in the transition from a round dance to a tail-wagging dance. Goals lying outside a certain radius are described by a directional tail-wagging run. Goals lying within the radius are communicated through nondirectional round dances. Dance language as an Adaptation- The Honey Bee evolved from Stingless Bees and later evolved into Bumblebees. Stingless Bees communicate by leaving odor trails, Honey Bees communicate through the dance language, and Bumblebees communicate the odors of a resource patch through nectar transfer.
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4. Roughly, what proportion of all insects are parasitic? Which orders include endoparasites? Which orders include ectoparasites? Describe three challenges that endoparasitic insects face when inhabiting the host's body. Describe three mechanisms by which host insects defend themselves against Endoparasites. Parasitism can be defined as a relationship between two species in which one, the parasite, obtains its nutritional requirements from the body material of the other, the host. The relationship is always detrimental to the host and beneficial to the parasite. Roughly 20% of all insects are parasitic in life history. Ectoparasites are parasites that feed on the blood or secretions of the host. They are generally much smaller than their host and do not kill their hosts. o Primarily parasitic orders include the Hemiptera, Phthiraptera, and Siphonaptera Endoparasites are parasites that are also called parasitoids. They generally live within the host body and consume the hosts internal organs leading to the death of the host. Endoparasites attack other insect or arthropod hosts. o Orders include Diptera, Hymenoptera, and Strepsiptera. Endoparasites face several biological problems: o Respiration- How to carry out respiration when living inside the hosts tissues. o Digestion/Excretion- How to excrete nitrogenous wastes when doing so may kill the host. o Host Endocrine system- How to isolate ones endocrine system form the hosts. Hosts have several ways of responding to parasites. o Hiding o Struggling o Some hosts have hardened, heavily sclerotized cuticles which make them difficult for predators to catch or parasites to parasitize.
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5. Insects and plants have a long and complex evolutionary history. Roughly half of all insects are herbivores and the earliest insects were probably herbivores. Describe three mechanisms plants use to defend themselves against insects. Describe one way that insects can overcome one or more of these plant defenses. Why do we say that insects and plants are in an evolutionary "arms race"? Over 50% of all insects are herbivores and insects have evolved mouthparts for feeding on an incredible diversity of plant tissues including roots, stems, leaves, flowers, fruits, and seeds. Most insect herbivores are specialists, meaning they eat just a few, closely related plant species. Plants have Physical defenses, Chemical defenses, and Induction. o Physical Defenses- Physical barriers include features of toughness, waxes, and resins. Plants may have structures such as horns and trichomes that act as physical defenses. o Chemical Defenses- One chemical defense is the lack of Nitrogen in a plant. Insects are about 7-14% Nitrogen, so if the plant lacks Nitrogen, this results in low nutrition. Plants also have defense enzymes, for example the protease inhibitor. The inhibitor interferes with the ability of a plant protease to make copies of it. o Induction- Many plant defenses are "turned on" all the time. This can be a waste of energy, so in some plants the defenses are "turned off" until needed. That is an "induced" defense. In most cases the defenses are turned on by attack, but in some cases there are plants that can detect signals from neighboring plants. When their neighbors are attacked they can up regulate their own defenses. This can help defend them against imminent attack. Fecal Shields- Insects pass the defensive chemicals through their body, where they become concentrated in the feces. They put these feces on their back because the chemicals are still strong enough to dissuade predators. Fecal shields actually contain plant toxins so that they are a way for the insect to simultaneously get the toxins out of the body but also use the toxins to defend against predators. The tight ecological interactions between insects and their host plants has lead to a seemingly endless arms race in which the plants evolve more elaborate mechanisms for protecting themselves from insects, and the insects evolve more complex ways of overcoming plant defenses. o This co-evolutionary arms race has lead to some remarkable outcomes, such as talking trees, plant-insect communication, and remarkable deception on the part of both insects and plants.
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