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Parasitoids (insects whose larvae are the actual “predator”) Parasitoids differ from parasites in that they almost always kill their hosts. The adult parasitoid only needs the host as food for its offspring Parasites are obligately dependent on their hosts – so better adapted parasites get what they need without killing their host! 1 Parasites can alter the behaviour of their hosts Note only does the liver fluke require the cow (and 2 other hosts), it has evolved a mechanism to alter the behaviour of those hosts to move it around! cercaria and metacercaria are just names for different fluke life stages 2 Dicrocoelium: the liver fluke A form of the parasite passes out of the infected sheep/cow in its feces Cionella, a snail, picks up the parasite while feeding on sheep/cow poop The parasite metamorphoses ending up in the snail’s “lungs” and is released along with the mucous in the snails’ slime trails Ants pick up the parasite while feeding on the snail slime One of the parasites migrates to the ant’s “brain” [Ants normally retreat to their burrows late in the afternoon remaining there until the next day.] However, parasitized ants climb up onto the tips of grass blades, clinging on by their jaws, throughout the night. Consequently the ant becomes a prime target for accidental ingestion by grazing cows/sheep, thus completing its life cycle. 3 Pathogens can mimic flowers Not all bright alpine meadow flowers are quite what they seem! This bright yellow, sweet smelling “flower” is actually a fungus parasitizing a mustard plant Insects, attracted to the structure, carry fungal reproductive cells to other infected mustard plants, promoting the cross fertilization prerequisite to fungal reproduction The fungal structure prevents the mustard from flowering and producing its own seed – leading to significantly reduced mustard success. 4 Nevertheless, exploitation is a two way street: prey are not passive victims! n n n Evolution of protective or defensive adaptations help species avoid exploitation Flight, aggressive posturing, cryptic colouration, herd behaviour, chemicals (animals) Thick bark, spines, thorns, chemical defenses, cryptic colouration (plants) 5 Protection in numbers: Predator satiation n n n n Emerge as adults once every 17 years (although broods emerge every year at different geographic locations in eastern NA location) Millions emerge from the ground over a period of only a few days with up to 4x106 or 3,700 kg of cicadas.ha-1! Males fly up into the tree tops, singing to attract females who lay their eggs in the twigs of trees and shrubs When the young cicadas hatch, they drop to the ground, burrow down to a tree root and begin to feed without moving around much for 17 years!! n Williams, et al. Ecology 74:1143-52 n Cicada mortality (%) -1 Live Cicadas (#.ha ) Periodic Cicadas n n n n Kathy Williams monitored bird predation rates on cicadas Her data support a predator satiation hypothesis Cicada abundance peaked in late May (50% of emergences were in 4 days) declining through June Predation is significant in early emergence when cicada density if low At peak emergence, predation declines markedly Predation climbs to 100% as cicada density declines 6 Protection by size Recall that the young of many species may be vulnerable to predators, while the adults are not (recruitment limitation) *Peckarsky. Aquatic insect predator-prey. Ecology 55: 1104-11 Sometimes just looking bigger might confer protection from predation: Stoneflies can be injured by large mayflies and tend to avoid them. Barb Peckarsky’s* data suggest that smaller mayflies, who present no danger to a stonefly, may protect themselves by adopting the “scorpion stance” i.e. trying to look larger. A stone fly, a predatory The herbivorous mayfly aquatic insect 7 Protection through crypticity katydid giant stick insect spanworm Fig. 4-5A (KR8C) 8 Protection through barriers The surface of the leaves of many plants are covered with protective trichomes that can negatively impact wandering herbivores by physically obstructing their movements Scanning electron micrograph of trichomes on the leaves of the passion flower, P. lobata 9 Protection by chemistry: A plant can ‘identify’ a specific herbivore from the nature of the damage it does to the plant Tortoise beetles nibble at the edges of leaves Flea beetles gnaw holes in the leaf’s centre 10 Once the plant has ‘identified’ the insect eating its leaves, it ‘retaliates’ n n It might release a chemical compound that interferes with the herbivore’s digestion, reproduction or otherwise kills the herbivore Or the plant might release ‘perfumes’ (volatile compounds) that signal the presence of the herbivore to a predator of the herbivore – usually a parasitoid – who finds and destroys the herbivore Hey remember these guys? 11 So there is an obvious advantage to a prey population that can defend itself against exploitation (often referred to as ploys), but of course there is a corresponding pressure for the exploiter to counter-attack (the counter ploy) n n n Suppose a plant does produce a chemical that interferes with a herbivore that is attacking it Herbivores also can produce saliva containing chemicals that move into the plant Such herbivore induced chemicals can alter the plant’s anti-herbivore chemicals, shifting the advantage back to the herbivore. 12 How might this work? (hopefully you know)! n n n n A random mutation could occur in a plant that creates a chemical that ‘inactivates’ an insect herbivore. The leaves of the plant with that chemical are in better shape than the leaves of plants without the chemical (i.e. they’re not being chewed). Healthier leaves increase photosynthesis (energy), ultimately leading to enhanced seed production for the plant (i.e. it leaves more offspring) Plants with these defensive chemicals are likely to be ‘selected for’ and come to dominate the population. 13 Of course, the same thing could happen with the development of the counter ploy in the herbivorous insect n n n An insect which acquires a counter ploy (or defense) to plant chemicals will feed more successfully than insects without counter chemicals These lucky insects will be able to acquire more food than their peers and leave more offspring (i.e. they will be selected for). Eventually the population of herbivores will be dominated by individuals with the ability to release counter defense chemicals. Since ploys/counterploys can only develop over evolutionary time, they are often referred to as “co-evolution” 14 Ploy counterploy in the parasitoid fly: Arachnidomyia lindae Flies deposit their eggs onto the egg sac of the spider. The developing fly larvae eat the spider’s eggs (not good for a spider’s fitness!) 15 The counter-ploy The spider can recognize this predatory fly by the ‘buzzing” of its wings, a wingbeat signature. (Think about the + fitness consequences for a spider that could do this! How would it happen?) n When facing this particular fly the spider starts a sequence of egg sac guarding behaviours that include: n • “shuttling” (the spider maneuvers around its egg sac to keep itself between the fly and its egg sac); • “grooming” (the spider searches the surface of its egg sac removing any eggs the fly managed to deposit). n This fly-spider interaction suggests that the behavior of these two ecologicallylinked species co-evolved in a stepwise fashion 16 The ploy: the “squirt gun” defense A rather dramatic anti-herbivore defense by a species of Bursera: The leaves have a network of pressurized canals – when an herbivore who is chewing on a leaf severs one of these, a spray of sticky terpenes shoots out. Herbivores hit by the sticky stream abandon the leaf quickly, try to clean themselves. Often they die. Becerra, et al. 2001. Interactions Between Chemical and Mechanical Defenses in the Plant Genus Bursera and Their Implications for Herbivores. American Zoologist. 41:865-876 17 Unfortunately for Bursera … the squirt gun is a bit of a one-trick pony n n After one leaf fires, no other leaves in a 20-30 cm radius seem to be able to respond for 2448 hours However, herbivores seem to be effectively deterred as the first leaf they choose responds This raises questions 1. How come insects don’t hang around, waiting for somebody else to get squirted and then move in for the feast? 2. Is herbivory not a sufficiently strong pressure to drive selection for more leaves that can respond? 18 Maybe there has just not been sufficient time (?) b A half-hearted counter-ploy: an evolutionary work in progress? nBoth the larva of nymphalid butterflies (a) and Chrysomelid beetles (b), common herbivores on Bursera, attempt to sabotage the squirt gun defense by severing the terpene canals before feeding (ok – that will work) nUnfortunately for the larva, this takes more time (30-90 minutes) than it would to consume a leaf (10-20 minutes) a a b The increased “handling time” leaves the larvae subject to predation (c), slows growth and time to pupation n Hmmm . . . 19 n c The pressures on competitors vs predators/prey vs responses to disturbance may be different . . . n The pressures on potential competitors for specializations that create unique ways to access resources • Reducing time/energy spent in competitive activities frees up more time time/energy to engage in other activities that promote survival and reproduction for an individual. n The pressures on prey for adaptations that make them less conspicuous or otherwise capable of avoiding exploitation. • Dying prior to reproduction definitely reduces an individual’s fitness. n n The pressures on exploiters that enhance their ability to capture prey The pressures on species to successfully weather disturbances whether that “disturbance” is fire, drought or etc. 20 But in spite of the variety of “pressures” acting on species, the outcome is the same: adaptation n n n Individuals with various traits that promote reproduction (and the number of offspring produced) will come to dominate the population over time Individuals without these adaptations are likely to disappear (eventually). Remember: this is what we mean by “survival of the fittest” • Where “fitness” is defined by the number of offspring particular individuals put into the next generation. 21 The complicated relationships we have been exploring can only develop over extremely long periods of time They help us understand: 1. Why anthropogenic activities (events occurring in microseconds of Earth’s history) are so antagonistic to the web of biological interactions that maintain K-system persistence 2. The futility of trying to preserve/protect biodiversity with anything other than habitat preservation 3. The devastating impacts of species introductions 22