Mutualism First - interspecific competition studies from Wednesday - Interspecific competition in barnacles vs. Barnacles (crustaceans, Arthropoda) start life as free-swimming larval forms. They then settle on rocks and grow in size by molting, but do not move. Researcher found two species: Balanus - covered by water most of the time Chthamalus - exposed most of the time From different areas he removed all adults of one or other species, and continued to remove their settling larvae. Results of manipulation Effects on Balanus - the one covered by water most of the time Distribution didn t change when Chthamalus removed - couldn t colonize area ordinarily occupied by Chthamalus because too dry
Results of manipulation So what does this have to do with niches? Effects on Chthamalus - the one exposed most of the time When Balanus removed, Chthamalus colonized the entire region. Ordinarily Balanus would out-compete Chthamalus in the lower regions by growing over them. So what does this have to do with niches? So what does this have to do with niches? Chthamalus Balanus The niche occupied by Balanus is unaffected by Chthamalus The niche occupied by Chthamalus is reduced in the presence of Balanus
The barnacle study provides an example of competitive displacement: one species niche was contracted in the presence of the other. What do you think would have happened to Chthamalus (the exposed species) if both species had the same fundamental niche? What do you think would have happened to Chthamalus (the exposed species) if both species had the same fundamental niche? The principle of competitive exclusion: when two species occupy the same fundamental niche, they cannot coexist. Chthamalus would have become extinct wherever Balanus was.
Competitive exclusion: An example from the Sonoran desert Graduate student at the U of A looked at competition for seeds among seed feeders 1) Competition among rodents Put fences around areas with holes that excluded kangaroo rats, allowed smaller rodents to pass Competitive exclusion: An example from the Sonoran desert In plots where Kangaroo rat the kangaroo rats were excluded: Copyright (c) Grolier Interactive Inc. There were more species of small rodents, and they were more abundant So, kangaroo rats competitively exclude other rodents Competitive dominance. Another example of competition for seeds in the desert. Competitive dominance. Perhaps most commonly, competition leads simply to the greater abundance of one species than the other. 2) Are ants competing with rodents for seeds? Harvester ant with large seed
2) Are ants competing with rodents for seeds? Removed ants from some plots, rodents from others, kept some as control plots. Rodents Ants Control removed removed plots 2) Are ants competing with rodents for seeds? Yes. Both kinds of seed predators are more abundant when the other kind is removed. No. ant Colonies 543 0 318 No. of Rodents 0 144 122 I. Introduction to mutualisms Mutualism - species interaction that benefits the participants Conditions for evolution - the benefits to individuals of participating must outweigh the costs Potential for conflicts between the participants A. Range of associations 1. Obligate vs. facultative Obligate for both species (i.e. neither partner can survive without the other) Obligate for one species Facultative for both species
A. Range of associations 2. Dependence on a particular mutualist partner Two species mutualism - both species depend entirely on one partner Multispecies mutualism - several species may fill the role of one or both partners A. Range of associations 3. Two species, obligate mutualisms lead to coevolution Coevolution - evolution of species in response to each other 3. Two species, obligate mutualisms lead to coevolution Co-speciation evidence for coevolution - when partners in a mutualism evolve into new species in parallel Aphids feed on phloem sap- deficient in some essential amino acids. Aphids carry bacteria that can synthesize amino acids in specialized organs. Bacteria are transmitted to aphid progeny through the egg. Example - bacterial symbionts of plant-feeding aphids Aphid Buchnera
Coevolution of aphids and symbiotic bacteria - Co-speciation When aphids speciate, so do their resident bacterial symbionts Bacteria Aphids II. Mutualisms in the evolution of life as we know it A. Mutualism between prokaryotes gave rise to the eukaryotes Heterotrophic energy-producing prokaryotes Æ mitochondria And in some, autotrophic prokaryotes Æ chloroplasts II. Mutualisms in the evolution of life as we know it B. Plant-fungus (mycorrhizae) mutualism likely to have been important in colonization of land by plants Plant - mycorrhizae mutualism - a review Mycorrhizae are fungi associated with plant roots
Some mycorrhize penetrate root cells, some stay within intercellular spaces Who does what for whom: Mycorrhizae: procure minerals, protect plant against pathogens Most (80-95%) plants have mycorrhizae Earliest plant fossils do too Mycorrhizae were likely important in allowing plants to colonize early sterile soils Plant: provides carbohydrate source, and in some cases, provides shelter II. Mutualisms in the evolution of life as we know it C. Plant - insect mutualisms important in radiation of both flowering plants and insects II. Mutualisms in the evolution of life as we know it C. Plant - insect mutualisms important in radiation of both flowering plants and insects Angiosperms (flowering plants) and pollinating and seed- dispersing insects radiated together
Mutualists are dominant ecologically III. Types of mutualisms - what does each partner contribute? Most plants have mycorrhizae, many have pollinators, fruit dispersers Corals? Photosynthetic protist symbionts Many if not most animals have symbiotic microbes in guts Do humans have mutualist species? Gut symbionts in mammalscommensal? New evidence suggests important in development and immunity A. Nutrition - nutrition/shelter Food exchange plus housing provided by the larger partner A. Nutrition - nutrition/shelter III. Types of mutualisms 2. N2 fixing bacteria and legume roots A. Nutrition - nutrition/shelter Bacteria: convert atmospheric N2 to nitrogenous compounds 1. Fungal (mycorrhizae) plant Plant: Provides anaerobic housing (nodules) and carbohydrates
A. Nutrition - nutrition/shelter Lichen species are differentiated by their morphology - determined by the algal partner. The same fungus, in association with different algal species is classified as different species. 4. Fungal - algal association - lichens Should there be such thing as a lichen species? Or is a lichen just a sum of its fungal and algal parts? Alga: provides carbohydrate Fungus: provides shelter Lichens can live for thousands of years, live in incredibly harsh environments A. Nutrition - nutrition/shelter 5. Insect - fungal association - e.g. leaf cutter ants A. Nutrition - nutrition/shelter 5. Insect - fungal association - e.g. leaf cutter ants Fungus garden Ants: provide shelter, microclimate, dispersal Fungus: provides carbohydrates from cellulose Fungus garden Recent discovery of even more complexity! Garden fungus is attacked by a pathogenic fungus. Ants carry a specialized bacterium that kills pathogenic fungus.
C. Nutrition - defense mutualisms C. Nutrition - defense mutualisms 1. Ant - acacia mutualism Ants are involved in several of these Certain tropical acacia trees have evolved hollow thorns where ants build their nests C. Nutrition - defense mutualisms C. Nutrition - defense mutualisms 1. Ant - acacia mutualism 1. Ant - acacia mutualism Plant: Provides housing and food (plant grows specialized proteinrich tissues) Ants: Provide defense against herbivores and plant competitors Protection against plant competitors: ants clip new new seedlings around the base of the acacia tree
C. Nutrition - defense mutualisms Nutrition-defense mutualisms 2. Ant-lycaenid interactions 2. Ant - lycaenid butterfly mutualism The two lycaenid species had very different interactions with the ant species. How would you characterize the two sets of species interactions? Almost all species of moths are herbivores. How do you think predation in the second lycaenid caterpillar species evolved? Caterpillars: Have specialized sugary and amino acid secretions the ants feed on Ants: Provide defense against predators and parasitic wasps C. Nutrition - defense mutualisms 3. Hermit crab - anenome III. Pollination mutualisms - case studies of multispecies and two species mutualisms A. Multispecies mutualisms between pollinators and groups of plants Crabs: Provide bits of unconsumed food Plants often evolve a floral morphology that attracts a certain kind of pollinator What does a hummingbird-pollinated flower look like? Anenomes: provide defense against predators such as octopus
III. Pollination mutualisms - case studies of multispecies and two species mutualisms B. An example of a two species pollination mutualism A. Multispecies mutualisms between pollinators and groups of plants Pollinators too may be specialized Vertebrates may have adaptations for nectar harvesting What might be the costs and benefits of a two species pollination mutualism? Cost: Dependence on your mutualist partner through space and time Benefits: Efficient transfer of pollen III. Pollination mutualisms - case studies of multispecies and two species mutualisms III. Pollination mutualisms - case studies of multispecies and two species mutualisms B. An example of a two species pollination mutualism B. An example of a two species pollination mutualism Yuccas and yucca moths Yuccas and yucca moths Every species of yucca has its own species of yucca moth. When yuccas flower, moths emerges from soil, climb to flowers and mate. Within the flower, female moths collect pollen from the anthers, making a big ball stuck to their heads. Then they fly to another plant.
III. Pollination mutualisms - case studies of multispecies and two species mutualisms C. An example of a two species pollination mutualism Yuccas and yucca moths They then oviposit (lay eggs) in a flower, then move to the style and actively stuff pollen into it. then she moves to another flower. C. An example of a two species pollination mutualism -Yuccas and yucca moths Moth larvae develop on some of the developing seeds and fruits - others are unharmed. Moths are totally dependent on yuccas as their only food source. Yuccas are totally dependent on moths for sexual reproduction. A. Cheaters in pollination interactions IV. Mutualism/parasitism - closely related interactions In other cases, independent evolution of cheating, e.g. Deceitful plants Carrion flower A. Cheaters in pollination interactions Dung flower Some plants produce fly-attracting odors. Flies come, may oviposit, and in the process pick up pollen Relatives of the pollinator yucca moths lay eggs in the developing fruit without pollinating- parasitizing both yucca and pollinator. Predaceous lycaenid moth also likely evolved from mutualist
A. Cheaters in pollination interactions Deceitful plants-the lowest of the low A. Cheaters in pollination interactions Deceitful plants Some orchids look and smell like females of certain bees and wasps. males come and try to mate with them, in the process picking up pollen Recent study shows smell a volatile compound that s rare in plants, similar to compound produced by females. In tests of attractiveness, plant-produced compound more attractive than wasp product. For the deception to work as a pollination mechanism, males must make the same mistake twice, once to pick up the pollen, and the second time to deliver it B. Mutualism in one environment may be parasitism in a different environment A. Cheaters in pollination interactions An example with a yucca moth relative, Greya and a wildflower in the Northwest, Lithophragma Cheaters in mutualisms highlight the close evolutionary relationship between mutualism and parasitism At one time, too, mutualists in one environment may be parasites in another
B. Mutualism in one environment may be parasitism in a different environment Greya, like yucca moths, lay eggs in some ovules and pollinate others B. Mutualism in one environment may be parasitism in a different environment Unlike yucca, however, Lithophragma may be pollinated by other pollinators, such as beeflies Bee-flies are efficient pollinators and do not lay eggs in any flowers Mutualism in one environment may be parasitism in a different environment Lithophragma occurs in several mountain valleys and at different elevations in Oregon Mutualism in one environment may be parasitism in a different environment At high elevation sites, Greya is the only pollinator, and here it serves as a mutualist - the plant benefits by its presence
Mutualism in one environment may be parasitism in a different environment At lower elevation sites, the beeflies are present, and the plant sets more seed when Greya is excluded. Here Greya is a parasite, reducing plant fitness. Mutualism in one environment may be parasitism in a different environment So whether the interaction between Greya and Lithophragma should be termed a mutualism or parasitism of the plant by Greya depends on the presence of a third species! IV. Mutualism/parasitism - closely related interactions Mutualism may evolve into parasitism Parasitism may evolve into mutualism IV. Mutualism/parasitism - closely related interactions C. A story of parasitism leading to mutual dependency And some relationships may be difficult to classify
1. Parasitic wasps may be infected with a bacterium called Wolbachia The bacteria are transmitted only in the eggs Infected egg Uninfected egg 1. Parasitic wasps may be infected with a bacteria called Wolbachia It is not in the evolutionary interests of the bacteria to end up in a male wasp. Why not? The bacteria do not want to end up in a male. So. they make all male eggs female! How do they do that? They manipulate the haplodiploid sex determination of their wasp hosts Haplodiploidy n n 2n n Female Male
How does it do that? So in haplodiploid systems Females develop from fertilized, diploid eggs Males develop from haploid, unfertilized eggs In Wolbachia infected wasps, the chromosomes in the male eggs double and the egg develops as a female that can transmit the bacteria... When Wolbachia invades a population of parasitic wasps, eventually the males disappear In this species, the only way to see a male is to treat the females with antibiotics! And because there s no natural selection on male function, mutations accumulate and the males produced when bacteria is removed are sterile When you treat these females with antibiotics, you get males with no mature sperm So the wasp is completely dependent on the bacterium for reproduction and the strain of bacteria is completely dependent on the wasp for a home. Is this a mutualism? It may be difficult to categorize an interaction if you cannot compare species with and without the interacting species