Lecture XI – Symbioses + Sociality PDF

Lecture XI – Symbioses + Sociality  By the end of class, you should be able to… Define species interactions like mutualisms and group social interactions in terms of their costs and benefits Explain ‘case studies’...

Lecture XI – Symbioses + Sociality  By the end of class, you should be able to… Define species interactions like mutualisms and group social interactions in terms of their costs and benefits Explain ‘case studies’ of classic symbioses, like remoras and sharks, or oxpecker birds and ungulates Learning Differentiate between obligate and facultative mutualisms and describe how these interactions Objectives influence species distribution and ecosystem functioning Describe different forms of sociality (e.g., cooperation, altruism, eusociality) and explain how these behaviors increase survival and reproductive success in certain species. Define the terminology associated with this lecture  Terminology - be able to define the following: Coevolution - The process by which two or more species reciprocally influence each other’s evolution through interactions like predation, competition, or mutualism. Mutualism - A type of symbiosis where both species benefit from the interaction, such as bees pollinating flowers while collecting nectar. Commensalism - A symbiotic relationship where one species benefits while the other is neither helped nor harmed, like birds nesting in trees. Parasitism - A symbiotic relationship where one species (the parasite) benefits at the expense of the other (the host), often causing harm but not immediate death, like ticks feeding on mammals. Parasitoidism - A relationship in which a parasitoid (often an insect) lays its eggs on or inside a host, and the developing larvae eventually kill the host, as seen with certain wasps and caterpillars. Phoresy (or phoresis) - A form of commensalism where one organism uses another for transportation, such as remoras on sharks. Obligate mutualisms - A mutualistic relationship where both species are entirely dependent on each other for survival. Facultative mutualisms - A mutualistic relationship where both species benefit but are not dependent on each other for survival. Cooperation - A behavior where individuals of the same or different species work together for a common benefit, such as hunting in packs or sharing resources. Altruism - A behavior in which an individual sacrifices its own fitness to help others, often relatives, as seen when animals warn their group of predators at their own risk. Eusociality - A complex social organization, found in species like ants and bees, characterized by cooperative brood care, overlapping generations, and division of labor into reproductive and non-reproductive groups. Kin selection - A form of natural selection that favors altruistic behavior toward relatives, increasing the indirect fitness of the altruist by helping relatives pass on shared genes.  Case Study: Myxomatosis & invasive rabbits Two dozen rabbits were released on a ranch in Australia in 1859 Within decades, rabbit populations were in the hundreds of millions With plenty of food and no natural predators or competitors, rabbits exploded in population Scientists introduced a myxoma virus to the rabbits  Myxomatosis & invasive rabbits Myxoma is related to smallpox, but carried by mosquitoes Was common in South American rabbits First myxomatosis epidemic killed 99.8% of rabbits Then 90% of rabbits in 2nd season Then around 50% in 3rd season Coevolution between virus and rabbits to coexist  Fitness. Why do an organism’s ability to survive, mutualisms reproduce, and pass on its genes to the next generation. exist at all? the more successful an organism is at reproducing and ensuring the survival of its offspring, the higher its fitness.  mutualisms can enhance the survival and reproductive success (fitness) Mutualisms both organisms provide benefits to each other, enhance fitness such as food, protection, or other resources for both species which, in turn, improve their chances of surviving, reproducing Example: pollinators A bee pollinating a flower benefits by receiving nectar (increasing its fitness through nourishment) The plant benefits by having its flowers pollinated (increasing its fitness through successful reproduction). Mutualisms are the result of coevolution Coevolution: when populations of two or more species interact, each evolving in response to the other, and where both are optimizing their fitness  i.e., plants and animals use a variety of structures and behaviors to obtain resources and avoid being eaten or parasitized Coevolution: where predators, prey, and competitors select traits in each other that tend to alter their interactions Coevolution examples Ex. wing markings help moths to blend in with their background Aposematic animals coevolve with potential predators Flowers, with their colors and scent, call attention to themselves and attract pollinators like insects How is coevolution different from other adaptation scenarios? Coevolution is about how biological Coevolution stimulates phenomenon can mutual change in two shape adaptation (not agents physical explanations)  Ex. a cheetah, as a predator, helps shape their prey’s adaptations for escape Coevolution stimulates And also respond to their same changes mutual change in By consuming slower or more obvious prey, predators leave behind cryptic or faster prey two agents These lucky prey pass on their genes to the next generation… if predators remained static, they should see reducing success in prey capture with every new generation Putting the ecology into coevolution Coevolution began as an idea in genetics Ehrlich & Raven in 1964 popularized coevolution Ex. closely-related butterflies (Heliconius) fed on closely- related host plants (Passiflora) Suggesting that the butterflies and plants had a long evolutionary relationship  Symbiotic— intimate Not necessarily (involving mutualistic (can All mutualisms strong physical connection) and also be parasitic or are symbioses, prolonged interaction commensal) but not all symbioses are Nonsymbiotic— mutualisms. not intimate and/or short- Ex. Pollination lived interaction  Classic examples of symbioses (review) Commensalism: A symbiotic relationship where one species benefits, while the other is neither helped nor harmed. Example: Barnacles attached to a whale. The barnacles benefit by being transported (phoresy) to nutrient- rich waters, while the whale is unaffected. Classic examples of symbioses (review) Mutualism: A symbiotic relationship where both species benefit. Example: The relationship between bees and flowering plants. Bees get nectar (food) from the flowers, while plants receive the benefit of pollination, aiding in their reproduction. Types of Mutualism: Obligate: association is essential for survival and/or reproduction Ex. Corals and zooxanthellae Facultative: association is not strictly essential for fitness Ex. Seed dispersal by animals (birds, fish, mammals) Classic examples of symbioses (review) Classic examples of symbioses (review) Classic examples of symbioses (review)  Case Study: Ants & Acacias  Recreate the table shown here: Costs and Benefits For each of the following examples, fill in the table Group Exercise: with what you think the relative costs and benefits of the association between the two species. Think about what might affect their fitness You will have 3 minutes and then we will discuss as a class.  Do Mutualisms have a positive effect on each species’ populations mutualisms Each species’ fitness should make sense increase in the long Is this sustainable? Wouldn’t run? populations increase forever? Or are mutualism benefits just weak? Or have diminishing returns? This would mean that mutualisms have little effect on population growth What if we consider that the benefits of mutualisms can become saturated Or are mutualism benefits just weak? Or have diminishing returns? Thought experiment: Plants gain reproductive benefits when they are pollinated What happens as pollinators increase in abundance? What happens if more and more and more pollinators are added? Populations reach an asymptote where increases in the population of one mutualist do not cause an increase in the other Better reflects reality (probably) Another issue with mutualisms… Each species should evolve to maximize benefit to itself Mutualisms come at a cost for each associated species Mutualisms often evolve from existing parasitic or competitive interactions Gaining greater and greater benefit at less and less cost should be evolutionarily favored over maintaining a mutualism (i.e., “cheating”) BUT…Mutualisms are widespread Mutualisms are highly conserved Mutualisms rarely evolve into parasitic relationships Why and how are so many abundant and diverse mutualisms maintained when “cheating” should be evolutionarily favored? Then how are mutualisms maintained? Then how are mutualisms maintained? Partner fidelity Partner control Partner choice—choosing the most beneficial partner at the least cost from the start of the association Partner sanctions—negative selection against less beneficial partners E.g., Plant-mycorrhizal mutualisms engage in both partner choice and partner sanctions  Sociality INTRASPECIFIC POSITIVE SOCIAL BEHAVIOR CAN COOPERATION: TWO INTERACTION— INTERACTION FOR AFFECT THE FITNESS OR MORE INVOLVES TWO OR BOTH +/+ OF MORE THAN ONE INDIVIDUALS RECEIVE MORE INDIVIDUALS INDIVIDUAL A NET BENEFIT, FROM THE SAME DESPITE SOME SPECIES INCURRED COSTS Cooperation Kinship Prediction: cooperation and altruism should be highest among close relatives Inclusive fitness theory—Relatives are likely to share more genes than non-relatives Direct fitness—the number of offspring an individual produces Indirect fitness—the effect of the individual’s behavior on the fitness of its relatives Reciprocity Reciprocity Group Selection Group Selection Eusociality— extreme sociality among kin! Reproductive division of labor Cooperative rearing of young Overlapping generations that live and work together What organisms are eusocial?* Hymenopterans— wasps, bees, and ants Hymenopterans— wasps, bees, and ants Is being haplodiploid necessary for eusociality? No. All hymenopteran species are haplodiploid, but only some evolved eusociality Diploid species can also evolve eusociality (e.g. naked mole rats) Haplodiploidy alone doesn’t cause eusociality, but it can help explain why there are so many eusocial hymenopterans  Competition—Intraspecific competition for mates Social species don’t always get along Parental Investment—how much parental care does each mate provide? How much investment though… does each parent provide to the offspring? Siblings compete for resources