Mutualism Mutualism: Inter-specific relationship from which both species benefit Mutualism Symbiosis: Intimate (generally obligate) inter-specific relationships from which both partners benefit Mutualism Pollination by animals (ie birds, bees, moths, butterflies, beetles, ants, mammals) Pollinators receive food rewards (nectar and pollen), plants have pollen moved to other flowers 1. Antagonistic origin in a predator/prey relationship 1. Antagonistic origin in a predator/prey relationship Early plants were probably wind pollinated and insects were predators feeding on spores, pollen or ovules 1
1. Antagonistic origin in a predator/prey relationship Early plants were probably wind pollinated and insects were predators feeding on spores, pollen or ovules 2. Evolution of plant traits that minimize negative impact of insects a) protect ovules and pollen Closed carpel to protect ovules By chance, some floral visitors were less damaging and perhaps even beneficial in moving pollen between plants, thus selecting for traits in plants that would minimize damage and cost and maximize pollen transfer Defend pollen with chemical or physical defenses 2. Evolution of plant traits that minimize negative impact of insects a) protect ovules and pollen Bees are sophisticated pollen predators 2. Evolution of plant traits that minimize negative impact of insects b) minimize cost of rewards Pollen is an expensive reward, but nectar is cheaper Bilateral symmetry in flowers minimizes pollen predation by bees 2
3. Evolution of traits that attract beneficial insect pollinators By restricting access to only the most efficient pollinators, pollen will more likely be transferred to a conspecific (same species) rather than wasting pollen on the wrong species Visual attraction with UV patterns Long corollas require long tongues Visual attraction Olfactory attraction (nocturnal pollinators) Evolution of syndromes for a subset of pollinators, e.g. humming bird flowers are red, tubular, easy access for hovering birds, high amounts of nectar, low concentrations Evolution of syndromes for a subset of pollinators, e.g. bat-pollinated flowers are white, open for easy access, high amounts of nectar at night, lots of pollen to compensate for high nectar costs 3
Fly pollinated flowers smell like rotten flesh, are often purple or brown, can heat up and give no reward (faking out the carrion flies) Orchids have very specialized coevolved relationships with male orchid bees which visit flowers to collect chemicals to incorporate into their sexual pheromones (perfumes) 5. Animals will be under selection to maximize rewards and avoid defenses This orchid smells and looks like a female fly, so male flies visit the flower, try to copulate with the flower, and in the process transfer pollen (another example of faking out the flies 4
Scarlet gilia : an example of selection between pollinator and plant Common in mountain meadows throughout the west. Polymorphism for flower color (white and red) Scarlet gilia : an example of selection between pollinator and plant Seasonal shift selection for flower color: ref favored early and white favored late Percentage of total pollinators Percentage seed set white red July August Red preferred by humming birds, white by hawkmoths Percentage of total plants July August Fruit dispersal by wind, water, gravity and animals 1. Origin in seed predation Jaguars Jaguars Mammals Mammals Large <==> Small Large <==> Small Seeds Seeds Seeds Seeds Scatter hoarding by seed predators (storing seeds for later consumption), but some seeds escape and germinate Seed predators/dispersers influence seed establishment and plant composition 5
2. Seeds are expensive and valuable, so plants evolve mechanisms to defend the seed (usually with toxins). 3. Plants evolve a cheaper reward to attract dispersers (fleshy fruits). 4. And attractive displays (color). 2. Seeds are expensive and valuable, so plants evolve mechanisms to defend the seed (usually with toxins). 3. Plants evolve a cheaper reward to attract dispersers. 4. And attractive displays (color). Acacia seeds with fleshy aril for dispersay by birds and ants Evolution of edible fruit parts and inedible seeds (offspring) minimizes seed destruction and maximizes dispersal Advantages to the animals - food supply Advantages to the animals - food supply Resplendant Quetzal and wild Avocado (Lauraceae) Some plants have adaptations for specific dispersers 6
Advantages to the plants 1. Reduces competition between seedlings and parent plant Advantages to the plants 2. Gets seeds deposited with package of nutrients Advantages to the plants 3. Targeted dispersal to specific specialized sites mistletoe plant mistletoe seeds stuck to bark Advantages to the plants 4. Avoid specialized herbivores and seed predators that are concentrated on the parent tree 7
Advantages to the plants: an example from wild nutmeg (Virola) Number of seeds dispersed Greatest success of seedlings Number of seedlings surviving Distance from parent from Janzen and Connell If all seeds landed under the parent plant, there would be no successful recruitment of seedlings due to specialized herbivores and seed predators This will prohibit the establishment of single species stands and increase forest diversity All seeds killed by weevils Increased seed survival farther from parent 8