Coevolution

• reciprocal evolutionary change between interacting species (different species evolve together due to close physical proximity)
• Species exist in web of interaction, can lower or increase fitness
• Coevolution observed at both micro (new traits among pop.) and macro (origination of new species) levels of evolution
• lead to adaptations (and counter-adaptations), diversification and ultimately speciation (micro), phylogenies of clades appear congruent (macro)

Example: monarch caterpillar evolved adaptation to feed on highly toxic milkweed (coadaptation and coevolution on micro level)

The strength of reciprocal selection shows

geographic variations

reciprocal selection

selection that occurs in two species due to interactions with each other

Geographic mosaic theory of evolution

geographic structure (mosaic) of populations central to dynamics of coevolution

Coevolution occurs via

natural selection acting on variations affecting species interactions

Applies to mutualism

long-tongued flies feed on flowers with long tubes, longer tongue = more nectar -> longer flower tube = longer time to drink -> more time spent at flower = more pollination rates

Geographic Selection Mosaics

natural selection differs between environments (epigenetics)

Coevolutionary Hotspots

reciprocal selection differs among environments (imbedded within coldspots where non-reciprocal selection occurs)

trait remixing

Genetic structure of coevolving species continually changing via a bunch of stuff

Coevolutionary alteration

one species is in antagonistic relationship with other species (prey coevolves with predator until predator seeks out new prey)

example of coevolutionary alteration

cuckoos obligate brood parasites, host birds developed defenses, cuckoos then make their eggs look like host eggs

example of trait remixing (and maybe coevolutionary alteration)

Rough skinned newt has toxin, garter snake immune to toxin (geo mosaic shown as some snakes have greater immunity, while some newts have more toxin)

Attenuated coevolution

rabbits into australia, invasive -> virus released to kill pop., 90% killed, rest survive -> sequence repeated with same end results

Less virulent strains able to spread more than more virulent strains due to higher death rate

Basically virus goes from lethal to background infection

Coevolutionary categories

two types (mutualism and commensalism), both under facilitation

facilitation

enhancement of population of one species by another

Mutualism

positive/positive relationship between species that raises both fitnesses

• occurs via positive frequency-dependent selection

mutualistic pollinator systems

plant and pollinator benefit, plant by transfer of pollen and pollinator by nectar meal

5 different types of mutualism

obligate, facultative, dispersive, defensive, resource-based

1. obligate

neither species can live without the other (lichens are inseparable mix of fungi and algae)

2. facultative

interaction beneficial but not essential for survival/reproduction of species (ants milk aphids, but can live without aphids if necessary)

3. dispersive

include plants and pollinators that disperse pollen and plants and fruit-eaters that disperse seeds

4. defensive

animals defending plant or herbivore

5. resource-based

increased acquisition of resources for both species

Dispersive Mutualism

Dispersal of pollen and seeds (specialist), 2 ways for plants to prompt pollinator fidelity:

• Specific flowering at certain times of year
• Synchronized flowering of all individuals of a species

Pollination syndromes

some pollinators visit only one plant species (look at picture of coevolution results)

Seed dispersal (mutualistic)

fruits provide nutrients, animals then digest enclosed seeds and disperse, plants signal ripeness via color change

seed dispersal is so advantageous to plants because of

competition avoidance, predator escape, colonization, directed dispersal

Directed dispersal example

mistletoe (obligate parasite) contains sticky substance called viscin (causes seeds to clump together), birds eat seeds, remain sticky through gut, wipe sticky clump onto branch, seeds on ground die

Defensive Mutualism Example

ants and aphids, aphids secrete sugar fluids (honeydew), ants drink honeydew and protect aphids from predators -> cows are to humans as aphids are to ants

Resource-based mutualism Example

both partners can improve supply of essential resources, 90% of seed plants have mutualistic associations with fungi that live in or on root tissue (associations called mycorrhizae)

Common in tropics, allows for greater nutrient absorption

Commensalism

positive/neutral relationship, benefits one species, but has neutral effects on the other

Example:

1. some forms of seed dispersal, barbed seeds transported to new germination sites in mammal furs (seeds benefit, mammals are neutral)
2. cattle egrets feed on beetles near where cattle kick up dirt, good for egrets, cattle not affected

4 types of commensalism

inquilinism (housing), phoresy (transport), metabiosis (use after death), associational resistance (good lives with bad protection)

Inquilinism (housing)

one species uses second species for housing (i.e. orchids grow in forks of tropical trees)

Phoresy (transport)

one organisms uses second organism for transportation (i.e. flower-inhabiting mites travel between travel between flowers in the nostrils of hummingbirds)

Metabiosis (use after death)

organism uses something produced by the first, usually after its death (i.e. hermit crabs uses snail shell for protection

Associational resistance (good lives with bad for protection)

palatable plants gain protection via association with unpalatable plants (ex. marigolds put around garden to ward off deer)

Coevolutionary requires genetic variation

Parasitoid wasp (remember parasite vs. parasitoid) aphidius ervi lays eggs inside aphids -> wasps attack genetically identical aphids, different levels of success observed (this shows little coevolution between species)

Genetic variation can fuel rapid evolution

soapberry bugs example (longer beaks -> longer established balloon vines)

Mullerian mimicry

harmful/distasteful species resemble each other in appearance, facilitates learned avoidance of predators

(ex.) heliconius butterflies produce toxic compounds to birds, butterflies converge on similar wing patterns

Batesian mimicry

harmless species resemble harmful species, thus deriving protection from predators due to resemblance

(ex.) non-venomous scarlet kingsnake greatly resembles venomous coral snake (red touching black, safe for jack, red touching yellow, kill a fellow)

Diversifying Coevolution

increase in genetic diversity caused by heterogeneity of coevolutionary processes across range of ecological partners

(ex. crossbills feed on variety of conifer seeds within cones, bill depth influences feeding efficiency, fitness of trees is then determined by thickness of the scales)

Plants evolve innovations to escape predation (radiation), herbivores then evolve to overcome defenses (radiation)

Endosymbionts

mutualists that live within another organism

example of endosymbionts

(aster leafhoppers are nutritionally dependent on bacterial endosymbionts (sulcia and nasuia), bacteria live in specialized organs of leafhopper called bacteriomes, bacteria synthesize amino acids to provide to leafhoppers)

(mitochondria once free-living bacteria, engulfed by single-celled ancestors (became endosymbionts), plant plastids are similar)

Endogenous retroviruses make up

8% of human genome

Retrovirus

RNA virus uses reverse transcriptase to become part of host cell’s DNA.

Mobile Genetic Elements (MGEs)

genetic material that can move around within genome, or transferred from one species to another, 50% of human genome thought to be MGEs

Retrotransposons

transposons that move in genome, transcribed into RNA and later into DNA by reverse transcriptase. Many retrotransposons also exhibit replicative transposition. ONLY IN EUKARYOTES, two types:

• Long terminal repeats (LTRs)
• Non-LTR transposons: further classified into- long interspersed nuclear element (LINEs) and short interspersed nuclear element (SINEs)

how parasites affect the fitness of their hosts and vice versa

Parasites have to constantly coevolve with hosts to decrease the fitness, but the host evolves new defenses, thus increasing fitness (red queen effect)

Rat introduction on mainland of new zealand

decreased endemic bird pop. -> also decreased Rhabdothamnus solandri flower pollination

Observed that flowers on the mainland are pollinated

less than flowers on surrounding islands because of pollinator extinction