BIOL214 Post Exam 3 - Macroevolution & Coevolution (lec 23+24)

How many species are currently described?

~1.8 million described species

• Stork (2018) suggests there are:

  • 1.5 million beetle species

  • 5.5 million insect species

  • 7 million arthropod species

Microevolution

• evolution occurring within populations

• adaptive and neutral changes in allele frequencies

Macroevolution

• evolution above the species level

• origination, diversification, and extinction of species over time

Biogeography

• the study of the distribution of species across space and time

Latitudinal Species Richness Gradient

• the number of species of taxa generally increases from polar to temperate to tropical areas

  • e.g. species increases tropical>temperate>polar regions

    • avian species richness in North America follows this pattern

Species-Time Hypothesis

• suggests communities diversify (gain species) with time and that temperate regions are less species-rich than tropical regions because they are younger

  • temperate regions have only more recently recovered from glaciations and severe climate disruption

Species-Area Hypothesis

• proposes that large areas contain more species than small areas because they can support larger populations and a greater range of habitats

  • larger pop. more resistant to extinctions

  • tropics have the largest land area compared to other biogeographical regions

Species-Energy Hypothesis

• proposes available energy determines species-richness

• increased solar energy in the tropics (along with water abundance) results in high productivity in plants → increase in plant material

• this leads to an increase in herbivores and eventually an increase in predator, parasite, and scavenger species

Biogeographical Region with the Highest Species Diversity

• the tropics

  • includes tropical rain forest, tropical seasonal forest/savannah, etc.

• highest bird species richness, coral diversity, etc.

  • coral diversity may be associated with frequency of storms in the tropics carrying nutrients

Biogeographical patterns and divisions can be explained by…

• dispersal of populations

• vicariance

Dispersal

• movement of populations from one region to another with limited or no return exchange

• used to explain biogeographical divisions

Vicariance

• formation of geographic barriers to dispersal that divide a once-continuous population

• used to explain biogeographical divisions

• leaves a distinct phylogenetic signature

  • phylogeny reflects geological history (ex. continent splitting)

Marsupials Example

• marsupials evolved through a mix of vicariance and dispersal

  • dispersal: migration during the late-jurassic→early-cretaceous across land masses

  • vicariance: land masses drifted apart → geographical barrier

    • occurred multiple times

Extinction Rate

estimate of total number of species alive on Earth (present)

---

the average life span of a species in the fossil record

= average extinctions each year (species)

Extinction Rate (current)

10 million species alive on Earth at the present / 4 million years (average life span of a species in the fossil record)

= 2.5 species (average extinctions per year)

Interplay between Speciation and Extinction Determines…

diversity

D₁ (diversity) + originations – extinctions  = D₂ (new diversity)

Fauna

• assemblage of different animal species that live together

  • may comprise the species in a single ecosystem, region, or across the planet

• turnover among faunas and changes in overall diversity can be due to many causes

  • likely due to intrinsic properties of the species or large-scale climate/environment changes

Flora

• assemblage of different plant species that live together

  • may comprise the species in a single ecosystem, region, or across the planet

Standing Diversity

• determined by rate of origination and rate of extinction

  • represents the number of species (OTU) present in a particular area at a given time

• rate of origination (α)

• rate of extinction (Ω)

• turnover = number of species eliminated and replaced per unit of time

The 3 Evolutionary Faunas

• identified by Sepkoski (1981)

1) Cambrian Fauna

• evolved at the beginning of the Paleozoic and rapidly disappeared

2) Paleozoic Fauna

• rose in the Ordovician and died out in the Permian Extinction

3) Modern Fauna

• arose in the Mesozoic Era

Net Imbalance in Earth’s Energy Budget

• imbalance between solar radiation entering the atmosphere and thermal radiation leaving the atmosphere

  • more solar radiation entering than leaving

• due to human emissions

Taxonomic Diversity vs. Mean Temperature

• positive correlation between temperature and diversity

  • higher standing diversity with higher temperatures

Anagenesis

• wholesale transformation of a lineage from one form to another

  • alternative to splitting lineage or speciation

Punctuated Equilibria

• periods of stasis punctuated by brief periods of rapid change

  • associated with speciation events

Gradualism

• slow, gradual morphological changes over time

  • can include speciation events; traditional view

Explanations for Incomplete Fossil Records

1. old species underwent anagenesis; gradually evolving a new morphology

2. a new species may have branched off the old one, rapidly evolving morphological differences before entering its own stasis

Adaptive Radiation

• when rate of origination (α) eclipses rate of extinction (Ω)

  • ex. Silverswords in the Hawaiian archipelago

    • Silversword species and Tarweeds are sister groups

    • common ancestor for Silversword species radiated into several species from node

Key Innovation

• novel trait that allows the subsequent radiation and success of a clade

  • ex. nectar spurs

    • allowed the columbine clade to rapidly diversify

    • nectar spur holds nectar and pollinator picks up pollen while feeding on it

Cambrian Radiation of Animals

Mechanism

• environmental change, key innovations (Hox genes, body segments, skeletal structures)

Opportunity

• increased O2 availability, increased developmental capacity to diversify in form, colonization of new lifestyles (predators, habitats)

Devonian Radiation of Plants

Mechanism

• Key Innovations

  • seeds, vascular tissue

Opportunity

• colonization of terrestrial environments

Cretaceous Radiation of Angiosperms

Mechanism

• Key Innovation

  • flowers

Opportunity

• initiation of mutualistic coevolution with insects

Cenozoic Radiation of Mammals

Mechanism

• extinction of dinosaurs, large reptiles

Opportunity

• undercontested resources/niches

Radiation of Darwin’s Finches

Mechanism

• colonization of Galapagos archipelago

Opportunity

• undercontested resources/niches

Radiation of Silverswords, Fruit Flies, Honeycreepers

Mechanism

• colonization of Hawaiian archipelago

Opportunity

• undercontested reources/niches

Radiation of Columbines

Mechanism

• Key Innovation

  • nectar spurs

Opportunity

• increased reproductive success and reproductive isolation

Explanation for Cambrian Explosion

• animals diversified way before the Cambrian Explosion arose

  • animal kingdom arose ~750mya

  • Cambrian Explosion arose ~541mya

• Change in ecology spurred the Cambrian Explosion

Changes in Ocean Ecology Gave Rise to the Cambrian Explosion

• during the Cambrian

• series of interlinked geological, geochemical, and biological factors → feedback loops

• soil erosion deposits calcium ions into the ocean → biomineralization that leads to shells and hard body parts → explosion in animal diversity

  • there’s more to it but yeah

Background Extinction

• normal rate of extinction for taxa or biota

Mass Extinction

• a statistically significant increase above background extinction rates

Permian Extinction is Linked to Large Igneous Provinces

• largescale volcanism releases quantities of CO2 and SO2 that are catastrophic to biota

  • cause excessive warming and marine anoxia

K-T Boundary

• layer contains a high level of iridium which suggests an extraterrestrial impact 66 mya

Human-Caused Habitat Loss Drives Species Toward Extinction

• dramatic rise in vertebrate extinctions over the past few centuries

  • highest increase is in mammals and birds

Increasing Carbon Dioxide Levels

• leads to warming temperatures

• now ~exponentially increasing

• lowers pH of the ocean

Ocean Acidification

• decrease in ocean’s pH caused by an increase in atmospheric carbon dioxide levels

  • carbon dioxide from human activities

• decreases amount of bicarbonate available in the ocean → loss of species

  • bicarbonate (basic) is used to make shells and other hard body parts in shellfish species

Species Exist in a Web of Interactions

• each interaction can potentially raise or lower an organism’s fitness and therefore be subject to evolution

Coevolution

• reciprocal evolutionary change between interacting species

  • driven by natural selection

• arises from the selection imposed by interactions between species, and from the other species’ ability to evolve, thereby necessitating a continual (sometimes rapid) evolutionary change

Coevolution from a Microevolutionary Perspective

• coevolution can give rise to rapid evolutionary dynamics which can affect ecological processes

• coevolution leads to the evolution of adaptations (and counter-adaptations) in interacting species

  • may give rise to coadaption of traits between species

• can drive divergent microevolutionary trajectories both within and between populations

  • potentially leads to diversification → speciation

Categories of Coevolution

• Facilitation

• Mutualism

• Commensalism

Facilitation

• the enhancement of a population of one species by another

• encompasses mutualism and commensalism

Mutualism

• positive/positive relationship

• both species raise each other’s fitness

  • typically occurs through positive frequency-dependent selection

• ex. pollinator and plant

  • pollinator receives food, plant pollen is dispersed

• types of mutualism

  • obligate

  • facultative

  • dispersive

  • defensive

  • resource-based

Commensalism

• positive/neutral relationship

• benefits one species and has a neutral effect on the other

• ex. barbed seeds

  • barbed seeds get stuck in mammal fur and the mammal (unaffected) disperses the seeds

• ex. cattle egrets

  • cattle egrets feed in pastures among cattle, whose movements stir up insect prey for the birds; cattle unaffected

Obligate Mutualism

• neither species can live without the other

• ex. lichens

  • inseparable mix of fungi and algae

Facultative Mutualism

• interaction is beneficial to both species, but not essential to survival or reproduction of either species

• ex. ants and aphids

Dispersive Mutualism (Plant’s Perspective)

• involves dispersal of pollen and seeds

• an ideal pollinator (to the plant) would be a specialist (high fidelity to the specific plant species)

• fidelity is promoted by:

  • specific flowering at certain times in the year

  • synchronized flowering of all individuals within a species

• specializations are called pollinator syndromes

Dispersive Mutualism (Pollinator’s Perspective)

• it would be best to be a generalist and obtain nectar/pollen from as many flowers as possible

  • minimizes energy spent on flight

Defensive Mutualism

• involve an animal defending a plant or an herbivore

• ex. ants and aphids

  • aphids are defenseless and feed on plant sap (excretions are called honeydew)

  • ants feed on honeydew and in return, protect aphids from predators

Resource-Based Mutualism

• involve the increased acquisition of resources for both species

• 90% of seed plants have mutualistic associations with fungi that live on or in root tissue

  • associations are called mycorrhizae

Pollination Syndromes

• when pollinators visit the flowers of only one plant species

• result of coevolution between pollinator and plant

Bee Pollination Syndrome

Bees

• color vision includes UV; no red

• good sense of smell

• require nectar and pollen

Flower

• colorful; not red

• fragrant

• provide nectar and pollen

Butterfly Pollination Syndrome

Butterflies

• good color vision

• sense odors with feet

• need landing place

• feed with tubular tongue

Flower

• come in many colors

• light floral scent

• landing place

• nectar in tubes

Bird Pollination Syndrome

Birds

• color vision includes red

• require perch

• poor sense of smell

• feed in daytime

• high nectar requirement

Flower

• often red

• strong, damage-resistant structure

• no fragrance

• open in daytime

• copious nectar

Bat Pollination Syndrome

Bats

• colorblind

• good sense of smell

• active at night

• high food requirement

• perch needed

Flower

• white/light colored

• strong ordors

• open at night

• copious nectar

• borne out of trunks

Mutualism and Seed Dispersal

• fruits provide a valuable source of carbohydrates and vitamins

• in return, animals unknowingly disperse enclosed seeds (through waste)

Competition Avoidance Hypothesis

• hypothesis as to why seed dispersal is advantageous to plants

• competition with the parent plant is avoided

• no guarantee the seed will fall into optimal habitat

Predator Escape Hypothesis

• hypothesis as to why seed dispersal is advantageous to plants

• seed predators congregate under parent trees to feed on fallen seeds

• well-dispersed seeds avoid this predation

Colonization Hypothesis

• hypothesis as to why seed dispersal is advantageous to plants

• constantly shifting environmental conditions for seed germination means that parental location is not always a good predictor of seedling success

Directed Dispersal Hypothesis

• hypothesis as to why seed dispersal is advantageous to plants

• some dispersers distribute seeds into optimal sites

• ex. Mistletoes

  • obligate stem parasites whose seeds are dispersed by passerine birds

  • seeds must be deposited directly on tree twigs

  • bird eats the seeds and wipes waste onto the branches

Mycorrihizae

• associations between plant roots and fungi

• the fungi require soluble carbohydrates from plant host

• fungi supply plant host with mineral resources and water, which they can extract from the soil more efficiently than the host can

Commensalism Relationship Categories

• inquilinism

• phoresy

• metabiosis

• associational resistance

Inquilinism

• type of commensalism

• occurs when one species uses a second species for housing

• ex. orchids

  • grow in forks of tropical trees

Phoresy

• type of commensalism

• occurs when one organism uses a second organism for transportation

• ex. flower-inhabiting mites

  • travel between flowers in the nostrils of hummingbirds

Metabiosis

• type of commensalism

• an organism uses something produced by the first, usually after death

• ex. hermit crabs

  • use snail shells for protection

Associational Resistance

• type of commensalism

• palatable plants can gain protection against herbivores through an association with unpalatable neighbors

Coevolution Requires Genetic Variation

• parasitoid wasp Aphidius ervi lays its eggs inside of aphids

• when these wasps attack genetically identical aphids, they had different levels of success

Genetic Variation can Fuel Rapid Evolution

• Soapberry bugs feed by inserting their beaks into fruits to reach seeds

• Soapberry bugs that feed on Balloon Vine have evolved considerably longer beaks than soapberry bugs that don’t

Reciprocal Selection

• describes selection that occurs in two species due to their interactions with one another

  • critical for coevolution

• ex. Drosophila melanogaster and wasp Asobara tabida

Pleiotropy and Resistance

• variation can be maintained when traits have other costs

  • pleiotropy

• in locations with low amounts of food, control D. melanogaster larvae outperform resistant larvae (from example before)

Geographic Mosaic Theory of Coevolution

• proposes that the geographic structure of populations is central to the dynamics of coevolution

• direction and intensity of coevolution vary from population to population

  • coevolved genes from these populations mix due to gene flow

• theory argues that coevolution proceeds by natural selection acting on the sources of variation that affect interactions among species

Geographic Selection Mosaics

• structure of natural selection on interactions differs among environments

  • ex. high vs. low temps, high vs. low nutrient conditions, species rich vs. species poor

  • variation occurs because genes are expressed in different ways in different environments (GxE)

  • how one species affects the evolutionary fitness of another species depends upon the environment in which interaction occurs

Coevolutionary Hotspots

• the intensity of reciprocal selection differs among environments

• interactions are subject to reciprocal selection only within some local communities

  • these hotspots are embedded in a broader matrix of coevolutionary coldspots (where selection is non-reciprocal or only one participant occurs)

Trait Remixing

• overall genetic structure of coevolving species continually changes through new mutations, genomic alterations, gene flow, genetic drift, and extinction of local pop. that differ in the combinations of coevolving traits they harbor

• new genetic material can result from mutations, chromosomal rearrangements, hybridization between populations, or polyploidy

• these processes contribute to the shifting geographic mosaic of coevolution

  • altering spatial distributions

Attenuated Coevolution

• ex. Myxoma virus

  • introduced to Australia to control the introduced rabbit population

  • less virulent strains of the myxoma virus were able to spread more effectively than more virulent ones

Mullerian Mimicry

• several harmful or distasteful species resemble each other in appearance

• facilitates learned avoidance from predators

• ex. Heliconius butterflies

  • produce compounds that are toxic to birds

  • converge on similar wing patterns

  • optix expression gives Heliconius species similar wing patterns

Batesian Mimicry

• harmless species resemble harmful or distasteful species

• harmless species derive protection from predators

• ex. coral snakes and scarlet kingsnakes

  • scarlet kingsnakes look like coral snakes

  • coral snakes are venomous

  • scarlet kingsnakes are nonvenomous

Diversifying Coevolution

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

Coevolution Drives Species Diversity

• plants evolve innovations to escape predation

  • leads to radiation

• herbivores evolve to overcome defenses

  • leads to radiation

Introduced Predators can Disrupt Mutualisms

• ex. Rhabdothamnus solandri

  • R. solandri is a flower that depends on the tui and other bird species

    • bird species ~50% extinct

  • mainland flowers are able to produce less fruit than island flowers due to extinction of pollinators

Endosymbionts

• mutualists that live within another organism

• ex. aster leafhoppers

  • depend on two bacterial endosymbionts

  • the bacteria live in bacteriomes (organs) and synthesize amino acids they provide to the leafhoppers

Mitochondria are Derived from Free-living Bacteria

• mitochondria were originally free-living bacteria that were later engulfed by our single-celled ancestors

Endogenous Retroviruses

• make up ~8% of the human genome

• a retrovirus is an RNA virus that uses reverse transcriptase to become part of the host cell’s DNA

Mobile Genetic Elements

• mobile genetic elements (genetic material that can move around within a genome) are also thought to be a signficant part of the human genome ~50%

Retrotransposons

• transposons that move in the genome, being transcribed into RNA and later DNA by reverse transcriptase

  • a transposon is a mobile genetic element that can insert itself into the genome

• in eukaryotes only

• two types:

  • long terminal repeats

  • non-long terminal repeats

    • classified into long interspersed nuclear elements or short interspersed nuclear elements