Mutualism

Question 1

Definition

Answer 1

a sub-category of symbiosis involving mutually beneficial interspecific interactions which enhance overall biological fitness

Question 2

Benefits of mutualism:

Answer 2

Resilience to environmental stress
Pollination
Digestive aid
Resource access
Protection
Hygeine
Habitat/shelter
Seed dispersal

Question 3

Proximate mutualism

Answer 3

Proximate mutualism:
“interspecific interactions in which the removal of each partner results in decreased performance of the other” (BES journal 2005)

Proximate response vs proximate mutualism:
-Response -> short-term effects
Mutualism -> removal of one partner results in a decreased performance

Example: fungus and leaf cutter ants – fungus recruits ants to collect the right types of leaves for it to grow and the fungus produces hyphal growths to feed the ants

Proximate mutualism is usually assumed as it can be assessed in the short time so requires less funding

Question 4

Ultimate mutualism

Answer 4

Definition: “an interaction in which each partner could never have performed as well without the other, even if it was adapted to the absence of the partner de Mazancourt,Loreau and Dieckmann (2005)

Difficult to measure – measure coevolved with mutualistic partner/compared to one without and assess fitness

Example: clown fish and anenomes – fish are protected by anenomes and they clean it

Question 5

Facultative Mutualism

Answer 5

Both organisms highly dependent on each other once an association has been formed

However, they can survive independently if this association is not formed.

Often seen in diffuse relationshis involving a mixture of species

E.g. seagrass and lucinid bivalves – seagrass provides habitat and O2 whilst bivalves filter water for the grass

Question 6

Obligate mutualism

Answer 6

Mutualistic interactions are essential for the survival of all organisms involved. Absence of these specific interactions may result in death/extinction of species.

Example: Yucca plant and Yucca moth – moth lays eggs in the plant corrola young feed on the plant and adults act as pollinators

Interactions can be obligate-obligate, facultative-facultative or obligate - facultative

Question 7

Dispersive mutualism

Answer 7

Occurs when one or more species benefits from dispersal services provided by another organism

One organism receives food whilst the other benefits from a larger spread of its genotype across the surrounding exosystem e.g. plants and pollinators, seeds of ulex species and ant species Myrmica ruginodis – they feed their young on the nutrient coating leaving the seeds to grow in the rich soil of the ant nest

Question 8

Trophic mutualism

Answer 8

Both partners are specialised in complimentary ways to efficiently obtain nutrients or energy from one another. E.g. Ruminoccus and Selemonas bacterium and cows (specifically dairy cows) - bacteria help them break down grass and feed and are provided with nutrients in the gut

Question 9

Defensive mutualism

Answer 9

Partner one receives food and/or shelter

Partner two receives defence and/or protection from predators

e.g. ants and aphids – ants protect aphids from predators and consume honeydew produced by aphids as upto 90% of their diet – aphids cannot escape quickly when they are feeding as their mouthparts are deep in phloem hence they need protection when feeding

Question 10

Wider importance of mutualism: conservation

Answer 10

Mutualism plays an integral role in ecosystem resilience and biodiversity

Decrease in plant density due to pollution, land use change and climate change results in a reduction of pollinator species – 1/3 of all food resources depend on pollinators a reduction in pollinators will also reduce genetic diversity in plants

Mutualistic relationships change due to stress levels

Mutualisms have the potential to lead to extinction – population of one species effects the other

Relationships enhance survival and productivity

Question 11

Wider importance of mutualism: biodiversity

Answer 11

Mutualisms shape biodiversity

Niche differentiation and complex networks

E.g. pollination networks

Question 12

Coevolution

Answer 12

Reciprocal evolutionary changes are observed in interacting species (Janzen, 1980)

e.g. lichen – coevolution of symbiotic algae and funghi allowing algae to colonise land, or of pollinator beaks and flower shapes

Understanding can be applied to community dynamics for conservation purposes

Reciprocal evolution occurs at multiple levels of organisation:

Intramolecular (nucleotides) intermolecular (molecules) and intergenomic (genomes)

Driven by selective pressures of resource access/ environmental conditions

Question 13

Methods of study

Answer 13

Observational field studies
- direct behavioural recording in-situ
- Short term and relatively unobtrusive, quantifying proximity/physical interaction
- e.g. tarantula and tiny frog mutualism – timing periods of time spent in tarantula burrow and regularity of mutual contact
- Limitations: microscopic, cryptic or hidden interactions are unobservable
- e.g. not possible to observe interactions of frog and spider in the burrow

Long term monitoring
- to understand change of interactions over time
- Genetic analysis, tracking, field observation and ecological research sites
- Limitations: cost-benefit analysis, data management, control of confounding variables
- e.g. florida coastal birds and alligator mutualism – alligators protect birds in exchange for discarded hatchlings

Isolated laboratory study
Benefits:
- Precise control over environmental variables and conditions, possible to remove external variables.
- Mutualistic relationships can be explored in the presence/absence of the partner
- useful for microscopic organisms e.g. nemotode and bacterial mutualism studied by separating the organisms.
- Genetic modifications and isolations of specific interactions can be made.
- Replicable and standardised experiments
Limitations:
- isolation from ecological context
- cross connections
- shared partners
- space limitations
- small sample and inbreeding risk

Genomic analysis
- comparing genetics, sequencing, protein analysis, DNA barcoding
- molecular systematics (phylogenetic analysis)

Question 14

Genomic analysis example: Wolbachia bacteria and nematode study of what causes parasitism/mutualism interactions by genome sequencing and phylogenetic analysis

Answer 14

The analyses demonstrated that arthropod (A & B) and nematode (C & D) wolbachia originated after the split of an ancestral lineage

A monophyletic origin of C & D groups is congruent with the idea that there are characteristics shared by these two upper groups

Wolbachia strains probably share common metabolic traits that underpin their mutualistic relationship with filarial hosts

Phylogenetic analysis identified co-evolutionary patterns and assessed shifts to parasitic traits

Question 15

Reconciliation

Answer 15

Another phylogenetic method to map the overlap of two coevolving species

Duplication, transfer and loss model – mapping one evolutionary tree over the other

(host blue and symbiont red) codiversification/speciation occurring same time and independent species loss or evolution can provide guidance on intensity of interdependence

possible to map more than two coevolving species

Possible to visualise host or partner switches

Question 16

Mathematical framework

Answer 16

Symbiosis consists of complicated networks of interactions within an ecosystem.
These are condensed into simplified equations for quantitive analysis

e.g. Modified Lotka-Volterra
Obligate+obligate+facultative mutualist (extinction avoidance)
Boundaries to parasitism
Each equation is almost identical to Lotka-Volterra, alpha sign is changed to positive due to addition of mutualistic species.

e.g. facultative and obligate mutualisms can be displayed graphically as can parasitic boundaries

(see notes for equation and graphs)

Question 17

Mutualism and parasitism

Answer 17

Both facultative and obligate symbioses can make shifts along the parasite–mutualist continuum that do not involve evolution, often occurring within a generation and driven by ecological change or opportunity.

• Abiotic factors can affect the distribution of costs and benefits incurred by the host and symbiont relationship.
• Defensive symbioses present a clear demonstration of community context-dependent shifts, whereby benefits to the host are contingent on the presence of an enemy species.
• In the absence of the enemy, the host pays the cost with no detectable benefit, and the association moves towards one that is parasitic.

Community composition can cause switch between the two depending on context

e.g. if there is nothing to be protected from the species benefitting from given food becomes a parasite

Question 18

Mutualism and commensalism

Answer 18

Mutualism = both benefit

Commensalism = one partner benefits and the other partner neither benefits nor is harmed

e.g. Tarantula and frog – frog eats ants that would otherwise eat the leftover prey and eat tarantula eggs – the tarantulas mouth parts are too large to consume the ants directly and the frog is toxic preventing it being preyed upon

This relationship may simply be commensalism the tarantula tolerating the frog as it can’t eat it since the frog is toxic

How could you find out if the frog and tarantula relationship was commensalist or mutualistic?
By removing the frog - observing if negative impact to spider

Question 19

Additional notes

Answer 19

Plant species rely more on pollinators than the pollinators rely on those specific species – they have other plant options. Additionally some pollinator species have evolved to burrow into flower nectaries without pollinating the flowers thus avoiding the physical burden of pollen and acting more parasitically than mutualistic.

Wolpachia secretes a chemical ancarin that manipulates the nematodes reproductive system

Question 20

Example of species that switch back and forth between mutualism and parasitism?

Answer 20

Annelids and crayfish. Annelids are cleaners but if there is more availability of crayfish they may consume the gills becoming parasitic

Question 21

Mutualisms between humans and other species?

Answer 21

Gut bacteria within humans

Domesticated animals e.g. truffle pigs or dogs – this can easily shift to commensalism

Question 22

Mutualism as a sub-category of symbiosis? How are they the same and how do they differ?

Answer 22

Timescale – symbioses are obligate and longterm

Mutualisms can be short-lived depending on conditions

Mutualism has a positive effect whereas symbiosis can be pos or neg