Mutualism Flashcards
Definition
a sub-category of symbiosis involving mutually beneficial interspecific interactions which enhance overall biological fitness
Benefits of mutualism:
Resilience to environmental stress
Pollination
Digestive aid
Resource access
Protection
Hygeine
Habitat/shelter
Seed dispersal
Proximate mutualism
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
Ultimate mutualism
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
Facultative Mutualism
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
Obligate mutualism
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
Dispersive mutualism
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
Trophic mutualism
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
Defensive mutualism
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
Wider importance of mutualism: conservation
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
Wider importance of mutualism: biodiversity
Mutualisms shape biodiversity
Niche differentiation and complex networks
E.g. pollination networks
Coevolution
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
Methods of study
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)
Genomic analysis example: Wolbachia bacteria and nematode study of what causes parasitism/mutualism interactions by genome sequencing and phylogenetic analysis
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
Reconciliation
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
Mathematical framework
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)
Mutualism and parasitism
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
Mutualism and commensalism
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
Additional notes
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
Example of species that switch back and forth between mutualism and parasitism?
Annelids and crayfish. Annelids are cleaners but if there is more availability of crayfish they may consume the gills becoming parasitic
Mutualisms between humans and other species?
Gut bacteria within humans
Domesticated animals e.g. truffle pigs or dogs – this can easily shift to commensalism
Mutualism as a sub-category of symbiosis? How are they the same and how do they differ?
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
