4. The Geography and Ecology of Speciation Flashcards
Structure of the lecture
- Local adaptation in special systems
- LA and the Red Queen hypothesis
- LA and eco-evo dynamics
- Local Maladaptation and climate change
What are two examples of LA in special systems?
1
- The ocean
- When mediated by microbes
How can LA occur in the ocean?
1.1
The assumption for a long time was that LA does not occur in the ocean due to the long dispersal distances, and the immense homogeneity
However, evidence is showing more local variation and shorter dispersal distances in the ocean than previously thought
Sanford and Kelly, 2011 performed a metanalysis of LA in marine invertebrates, and concluded that LA was occurring in 66% of species studied.
They found that this form of adaptive divergence occurs over a range of spatial scales
How can LA be microbially mediated?
1.2
We would assume that the host genes will lead to LA in their microbes. However, there are likely to be many other factors at play. For example:
1) The environment impacts both the host and microbe
2) The microbes and host reciprocally affect each other
3) The local and non-local microbe communities can differently impact the host, This is called Microbially Mediated Local Adaptation, and it is a product of Microbially Mediated Adaptive Plasticity
Give an example of how MMLA can occur?
1.3
Petipas et al., 2020 performed a factorial experiment on St. John’s Wort. They compared old field and harsh limestone (alvar) habitats.
They found that alvar plants grown in association with alvar microbes outperformed the old field plants in the alvar environment, whilst the old field plants showed signs of Local Maladatpation. This suggests evidence for Microbially Mediated Local Adaptation.
Define the Red Queen Hypothesis
2.1
The Red Queen Hypothesis states that species must be constantly adapting, evolving and proliferating in order to survive, whilst be pitted against ever-evolving species
This is characterised by an endless cycling of alleles that produces an advantage for rare victim phenotypes
How can we understand Red Queen-LA dynamics in the snail-parasite system in NZ?
2.2
**The system: **Snails are native to NZ, and involve mixed populations of obligate sexuals, and parthogenetic asexuals. The snails can be infected by trematode parasites, which sterilise the snails. The trematode undergoes part of its lifecycle within the snail before being taken up by the ducks. However, ducks can only swim in shallow waters, meaning that the trematodes cannot complete their life cycle in deep waters, since no ducks
Observation: There are more males in the shallower areas where there is a higher risk of parasitism due to the increased presence of ducks. The males are only needed for sex, so the two-fold risk of sex is outweighed by the need to introduce more new genetic material to the population.
Method: Researchers exposed shallow-water and deep-water snails to parasites from either shallow- or deep- waters, and measured the prevalence of infection
Finding: Researchers found that the parasites were only adapted to the snails in the shallow water.
Conclusion: The parasites were only able to infect the hosts with the relevant ‘matching’ genotypes. This exhibits the local adaptation of the parasites
This shows evidence of LA over space
How are Red Queen dynamics being exhibited in Daphnia water fleas?
2.3
Decaestecker et al., 2007
Study system: Daphnia produces resting eggs every winter. However, it can be infected with a sterilising bacterial parasite called Pasteuria that lead to the resting eggs and bacterial spores falling to the bottom of the lake, and being conserved in the sediment
Method: Extraction of the sediment core, and isolation of hosts and parasites over 4-year period
Results: Researchers were able to observe that the past and future parasites do not match well.
Conclusion: This provides evidence for LA over TIME
Bassar et al., 2010: How can LA and eco-evo dynamics interact with each other?
Hint: Trinidadian guppy system
3
System: There are two pools of guppies on either side of a waterfall. Those at the top of the waterfall exist in a low-predation environment and have appropriately adapted morphologies and life-history patterns. Those at the bottom of the waterfall exist in a high-predation, and have smaller morphs and faster life-history traits
Methods: Replication of the populations from the HP and LP environments, with another no guppy treatment.
Results: Post-mortem analysis of the guppies revealed marked dietary differences between the HP and LP fish
Link to eco-evo: These results translate into opposing effects on the algal and invertebrate densities in mesocosms, which was determined by the LA of the guppies
Conclusion: Guppies exhibited LA to their local environments, which triggered changes in the ecosystems of the waterfall
Define local maladaptation
4.1
Lowered fitness in the home environment
How common is local maladaptation?
4.2
Hereford, 2009
Performed a review of local maladaptation, and concluded that it wa not common.
Critical perspective: (1) Used a restricted set of species that only used species where RTE are possible. (2) Used a common and widespread range of species that are the ones always picked for these models, (3) No temporal information about the shifting extents of LA
How can climate change influence LMA?
4.3
Species will no longer match their environments. This LMA will be accelerated for species with:
- Local dispersal ability
- Slow generation time (limited by plasticity, and therefore adaptive evolution)
We can predict how species will undergo LMA via genomic data, by using analyses of matches between genetic and climate data, to understand how changing climate forecasts will influence species
The process for predicting LMA goes: (1) Data acquisition, (2) Identifying the genomic basis of LA, (3) Generalisation of the genetic-environmental relationship, (4) Measuring the shift in the genetic continuum
**Caqblanq et al., 2020 **
Changes to the yellow warbler from LMA?
4.4
Bay et al., 2018
Modelled the difference between today’s and the future climate’s forecast in 2050 to allow them to understand the spatial variation that is predicted in LA
Results: Found that geographic distance and environmental distance explained population differenitation, and that the variation in current population trends agree with some of the predicted measures of genomic vulnerability
Critic’s perspective: A sophisticated model of predicting the impacts of climate change
How could microbiota be used to save species from LMA under climate change?
4.5
Allsup et al., 2023
Could we move beneficial microbial communities to areas at high risk from climate change to help species adapt to new environments?
