Lecture 4d: species level climate change impacts: micro-evolution Flashcards
Plasticity, micro-evolution and local adaptation
Understanding how populations adapt to changing environments is of fundamental
importance for assessing their evolutionary and ecological dynamics, and for
predicting population resilience to climate change.
see Huntley et al 2010 figure 1 (in notes)
Micro-evolution (local adaptation)
Local adaptation:
When populations evolve (adapt) to be better suited to their local environment than other members of the same species
multiple genotypes:
The genes individuals have multiple genotypes
Multiple phenotypes:
An organism’s characteristics due
to both genotype and environment
Example habitat: Green individuals do best.
Individuals with genotypes for green survive
and the population becomes locally adapted
Comparatively in phenotypic plasticity:
Phenotypic Plasticity:
The ability of one genotype to produce more than one phenotype when exposed to
different environments
Single genotype
The genes individuals have a single genotype
Multiple phenotypes
An organism’s characteristics due
to both genotype and environment
Example habitat: Green individuals do best.
The same genotype can result in multiple
colours, in this case green
Which traits have evolved or would be beneficial to evolve in response to climate change?
Example: Migratory behaviour of Eurasian Blackcap (Sylvia atricapilla)
^ Breeds widely throughout Europe and exhibits a variety of migratory behaviour:
^ Whereas some populations migrate to sub-Saharan Africa for the non-breeding season, others migrate only as far as the Iberian Peninsula or other areas of Europe and north Africa in the Mediterranean region.
Changes in migratory behaviour of Eurasian Blackcap: Berthold et al 1992:
Occasional over-wintering individuals were reported in the British Isles from the 1950s onwards
Ringing recoveries showed these to be from central European breeding populations.
By 1965 members of some central European populations were regularly migrating to spend the non-breeding season in the British Isles, 1000–1500 km north of other wintering areas around the western Mediterranean
Migratory behaviour changes are a heritable trait:
e.g. Berthold et al 1992: Eurasian Blackcap
Process of selection for migratory behaviour:
At the end of the nesting season, long days terminate reproductive behaviour.
This refractory state is generally terminated by exposure to short days → termination of refractoriness proceeds faster at shorter than longer winter day lengths.
Midwinter day lengths are shorter at more northern latitudes (Britain) than at more southern latitudes (Spain).
Hence, birds overwintering in Britain terminate refractoriness earlier than those in Spain and can respond more immediately to the increasing day lengths of spring.
British birds begin to migrate back to Germany earlier than Iberian birds, have a shorter migratory distance to cover and arrive at the nesting areas earlier than the Iberian birds
Positive selection:
Early-arriving males can defend the best territories, and early arriving females consort with males that have the best territories and realize greater reproductive success than late-arriving birds
This assortative mating reinforces the increasing tendency of birds to overwinter in Britain.
Positive and negative selection
e.g. Berthold et al 1992: Eurasian Blackcap
positive:
-Food availability prior to departure
-Weather en-route - winds, precipitation etc.
-Onsent of the Sahelian dry
season
Negative: see Howard et al 2018
Body size change
Example: Bushy tailed wood rat (Neotoma cinerea) Smith et al 1995
Found today across a range of latitudes in western North America
Exhibits a body-size cline with latitude
individuals from the north of the species’ range being on average larger than those from the south (Bergman’s Rule)
Body mass greater than today during last glacial and showed a minimum corresponding to independently inferred maximum regional temperatures during the early Holocene
Inferred to be an adaptive response to climatic change, and most probably a genetically determined response
Range of inferred body mass falls within the range observed at the present day along the cline - suggests adaptive response limited by species’ inherent genetic variability
Understanding changes in body size: Adaptive vs spatial responses
see figure in notes depicting model scenario: observed adaptive genetic responses are the local expression of the spatial response
Possible that most species could not realise such adaptive responses without also realising a spatial response the breadth of response seen in the Neotoma cinerea (bushy tailed wood rat) example probably made possible only by movement of the species’ range, and of populations across that range, in response to the climatic changes
Summary
*The consideration of not just species, but populations within species that may show differential adaptation/plasticity is very important.
*Teasing out the genotypic from the phenotypic adaptations is often complex, as shown in the Blackcap example, but vital if we are to fully understand climate change impacts and responses of organisms.
*Micro-evolution requires genetic, not simply phenotypic, diversity
*Both modern day and quaternary evidence (from the fossil record) reveals the possibilities of local adaptation in response to climatic change – however micro-evolution has received relatively little attention compared to other responses to climate change
*Recent modelling studies are better addressing the key challenges of potential variable plasticity vs. micro-evolution across a species’ range.
See Valladres et al. (2014)
