W10L1 evolution under climate change

Question 1

Climate change - where we are

Answer 1

• Global mean temperature has increased over the last several decades, and is forecast to increase further
• Associated effects on water availability, natural disasters, ocean levels etc.
• What are the consequences of rapid changes in selective forces?

Question 2

Other effect of climate change aside from increase in temperature

Answer 2

• Changes in aridity can reduce availability of water or perturb cooling strategies (higher humidity reduces heat loss from skin)
• Sea level rise and natural disasters are a major threat to organisms with limited dispersal capability
• Increased carbon dioxide also interacts with ocean ecosystems, e.g. decreased availability of carbonate needed in coral skeletons and mollusc shells

Question 3

Heat stress - a conserved response?

Answer 3

• Physiological responses to heat stress vary greatly across organisms
• At the molecular level some similarities are apparent, e.g. a role for TRP ion channels across animals, but also many differences
• Prokaryotes and eukaryotes share ‘heat shock’ proteins, induced by high temperature and assisting in correct protein folding

Question 4

Non-lethal effects of increase in temperature

Answer 4

• Exposure to elevated temperatures below the lethal point can perturb developmental timing, reduce longevity and impair fertility
• Laboratory studies make somewhat arbitrary choices of testing conditions
• Field evidence mostly from agriculture (e.g. DNA damage in boar spermatozoa)

Question 5

Indirect heat effects

Answer 5

• Shifts in seasonally timed events (e.g. flowering in plants, reproduction in some animals -phenology)
• Positive selection for earlier flowering documented from numerous plants, but several possible risks are associated with this shift:
• Greater chance of frost exposure (if early heat not sustained)
• Greater drought risk with longer growing season
• Failure to shift also potentially harmful, e.g.reduced access to pollinators

Question 6

Possible biological responses to climate
change

Answer 6

• Population/species loss
• ‘Plasticity’ – phenotypic changes in an organism improving its performance under existing conditions
• Relocation – movement to a new area which offers a more suitable climate
• Evolution?

Question 7

Phenotypic plasticity`

Answer 7

• Individuals with identical genotypes may develop differently in response to different environmental cues - limited in scope
• Potentially assists adaptation to changing climate, but requires reliable cues
  *

Question 8

Mechanisms of cue disruption under climate change:

Answer 8

• Disconnection of cue and relevant environmental factor, e.g. air temperature and snowmelt
• Species mismatch due to disconnection of cues used by each species

Question 9

Acclimation

Answer 9

• Improved performance after a period of exposure to an environmental stressor, e.g.high altitude
• Briefer, more intense stress exposure is sometime distinguished as ‘hardening’
• Mechanisms can be extremely diverse, encompassing physiology and behaviour:
• Blood flow changes in rats to promote cooling
• Birds shading eggs under hot conditions

Question 10

Mechanisms of acclimation

Answer 10

• Changes in gene expression play important roles, e.g.constitutive expression of heat shock proteins
• Differences between even closely related species in capacity for acclimation, e.g.Drosophila melanogaster vs. D. subobscura – additional gene copies, greater expression

Question 11

Heat response genetics

Answer 11

• Changes in gene expression in response to heat are not restricted to heat shock genes
• Melanotaenia – rainbow fishes originating in New Guinea, now found in many regions of Australia
• Strikingly different patterns of gene expression in response to heat

Question 12

Relocation

Answer 12

• Range shifts in response to climate change seem to have been historically common, e.g. expansion of species through Europe at the end of the last Ice Age
• Climate change may outpace the dispersal speed of some organisms (e.g. wind-dispersed plants)
• New environments may pose new challenges, e.g. reduced oxygen concentration with increased altitude

Question 13

Identifying range shifts

Answer 13

• Detection of shifts can be complicated by fluctuations in species distribution, prediction by microclimatic variation
• Some observations of range shifts (e.g. North American birds, North Sea invertebrates) have been made
• Most shifts do not compensate completely for warming

Question 14

Intra-species variation and climate adaptation

Answer 14

• Differences in average thermal tolerance according to sex, age etc. are common
• Differences in heat response according to genetic background apparent in some species
• How much genetic diversity is needed to adapt to climate change? How much will be lost

Question 15

Evolutionary potential

Answer 15

• The speed of change in climate and the more variable conditions likely to be encountered pose a difficult evolutionary challenge
• Capacity to adapt depends heavily on pre-existing genetic diversity
• Adaptive capacity particularly limited in small or inbred populations and at existing edges of species range

Question 16

Evolution vs. plasticity

Answer 16

• Distinguishing between the effects of evolution and plasticity is not necessarily simple
• Change in a trait in a way which improves performance under novel climactic conditions does not in itself demonstrate adaptation
• Decreasing body size in Soay sheep despite positive selection for larger size
  – shorter winters allow greater population size, increasing competition

Question 17

Evolution or plasticity

Answer 17

• When evolution and plasticity both push a trait in the same direction, determining the contribution of each can be difficult
• Declines in body size common in response to global warming often interpreted as reflecting pressure for increased surface-volume ratio
• Competition, predation, parasitism and poor diet (e.g. due to habitat fragmentation) are potential confounding factors

Question 18

Common gardens and reciprocal transplants

Answer 18

• If individuals with different genetic backgrounds develop under identical conditions, genetic and environmental effects can be separated - ‘common garden’
• Reciprocal transplants involve swapping individuals derived from populations living in distinct habitats
• Extensive history of use in plants

Question 19

Evolution plus plasticity

Answer 19

• In Drosophila melanogaster, a period of reduced activity during the day (‘siesta’) occurs much more frequently in flies adapted to warmer conditions
• The period gene contains an intron which is removed more frequently at lower temperatures
• Multiple genetic variants can further ‘calibrate’ Period activity

Question 20

Is adaptation to climate change occurring

Answer 20

• Sometimes: changes in timing of diapause in pitcher plant mosquitoes, flowering time in canola, reproduction in pied flycatchers…
• However, little evidence of adaptation in most species with long generation times
• Many species simultaneously confronting other challenges, such as habitat loss, which might reduce genetic diversity

Question 21

Can human intervention assist

Answer 21

• Captive breeding could favour adaptive alleles, but these are not known for most species
• Translocations can be used to increase genetic diversity within a population, but requires existing variation between populations
• Habitat restoration may provide some protection, but will be slow
• “The major source of uncertainty… arises from our poor understanding of animals from many geographical regions of the world” (White et al., 2021)