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Embryonic physiological plasticity induced by high altitude hypoxia in lowland-native wall lizards

Andersson, Bea Angelica (2017) BIOP01 20162
Degree Projects in Biology
Abstract
To colonize novel environments, species need to adapt. However, if suitable phenotypes are not already present in the population, the population may go extinct before adaptive mutations emerge. Phenotypic plasticity offers a mechanism for species to mitigate effects of selection and to maintain a viable population size under stressful conditions. This may in turn increase the chances of future adaptation to the new environment. We designed an experiment to simulate a rapid altitudinal range expansion of a lowland wall lizard population in southern France to assess the extent of phenotypic plasticity during embryonic development under high altitude hypoxia. The experiment included subjecting embryos to hypoxia during incubation and was... (More)
To colonize novel environments, species need to adapt. However, if suitable phenotypes are not already present in the population, the population may go extinct before adaptive mutations emerge. Phenotypic plasticity offers a mechanism for species to mitigate effects of selection and to maintain a viable population size under stressful conditions. This may in turn increase the chances of future adaptation to the new environment. We designed an experiment to simulate a rapid altitudinal range expansion of a lowland wall lizard population in southern France to assess the extent of phenotypic plasticity during embryonic development under high altitude hypoxia. The experiment included subjecting embryos to hypoxia during incubation and was complemented by an experiment where gravid females were transplanted to high altitudes during gestation. The results demonstrate that hatchlings respond to hypoxic incubation by reducing metabolic activity, as seen by decreased heart rates as well as reduced CO2-production during week 6 and 7 of incubation. Embryos of mothers subjected to hypoxia (i.e., while still inside the oviduct) reduced heart rate even more than hatchlings subjected to hypoxia during egg incubation only, implying that maternal effects and/or the stage of development where hypoxia is introduced may play a role in shaping the intensity of the response. (Less)
Popular Abstract
Are lizards able to colonize high altitudes?

Wall lizard embryos moved to high altitude have lower heart rates and consume less oxygen, but hatch at the same time and at almost the same size. Low oxygen therefore seems unlikely to restrict their colonization of high altitudes if temperatures increase.

Animals living at high altitude need to adapt to the low oxygen levels. If we look at high altitude populations, many have genetic mutations that makes it possible for them to survive on less oxygen, or makes them better at taking up oxygen from the air. However, animals moving into high altitude may not have the time to develop these adaptations. If the lack of oxygen is too stressful, they might die before natural selection has run... (More)
Are lizards able to colonize high altitudes?

Wall lizard embryos moved to high altitude have lower heart rates and consume less oxygen, but hatch at the same time and at almost the same size. Low oxygen therefore seems unlikely to restrict their colonization of high altitudes if temperatures increase.

Animals living at high altitude need to adapt to the low oxygen levels. If we look at high altitude populations, many have genetic mutations that makes it possible for them to survive on less oxygen, or makes them better at taking up oxygen from the air. However, animals moving into high altitude may not have the time to develop these adaptations. If the lack of oxygen is too stressful, they might die before natural selection has run its course. But animals can have built-in ways to respond to a lack of oxygen that changes how they develop. This capacity to acclimate involves plasticity, and means that individuals with the same genes could develop to look/function differently depending on the environment they experience during their life, most importantly during embryonic development.

In this study, we wanted to test this capacity in wall lizards. We collected females from low altitude in southern France and moved half of the eggs to about 3000 m altitude, above the species’ current distribution. At this altitude, oxygen levels are around 16% - much lower than the regular 21% experienced at low altitude. To examine the effects of the mother’s environment, we also moved pregnant females to high altitude. As the eggs were incubated, we measured heart rate and metabolism of the embryos, and after hatching we compared body and heart size of the hatchlings.
Embryos respond like high altitude species
We found that heart rate was consistently lower in embryos that were kept at high altitude compared to those kept at low altitude. CO2-production (an estimate of metabolism) was also lower. Despite this, body size was not much affected. Upon close inspection, however, hatchlings from large eggs were not able to fully utilize the resources, which suggests that low oxygen imposes some constraint on conversion of yolk to tissue. Interestingly, embryos from mothers kept at high altitude had even lower heart rates than those only kept at high altitude after egg-laying. This suggests that the time of exposure to high altitude affects the embryo’s response. Overall survival of embryos was the same across all treatments.

The responses wall lizards from low altitude display are very similar to species living permanently at high altitude. Currently, temperatures are too low for wall lizards to survive high in the mountains. However, if temperatures rise as climate change progresses, it may soon be possible for them to colonize these habitats. This could pose a risk to the endangered Rock lizard, which many researchers think is confined to high altitudes due to competition with wall lizards. It is therefore important to follow up on this research also from a conservationist perspective.

Master’s Degree Project in Biology (Animal Ecology) 60 credits 2017
Department of Biology, Lund University

Advisor: Tobias Uller
Department of Biology, Lund University (Less)
Please use this url to cite or link to this publication:
author
Andersson, Bea Angelica
supervisor
organization
course
BIOP01 20162
year
type
H2 - Master's Degree (Two Years)
subject
language
English
id
8906926
date added to LUP
2017-05-15 11:44:40
date last changed
2017-05-15 11:44:40
@misc{8906926,
  abstract     = {To colonize novel environments, species need to adapt. However, if suitable phenotypes are not already present in the population, the population may go extinct before adaptive mutations emerge. Phenotypic plasticity offers a mechanism for species to mitigate effects of selection and to maintain a viable population size under stressful conditions. This may in turn increase the chances of future adaptation to the new environment. We designed an experiment to simulate a rapid altitudinal range expansion of a lowland wall lizard population in southern France to assess the extent of phenotypic plasticity during embryonic development under high altitude hypoxia. The experiment included subjecting embryos to hypoxia during incubation and was complemented by an experiment where gravid females were transplanted to high altitudes during gestation. The results demonstrate that hatchlings respond to hypoxic incubation by reducing metabolic activity, as seen by decreased heart rates as well as reduced CO2-production during week 6 and 7 of incubation. Embryos of mothers subjected to hypoxia (i.e., while still inside the oviduct) reduced heart rate even more than hatchlings subjected to hypoxia during egg incubation only, implying that maternal effects and/or the stage of development where hypoxia is introduced may play a role in shaping the intensity of the response.},
  author       = {Andersson, Bea Angelica},
  language     = {eng},
  note         = {Student Paper},
  title        = {Embryonic physiological plasticity induced by high altitude hypoxia in lowland-native wall lizards},
  year         = {2017},
}