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Tadpole tolerance
Could you expand on the importance
of understanding and predicting the
vulnerability of animal populations to
climate change?
Assessing the impacts of climate change in
amphibians and other organisms will require
an integrative approach that assesses the
sensitivity of organisms – for instance by
measuring their thermal resistances – and
combines these data with environmental
information that evaluates their exposure
to climate changes at regional, local and
microenvironmental levels. This bigger picture
of sensitivity and exposure will be essential
for identifying which species and ecosystems
are most vulnerable, and thus prioritising
them in management programmes.
To begin, can you discuss the primary
focus of your research group on
evolutionary biology?
The project has a number of international
collaborators. Can you outline the
benefits of cooperating at a global level?
The group I am leading is mainly concerned
with the adaptive response of amphibians
to stressful environmental conditions,
especially during their aquatic larval
stage. We have previously conducted
research to identify local adaptations
and the role of phenotypic plasticity as
a potential mechanism of adaptation to
stressful environments, such as drying
ponds, salinity and other pollutants. At
present, we are concerned with analysing
the thermal adaptations of amphibians
living in contrasting thermal environments
and providing a mechanistically-based
assessment of amphibian tadpoles’
vulnerabilities to heating stress in the
coming decades at the population, species
and community levels.
Amphibians, and most ectothermic
biodiversity, are concentrated in the
tropics. Especially rich are Neotropical
realms, where 50 per cent of all recognised
amphibian species live. Our collaborations
with local South American herpetologists
in Argentina, Brazil, Ecuador and Colombia
allow the examination of vulnerabilities
from different Neotropical biomes, such
as tropical mountain forest, high páramos,
tropical and subtropical savannahs, and dry
forests. This is fundamental to providing
a comprehensive risk assessment of the
impressive frog diversity.
How did the focus on amphibian risk of
heating stress arise?
This project emerged by serendipity in
2006, during a field trip through the
Gran Chaco with my colleague Federico
Marangoni. We were astonished to find
water temperatures exceeding 41 °C in
ponds that swarmed with hundreds of
tadpoles. How could these species face
such extreme thermal conditions? And
more pressingly, how would they face
the likely increase in thermal stress in
the coming decades? This led me to think
that heating damage could be a potential
source of amphibian population decline and
species extirpation (localised extinction) in
the future.
species may be fundamental when
designing the architecture, location and
surrounding habitats of these ponds, in
order to recreate optimal thermal pond
microenvironments.
DR MIGUEL TEJEDO
Amphibians living in tropical and subtropical climes face a host of challenges to their survival. Here,
Dr Miguel Tejedo explains how future changes in the Earth’s climate may further increase this pressure
The analysis of species thermal sensitivity
requires standardised methods in the
experimental assays that are conducted
in remote field sites. We have developed
self-made portable instruments that
are receiving patent licensing in a joint
technological transfer with LorEnergía, Ltd.
Are effective strategies to protect
at-risk amphibians and other animals
being developed? Could you discuss the
challenges to their implementation?
Unfortunately, it appears that mitigating
strategies at the global or even regional
scale will not prove viable. The only
realistic strategy will be a reduction
of global greenhouse gas emissions.
Optimistically, some capacity to
ameliorate impacts could be developed at
the local level by imaginative management
actions to both reduce exposure and
increase resilience of the most endangered
species or ecosystems.
Collaborators in temperate areas, like the US,
are also crucial for clarifying whether coldadapted species from higher latitudes are
also vulnerable to heat impacts. We predict
that, in other frog communities under similar
climatic conditions from other continents,
we may find a similar pattern of warming
tolerances as those obtained in the studied
temperate and tropical communities, but this
will require further research.
Do you have partnerships outside of
the research community? What are the
benefits of this cooperation?
Aside from academic forums, we also
collaborate with species conservation
agencies to help with compensatory
actions, such as construction programmes
for new ponds to potentiate amphibian
populations. A precise knowledge of
thermal sensitivity of target endangered
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DR MIGUEL TEJEDO
Tropical survival
With the future of the world’s tropical and subtropical amphibians at risk,
evolutionary ecologists at the Doñana Biological Station in Seville are using a novel
metric to enable precise predictions on the biological consequences of climate change
DURING THE 20TH CENTURY, the Earth’s
temperature rose by 0.6 °C, a rate of warming
that has resulted in rapid environmental changes.
According to the Intergovernmental Panel on
Climate Change (IPCC), it is likely that the current
rate will increase fivefold before the end of this
century. The effects of rising temperatures can be
seen most strikingly in the shifting landscape at the
planet’s poles but the predicted increase in warming
will have visible consequences for ecosystems in
the Earth’s more habitable regions.
Representing 80-90 per cent of the world’s
amphibious fauna, tropical and subtropical
The brazilian frog Phyllodytes luteolus in a water body
inside a bromeliad. Amphibians can breed in aquatic
environments of reduced dimensions and these
microenvironments suffer very extreme temperatures.
© Miguel Tejedo
amphibians are already the most endangered
vertebrates due to a host of anthropogenic factors
such as the destruction of natural habitats, pollution
and the emergence of infectious diseases. Climate
change can be added to the already extensive list of
risk factors threatening their existence as concerns
arise over the likelihood that rates of warming
will outpace their evolutionary adaptation. As
ecosystems change, it is vital to identify which
species and communities are most in danger of
extinction, in order to make accurate predictions
of the biological consequences of global warming.
EVOLUTIONARY ECOLOGY
AND CONSERVATION
Belonging to the Spanish Council for Scientific
Research (CSIC), the Doñana Biological Station in
Seville is dedicated to uncovering the mechanisms
that underpin biodiversity, how it is sustained and
what leads to its decline. Dr Miguel Tejedo is an
assistant professor of research at the Department of
Evolutionary Ecology. Using macrophysiology (the
evolution of large-scale physiological variation)
and comparative phylogenetic approaches, the
group study the evolution of thermal adaptations
of amphibians living in contrasting thermal
environments, including tropical, subtropical and
temperate communities through Europe and North
and South America.
Field work with Tejedo and colleagues at the Caatinga
reserve of Contendas do Sincorá, Bahia, Brazil.
© Miguel Tejedo
Such a broad geographical range of field studies
means collaboration with local scientific research
institutions is vital. With funding from Spain’s
Ministry of Economy and Competitiveness
(MINECO) and the Spanish Agency for International
Cooperation for Development (AECID), Tejedo’s
research focuses on a global risk assessment
of warming-induced stress on amphibians, in
order to determine which communities are more
susceptible to suffer population decline and species
extirpation in the near future.
Amphibians are most vulnerable to heat stresses
when they are still aquatic tadpoles. This is because
water not only has a high heat capacity but is also
an excellent conductor, meaning a warm pond is
likely to be uniform in its heat distribution with
no sanctuary of cooler microhabitats. Regarding
the position these tadpoles may face, Tejedo is
unequivocal: “In this limiting situation, they must
have the ability to withstand heating or else they
will die”. In order to make precise predictions about
their fate, Tejedo hopes to perform a physiological
assessment of their vulnerability and identify the
most at-risk communities and species.
WARMING TOLERANCE METRICS
Based on the available data describing tadpole
critical thermal limits, it is predicted that
amphibians residing in tropical and subtropical
climes may face the highest risk of extinction as
a result of global warming. In low-latitude regions
‘cold-blooded’ ectotherms, such as tadpoles, live
in environments that are more similar to their
optimal temperature than those living at highlatitudes. As upper thermal limits are not coupled
with geographic location, tadpoles in low-latitude,
tropical and subtropical regions are subject to
environmental temperatures much closer to their
upper thresholds.
To make possible the delivery of an integrative
framework
that
evaluates
amphibian
vulnerability, Tejedo needs data regarding
species’ sensitivity to heat stress and their
exposure to changes in the climate. Previous
efforts to establish such a framework have
focused on the current distributional range of
climatic parameters to produce estimations of
ectothermal sensitivity to heat stress, but this
methodology has its limitations.
Professor Mirco Solé and his team conducting field
work at the Mata Atlantica reserve of Serra Bonita,
Bahia, Brazil. © Miguel Tejedo
72INTERNATIONAL INNOVATION
Without taking into account the circumstances
of a species’ biogeographical history it is difficult
to produce estimates with real meaning.
INTELLIGENCE
VULNERABILITY OF
AMPHIBIANS TO WARMING
OBJECTIVES
To provide a physiologically-based assessment
of amphibian risk of heating stress due to global
warming and identify the most vulnerable of the
world’s biomes and amphibian communities to
possible loss of population and species.
KEY COLLABORATORS
Juan F Beltrán, Universidad de Sevilla, Spain
• Manuel Hernando Bernal, Universidad del
Tolima, Colombia • Federico Marangoni,
Instituto de Biología Subtropical (IBS; FCEQyNUNaM; CONICET), Argentina • Andrés MerinoViteri; Santiago Ron, Pontificia Universidad
Católica de Ecuador • Carlos A Navas, Instituto
de Biociências, Universidade de São Paulo, Brazil
• Alfredo G Nicieza, Universidad de Oviedo,
Spain • Rick A Relyea, University of Pittsburgh,
USA • Mirco Solé; Andrés Egea, Universidade
Estadual de Santa Cruz, Brazil • Enrique MartinLorente, LorEnergía, Ltd, Spain
FUNDING
Ministry of Economy and Competitiveness
(MINECO) – award no. CGL2012-40246-C02-01
(2013-2015) • Spanish Agency for International
Cooperation for Development (AECID) –
award no. A/016892/08, A/023032/09 and
AP/038788/11
Waxy monkey frog Phyllomedusa sauvagii from the
subtropical Gran Chaco region of Argentina.
© Miguel Tejedo
Hampering this approach further is the almost
total lack of micro-environmental climatic variation
analysis in available literature. However, by
establishing physiological assays and monitoring
microenvironmental temperatures, Tejedo has
arrived at the warming tolerance metric, a simple
measure that describes the difference between
the maximum temperature tolerated by an
organism and the maximum microenvironmental
temperature it experiences, or will do in the future.
Crucially, special attention has been paid to the
IPCC’s predicted increase in the rate of warming.
With this metric it is possible to derive data on the
susceptibility to heat stress of a particular species,
population or community. “The range of tolerances
obtained will describe the level of vulnerability at
present and in the coming decades,” states Tejedo.
COPING WITH STRESS
Consistent with their predictions, the group’s
physiological assays show that tropical and
subtropical, low-latitude communities, are
generally the most vulnerable to the dangers
of heat stress, with some exceptions of lowtolerance communities in temperate climes. Their
ability to survive the future rise in temperatures is
hampered considerably by low levels of migratory
dispersal and their inability to adapt fast enough to
environmental changes. Although their phenotypic
plasticity means that acclimatisation is a tadpole’s
best bet, they may only be able to cope with a
maximum increase of 1-3 °C. Unlike temperate
communities, however, Tejedo has found that
most subtropical species exhibit a potential for
short-term acclimatisation where a quick increase
in their thermo-tolerance can alleviate specific
episodes of heat shock such as heat waves – a
useful strategy for protection during the larval
CONTACT
Tropical and subtropical
amphibians are the world’s most
endangered vertebrates
stage that could be essential to their survival
beyond the end of the century.
Within the tropical and subtropical category
there exists a divide between amphibians
breeding in ponds open to the elements and those
breeding in forested habitats, where the natural
canopy provides shelter from dangerous peak
temperatures. Though seemingly living a more
assured existence, the tadpoles with protective
cover actually have a much lower thermal
resistance than their open forest-dwelling cousins.
As Tejedo explains, for these covered communities,
deforestation can have dire consequences: “If the
protective umbrella disappears, these species will
become highly vulnerable”.
Dr Miguel Tejedo
Assistant Professor of Research
Estación Biólogica de Doñana
Spanish Council for Scientific Research (CSIC)
41092 Sevilla, Spain
T + 34 629 58 10 51
E [email protected]
www.ebd.csic.es/website1/Departamentos/
NEvolEcol.aspx
MIGUEL TEJEDO is CSIC Assistant Professor
of Research at the Biological Station of Doñana
in Seville. His current interest is the analysis of
thermal adaptations of amphibians to their local
climatic environments. The main objectives are
to provide a physiological basis of vulnerability
to global change in tropical and temperate frogs
and to understand whether thermal evolution
is a potential engine of frog species radiation in
tropical mountains.
Given the ongoing high levels of deforestation
in South America, alongside a raft of other
vulnerability factors, Tejedo is not optimistic about
the chance of survival for tropical and subtropical
ectotherms. However, potential avenues do exist
through which the risk posed by heat stress could
be mitigated, such as the construction of ponds
in shaded microenvironments and the upkeep of
fragmented canopies. Although assistance on a
large scale may not yet be forthcoming from natural
resource agencies, the Evolutionary Ecology Group
at the Doñana station has provided the tools for a
better understanding of the phenomena affecting
these species’ safety.
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