R
robert
Guest
I saw this and wondered if this practice was well-known/still used.
Anybody?
From:
Robert M. May
Department of Zoology
University of Oxford
Oxford OX1 3PS, United Kingdom
email: robert.may@zoology.oxford.ac.uk
A statistical study shows convincingly that a technique for marking frogs in
ecological field experiments compromises the results. Present practices need a
rethink - and not only for practical reasons.
It was 25 years ago, at an ecology seminar at Princeton University, that I first
learned of the standard method for marking individual newts or other amphibians
by clipping their toes. In this way, each individual can be identified by the unique
combination of digits removed. I remember being impressed by the elegance of
the experiments concerned - but even more impressed by the casual barbarity
of the toe clipping.
Seeking to avoid a larger ethical minefield, I asked whether such removal of
digits would affect survival, particularly in more heavily clipped individuals, thus
compromising the conclusions. My question was swept aside as silly (the sort of
thing you might expect a theoretician to ask). But it now appears to have been
answered. Writing in the Journal of Applied Ecology, McCarthy and Parris (2004)
find that "toe clipping reduces the return rate [recapture of marked individuals]
by 4-11% for each toe removed after the first, assuming the effect is the same
for all toes."
The intervening years have, indeed, seen studies of the possible adverse effects
of toe clipping of amphibians, including inflammation and infection of feet and
limbs. Some of these studies indicate lower rates of return of marked
individuals, others have found no such effects; Williamson and Bull (1996) give a
good review.
In an earlier paper, Parris and McCarthy (2001) suggested that these apparent
inconsistencies arise from a lack of statistical power (sample sizes too small for
statistically significant conclusions to be drawn) in some previous work, rather
than from the absence of real effects. They estimated that return rates decline
by 6-18% for each toe removed after the first. In this earlier paper (Parris and
McCarthy 2001), however, they could not provide meaningful confidence
intervals or a measure of how the effects would change with the number of toes
removed.
The new paper gives a Bayesian reanalysis of data drawn from four published
studies on the return rate of toe-clipped frogs: 1,333 individuals of Crinia
signifera (a small ground-dwelling Australian frog) with up to seven toes removed
(Williamson & Bull 1996); 306 individuals of the same species with between two
and four toes removed (Lemckert 1996); 733 individuals of Bufo fowleri (a large
ground-dwelling toad from eastern United States) with up to eight toes removed
(Clarke 1972); and 1,307 individuals of Hyla labialis (a medium-sized tree frog
from the Colombian Andes) with up to seven toe-disks removed (Lüddecke &
Amézquita 1999). The authors' Bayesian model, employing a freely available
statistical program (Spiegelhalter et al. 2003), helps "define the relationship
between the number of frogs that are recaptured and the effect of toe-clipping
as a function of the number of toes removed."
The estimated decline in return rate of 4-11% for each toe clipped assumed that
the adverse effects are independent of the total number of toes clipped.
McCarthy and Parris (2004) also provide a more refined analysis, allowing
effects of toe removal to change linearly with the number removed. This
indicated, for example, that the removal of a second toe reduced return rate by
3.5% (with a 95% "creditability interval" of 0-7%), whereas return rate was
reduced by 30% (95% "creditability interval" of 20-39%) on removal of an eighth
toe. Overall, the cumulative effect of toe clipping appears to be such that the
return rate for frogs with two toes removed was around 96% of those with one
toe removed, declining to 28% for the return of frogs with eight toes gone.
The authors justifiably conclude that these effects should be more explicitly
recognized in future studies that use toe clipping to mark individuals in ecological
studies. They also tellingly add that "our study has important implications for
the ethical treatment of animals, the continued use of clipping to mark species
of conservation concern, and the removal of multiple toes from an individual frog
or toad." It seems to me that all these conclusions apply to all amphibians.
More generally, I see McCarthy and Parris's (2004) paper as a notable addition to
a growing literature that raises both practical and larger ethical questions about
time-honoured procedures in some ecological field studies. There are obvious
parallels with the recent study of long-term effects of flipper tags on penguins,
by Gauthier-Clerc et al. (2004). This work attracted considerable media
attention with its finding, after five years' work on king penguins implanted with
electronic tags (some also with flipper bands and others not), that "banding
results in later arrival at the colony for courtship in some years, lower breeding
probability and lower chick production". Gauthier-Clerc et al. (2004). also found
that unbanded king penguin chicks had roughly twice the survival rate after 2-3
years of those encumbered with flipper bands.
Scientific and medical understanding gained by the use of non-human animals in
laboratory studies is widely recognized as producing great benefits, primarily for
humans but also for other animals themselves. At the same time, such research
is properly strictly regulated. And I for one welcome
the attention increasingly given to the rights of non-human animals by
philosophers such as Peter Singer. But field studies of the ecology and behaviour
of non-human animals can also raise difficult questions of costs and benefits. As
a sixth wave of mass extinction looms, conservation biologists desperately need
the knowledge that comes from such field studies. As the work described here
clearly shows, however, there are good reasons why we need to think more
carefully about some present practices.
References
McCarthy, M. A. & Parris, K. M. 2004. J. Applied Ecology 41: 780-786.
Williamson, I. & Bull, C. M. 1996. Wildlife Research 23: 249-266.
Parris, K. M. & McCarthy, M. A. 2001. Amphibia-Reptilia 22: 275-289.
Lemckert, F. 1996. Amphibia-Reptilia 17: 287-290.
Clarke, R. D. 1972. Copeia 1972: 182-185.
Lüddecke, H. & Amézquita, A. 1999. Copeia 1999: 824-830.
Spiegelhalter, D. J. et al. 2003. WinBUGS User Manual Version 1.4 (MRC Biostat
Unit Cambridge)
Gauthier-Clerc, M. et al. 2004. Proc. Royal Society London B:10:1098.
__________________
Anybody?
From:
Robert M. May
Department of Zoology
University of Oxford
Oxford OX1 3PS, United Kingdom
email: robert.may@zoology.oxford.ac.uk
A statistical study shows convincingly that a technique for marking frogs in
ecological field experiments compromises the results. Present practices need a
rethink - and not only for practical reasons.
It was 25 years ago, at an ecology seminar at Princeton University, that I first
learned of the standard method for marking individual newts or other amphibians
by clipping their toes. In this way, each individual can be identified by the unique
combination of digits removed. I remember being impressed by the elegance of
the experiments concerned - but even more impressed by the casual barbarity
of the toe clipping.
Seeking to avoid a larger ethical minefield, I asked whether such removal of
digits would affect survival, particularly in more heavily clipped individuals, thus
compromising the conclusions. My question was swept aside as silly (the sort of
thing you might expect a theoretician to ask). But it now appears to have been
answered. Writing in the Journal of Applied Ecology, McCarthy and Parris (2004)
find that "toe clipping reduces the return rate [recapture of marked individuals]
by 4-11% for each toe removed after the first, assuming the effect is the same
for all toes."
The intervening years have, indeed, seen studies of the possible adverse effects
of toe clipping of amphibians, including inflammation and infection of feet and
limbs. Some of these studies indicate lower rates of return of marked
individuals, others have found no such effects; Williamson and Bull (1996) give a
good review.
In an earlier paper, Parris and McCarthy (2001) suggested that these apparent
inconsistencies arise from a lack of statistical power (sample sizes too small for
statistically significant conclusions to be drawn) in some previous work, rather
than from the absence of real effects. They estimated that return rates decline
by 6-18% for each toe removed after the first. In this earlier paper (Parris and
McCarthy 2001), however, they could not provide meaningful confidence
intervals or a measure of how the effects would change with the number of toes
removed.
The new paper gives a Bayesian reanalysis of data drawn from four published
studies on the return rate of toe-clipped frogs: 1,333 individuals of Crinia
signifera (a small ground-dwelling Australian frog) with up to seven toes removed
(Williamson & Bull 1996); 306 individuals of the same species with between two
and four toes removed (Lemckert 1996); 733 individuals of Bufo fowleri (a large
ground-dwelling toad from eastern United States) with up to eight toes removed
(Clarke 1972); and 1,307 individuals of Hyla labialis (a medium-sized tree frog
from the Colombian Andes) with up to seven toe-disks removed (Lüddecke &
Amézquita 1999). The authors' Bayesian model, employing a freely available
statistical program (Spiegelhalter et al. 2003), helps "define the relationship
between the number of frogs that are recaptured and the effect of toe-clipping
as a function of the number of toes removed."
The estimated decline in return rate of 4-11% for each toe clipped assumed that
the adverse effects are independent of the total number of toes clipped.
McCarthy and Parris (2004) also provide a more refined analysis, allowing
effects of toe removal to change linearly with the number removed. This
indicated, for example, that the removal of a second toe reduced return rate by
3.5% (with a 95% "creditability interval" of 0-7%), whereas return rate was
reduced by 30% (95% "creditability interval" of 20-39%) on removal of an eighth
toe. Overall, the cumulative effect of toe clipping appears to be such that the
return rate for frogs with two toes removed was around 96% of those with one
toe removed, declining to 28% for the return of frogs with eight toes gone.
The authors justifiably conclude that these effects should be more explicitly
recognized in future studies that use toe clipping to mark individuals in ecological
studies. They also tellingly add that "our study has important implications for
the ethical treatment of animals, the continued use of clipping to mark species
of conservation concern, and the removal of multiple toes from an individual frog
or toad." It seems to me that all these conclusions apply to all amphibians.
More generally, I see McCarthy and Parris's (2004) paper as a notable addition to
a growing literature that raises both practical and larger ethical questions about
time-honoured procedures in some ecological field studies. There are obvious
parallels with the recent study of long-term effects of flipper tags on penguins,
by Gauthier-Clerc et al. (2004). This work attracted considerable media
attention with its finding, after five years' work on king penguins implanted with
electronic tags (some also with flipper bands and others not), that "banding
results in later arrival at the colony for courtship in some years, lower breeding
probability and lower chick production". Gauthier-Clerc et al. (2004). also found
that unbanded king penguin chicks had roughly twice the survival rate after 2-3
years of those encumbered with flipper bands.
Scientific and medical understanding gained by the use of non-human animals in
laboratory studies is widely recognized as producing great benefits, primarily for
humans but also for other animals themselves. At the same time, such research
is properly strictly regulated. And I for one welcome
the attention increasingly given to the rights of non-human animals by
philosophers such as Peter Singer. But field studies of the ecology and behaviour
of non-human animals can also raise difficult questions of costs and benefits. As
a sixth wave of mass extinction looms, conservation biologists desperately need
the knowledge that comes from such field studies. As the work described here
clearly shows, however, there are good reasons why we need to think more
carefully about some present practices.
References
McCarthy, M. A. & Parris, K. M. 2004. J. Applied Ecology 41: 780-786.
Williamson, I. & Bull, C. M. 1996. Wildlife Research 23: 249-266.
Parris, K. M. & McCarthy, M. A. 2001. Amphibia-Reptilia 22: 275-289.
Lemckert, F. 1996. Amphibia-Reptilia 17: 287-290.
Clarke, R. D. 1972. Copeia 1972: 182-185.
Lüddecke, H. & Amézquita, A. 1999. Copeia 1999: 824-830.
Spiegelhalter, D. J. et al. 2003. WinBUGS User Manual Version 1.4 (MRC Biostat
Unit Cambridge)
Gauthier-Clerc, M. et al. 2004. Proc. Royal Society London B:10:1098.
__________________