Affects Of Temperature And ….. Essay, Research Paper
Richard Shine, Thomas R. L. Madsen, Melanie J. Elphick, and Peter S. Harlow
authored the journal entry titled, ?The Influence of Nest Temperatures and Maternal
Brooding on Hatchling Phenotypes in Water Pythons? and had it published in volume
78(6) of Ecology in 1997. The work deals with the Water Python (Liasis fuscus) of
Northern Australia and how temperature and the amount of maternal brooding results in
different phenotypes in hatchlings. In the experiment the authors measured body size,
shape, behaviour and performance of the young pythons. To understand the experiment?s
procedures and results, one must first understand some of the background behind it.
Phenotypic plasticity is the ?modification of the phenotype by direct
environmental influences with no genetic underpinnings?, and is measured in the
experiment. Little research has been done in this area with the snake species, let alone
the Water Python. Turtles and lizards have been used previously in similar studies, but
were placed in laboratory incubators rather than ?realistic simulations of thermal regimes
in natural nests?. The water python is one of the primitive snake species that
demonstrates the rare task of providing elaborate care of its young. The snake will wrap
around the eggs after oviposition (eggs have been layed) and remain with them until they
have hatched. This behaviour has been believed to be very limited in the Serpents but
may be common with all pythons. Some species of snakes, for example the Indian
Python, have been found to incubate their clutch with their own body. The snake will
produce body heat by rhythmic muscle contractions along its body, an occurrence known
as shivering thermogenesis. Past studies have found the shivering act only in temperate
zone dwelling snakes like the Indian Python, but some scientists now believe that it may
also occur in the tropical zone dwelling Water Python. A previous experiment of the
Water Python was used as a home base for this study.
The base of the experiment came from the result of another study that dealt with
Water Pythons of the same population and tested the two common nesting areas of the
females. The females were found to nest either in the burrows of varanid lizards where
the temperatures were high and fairly constant, or inside root boles of paperbark trees
where temperatures were cooler and more variable. In the hot nests the females deserted
the eggs soon after laying, while the in the cooler nests the females attended throughout
incubation. Shine and the others used the results of the previous experiment to shape the
study of their own.
This study occurred on the floodplains of the Adelaide River in the Northern
Territory of Australia, where temperatures are high and stable year round. The female
pythons were hand collected and the gravid ones were transferred to the University of
Sydney where they were cared for until oviposition. The snakes were kept at a warm 32
degrees Celsius in tubs of moistened straw. After the eggs were layed the scientists
attempted to separate them to obtain better results; some were destroyed in the process.
They used incubators to simulate three different environments; (1) varanid burrow nests
at 32 degrees, (2) paperbark nests with maternal attendance with temperatures fluctuating
from 27.4 to 32.9 degrees, and (3) paperbark nests without maternal attendance with
temperatures fluctuating from 24.3 to 32.9 degrees. They referred to these different
settings as (1) 32 degrees Celsius, (2) hot, and (3) cold. See figure 1. The number of
eggs placed in each incubation treatment differed because previous studies had shown
that 32 degrees was the prosperous temperature for hatchling survival and that the cold
was detrimental. From that, 104 eggs were placed at 32 degrees Celsius, 56 at the hot
treatment, and 27 at the cold treatment. The eggs were placed in large buckets
containing moist vermiculite and covered with plastic wrap to retain moisture but allow
oxygen exchange. The incubator temperatures were monitored with data-logger probes
inside condoms that were made to resemble python eggs and placed in identical
incubators to those with the real eggs. The eggs were inspected daily until they hatched.
The hatchlings were then measured, and weighed, and their sex was determined. The
young were then placed in plastic cages with temperatures at 30 degrees Celsius until
they were old enough to be tested on.
When the hatchlings were approximately ten days old, two traits were assessed;
their propensity to strike defensively at the experimenter, and their locomotor
(swimming) ability. The python was tapped on the head with a small paintbrush until it
would strike. The number of taps before a strike was launched measured the propensity
to strike. Swimming ability was measured by placing the pythons in a small racetrack
pool while a wire rod splashed into the water behind them, encouraging them to keep
swimming. Trials were videotaped and the time taken to complete each circuit, number
of splashes needed to keep them moving in each circuit, and the number of circuits
completed prior to exhaustion were all measured. Notes were also made if the snake?s
head came out of the water on a lap or if the snake managed to crawl over the plastic
walls. All tests were repeated when the young were one month old. Also tested was the
snakes? readiness to feed at five weeks of age. A dead mouse was placed in the cage and
the number of times a python was offered food and did not eat was recorded. The data
was then analyzed and charted and results were made.
The scientists first examined the influence of offspring size and sex on other
traits. The sex of the python had negligible influence on its size, shape, or behaviour.
Body size, on the other hand, had various effects. The longer pythons were found to be
heavier at each age and the tests resulted that they were faster swimmers, needed fewer
taps per lap to persuade them to keep swimming, swam more laps before becoming
exhausted, and required fewer taps before they launched a retalitory strike at the
paintbrush. The scientists then examined which effects were due to body size and which
were not. The survival rate, incubation period, morphology, locomotory performance,
prpensity to strike, and willingness to feed were all examined and compared between the
three different incubation processes.
In the survival rate studies the hatching success did not vary significantly among
the three incubation treatments, even though previous studies had shown that the 32
degrees was benificial and the cold treatment was detrimental. With the incubation
period studies, the eggs maintained in the hot treatment hatched significantly earlier than
the eggs at 32 degrees. ?Maternal effects were also highly significant, as was the
interaction between clutch number and incubation treatment (Table 1). Thus, thermal
regimes affected incubation periods differently in different clutches?. In the morphology
studies, strong maternal effects were evident on the size and shape at hatching. See
Table 1. They did not detect any main effects of incubation temperature, but there were
strong interactions between the clutch number and temperature for both size and shape.
See Table 1. ?The increasing effect of incubation treatment on body sizes suggests that
growth rates differed among hatchlings from the different incubation treatments?. The
incubation treatments ended up affecting the growth rates as well as body shape. With
the locomotory performance studies, maternal identity was the strongest influence.
There was no significant ineteractions detected between clutch number and incubation
treatment for performance traits, and main effects of incubation regime were evident for
only a few traits. 63% of the cold environment hatchlings crawled over the plastic walls
in the swimming pool testing while the hot hatchlings were at 27%, and the 32 degrees
were at 7%. This trait dissapeared at thirty days of age. In the propensity to strike
studies nothing determinate was found. And lastly in the willingness to feed study, 59%
of the 32 degree incubated, 34% of the cold-incubated, and 16% of the hot-incubated
python hatchlings ate the mouse immediately. From those findings the scientists
discovered that the ?differences enable strong rejection of the null hypothesis of equal
willingness to feed regardless of incubation regime?. After the results were discovered a
discussion could be made.
A statement directly from the journal article that states the experiments findings
is ?Our data confirm and extend previous experimental studies that have demonstrated
phenotypic plasticity in the size, shape, and behaviour of hatchling reptiles in response to
the thermal conditions which these animals experience as embryos.? The Liasis fuscus is
a good representative of how phenotypic plasticity can be affected by different thermal
incubation temperatures. The scientists believed that because they duplicated the water
python?s natural nest settings of the wild in a laboratory, the results seen would be
identical to those directly from the wild. This study was the first to provide evidence on
the effects of nest attendance and shivering thermogenesis of the female python.
Shivering thermogenesis and female nest attendance may in fact be found in all species
of python. One thing that surprised the scientists was the fact that the incubation had
little to due with the survival of the hatchlings even though in previous studies it had. If
the eggs can develop quite fine in colder temperatures, why do female pythons remain at
high cost to incubate their young? The study suggests that the hatching time is speeded
up when the female is in attendance and ?may also affect offspring viability by inducing
particular developmental pathways?.
In conclusion, a signifigant amount of sensitivity of embryogenesis to incubation
temperatures was found by placing python eggs into three recreations of nesting sites of
different temperatures. ?Both maternal nest choice and shivering thermogenesis can
substantially affect not only the time at which the eggs hatch, but also the size, shape, and
behaviour of the hatchlings.? This study may lead to the revelation that phenotypes are
affected by environmental conditions, along with intrnsic causes. Science?s
understanding of the relationship betwen natural selection and direct evolutionary
changes may in fact be false, or may at least require a few changes in the case of the
Water Python.
Works Cited
Halliday, Tim Dr., and Adler, Kraig Dr. The Encyclopedia of Reptiles and
Amphibians. New York, NY: Facts on File Inc, 1994.
Shine, Richard, et al. ?The Influence of Nest Temperatures and Maternal Brooding on
Hatchling Phenotypes in water Pythons.? Ecology 78 (1997): 1713-1721.
Bibliograpy
Halliday, Tim Dr., and Adler, Kraig Dr. The Encyclopedia of Reptiles and
Amphibians. New York, NY: Facts on File Inc, 1994.
Shine, Richard, et al. ?The Influence of Nest Temperatures and Maternal Brooding on
Hatchling Phenotypes in water Pythons.? Ecology 78 (1997): 1713-1721.
This is a Journal Critique and at the bottom is a Presentation format
AFFECTS OF TEMPERATURE
AND MATERNAL BROODING
ON PHENOTYPIC PLASTICITY
IN WATER PYTHONS
HUH??
Water Python (Liasis fuscus)
-tropical sake of Northern Australia
-maternal brooding & shivering thermogenesis
Two Nesting Sites
1) Burrows of varanid lizards
-hot, stable temperatures
-females leave eggs after laying
2) Inside root boles of paperbark trees
-cool, more variable temperatures
-maternal brooding
Does temperature & brooding affect phenotypic
plasticity?
Phenotypic Plasticity=modification of the phenotype
by direct environmental influences, with no
genetic underpinnings.
Little Research
-turtles and lizards
-no tropical species
HOW??
-Floodplains of Adelaide River in Northern Territory
of Australia
-Collected Water Python females
->Maintained until oviposition
-Collected 187 eggs
-Created three incubation systems
1) 32 degrees Celcius
-varanid burrow nests
2) Hot
-paperbark nests with maternal brooding
3) Cold
-paperbark nests without brooding
-104 eggs @ 32 degrees
-56 eggs @ Hot
-27 eggs @ Cold
->previous studies
GO ON…….
Hatchlings Emerge & Testing Begins
10 days old
-> measured, weighed, sex determined
-> Propensity to Strike
-paintbrush tap
-> Locomotory Performance
-pool race track
-wire rod prod
-recorded time to complete, # splashes
to keep going, & # circuits complete
before exhaustion
5 weeks old
-> Willingness to Feed
-dead mouse offering -2 hours
-ten day old tests were repeated at one month of age
AND??
BODY SIZE
-Larger pythons heavier at each age
-> faster swimmers
-> fewer taps to keep swimming
-> swam more laps
SEX
-Little influence
-Males = Females
SURVIVAL RATE
-No variation with incubation
->surprising
INCUBATION PERIOD
-32 degrees, then hot, then cold
-Maternal brooding highly significant
-Thermal regimes affected incubation periods
in different clutches
MORPHOLOGY
-Maternal effects on size and shape
-Incubation treatments affected growth rates
and body shape
LOCOMOTORY PERFORMANCE
-Maternal identity was the primary influence
->some clutches swim faster than others
PROPENSITY TO STRIKE
-Nothing
WILLINGNESS TO FEED
-Incubation was a major factor
-> 59% immediately ate @ 32 degrees
-> 34% immediately ate @ Cold
-> 16% immediately ate @ Hot
SO??
-Phenotypic plasticity affected by different thermal
incubation temperatures
-This was the first study to provide evidence on
effects of nest attendance and shivering
thermogenesis of female python
-> True in all pythons species?
-Temperature didn?t affect survival
->Why stay and incubate if costly?
–>Hatching time is speeded up and
offspring viability is affected
-Phenotypes affected by environmental conditions
as well as intrinsic (genetic) causes
->understanding of the relationship between
natural selection and direct evolutionary
changes may need to be reconsidered
TAH DAH!!
?Both maternal nest choice and shivering
thermogenesis affect not only the time at which eggs
hatch, but also the size, shape, and behaviour of the
hatchlings?