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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"

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