Affects of Temperature and .....

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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 bole

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