3.6 Length of torpor bouts in hibernation

It is obvious that there is a very high energetic cost to arousal, and an even higher one to the periods of euthermic wakefulness prior to re-entering torpor. If an animal could simply enter torpor once, and arouse 2, 4 or 6 months later, depending on the environment, it would represent a huge energy saving. Thus, it has been assumed that either prolonged torpor is physiologically impossible, or there is some strong selective value to the species in regular arousal. In the case of some small
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2.3 Hibernators as eutherms

Hibernating endotherms are not the easiest animals to study. Thus, until the late 1960s many biologists believed that mammalian hibernation was a process in which thermoregulation was simply ‘switched off’, following the receipt of a set of ‘cues’. These cues included a declining T a, a shortening daylength, the extent of body fat and a lack of food etc. With this model, the hibernator essentially becomes an ectotherm whose T b follows the T
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2.2 Species showing torpor or deep hibernation

Among the birds, torpor occurs in a number of species in the orders Apodiformes (hummingbirds and swifts), Caprimulgiformes (nightjars, nighthawks, goatsuckers and poor wills) and Coliiformes (mousebirds). In all of the hummingbirds (family Trochilidae) studied to date, torpor, if it occurs, takes place on a daily (or more usually nightly) basis. They are able to re-warm themselves independently of T a and show an increased thermogenesis if T a falls below
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2.1 Degrees of torpor

Adaptive hypothermia occurs in at least six distantly related mammalian orders (Table 1) and in several orders of birds. There is a spectrum running from those species which can tolerate a drop in T b by 2° C for a few hours, to the seasonal deep hibernators which maintain a T b as low as 4° C for weeks on end.

Table 1 Groups o
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5.4.1 Summary of Section 5

Several anatomical and biochemical adaptations to living in very cold water have evolved in polar fish, particularly those of the southern oceans, which have evolved in isolation for many millions of years. Cold, turbulent water is rich in oxygen. One family of fairly large fish lacks blood pigments but its blood is less viscous and it has additional respiratory surfaces. Many fish have cryoprotectants in the blood and other body fluids, and the muscles of some contain numerous mitochondria a
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3.1 Introduction

It is clear from Sections 1 and 2 that seasonal or irregular periods of fasting are an integral part of living at high latitudes, especially for large animals. When people (and many tropical and temperate-zone mammals) lose weight, either because they are eating less or because they are suffering from a digestive or metabolic disorder, protein is broken down in substantial quantities long before the lipid stores are exhausted. Even frequent and vigorous exercise cannot prevent the breakdown o
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2.4.1 Summary of Sections 1 and 2

Large seasonal changes in temperature and sunlight dominate primary plant production and hence the food supply. Food intake is regulated by the endogenous seasonal control of appetite, fattening and activity, as well as by food availability. Energetically demanding activities such as breeding and migration are only feasible during a brief period and must be tightly synchronized to season. Greater accessibility of food suitable for chicks makes long-distance migration to and from high arctic r
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References

Blakemore, C. and Cooper, A. (1970) Development of the brain depends on visual environment, Nature, 228, pp. 477–8.
Caspi, A., McClay, J., Moffitt, T. E., Mill, J., Martin, J., Craig, I. W., Taylor, A. and Poulton, R. (2002) Role of genotype in the cycle of violence in maltreated children, Science, 297, pp. 851–4.
Caspi, A., Sugden, K., Moffitt, T. E., Taylor
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End of unit questions

Question 1

Explain your reasons for agreeing or disagreeing with each of the following sentences.

(a) If a disease has a genetic basis and someone has the (abnormal) alleles for the disease, then that person will have the symptoms of the d
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10 Unit summary

The unit began by considering what factors contribute to individual differences. The case was made, with the spiders, and later with genetic diseases, that the genome was very important. Subsequent sections revealed that the external environment (e.g. maternal care, the presence of light) and the internal environment (e.g. hormones and drugs) were very important and that they can both shape and determine the development of the organism. Environmental factors, in the form of hormones and drugs
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9.4 Summary of Section 9

This section has illustrated what has to be done, by way of a long-term study, to yield meaningful information on the relationship between genes and development and the behaviour of the organism. It also illustrates the hugely complex nature of the relationship between genes and development and the behaviour of the organism. Yet this complexity is not the exception, it is the rule.


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9.2 Antisocial behaviour disease

The psychological arena is hugely complex because there are additional issues of responsibility and treatment. Briefly, society takes a more lenient attitude towards the behaviour of someone who is ill (diseased) compared to someone who is well. The diseased person is not fully responsible for their actions (‘They can't help it’). Therefore any individual with antisocial (aggressive) behaviour who is diagnosed as having a disease is largely absolved of blame. Having a disease, means, at l
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8.4 Fragile X syndrome

Fragile X syndrome is the final example of a genetic disease considered here.

Activity 21

What does the term ‘genetic disease’ mean?

Answer

Genetic disea
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8.3 Lissencephaly

Lissencephaly, literally meaning ‘smooth brain’, is characterised by the absence of sulci and gyri, and by a four-layered cortex, instead of the usual six layers, with the majority of cortical neurons in layer four (Figure 22). Babies born with lissencephaly have a very poor prognosis; the disease proving lethal be
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8.2 Wilson's disease

The effects of a protein that is absent, or present but not doing its job, may not be evident for many years. This is called late onset, and is exemplified by Wilson's disease. Many molecules within the body require small amounts of minerals such as iron, magnesium or copper to function properly. There are mechanisms for absorbing these minerals from the diet. However, in excess, these same minerals can be toxic, as is the case with copper. So there are also mechanisms for getting rid
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7.8 Summary of Section 7

This section has sought to illustrate the formation of connections between neurons and their targets by exploring a few examples. The picture that emerges is one of cells at different stages of development subjected to a vast array of signals. These signals are the medium through which environmental factors exert their effects. To some of these signals, some cells respond; to other signals, other cells respond. What a cell, a neuroblast, a growth cone actually does is dependent on the combina
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7.6 Synaptogenesis

The formation of synaptic connections is an essential property of nervous system development. Synapses are formed between neurons and also with targets that are not part of the nervous system, e.g. muscle. Axon terminals, under the direction of a variety of extracellular cues, grow towards particular targets. Once they arrive at the target, they stop growing and the growth cone changes to form a synapse. As with axon growth, the formation of the synapse is dependent on an interaction between
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7.4 Elixirs of the nervous system: neurotrophins

According to Section 7.2 axons obtain an elixir from targets at their synapses.

Confirmation that there is indeed an elixir came from a series of events that reveals how much of science really works. Elmer Bucker, working with Hamburger in the mid-1940s, had removed a limb bud from a chick and replaced it with a tumour from
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7.2 Selected to survive: studies of the PNS

Viktor Hamburger carried out a series of classic embryologieal experiments over a period of about 30 years. He investigated the relationship between the size of target tissue in chick embryos and the size of the pool of neurons that innervated it. His technique was to remove or add target tissue to the tissue which would eventually form a limb, usually the hind limb, and is called the limb bud. A few days later he observed the effect of the tissue addition or removal on the pool of neurons de
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7.1 Neuron proliferation

There is a huge proliferation of neurons in early life. Even whilst that proliferation continues, some cells, e.g. neuroblasts, stop being able to divide. At some later stage the proliferation itself virtually ceases. It follows that cells switch from being able to divide, to being unable to divide, and that they switch at the appropriate time: the process of cell proliferation is controlled. The details of the control of proliferation are not yet understood and are not considered here. But o
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