Ground squirrels of the genus Marmota are known for their ability to tolerate bitterly cold climates, which they in part accomplish with their exceptional ability to hibernate for as much as eight months a year (Armitage et al., 2003). Most of the 15 living species are associated with montane habitats, and those that are not, like the North American woodchuck (Marmota monax) and the eastern European and central Asian bobak (M. bobak) inhabit regions with strongly seasonal climates and often bitterly cold winters (Armitage, 2000) (Figure 9.1). All marmots construct burrows, which can be more than one metre deep even in comparatively mild climates and as much as seven metres deep in the harsh climates of the Himalayas (Barash, 1989). During the cold phases of the last half of the Quaternary the fossil record demonstrates many marmots inhabited periglacial environments (Zimina and Gerasimov, 1973; Kalthoff, 1999). For these reasons, marmots are sometimes considered to be a quintessentially Quaternary clade, specialists on the cold variable climates that are unique to the past 2.6 million years of Earth's history. The world in which they originated, however, was very different; a warmer one in which there were no tundra biomes, no glacial–interglacial cycles, and no permanent ice cover in the Northern Hemisphere. In this chapter, we review the fossil and phylogenetic history of marmots, the palaeoenvironments in which they originated, and their relationship to glacial–interglacial cycles to better understand the contexts in which the specializations of this unique clade of rodents arose.
The Quaternary, the current geological period, is defined by the onset of permanent ice sheets in the Northern Hemisphere 2.58 million years ago and is by far the coldest period since the extinction of the last non-avian dinosaurs 65 million years ago (Zachos et al., 2001; Gibbard et al., 2010).
Potato is South America's greatest gift to world agriculture and human nutrition (Graves, 2001). A dietary staple of indigenous Andean peoples for eight millennia, potato was unknown to the rest of the world before the mid sixteenth century. Today, potato is the world's fourth most important food crop, after maize, wheat and rice, and is grown on a significant scale in more than 130 countries on six continents with annual tuber production exceeding 320 million tonnes (Food and Agriculture Organization, 2007). In recognition of potato's potential to provide food security and eradicate poverty, 2008 has been proclaimed International Year of the Potato.
In most production systems, potato is clonally propagated from “seed” tubers. Clonal propagation offers agronomic and genetic advantages, e.g. vigorous early growth, higher yields and consistent expression of desirable traits. More than 10% of world potato production is used to provide “seed tubers” for planting the next production season. Seed potato tubers can be infected with a wide range of pests and pathogens which may affect growth of the crop and health of progeny tubers. Thus, access to high-quality, disease-free seed potatoes has been described as “the single most important integrated pest management practice available to potato growers” (Gutbrod & Mosley, 2001). Seed potato lots can be downgraded or rejected for recertification for myriad causes from “varietal mix” to herbicide injury. However, aphid-transmitted, tuber-borne potato viruses far exceed all others.
I have often wondered that, in so inquisitive an age as this, among those many learned men that have with much freedom, as well as acuteness, written of the works of nature (as they call them) – and some of them of the principles too – I have not met with any that has made it his business to write of nature herself. This will perhaps hereafter be thought such an omission as if, in giving an account of the political estate of a kingdom, one should treat largely of the civil judges, military officers and other subordinate magistrates, and of the particular ranks and orders of inferior subjects and plebeians, but should be silent of the prerogatives and ways of administration of the king; or (to use a comparison more suitable to the subject) as if one should particularly treat of the barrel, wheels, string, balance, index and other parts of a watch, without examining the nature of the spring that sets all these a moving. When I say this, I do not forget that the word ‘nature’ is everywhere to be met with in the writings of physiologers. But though they frequently employ the word, they seem not to have much considered what notion ought to be framed of the thing, which they suppose and admire, and upon occasion celebrate, but do not call in question or discuss.
A considering person may well be tempted to suspect that men have generally had but imperfect and confused notions concerning nature, if he but observes that they apply that name to several things, and those too such as have (some of them) very little dependence on or connection with such others. And I remember that in Aristotle's Metaphysics, I met with a whole chapter expressly written to enumerate the various acceptions of the Greek word φύσις, commonly rendered ‘nature’, of which, if I mistake not, he there reckons up six. In English also we have not fewer, but rather more numerous significations of that term. For sometimes we use the word ‘nature’ for that author of nature whom the schoolmen harshly enough call natura naturans [literally, nature naturing], as when it is said that nature has made man partly corporeal and partly immaterial. Sometimes we mean by the nature of a thing the essence, or that which the schoolmen scruple not to call the ‘quiddity’ of a thing – namely, the attribute or attributes on whose score it is what it is, whether the thing be corporeal or not, as when we attempt to define the nature of an angel, or of a triangle, or of a fluid body as such. Sometimes we confound that which a man has by nature with what accrues to him by birth, as when we say that such a man is noble by nature, or such a child naturally forward or sickly or frightful.
I come now, Eleutherius, to acquaint you with some of the reasons that have made me backward to entertain such a notion of nature as I have hitherto discoursed of. And I shall at present comprise them under the following five.
1. The first whereof is, that such a nature as we are speaking of seems to me to be either asserted or assumed without sufficient proof. And this single reason, if it be well made out, may (I think) suffice for my turn. For in matters of philosophy, where we ought not to take up anything upon trust or believe it without proof, it is enough to keep us from believing a thing, that we have no positive argument to induce us to assent to it, though we have no particular arguments against it. And if this rule be to take place in lesser cases, sure it ought to hold in this, where we are to entertain the belief of so catholic an agent that all the others are looked upon but as its instruments, that act in subordination to it; and which, being said to have an immediate agency in many of the phenomena of the world, cannot but be supposed to be demonstrable by divers of them. I have yet met with no physical arguments, either demonstrative or so much as considerably probable, to evince the existence of the nature we examine.
But possibly the definition of a philosopher may exempt us from the perplexities to which the ambiguous expressions of common writers expose us. I therefore thought fit to consider, with a somewhat more than ordinary attention, the famous definition of nature that is left us by Aristotle, which I shall recite rather in Latin than in English – not only because it is very familiarly known among scholars in that language, but because there is somewhat in it that (I confess) seems difficult to me to be without circumlocution rendered intelligibly in English: Natura, says he, est principium et causa motus et quietis ejus, in quo inest, primo per se, et non secundum accidens, [Nature is the principle and cause of movement and rest in the thing to which it belongs primarily, in virtue of itself, and not contingently.] But though, when I considered that according to Aristotle the whole world is but a system of the works of nature, I thought it might well be expected that the definition of a thing, the most important in natural philosophy, should be clearly and accurately delivered.
Yet to me, this celebrated definition seemed so dark, that I cannot brag of any assistance I received from it towards the framing of a clear and satisfactory notion of nature. For I dare not hope, that what as to me is not itself intelligible should make me understand what is to be declared or explicated by it.
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