cline

Noun

cline (plural clines)

1. (systematics, evolution, biogeography) A gradation in a character or phenotype within a species, deme, or other systematic group.
   • 2000 Michael J. O'Brien and R. Lee Lyman: Applying Evolutionary Archaeology →ISBN

     [A cline is a] character gradient, wherein a character such as length increases or decreases gradually and continuously. A cline distributed over geographic space is a "chorocline"; a cline distributed over time is a "chronocline." Compare with chorospecies and chronospecies. . .
     Simpson termed the change through time a "chronocline", where a cline represents a character gradient. A chunk of a chronocline comprises a chronospecies. The difficulty with identifying a chronospecies resides, then, in first identifying a chronocline, or temporal gradient in a character or attribute. As pointed out by Kevin Padian, some characters "change more or less uniformly through time, but others change not at all, and still others vacillate with no clear trend. This is ... one reason to be suspicious of the evolutionary utility of clines: no criterion for identifying a cline seems to be in force. A cline is simply a gradient in character state along a continuum, and it may be broken, temporarily reversed, or stepped. Furthermore, there is no criterion for a cline's magnitude and no control on its probability."

   • 2002 The Future of Evolution. Proceedings of the National Academy of Sciences

     Recent studies have shown that invaders can rapidly adapt to the new environments in which they find themselves. Huey et al. demonstrated how an introduction of a new fruit fly into the west coast of North America resulted in the evolution, in only 20 years, of an apparently adaptive cline related to wing size, throughout the vast new latitudinal range extending from southern California to British Columbia. The cline that developed in North American female flies was similar to that found in the European native populations. Interestingly, the developmental basis for the cline of wing size was different in Europe than for the invader in North America, although the functional result was the same, providing additional evidence for the adaptive advantage of this set of traits.

   • 2012 Donald W. Linzey. Vertebrate biology →ISBN

     Subspecies of the song sparrow form a cline in body size, plumage coloration, and song characteristics. There is a dramatic difference in appearance between the small, pale Melospiza melodia saltonis subspecies of the southwestern desert region and the large, dark Aleutian subspecies, M. m. maxima. It seems unlikely that the desert-dwelling subspecies saltonis would easily breed with the large Alaskan subspecies maxima, even if the ranges of the two subspecies were to overlap in the future. If some catastrophe completely eliminated the central west coast populations of the song sparrow, the northern and southern ends of the cline would likely become two distinct species of sparrow.
     Equus quagga is an extinct southern African mammal that resembled a zebra. . . Some observers considered it to be most closely related to the horse based on analyses of mainly cranial characters. Others thought it was a distinct species of zebra . . . Still others felt it was merely the southern end of a cline and a subspecies of the plains zebra. Both DNA and protein analyses of samples from quagga skin confirmed that it was, indeed, related to the plains zebra.
     The deme is the ultimate systematic unit of species in nature. In some cases, a deme may correspond to a subspecies, but it is almost always a decidedly smaller group. Demes do not enter into classification, because they do not have long-continuing evolutionary roles and because adjacent demes often have no observable differentiation.
     Demes often differ from one another in a geographic series of gradual changes. A gradual geographic shift in any one genetically controlled trait is known as a character cline. A series of samples from along a cline reveals a gradual shift in a particular character like body size, tail length, number of scales, or even intensity of coloration. Because such situations add to the difficulty of deciding the true phylogenetic relationships of populations, the experience and judgment of the systematist play an important role.

2. Any graduated continuum.
   • "2004 Language typology: a functional perspective →ISBN

     The cline of instantiation is a dimension that organizes systems of all kinds — physical systems like that of meteorology, biological systems, social systems and semiotic systems. In the realm of semiotic systems, text lies at the instance end of the cline. Text is "semiotic weather"; but what about the "semiotic climate", weather patterns and subclimates? There are in fact clear semiotic analogies. The "semiotic climate" is the overall linguistic system; it is the meaning potential of a language. Thus a text instantiates the linguistic system; and the linguistic system "potentializes" innumerable texts.

   • 2005, Ronnie Cann, Ruth Kempson, Lutz Marten, The Dynamics of Language, an Introduction, page 412:

     This account effectively reconstructs the well-known grammaticalisation cline from anaphora to agreement, …

References

Noun

cline (plural clines)

1. (geometry, inversive geometry) A generalized circle.
   • 2001, Michael Henle, Modern Geometries: Non-Euclidean, Projective, and Discrete‎, page 77:

     Let C₁ and C₂ be two nonintersecting clines. Prove that there is a unique pair of points that are simultaneously symmetric to both C₁ and C₂.

   • 2009, Michael P. Hitchman, Geometry with an Introduction to Cosmic Topology‎, page 64:

     To visualize Möbius transformations, it is helpful to focus on fixed points and, in the case of two fixed points, on two families of clines with respect to these points.

   • 2011, Dominique Michelucci, What is a Line?, Pascal Schreck, Julien Narboux, Jürgen Richter-Gebert (editors), Automated Deduction in Geometry, 8th International Workshop, ADG 2010, Revised Selected Papers, LNAI 6877, page 139,

     Let Ω be a fixed, arbitrary, point. Then circles (in the classical sense) through Ω can be considered as lines. For convenience, such circles are called clines in this section. Two distinct clines cut in one point (ignoring Ω and the two cyclic points); it can happen that Ω is a double intersection point; in this case, one may say that the two clines are parallel, and that they meet at a point at infinity, which is Ω.