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Selection and Genetics of Behaviour of Horses Introduction At a time when humans are closer than ever to a precise knowledge of genes and approach an old dream of controlling nature via genetics, it is a paradox that we now see how far we are from understanding how genes code for characters, especially complex characters like behaviour. Much work is needed to fill the gap between molecular biology and organismic approaches to the study of behaviour. This may well lead us to entirely revise our theoretical views on the relationship between the gene, behaviour and selection. Already, there is evidence of scientific review of some ideas beginning to emerge as a result of the use of molecular genetics. For example, Vilà et al (2001) using mitochondrial DNA sequence analyses of domestic horses and equids from archaeological sites have suggested an alternative view of domestication. This work suggests that the diversity of modern horses can preferably be explained by an origin relating to the widespread capturing, taming or rearing of wild caught animals rather than the early selection of a few individuals on the basis of behavioural characteristics such as a lack of fearfulness (Grandin and Deesing, 1998). Increased knowledge in genomics also brings new difficulties: whereas a few decades ago, the difficulty was in identifying genes possibly involved in behaviour, nowadays we are confronted by the difficulty that a large number of genes are involved in even the basic elements of a behavioural sequence (Roubertoux et al, 1998). Perhaps more surprising still, is the finding that different behaviours appear to share the same physiological processes. Unexpected correlations can be found: weight gain, standing and opening of eyelids share the same chromosomal area in mice (LeRoy et al, 1999). A new view on the taxonomy of behaviours has to be expected or may be the new challenge for the near future. This is especially important where selection is involved and the classic study of Belyaev (1979) on silver foxes shows how complex the problem is: a selection made on the basis of tameness gives very familiar foxes in a few generations, but these tame animals are black and white with poor fur. However, at present we have to rely mostly on comparisons, between breeds, strains, bloodlines, calculations of heritabilities and variance on single characters in order to have some idea of the genetic bases of behaviour. We have to admit that these are gross approximations but our sole tools at the present time. Whereas data can be quite precise on traits like morphometric features (Zechner et al, 2001) or performance, estimating behavioural aspects has remained rather intuitive until lately in species like the horse (Langlois, 1984). Aspects of Selection in Horses Selection of particular traits for a better use of horses is an old dream of all equestrian cultures, even Xenophon gave advice about traits that should be considered in the choice of a horse. Morphological traits have been selected for with success in modern breeding when direct parameters (performances) were being selected (Langlois, 1984). Indeed, carriage horses do not look like race horses. Differences between studs in morphometric characteristics could even be found in Lipizzan horses (Zechner et al, 2001). Favourable behavioural traits are mentioned in most cases, but have not been selected for, especially because temperament was evaluated on an intuitive basis (Langlois, 1984). Behaviour as a Possible Basis for Selection? Individual variations in behaviour are a prerequisite for a selection on a genetic basis and many studies, especially in recent years, have concentrated on evaluating interindividual differences. A variety of methods have been used: observations in natural situations (Verbeek et al, 1994), questionnaires to observers (Stevenson-Hinde et al, 1980a; Gosling, 1998), physiological measurements, or experimental tests (see Hall, 1941). All have proven the existence of individual differences in the behaviour of animals. Unusual situations however seem to be more appropriate in order to reveal more "fundamental" (? genetically-based) characteristics (Gerlai and Csanyi, 1990). Hall (1941) defined the "temperament" of animals as the raw material of individuals, independent of environment and culture. For this author when environment and culture are referred to, it becomes personality ("behavioural style" for Feaver et al, 1986 or Lyons, 1989). Similarly Bates (1989) refer to temperament as an ensemble of individual biological differences in behavioural tendencies that appear early in life and remain relatively stable across time and situations. These criteria are rarely met in the species studied up to now, perhaps because of the problems associated with their definition. In many cases, temperament, fear, emotivity are used interchangeably as unitary concepts (see Boissy, 1998) whereas several studies (e.g. Budaev, 1997) found different responses to different types of anxiogenous situations (e.g. predator avoidance, open field test etc.). Some consistency of fear reactions was found in the fear reactions of wolves (Mc Donald, 1983), cattle (Kerr and Wood-Gush, 1987) whereas none was found for aggressiveness in fish (Francis, 1990) and differences in consistency over time was found according to the type of emotivity considered in rhesus macaques (Stevenson-Hinde et al, 1980b). Consistency across situations is even more difficult to assess as one can not be sure it measures the same behavioural trait. The search for early predictors has been a challenge and few studies give real evidence for this. One difficulty lies in the finding that young animals and adults may express the same levels of emotivity in different ways. Nonetheless, genetic effects on behaviour do appear through comparisons of sires (e.g. cats: McCune, 1995), strains (e.g. fowls: Jones, 1977), breeds (e.g. Goddard and Beilharz, 1985) or the divergent selection of emotive or social strains (quails: Mills et al, 1994; foxes: Belyaev and Trut, 1975; mink: Hansen, 1996). Genetics of Behaviour in the Horse In a recent review, Houpt and Kusunose (2001) mentioned that "equine behavioural genetics is still in its infancy." As a paradox, whereas behaviour is of the highest importance for its use, the behaviour of the domestic horse and especially the genetical aspects have been much less studied than in many other domestic animals. However several studies have been published in the last ten years and give us hints about the impact of both genetic and environmental factors. As a prerequisite for genetic influence, individual differences in the behaviour of horses have been shown in a variety of studies using experimental tests (McCann et al, 1988a; Wolff and Hausberger, 1992; Mackenzie and Thiboutot, 1997) or behavioural observations (McCann et al, 1988b; Wolff and Hausberger, 1994), some concentrating on learning abilities (McCall et al, 1981; McCall, 1989; Fiske and Potter, 1979; Hausberger et al, 1996). Consistency across situations of these differences have been little investigated but LeScolan et al (1997) found correlations between evaluations of behavioural traits by riding school teachers and results in experimental tests. Consistency over time is more difficult to assess. Visser et al (1991) repeated the same experimental tests at different ages and found consistency in the ranking of the animals. Hausberger et al (submitted) found behavioural profiles in young foals that are predictive of later adult reactions in tests. This raises the whole question of the relative weight of genetic and environmental factors. Both Wolff et al (1997) and Visser et al (2001) found individual differences in young horses of same sex, age, breed and raised in homogeneous conditions, which suggests that even with little environmental variation, individual variations do occur. In these same horses, Wolff et al (1997) and Wolff and Hausberger (1996) found paternal effects, a finding confirmed by Lankin and Bouissou (1998). Paternal effects have been found even in the behaviour of young foals with their dam (Wolff and Hausberger, 1994). Kusunose (cited in Houpt and Kusunose, 2001) found strong sire effects on the behaviour of thoroughbreds dispersed in two horse racing. Breed differences have been mentioned in different studies: learning abilities (Mader and Price, 1980), emotional reactions (Budzynski et al, 1992; Hausberger et al, 1996), stereotypies (Gautier et al, in prep) and maternal behaviour (Crowell Davis et al, 1985). In a large series of studies based on experimental tests and multivariate statistical analyses performed on more than 700 horses, Hausberger et al (submitted) looked at the interplay of genetic (breed, sire, sex) factors and environmental (housing, type of work, site, etc) factors. Some behavioural traits seemed to be more influenced by genetic factors (fear reactions) whereas others were more related to environmental factors like the type of work (gregariousness, learning). No clear interaction gene-environment was found but additive effects clearly appeared in a study comparing breeding stallions housed in different studs. References Bates JE (1989) Concepts and measures of temperament. 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