ResearchMotor laterality in 4 breeds of dog
Introduction
It was originally thought that lateralization (handedness) was a quality possessed only by human beings, but this has been discounted many times. Indeed, Rogers (2002) emphasized that there is a basic pattern of lateralization common to all vertebrates, including human beings (Meador et al., 2004, Upadhyay et al., 2004), nonhuman primates (Cameron and Rogers, 1999, Westergaard et al., 2001a, Westergaard et al., 2001b, Westergaard et al., 2003), Equidae (McGreevy et al., 2007), dogs (Wells, 2003, Quaranta et al., 2004, Branson and Rogers, 2006), cats, whales, and rodents, as well as birds and amphibians, (Rogers, 2002), and fish and reptiles (Bisazza et al., 1998). The wide range of lateralized animals identified suggests that modern species may have inherited brain lateralization from a common ancestor.
Associations between brain lateralization and behavioral phenotypes have been widely reported. For example, Cameron and Rogers (1999) reported evidence in common marmosets for behavioral differences that were linked with hand preference and hemisphere lateralization. Right-handed (left-hemisphere-dominant) marmosets entered a novel room faster and touched more of the novel objects than did their left-handed (right-hemisphere-dominant) counterparts. These workers concluded that left-handedness was associated with fearfulness whereas right-handedness was associated with exploration and approach.
Meanwhile, a lack of significant bias may compromise biological fitness. Nonlateralized rats and human beings have difficulty resolving spatial problems, particularly those involving left or right discriminations (Bradshaw, 1991), suggesting that lateralization is important for problem solving. Furthermore, it has been shown that dogs without a significant paw preference were significantly more reactive to certain sounds (i.e., an audio recording of the sounds of thunderstorm and fireworks) than dogs with either a left-paw or right-paw preference (Branson and Rogers, 2006).
Breeds of diverse morphology tend to differ behaviorally according to the purpose for which they were bred (Goodwin et al., 1997), which means that behavioral differences may arise from developing breeds of dog for differing purposes (e.g., from fighting and guarding to companionship) (Bradshaw et al., 1996). For example, the long nose of the dolichocephalic dog is a universal characteristic of sight hounds that track prey with their eyesight rather than, for example, olfaction. In contrast, the short compact muzzle of the brachycephalic types is believed to reflect jaw strength in breeds selected to fight and bite and also represents neoteny in the toy breeds (McGreevy, 2009). Traditionally, dog breeds have been developed to meet both morphological requirements (kennel club specifications and consumer demand) and functional needs. Although popular opinion often supports the position that morphology or phenotype (dog breed) is associated with certain behavioral traits, little scientific research has examined this association since Scott and Fuller's work (1974). Given that there is such a paucity of scientific data on breed-specific behavior, the aim of this study was to explore possible breed differences in a basic behavioral phenotype (motor laterality) in dogs.
Ofri et al. (1994) and McGreevy et al. (2004) suggest that different dog breeds have retinal differences that may lead to their having different visual perspectives. This is supported by recent evidence that skull shape affects a dog's attention to human visual signaling (Gácsi, et al., 2009). On the basis of the predication of these reported differences related to morphology and recent reports of differing strengths of laterality in breeds of horses (McGreevy and Thomson, 2006), we hypothesized that motor laterality would differ in morphologically disparate dog breeds. The reported effect of pedomorphic characteristics, including brachycephaly, on the visual signals of dogs (Goodwin et al., 1997) and the reactivity of dolichocephalic breeds (Bradshaw et al., 1996) suggested that comparing 4 breeds clustered at either end of the skull-length spectrum (whippets and greyhounds vs. pugs and boxers) would be worthwhile. By sampling 2 large breeds (greyhounds and boxers) with 2 smaller breeds (whippets and pugs), we were also able to collect data on 2 breeds for both categories of skull shape. This allowed us to broaden the extent to which we could generalize any finding related to skull shape.
This project was also designed to explore the effect of age on motor laterality. So far, no significant age effects on laterality have been identified in the domestic dog (Tomkins et al., 2010). However, in a pilot study of 5 dogs, several measures of motor laterality (direction of paw preference, strength of paw preference, and the concurrent use of both paws) appear to be relatively stable between 2 and 10 months of age (Branson, 2006). However, studies in other mammals demonstrate age differences in lateralization (reindeer, Espmark, 1977; lemurs, Ward et al., 1990; vervet monkeys, Harrison and Byrne, 2000). Extant evidence suggests that on certain motor laterality tasks, male dogs are more likely to be left-pawed than female dogs, and female dogs are more likely to be right-pawed than male dogs (Wells, 2003, Quaranta et al., 2004). The current laterality study used the largest sample size of dogs so far reported (the next largest study used 80 dogs; Quaranta et al., 2004) and used a balance of male and female subjects to explore any association between sex and paw preference.
Section snippets
Subjects
With the approval of both the University of Sydney Animal Ethics Committee and the University of Sydney Human Ethics Committee, breeders of whippets, greyhounds, pugs, and boxers were asked to participate in the study. Dogs aged <16 weeks, those that were desexed, and those that were not able to bear their weight on all 4 limbs were not included in the study population. This selection protocol provided a study population of 183 dogs (aged between 4.25 and 181.5 months; mean 44.77 ± SD 39.35
Results
The number of paw-use scores required to calculate a dog's paw preference is determined by the desired level of accuracy. If we require the sampling error (ɛ) to be no larger than some bound B, this can be calculated using the equation:therefore:
if n = 100, ɛ ≤ 0.1 or 10%
if n = 499, ɛ ≤ 0.05 or 5%.
The 100 repetitions used in this study to obtain the proportion of L and R paw uses gives an accuracy of ±10%. If, for example, we had used 400 repetitions per dog, the accuracy would have
Discussion
Age had no significant effect on any of the lateralization variables tested in the current population of dogs. This is similar to reports from marmosets, sifakas, tamarins, macaques, and chimpanzees (Hook and Rogers, 2000), although age effects have been reported for reindeer (Espmark, 1977), horses (McGreevy and Rogers, 2005), vervet monkeys (Harrison and Byrne, 2000), and lemurs (Ward et al., 1990).
The LI was normally distributed across the study population, with no overall population bias
Conclusions
The absence of breed differences in motor laterality is of interest because domestic dog breeds were historically bred to different phenotypical and behavioral standards. The absence of breed differences in the LI for paw use suggests that the food-retrieval from a rubber cylinder (such as a Kong) can be used as a reliable and accurate measure of motor laterality across different breeds of domestic dogs. Furthermore, the reliability of this measure is strengthened by our finding that LI did not
Acknowledgments
The authors thank Prof. Lesley Rogers for her comments on the need for and design of studies of this sort and to 2 anonymous referees whose comments on an earlier version of this article were greatly valued.
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