The tail of dogs and allies (Canidae) is important for intraspecific communication. We used a life-sized dog model and varied the tail length and motion as an experimental method of examining effects of tail-docking on intraspecific signaling in domestic dogs, Canis familiaris. We videotaped interactions of 492 off-leash dogs and quantified size and behaviour of approaching dogs to the model's four tail conditions (short/still, short/wagging, long/still, long/wagging). Larger dogs were less cautious and more likely to approach a long/wagging tail rather than a long/still tail, but did not differ in their approach to a short/still and a short/wagging tail. Using discriminant analyses of behavioural variables, dogs responded with an elevated head and tail to a long/wagging tail model relative to the long/still tail model, but did not show any differences in response to tail motion when the model's tail was short. Our study provides evidence that a longer tail is more effective at conveying different intraspecific cues, such as those provided by tail motion, than a shorter tail and demonstrates the usefulness of robotic models when investigating complex behavioural interactions.
Fluctuating asymmetry (FA) has been used as a measure of developmental stability across many taxa, with asymmetric individuals presumed to have reduced fitness. FA has also been suggested for use in conservation biology as a measure of the health of populations. Here we assess the suitability of these uses of FA by using a novel measure of asymmetry in the bony lateral plates of threespine stickleback (Gasterosteus aculeatus) from 60 insular and endemic freshwater populations from the Queen Charlotte Islands. The frequency of asymmetric G. aculeatus individuals among populations varied from 1% to 76% with a mean of 42%. Extreme variation in the frequency of asymmetries among lateral plate positions within samples was also observed. Plates important to the structural integrity of predator defences were least asymmetric, either due to selection against asymmetry at these positions or to variation in the temporal development of the plates. These results emphasize the need for caution when interpreting differential levels of FA among traits in individuals and populations, as the differences may be due to variation in the strength or direction of selection for symmetry, and not exclusively to differences in fitness.
The completely plated morph in the threespine stickleback (Gasterosteus aculeatus) is considered to be the ancestral plate condition and is the predominant morph inhabiting marine waters and numerous northern freshwaters. Evolutionary aspects of this distribution have been widely addressed yet functional mechanisms remain obscure. Experiments described here using the common piscivore (Oncorhynchus clarki) show that the posterior plates of G. aculeatus interfere with the swallowing abilities of the piscivore, possibly by disrupting pharyngeal jaw retraction, and this leads to increased escape opportunities of the stickleback. The advantage of the completely plated condition is most expressed at higher ratios of prey diameter to predator mouth diameter and appears to have a defensive effect comparable to that of dorsal and pelvic spines. This attribute, combined with the physical protection that plates offer against puncturing, would be particularly beneficial where there is high probability of capture by toothed predators. Such a selection regime appears to characterize the predominantly limnetic and pelagic habitats where marine stickleback are found and may account for the wide geographical distribution of the completely plated morph and its persistence from the Miocene.