Evolution of Skull and Mandible Shape in Cats (Carnivora: Felidae)

The felid family consists of two major subgroups, the sabretoothed and the feline cats, to which all extant species belong, and are the most anatomically derived of all carnivores for predation on large prey with a precision killing bite. There has been much controversy and uncertainty about why the skulls and mandibles of sabretoothed and feline cats evolved to become so anatomically divergent, but previous models have focused on single characters and no unifying hypothesis of evolutionary shape changes has been formulated. Here I show that the shape of the skull and mandible in derived sabrecats occupy entirely different positions within overall morphospace from feline cats, and that the evolution of skull and mandible shape has followed very different paths in the two subgroups. When normalised for body-size differences, evolution of bite forces differ markedly in the two groups, and are much lower in derived sabrecats, and they show a significant relationship with size and cranial shape, whereas no such relationship is present in feline cats. Evolution of skull and mandible shape in modern cats has been governed by the need for uniform powerful biting irrespective of body size, whereas in sabrecats, shape evolution was governed by selective pressures for efficient predation with hypertrophied upper canines at high gape angles, and bite forces were secondary and became progressively weaker during sabrecat evolution. The current study emphasises combinations of new techniques for morphological shape analysis and biomechanical studies to formulate evolutionary hypotheses for difficult groups

Consistency of Leadership in Shoals of Mosquitofish (Gambusia holbrooki) in Novel and in Familiar Environments

In social animal groups, an individual's spatial position is a major determinant of both predation risk and foraging rewards. Additionally, the occupation of positions in the front of moving groups is generally assumed to correlate with the initiation of group movements. However, whether some individuals are predisposed to consistently occupy certain positions and, in some instances, to consistently lead groups over time is as yet unresolved in many species. Using the mosquitofish (Gambusia holbrooki), we examined the consistency of individuals' spatial positions within a moving group over successive trials. We found that certain individuals consistently occupied front positions in moving groups and also that it was typically these individuals that initiated group decisions. The number of individuals involved in leading the group varied according to the amount of information held by group members, with a greater number of changes in leadership in a novel compared to a relatively familiar environment. Finally, our results show that the occupation of lead positions in moving groups was not explained by characteristics such as dominance, size or sex, suggesting that certain individuals are predisposed to leadership roles. This suggests that being a leader or a follower may to some extent be an intrinsic property of the individual

Cheetah mothers' vigilance: looking out for prey or for predators?

Free-living cheetah ( Acinonyx jubatus ) cubs are killed by a number of predators, thus vigilance in cheetah mothers may be a form of anti-predator behaviour as well as a means of locating prey. Mothers' vigilance during the day was closely associated with measures of hunting but not with measures of anti-predator behaviour. In contrast, mothers' vigilance at kills was not related to hunting but was related to anti-predator behaviour. Both forms of vigilance decreased as cubs grew older. Vigilance during the day increased with litter size which supports a model of ‘shared’ parental investment (Lazarus and Inglis 1986) because after prey had been located and caught by mothers, cubs shared the prey between them. Vigilance at kills did not increase with litter size when cubs were young; in these situations predators stole cheetahs' prey and rarely chased cubs so, at most, only a single cub would be taken. Mothers' anti-predator behaviour away from kills did increase with litter size at young cub ages however; more cubs are killed in these circumstances the greater is the size of the litter. When cubs were older and could outrun predators, neither vigilance at kills nor anti-predator behaviour increased with litter size. These results strongly support two models of ‘unshared’ investment (Lazarus and Inglis 1986) and demonstrate, not only that superficially similar behaviour has different functions in different contexts, but that parental investment is shaped by the type of benefits accrued from it.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/46879/1/265_2004_Article_BF00300681.pd

Investigating determinants of yawning in the domestic (Equus caballus) and Przewalski (Equus ferus przewalskii) horses

International audienceYawning is rare in herbivores which therefore may be an interesting group to disentangle the potential function(s) of yawning behaviour. Horses provide the opportunity to compare not only animals living in different conditions but also wild versus domestic species. Here, we tested three hypotheses by observing both domestic and Przewalski horses living in semi-natural conditions: (i) that domestic horses may show an elevated rate of yawning as a result of the domestication process (or as a result of life conditions), (ii) that individuals experiencing a higher level of social stress would yawn more than individuals with lower social stress and (iii) that males would yawn more often than females. The study involved 19 Przewalski horses (PHs) and 16 domestic horses (DHs) of different breeds living in large outdoor enclosures. The results showed that there was no difference between the PH and DH in yawning frequency (YF). PHs exhibited much higher levels of social interactions than DHs. There was a positive correlation between yawning frequency and aggressive behaviours in PHs, especially males, supporting the idea that yawning may be associated with more excitatory/stressful social situations. A correlation was found between yawning frequency and affiliative behaviours in DHs, which supports the potential relationship between yawning and social context. Finally, the entire males, but not castrated males, showed much higher levels of yawning than females in both species. The intensity (rather than the valence) of the interaction may be important in triggering yawning, which could therefore be a displacement activity that helps reduce tension

Ein neues Verfahren der Sch\ue4deluntersuchung zur Anwendung in der S\ue4ugetiersystematik

Volume: 43Start Page: 215End Page: 22