B. P. Springett

Comparison of tooth morphology and wear patterns in four species of wallabies

Tooth morphology of two browsing macropods (brush-tailed rock-wallabies and swamp wallabies), one grazing species (tammar wallaby) and one mixed feeder (parma wallaby) are compared. The dental action of a single tammar wallaby was studied by cinefluoroscopy. Cinefluoroscopy showed independent rotation of each hemi-jaw on occlusion in the tammar, and the disposition of molar striae suggest a similar pattern of jaw movement in all four species. There was a close relationship between incisor and molar action in both grazing and browsing species. Initial occlusion of the anterior facets of the incisors brought about a grasping action in browsing species and a fine cutting action in grazing species. In both grazing and browsing species these incisor actions were coincident with a cutting action by the transverse lophs during molar occlusion. Subsequent independent rotation of each hemi-jaw results in fine cutting by the lateral facets of the incisors, in both grazers and browsers, at the same time as the molar arrays perform a crushing action in browsers and a secondary cutting action in grazing species. Thus the teeth of the four species showed a number of similarities (independent rotation of each hemi-jaw) along with some differences (incisor and molar actions) that appear to represent adaptations for efficient aquisition and oral processing of browse or graze.

Observations on fresh forage intake, ingesta particle size and nutrient digestibility in four species of macropod

The particle-size distributions of the ingesta of the sacciform forestomach in free-ranging animals of a grazing macropod species [Macropus eugenii (tammar wallaby)], a grazer/browser [Macropus parma (parma wallaby)], a browser/grazer [Petrogale penicillata (brush-tailed rock-wallaby)] and a browser [Wallabia bicolor (swamp wallaby)] from Kawau Island, New Zealand, were compared with those of captive animals maintained on a standing ryegrass (Lolium perenne) sward. Nutrient digestibility was also measured in tammar and parma wallabies fed ryegrass or browse, i.e. fresh mahoe (Melicytus ramiflora) and this was related to particle-size distributions of the ingesta. There were significant differences in the particle size distributions of digesta from tammar and parma wallabies in the wild but not in captivity. In free-ranging animals the ingesta from both browsing species, the brush-tailed rock-wallaby and the parma wallaby, contained consistently greater proportions of coarse particles and smaller proportions of fine particles than did those of the tammar wallaby. These differences may be correlated with reported differences in their tooth morphologies. However, the presence of significant differences in particle-size distributions of the digesta between brush-tailed rock-wallabies and parma wallabies when constrained to grass, despite reported similarities in their tooth morphology, suggests that factors other than tooth morphology contribute to differences in the oral processing of food by browsing and grazing macropods. There were greater proportions of grass fragments in the coarse than in the finer fractions of ingesta from free-ranging brush-tailed rock-wallabies, indicating that this species is less effective at chewing grass. There were no overall differences between tammar and parma wallabies in the digestibilities of organic matter, neutral-detergent fibre (NDF) or acid-detergent fibre (ADF) but the NDF and ADF digestibilites of both species increased significantly with increase in the proportion of fine ingesta particles and with increase in mass of fermentative digesta. These findings indicate the importance of oral processing to digestive efficiency in macropods and the relationship between oral processing and tooth morphology.

The histology and morphometrics of the major salivary glands of four species of wallabies (Marsupialia: Macropodiae) from Kawau Island, New Zealand

Allometric analyses of the three major salivary glands of 44 tammar wallabies Macropus eugenii and 58 parma wallabies Macropus parma from Kawau Island, New Zealand, indicate that tammar wallabies have larger parotid glands while parma wallabies have larger mandibular glands. The difference can be related to the importance of cooling in tammars, an arid-zone species, and the need for greater buffering of forestomach digesta in parma wallabies because of their greater daily food intakes and a higher browse component in their natural diet. Comparisons of sublingual gland size of these two species viewed in terms of their capacity for mucus production suggest that this may be influenced by the need to protect mucosa from mechanical and chemical injury from browse. Sample sizes of brush-tailed rock-wallabies Petrogale pencilliata and swamp wallabies Wallabia bicolor were too small for similar statistical comparisons, but they confirmed that salivary gland histology was broadly similar among all four species.

Comparisons of indices of molar progression and dental function of brush-tailed rock-wallabies (Petrogale penicillata) with tammar (Macropus eugenii) and parma (Macropus parma) wallabies

We measured parameters of molar progression and dental function in the brush-tailed rock-wallaby (Petrogale pencilliata) (a browser/grazer) and compared them with data from the tammar wallaby (Macropus eugenii) (a grazer) and the parma wallaby (Macropus parma) (a grazer/browser). Although the mean value of the molar index (MI) was higher in rock-wallabies than in parma and tammar wallabies the mean rate of increase of log(MI) with log(body mass) was similar in the three species. Reported differences between these species in their rates of molar progression with age may therefore result from differences in their rates of bodily growth. The findings indicate that molar progression in the rock-wallaby is governed by the growth of the bones of the viscerocranium (mesial shift), rather than by diet-induced movement of the teeth within the bones of the viscerocranium (mesial drift), and was not influenced by the persistence of P4 premolars. It is therefore unlikely that differences in the rate of molar progression are directly linked to differences in diet. The relationship between functional dental parameters and body mass differed between brush-tailed rock-wallabies and tammar wallabies, species of differing dietary habit, but did not differ between brush-tailed rock-wallabies and parma wallabies, species of more similar dietary habit. Thus the total length of upper transverse lophine ridges and the interlophine distances of the M1 to M3 upper molars of brush-tailed rock-wallabies were not different from those of parma wallabies but were significantly greater than those of tammar wallabies. These differences can be interpreted in terms of greater emphasis on crushing/grinding of browse in the rock-wallabies and parma wallabies.

Differences in renal and alimentary water conservation account for differences in the distribution of tammar and parma wallabies on Kawau Island, New Zealand

Surveys of two wallaby species on Kawau Island, New Zealand, indicated that their distribution was stable so as to permit niche partitioning. Multivariate analysis of environmental factors associated with the relative distribution of tammar and parma wallabies suggested that their distribution may be influenced by the availability of fresh water. Tammar wallabies have greater renal size, mass and relative medullary area than parma wallabies and thus may have greater renal water-conserving capabilities. The tammar colon is significantly longer than that of the parma wallaby and the water content of distal digesta is lower in tammar than in parma wallabies, indicating that the former species may also have greater colonic water-resorption capabilities. A laboratory comparison of the water consumption of tammar and parma wallabies showed that the former drink significantly less than the latter. The superior ability of tammar wallabies to colonise drier areas may have contributed to their survival in the presence of the closely related parma wallaby.

The temporal organisation of the feeding behaviour of four species of wallaby: examining chronobiological and homeostatic influences

We studied the temporal distribution of feeding events of tammar wallabies, parma wallabies, brush-tailed rock-wallabies and swamp wallabies by infrared video-recording of captive animals maintained in a 12 : 12 light : dark cycle with constant temperature, and by radio-microphone surveillance of free-ranging animals on Kawau Island, New Zealand. Analyses of mean time spent feeding per 20-min period for tammar and parma wallabies showed significant circadian variation in both captive and free-ranging animals but not in captive or free-ranging brush-tailed rock wallabies or swamp wallabies. While there was no significant difference in the extent of circadian variation of feeding rate between tammar and parma wallabies there were significant differences according to the type of food being fed. Thus, circadian variation in feeding rate was greater in both species when standing sward was fed. None of the survivorship curves of the interfeed intervals of either captive or free-ranging animals showed a discontinuity suggestive of organisation of feed events into meals. There were bicrepuscular peaks of feed-event density in both captive and free-ranging tammar and parma wallabies. There was a similar bicrepuscular distribution of feed-event density in free-ranging brush-tailed rock-wallabies but a more uniform temporal distribution of this parameter in captive specimens. There was a more uniform circadian distribution of feed-event density in a single captive and a single free-ranging swamp wallaby. Thus the circadian incidence of the feeding events of tammar and parma wallabies were more resistant to changes in the incidence of stochastic environmental variables such as predation whereas those of bush-tailed rock-wallabies and swamp wallabies were more susceptible to changes in these stimuli.

Foraging behaviour in tammar (Macropus eugenii) and parma (Macropus parma) wallabies

Captive parma and tammar wallabies, when offered ryegrass sward in plots, visited ungrazed plots more frequently and spent longer grazing on them than on plots that were previously grazed but not visibly depleted. There was no significant difference between the two species with respect to the pattern of time spent grazing between plots, but parma wallabies tended to visit ungrazed plots more frequently than tammar wallabies. When offered carrot pieces of different dimensions both species preferred carrot pieces of greater mass, regardless of shape. Both species favoured eating in the upright (bipedal) position despite the fact that the use of this position prolonged search time between bites. Although the two species are able to forage optimally when grazing, the greater efficiency of the bipedal posture in predator avoidance may result in the selection of larger food items whenever possible.