The paradoxical effects of nutrient ratios and supply rates on an outbreaking insect herbivore, the Australian plague locust.

1. The Australian plague locust, Chortoicetes terminifera, develops following rainfall in an environment dominated by two host plants, the annual Dactyloctenium radulans and the perennial Astrebla lappacea. This simple system provides an ideal opportunity to explore the relationship between plant quality, individual herbivore performance and population responses. 2. We compared the two grasses chemically and structurally, and the behavioural, physiological and developmental responses of locust nymphs to these diets. 3. The grasses appeared to be of similar nutritional quality in terms of their chemical composition, although they differed in their physical properties. Early instar nymphs performed equally well on both grasses. However, older nymphs consuming D. radulans developed faster, survived better and attained a higher body weight compared with those consuming A. lappacea. 4. The differences in performance by the older nymphs related to the rate and ratio of supply of carbohydrate and protein from the two grasses, with less carbohydrate being assimilated from A. lappacea than D. radulans per unit of protein assimilated. Experiments showed that these differences arose as a direct result of the physical barrier to nutrient extraction provided by cell walls and indirectly through the amount of water contained within each cell. Paradoxically, nitrogen did not limit performance in the traditional sense through shortage,but rather its relative excess in A. lappacea appeared to impede intake and assimilation of adequate carbohydrate. 5. As a consequence, we predict that the length of time D. radulans remains available following rainfall will influence plaguing dynamics, although not for the reasons previously thought. 6. The results highlight the need to consider nutrient balance and actual rates of supply (rather than simply measuring the chemical composition of the plant) when attempting to understand herbivore nutritional ecology.

Confocal imaging, visualization and 3-D surface measurement of small mammalian teeth.

The difficulties traditionally faced by functional morphologists in representing and interpreting three-dimensional objects can now be mostly overcome using available laser and computer imaging technologies. A practical method for three-dimensional imaging of small mammalian teeth using confocal microscopy is reported. Moulding and casting of the teeth were first performed, followed by confocal fluorescence imaging. Accuracy and precision of the scanned structures were tested in morphometric studies by using a new technique to measure the noise in the scan of a three-dimensional surface, and linear and angular dimensions of the scans were compared with measurements made using traditional morphological tools. It is shown that measurements can be taken with less than 4% difference from the original object. Teeth of the microchiropteran bat Chalinolobus gouldii were scanned and measured to show the potential of the techniques. Methods for visualizing the small teeth in three-dimensional space, and animating the teeth in occlusion, show the power of this approach in aiding a three-dimensional understanding of the structure and function of teeth and other three-dimensional structures.

Thegosis--a critical review.

The evidence for tooth sharpening has been examined and it has been concluded that there is no evidence for a posterior tooth sharpening mechanism which is independent of masticatory function and improves the efficiency of that function. Anterior tooth sharpening may occur in some species as behavioural activity but it is not accepted that this sharpening is directed towards the production of new incisiform weapons as distinct from the improvement of existing caniniform weapons, or more efficient tools for the manipulation of food. Thegosis (from the Greek, thego to whet or sharpen) is a term which could be used to describe the sharpening of anterior teeth under specific often socially context driven situation. Stress is accepted as a cause of non-masticatory tooth to tooth contact as is the suggestion that excessive tooth grinding and clenching is pathological and stress related. Bruxism and pathological thegosis are suggested synonymous terms for this activity.

Salivary proline-rich proteins in mammals: Roles in oral homeostasis and counteracting dietary tannin.

We review information on the structure of proline-rich proteins (PRPs), their various functions related to oral homeostasis and dietary tannin, and the structural basis of these functions. Consideration of the multifunctional nature of these salivary proteins helps explain both the subtle and large variations found in structure and secretion rates both within individuals and between species. We propose that the ancestral function of PRPs is in maintaining oral homeostasis and that counteracting dietary tannins by binding with them is a derived function. PRPs are effective in oral homeostasis at low secretion levels, whereas counteracting tannin depends on high secretion levels. In the dietary habits ranging from carnivores through omnivores to exclusively planteaters, the dietary nitrogen level is progressively reduced, and plant allelochemical intake, including tannins, increases. We suggest that during this evolution from meat-eater to plant-eater, there was some point in omnivory at which selective pressure from nitrogen limitations, arising from a low nitrogen/high tannin diet, became sufficiently great for the evolution of increased secretion level and diversification of PRPs for dealing with tannin. If this hypothesis is correct, carnivorous mammals should secrete low levels of PRPs for oral homeostasis, but should never secrete high levels, unless they are secondarily carnivorous. Omnivores consuming a diet of very little animal tissue but higher levels of tannin-containing foliage or fruit should generally have the capacity to produce high levels of salivary PRPs. Browsers and frugivores should also produce high levels of PRPs, but grazers may have reduced secretion rates depending on the antiquity of the dietary habit. This hypothesis is consistent with the limited information available on the abundance, type, and distribution of PRPs in mammals. Studies are suggested which would test the functional and evolutionary arguments presented.

On the nature of the opaque and translucent enamel regions of some macropodinae (Macropus giganteus, Wallabia bicolor and Peradorcas concinna).

Teeth of three macropod species, M. giganteus, W. bicolor and P. concinna, have been studied using the techniques of light microscopy, scanning- and transmission-electron microscopy and hardness measurement. Light microscope observations showed that the teeth of these species had a translucent enamel region close to the dentine and an outer opaque enamel region at the tooth's surface. These regions were not related to the presence or absence of tubules which are a characteristic feature of marsupial enamel. Hardness tests showed that the opaque enamel was softer than the translucent enamel. Scanning electron microscope observations revealed that there was no correlation between any particular prism packing or orientation and the opaque and translucent enamel regions. Transmission electron microscope observations showed that the translucent enamel region consisted of well defined prisms and well packed, lath-like crystals, whereas the opaque enamel was disrupted by voids (which ranged in size from enlarged micropores to about 2 microns in diameter in extreme cases) between crystals and some randomly oriented, loosely packed crystals. This disruption within the opaque enamel region was more common at prism boundaries but pockets of disrupted enamel were also found within prisms and interprismatic regions. The opacity of the enamel was caused by scattering of light from the voids. The ultrastructure of the opaque enamel region indicated that this region was hypomineralized; hardness tests and polarized light microscope observations were consistent with these results.