Behavioural factors that are likely to contribute to the coexistence of tiger Panthera tigris, leopard P. pardus and dhole Cuon alpinus, were investigated in the tropical forests of Nagarahole, southern India, during 1986–1992. Examination of predator scats and kills were combined with radiotracking of four tigers, three leopards, and visual observations of a pack of dhole. The three predators selectively killed different prey types in terms of species, size and age-sex classes, facilitating their coexistence through ecological separation. There was no temporal separation of predatory activities between tigers and leopards. Hunting activities of dholes were temporally separated from those of the two felids to some extent. Rate of movement per unit time was higher for leopards compared to tigers during day and night. In general, the activity patterns of predators appeared to be largely related to the activities of their principal prey, rather than to mutual avoidance. The three predator species used the same areas and hunted in similar habitats, although tigers attacked their prey in slightly denser cover than leopards. Both cats attacked their prey close to habitat features that attracted ungulates. There was no evidence for inter-specific spatial exclusion among predators, resulting either from habitat specificity or social dominance behaviours. Our results suggest that ecological factors, such as adequate availability of appropriate-sized prey, dense cover and high tree densities may be the primary factors in structuring the predator communities of tropical forests. Behavioural factors such as differential habitat selection or inter-specific social dominance, which are of crucial importance in savanna habitats, might play a relatively minor role in shaping the predator communities of tropical forests.

In most invertebrate taxa, males are smaller than females and large male sizes are only favoured when male–male competition for access to females is intense. In addition, in species where sperm competition is important, relatively large investments in testis growth and ejaculate size will also be selected. The use of copulatory plugs by males of some taxa, however, can prevent sperm competition. We hypothesized that, across related species in which males use plugs, relative testis size would decrease with increases in the severity of male–male competition. We tested this prediction across 112 species of acanthocephalan parasites, worms that use copulatory plugs and in which male–male competition occurs. As a measure of the intensity of male–male competition in a given species, we used sexual size dimorphism. Male and female body volume covaried allometrically, suggesting that sexual size dimorphism in acanthocephalans is the product of sexual selection. Our main finding is that relative testis volume, corrected for male body volume, decreases significantly as male body volume relative to female volume increases, i.e. as the sexual size dimorphism becomes less female-biased. All our results remained unchanged after we controlled for potential phylogenetic effects. The relationship indicates that investment in testis growth beyond the minimum size required for efficient fertilization becomes increasingly less important in species where males appear to compete intensely for mating opportunities.

The mortality rates of badgers Meles meles were estimated, using data from a long-term capture–mark–recapture study of an undisturbed badger population in south-west England. Two life table methods were used: fusion and discounting. Badgers were allocated to a particular TB status for all or part of their lives according to their degree of infection with bovine tuberculosis Mycobacterium bovis. Separate life tables were created for animals with each TB status, and for males and females, and the estimated mortality rates were compared statistically. The progression of M. bovis infection, and the positions of M. bovis lesions were also analysed. The main findings are: (a) uninfected male badgers have a significantly higher mortality rate than uninfected females, (b) infected badgers which are not excreting M. bovis do not have a significantly higher mortality rate than uninfected badgers, (c) badgers which are excreting M. bovis have a much higher mortality rate than uninfected badgers, (d) male badgers appear to cope with M. bovis infection less well than females, and (e) there may be sex differences in the mode of spread of M. bovis in badgers.

The triple jaws of the leeches Limnatis nilotica and Hirudo medicinalis (both Hirudinidae, Hirudininae) are compared, using the stereomicroscope and scanning electron microscopy (SEM). The jaws of Limnatis are relatively small, rounded and soft, bearing about 30 flat-topped, rough-surfaced teeth, and papillae which presumably secrete saliva. Limnatis sucks blood in stages from internal soft vascular tissue, often in the pharynx, and may stay inside the host for several weeks. Evidence is strong that it is unable to pierce external skin. Hirudo jaws are rigid, have no papillae and bear about 60 sharp teeth, each tooth possessing a secretory aperture on its side, close to the tip. In contrast to Limnatis, Hirudo is an external feeder. It pierces the skin and usually gorges itself with blood in one meal, after which it detaches itself from the host. It gains from six to nine times its weight in a meal, and remains satiated for 3–18 months. The ingested blood of Limnatis, unlike that ingested by Hirudo, is particulate and resembles a liver homogenate. This is probably a result of some scraping by its teeth as the jaws thrust towards a blood vessel. The relationship between jaw anatomy and feeding habits of L. nilotica and H. medicinalis is shown. Clearly, each species has adapted to the particular environment supplying its food (soft internal tissues, external skin).

Toe-pad development in Phyllomedusa trinitatis is described using light microscopy, SEM and TEM. Pad development in forelimbs was slightly in advance of hindlimbs. The first sign of a difference between pad (ventral) skin and dorsal skin occurred at Gosner stage 37 as a convolution of the basal side of the epidermis. By stage 39, pad basal cells were elongated in shape, with highly convoluted basal sides, whereas the dorsal epidermis had a basal layer of cuboidal cells with relatively straight bases. Mucous glands developed from pad epidermis earlier than at the dorsal side, and penetrated deeply into a matrix-rich dermis with a sparse cell population. Specialization of digit tip shape first became apparent at stage 38, with appearance of the distal circumferal groove. Widening of toe tips occurred at stage 39. Surface cells of the digital pads began to be shed by stage 40, in advance of epidermis elsewhere. Specialized pad surface cells were fully developed by stage 46, the end of metamorphic climax. During growth to adulthood, pads increased in overall area, but pad surface cells did not alter their dimensions. However, pad epidermis did become several cell layers thicker, much more so than in most other species described so far. Pad cells also had a surface area higher than in many other described species. The value of developmental studies in aiding our understanding of the multiple origins of adhesive pads in different anuran lineages is discussed.

Weapon size has been shown to be a better predictor of competitive success than body size (carapace width) in fights between shore crabs, Carcinus maenas. However, when the weapon size disparity is small between two opponents, it is still difficult to predict the victor. The role of weapon strength in pairwise fights between male shore crabs was investigated, to determine if relative force influences contest content, duration and outcome. Weapon strength was ascertained using a force transducer on live crabs, then fights between crabs were staged between size matched males. Winning crabs had major (crusher) claws and minor (cutter) claws that exerted a significantly greater force than losing crabs even when claw length was the same. Winners and losers were matched for carapace width, claw length and dactyl length but not claw height or claw length minus the dactyl. Winners had greater claw height and claw length to the dactyl in the major claw giving them a higher mechanical advantage when closing the claw and thus exerting a greater force. The forces exerted by the major and minor claws were analysed for any relationship between force and morphological measurements. Winning crabs appear to be fitter in having a better claw structure which exerts a greater force and they are more successful in agonistic interactions.

The developmental pattern of Polystoma indicum Diengdoh & Tandon, 1991 occurring in the urinary bladder of the frogs Rhacophorus nigropalmatus, R. reinwardtii and Polypedates leucomystax from Meghalaya (north-east India) was studied. Non-ciliated larval stages were recovered in the gyrodactyloid-I and post-gyrodactyloid-I stage mostly from the branchial chambers of the tadpoles; only rarely were they found in the intestines. These stages possessed features of bladder-destined forms and showed a gradual acquisition of 2, 4 and then 6 opisthaptoral suckers, coupled with an increase in the size of the body and various structures. While a conspicuous increase was noticeable in the dimensions of the hamuli, the size of the microhooks remained almost the same from the 2-suckered larval stage to the adult. The larval migration to the final destination seems to follow an external route leading to the cloaca of the metamorphosing host. The prevalence data of both the larvae and the adult flukes indicate a preference towards R. nigropalmatus amongst the three rhacophorid host species. The gyrodactyloid-II, i.e. neotenic larvae were not encountered at all either on the external gills of the very young tadpoles or even in the branchial chambers of the older ones.

The visual predation hypothesis of primate origins was introduced by M. Cartmill in the 1970s. In outlining a series of predictions regarding changes in orbital orientation, he further posits that the formation of a bony postorbital bar is correlated with greater orbital convergence, which in turn appears to be linked to selection for increased stereoscopic visual acuity in a nocturnal milieu. A series of predictions related to this model is tested in living analogues that vary in postorbital bar formation: felid and herpestid carnivorans and the pteropodid megabats. Bivariate correlations and regressions, ANOVA and ANCOVA are used to assess the intrinsic allometric and non-allometric factors thought to affect two aspects of orbital orientation, convergence and frontation. These angles of orbital orientation are then examined in an effort to determine how they are associated with the development of a postorbital bar. Cartmill suggested that convergent orbits develop from changes in relative orbit diameter and relative interorbital breadth. This study indicates that felids show only weak support for these predictions, while herpestids do not provide support and pteropodids show some support. Instead, in response to natural selection, convergence seems to develop to improve stereoscopic vision and depth perception in nocturnal predators. As predicted, felids show a significant positive relationship between orbital frontation and relative brain size. Analyses in herpestids, however, do not show significant relationships between frontation and relative palate length or relative brain mass. Pteropodids also do not support the model regarding intrinsic frontation factors. In both carnivoran groups, convergence and frontation are positively correlated, whereas they are not correlated in Pteropodidae. In partial contrast to Cartmill's predictions, we found that orbital convergence and/or orbital frontation are generally higher in carnivorans and bats with postorbital bars. Therefore, a greater emphasis on nocturnal stereoscopic visual predation and increased relative brain size both move the orbital aperture out of the plane of the temporal fossa and a postorbital bar thus provides adequate rigidity to the lateral orbital margin. In the more encephalized Felidae, orbital frontation is positively correlated with relative brain size; as smaller mammals have relatively larger brains, this explains why postorbital bars tend to be found in smaller felids. In herpestids and pteropodids, postorbital bars tend to occur in larger taxa which are more convergent than smaller forms.

Patterns of habitat selection by American mink Mustela vison within foraging areas located on the shore, were studied in a coastal environment of Scotland from November to March in 1983/84, 1984/85 and 1994/95. The abundance of prey in the intertidal zone was modelled in relation to abiotic environmental characteristics. Four factors were found to be important predictors of prey abundance: the position within the tidal zone, the abundance and size of rockpools, the nature of the substratum and the presence of fresh water streams. The model was used to predict prey abundance in different areas of the shore. We then investigated whether mink were choosing areas with higher prey abundance at different tidal levels and within, as opposed to between, core areas (areas with a relatively high density of fixes, encompassing usually one or more dens). Only when foraging at low or mid-tide and within core areas were mink found to behave selectively. They showed no significant preference for areas rich in prey when foraging at high tide and between core areas. Mink were also found to avoid areas with fresh water streams and to prefer foraging in the mid-tide zone. The findings are discussed in relation to prey abundance and competition with the otter Lutra lutra.