Constriction of prey by gopher snakes Pituophis melanoleucus and king snakes Lampropeltis getula is highly variable in posture, muscular activity and force exertion. These snakes typically use lateral bends of the anterior trunk to wind the body into a vertical coil around the prey. Three common constriction postures are fully encircling loops that form a coil, partially encircling loops, and non-encircling loops that pinion the prey. Initial tightening of a coil occurs by winding or pressing the loops tighter to reduce the diameter of the coil. The epaxial muscles are highly active during striking and coil formation and intermittently active during sustained constriction. These results refute the hypothesis of a mechanical constraint on constriction in snakes with elongate epaxial muscles. Constricting gopher and king snakes can detect muscular, ventilatory and circulatory movements in rodent prey. In response to simulated heartbeats or ventilation in mice, the snakes twitch visibly, recruit epaxial muscle activity, and increase constriction pressure temporarily, but then quickly relax. Muscular activity and constriction pressure are increased most and sustained longest in response to muscular struggling in prey. Although muscle activity and pressure exertion are intermittent, the constriction posture is maintained until the prey has been completely still for several seconds; thus, a snake can reapply pressure in response to any circulatory, ventilatory or muscular movement by the prey. The pressures of 6.1–30.9 kPa (46–232 mm Hg) exerted on small mammal prey by constricting snakes range from about half to over twice a mouse's systolic blood pressure, and are probably 10 times larger than the venous pressure. These high pressures probably kill mammalian prey by inducing immediate circulatory and cardiac arrest, rather than by suffocation alone.

Four main types of radula are found within the gastropod superfamily Conoidea. Type 1, the Clavidae type has five teeth in each row with comb-like laterals and flat pointed marginals. Type 2, the Turridae type has two or three teeth in a row with the marginals comprised of teeth with the duplex or wishbone form. Type 3, the Pseudomelatomidae/Pervicaciinae type has two or three teeth in a row with the marginals curved and solid. Type 4, the hypodermic type has two hollow, enrolled, marginal teeth in each row with the radular membrane reduced or absent. Study of the maturing teeth along the radular membrane in gastropods with the Type 2 radula shows that the duplex teeth are not formed from two separate elements but develop from a flat plate, by thickening of the tooth edges and elevation of the posterior edge from the membrane. Semi-enrolled and enrolled teeth of Pilsbryspira, Imaclava and Toxiclionella develop in a similar way. In Conidae where a vestigial radular membrane is attached only at the base of the teeth, the teeth are enrolled from first formation in the radular sac. This study demonstrates that duplex and enrolled teeth develop by a similar process, allowing the possibility of deriving hypodermic teeth from duplex clades as has been suggested by previous phylogenetic analysis.

We examined 3747 teeth from 134 hares (Lepus sp.) collected at 46 sites in Israel to test whether variation in epigenetic occlusal characters was linked to ecogenetic or phylogenetic factors. Collection sites encompassed a wide range of ecogeographical and climatic regimes. We compared data from Israeli hares with occlusal characters of 160 cape hares L. capensis from East Africa and 68 brown hares L. europaeus from central Europe. Only three teeth (I1, I2, M3) did not show occlusal variation. Thirty-eight occlusal characters were derived from dental variants by dichotomous (0/1) scoring. Absence of association of character states among characters of single teeth indicated a lack of morphotypes. Epigenetic differentiation among hares from northern, central and southern Israel, and the two East African, and two central European samples, was revealed by pairwise C. A. B. Smith's ‘mean measures of divergence’ (MMD), based on frequencies of character states. Cluster analyses of MMD values revealed little epigenetic differentiation between northern and southern Israeli hares, but greater differentiation between central European and East African hares. Concordance of the MMD matrix with linear geographical distances among sampling regions was demonstrated by a Mantel test. No frequencies of character states exhibited significant changes across the climatic parameters among hares from northern and southern Israel. But the individual folding index, which expresses the degree of enamel on the occlusal surface, slightly decreased from north to south. Our results support a phylogenetic interpretation of occlusal character variation. Despite distinct differences in external appearance, hares from northern and southern Israel probably comprise a single species that encompasses two closely related geographical populations with a probable area of overlap. Israeli hares are intermediate between European brown hares and East African cape hares, with a slightly closer relationship to the cape hares.

Jaguars (Panthera onca) and pumas (Puma concolor) are sympatric over much of their geographic range in Mexico and South and Central America. We investigated diets of these felids in and around the Chamela-Cuixmala Biosphere Reserve in western Jalisco, Mexico. Diets were determined from scat analyses and documentation of prey cadavers. Relative biomass of each prey species consumed by pumas and jaguars was estimated from analysing 65 puma and 50 jaguar scats collected from 1995 to 1998. Both jaguars and pumas fed mainly on mammals, with white-tailed deer (Odocoileus virginianus) dominating the biomass of the diet of each species (54% and 66% respectively). There was a high degree of overlap between jaguar and puma diets, but pumas had a broader food niche than jaguars, and their ability to exploit smaller prey may give them an advantage over jaguars when faced with human-induced habitat changes.

Models of host–parasite co-evolution suggest that parasites can exert frequency-dependent selection on their hosts, favouring rare alleles that confer resistance against widespread parasites and thus contributing to the maintenance of genetic variation, at some loci at least. If parasites are important in maintaining variation at many loci, then host species incurring a high prevalence of parasite infections should exhibit greater levels of genetic variation than host species incurring a lower prevalence. Using data from electrophoretic studies and from field surveys of haematozoan infections, we constructed a dataset including 103 species of North American and European birds to test this prediction. After controlling for sampling effort and phylogenetic influences, we found no relationship between parasite prevalence and either heterozygosity or polymorphism. These results do not support a role for parasites in the overall maintenance of genetic variation via frequency-dependent selection.

Contrary to large-scale disturbances, animals constantly create small-scale patches of various kinds during the course of their daily life. For example, rooting by wild boars is a recurrent disturbance regime, which varies in frequency and extent. Rooting by wild boars (Sus scrofa L.) in south-central Sweden was therefore studied by censusing three times per year during 1992–1995 along fixed transects in the Tullgarn Nature Reserve. Significant differences were found in soil surface area being rooted by wild boar between year, season, habitat type and soil category. The amount of surface being rooted varied between 2.4 and 14.2 ha on 226 ha censused. The rooted surface in relation to the ground available was higher in deciduous compared to coniferous forests and grassland. Furthermore, the rooted surface in relation to available ground to root was much higher in damp soil than in dry soil. Mesic soil was used according to availability. Rooted patches showed large variation in size between year, season, habitat type and soil category. Within the three habitat types the largest patches were found in deciduous forests and the smallest in grasslands while in the different soil categories, the largest patches were found in damp soils and the smallest in dry soils. Results are discussed in terms of plant species diversity on a regional scale.

Three Iceland gull taxa were defined mainly from adult wingtip melanism. Up until about 1860, nominate glaucoides (no melanism) was known to breed from Greenland to western High Arctic Canada, but by about 1900 it was essentially confined to Greenland. Until 1860, thayeri (most melanism) was known only from western High Arctic Canada, but from 1900 to 1980 it was found throughout High Arctic Canada and in a small part of north-west Greenland. At high latitudes in Canada it replaced glaucoides, with which it was formerly sympatric in the west and probably interbred. The first known kumlieni (intermediate, variable melanism) were from west Greenland in the 1840s, and by 1900 the western and northern limits of most of its breeding range in the eastern Canadian Low/High Arctic were known. The range of kumlieni lies between those of thayeri and glaucoides and overlaps both; kumlieni bred in Greenland by 1964. It freely interbreeds with thayeri and probably with glaucoides. Winter ranges of glaucoides and thayeri have changed little since they were first determined for glaucoides by 1860 and for thayeri by the 1920s. However, winter adult kumlieni was unknown from Greenland to the British Isles until 1900; there were a few records prior to 1915 and progressively more after 1950. The study adds to the evidence that kumlieni represents introgressive hybridization by western thayeri into eastern glaucoides.

D. N. Weir died 15 August 2000.

Though most Xenopus species are polyploid and can be hybridized in the laboratory, natural hybridization seems to be restricted to hybrids of X. laevis laevis×X. gilli. A parapatric distribution pattern between X. l. laevis and X. muelleri seems to prevent interbreeding. We found X. l. laevis and X. muelleri living sympatrically in water bodies in the Republic of South Africa west of Kruger Park and report a natural hybrid of X. l. laevis×X. muelleri. Natural occurrence of such a hybrid has not been reported previously. The hybrid character was confirmed by analysis of its advertisement calls, which were intermediate between those of the parental species, by analysis of its serum albumin pattern, and by determination of the nuclear DNA content of its erythrocytes. The results indicate that this specimen is an F1 hybrid between X. l. laevis and X. muelleri. Backcrossing with both parental species indicated that the hybrid is sterile. It is discussed why sympatry between X. l. laevis and X. muelleri though possible might be rare.

Twenty-three species of erect, fenestrate bryozoans belonging to the family Phidoloporidae Gabb & Horn 1862, popularly termed lace corals, are described from the coasts of Australia, Torres Strait and Fiji, and illustrated by scanning electron microscopy. Nine species of Triphyllozoon are re-examined, including seven originally described by Harmer (1934). Seven new species are described in Reteporella and one each in Schizoretepora and Reteporellina. Of the remaining four species, two species of Reteporellina are reported for the second time since their original description and two first described by MacGillivray (1883) are redescribed from additional materials.

Young, relatively undeveloped sugar gliders Petaurus breviceps have been observed to be left alone in the nest while the mother forages and may be subject to considerable thermal or energetic stress. As no information is available on the development of thermoregulation in this species, which begins reproduction in winter, we measured resting metabolic rate (RMR), body temperature (Tb) and thermal conductance over a range of ambient temperatures (Ta) in 10 sugar gliders from c. 55 days of age until they had grown to adult size. Sugar gliders were unable to maintain a stable Tb over a Ta range of 30–15 °C until the age of 95–100 days, although they raised RMR somewhat as Ta decreased. Further growth resulted in a steady decrease in mass-specific RMR, an increase in Tb and a substantial decrease in thermal conductance. Our study shows that young gliders below the age of 100 days rely largely on heat produced by adults to maintain a high Tb, but are well able to cope with regular falls in Tb of > 10 °C and a concomitant decrease of RMR. This thermal tolerance and reduction in energy expenditure should allow the mother to forage and replenish her own body fuels while her offspring are left alone in the nest.

Seasonal body weight changes were investigated in red and grey squirrels in spruce-dominated conifer plantations in the north of England. Annual seed food availability, particularly in the spruce plantations, varies markedly and is characterized by years with large cone crops (‘mast crops’) followed by several years of intermediate or low crops. The last mast crop in Kielder Forest District occurred in 1991 and we studied the two squirrel species when food availability was intermediate and low between 1992 and 1999. Neither red nor grey squirrels in the conifer plantations significantly increased their body weight for the autumn or winter. The responses of red and grey squirrels to the different foraging conditions in deciduous and conifer woodlands and the accumulation of seasonal fat stores may have to be seen in the context of habitat type and the pattern and predictability of seed availability. Our findings suggest that fat accumulation is likely to be less pronounced in conifer habitats where autumn and winter food supplies are more predictable, and manoeuvrability to feed on cones in the canopy is important.

Post-hatching changes in brain mass were investigated in mallards and four stocks of domesticated ducks, using growth curve analysis and allometry. The birds varied in age between hatching and 154 days. Percentage brain size at hatching in ducks varies between 22.5% and 28% which fits well into the precocial category. Brain growth shows a sigmoid course. The point of inflection is very early when compared to other organs. However, growth is slow after passing the growth rate maximum. Pekins show higher absolute brain masses than mallards. However, the growth patterns with respect to time are very similar among stocks. Strongly negative allometry is found with allometric exponents between 0.31 and 0.37 with the highest value in mallards. Allometrically, there is an increasing reduction of brain mass in Pekins when compared to mallards to about 12.5% in adults. No differences were found between mallards and either Muscovies or the Muscovy × Pekin cross. The reduction in relative brain size in domesticated animals when compared to their wild ancestors is generally attributed to a decrease in functional demands resulting from the artificial environment. Because brain growth is more conservative and less influenced by selection than body weight, we assume that this reduction is, at least in part, a result of the constancy of brain growth patterns.

The effect of diet quality on basal metabolic rate (BMR) over time was studied in female Octodon degus. Degus fed on a low-quality diet maintained a constant BMR over time, while those fed on a high-quality diet showed an increased BMR after 30 days. After 120 days of dietary acclimation, individuals fed on a high-quality diet exhibited comparatively higher BMRs. Thus, we hypothesize that when environmental food quality is high, degus are able to increase their BMR quickly, allowing high rates of biosynthesis.

Genetic diversity in four populations of the Eurasian badger Meles meles from Denmark was estimated by allozyme electrophoresis. Low genetic variability was found within populations as compared to the variability found in badger populations from other countries, whereas significant genetic differentiation was found between populations. The low genetic variability and the differentiation between populations is explained by the fragmentation of the Danish landscape, which reduces the effective population size of local populations and the gene flow between them. Low genetic variability found for Danish badgers also supports the hypothesis of a rapid recolonization following the last glaciation.

Shark-inflicted mortality on harbour seals Phoca vitulina on Sable Island, Nova Scotia, was studied from 1980 to 1997, based on carcasses washed up on shore. During this period, pup production declined dramatically from over 600 in 1989 to 40 in 1997. Between 1980 and 1992, pup deaths only were recorded, and only during the May–June pupping period, while deaths in all age groups were recorded year-round between 1993 and 1997; 458 pups, 23 juveniles and 241 adults were found. Shark-inflicted mortality in pups, as a proportion of total production, was under 10% during 1980–93, roughly 25% in 1994–95, and increased to 45% in 1996. Shark-inflicted mortality occurred in all months except December, January and February, with c. 80% of the pups killed during the pupping period, and 97% of the adults killed outside the pupping period. The decline in pup production was not only a result of reduced recruitment owing to pup mortality. A greater proportion of reproductive females than males was killed. We estimate that shark-inflicted mortality on pups and adult females reduced pup production on Sable Island by 43 to 154 pups annually between 1993 and 1997. Our results indicate that sharks are having an impact on Sable Island harbour seals, possibly to the extent of limiting population growth, or contributing to the observed population decline. Potential reasons for this increased mortality are discussed.

Echinostoma sp. use larval anurans as intermediate hosts. The cercariae enter the tadpoles via the cloacal opening and form metacercarial cysts in the kidneys, pronephroi, and Wolffian ducts. To examine the distribution of Echinostoma metacercariae in Rana sylvatica and Rana clamitans tadpoles, 200 individuals of each species were exposed to free-swimming cercariae. There was a significant left:right bias in the distribution of metacercariae within both R. sylvatica and R. clamitans tadpole hosts, with trematodes preferentially encysting in nephric structures on the right side. In R. sylvatica and R. clamitans, respectively, 56.7% and 96.8% of the metacercariae were on the tadpoles' right side. Asymmetry in the distribution of parasites followed the direction of the asymmetry in tadpole kidney size, but was much greater. Trematodes preferentially encysted in the head kidneys of R. clamitans, which regress at metamorphosis. The right head kidney was the most commonly infected structure in R. clamitans tadpoles, containing 72.7% of all cysts in that species. Despite the preference of trematodes to encyst in the head kidney, there was no correlation between the number of cysts in the right kidney and the number in the right head kidney. This suggests that limited space in the head kidney does not influence metacercarial formation in the kidney proper. The high frequency of unilateral encystment in both anurans, and in the head kidneys of R. clamitans, may be the result of a co-evolved relationship that ultimately benefits both the host and parasite by ensuring host survival.