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Bite strength is of great importance to carnivores, as their jaws must produce forces of sufficient magnitude to kill and consume their prey. Spotted hyenas, well known for crushing and consuming bones, were studied to determine how tooth and jaw growth affect bite strength and feeding behaviour. Nine captive individuals, aged 6 months to 2 years of age, were sampled as they grew. At 8- to12-week intervals, morphological measurements that estimated jaw muscle mass, tooth size and skull size were taken. Using a force transducer, bite force was measured directly for these juveniles as well as other captive individuals of different ages. In addition, feeding behaviour and performance were quantified periodically by bone tests in which individuals were offered a sheep femur for 15 min. Behaviour and performance were expected to change with the shift from juvenile to adult dentition. Results were not entirely as expected. Morphological measurements of growth reached a plateau at about 20 months, whereas bite strength increased in a linear fashion up to 5 years of age. A fundamental change in tooth use during bone cracking followed the replacement of deciduous teeth with permanent teeth; the primary area of tooth use moved from anterior to rearmost premolars, increasing the mechanical advantage of the jaw adductors. The timing of this shift seemed to be a function of a decrease in gape limitation as a result of growth as well as caudal movement of the premolars. Our data demonstrated that juvenile hyenas had not achieved adult feeding performance levels at 12 months of age, when they are typically weaned in the wild. This suggests that recently weaned cubs may be at an increased risk of starvation and that selection might favour later weaning times.
Three groups of factors which might affect the blood biochemistry of red deer (Cervus elaphus) were examined. These were the wounding site (head/neck versus chest), the stalker who collected the blood (coupled with the geographical area where each deer was shot), and the sex and nutritional status of the deer. The activities of muscle enzymes, creatine kinase, aspartate amino transferase, and lactate dehydrogenase, were markedly higher in the plasma of deer shot in the chest as compared with those shot in the head or neck; the plasma also looked different, being deep cherry red in colour in the chest-shot deer. Other biochemical measures were unaffected by the wounding site. Blood collected by one stalker from the chest cavity had higher activity of the liver enzyme, glutamate dehydrogenase, higher concentration of potassium and lower concentrations of sodium and chloride than blood collected by another stalker from a knife wound in the base of the neck. Otherwise the method of collecting blood had very little effect on blood biochemistry. Cortisol was unaffected by the wound site nor, probably, by the method of collecting blood, but was highest in the stags living in a more mountainous region and in those deer that had to be shot twice before they died. Stags, which were shot in the rutting season and were probably fasting, had significantly higher concentrations of free fatty acids than hinds. Lactating hinds had significantly less fat on their kidneys than non-lactating hinds and stags. All hinds, which were shot in winter, had lower concentrations of urea than stags, which were shot in the autumn.
Following deglaciation of the Cook Inlet region of Alaska approximately 16 000 years ago, anadromous threespine stickleback (Gasterosteus aculeatus) rapidly colonized emerging lakes and rivers forming resident, freshwater populations. Although the precise body shape of the ancestral marine population is unknown, marine sticklebacks sampled from both Pacific and Atlantic sites present remarkably little body shape variation among populations, which suggests that the morphology of any of the marine populations could be used to represent the ancestral phenotype. To infer the net evolutionary trajectories of body shape change in the Cook Inlet radiation, derived body shapes of lacustrine samples were compared to the presumptive, primitive body shape, represented by the mean shape of two anadromous samples from Cook Inlet. In general, some derived body shape traits are shared by all freshwater populations but many traits evolved in opposite directions. The principal axes of shape variation among freshwater sample means were computed using Principal Components Analysis. The strong correlation between the direction of the principal component axes and lake habitat variables suggest that populations evolved toward selection peaks that are biased along the component axes due to biotic and abiotic features of the lakes.
Recent characterization of nuclear ribosomal small subunit (SSU) genes has shown that variant nucleotides within this region could be useful for species and species group identification within the genus Lymnaea (Gastropoda: Lymnaeidae). This study aimed to characterize a range of populations of Lymnaea natalensis Krauss, 1848 on Madagascar, and addressed two related questions. First, is there any evidence of intraspecific variation of the SSU and, if so, what might be its significance? Secondly, might this variation jeopardize the use of SSU for lymnaeid taxonomy and phylogeny? Lymnaea natalensis (n = 212) was collected from 17 sampling localities, spanning the northern and southern ends of the island. Variation within a selected region of the SSU known to vary between species, the V1 and V2, was assayed by polymerase chain reaction (PCR) linked restriction fragment length polymorphism (RFLP) and denaturing gradient gel electrophoresis (DGGE) analysis. The PCR-RFLP profiles indicated a striking dimorphism across populations at two restriction site loci (CfoI & MspI) within the E10-1 helix of the V2 region. The observed RFLP variation was confirmed by direct sequencing and by genomic digestion with subsequent hybridization. Putative heterozygotes were also encountered and in these individuals the SSU arrays composed of two distinct types approximately 1% divergent. A severe departure from Hardy–Weinberg equilibrium with a highly statistically significant (P < 10-5) heterozygote deficiency was found and genetic variation among populations was highly structured (Fst = 0.53). The geographic distribution of the variants was mapped, revealing that one variant was restricted to higher, predominately colder environments and was thought to be an adaptation. The molecular basis of the SSU variation was caused by single nucleotide polymorphisms (SNPs). To test for the possibility of cryptic taxa, an analysis of individuals representative of the SSU variant types with isoenzyme analysis (ISA), randomly amplified polymorphic DNA (RAPDs) and PCR-RFLP analysis of the ribosomal Internal Transcribed Spacer (ITS) was performed. Little variation was revealed and none that correlated to the groups suggested by SSU, confirming that the SSU variation was intraspecific. The levels of intraspecific divergence of the V1 and V2 within Lymnaea were not appreciably different (1%) from interspecific and would therefore question the validity of these data for lymnaeid taxonomy and phylogeny.
The rare Australian venomous elapid snake ‘Echiopsis’ atriceps has been the subject of considerable taxonomic instability with the five known specimens assigned to four genera by various authorities. Phylogenetic affinities of the rare Elapognathus minor also are poorly understood and have been the subject of some disagreement. To examine the phylogenetic affinities of these two rare taxa, a molecular data set comprising 1680 base pairs of mtDNA was assembled from a representative of each of the terrestrial Australian viviparous elapid genera and two species of Drysdalia, a genus about which there also has been phylogenetic controversy. A total of 936 base pairs of 12S rRNA, 454 base pairs of 16S rRNA and 290 base pairs of cytochrome b mtDNA were sequenced for 15 species. The Asian elapid Naja naja was used as the outgroup. These mtDNA regions provided 195, 38 and 72 parsimony informative sites, respectively, for a total of 315 parsimony informative characters. Unweighted phylogenetic analyses were performed under both parsimony and neighbour-joining criteria. Parsimony analyses of the unweighted, combined data set resulted in a single fully resolved most parsimonious tree 1225 steps long. The neighbour-joining tree differed by only a single weakly supported branch. These data strongly support a sister group relationship between ‘Echiopsis’ atriceps and the Australian broadheaded snakes of the genus Hoplocephalus with a bootstrap value of 99%. Templeton tests soundly reject all previous taxonomic arrangements for this species. Our data also strongly support a sister group relationship between Elapognathus minor and Drysdalia coronata with a bootstrap value of 98%. Importantly, Drysdalia coronata and Drysdalia coronoides do not form a monophyletic group, supporting some previous studies. Based on our results, we allocate ‘Echiopsis’ atriceps to a new monotypic genus and re-describe Elapognathus to include ‘Drysdalia’ coronata.
Most Australian birds do not migrate over long distances and therefore have to cope with seasonal changes in weather and food availability. We investigated whether the small (11 g) silvereye Zosterops lateralis changes its thermal tolerance from winter to summer. Body mass and body temperature of silvereyes exhibited little seasonal variability. However, metabolic rates (MR) and thermal conductance showed significant changes. Below the thermoneutral zone (TNZ), winter-acclimatized birds had significantly lower resting MR and thermal conductance than summer-acclimatized birds. Within the TNZ (˜27.0–33.6 °C winter; ˜25.4–33.5 °C summer) basal MR of winter-acclimatized birds (2.30 ± 0.29 mL O2 g-1 h-1) was significantly lower than that of summer-acclimatized birds (2.88 ± 0.43 mL O2 g-1 h-1). The average daily MR also differed significantly between summer and winter largely due to a greater reduction of MR at night and the decreased conductance. Our study shows that small passerines such as silvereyes exhibit seasonal variability in physiology and thermal energetics, even when they live in areas with a relatively mild climate, to help overcome seasonal changes in weather conditions and food availability.
The gut contents of a female specimen of Graneledone cf. boreopacifica collected from the caldera wall of Axial Volcano, near an active hydrothermal vent in the Northeast Pacific Ocean are reported. At least 30 individual gastropods and 46 individual polychaetes are represented in the gut contents by hard parts. Shell fragments and shells removed from the gut allow ready identification of the gastropods Provanna variabilis and Lepetodrilus fucensis, both of which are known only from North Pacific hydrothermal vents. Jaws of polychaete worms are identified as those of the nereidid, Nereis piscesae, and the predatory polynoids, Levensteiniella kincaidi and an unidentified species in the subfamily Branchinotogluminae. Not only was a considerable volume of prey hard parts ingested, the gastropod shells had been crushed before being ingested. The large size of the beaks in this genus of octopus and the increased area they offer for insertion of the superior mandible muscle, the prime mover in beak closure, support the hypothesis that these beaks exert sufficient force to crush the gastropod shells. Although cephalopods had been reported to be absent from hydrothermal vents, the data presented here demonstrate that not only do they occur in vent habitats, they actively prey on vent fauna.
The mouse-like marsupial Antechinus agilis is common to south-eastern Australia with breeding and life-history traits being highly synchronous. Mating activity is confined to a 10- to 15-day period in August, at the end of which all males die as a result of a stress-induced suppression of the immune system. Ovulation occurs at this time and females rely on stored sperm from specialized crypts in the lower isthmus of the oviduct for successful fertilization. Here we report a high incidence of mixed paternity litters, which can be attributed to sperm from multiple males being stored in the isthmic crypts. Data from this study also suggest a possible second male siring advantage in controlled ex situ sperm competition mating trials, irrespective of the delay between the two males being given mating access to the female or of the mating time relative to ovulation. In determining paternity through DNA profiling, population genetic data were obtained that showed significant differences in the genetic heterozygosity between unrelated adults, half siblings and full siblings. We suggest that the isthmic crypts, in addition to storing viable sperm, are capable of releasing a mix of sperm that increases the likelihood of mixed paternity litters. This allows all mating males the opportunity to sire young, increases female reproductive fitness and overall maintains high levels of population genetic heterozygosity in the face of total male mortality annually.
Mitochondrial DNA sequences consisting of 645 sites from the 12S rRNA and 16S rRNA genes were used to estimate the phylogeny of 15 of the 32 species of spiny-footed lizards Acanthodactylus. The resultant tree has similarities to that produced from a differentially weighted data set of 32 morphological characters but there are also significant differences. However, combined analysis of molecular and morphological data sets produces the same tree topology as DNA sequence alone. The molecular data confirm that there are distinct eastern and western clades within Acanthodactylus, but place A. boskianus in the former while the A. scutellatus group constitutes a third clade. Species for which only morphological information is available were integrated with the combined tree to give a provisional phylogeny for 31 species. This phylogeny indicates that the ancestor of existing Acanthodactylus probably originated in south-west Asia and that North Africa was invaded by more than one lineage of the genus. It also suggests that soft aeolian sand habitats may have been independently occupied more than once. Molecular data provide independent evidence that the differential weighting of morphological characters in past analyses was appropriate.
The diet of 789 stoats Mustela erminea and 458 weasels M. nivalis collected in Great Britain between 1995 and 1997 is described from analyses of their gut contents. As a percentage frequency of occurrence, stoat diet consisted of 65% lagomorphs, 16% small rodents and 17% birds and birds' eggs. Weasel diet consisted of 25% lagomorphs, 68% small rodents, mainly Microtus agrestis, and 5% birds and birds' eggs. Male stoats ate a greater proportion of lagomorphs than females, which ate more small rodents. No differences in diet between the sexes of the weasels were detected. The proportion of lagomorphs in the diet of both species was greatest in the spring. Both species ate more lagomorphs in the 1990s than in the 1960s as a result of increasing rabbit populations following recovery from myxomatosis. The importance of small rodents had decreased for stoats and increased for weasels. Both species had a dietary niche that was more specialized than in the 1960s. The implications of these findings for stoat and weasel conservation are discussed.
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.
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.
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.
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.