bluuebunny/crossref_metadata_2025_split huggingface dataset:
A description of the nuchal organ, a possible photoreceptor, in Euprymna scolopes and other cephalopods
Authors: Parry Matthew 
Published: February 2006

AbstractA type of apparent photoreceptor, the nuchal organ, is described in the sepiolid squid Euprymna scolopes. These vesicles are identified in a variety of other cephalopod species. The nuchal organs have specific structural similarities to the already well‐described photosensitive vesicles. Both organs have a distinct vesiculate structure and possess a rind consisting of several types of cells. Certain rind cells from both organs send processes with microvilli into the lumen of the vesicle forming a core area. Within the cores of both organs numerous microvilli occupy much of the core volume. These histological similarities provide strong evidence that the nuchal organs, like the photosensitive vesicles, are photoreceptors. Three distinct differences also exist between the nuchal organs and photosensitive vesicles: (1) the location of the nuchal organs differs from that of all known photosensitive vesicles in cephalopods; (2) the location of the nuchal organs is highly conservative in decapod cephalopods compared to the varying locations of the photosensitive vesicles; (3) the degree of structural order generally found within photosensitive vesicles is not apparent in the nuchal organs. The function of the nuchal organ is probably different from previously described photoreceptors in cephalopods.
Variation of eye size in butterflies: inter‐ and intraspecific patterns
Authors: Rutowski Ronald L. 
Published: February 2006

AbstractDifferences in behaviour, such as the mate‐locating tactic, may favour the evolution of interspecific and intersexual differences in the structure of the visual system. This notion was tested by examining the relationships between eye size, body size, sex and mate‐locating tactic in 16 species of butterflies. The 16 species were grouped in eight phylogenetically close pairs that differed in the mate‐locating tactic displayed by the males. Eye size was characterized by eye surface area, which was estimated from a set of linear eye measurements made on 10 individuals of each sex in each species. The major findings were that eye surface area was positively correlated with body size both among and within species, males have larger eyes relative to their body size than females, and after controlling for body size and phylogeny, interspecific differences in the mate‐locating tactic of males does not explain interspecific variation in the size of male eyes or in the magnitude of sexual difference in eye size. The optical and behavioural consequences of variation in eye size with body size and sex will await a better understanding of how eye structure varies with size within and between species.
Factors affecting the abundance of rabbits (Oryctolagus cuniculus) in England and Wales
Authors: Trout R. C. , Langton S. , Smith G. C. , Haines‐Young R. H. 
Published: February 2006

AbstractData gathered from the Ministry of Agriculture, Fisheries and Food (MAFF) National Rabbit Survey sites in the 1980s showed substantial site‐to‐site and year‐to‐year variation in rabbit Oryctolagus cuniculus abundance. Data on physical and biological factors from 450 sites were collected to seek explanations for this variation. The rabbit abundance index on the 2.25 km transects (walked along the edge of fields, woods, hedges, etc.) was used as the dependent variable for multiple regression and principal components analyses. Additionally, a preliminary attempt at mapping rabbit abundance and distribution in England and Wales using a GIS system was made. Each of the analyses produced a list of the important variables enhancing or reducing rabbit indices. Common to each list were aspects of woodland – area, number of pieces and length of edge; the dryness and patchiness of soils on site; rainfall in late winter, or variables associated with wetness of soil (e.g. number of days with rain, altitude). Other important variables included predator removal policy and the site location nationally. The two strongest components, woodland parameters and predator removal policy, are under human influence. The effects of region, county and year were small, but year‐to‐year variation within sites was larger, suggesting that rabbit populations were reacting markedly to unmeasured variables, e.g. myxomatosis outbreaks. The analysis provides a useful explanation of the factors that affect rabbit populations and a basis for how these factors may be manipulated.
Allozymic variation and systematic relationships of the Octodontidae and allied taxa (Mammalia, Rodentia)
Authors: Köhler N. , Gallardo M. H. , Contreras L. C. , Torres‐Mura J. C. 
Published: February 2006

AbstractGenetic variation and the allozymic relationships of five families comprising 23 species of hystricognath rodents were examined using electrophoretic data from 19 presumptive gene loci. Direct‐count heterozygosity ranged from 0% to 13.6%, and polymorphism varied from 0% to 36.8%. Fixed allele differences were instrumental for the segregation of taxa as summarized by the Distance Wagner procedure and by majority‐rule consensus trees. The monophyly of the Octodontidae, and the family rank of the Abrocomidae and Ctenomyidae is supported by the data. Monotypic Myocastor coypus is not resolved as a distinct family but appeared within the Caviidae. Within the Octodontidae, paraphyly was detected in polytypic Octodon, whereas a high bootstrap value supported the node containing the desert specialists O. mimax (2n= 56) and Tympanoctomys barreare (2n= 102). The implications of allozymic data as a robust phylogenetic signal that connected biochemical associations to the prediction of tetraploidy in T. barrerae are discussed.
Development of bite strength and feeding behaviour in juvenile spotted hyenas (Crocuta crocuta)
Authors: Binder Wendy J. , Van Valkenburgh Blaire 
Published: February 2006

AbstractBite 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.
Molecular characterization of the freshwater snail Lymnaea natalensis (Gastropoda: Lymnaeidae) on Madagascar with an observation of an unusual polymorphism in ribosomal small subunit genes
Authors: Stothard J. R. , Brémond P. , Andriamaro L. , Loxton N. J. , Sellin B. , Sellin E. , Rollinson D. 
Published: February 2006

AbstractRecent 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.
Seasonal variations in thermal energetics of Australian silvereyes (Zosterops lateralis)
Authors: Maddocks Tracy A. , Geiser Fritz 
Published: February 2006

AbstractMost 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.
Sperm competition and genetic diversity in the agile antechinus (Dasyuridae: Antechinus agilis)
Authors: Shimmin G. A. , Taggart D. A. , Temple‐Smith P. D. 
Published: February 2006

AbstractThe 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.
Elucidation of the relationships of spiny‐footed lizards, Acanthodactylus spp. (Reptilia: Lacertidae) using mitochondrial DNA sequence, with comments on their biogeography and evolution
Authors: Harris D. James , Arnold E. Nicholas 
Published: February 2006

AbstractMitochondrial 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.
Food habits of jaguars and pumas in Jalisco, Mexico
Authors: Núñez Rodrigo , Miller Brian , Lindzey Fred 
Published: February 2006

AbstractJaguars (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.
Genetic variation and prevalence of blood parasites do not correlate among bird species
Authors: Poulin Robert , Marshall Leigh J. , Spencer Hamish G. 
Published: February 2006

AbstractModels 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.
Development of thermoregulation in the sugar glider Petaurus breviceps (Marsupialia: Petauridae)
Authors: Holloway Joanne C. , Geiser Fritz 
Published: February 2006

AbstractYoung, 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.
Brain growth in mallards, Pekin and Muscovy ducks (Anatidae)
Authors: Gille Uwe , Salomon Franz‐Victor 
Published: February 2006

AbstractPost‐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 a population of harbour seals (Phoca vitulina) at Sable Island, Nova Scotia
Authors: Lucas Z. , Stobo W. T. 
Published: February 2006

AbstractShark‐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.
Hyperextended call note repertoire of the endemic Madagascar treefrog Boophis madagascariensis (Rhacophoridae)
Authors: Narins P. M. , Lewis E. R. , McClelland B. E. 
Published: February 2006

AbstractVocalizations of Boophis madagascariensis (Rhacophoridae) males were recorded in a mid‐elevation rain forest in eastern Madagascar. Call notes made by males of this species were classified into 28 types. This represents the largest known call repertoire of any amphibian. The calls range widely in spectral characteristics from a narrowband, nearly pure‐tone to broadband ‘rip’ notes, to even broader band, pulsatile ‘iambic’ notes consisting of up to 23 pulses. Even considering all ‘iambic’ notes as variants of one type, there remain eight distinct call notes produced by this species. Morphological analysis of the vocal musculature of B. madagascariensis revealed no obvious adaptations for unusual glottal flexibility or function. Playback studies using a subset of the call notes as stimuli were carried out in the animals' natural habitat to determine the functional significance of several of the call notes. At the lowest playback levels, there was a significant tendency for males to produce rip notes in immediate response to either rip or iambic note stimuli. At the higher playback levels, we identified one sequence of iambic notes that consistently evoked a significant iambic note response from males. A permutation test on call note transitions during spontaneous calling revealed that call note pairs occurred inconsistently and unpredictably. The evolutionary significance of an extended vocal repertoire, matched counter‐calling and a random call note production scheme is discussed.