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John D. Pettigrew - One of the best experts on this subject based on the ideXlab platform.

  • paddlefish and platypus parallel evolution of passive electroreception in a rostral bill organ
    2003
    Co-Authors: John D. Pettigrew, Lon A Wilkens
    Abstract:

    A comparison is made between a mammalian, monotreme species and an actinopterygian fish that have each, indepen dently, evolved a similar, spoonbill-shaped rostral bill organ whose array of electroreceptors provides sufficient spatial information for prey capture in a freshwater environment without the need for visual cues. The platypus, Ornithorhyncus anatinus (Monotremata, Mammalia), has approximately 40,000 electroreceptors arranged in parasagittal rows on the bill organ. By means of behavioral and electrophysiological recording experiments in platypus, it has been shown that this array of electroreceptors can trigger an accurately directed head saccade to intersect aquatic prey that emit electrical signals. The threshold field strength for prey detection by platypus is 50 microvolts/cm, two orders of magnitude more sensitive than individual electroreceptors. The paddlefish, Polyodon spathula (Osteichthyes, Actinopterygii), can similarly execute a lateral head saccade to intersect prey, with a threshold field strength around 10 microvolts/cm, considerably more sensitive than the presumed sensitivity of individual electroreceptors. The remarkable anatomical and behavioral similarities between these two independent electroreceptive systems are described and discussed. Major differences between the two bill-organ systems include the mechanism of transduction at the electroreceptors and a prominent cooperative role played by 60,000 mechanoreceptors that are interdigitated among the electroreceptors in the platypus bill but not in the paddlefish.

  • electroreception and the feeding behaviour of platypus ornithorhynchus anatinus Monotremata mammalia
    Philosophical Transactions of the Royal Society B, 1995
    Co-Authors: Paul R Manger, John D. Pettigrew
    Abstract:

    It has previously been shown that platypus are sensitive to small electrical fields. It was predicted that platypus use their electrosensitivity to locate the source of foodstuffs on the bottom of the freshwater river systems in which they live, because the platypus are nocturnal, and close their eyes, ears and nostrils while underwater. In this paper we demonstrate for the first time that platypus are indeed sensitive to electrical waveforms that imitate the electromyogenic potential’s of fleeing prey, and following stimulation show interest in area surrounding the electrodes. We also show that platypus respond with a reflex after stimulation with a square wave, and show that this reflex is directionally tuned to the origin of the electrical pulse, with a preferential sensitivity axis 40 times more sensitive than non-preferred axes. The strong directional sensitivity explains previous discrepancies in the lowest threshold for platypus electroreception, which we find to be 50 μV cm -1 . Platypus are also sensitive to galvanic fields. We present the data in the light of standardized feeding strategies of the platypus, and discuss the integration of the findings into these feeding strategies. We surrounded our platypus enclosure with a Faraday cage, thereby eliminating excess electrical noise, a suggested new addition to the husbandry regime of platypus.

  • Cone photoreceptors lacking oil droplets in the retina of the echidna, Tachyglossus aculeatus (Monotremata).
    Visual neuroscience, 1991
    Co-Authors: Heather M. Young, John D. Pettigrew
    Abstract:

    The echidna, Tachyglossus aculeatus, a monotreme mammal, is thought to possess an all-rod retina (O'Day, 1952). This study provides anatomical evidence for the presence of cone-like photoreceptors in the retina of the echidna. The cones, which constitute 10-15% of the photoreceptors, have all of the ultrastructural characteristics previously shown in the cones of placental mammals, and, like the cones of other animals (Blanks & Johnson, 1984), they bind peanut agglutinin. Unlike the cones of another monotreme, the platypus, the cones of the echidna retina do not possess oil droplets. Twin cones, pairs of cones in which there is no obvious difference in the size, shape, or ultrastructural features of the members of a pair, are common. The density of cones varies from 9000 cells/mm2in the superior periphery to 22,000 cells/mm2in the central retina. Nearest-neighbor analysis suggests that the cone mosaic in the echidna retina results from the presence of single and twin cones in a relatively regular array.

Max Abenspergtraun - One of the best experts on this subject based on the ideXlab platform.

  • the foraging ecology of a termite and ant eating specialist the echidna tachyglossus aculeatus Monotremata tachyglossidae
    Journal of Zoology, 1992
    Co-Authors: Max Abenspergtraun, E. S. De Boer
    Abstract:

    This study investigates the effect of food distribution on the selection of foraging habitats, and the relationship between food availability, diet, ambient temperature, activity, use of shelter and energy budgets, in a termite-and ant-eating mammal, the echidna, Tachyglossus aculeatus. In two Nature Reserves in the wheatbelt of Western Australia, 10 adults and six juveniles were radio-tracked for II months during 1988. Animals were weighed monthly and their fresh faeces collected for dietary analysis. Available termite and ant energy was measured simultaneously in habitats where the echidnas foraged: woodland, mallee**, shrubland and heath. Termite energy formed the principal food of echidnas, possibly because of their greater abundance. Highest ingestion rates of termite energy during the hottest time of year may reflect increased moisture requirements. Adult animals preferred woodland and mallee for foraging, possibly because termite and ant energy was highest there. Juveniles exhibited no obvious habitat preference. Echidnas were active year-round, with foraging peaks during spring and autumn, and animals gained weight then. Despite termite energy being highest in winter, echidnas were in negative energy balance during this period, possibly because they make smaller foraging efforts and have higher thermoregulatory costs. Foraging was principally nocturnal in summer, and mixed nocturnal/diurnal in winter. No foraging was observed below 9° and above 32°C, with a preferred range of 16–20°C. Echidnas were not apparently food-limited because: (a) both adult and juvenile animals maintained, or gained, body weight even when termite energy was low; (b) juveniles foraged anywhere, irrespective of habitat, but still gained weight; and (c) there was no evidence for hibernation by wheatbelt echidnas, unlike in other parts of Australia where echidnas routinely hibernate in winter, possibly in response to food shortage. However, echidnas did show signs of short-term torpor. Echidnas were active throughout the year, possibly because food was unlimited, and because use of subterranean shelter reduced thermoregulatory costs. The results of this study suggest that food distribution and ambient temperature play an important role in influencing daily and seasonal foraging activity in wheatbelt echidnas.

  • patch use and prey defence in a mammalian myrmecophage the echidna tachyglossus aculeatus Monotremata tachyglossidae a test of foraging efficiency in captive and free ranging animals
    Journal of Zoology, 1991
    Co-Authors: Max Abenspergtraun, Chris R Dickman, E. S. De Boer
    Abstract:

    Echidnas (Tachyglossus aculeatus) in wheatbelt reserves in Western Australia are primarily termite- and ant-eaters. Using captive and free-ranging animals, we tested whether echidnas respond to high density patches of these prey and also to differences in their mechanisms of defence. When feeding on termites, free-ranging echidnas generally adjusted their foraging effort in response to prey abundance, increasing their rate of energy intake by digging deeper and allocating more time to patches where prey were abundant. Such efficient foraging occurred irrespective of whether termite defence was mandibulate, chemical, or a combination of both, as in Amitermes neogermanus. Echidnas invested little effort in species of Drepanotermes in the field despite their abundance at local food patches, probably because the soldiers are large and aggressive and produce copious quantities of pungent defence secretions. Echidnas also avoided Nasutitermes exitiosus in the field but ingested other species with chemical defence such as Tumulitermes. Captive echidnas decreased their foraging effort on N. exitiosus only when soldiers were abundant (400 per unit area) and the soldier to worker ratio was high (80:20), hence avoidance of this species by free-ranging echidnas may reflect the species'ability to mobilize quickly large numbers of soldiers to colony breaches. When feeding on ants in the field, foraging effort and prey energy in food patches were not correlated, possibly because ants responded rapidly to colony breaches by emerging to meet the predator. More extensive soil excavations by foraging echidnas to capture ants were thus unnecessary, minimizing foraging effort. Captive and free-ranging echidnas rejected ants 7 mm (except in the presence of energy-rich eggs), and > 10 mm long, respectively, reducing foraging efficiency to zero when encountering such prey. With such exceptions, the results suggest that echidnas make efficient use of patchily distributed prey and generally adjust their foraging efforts to match actual energetic returns.

  • survival strategies of the echidna tachyglossus aculeatus shaw 1792 Monotremata tachyglossidae
    Biological Conservation, 1991
    Co-Authors: Max Abenspergtraun
    Abstract:

    The area occupied by the Western Australian wheatbelt has experienced extensive land clearing for agriculture between 1900 and 1970. In many areas >90% of the original vegetation has been cleared, and exotic predators (fox and cat) are common. Of the 56 mammal species recorded for the region since agricultural settlement, 25% have become extinct and a further 21% have declined in range. Yet not all species have been equally affected. The echidna Tachyglossus aculeatus acanthion, a termite- and ant-eating specialist, remains ubiquitous and its populations are stable. It is successful because (a) it is not restricted by habitat; (b) it specializes on an abundant and reliable food source for which there is no apparent competition: (c) it is metabolically capable of tolerating low energy conditions, such as drought- or fire-induced food shortages; (d) its shelter requirements are independent of vegetation; (e) predation on adult animals is minimal; and (f) it can survive outside nature reserves, and is capable of dispersing to distant remnants. Morphological and physiological adaptations to myrmecophagy (termite- and ant-eating) now enable Tachyglossus to cope with exotic predators and the loss and fragmentation of habitat. These adaptations are likely to benefit other mammalian myrmecophages living in similar environments. The native numbat Myrmecobius fasciatus is an exception. It has declined to <10% of its former range because it lacks an effective defence against exotic predators, and is today restricted to habitats where log shelters provide a measure of protection from fox and feral cat.

M Serena - One of the best experts on this subject based on the ideXlab platform.

  • spatial organization and movement patterns of adult male platypus ornithorhynchus anatinus Monotremata ornithorhynchidae
    Australian Journal of Zoology, 1995
    Co-Authors: Janet L Gardner, M Serena
    Abstract:

    Home-range size and overlap and movement patterns of adult male platypus, Ornithorhynchus anatinus, occupying streams in southern Victoria were investigated near the start of the breeding season using radio-tracking techniques. On the basis of a sample of males monitored for four or more complete activity periods, home-range size varied from 2.9 to 7.0 km, with individuals (n = 4) moving a mean net distance of 2.0 +/- 1.4 km per activity period. Longer-range movements were also observed, with one male travelling at least 15 km from one stream catchment to another via an intervening stretch of river. Some home ranges of males were mutually exclusive whereas others overlapped substantially; in the latter case, males largely avoided each other, spending most of their time in different parts of the shared area. All home ranges of males apparently overlapped those of two or more adult females. Three patterns of travel over complete activity periods were recognised, including unidirectional travel (point A to B), return travel (A to B to A) and multidirectional travel with multiple, relatively short-range backtracking. Males occupying overlapping areas often moved multidirectionally and rarely undertook unidirectional travel, whereas the converse applied to males occupying exclusive areas.

  • use of time and space by platypus ornithorhynchus anatinus Monotremata along a victorian stream
    Journal of Zoology, 1994
    Co-Authors: M Serena
    Abstract:

    Radio-tracking and mark recapture methods were used to characterize the spatial organization and temporal activity patterns of free-ranging platypuses in southern Victoria. The study area supported an estimated 1.3-2.1 adult or subadult animals per kilometre of stream in the three summers sampled. The individual home ranges of 15 radio-tagged animals comprised 0.33-2.28 km of stream; animals foraging exclusively in the stream had significantly longer ranges (mean=1.40 km) than animals which also foraged in associated pond habitats (mean=0.64km). Home ranges of grown females overlapped with those of neighbouring grown females, subadult and adult males, and juveniles (subadult and adult male, and subadult and juvenile male also overlapped substantially, only one sexually mature male was trapped at any given point in time, suggesting that adult males may occupy mutually exclusive home ranges in the study area. Most platypuses were observed to den at more than one location: burrow sharing was recorded in the case of a subadult and adult male, two grown females, a grown female and independent first-year female, and two independent first-year females. The mean length of time that nine individuals spent in dens per resting period varied from 11.6-16.7 h. In addition, two grown females remained inactive in dens for longer periods (3-6.5 days) in late May-June.

E. S. De Boer - One of the best experts on this subject based on the ideXlab platform.

  • the foraging ecology of a termite and ant eating specialist the echidna tachyglossus aculeatus Monotremata tachyglossidae
    Journal of Zoology, 1992
    Co-Authors: Max Abenspergtraun, E. S. De Boer
    Abstract:

    This study investigates the effect of food distribution on the selection of foraging habitats, and the relationship between food availability, diet, ambient temperature, activity, use of shelter and energy budgets, in a termite-and ant-eating mammal, the echidna, Tachyglossus aculeatus. In two Nature Reserves in the wheatbelt of Western Australia, 10 adults and six juveniles were radio-tracked for II months during 1988. Animals were weighed monthly and their fresh faeces collected for dietary analysis. Available termite and ant energy was measured simultaneously in habitats where the echidnas foraged: woodland, mallee**, shrubland and heath. Termite energy formed the principal food of echidnas, possibly because of their greater abundance. Highest ingestion rates of termite energy during the hottest time of year may reflect increased moisture requirements. Adult animals preferred woodland and mallee for foraging, possibly because termite and ant energy was highest there. Juveniles exhibited no obvious habitat preference. Echidnas were active year-round, with foraging peaks during spring and autumn, and animals gained weight then. Despite termite energy being highest in winter, echidnas were in negative energy balance during this period, possibly because they make smaller foraging efforts and have higher thermoregulatory costs. Foraging was principally nocturnal in summer, and mixed nocturnal/diurnal in winter. No foraging was observed below 9° and above 32°C, with a preferred range of 16–20°C. Echidnas were not apparently food-limited because: (a) both adult and juvenile animals maintained, or gained, body weight even when termite energy was low; (b) juveniles foraged anywhere, irrespective of habitat, but still gained weight; and (c) there was no evidence for hibernation by wheatbelt echidnas, unlike in other parts of Australia where echidnas routinely hibernate in winter, possibly in response to food shortage. However, echidnas did show signs of short-term torpor. Echidnas were active throughout the year, possibly because food was unlimited, and because use of subterranean shelter reduced thermoregulatory costs. The results of this study suggest that food distribution and ambient temperature play an important role in influencing daily and seasonal foraging activity in wheatbelt echidnas.

  • patch use and prey defence in a mammalian myrmecophage the echidna tachyglossus aculeatus Monotremata tachyglossidae a test of foraging efficiency in captive and free ranging animals
    Journal of Zoology, 1991
    Co-Authors: Max Abenspergtraun, Chris R Dickman, E. S. De Boer
    Abstract:

    Echidnas (Tachyglossus aculeatus) in wheatbelt reserves in Western Australia are primarily termite- and ant-eaters. Using captive and free-ranging animals, we tested whether echidnas respond to high density patches of these prey and also to differences in their mechanisms of defence. When feeding on termites, free-ranging echidnas generally adjusted their foraging effort in response to prey abundance, increasing their rate of energy intake by digging deeper and allocating more time to patches where prey were abundant. Such efficient foraging occurred irrespective of whether termite defence was mandibulate, chemical, or a combination of both, as in Amitermes neogermanus. Echidnas invested little effort in species of Drepanotermes in the field despite their abundance at local food patches, probably because the soldiers are large and aggressive and produce copious quantities of pungent defence secretions. Echidnas also avoided Nasutitermes exitiosus in the field but ingested other species with chemical defence such as Tumulitermes. Captive echidnas decreased their foraging effort on N. exitiosus only when soldiers were abundant (400 per unit area) and the soldier to worker ratio was high (80:20), hence avoidance of this species by free-ranging echidnas may reflect the species'ability to mobilize quickly large numbers of soldiers to colony breaches. When feeding on ants in the field, foraging effort and prey energy in food patches were not correlated, possibly because ants responded rapidly to colony breaches by emerging to meet the predator. More extensive soil excavations by foraging echidnas to capture ants were thus unnecessary, minimizing foraging effort. Captive and free-ranging echidnas rejected ants 7 mm (except in the presence of energy-rich eggs), and > 10 mm long, respectively, reducing foraging efficiency to zero when encountering such prey. With such exceptions, the results suggest that echidnas make efficient use of patchily distributed prey and generally adjust their foraging efforts to match actual energetic returns.

Wigness John - One of the best experts on this subject based on the ideXlab platform.