Biomedical subjects

J Speakman

Publications and source records attributed to J Speakman.

17 recordsLinked to original sources

PubMed1997

Factors influencing the daily energy expenditure of small mammals.

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Animals↗

PubMed1995

Daily variations in the response of wood mice Apodemus sylvaticus to noradrenaline

Non-shivering thermogenesis (NST) is an important mechanism for heat production in many small rodent species. Daily rhythms of body (rectal) temperature (Tb) reflect the relationship between heat production and heat dissipation. The roles of photoperiod and the time of day at which NST is measured were studied in wood mice Apodemus sylvaticus. Mice of both sexes (N=18) were acclimated to two different photoperiod regimes (16 h:8 h L:D and 8 h:16 h L:D) at a constant ambient temperature (Ta) of 24 °C. Non-shivering thermogenesis was measured as the maximal response of oxygen consumption (V(dot)O2NA) and body temperature (TbNA) to a noradrenaline (NA) injection (1.5 mg kg-1 subcutaneously) in unanaesthetized mice at three different times in the daily rhythm of Tb (N=6 in each group). Mice acclimated to 8 h:16 h L:D had a greater response to noradrenaline at the three different times of the day compared with those acclimated to 16 h:8 h L:D. The extent of the response to noradrenaline within each group varied with time of day; the smallest response was recorded at 18:00±1.5 h, and the greatest was at 01:00 h. These results suggest that photoperiod is an important cue for seasonal acclimatization in this species and that the response to noradrenaline follows a daily rhythm.

Journal Article↗

PubMed1994

ENERGY SAVINGS IN FORMATION FLIGHT OF PINK-FOOTED GEESE

Fifty-four skeins of pink-footed geese (Anser brachyrhynchus) were photographed from directly underneath to eliminate the effects of perspective distortion, and the wing-tip spacings (the distance between adjacent birds' wing tips perpendicular to the flight path at maximum wingspan) and depths (the distance between adjacent birds' body centres parallel to the flight path) were measured at the same time as local wind speeds. The photographs were used to test for savings in induced power from wing positioning relative to the predicted positions of vortices generated by other wings, using a theoretical model. The mean wing-tip spacing corresponded to a saving in induced power of 14 %, less than one-third of the maximum possible. The saving in total power might be as low as 2.4 %. The high variation in wing-tip spacing suggests that pink-footed geese found difficulty maintaining position and thus adopted a strategy of flying outboard of the optimal position that maximises savings. This may minimise the risk of straying into a zone where savings are negative. There was a significant correlation between depth and wing-tip spacing, supporting an alternative communication hypothesis, whereby the birds position themselves to obtain maximum information on their neighbour's position. In high winds, there was little change in wing-tip spacing variation but a decrease in depth variation, suggesting a shift towards more regularly spaced skeins.

Journal Article↗

PubMed1982