Biomedical subjects

M Lindeque

Publications and source records attributed to M Lindeque.

4 recordsLinked to original sources

PubMed1997

The influence of surface atmospheric conditions on the range and area reached by animal vocalizations.

Low-level vertical changes in temperature and wind exert powerful and predictable influences on the area ensonified by animal vocalizations. Computer modelling of low-frequency sound propagation in measured atmospheric conditions predicts that the calls of the savanna elephant at these frequencies can have ranges exceeding 10 km and that the calls will be highly directional in the presence of wind shear. Calling area is maximized under temperature inversions with low wind speeds. Calling area changes substantially over 24 h periods; on any given day, the calling area undergoes an expansion and contraction which may be as large as one order of magnitude. This cycle is modulated by topography, regional weather patterns, seasonality and possibly by climate variation. Similar influences affect the somewhat higher-frequency calls of lions and may be a selective pressure towards their crepuscular and nocturnal calling behaviour. Coyotes and wolves, which also live in areas with strong and prevalent nocturnal temperature inversions, show similar calling patterns, maximizing their chances of being heard over the longest possible distances. The pronounced dawn and evening vocalization peaks in other animals including birds, frogs and insects may reflect the same influences in combination with other factors which selectively limit high-frequency sound propagation. Atmospheric conditions therefore need to be taken into account in many field studies of animal behaviour. A simplified method for estimating sound propagation during field studies is presented.

Animals↗

PubMed1995

Atmospheric controls on elephant communication.

Atmospheric conditions conducive to long-range transmission of low-frequency sound as used by elephants are found to exist in the Etosha National Park in Namibia during the late dry season. Meteorological measurements show that strong temperature inversions form at the surface before sunset and decay with sunrise, often accompanied by calm wind conditions during the early evening. These observations are used in an acoustic model to determine the sensitivity of infrasound to the effects of (a) the strength, thickness and elevation of temperature inversions, and (b) the growth and decay of an inversion typical of dry, elevated African savannas. The results suggest that the range over which elephants communicate more than doubles at night. Optimum conditions occur 1-2 h after sunset on clear, relatively cold, calm nights. At these times, ranges of over 10 km are likely, with the greatest amplification occurring at the lowest frequency tested. This strong diurnal cycle in communication range may be reflected in longer-lasting changes in weather and may exert a significant influence on elephant behaviour on time scales from days to many years.

Acoustics↗

PubMed1986

Adrenal and gonadal contribution to circulating androgens in spotted hyaenas (Crocuta crocuta) as revealed by LHRH, hCG and ACTH stimulation.

Single venous blood samples were collected from 52 hyaenas and serial samples via indwelling jugular catheters from 8 hyaenas. Social status of the hyaenas was unknown. Radioimmunoassay estimations were specific for testosterone, androstenedione, cortisol and LH. No significant differences could be found between the sexes for concentrations of testosterone (adult males 2.9 +/- 1.3 nmol/l; adult females (non-pregnant) 1.6 +/- 0.3 nmol/l). Androstenedione concentrations in sub-adult males were significantly lower than those in females (2.3 +/- 0.05 and 5.5 +/- 1.2 nmol/l). Testosterone and androstenedione concentrations were significantly higher in parous pregnant than in parous non-pregnant females (4.3 +/- 1.4 and 1.6 +/- 0.3; and 23.7 +/- 11.6 and 6.7 +/- 0.9 nmol/l respectively). Both LHRH and hCG elicited elevated androgen concentrations in females in different reproductive categories. Androgens are produced by the ovary in the absence of follicular or luteal structures, indicating androgen production by the interstitial tissue of the ovarian stroma.

Adrenal Glands↗

PubMed1982

Fetal androgens and sexual mimicry in spotted hyaenas (Crocuta crocuta).

Sexual differentiation of the Müllerian duct system and gonad in female fetuses conformed to the general mammalian pattern, whereas the external genital anlage in male and female fetuses developed into the male facies. Interstitial cells occurred in the primary germinal cords of both male and female fetal gonads and are suggested to be the source of androgen production in spotted hyaena fetuses. Maternal transfer of androgens to the fetus via the placenta was negligible. Male fetuses had higher gonadal and plasma concentrations of testosterone than female fetuses, and vice versa for androstenedione. Plasma testosterone was nearly as high in a female 31-day-old fetus as in the twin male, and masculinization of the genital tubercle probably results from an episode of androgen secretion by the fetal gonad although the Wolffian ducts in the female do not respond.

Adrenal Glands↗