A Comparison Of Thermoregulation In A Number Of East African Animals

Abstract

Three primate species, the greater galago (Galago crassIcaudatus) the baboon (Paulo cynocephalus) and the chinpaoxoe (Pan satyrus) were exposed to , o environmental temperatures of up to 43 C in a climatic chamber, and their thermoregulatory responses were measured. In the field the thermoregulatory responses to the changes in solar radiation load through the day were measured in the elephant (Loxodonta africana)t the black rhinoceros (Picpros bicornia), the white rhinoceros (Ceralotherium siraum) and the zebra (Emma burchelll). It was necessary to tranqulllise the baboons and the chimpanzees with phencyclidine hydrochloride in order to measure cutaneous moisture loss (C.M.L*) and rectal temperature. Initial experiments were, therefore, carried out to ensure that the tranquilliser was not: 1* having any significant effect on the ability of these animals to thormoregulate. 2. inhibiting their response to sympathetic and parasympathetic drug administration. The tranquilliser was found to have a minimal effect in this respect. The baboon and the chimpanzee increased both their C.M.L. (i.e. sweated) and respiration rate (i.o. panted) on heat exposure. This is in contrast to the galago which was found to use panting as its

only method ot evaporative heat lose* All tho animal a were able to maintain a fairly stable rectal . o temperature on exposure to 40 C. The administration of adrenaline, noradrenaline, acetylcholine, and atropine, both intradormally and intra*venouely, showed that the sweat glands in the baboon and the chimpanzee were under cholinorgic control. In the galago no sweat gland activity could be initiated by these drugs or by local or generalised heating of the animal. A akin sample was taken from each animal and the sweat gland structure described. The measurements of C.M.L. from the rhinoceros and the elephant produced the following results. 1. An Increase in insensible C.M.L. between two sets of experiments twelve months apart. It is suggested that this is associated with the state of hydration or, possibly, with the age difference of the animals. 2. A very high C.M.L. at 07*00 hra. This was sig* nlficantly increased at mid-day in the rhinoceros, i.e. it was sweating| but showed no significant change during the day in the elephant. The rhinooeroe also showed an increase in res* pirstion rate and, therefore, appears to thorrnoreg* ulate by both sweating and panting. Rectal temper* ature through the day in this animal varied by 1.0°C (c.f. Bligh and llerthorn 1965), while the

o diurnal air temperature variation was between 19 C and 31°C. It waa found, however, that the elephant neither eveate nor pants. It ie suggested that it was able to Maintain a relatively stable body temperature in the present experiments (maximum diurnal rectal o temperature variation, 2.0 C, diurnal air temper* ature variation 12.0°C) by the following means: 1. non*evaporative heat loss (convection, con* duction, radiation). 2. a high "insensible" moisture loss through the skin. 3. by means of its ears to lose heat, more esp* ccially in the cooler part of the day. 4. by its behavioural pattern (s.g. shade seek* lug, bathing, and spraying with exogenous water). The sebra was found to have an increase in C.M.L. during the day, like other equines, and also an Increase in respiration rate. Rectal temperature increase in these animals varied between 0.6°C and o o 2.9 C as air temperature increased from 20 C to 31°C. The results obtained are then discussed on a comparative basis