EFFECT OF CONTROLLED TEMPERATURES ON GAMETOGENESIS IN THE GASTROPODS PHYSA ACUTA (PHYSIDAE) AND BULINUS TROPICUS (PLANORBIDAE)

The effects of a range of constant temperatures on gametogenesiswere investigated in two freshwater snail species which occursympatrically in the Umsin-dusi River, Natal, South Africa,Physa acuta (invasive) and Bulinus tropicus (endemic). Bothwere shown to be simultaneous hermaphrodites with slight protandry.An increase in temperature accelerated the process of gametogenesisbut P. acuta responded more rapidly to these changes than B.tropicus. This, coupled with the greater fecundity and shorterincubation period of P. acuta, gives it a reproductive advantageover the endemic species, providing a possible explanation forthe invasive's success in rapidly repopulating disturbed riverinehabitats. (Received 16 November 1990; accepted 1 May 1991)     

MORPHOLOGY OF THE MATURE SPERMATOZOON OF PHYSA ACUTA (DRAPARNAUD, 1801) (GASTROPODA: PHYSIDAE)

The morphology of the spermatozoon of Physa acuta (Draparnaud,1801) was examined using TEM. It was found to be of the modified-type,sharing characteristic features of other basommatophoran species.However, differences were noted in some cases, for example,in P. acuta the nucleus was torpedo-shaped with two helicalkeels, the midpiece possessed a maximum of three glycogen helices,the end piece was long and tapered and the total length of thespermatozoon was 365 µm. No identical spermatozoa havebeen found in other basommatophoran gastropods studied so far.If spermatozoon morphology is unique for individual specieswithin the genus Physa, it may provide a useful taxonomic toolin helping to clarify the uncertainty that surrounds the systematicsof this genus. (Received 26 February 1990; accepted 28 June 1990)     

Physiological Responses Of Birds To Flight And Running

1. The energy required for sustained physical activity in flying and running birds is obtained from fatty acids mobilized from adipose stores under the influence of hormones. There is some evidence that glucagon, insulin and growth hormone may be involved in this process. 2. Energy expenditure can increase up to 14 times and 12 times resting values in flying and running birds, respectively. Energy expenditure varies only slightly over the normal range of flight speeds in individual species, but in running birds there is a linear correlation between oxygen consumption and speed. The slope of this relationship is an inverse function of body weight and indicates the energy cost of transport in ml O₂.kg^-1.m^-1. 3. Increased oxygen demands by the working muscles are met by increased ventilation and circulation. Increased oxygen delivery by the blood is achieved by rises in cardiac output and oxygen extraction. Cardiac stroke volume changes relatively little and the increased cardiac output results mainly from an increase in heart rate. Regional blood distribution during exercise may be determined not only by the demands of the locomotory muscles but also by the need to increase heat loss from the skin and respiratory tract. 4. Ventilatory movements during flight are frequently synchronized in a I:I fashion with wing movements. Increased ventilation during flight and running may be stimulated, not only by the need for increased gas exchange, but also in order to raise heat loss by respiratory evaporation. Thermal hyperventilation carries a risk of CO, washout from the lungs and consequent blood alkalosis. The risk is minimized in some species by appropriate alterations in the rate and depth of breathing, which help to confine excess ventilation to the respiratory dead space. 5. Metabolic heat produced during exercise is either lost from the respiratory linings and the skin, or stored by the body with a resultant rise in body temperature. Changes in peripheral blood perfusion and active regulation of the feathers may assist cutaneous heat loss. Respiratory evaporation usually accounts for less than 30% of the total heat loss, even at high air temperatures, and becomes progressively less efficient at higher exercise intensities. At high air temperatures and high exercise intensities, most of the metabolic heat is stored, and exercise duration is limited as the body temperature approaches the upper lethal limit.     

A COMPARATIVE STUDY OF THE MATURE SPERMATOZOA OF BULINUS AFRICANUS (KRAUSS, 1848) AND B. GLOBOSUS (MORELET, 1866) (GASTROPODA: PLANORBIDAE)

The morphology of the mature spermatozoa of the closely-relatedfreshwater pulmonates, Bulinus africanus and Bulinus globosus,was examined using scanning and transmission electron microscopy.A comparison showed no useful differences that could be usedto distinguish the species though they did differ in one respectfrom Bulinus tropicus, the only other bulinid for which spermmorphology is known. (Received 12 August 1996; accepted 6 December 1996)     

Novel locomotory mechanisms in caterpillars: life-line climbing in Epinotia abbreviana (Tortricidae) and Yponomeuta padella (Yponomeutidae)

Abstract. When alarmed, caterpillars of the tortricid Epinotia abbreviana (Fabricius) and the yponomeutid Yponomeuta padella (Linnaeus) parachute at the end of a single life-line spun out by the head spinnerets.Two methods are employed to climb back up the line.The first makes use of alternate movements of the left and right set of thoracic legs, aided by side-to-side movements of the body.This results in the life-line being wound in around the third pair of thoracic legs.The second method is based on the normal peristaltic rhythm used when walking on a solid substrate.Dorsoventral curling movements gradually transfer life-line from the thorax along the succession of abdominal pro-legs to the claspers at the end of the body.The life-line has similar physical characteristics to spider orb-web silk, and a breaking force equivalent to 5–8 times body weight.The holding force of the claspers when in contact with the ground exceeds the breaking force of the life-line.These studies demonstrate the flexibility of caterpillar locomotion, when confronted with a novel situation.