Shirley A. Hanrahan

Lizard herbivory in a sand dune environment: the diet of Angolosaurus skoogi

SummaryEarly observations of the feeding habits of Angolosaurus skoogi (Andersson), a 50–120 g lizard inhabiting the almost vegetationless dunes of the northern Namib Desert, indicated that this species was herbivorous. Less than two percent of living lizard species are predominantly herbivorous and these species tend to have a high body mass (>100 g). We therefore analysed fecal pellets of A. skoogi to obtain dietary details of this relatively rare lizard. Eighteen food taxa were identified: 81 percent by mass was composed of vegetable matter, of which 56 percent was an endemic, perennial cucurbit Acanthosicyos horrida. Both spatial and temporal variation in dietary composition were apparent. Ready access to water in the form of A. horrida is postulated to have allowed Angolosaurus to occupy this extreme habitat and to forage on components of the windblown detritus, a food source that would probably not be usable in other circumstances.

Ultrastructure of the malpighian tubules of Onymacris plana plana peringuey (Coleoptera : Tenebrionidae)

Abstract The structure of the free segment of the malpighian tubules of Onymacris plana plana Peringuey (Coleoptera : Tenebrionidae) has been examined to complement observations on tubule activity (Nicolson and Hanrahan, 1986). O. plana lives in arid conditions in the Namib desert and may be subject to periods of desiccation and to fogs when humidity is high. Cell structure of malpighian tubules from the following were examined; beetles from the field, beetles kept in humid and arid laboratory conditions, in vitro tubule preparations treated with substances such as CAMP and corpora cardiaca extract. The free segment is composed of a longer yellow distal region and a shorter colourless proximal region. Type 1 and Type 2 cells were present in the distal region, the latter being few in number, irregular in shape, and relatively small. Type 1 cells varied in appearance when the tubules were exposed to different conditions. Laminate spheres were common in these cells when the beetles had been desiccated, either under laboratory or field conditions. Few were present in the tubules of insects kept in water balance. Exposure to dilute Ringer or cAMP caused the channels between the basal infoldings to widen. Exposure to extracts of brain or corpora cardiaca containing diuretic hormone did not have this effect. In dehydrated beetles, the laminate spheres did not disappear when the tubules were treated with diuretic hormone. Type 1 cell structure is influenced by the conditions that the beetle experiences.

Sperm competition in the Namib Desert beetle, Onymacris unguicularis

Abstract Sperm competition occurs when a female remates before her initial sperm supply is exhausted. Sperm remained viable in a female Onymacris unguicularis (Haag) (Tenebrionidae: Coleoptera) for 7 weeks, but laboratory observations showed a mean number of 5 days between matings. An anatomical basis for sperm displacement was indicated whereby the previous spermatophore was ejected from the female during a subsequent mating. Using the sterile-male technique, there was shown to be a large measure of sperm precedence from the last male to mate with the female.

Assimilation efficiency and gut passage time in an African elapid snake, Hemachatus haemachatus

Abstract We measured apparent assimilation efficiency (AAE) and gut passage time in the African elapid snake Hemachatus haemachatus under laboratory conditions. AAE was dependent on food type, being 89.8% when snakes were fed frogs and 82.8% when fed mice. Differences in AAE for different meal types could be ascribed to the indigestible hair in mouse meals because differences were lost once this component of the mouse meals was removed from the calculation. AAE did not depend on snake body mass and there was no significant difference between AAE measures made at 20°C and 27°C for mouse meals. Gut passage time was 25% faster at 27°C than at 20°C, but was not affected by food type or snake body mass. Larger meals took longer to digest. Thus, H. haemachatus appears to offset reduced digestive performance at lower temperatures by retaining food in the gut for longer when at lower body temperatures (Tbs). These results fit an emerging pattern in snakes whereby digestive efficiency is generally high and insensitive to Tb over the selected thermal range, but may become dependent at lower Tbs when digestion is eventually arrested. The rate of digestion is highly temperature-sensitive and is fastest in the selected Tb range. Diet appears to affect digestive efficiency owing, mainly, to the presence of indigestible components such as hair. Using a comparative framework, venom does not appear to improve digestion for this species, at least over the temperature range tested, relative to other snake species in the literature.

Metabolic rate in diapause and nondiapause brown locust eggs correlated with embryonic development

Insects use dormancy to survive adverse conditions. Brown locust Locustana pardalina (Walk.) eggs offer a convenient model to study dormancy (diapause and quiescence), which contributes to their survival under arid conditions. The metabolic rates of developing nondiapause, diapause and quiescent eggs are compared in the present study using closed‐system respirometry. The embryo becomes committed to continue development and hatch or to enter diapause 6 days after the eggs are placed on moist soil. The metabolic rate of nondiapause eggs increases exponentially until hatching, whereas that of diapause eggs is low and stable. The metabolic rate of diapause laboratory eggs (1.9 ± 0.6 µL CO2 mg−1 h−1) is significantly higher than that of field eggs (0.5 ± 0.3 µL CO2 mg−1 h−1), although the ranges of metabolic rate overlap and the embryos are all in late anatrepsis. The metabolic rate of quiescent eggs is similar to that of diapause eggs but decreases with time. Low metabolic rates during arrested development allow eggs to persist over long periods before hatching.

Larval structures associated with larva-to-adult trophallaxis in Platythyrea (Hymenoptera : Formicidae)

Abstract Larvae of Platythyrea arnoldi, P. modesta, P. schultzei and P. sp. (Hymenoptera : Formicidae) were found to have a well-developed, distinctive median tubercle on their 7th abdominal sternites. The first 2 species also had a tubercle on the 8th abdominal sternite. Specialised epithelial cells surround a deep invagination that opens through an orifice to the base of the tubercle on the 7th abdominal sternite of at least 3 of the species. P. lamellosa has a poorly developed tubercle. A secretion was seen at the base of the tubercle of a P. arnoldi larva, and adult ants of this species and of P. sp. and P. schultzei were often seen licking the posterior face of the tubercles for extended periods. They were feeding on a secretion originating from the orifice beneath the tubercle.

The effect of wind on foraging activity of the tenebrionid beetle Lepidochora discoidalis in the sand dunes of the Namib Desert

The foraging activity of the tenebrionid beetle, Lepidochora discoidalis, was studied in the sand dunes of the Namib Desert. The surface activity of this beetle species was found to be correlated both with time of day and wind speed. Higher numbers were observed on the dune surface between 17:00-19:00 h when wind speeds were consistently higher than 9 m/s. Noise and vibrations in the dune sand were found to be highly dependent on wind speed. Wind blowing at speeds higher than 5 m/s lifts the surface sand grains and generates vibrations in the sand. The peak frequency of these vibrations is in the range of 700-1000 Hz. The vibrational amplitude at the peak frequency is on average 40 dB higher at those wind speeds when the beetles are active compared to lower wind speeds. The results indicate that wind is an important cue for these beetles and can be perceived by buried beetles through substrate vibrations.

Respiratory patterns in field collected brown locust, Locustana pardalina, in the gregarious phase

In this paper we report on the metabolic rates and respiratory patterns measured from gregarious brown locusts, Locustana pardalina, collected from the Nama Karoo region in South Africa. All five instar hopper stages and adults were collected over a three year period when significant numbers of locust swarms were seen. Flow-through respirometry was used to measure the CO2 emission from individual locusts from all the developmental stages and adults within a week of collection. Carbon dioxide emission scaled hypometrically with mass, 0.863 ± 0.026. Except in the 1st and 5th instar stage there was no difference in the mass specific rate of CO2 emission (V̇CO2). These had significantly higher metabolic rates compared to the other stages which reflects their biology, with the 1st instar undergoing rapid growth and the 5th instar also undergoing rapid growth and development in preparation for becoming an adult. The 1st instars used a form of continuous gas exchange while all the other stages showed discontinuous gas exchange cycles. A clear burst phase and interburst periods could be seen. The 2nd and 3rd instars use mainly diffusion to expel CO2 and so exhibited an open form of the burst phase. There was an increase in CO2 volleys seen in the burst phase from the 4th instar stage onwards thus indicating an increased use of convection. There was no change in the duration or frequency of the discontinuous gas exchange cycles through the locust development or with body mass.

Amoebiasis and its Effect on Cell Division in the Midgut of the African Migratory Locust

Malameba locustae (King & Taylor), a protozoan parasite of many laboratory-reared locusts, is known to damage epithelial cells of the host midgut regions. Mitotic and labelling indices in both caecal and ventricular regions of parasite-free and infected Locusta migratoria migratoriodes (Reiche & Faimaire) were investigated in the laboratory. Infected locusts were found to have significantly higher mitotic index values in both regions of the midgut than those found in parasite-free locusts. No significant differences were found in the labelling index between infected and parasite-free locusts indicating that one of the gap phases in the cell cycle becomes altered. This would account for the observed increase in cell division. A significantly larger number of cells was noted in the nidi of the ventricular regions of locusts infected with parasites.