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A thesis submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Doctor of Philosophy. Johanneburg, 2010. / Unable to load abstract

A Dissertation submitted to the Faculty of Science, University of the Witswatersrand, Johannesburg, in fulfilment of the requirements for the degree of Master of Science Johannesburg February 2013 / Foraging is an essential part of an animal’s everyday life, during which it has to balance out many costs and rewards while making decisions on where, what, when and how to forage. The aim of my study was to investigate how different cost/benefit foraging scenarios affect foraging decisions in captive Bushveld gerbils. The foraging behaviour of Bushveld gerbils was studied in four experiments to establish the effect of cost/benefit scenarios on their foraging behaviour, specifically I tested i) how much gerbils will work for seeds of different quality; ii) how seed presentation (piled/scattered) influences foraging behaviour; and iii) the effect of potential predation risk on foraging decisions. Initial seed preference studies for five commercially available seeds (sunflower, sorghum, oats, maize and wild rice) indicated that the gerbils displayed individual seed preferences, and this information was then used to tailor the experiments to the preferences of individual gerbils. The experimental apparatus consisted of 2 joined tanks, one of which, the experimental tank, was designed to impose a cost (weighted door) to access reward (food). The weight of the door was altered to create a low cost door (light door) or a high cost door (heavy door) that was individually tailored to the gerbils by using their individual body weights to create a heavy door approximately the same weight as the gerbil. Most and least preferred seeds were used to create a high reward and a low reward, respectively. Using the door in combination with the preferred seeds, 4 treatments were created, namely, low cost low reward, low cost high reward, high cost low reward, and high cost high reward. These treatments were run in 4 different experiments that were designed to assess the decisions Bushveld gerbils made during foraging. My results indicated that the gerbils employed foraging strategies which, firstly, favoured a reduced cost, possibly linked to reduced energy expenditure, and secondly, gaining the highest rewards. The gerbils consumed less in high cost and low reward treatments, and consumed more in low cost and high reward treatments. The data also revealed that the presentation of the seeds influenced foraging decisions, where seed consumption and exploratory behaviour differed when seeds were piled rather than scattered, depending on the cost/reward structure. Under potential predation risk, the gerbils employed predator avoidance strategies by using cover more and reducing foraging, indicating they were trading-off foraging against predation risk. Demand curves generated to assess decision-making indicated that the gerbils made consistent decisions except under particular circumstances, such as when there was a large difference in food value and cost. Ultimately, my study showed that Bushveld gerbils change their foraging decisions in a predictable way to exploit low cost and high reward situations. Their decision-making was largely inelastic, indicating that foraging decisions were similar under different circumstances, except when there is a large discrepancy between the qualities of seeds presented.

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Mongolian Gerbils with lesions in the ventromedial hypothalamus show two major similarities with rats lesioned in the same area: an unusually long meal soon after surgery (acute dynamic period), and changes in day-night feeding patterns (chronic dynamic period). They do not share the hypoactive and ragic behavior of the ventromedial hypothalamically-lesioned rat. Tests and observations showed little or no difference between the general demeanor of lesioned and normal animals.

A model for experimental cecal and hepatic amebiasis was developed and characterized in the gerbil (Meriones unguiculatus). Pathogenic and non-pathogenic Entamoeba histolytica strains were shown to cause damage in the cecum, proportional to their previous behavior in humans. Secretion of intestinal mucus, crypt hyperplasia and cytolysis of interglandular epithelium were prerequisites for amebic invasion. Ulcerative lesions with destruction of mucosal and submucosal tissues led to amebic dissemination to the liver. Formation of amebic liver abscesses followed subacute changes in the liver. Liver lesions resulted from the cytolytic effects of the enzymes of destroyed neutrophils. Growth of liver abscesses followed cytolysis of the fibrogranuloma walls. Immunodepression in amebiasis was confirmed by serologic findings and histologic alterations in the lymph nodes and spleen, and by a lowered antiamebic effect of lymphoid cells in vitro. A neutrophil stimulating and chemotactic factor from pathogenic amebic membranes was isolated and characterized. It was shown that both host and parasite factors are involved in the pathogenesis and pathology of amebiasis.

Agonistic behaviour was investigated by means of staged encounters in three species and two subspecies of deserticolous rodents of the genus Gerbillurus Indiviuals of the species G.paeba paeba, G.paeba exilis, G. tytonis, G. setzeri, and G. vallinus were used in intraspecific and interspecific encounters. Intraspecific territoriality was tested in animals of the same sex G.paeba paeba, G. tytonis, and G. setzeri Analysis of agonistic behaviour permitted identification of four groups of behaviours in most classes of intraspecific encounters. These were "exploratory and solitary", "aggressive", "submissive", and "sexual" behaviours. Males of four species were less aggressive than females in same-sex encounters, and were dominated by females in different-sex encounters; the reverse was observed in G. setzeri. Male G. tytonis and G. setzeri were more tolerant of conspecifics in the territoriality apparatus than females were. In G. tytonis-G.p. paeba encounters a hierarchy emerged: female G.. tytonis were most aggressive, followed by female G.p. paeba, male G. tytonis, and finally male G.p. paeba. In areas of syntopy, G. tytonis displace G.p. paeba through aggressive interactions. A reduction in the level of aggression was exihibited in G.p. paeba-G. setzeri and G. tytonis-G. interactions. This result may reflect the phylogenetic divergence and selection of a different habitat by G. setzeri. G. vallinus dominated G.p. paeba, a result which may have been influenced by past experience and body size, since these two species are syntopic and G. vallinus is larger than G.p. paeba. Cluster analysis of behaviour profiles of different species and sexes revealed two groups, which agree partially with the karyology of the genus. G.p. paeba and G. tytonis formed one cluster, while G. setzeri and female G.p. exilis formed a second group. Male G.p. exilis and G. vallinus were less closely related to both groups. It is suggested that several stages in the process of speciation are represented in species of this genus . A range of social types is exhibited from solitary (G.p. paeba and G. tytonis) through semi-tolerant (G. setzeri and G. tytonis) through semi-tolerant (G. setzeri and female G.p. exilis) to tolerant (male G.p. exilis and G. vallinus). Habitat has a strong influence on social type. / Thesis (M.Sc.)-University of Natal, Pietermaritzburg.

To determine the effects of different social conditions on play and agonistic behaviour, 25-day old golden hamsters and Mongolian gerbils were divided into four groups which differed with respect to social experience after weaning. Every day, from 26 to 61 days of age, the young hamsters were observed for numbers and durations of fight-type interactions in a 15-minute period. Every third or sixth day from 27 to 60 days of age, the gerbils were similarly tested. Seven to 14 percent of play fights between hamsters involved more than two animals simultaneously. Communally reared hamsters mixed with strangers played with strangers 71 percent of the time, while 90 percent of real fights involved strangers. Neither of these measures involved the effects of early social experience. Isolation causes earlier cessation of play and earlier onset of real fights in golden hamsters. Isolation also leads to a significant increase in the amount of play and real fighting in these animals. Gerbils raised in isolation with a toy show significantly more play than do gerbils reared under different social conditions. Gerbils reared communally with the mother fight significantly more with strangers than they do with familar animals, and fight significantly more than do animals reared communally with siblings, or in isolation with or without a ping pong ball. / Science, Faculty of / Zoology, Department of / Graduate

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