Extract from: Comparative Ecophysiology of two Varanids in the Sahelian Milieu (Senegal)

Transcription

1 Extract from: Comparative Ecophysiology of two Varanids in the Sahelian Milieu (Senegal) Doctoral thesis of Mamadou Cissé (La Faculte des Sciences et a l Institute Fondamental d Afrique Noir (University of Dakar)). Submitted to the University of Nice, 11 th January ST5809 Pages Translated by Daniel Bennett. Translator s note. These translations are from a pdf copy of the manuscript available online from the Bibliothèque Centrale de l Université Cheikh Anta Diop de Dakar. A few pages are missing, the pictures are mostly illegible and the quality of the pages is insufficient for accurate text character recognition. It appears to be a scan of a photocopy. In the absence of a better copy of the work, and mindful that my French is very poor and this translation has been done in a hurry and not been checked, I have included my transcript of the original text as an editable document. Mamadou Cisse was born in Senegal in His PhD thesis is the most detailed account of the life cycle of Varanus exanthematicus ever undertaken. With the exception of a citation in Buffrenil (1993) it appears to have remained unnoticed for almost 40 years. None of the chapters were ever published and Dr Cisse left his position at IFAN in I have been unable to find any subsequent record of him. The PhD appears to be work conducted after 1976, and uses samples unconnected with his earlier (published) work on savannah monitors. Despite its long period of latency, dissemination of Dr Cisse s contribution is particularly timely because of the growing recognition that no acceptable husbandry regime has ever been demonstrated for Varanus exanthematicus, despite it being by far the most abundant monitor lizard in captivity. In boxes the animals fill with fat and die very early. His observations on the annual cycles of the lizards will hopefully inspire keepers to find ways to maintain the animals acceptably in captivity, or abandon the species as a suitable pet species. I am grateful to the secretary at IFAN for providing details about Dr Cisse, and to Joshua Richholt for technical help with retrieving the PDF file. Daniel Bennett Glossop, 18 th March De Buffrenil, V Les Varans Africains. Varanus niloticus and Varanus exanthematicus. Donnees de syntheses ur leur biologie et exploitation. CITES, Geneva

2 [page 270] Chapter 4. General conclusions of the experimental study These experiments highlight the influences of temperature, moisture, reserve fats and the state of hydration of the internal environment on the chronobiology of Varanus exanthematicus. The low temperatures (below 24oC under the Sahelian climate of Senegal) seem to inhibit the physical activity of the Varanus as well as the whole of their gonado-endocrine system with the exception of the pancreas. The high temperatures (between 24 and 30oC in a humid atmosphere) stimulate, on the contrary, all the physiological processes of the animals, without, however, appearing to have an appreciable influence on the evolution of the Langerhans flows..- As for the reserve fats, their presence seems necessary to the reactivation of the gonadoendocrine system which occurs before the restoration of the feeding behavior during the annual cycle. [271] With regard to the hydric state of the internal environment, its influence would be even more decisive than that of previous parameters; artificial hydration of the Varans during the fasting period causes an anticipated recovery of all vital processes, not only in normal animals, but also in those with fat bodies removed. But, it is remembered that during the annual cycle, endocrine and metabolic gonad reactivation is accompanied by intense lipolysis and increased internal hydration. Now it follows that the mobilization of reserve fertilization would be carried out in a certain way by the water which results from their lysis. These considerations make it possible to predict the determinism of the phases of the annual cycle of Varanus of the Sahel. 1o. Early Latency At the end of the rainy season, while the Varanus are still feeding, the temperature of the biotope drops, leading to a numbness of organisms. This state is gradually aggravated by the rarefaction of the preys and the decrease in the ambient humidty resulting in a dehydration of the internal environment. There is then a gradual decline in endocrine activity [272] followed by a halt with, sometimes, tissue alterations. Thus, the freshness of the end of rains, as an inhibitory factor of the physical activity of the Varans, predisposes them to starvation, one of the major causes of which is bodily dehydration. This being. moreover, favored by the fall of the ambient hygrometry, would be at the origin of the physiological blockage, translating it among others: by the abolition of the food need. The organism is thus prepared to undergo the rigors of the hard season. What name should be given to the latency life of Varans during the dry season? Is this a diapause which designates in Insects "a phase of slowed down life with compulsory character "or a quiescence" simple functional blocking immediately reversible upon return of suitable conditions "(SACCHI and TESTARD, 1971) To decide whether to recall the characteristics that these authors attribute to the two physiological states In the case of diapause, the insect approaches the difficult period by a complex physiological preparation; it is at the beginning of the diapause that one usually attends the cessation [273] of the mitotic processes, to a certain dehydration of the tissues, to the slowing down of the respiration, therefore; lowering

3 energy metabolism and increasing lipid content. This gradual transformation results from complex hormonal correlations, in response to environmental stimuli that annihilate a deterioration of the climate. This adaptive reaction is in principle necessary to the normal development of the life cycle of the animal that manifests it. As for the quiescence, it is only a transitory state of rest immediately imposed on the organizations by the external conditions and so they are released immediately by the return to more favorable conditions. Referring to these precisions, we are attempting to consider the latency state of Varanus exanthematicus as a diapause. Indeed, as we have seen in the 1st and 2ns and parts, the characteristics of this latency closely recall those that SACCHI and TESTARD, 1971, defined as being typical of diapause. In particular, in Varanus exanthematicus, a physiological preparation is expected at the entry into the dry season; increase in organic lipids, involution of the gonadoendocrine system and slowing of [274] metabolic processes. In addition, this latency seems necessary for the survival of animals and a season where life conditions are hardly suitable. If feeding behavior was to persist in Varanus exanthematicus, the animal would probably starve for lack of food. But as far as Varanus niloticus is concerned, its rest in the dry season would be a quiescence imposed apparently by the lack of water in its vital domain and immediately interrupted when the Qnimal is in the presence of water (it is remembered that when water was presented to the two Varans rested during the dry season, only Varanus niloticus drank. 2o Late latency Towards the end of the dry season, while Varans are still fasting, the temperature and humidity of the environment is increasing. The rise of these two parameters has the value of a stimulus that would be perceivedat the level of specific receptors in connection with the activators of metabolism including lipolytic agents. There is fat mobilization with release of water. This water rehydrates the tissues that revitalize the energy provided by the fatty acids [page 275 missing!] [276] 4 th Part. Discussion and Conclusion [277]4 th Part. Discussion and Conclusion The Varans, Lacertilian reptiles of the Varanid family originate in South East Asia from the genus Telmasaurus of the late Cretaceous of Mongolia. They are represented today by the only genus Varanus whose species are confined to the Old World (Asia, Australia, India, Soviet Union, Middle East and Africa with the exception of Madagascar). The family has reached the African continent during the Micoene and is represented in Senegal by two species: Varanus exanthematicus (Bosc) and Varanus niloticus niloticus (Linnaeus). The Senegalese environment is characterized by a Sahelian climate divided into two contrasting seasons, a dry season from January to June and a wet season from July to December. The present work has tried to highlight some of the mechanisms of the adaptation of Varans to this environment. [278] From the ecological point of view, the two species living in Senegal presented an annual cycle of activity tracing the rhythm of the seasons. They are at rest during the dry period and active during the wet season. However, the latency modalities vary from one

4 to the other species according to the conditions of the environment: Varanus exanthematicus invariably begins diapause from the end of December to the end of June, whereas Varanus niloticus enters latency only if the water runs out in its vital domain. During the active period, the two Varans have a comparable life: they manifest themselves only during the day; they are diurnal Reptiles. They have a strictly carnivorous diet, Varanus exanthematicus preferring live invertebrates and Varanus niloticus feeding on all living or dead prey. 2) The analysis of the sexual and endocrine cycles has shown that these biorhythms are also related to the evolution of climatic factors. In general, the gonads and endocrine glands are resting during the dry season and active during the wet season. In fact, this table is nuanced according to the times of the year. It is [illegible [279] as well as these structures are at complete rest only from January to April, rest besides interrupted by an abortive testicular shoot in February. They resume their activity from May, 2 months before the first rains and the resumption of food. Also in November, that is to say 2 months before the beginning of the dry season, are shown the first signs of the gonado-endocrine involution that leads to rest in January. Thus, the sexual and hormonal cycles are 2 months ahead of the rain cycle, but in phase with the thermo-hygrometric evolution of the biotope. But, endocrine evolution itself, has specific peculiarities in relation to the circannual behavior of the animals. Thus, during the resting period, it is possible to find in Varanus niloticus individuals having the intermediate pituitary gland and the active pancreas. These are probably animals living near a permanent waterhole and therefore not subject to quiescence during the dry season. [280] 6o As for the metabolic cycles, they were studied only in Varanus exanthematicus. That species alone presents, in fact, a regular eating behavior that is characterized by a complete fast during the dry season. In this species, therefore, the study of the evolution of reserve lipids and hepatic glycogen, on the one hand, and circulating metabolites, on the other, was carried out. A0 lipid glucido metabolism a1) From November to April Immediately after the end of sexual activity, at the beginning of November, lipiogenesis predominated, followed, from February to April, by a cessation of objective lipid metabolism by the absence of ILFA in the serum in March and April. From the glucose point of view, the blood glucose level goes down in November-December at a relatively low rate which remains constant at the beginning of the rest phase. Hepatic glycogen steadily decreases from January to April and suggests carbohydrate use during this period. [281] A2 May to October This period corresponds to the gonadal maturation which is reached in September, the egg laying occurs at the end of October and beginning of November. Carbohydrates and lipids show a reverse evolution of the previous one. Hepatic glycogen and reserve fat undergo intense lysis in May and June. They then come down to a rate that is constantly reduced until October despite the resumption of food since July. On the other

5 hand, cholesterol and phospholipidemia increase. The AGNEs go through a maximum in July to stabilize at an average rate until January. This phase is under the predominant influence of lipolytic hyperglycemic hormones, especially glucagon. [282] Proteinogram The modifications of the different fractions during the annual cycle, as interesting as they are, are eclipsed by the variations of 2 of them P-a and P-d. Indeed, the fraction P-a undergoes in some animals, indifferently males or females, a dissociation in 2 subfractions P-a. and P-a2 during the wet season (except in October) and transiently in March. This phenomenon may be related to gonadal evolution, given their synchronism. Moreover, this dissociation does not occur in October, the month during which the proteins of the egg are formed. Is there a relationship between the two phenomena? As for the fraction P-d, it disappears completely from January to March to reappear and has a very high rate, only in May. This rate then stabilizes more or less in June of December. The most notable fact appears to be the synchronism between the disappearance of the AGNE and this P-d fraction which should be the support of the antibody properties of Varan. [283] c) Hydration of the bodily compartments From November to April, the hydration is average, despite the relative drought of the biotope from January. In May and June the animal goes through a phase of maximum dehydration objected by the drop in weight / length[?] ratio and hemoconcentration (high protein) This phenomenon will then reverse from July to October; on the contrary, hyperhydration is preferable, culminating in September at the time of gonadal maturation and the maximum humidity of the biotope. d) All these facts show that the sexual, endocrine and metabolic cycles of Varanus exanthematicus are 2 months ahead of the rainfall regime, but in phase with the thermal evolution of the biotope. The temperature thus appears as a determining factor in the chronobiology of this reptile under the Sahelian climate of Senegal. Its effects have been studied experimentally. At low values, temperature inhibits the activity of Varans; at average values (between 24 and 30 C in a humid atmosphere), it stimulates all their functions. [284] In fact, it is only one of the parameters of a multifactorial system of regulation, of which many factors still remain to be determined. This is how moisture in the middle seems to also have a decisive role. Its importance has been emphasized in the determinism of latency in Varanus niloticus. But, moreover, May and June that precede the return to activity, are more humid months than the 4 previous months like November and December, which announces the functional decline are drier than the 4 months that precede them. It should also be remembered that the hydric state of the corporal areas of Varanus exanthematicus has always been related to the ambient humidity. Since it is known that the mobilization of reserve fats releases metabolic water, it may be accepted that thanks to this water and free fatty acids provided, there is a resumption of gonado-endocrine activity in the absence of any exogenous nutrient. This explains the difference between the evolution of the sexual and endocrine glands and the alternation of the two dry and rainy seasons.

6 In addition to temperature and humidity, it is very likely that light, too, is an active factor in the annual cycle [285] of Varans as well as the nervous system whose role is objective by the pituitary activity. (e) As to the hormonal regulation of the metabolism of Varanus exanthematicus, its interpretation follows from the preceding considerations. Only hepatic glycogen is used. The involution of the hyperglycaemic system at this time shows that only the endocrine pancreas is in activity even reduced. The carbohydrate regulation is essentially due to the pancreas. In May-June, the awakening of the hyperglycemic system raises glycaemia and lipolysis come into play; it appears to be essential for the reactivation of the endocrine glands and the induction of gonadal maturation. Endocrine and gonadal activity culminates in September-October, while reserve lipids are at their minimum. At the end of the year [286] insulin and lipogenetic hormones appear to be predominant. The storage of lipids corresponds to gonado-endocrine involution. This tends to prove the essential role of lipids in the biological cycle of the lizards. As for the endocrine pancreas, it has presented as well in the course of its circannual evolution as in the experiments carried out, particularities of which attract attention. During the course of the annual cycle, Langerhans' floods are resurrected: from May [illegible] probably also, by metaplasm [illegible] *acinous cells. This situation suggests that the pancreas of V. exanthematicus traces during its annual cycle some phases of its embryonic gen [illegible]. During the experiments that took place, the singularity of the pancreas appeared to enclose even more strikingly. In effect the Langerhansian elements, unlike the other endocrine glands have been affected neither by thermal tests nor by removal of reserve fat. [287] On the other hand, they showed a positive reaction to the effect of hydration of the internal environment. This would tend to show that the state of hydration of the animals is one of the essential factors of the control of the annual pancreatic cycle. But the hydration of the internal environment also seems to favor the development of the pituitary gland, the overrenals and the gonads. Even in animals that have been removed from reserve fat. Its influence, like that of temperature, is therefore exerted on the entire gonadoendocrine system. But, its action seems much more extensive in that it also interests the endocrine pancreas. And, since it is known that reserve fats constitute a source of metabolic water, we can think that, to a certain extent, they intervene in the control of endogenous cycles by the water they release at the moment of their mobilization., in addition to free fatty acids. The action of fat reserves is thus more or less confused with that of organic water. The hydrous state of the internal environment thus seems to be the common factor which influences all the endogenous cycles. But this internal hydration itself depends on the conditions of the environment (hygrometry, ambient, food available). [288] The annual cycle of Varans could therefore be considered to be essentially controlled by the factors of the environment and the state of hydration of the internal environment.

7 Thus, the mechanisms of adaptation of the Varans to the Sahelian environment of Senegal reside mainly in the physiological processes that they bring into play in order to face, on the one hand, the ambient thermal conditions and, on the other hand, the variations the state of internal hydration. In this regard, the two Varans we have studied do not seem to present a fundamental difference in temperature. In one as in the other, thecycle of the gonado-endocrine system follows the thermal evolution of the environment. With regard to water conditions, however, a difference appears in Varanus niloticus, which is independent of the biotopes, remains active during the dry season if it has water in its home range. This state of activity is explained by the dynamogenic effect that internal hydration under ambient water conditions, exerts on the internal structures. This is indicated by, among other things, the highly functional condition of the intermediate pituitary gland of individuals living near water points during the dry season. [289] Varanus exanthematicus, on the other hand, lives far from watering points, and suffers early from the dehydration at the end of the rains. This would cause an alteration of the endocrine function and a halt of physical activity accompanied by a complete fast. Also, the difference between the annual cycle of Varanus niloticus and that of Varanus exanthematicus under the Sahelian climate of Senegal lies in the difference in the affinities of the two animals with respect to water. But, in fact, this study can not be said to be exhaustive. In particular, an interpretation of the state of hydration of the body compartments would require a dosage of Na + and K + ions. Moreover, many riddles still remain to be elucidated in this essay analyzing the chronobiology and annual cycles of Varans. First, the protein fraction P-d of the proteinogram; it disappears at the same time as the nonesterified fatty acids. Would the repressors that modulate the function of the genes controlling the biosynthesis of lipase and this P-d fraction be identical and only act during the complete rest period from January to April? Moreover, this fraction which migrates little to electrophoresis seems to be the medium [290] of the serum antibody properties of Varan; it would then be surprising that this function is practically suspended during the rest period of the animal, although in Reptiles, cellular immunity is predominant over humoral immunity. A second remark is the testicular surge of the Varans in February when the temperature of the biotope is below the annual average. What could be the explanation? As a hypothesis, it may be thought that this surge would be the remnant of another normal spermatogenesis that would have existed in Varans in their original biotope. Two findings would support this view. First, in another Lacertilian reptile, Agama agama, the sex cycle is strongly influenced by the climatic regime of the region it lives. In fact, males of this species have continuous spermatogenesis under the hot and humid climate of the southern areas of West Africa, while those living in the Sudano-Sahelian climate of the Dakar region have a seasonal cycle just like monitor lizards. These are from Southeast Asia. It is known that in this country there was a humid tropical climate during the Tertiary Era until the Late Miocene, when Varans reached the African continent. On the other hand, the experiments described above have demonstrated the possibility of inducing an anticipated spermatogenesis in animals by the action of moist heat. [291] These various facts suggest that the humid tropical climate of the original biotope of these reptiles were to allow for them, the existence of at least one other spermatogenic cycle, if not a continuous spermatogenesis, which would make conceivable, the hypothesis of seeing in the abortive thrust of February, a relic of this original sexuality.

8 Thus the climatic regime appears as the main integrator of the various influences which are exerted on the annual cycle of Varans. And the conclusions of this work can be summed up thus: The behavioral changes of the Varans during their annual cycle in Senegal appear to be influenced by seasonal variations in the humidity of their biotope. The internal biological cycles: sexual, endocrine and metabolic cycles, would be under the control of the thermal evolution of the environment and the state of hydration of the animals, linked to the ambient hygrometry and to the metabolism of lipid reserves. liberating water and free fatty acids. [292] But, as we have said, these results are only a preliminary step in a very limited area of the Sahel. There is still a lot to do. May new and fruitful studies deepen these observations for a better knowledge of the correlations between the Sahelian environment and animal life.