The primary structure of hemoglobin D from the Aldabra giant tortoise,Geochelone gigantea

The complete primary structures of alpha D-2- and beta-globin of hemoglobin D (Hb D) from the Aldabra giant tortoise, Geochelone gigantea, have been constructed by amino acid sequencing analysis in assistance with nucleotide sequencing analysis of PCR fragments amplified using degenerate oligonucleotide primers. Using computer-assisted sequence comparisons, the alpha D-2-globin shared a 92.0% sequence identity versus alpha D-globin of Geochelone carbonaria, a 75.2% versus alpha D-globin of Aves (Rhea americana) and a 62.4% versus alpha A-globin of Hb A expressed in adult red blood cells of Geochelone gigantea. Additionally, judging from their primary structures, an identical beta-globin was common to the two hemoglobin components, Hb A and Hb D. The alpha D-2- and beta-globin genes contained the three-exon and two-intron configurations and showed the characteristic of all functional vertebrate hemoglobin genes except an abnormal GC dinucleotide instead of the invariant GT at the 5' end of the second intron sequence. The introns of alpha D-2-globin gene were both small (224-bp/first intron, 227-bp/second intron) such that they were quite similar to those of adult alpha-type globins; the beta-globin gene has one small intron (approximately 130-bp) and one large intron (approximately 1590-bp). A phylogenetic tree constructed on primary structures of 7 alpha D-globins from Reptilia (4 species of turtles, 2 species of squamates, and 1 species of sphenodontids) and two embryonic alpha-like globins from Aves (Gullus gullus) and Mammals (Homo sapiens) showed the following results: (1) alpha D-globins except those of squamates were clustered, in which Sphenodon punctatus was a closer species to birds than turtles; (2) separation of the alpha A- and alpha D-globin genes occurred approximately 250 million years ago after the embryonic alpha-type globin-genes (pi' and zeta) first split off from the ancestor of alpha-type globin gene family.     

Crystallization and preliminary X-ray diffraction study of hemoglobin D from the Aldabra giant tortoise, Geochelone gigantea

Hemoglobin D (Hb D) from the Aldabra giant tortoise, Geochelone gigantea, was crystallized by the hanging drop vapor diffusion technique with a precipitant solution containing 10% polyethylene glycol 3350 and 50 mM HEPES-Na, pH 7.5. The Hb D crystals of G. gigantea, which diffract to at least a 2.0 A resolution, belong to the monoclinic space group C2 with unit cell dimensions of a = 112.1 A, b = 62.4 A, c = 54.0 A, and beta = 110.3 degrees. One alphabeta dimer molecule of Hb D existed in an asymmetric unit, with a calculated value of Vm of 2.77 A(3)Da(-1).     

Population processes in a large herbivorous reptile: the giant tortoise of Aldabra atoll

Summary Physical barriers divide the population of giant tortoises (Geochelone gigantea Schweigger) on Aldabra into several sub-populations of different density, which nevertheless are similar genetically. We measured individual growth rates in each sub-population. Mortality was estimated using data from Bourn and Coe (1979). Reproduction and recruitment were studied using data from previous work (Swingland and Coe 1979) and our own estimates of clutch size, egg weight, and laying frequency from 1975 to 1981.Individual growth rates were strongly dependent only on individual size and sub-population density and not on age or sex. Within a sub-population, the relationship between specific growth rate and size (linear measure) was best fitted by a Gompertz model, except for very young tortoises which grew faster in volume, though not in weight, than expected. Animals at high densities grow slowly to a small size whereas those at low densities grow fast to a large size. At very high density many juveniles remain at a small size without growing or maturing.Mortality of larger (>ca. 5 years old) animals was independent of density, but did depend on size in the highest-density sub-population, as predicted by the Gompertz growth model.Reproduction and recruitment were negatively density-dependent over the whole density range (5 to 35 animals ha^-1) studied. Clutch size and laying frequency were strongly influenced by sub-population density, but egg weight was not. Laying frequency varied within sub-populations according to rainfall (presumably via annual food supply).All except one sub-population are seen as stages in the development of the same interactive system. Competition between individuals is nearly, but not purely, of scramble type. The remaining sub-population is either a distinct interactive system in which food supply for very young animals is important, or it is a non-interactive system controlled by the effect of natural enemies on very young animals. This suggests that the equilibrium density and/or dynamics of giant tortoise populations are highly sensitive to mortality factors affecting very young animals.In low density sub-populations the animals are large, have many young, low relative reproductive effort, and a short generation time. In high density sub-populations they are small, have few young, high relative reproductive effort, and a long generation time. This variation is largely phenotypic. It is anomalous with respect to r-K life history theory but is a logical consequence of indeterminate growth combined with size-determined risk and benefit functions and may have contributed to the giant tortoises' success as island colonisers.     

Plant dispersal by the Aldabran giant tortoise,Geochelone gigantea (Schweigger)

Summary A total of 28 species of grasses, herbs, and woody plants germinated from faeces of Aldabran giant tortoises. It seems likely that all members of the land flora can be ingested by tortoises and so may be dispersed by them over short distances.The tortoises are thought to have derived from a Madagascan stock and reached Aldabra from time to time by transmarine migration until the extermination of the Madagascan tortoises about 1100 years ago. The time taken by a tortoise to void its last meal is much longer than that required to float, at present current speeds, from Madagascar to Aldabra. If neither of these parameters have changed since the tortoise migrations to Aldabra, the tortoises may have been responsible for the introduction of plant species to Aldabra.     

The natural regulation of Giant tortoise populations on Aldabra Atoll. Reproduction

A two-year reproduction study of three isolated populations of different densities of the Aldabra Giant tortoise ( Geochelone gigantea Schweigger) showed dissimilarity in gonadal parameters; (i) as population density increased age at sexual maturity was delayed in males and females; (ii) although the mean number of mature follicles was similar in all populations, preovulatory follicular atresia was only found in the high density population; (iii) annual variation in preovulatory follicular atresia was dependent on rainfall and food availability; (iv) the number of clutches laid/♀/year decreased with increasing population density as did clutch size; in the high density population (and depending on rainfall) only 30–80% of the mature females bred. The discussion considered the importance of movement in determining survival/reproduction.     

A preliminary study of insect abundance on West Island,Aldabra Atoll,Indian Ocean

• 1 Heath and Rothamsted light traps and a Johnson-Taylor suction trap were used to sample flying insects on Aldabra Atoll.
• 2 The present study extended over two wet seasons. The pattern of relative monthly insect activity resembled the rainfall pattern. Catches were greatest during the months when there was a sudden marked increase in precipitation.
• 3 Lepidoptera dominated light trap catches and Diptera suction trap catches, the total monthly insect numbers therefore reflecting the abundance of these two orders. Hemiptera, Coleoptera and Hymenoptera were also common.
• 4 Predominant families were represented by only a few or even only one dominant species. These species were present throughout the study period although their monthly totals varied considerably, different species dominating the catches during different months.
• 5 The composition and size of catches in the three light traps was affected by the type of light source and surrounding vegetation.
• 6 A comprehensive list of families and selected common species is given with their relative monthly abundance in the light traps.
• 7 Suction trap catches were segregated on an hourly basis to give a broad indication of insect flight periodicity.

     

The distribution of fishes on the outer reef slopes of Aldabra (Indian Ocean) in relation to bottom temperatures

Synopsis Ninety six fish belonging to 19 species were taken by deep water line fishing off Aldabra. Analysis of the results shows how various factors such as hooking time changed with depth. The change of bottom temperature with depth was examined. The zone between 100 m and 150 m was found to have considerable temperature variations. The distribution of some serranids and lutjanids appeared to be stratified though there was usually overlap in the range of adjacent species. The results are compared with previous line-fishing off the South coast of Aldabra from deeper water and other areas of the western Indian Ocean.     

The seasonal pattern and distribution of green turtle (Chelonia mydas) nesting activity on Aldabra Atoll, Indian Ocean

Green turtles nest all year round on Aldabra, but nesting activity was found to be concentrated during the monsoon season (late November-April) rather than the dry season as previously reported. More trial nests and emergences were made during the dry season. This was considered to be the result of difficulties in nesting during this time of the year rather than to more females attempting to nest, because fewer nests were dug during this season. The number of beaches being used by the turtles has apparently increased but no clear reason could be provided for the varying levels of use of different beaches.     

The life history and post-embryonic development of Spirobolus bivirgatus (Diplopoda: Spirobolida) on Aldabra, Western Indian Ocean

Spirobolus bivirgatus, recently known as Mystalides bivirgatus, passes through 15 stadia. These were differentiated by the ocular field method. Development is anamorphic from stadia I to VIII and epimorphic from stadia IX to XV. Maturity is reached in a few males in the eighth stadium but more normally it occurs in the ninth to twelfth stadium. Females are mature in the ninth to fifteenth stadium. Adult males possess fully developed gonopods as well as soft pads on the ventral surface of the tarsi. The pads are illustrated with scanning electron micrographs. Males die after breeding but females probably breed in three or more successive years. Eggs are laid during the wet season, December to April, and these reach maturity within the second or, possibly, the first year of growth. The density, distribution and food of S. bivirgatus is briefly described.     

The ecology of a Mediterranean tortoise (Testudo hermanni): Reproduction

A three-year study on reproduction in wild populations of Testudo hermanni has shown that:
( a ) sexual activity occurs between March and October, except the nesting season (May and June), and is most frequent in August and September,
( b ) tortoises are promiscuous in their mating habits, there is no evidence of mate selection in relation to size,
( c ) nest site selection is correlated to ground temperature and nesting itself mainly occurs in the early evening before dark, when the ground temperature characteristics are most indicative of a specific site's relative temperature,
( d ) incubation takes about three months and is probably temperature dependent,
( e ) most nests are preyed upon by mammalian predators within a few days after laying (> 90% being destroyed), the main cue being the smell of the eggs,
( f ) average clutch size in Greece is higher than in France, while mean egg weight in France is higher than in Greece, and there is no strong relationship between body size or weight and egg or clutch weight in either country,
( g ) in contrast to other studies, there is no apparent correlation between rainfall and reproduction parameters,
( h ) some females nest in successive years, and more than once in a year, with a laying interval of 10–20 days,
( i ) mean size of sexually active individuals is not significantly different from the mean size of adults, although nesting females are significantly bigger; the minimum size for sexually active males is about 120 mm and for females 130 mm.
The discussion examines these observations in an evolutionary context.     

The biology of terns nesting at Aldabra Atoll, Indian Ocean, with particular reference to breeding seasonality

Five species of tern breed on Aldabra Atoll (09° 24' S; 46° 20' E). The Caspian tern Sterna caspia and Crested tern S. bergii feed exclusively in very shallow reef/lagoon water, the Fairy tern Gygis alba and Brown noddy Anous stolidus feed out at sea, and the Black-naped tern Sterna sumatrana is intermediate in its foraging. Both of the shallow-water species lay during the south-east monsoon season, the Caspian tern from April to August and the Crested tern from June to August, but the Crested tern also lays in December and January. The remaining three species have extended laying periods largely circumscribed by the north-west monsoon season from November to March. Breeding population size of the Caspian tern is in the low tens and of the Brown noddy in the low thousands, with the other species each numbering in the hundreds. The distribution and abundance of the nine species of tern breeding within the Seychelles ( sensu lato ) vary on the different island groups in a manner interpretable in terms of depth of the surrounding waters. Systematic differences between the central Seychelles and Aldabra groups in timing of breeding by terns which feed out at sea may be associated with seasonal latitudinal movement of the divergence zone between the South Equatorial Current and the Equatorial Counter-current, acting via correlated latitudinal shifts of prey species and game-fish abundance.     

The predatory behaviour of Caranx melampygus (Pisces) in the channel environment of Aldabra Atoll (Indian Ocean)

Aspects of the predatory behaviour of free ranging Curanx melampygus have been examined in the shallow channel environment of Aldabra Atoll, Indian Ocean. Differences in the frequency of occurrence and number of fish hunting at two adjacent observation areas are described. The numbers of Caranx moving through the area appears to be influenced by tidal factors and possibly the abundance of prey and other environmental factors. The percentage offish hunting increases progressively throughout the day and is most commonly performed by solitary fish or small groups. While approximately equal numbers of Caranx move up or down stream significantly more fish engage in hunting activity when moving down stream which suggests the mechanical advantage of moving with the flow of water has advantages to the hunting fish. Several types of interspecific feeding association are described in which the Caranx is able to scavenge from others or to exploit the hunting methods of other species. More small Caranx form associations than do large Caranx . There is a relationship between the length of a hunting Caranx and the size and/or type of prey that makes an avoidance reaction to it. This relationship between different group sizes and the prey avoidance response is less clearly defined and it is suggested that whether hunting in groups or singly the final interaction is between a single predator and single prey. Ways by which group advantages may occur on grouped prey are described and are considered the result of independent individual action rather than group co-operation. Coastal observations indicate that Caranx use topographic features to shield their approach to areas of high prey density.     

On the biology of the desert tortoise Testudo sulcata in Sudan

Copulation takes place from June until March inclusive but is most frequent between September and November. This is also the season for oviposition, the eggs hatching the following summer. The growth curve of young tortoises shows a close correlation between body weight and length of carapace. Irregularities of the laminae are frequent. These tortoises can survive indefinitely without water if provided with succulent green food. The rate of transpiration in dry air is low: it takes place mainly through the lungs in baby animals but cutaneous transpiration accounts for about half the evaporative water-loss from older tortoises. A complete water and metabolic balance sheet has been drawn up and an analysis of urine made. Tortoises show behavioural thermoregulation and, if the body temperature reaches40–41°C, copious salivation produces evaporative cooling which prevents any further rise. Reactions to high temperatures are direct and are not mediated through responses to light intensity. There is a well marked temperature-independent circadian rhythm of activity which is neither accelerated nor retarded by constant light or darkness. Locomotion is stimulated by light and inhibited by darkness, but the phase of the rhythm is not reset by three-hour periods of light when the animals are kept in darkness not by three-hour periods of dark when they are kept in light, at whatever hour of the 24-hour cycle these changes are applied.     

Intestinal Cryptosporidium sp. infection in the Egyptian tortoise, Testudo kleinmanni

An adult Egyptian tortoise (Testudo kleinmanni) presented with clinical signs of enteritis and died 5 weeks after initiation of antibiotic therapy. Histological examination of the small intestine revealed heavy infection with Cryptosporidium sp.; over 80% of epithelial cells harboured the pathogen. No Cryptosporidium developmental stages were present in the stomach or the lungs. The intestinal lamina propria and mucosa were infiltrated by heterophils, lymphocytes and macrophages. The present study constitutes the first report of Cryptosporidium sp. infection in T. kleinmanni, and the first histological documentation of intestinal cryptosporidiosis in Chelonia.