Mechanisms for Speciation inGalago andTarsius

Patterson's Recognition Concept of Species has profound implications for the way we analyze the process of species formation. It emphasizes absolute rather than relativistic mechanisms, and concentrates on adaptive processes within population isolates rather than competitive exclusion or competition. Environmental change is seen as a major force initiating speciation. In the case of two species ofGalago, environmental degradation and the breakup of forest blocks is likely to have been the major initiator; while changes in sea-level may have lead to the fragmentation of populations ofTarsius. In both cases, however, the relationships of body size, energetics, heterochrony and species strategies most likely provided the engine for further behavioural and morphological divergence.     

Germinal cell ectopism in the strepsirhine prosimian Galago crassicaudatus crassicaudatus

The presence of germinal cells outside of the embryonal and fetal gonads of the strepsirhine prosimian Galago crassicaudatus crassicaudatus is described. Forty-three embryos and fetuses from day 26 or 27 of gestational age to near term were studied: more than 90% possessed germinal cells in ectopic sites situated either far from (extragonadal ectopism) or close to the gonads (perigonadal ectopism). The first sites were the walls of the aorta and mesenteric artery, the stroma between the aorta and the cardinal vein, and the retroperitoneal neuroganglia. The second were the mesenchyme dorsal to the gonads and around the vestigia of the mesonephric glomeruli and tubules, and the rete ovarii and testis. The ectopic cells were generally present in conscpicuous numbers, in some animals being more numerous than in the gonads. Those situated far from the gonads underwent degeneration and decreased significantly in numbers during post-embryonal stages of development, while the others remained numerous and functionally active up to near term. While the differentiation of the extragonadal germinal cells after day 60 of gestational age could not be studied due to technical difficulties, the XX and XY cells in perigonadal sites appeared to follow patterns of differentiation identical to those of their entopic counterparts.     

Cycles of mating behaviour, oestrogen and progesterone in the thick-tailed bushbaby (Galago crassicaudatus crassicaudatus) under laboratory conditions

Vaginal smears and blood samples were taken throughout the reproductive cycle of female Galago c. crassicaudatus. Blood plasma was assayed for oestradiol and progesterone, and vaginal smears were initially classified dioestrus or vaginal oestrus. During vaginal oestrus the females were tested daily for sexual receptivity by being placed with a male. Those days on which the male achieved intromission were reclassified as behavioural oestrus. During dioestrus the females were tested weekly with males. Female receptivity increased and then declined across a 6-day period of behavioural oestrus during the 44-day cycle. Fully cornified smears were characteristic of the period of maximal receptivity and oestradiol secretion. The luteal phase lasted 24 days with a plasma progesterone peak midway through dioestrus.     

Static intraspecific allometry of the dentition in Otoletnur crassicaudatus

Adult static intraspecific allometry of tooth size was evaluated in a sample of 66 Otolemur crassicaudatus (34 male, 32 female). Tooth areas were calculated from mesiodistal and buccolingual measurements of canines and postcanine teeth of both arcades and were scaled to four viscerocranial measurements: bimaxillary width; maxillo-alveolar length; mandibular length and bigonial width. Individual tooth crown areas were also scaled to total skull length, body length and body weight. From the log-transformed analyses it is concluded that postcanine tooth size was unrelated to body length or weight, and poorly correlated to skull length or jaw size. Although viscerocranial size appears to be independent of body size, these measures are well correlated to skull length. It is shown that the longer the skull, the shorter and narrower the maxilla, and the longer and broader the mandible. Canines are shown to scale negatively allometric to skull length, hence, large animals will have relatively small canines.     

Comparative studies of morphology and reproduction in two subspecies of the Greater bushbaby, Galago crassicaudatus crassicaudatus and G. c. argentatus

Two subspecies of the Greater bushbaby, Galago crassicaudatus argentatus and G. c. crassicaudatus , are known to differ morphologically, but quantitative studies of the differences, or of reproductive compatability between the subspecies, have not previously been attempted. Somatic measurements were made on living specimens of both subspecies and controlled experiments were conducted to determine whether fertile matings would occur between them.
G. c. argentatus is heavier than G. c. crassicaudatus and has longer ears, a longer ulna and fibula and a greater biorbital breadth. A significant degree of sexual dimorphism in body weight and length of the fibula and ulna occurs in G. c. argentatus , males being larger than females. In G. c. crassicaudatus however, there are no statistical differences between the sexes in these somatic measurements. The morphology of the male and female external genitalia differs between the two subspecies.
In six pairs of male argentatus and female crassicaudatus , only one pair mated and no offspring resulted. In seven pairs of female argentatus and male crassicaudatus , matings occurred in all pairs but only one female conceived and this pregnancy ended prematurely in a spontaneous abortion. In control experiments using six oppositely-sexed pairs of G. c. crassicaudatus , however, all females became pregnant and produced live offspring.
The morphological and reproductive differences between G. c. argentatus and G. c. crassicaudatus are more pronounced than previously realized and it is possible that the two varieties may merit separation as distinct species of Galago.     

Mother-infant cannibalism in thick-tailed bushbabies (Galago crassicaudatus umbrosus)

Mother-infant cannibalism in species of galagos as in several other species of non-human primates is a common phenomenon. In non-human primates kept in laboratory conditions many of the observed cases of cannibalism were not associated with starvation and with infanticide. Cannibalism in galagos was observed in at least five different species. In several laboratories, like the Duke University Primate Center, the frequencies of cannibalism in galagos species in captivity have been reduced by the isolation of pregnant female before the parturition from her companions, especially adult males. At the Primate Behaviour Research Group (University of Witwatersrand, Johannesburg, South Africa) three cases of cannibalism were observed in twoGalago crassicaudatus umbrosus' mothers before the end of the third day after birth. To understand the reasons why the mothers cannibalize their own infants, it was decided to analyze the mother-infant interaction which preceded the death of the infants. InGalago crassicaudatus twin and triplet births are very common. In one of our two observed mothers who cannibalized their infants, there was one triplet birth. In this study the two pregnant females were isolated in two separated cages ten days before giving birth. One of the two observed mothers gave birth to triplets, the other had a single birth. At the end all four infants were cannibalized. In all cases the cannibalization started after the infant's death. The infants' deaths were caused by lack of maternal care which caused them to starve. The results show that the triplet's mother differed in some of her behaviour towards her infants. In one of the cannibalized infants behaviours such asNipple andMother Passive Prevent were never seen before death. In our cases it seems that cannibalism was probably due to the laboratory condition that for generation to generation caused stress to the mothers and changed their maternal behaviours, which lead to the death of the offspring which after death became a consumable resource.     

In vivo bone strain in the mandible of Galago crassicaudatus.

Single element foil strain gages were bonded to mandibular cortical bone in eight specimens of Galago crassicaudatus. The gage was bonded below the Pm4 or M2 adjacent to the lower border of the mandible. The bonded strain gage was connected to form one arm of a Wheatstone bridge. Following recovery from the general anesthetic, the restrained Galago bit either a piece of wood, a food object, or a bite force transducer. During these biting episodes, mandibular bone strain deformed the strain gage and the resulting change in electrical resistance of the gage caused voltage changes across the Wheatstone bridge. These changes, directly proportional to the amount of bone strain along the gage site, were recovered by a strip chart recorder. Bone strain was measured on both the working and balancing sides of the jaws. Maximum values of bone strain and bite force were 435 microstrain (compression) and 8.2 kilograms respectively. During bending of the mandible, the correlation between bone strain (tension or compression) and bite force ranged from -0.893 (tension) to 0.997 (compression). The experiments reported here demonstrate that only a small percentage of the Galago bite force is due to balancing side muscle force during isometric unilateral molar biting. In addition, these experiments demonstrate that the Galago mandible is bent in a predictable manner during biting. The amount of apparent mandibular bone strain is dependent on (1) the magnitude of the bite force and (2) the position of the bite point.     

Patterns of sexual dimorphism and of variability in the dentition ofOtolemur crassicaudatus

Normative odontometric data are presented on a sample of 66 adult thick-tailed bushbabies Otolemur crassicaudatus(34 male, 32 female). This species is characterized by low levels of sexual dimorphism, with univariate differences centered on the canines and the maxillary third molar. Multivariate canonical analysis isolates a third discriminator, the maxillary second molar. Stepwise discriminant analyses, performed after jackknifing, indicate high percentages of correct classification (males, 79.8–81.8%;females, 81–85.2%). When variability profiles consisting of arrays of CVs are compared, males and females are found to share similar patterns. Data for maxillary teeth offer support for Gingerich’s occlusal complexity model, while morphogenetic clusterings within regressions of variability on tooth size conform to those previously reported in other species. These relationships are lost in the mandibular dentition, suggesting an independence of upper from lower toothsize determination.     

Fetal development in the normal thick-tailed bushbaby (Galago crassicaudatus panganiensis)

Fetal development was examined at days 60, 75, 90, 105, 120, or 135 of gestation in 19 thick-tailed bushbaby fetuses (Galago crassicaudatus panganiensis) from 17 normal, timed pregnancies. With the exception of day 135, all fetuses were collected by hysterotomy (gestation = 133 ± 2 days). Various weights and measurements were taken. Although fetal sizes varied widely, crown-rump, crown-heel, upper and lower arm and leg lengths, hand and foot lenghts, and fetal organ weights correlated well with fetal age. Key changes in gross brain morphology and skeletal ossification of cranium, pelvis, tarsals, carpals, and epiphyses were noted. Sternabrae ossification proved highly variable, while ossification in the otic capsule and associated ear structures correlated well with age. These data provide a normal base for studies using fetal developmental parameters whether the purpose is to determine gestational age or to design future studies.     

Reproduction of the greater bushbaby (Galago crassicaudatus panganiensis) under laboratory conditions

A breeding colony of Galago crassicaudatus panganiensis was maintained under laboratory conditions for four years, August 1971 to July 1975. The estrous cycle and the gestation period averaged 39 and 132 days in length, respectively. Twinning occurred in 14.5% of the pregnancies. No postpartum estrus was observed, although 1.2 conceptions per female per year were recorded. Breeding occurred throughout the year. Puberty occurred between ten and 18 months of age, the first conception occurred between 15 and 18 months of age, and reproductive capability decreased rapidly between ten and 12 years of age.     

Progesterone Levels During Pregnancy in the Greater Thick-tailed Galago (Galago crassicaudatus)

Serum progesterone concentrations in Galago crassicaudatus were quantified at 3-week intervals throughout the 136-day pregnancy. Progesterone concentrations were significantly elevated over those of nonpregnant controls as early as 6 weeks after conception. Progesterone continued to increase throughout gestation. The progesterone profile in pregnant G. crassicaudatus quantitatively resembles that of chimpanzees and qualitatively resembles that of humans. In two animals that aborted, progesterone concentrations after abortion decreased to values comparable to those seen in nonpregnant animals.