The effect of reference sample composition and size on dental age interval estimates

Objectives

Validation studies in juvenile dental age estimation primarily focus on point estimates while interval performance for reference samples of different ancestry group compositions has received minimal attention. We tested the effect of reference sample size and composition by sex and ancestry group on age interval estimates.

Materials and Methods

The dataset consisted of Moorrees et al. dental scores from panoramic radiographs of 3334 London children of Bangladeshi and European ancestry and 2–23 years of age. Model stability was assessed using standard error of mean age-at-transition for univariate cumulative probit and sample size, group mixing (sex or ancestry), and staging system as factors. Age estimation performance was tested using molar reference samples of four sizes, stratified by year of age, sex, and ancestry. Age estimates were performed using Bayesian multivariate cumulative probit with 5-fold cross-validation.

Results

Standard error increased with decreasing sample size but showed no effect from mixing by sex or ancestry. Estimating ages using a reference and target sample of different sex reduced success rate significantly. The same test by ancestry groups had a lesser effect. Small sample size (n < 20/year of age) negatively affected most performance metrics.

Discussion

We found that reference sample size, followed by sex, primarily drove age estimation performance. Combining reference samples by ancestry produced equivalent or better estimates of age by all metrics than using a single-demographic reference of smaller size. We further proposed that population specificity is an alternative hypothesis of intergroup difference that has been erroneously treated as a null.     

Successful sons or superior daughters: sex-ratio variation in springbok

Mothers would often benefit from producing more offspring of one sex than the other. Although some species show an astonishing ability to skew their sex ratio adaptively, the trends found in many studies on vertebrates have proved inconsistent. Furthermore, evidence for a mechanism by which such a bias is achieved is equivocal at best. Here, we examine sex-ratio variation over 30 years, both at an individual and a population level, in the highly polygynous, size-dimorphic springbok (Antidorcas marsupialis). Many previous studies of similar species have shown that mothers in superior condition preferentially produce sons, whereas those in poorer condition produce more daughters. We found the opposite to be true in springbok, perhaps because daughters provide mothers in superior condition with a more rapid and secure fitness return. This theory was supported by the findings that earlier-conceived offspring tended to be female and that an increased proportion of daughters were produced with increasing rainfall (which was likely to reduce nutritional stress). We also show that selective reabsorption of embryos is unlikely to be the main mechanism by which deviations from an equal sex ratio are achieved. Hence, either differential implantation occurs or females are able to influence the sex of the sperm fertilizing an egg.     

OFFICIAL ANNOUNCEMENTS

The Lesser Crested Tern Thalasseus bengalensis emigratus breeding population in the Mediterranean is found exclusively in Libya, on the two coastal islands of Gara and Elba and one wetland on the mainland coast at Benghazi. In order to improve knowledge of the species migration to wintering quarters in West Africa, a ringing programme was conducted from 2006–2008 and 2009–2012. From a total of 1 354 nestlings ringed using metal and/or colour rings, 64 were recovered along their flyway and in their wintering range, representing 6.9% of birds ringed with both colour and metal rings. This provided the opportunity to collect information on post-natal movements (staging and wintering ranges), breeding philopatry and recruitment, in addition to a preliminary estimate of their migration journey duration. This paper indicates sighting and recovery distributions in space and time, highlighting the important areas for the species during its journey between breeding and wintering sites. The findings indicate that several areas where ringed terns stop-over during pre- and post-breeding migration journeys are not protected, causing an additional threat to their survival, as some wintering areas are also not protected. Conservation of this highly localised and threatened population needs not only to address protection at breeding sites but also at migratory stop-overs and wintering strongholds.     

THE BIRD POPULATION OF THE DAMS ON THE FREE STATE GOLDFIELDS

Taylor, P. B. 1987. A field study of the Spotted Crake Porzana porzana at Ndola, Zambia. Ostrich 58: 107-117. From 1974 to 1980 field observations were made of Spotted Crakes Porzana porzana at Itawa Swamps and Kanini Sewage Works, Ndola, Zambia. Field identification characters, behaviour, food and feeding methods, activity times, interspecific interactions, aggression and voice are described. Habitat at Ndola is seasonal and temporary: shallowly flooded or moist grass and other vegetation with patches of open water and mud, near swamps and at sewage settling ponds. Wintering crakes were itinerant from December to April with a February-March peak and remained at one site for up to 25 days, occupying temporary territories 210-315 m2 in extent. Arrivals were associated with heavy rainfall and most departures with major habitat changes. Local movements took place. Behaviour is similar to diat in the Palaearctic. Comparisons are made with the habitat, movements, dispersion and behaviour of other rallid species at Ndola. The Spotted Crake is ecologically separated from other wetland rallid species in habitats in Zambia and Kenya by its preference for very temporary habitats and also by differences in food and feeding methods. All Zambian records of this species up to the end of 1984 are reviewed.     

BREEDING NOTES ON THE BLACK-NECKED GREBE PODICEPS NIGRICOLLIS BREHM

Summary

Tarboton, W. R. &; Fry, C. H. 1986. Breeding and other behaviour of the Lesser Jacana. Ostrich 57: 233–243.

Breeding Lesser Jacanas were studied briefly at Lake St Lucia (Zululand), Hwange (Zimbabwe) and the Okavango Delta (Botswana). The species is monogamous and breeding birds are dispersed as territorial pairs. Male and female share incubation nearly equally, alternating at the nest in shifts averaging 39min; the eggs are attended (incubated or shaded), on average, for 82% of the daylight hours. Eggs are incubated by holding them against the breast with the underside of the wings; at least one chick was seen carried under a parent's wing. The pullus, foraging behaviour, courtship and vocalisations are described. It is suggested that the Lesser Jacana's small egg necessitates a high rate of nest attendance which could account for the sociosexual differences between this species and other jacanas.     

Human tooth development,tooth length and eruption; a study of British archaeological dentitions

Abstract

Human teeth erupt during root growth but few studies report the relationship between fractions of root development and eruption levels. The aim of this study was to assess root stages of deciduous and early erupting permanent teeth (maxillary and mandibular central incisors and first molars) at eruption levels and relate this to root fraction and tooth length. The sample consisted of 620 modern human skeletal remains with developing teeth. Tooth stage (based on Moorrees crown and root stages) and eruption levels of all developing teeth were assessed where possible. Tooth length of isolated teeth was measured. The distribution of root stage at eruption levels was calculated. Results showed that root stage at alveolar eruption was less variable than at partial eruption. Most teeth (72% of 138) at alveolar eruption were at root a quarter (R¼) whereas teeth at partial eruption were at R¼ or root half (R½) (38 and 50% of 128 respectively). These findings suggest that the active phase of eruption is probably a rapid process and occurs during the first half of root growth.     

THE BIRDS OF LANGEBAAN LAGOON

Data are presented on breeding success of Red Bishops (Euplectes orix) collected over four breeding seasons at a colony in the Addo Elephant National Park, Eastern Cape, South Africa. Overall hatching and fledging success were 53.8% and 26.0% of all eggs laid, respectively, and the overall mean number of fledglings per breeding attempt was 0.77. Hatching and fledging success varied significantly among seasons, with both clutch and brood losses due to predation being the main reason for the observed differences. Hatching success also differed significantly among clutch sizes, being highest for four-egg clutches (63.2%), intermediate for three-egg clutches (55.5%) and lowest for two-egg clutches and five-egg clutches (33.2% and 34.3%, respectively). However, fledging success was not significantly different among clutch sizes. The mean number of fledglings per breeding attempt was 0.44 for two-egg clutches, 0.80 for three-egg clutches, 1.10 for four-egg clutches, and 0.57 for five-egg clutches. The height of accepted nests (i.e.nests in which at least one egg was laid) was significantly lower than the height of nests not accepted. In addition, accepted nests in which eggs hatched and young fledged were significantly lower than accepted nests in which no eggs hatched and no young fledged. These overall effects of nest height on nest acceptance and hatching and fledging success were, however, due only to nests built above water, since no such effects were found when nests built above ground (i.e.on dry land) were analysed separately. I detected no effect of nest coverage on the probability of a nest being accepted, nor was there any effect of nest coverage on hatching or fledging success. Nests above water were significantly more likely to be accepted than nests above ground; however, hatching and fledging success of nests that were accepted did not differ significantly between nests built above water and those built above ground.     

Nasal delivery of a vasopressin antagonist in dogs

The dosage form (drop or spray) and site of administration (dorsal or ventral surface of the nostril) profoundly affect the distribution and clearance of a gamma-emitting 99mTc-labeled diethylenetriamine pentaacetic acid (99mTc-DTPA) solution in dogs. The slowest nasal clearance was observed for dorsally administered drops. Administration of drops to the ventral surface or sprays to either dorsal or ventral surface results in rapid clearance and little deposition in the turbinates. The octapeptide vasopressin antagonist, SKF 101926, was administered intravenously (0.3, 1.0, 3.0, and 10 micrograms/kg) and then on separate occasions intranasally (10, 25, and 50 micrograms/kg as a drop to the ventral surface) to four conscious, trained, female, water-loaded, vasopressin-infused dogs. SKF 101926 reversed the antidiuretic response to vasopressin after administration by either the intravenous or intranasal route in a dose-dependent fashion. Peak dilution of urine occurred within 50- to 60-min postdosing by both routes. Estimated doses to reduce vasopressin antidiuresis by 50% were 1.4 micrograms/kg intravenously and 23 micrograms/kg intranasally. After recovery to at least 70% of antidiuretic base line, and then administration of a second dose of SKF 101926 (3 micrograms/kg), subsequent dilution of urine osmolality was inversely related to the magnitude of the previously administered dose. It is concluded that the estimated relative effectiveness of intranasally administered SKF 101926 is 3-21%, compared with intravenous administration. Acute tachyphylaxis to repeated dosing was observed. The mechanism of the apparent tachyphylaxic response was not elucidated. No tachyphylaxis to less frequent (weekly) dosing was observed.