Search

Lower jaws (containing the teeth), eyes, and skin samples were collected from harp seals (Pagophilus groenlandicus) in the southeastern Barents Sea for the purpose of comparing age estimates obtained by 3 different methods, the traditional technique of counting growth layer groups (GLGs) in teeth and 2 novel approaches, aspartic acid racemization (AAR) in eye lens nuclei and telomere sequence analyses as a proxy for telomere length. A significant correlation between age estimates obtained using GLGs and AAR was found, whereas no correlation was found between GLGs and telomere length. An AAR rate ([k.sub.Asp]) of 0.00130/year [+ or -] 0.00005 SE and a D-enantiomer to L-enantiomer ratio at birth (D/[L.sub.o] value) of 0.01933 [+ or -] 0.00048 SE were estimated by regression of D/L ratios against GLG ages from 25 animals (12 selected teeth that had high readability and 13 known-aged animals). AAR could prove to be useful, particularly for ageing older animals in species such as harp seals where difficulties in counting GLGs tend to increase with age. Age estimation by telomere length did not show any correlation with GLG ages and is not recommended for harp seals. DOI: 10.1644/10-MAMM-A-080.1. Key words: age determination, age estimation, amino acid racemization (AAR), aspartic acid, eye lens, growth layer group (GLG), Pagophilus groenlandicus, population management, telomere

Because absolute mammalian age is difficult to measure directly, various methods have been used for its estimation. Among these methods, the degree of molar eruption and wear are considered to be the most reliable indicators of relative age. We used the nature and extent of maxillary molar toothrow eruption and wear to assign individuals of the solitary South African endemic Cape dune mole-rat (Bathyergus suillus) collected from a single population on the grounds of Cape Town International Airport, Cape Town, South Africa, to 9 relative age classes. We then used cranial morphometric analysis, and for comparative purposes, an assessment of the nature and extent of variation in body mass and body length, to investigate the nature and extent of sexual dimorphism and age variation in this little-studied species of mole-rat. Both univariate and multivariate analyses distinguished relative age classes 2 and 3 from 6-9, but age classes 4 and 5 were intermediate between the 2 other age-class groupings, suggesting that individuals of age classes 4 and 5 may be at a point on a hypothetical growth curve where the curve begins to stabilize. Examination of our data showed the absence of sexual dimorphism in younger individuals of age classes 2-5, and its presence in older individuals of age classes 6-9. Together with a proposed study of microsatellites, our analyses may improve our understanding of the population structure of the Cape dune mole-rat. Key words: age variation, Bathyergus suillus, body mass/length, Cape dune mole-rat, cranial morphology, molar morphology, morphometrics, sexual dimorphism, southern Africa

Patterns of growth and development provide information critical for documenting population demographics. Herein we document the reproductive biology for and provide equations that accurately predict the ages of 2 widely sympatric species of bats from central Indiana--the northern myotis (Myotis septentrionalis) and the little brown myotis (Myotis lucifugus). Young of M. septentrionalis were born synchronously (within a 6-day period) and within a narrow size range (mean length of forearm = 12.78 mm, 95% confidence interval [95% CI] = [+ or -] 0.52 mm; mass = 1.91 g, 95% CI = [+ or -] 0.11 g). Young of M. lucifugus were born during a 42-day period and within a narrow size range (mean length of forearm = 14.26 mm, 95% CI = [+ or -] 0.23 mm; mean body mass = 2.19 g, 95% CI = [+ or -] 0.08 g). Young of M. septentrionalis were born significantly smaller (t = 4.52, d.f. = 137, P < 0.001) and lighter (t = 2.57, d.f. = 137, P < 0.05) than were young of M. lucifugus. We developed species-specific equations that made it possible to estimate the age of both species of bat to within 1 day. These results indicate that similar-sized and closely related bats grow at comparable rates and provide the 1st detailed information about reproductive biology of M. septentrionalis. Key words: bats, demographics, growth models, Myotis lucifugus, Myotis septentrionalis, reproduction

New Zealand fur seals (Arctocephalus forsteri) are common in the Australian-New Zealand region, but vital demographic data are lacking. Accurate determination of the age of individuals is critical to the study of age-specific life-history parameters. A cross-sectional sample of female and male New Zealand fur seals was caught and animals were individually marked on Kangaroo Island, South Australia, between 2000 and 2003. Seals were aged through examination of a postcanine tooth, which was removed from each animal. Annual formation of cementum layers was confirmed and accuracy in age estimation was determined by examination of teeth removed from individuals of known age. Indirect methods of assessing reproductive maturity based on characteristics of mammary teats indicated that females 1st gave birth between 4 and 8 years of age, with an average age at reproductive maturity (ARM) of 5 years. No females were observed to breed beyond 22 years. Age of 1st territory tenure in males ranged from 8 to 10 years. Variation in ARM between individuals appears to be related in part to body size and condition. Classification of mammary teat status in combination with techniques for aging live animals provided a means of assessing ARM in the absence of extensive longitudinal data. Key words: age estimation, Arctocephalus forsteri, cementum, longevity, reproduction

Otolith-based age estimates for Greenland halibut (Reinhardtius hippoglossoides) have low precision, and there is general uncertainty about their accuracy in older fish (Anon. (1); Alpoim et al. (2)). Low precision [...]

Indirect estimates of instantaneous natural mortality rate (M) are widely used in stock assessment and fisheries management. They are essentially a form of meta-analysis, in which prior information on M [...]

Abstract--Growth parameters were estimated for porbeagle shark (Lamna nasus) in the northwest Atlantic Ocean on the basis of vertebral annuli. A total of 578 vertebrae was analyzed. Annuli were validated [...]

The accuracy and precision of tooth wear for aging gray wolves is evaluated.

Ages of Montana ungulates determined by eruption-wear criteria were often overestimated for younger animals and underestimated for older animals. Ages determined by eruption-wear criteria did not give an accurate estimate of age structure and relative cohort significance for population modelling.

Researchers investigated the accuracy of estimating sea otter age by counting the number of layers of cementum in their teeth. This practice has been employed in a number of pieces of research but the technique has not been validated. The researchers asked three readers to estimate the ages of 20 sea otters and compared the results with the known ages. The researchers found that the readers used different criteria to interpret the layers. The three readers produced estimates of mean ages of 4.4, 5.9 and 7 years, compared to the actual mean age of 5.1 years.

Hoof growth accurately and reliably predicts neonatal age of white-tailed deer. Linear regression representing hoof growth describes 87% of variations and classifies 74% of the fawns within 3 days of age. The hoof growth model has the minimum squared deviation between actual and predicted ages. All morphometric measures except tail, hindfoot, and head length are low among fawns with low protein-fed dams. Primary body measures are associated with fawn age. Body mass, chest girth, and total length are influenced by maternal protein.

A study has been conducted to evaluate the aging techniques used for waterfowls and to compare the performance of aging birds by using discriminant functions and a posteriori clustering methods. The results revealed that all aging methods may be effective if the appropriate feather variables are used. A posteriori clustering was more effective in measuring large populations than discriminant functions because it avoids errors caused by biased estimators.

From 1977 to 1986, skulls and teeth of the South American sea lion, Otaria flavescens, found dead along 262 km of beaches of the southern coast of Brazil, between latitudes 31 degrees 51 prime S and 33 degrees 40 prime S, were collected for aging. Cranial sutures were examined in 126 skulls, and growth-layer groups were counted in longitudinally bisectioned canines of 175 specimens. Based on a known-age specimen, growth-layer groups were found to be formed annually. A high correlation was found between the ages estimated from teeth and those estimated by suture closure. The oldest males and females were 16 and 14 years, respectively. Ages 3-5 years were the most frequent. The Bertalanffy growth parameters adjusted with the Marquardt's algorithm were L infinity = 254.4 cm, K = 0.305, t(sub 0) = -1.6 years for males, and L infinity = 194.4 cm, K = 0.306, t(sub 0) = -2.0 years for females. Ninety-five percent of the maximum length is attained by 8 years of age for both sexes.

Wear-induced changes in the crown topography of molariform teeth have been widely used to index relative age in rodents. To assess the consistency of molar-wear estimates in natural populations of a sigmodont rodent (Bolomys lasiurus), we investigated the association between molar wear and two other age-dependent craniodental characters: degree of exposure of molar roots from the alveoli and ossification of the basisphenoid-basioccipital suture. We compared magnitudes of Spearman correlation coefficients among states of these characters in samples cross-classified by vegetation, season, and locality, under the null hypothesis of high correlation in the absence of differential environmental effects on molar wear. A bootstrap procedure was used to derive empirical sampling distributions of the age-index correlations and, thus, to establish realistic confidence intervals. We then employed a multivariate procedure to reduce subjectivity of classifying combinations of indices of age into age classes. Using a principal component analysis of the correlation matrix of craniodental indices, variation expressed among indices was summarized as a multivariate age factor. An objective ordering of sets of indices of age (the various combinations of tooth-wear, molar-root exposure, and suture-ossification conditions observed among all samples) was provided by projecting individuals onto the first principal component. The method revealed age-frequency differences between wet- and dry-season samples from northeastern Brazil, ostensibly due to the occurrence of a reproductive peak at the beginning of the rainy season, and predicted a maximum life span for B. lasiurus of ca. 1-1.5 years in the wild. Key words: Bolomys lasiurus, age factor, bootstrap, correlation structure, geographic variation, life history, multidimensional scaling, tooth wear