Periosteal versus true cross‐sectional geometry: A comparison along humeral,femoral, and tibial diaphyses

Cross‐sectional geometric (CSG) properties of human long bone diaphyses are typically calculated from both periosteal and endosteal contours. Though quantification of both is desirable, periosteal contours alone have provided accurate predictions of CSG properties at the midshaft in previous studies. The relationship between CSG properties calculated from external contours and “true” (endosteal and periosteal) CSG properties, however, has yet to be examined along the whole diaphysis. Cross‐sectional computed tomography scans were taken from 21 locations along humeral, femoral, and tibial diaphyses in 20 adults from a late prehistoric central Illinois Valley cemetery. Mechanical properties calculated from images with (a) artificially filled medullary cavities (“solid”) and (b) true unaltered cross‐sections were compared at each section location using least squares regression. Results indicate that, in this sample, polar second moments of area (J), polar section moduli (Z_p), and cross‐sectional shape (I_max/I_min) calculated from periosteal contours correspond strongly with those calculated from cross‐sections that include the medullary cavity. Correlations are high throughout most of the humeral diaphysis and throughout large portions of femoral and tibial diaphyses (R² = 0.855–0.998, all P < 0.001, %SEE ≤ 8.0, %PE ≤ 5.0), the major exception being the proximal quarter of the tibial diaphysis for J and Z_p. The main source of error was identified as variation in %CA. Results reveal that CSG properties quantified from periosteal contours provide comparable results to (and are likely to detect the same differences among individuals as) true CSG properties along large portions of long bone diaphyses. Am J Phys Anthropol, 2013. © 2013 Wiley Periodicals, Inc.     

Technical note: A stereological analysis of the cross‐sectional variability of the femoral osteon population

Unbiased selection of regions of interest (ROIs) and unbiased definition of histological structures are needed to improve the repeatability of microscopic methods for age at death determination and to reduce operator subjectivity. We present results obtained by selecting ROIs according to stereological principles on a sample of 28 femoral cross sections of Caucasoid males aged 20–89 years. A regular grid was overlaid on the cross section, and the ROIs were selected as close as possible to the periosteum in the anterior, lateral, and medial regions. The areas consisting of all intact secondary osteons plus fragments were outlined and osteon population density, percent osteon population, area, and perimeter were calculated using stereological methods and software. Overall, the analyses of intra‐ and inter‐section variability showed no significant difference between the ROIs, i.e., the location within the cross section of the ROIs does not affect the outcome of the analyses. The individual variability was found to be higher in adults aged 30–55 years than in other age ranges. ranges. Am J Phys Anthropol 2010. © 2010 Wiley‐Liss, Inc.     

The importance of accounting for the area of the medullary cavity in cross‐sectional geometry: A test based on the femoral midshaft

In cross‐sectional geometric (CSG) studies, both the subperiosteal and endosteal contours are considered important factors in determining bone bending rigidity. Recently, regression equations predicting CSG properties from a section's external dimensions were developed in a world‐wide sample of human long bones. The results showed high correlations between some subperiosteally derived and actual CSG parameters. We present a theoretical model that further explores the influence of endosteal dimensions on CSG properties. We compare two hypothetical femoral midshaft samples with the same total subperiosteal area but with percentages of cortical bone at the opposite ends of published human variation for population sample means. Even in this relatively uncommon scenario, the difference between the samples in the resultant means for predicted femoral polar second moment of area (J) appears to be modest: power analysis indicates that a minimum sample size of 61 is needed to detect the difference 90% of the time via a t‐test. Moreover, endosteal area can be predicted—although with substantial error—from periosteal area. Despite this error, including this relationship in subperiosteally derived estimates of J produces sample mean estimates close to true mean values. Power analyses reveal that when similar samples are used to develop prediction equations, a minimum sample of hundreds or more may be needed to distinguish a predicted mean J from the true mean J. These results further justify the use of regression equations estimating J from periosteal contours when analyzing behaviorally induced changes in bone rigidity in ancient populations, when it is not possible to measure endosteal dimensions. However, in other situations involving comparisons of individual values, growth trends, and senescence, where relative cortical thickness may vary greatly, inclusion of endosteal dimensions is still important. Am J Phys Anthropol, 2010. © 2010 Wiley‐Liss, Inc.     

A new longirostrine dyrosaurid (Crocodylomorpha,Mesoeucrocodylia) from the Paleocene of north‐eastern Colombia: biogeographic and behavioural implications for New‐World Dyrosauridae

Abstract: Fossils of dyrosaurid crocodyliforms are limited in South America, with only three previously diagnosed taxa including the short‐snouted Cerrejonisuchus improcerus from the Paleocene Cerrejón Formation of north‐eastern Colombia. Here we describe a second dyrosaurid from the Cerrejón Formation, Acherontisuchus guajiraensis gen. et sp. nov., based on three partial mandibles, maxillary fragments, teeth, and referred postcrania. The mandible has a reduced seventh alveolus and laterally depressed retroarticular process, both diagnostic characteristics of Dyrosauridae. Acherontisuchus guajiraensis is distinct among known dyrosaurids in having a unique combination of craniomandibular characteristics, and postcranial morphology that suggests it may have occupied a more placid, fluvial habitat than most known Old‐World dyrosaurids. Results from a cladistic analysis of Dyrosauridae, using 82 primarily cranial and mandibular characters, support an unresolved relationship between A. guajiraensis and a combination of New‐ and Old‐World dyrosaurids including Hyposaurus rogersii, Congosaurus bequaerti, Atlantosuchus coupatezi, Guarinisuchus munizi, Rhabdognathus keiniensis and Rhabdognathus aslerensis. Our results are consistent with an African origin for Dyrosauridae with multiple dispersals into the New World during the Late Cretaceous and a transition from marine habitats in ancestral taxa to more fluvial habitats in more derived taxa.     

First fossil Molinaranea Mello‐Leitão, 1940 (Araneae: Araneidae), from middle Miocene Dominican amber,with a phylogenetic and palaeobiogeographical analysis of the genus

The first fossil Molinaranea is described, from middle Miocene Dominican amber. This record extends the known range of the genus back 16 million years; it also extends the geographical range of the genus through time, with extant species known only from Chile, Argentina, the Falkland Islands, and Juan Fernandez Island. A parsimony‐based phylogenetic analysis was performed, which indicates that the fossil species, Molinaranea mitnickii sp. nov. , is nested with Molinaranea magellanica Walckenaer, 1847 and Molinaranea clymene Nicolet, 1849 . A modified Brooks parsimony analysis was conducted in order to examine the biogeography and origins of the fossil species in the Dominican Republic; the analysis suggests that M. mitnickii sp. nov. arrived in Hispaniola from South America as a result of a chance dispersal event. © 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 158 , 711–725.     

Estimating population structure under nonequilibrium conditions in a conservation context: continent-wide population genetics of the giant Amazon river turtle, Podocnemis expansa (Chelonia; Podocnemididae)

Giant Amazon river turtles, Podocnemis expansa, are indigenous to the Amazon, Orinoco, and Essequibo River basins, and are distributed across nearly the entire width of the South American continent. Although once common, their large size, high fecundity, and gregarious nesting, made P. expansa especially vulnerable to over-harvesting for eggs and meat. Populations have been severely reduced or extirpated in many areas throughout its range, and the species is now regulated under Appendix II of the Convention on International Trade in Endangered Species. Here, we analyse data from mitochondrial DNA sequence and multiple nuclear microsatellite markers with an array of complementary analytical methods. Results show that concordance from multiple data sets and analyses can provide a strong signal of population genetic structure that can be used to guide management. The general lack of phylogeographic structure but large differences in allele and haplotype frequencies among river basins is consistent with fragmented populations and female natal-river homing. Overall, the DNA data show that P. expansa populations lack a long history of genetic differentiation, but that each major tributary currently forms a semi-isolated reproductive population and should be managed accordingly.     

The presence of Tawera gayi (Hupé in Gay, 1854) (Veneridae, Bivalvia) in southern South America: Did Tawera achieve a Late Cenozoic circumpolar traverse?

Cenozoic Tawera Marwick, 1927 from the Southern Hemisphere exhibits a pattern of disjunt distribution around the southern oceans. A single species, Tawera gayi (Hupé in [Gay, C. (1854). Historia Física y Política de Chile, Zoología 8. Paris.]) is confined to southern South America. Taking into account the occurrence of Tawera in the fossil record, taxonomy based on shell morphology, and available information on extant species of Tawera, it is plausible that the genus appeared first in southern Australia during the Early Miocene, and then expanded and radiated to New Zealand. It also appears that Tawera first crossed from Australasia to South America during the Early Pleistocene. This picture can be better explained if Tawera was able to achieve circumglobal range by means of the Antarctic Circumpolar Current. Thus, different potential factors of dispersal (i.e., larval dispersal, drifting, kelp rafting and Pleistocene cooling) are considered and discussed.

Shell morphology and overall appearance of Tawera gayi is very similar to Tawera philomela (Smith, 1885) from South Africa and Tawera mawsoni (Hedley, 1916) from Macquarie Island, suggesting these taxa have a close relationship. One postulated explanation, which should be confirmed by means of a phylogenetic study, is a subsequent migration of Tawera from South America arriving first to the Southern African Region (via the West Wind Drift Islands Province), and then probably coming back again to Australasia. It could have been mediated via the same current during the Late Pleistocene and much later during the Holocene.     

The influence of social structure on brood survival and development in a socially polymorphic ant: insights from a cross‐fostering experiment

Animal societies vary in the number of breeders per group, which affects many socially and ecologically relevant traits. In several social insect species, including our study species Formica selysi, the presence of either one or multiple reproducing females per colony is generally associated with differences in a suite of traits such as the body size of individuals. However, the proximate mechanisms and ontogenetic processes generating such differences between social structures are poorly known. Here, we cross‐fostered eggs originating from single‐queen (= monogynous) or multiple‐queen (= polygynous) colonies into experimental groups of workers from each social structure to investigate whether differences in offspring survival, development time and body size are shaped by the genotype and/or prefoster maternal effects present in the eggs, or by the social origin of the rearing workers. Eggs produced by polygynous queens were more likely to survive to adulthood than eggs from monogynous queens, regardless of the social origin of the rearing workers. However, brood from monogynous queens grew faster than brood from polygynous queens. The social origin of the rearing workers influenced the probability of brood survival, with workers from monogynous colonies rearing more brood to adulthood than workers from polygynous colonies. The social origin of eggs or rearing workers had no significant effect on the head size of the resulting workers in our standardized laboratory conditions. Overall, the social backgrounds of the parents and of the rearing workers appear to shape distinct survival and developmental traits of ant brood.     

The effect of stocking with 0+ year age‐class Atlantic salmon Salmo salar fry: a case study from the River Bush,Northern Ireland

An enhancement programme based on stocking 0+ year age‐class Atlantic salmon Salmo salar, conducted in the River Bush, Northern Ireland, U.K. over the period 1996–2005, was reviewed with reference to the performance and biological characteristics of wild fish. Wild ova to 0+ year fry (summer) survival was c. 8% with subsequent wild 0+ year fry‐to‐smolt survival c. 9%. Stocked unfed 0+ year juveniles gave c. 1% survival to smolt whilst fed 0+ year S. salar stocked in late summer exhibited survival at c. 5%. Stocking with unfed and fed fry contributed to increased smolt production and helped attain local management objectives between 2001 and 2005. Significant differences in biological characteristics were observed between wild and stocked‐origin fish. Wild‐smolt cohorts were dominated by 2+ year age‐class fish on the River Bush whilst smolts originating from fed fry mostly comprised younger 1+ year individuals. The mean mass of 1+ year smolts derived from stocked fed fry was significantly lower than that of wild 1+ year smolts, although these differences were not evident between older age classes. Differences in run timing between wild smolts and smolts derived from stocked fry were also apparent with the stocked‐origin fish tending to run earlier than wild fish. Although the stocking exercise was useful in terms of maximizing freshwater production, concerns over the quality of stocked‐origin recruits and the long term consequences for productivity are highlighted.     

Fine‐scale microhabitat selection for dense vegetation in a heathland rodent,Rattus lutreolus: Insights from intraspecific and temporal patterns

Abstract Vegetation is a dynamic habitat component and successional changes in vegetation structure can lead to concomitant changes in the communities of animals living in a particular area. Heathland rodents are a classic example, with vegetation at different ages post fire being dominated by different species. While broad associations are often demonstrated between the distribution and abundance of species and vegetation structure, the causal relationships are poorly understood. Studies of temporal and sex‐ or age‐specific patterns can provide strong insights into the processes underling patterns of habitat selection. In an attempt to better understand the mechanistic links between rodent successional patterns and vegetation structure in heathlands, we conducted a detailed study of microhabitat use by the swamp rat, Rattus lutreolus, in a native heathland in south‐eastern Australia. Rattus lutreolus typically occurs in late‐succession heath and is frequently associated with high vegetation density. Our assessment of vegetation at trapping stations, and also along trails used by the animals (using the spool‐and‐line tracking technique), revealed strong selection by the rats for dense vegetation by both day and night. The spool‐and‐line tracking approach revealed distinct intraspecific and temporal patterns. During the day, females foraged in vegetation of much higher density than did juveniles, with males behaving intermediately. During the night, however, all animals selected dense vegetation irrespective of sex or age, although the mean density of vegetation selected during the night was lower than it was during the day. These patterns were independent of daily maximum and minimum air temperature and were therefore unlikely to be related to microclimate. We propose instead that high vegetation density acts as a source of protection from predators, allowing R. lutreolus to forage safely both by day and by night.     

The population demography of Betula maximowicziana,a cool‐temperate tree species in Japan,in relation to the last glacial period: its admixture‐like genetic structure is the result of simple population splitting not admixing

Conservation of the local genetic variation and evolutionary integrity of economically and ecologically important trees is a key aspect of studies involving forest genetics, and a population demographic history of the target species provides valuable information for this purpose. Here, the genetic structure of 48 populations of Betula maximowicziana was assessed using 12 expressed sequence tag–simple sequence repeat (EST‐SSR) markers. Genetic diversity was lower in northern populations than southern ones and structure analysis revealed three groups: northern and southern clusters and an admixed group. Eleven more genomic‐SSR loci were added and the demographic history of these three groups was inferred by approximate Bayesian computation (ABC). The ABC revealed that a simple split scenario was much more likely than isolation with admixture, suggesting that the admixture‐like structure detected in this species was due to ancestral polymorphisms. The ABC analysis suggested that the population growth and divergence of the three groups occurred 96 800 (95% CI, 20 500–599 000) and 28 300 (95% CI, 8700–98 400) years ago, respectively. We need to be aware of several sources of uncertainty in the inference such as assumptions about the generation time, overlapping of generations, confidence intervals of the estimated parameters and the assumed model in the ABC. However, the results of the ABC together with the model‐based maps of reconstructed past species distribution and palaeoecological data suggested that the modern genetic structure of B. maximowicziana originated prior to the last glacial maximum (LGM) and that some populations survived in the northern range even during the LGM.