Lemur Biorhythms and Life History Evolution

Weaning, parturitions and illnesses are recorded in rhesus macaque (Macaca mulatta) dental cementum microstructure

Many open questions in evolutionary studies relate to species' physiological adaptations, including the evolution of their life history and reproductive strategies. There are few empirical methods capable of detecting and timing physiologically impactful events such as weaning, parturition and illnesses from hard tissue remains of either extant or extinct species. Cementum is an incremental tissue with post eruption annual periodicity, which covers the tooth root and functions as a recording structure of an animal's physiology. Here we test the hypothesis that it is possible to detect and time physiologically impactful events through the analysis of dental cementum microstructure. Our sample comprises 41 permanent and deciduous teeth from male and female rhesus macaques (Macaca mulatta) with known medical, lifestyle and life history information. We develop a semi-automated method of cementum histological analysis for the purpose of event detection and timing, aimed at significantly reducing the amount of intra- and interobserver errors typically associated with histological analyses. The results of our work show that we were able to detect known events including weaning, parturition, illness and physical trauma with high accuracy (false negative rate = 3.2%; n = 1), and to time them within an average absolute difference of 0.43 years (R²  = .98; p < .05). Nonetheless, we could not distinguish between the several types of stressful events underlying the changes in cementum microstructure. While this study is the first to identify a variety of life history events in macaque dental cementum, laying foundations for future work in conservation and evolutionary studies of both primates and toothed mammals at large, there are some limitations. Other types of analyses (possibly chemical ones) are necessary to tease apart the causes of the stressors.

A wolf from Gravettian site Pavlov I, Czech Republic: Approach to skull pathology

OBJECTIVE

Describe pathological features on internal and external aspects of the skull of an ancient grey wolf.

MATERIALS

Wolf remains that were found at the southwestern settlement Area A of Gravettian site Pavlov I.

METHODS

Visual observation and description; microcomputed tomography; porosity and fragmentation indices for internal and external skull features; histological section of the fourth upper premolar tooth.

RESULTS

Dorsally, the sagittal crest revealed bone healing and remodeling. The sagittal lesion differential diagnosis was blunt trauma with or without fracture. Ventrally, otic region pathology included severe proliferation and lysis (osteomyelitis). The pathology was not resolvable among differential (microbial) causes of osteomyelitis, although other potential etiologies were ruled out.

CONCLUSIONS

Probable first report of otic region osteomyelitis in an ancient grey wolf.

SIGNIFICANCE

The proximity of the wolf remains to human-related findings, and presence of red ochre and shells, suggest human involvement in the burial.

LIMITATIONS

This is a single specimen with differential diagnoses that were not resolvable to a single definitive diagnosis.

SUGGESTIONS FOR FURTHER RESEARCH

Further investigation of the possible anthropological significance of the burial circumstances.

Mid-Cenozoic climate change, extinction, and faunal turnover in Madagascar, and their bearing on the evolution of lemurs

Background

Was there a mid-Cenozoic vertebrate extinction and recovery event in Madagascar and, if so, what are its implications for the evolution of lemurs? The near lack of an early and mid-Cenozoic fossil record on Madagascar has inhibited direct testing of any such hypotheses. We compare the terrestrial vertebrate fauna of Madagascar in the Holocene to that of early Cenozoic continental Africa to shed light on the probability of a major mid-Cenozoic lemur extinction event, followed by an “adaptive radiation” or recovery. We also use multiple analytic approaches to test competing models of lemur diversification and the null hypothesis that no unusual mid-Cenozoic extinction of lemurs occurred.

Results

Comparisons of the terrestrial vertebrate faunas of the early Cenozoic on continental Africa and Holocene on Madagascar support the inference that Madagascar suffered a major mid-Cenozoic extinction event. Evolutionary modeling offers some corroboration, although the level of support varies by phylogeny and model used. Using the lemur phylogeny and divergence dates generated by Kistler and colleagues, RPANDA and TESS offer moderate support for the occurrence of unusual extinction at or near the Eocene-Oligocene (E-O) boundary (34 Ma). TreePar, operating under the condition of obligate mass extinction, found peak diversification at 31 Ma, and low probability of survival of prior lineages. Extinction at the E-O boundary received greater support than other candidate extinctions or the null hypothesis of no major extinction. Using the lemur phylogeny and divergence dates generated by Herrera & Dàvalos, evidence for large-scale extinction diminishes and its most likely timing shifts to before 40 Ma, which fails to conform to global expectations.

Conclusions

While support for large-scale mid-Cenozoic lemur extinction on Madagascar based on phylogenetic modeling is inconclusive, the African fossil record does provide indirect support. Furthermore, a major extinction and recovery of lemuriforms during the Eocene-Oligocene transition (EOT) would coincide with other major vertebrate extinctions in North America, Europe, and Africa. It would suggest that Madagascar’s lemurs were impacted by the climate shift from “greenhouse” to “ice-house” conditions that occurred at that time. This could, in turn, help to explain some of the peculiar characteristics of the lemuriform clade.

Enamel multidien biological timing and body size variability among individuals of Chinese Han and Tibetan origins

AIMS

To measure the number of days of enamel formation between periodic striae of Retzius growth lines, the Retzius periodicity (RP), and to compare this multi-day, or multidien rhythm, to body height and weight among people from Beijing, China and Lhasa, Tibet/China.

SUBJECTS AND METHODS

Subjects requiring dental extractions from clinics in Beijing, China (N = 338) and Lhasa, Tibet/China (N = 227) provided a tooth and body size information. Multiple observers examined histological sections of the teeth and recorded RP. RP values were statistically compared to body height and weight.

RESULTS

In Beijing and Lhasa samples, respectively, average height was 166.38 and 165.70 cm, average weight was 59.53 and 66.53 kg, and average RP was 7.47 and 7.69 d. Statistically significant differences were found between Beijing and Lhasa weight and RP means. Correlations for height and weight against RP were significant, but only comparatively strong for height.

CONCLUSIONS

Supporting the negative correlation presented in previous studies, RP is negatively associated with height and weight among a large intraspecific sample of people from Beijing and Lhasa. RP represents a metabolic-mediated multidien biological timing mechanism responsible for the rate of cell proliferation and maintenance of the body.

Microscopic markers of an infradian biorhythm in human juvenile ribs

Recent studies have indicated that there may be an infradian systemic biorhythm that coordinates aspects of human hard tissue growth and influences adult body size. Here we investigate if evidence of this biorhythm retained in human teeth as the periodicity of Retzius lines (RP) corresponds with the microstructural growth of a non-weight bearing bone, the rib, in a sample of 50 human juvenile skeletons. Using static histomorphometric methods, the RP of one permanent tooth from each skeleton was calculated and combined with measures of bone remodeling in a rib from the same individual. Results provide the first evidence that the infradian biorhythm is linked to bone remodeling in children. Retzius periodicity was negatively correlated with relative osteon area (r = -0.563, p = 0.008) and positively related to Haversian canal area (r = 0.635, p = 0.002) and diameter (r = 0.671, p = 0.001) in children between the age of 8 to 12 years. There was also a negative correlation between RP and the relative cortical area of ribs (r = -0.500, p = 0.048). Relationships between bone remodeling and the biorhythm were much more variable in younger children. Results imply that as the biorhythm speeds up there is increased bone deposition during remodeling of the rib, leading to the larger osteonal lamellar bone areas and smaller Haversian canals in children between 8 and 12 years of age. Our results support the idea that there is an infradian biorhythm that coordinates aspects of human hard tissue growth.

Histology of dental long-period biorhythms in Canis familiaris

Our objective is to assess variation in Havers-Halberg oscillation (HHO) periodicities among domestic dogs (Canis familiaris). The HHO is hypothesized to be a hypothalamic-generated biorhythm coordinating multiple life history variables including body mass and lifespan. Dogs have a broad mass range spanning two orders of magnitude, but this variation has been shown to result from selection on very few genetic loci, and dogs have low variation in other life history traits. Therefore, we predict that HHO variation will not be correlated to body mass among domestic dogs, as it is in anthropoid primates. To test the prediction, we examined dog HHO periodicity via manifestations in tooth enamel and dentine, quantifying HHO rhythm histologically. HHO rhythm is reflected in teeth as the number of days between secretion of successive striae of Retzius (enamel) and Andresen lines (dentine), a value referred to as Retzius periodicity (RP). We counted ca. 24-h growth lines between successive Retzius and Andresen lines to determine RP in histological thin-sections from canine teeth of 19 dogs, representing different breeds and sizes. To test our hypothesis, we regressed RP periodicity against body mass data. Dogs have low RP variation for their body mass range, with a modal periodicity of 5 days and a range of 4-6 days. RP was not significantly correlated with body mass. We conclude that mass variation in dogs does not seem driven by HHO physiology, consistent with findings that IGF1 variants produce dog mass variation. However, low RP (and by extension HHO) variation is consistent with low variation in dog lifespan and gestation, suggesting that dog life history may still be governed by HHO mechanisms even if body mass does not reflect this.

The biorhythm of human skeletal growth

Evidence of a periodic biorhythm is retained in tooth enamel in the form of Retzius lines. The periodicity of Retzius lines (RP) correlates with body mass and the scheduling of life history events when compared between some mammalian species. The correlation has led to the development of the inter-specific Havers-Halberg oscillation (HHO) hypothesis, which holds great potential for studying aspects of a fossil species biology from teeth. Yet, our understanding of if, or how, the HHO relates to human skeletal growth is limited. The goal here is to explore associations between the biorhythm and two hard tissues that form at different times during human ontogeny, within the context of the HHO. First, we investigate the relationship of RP to permanent molar enamel thickness and the underlying daily rate that ameloblasts secrete enamel during childhood. Following this, we develop preliminary research conducted on small samples of adult human bone by testing associations between RP, adult femoral length (as a proxy for attained adult stature) and cortical osteocyte lacunae density (as a proxy for the rate of osteocyte proliferation). Results reveal RP is positively correlated with enamel thickness, negatively correlated with femoral length, but weakly associated with the rate of enamel secretion and osteocyte proliferation. These new data imply that a slower biorhythm predicts thicker enamel for children but shorter stature for adults. Our results develop the intra-specific HHO hypothesis suggesting that there is a common underlying systemic biorhythm that has a role in the final products of human enamel and bone growth.

Dental development and age at death of the holotype of Anapithecus hernyaki (RUD 9) using synchrotron virtual histology

The chronology of dental development and life history of primitive catarrhines provides a crucial comparative framework for understanding the evolution of hominoids and Old World monkeys. Among the extinct groups of catarrhines are the pliopithecoids, with no known descendants. Anapithecus hernyaki is a medium-size stem catarrhine known from Austria, Hungary and Germany around 10 Ma, and represents a terminal lineage of a clade predating the divergence of hominoids and cercopithecoids, probably more than 30 Ma. In a previous study, Anapithecus was characterized as having fast dental development. Here, we used non-destructive propagation phase contrast synchrotron micro-tomography to image several dental microstructural features in the mixed mandibular dentition of RUD 9, the holotype of A. hernyaki. We estimate its age at death to be 1.9 years and describe the pattern, sequence and timing of tooth mineralization. Our results do not support any simplistic correlation between body mass and striae periodicity, since RUD 9 has a 3-day periodicity, which was previously thought unlikely based on body mass estimates in Anapithecus. We demonstrate that the teeth in RUD 9 grew even faster and initiated even earlier in development than suggested previously. Permanent first molars and the canine initiated 49 and 38 days prenatally, respectively. These results contribute to a better understanding of dental development in Anapithecus and may provide a window into the dental development of the last common ancestor of hominoids and cercopithecoids.

Biorhythms, deciduous enamel thickness, and primary bone growth: a test of the Havers-Halberg Oscillation hypothesis

Across mammalian species, the periodicity with which enamel layers form (Retzius periodicity) in permanent teeth corresponds with average body mass and the pace of life history. According to the Havers-Halberg Oscillation hypothesis (HHO), Retzius periodicity (RP) is a manifestation of a biorhythm that is also expressed in lamellar bone. Potentially, these links provide a basis for investigating aspects of a species' biology from fossilized teeth. Here, we tested intra-specific predictions of this hypothesis on skeletal samples of human juveniles. We measured daily enamel growth increments to calculate RP in deciduous molars (n = 25). Correlations were sought between RP, molar average and relative enamel thickness (AET, RET), and the average amount of primary bone growth (n = 7) in humeri of age-matched juveniles. Results show a previously undescribed relationship between RP and enamel thickness. Reduced major axis regression reveals RP is significantly and positively correlated with AET and RET, and scales isometrically. The direction of the correlation was opposite to HHO predictions as currently understood for human adults. Juveniles with higher RPs and thicker enamel had increased primary bone formation, which suggests a coordinating biorhythm. However, the direction of the correspondence was, again, opposite to predictions. Next, we compared RP from deciduous molars with new data for permanent molars, and with previously published values. The lowermost RP of 4 and 5 days in deciduous enamel extends below the lowermost RP of 6 days in permanent enamel. A lowered range of RP values in deciduous enamel implies that the underlying biorhythm might change with age. Our results develop the intra-specific HHO hypothesis.

The Swine Plasma Metabolome Chronicles "Many Days" Biological Timing and Functions Linked to Growth

The paradigm of chronobiology is based almost wholly upon the daily biological clock, or circadian rhythm, which has been the focus of intense molecular, cellular, pharmacological, and behavioral, research. However, the circadian rhythm does not explain biological timings related to fundamental aspects of life history such as rates of tissue/organ/body size development and control of the timing of life stages such as gestation length, age at maturity, and lifespan. This suggests that another biological timing mechanism is at work. Here we focus on a "many days" (multidien) chronobiological period first observed as enigmatic recurring growth lines in developing mammalian tooth enamel that is strongly associate with all adult tissue, organ, and body masses as well as life history attributes such as gestation length, age at maturity, weaning, and lifespan, particularly among the well studied primates. Yet, knowledge of the biological factors regulating the patterning of mammalian life, such as the development of body size and life history structure, does not exist. To identify underlying molecular mechanisms we performed metabolome and genome analyses from blood plasma in domestic pigs. We show that blood plasma metabolites and small non-coding RNA (sncRNA) drawn from 33 domestic pigs over a two-week period strongly oscillate on a 5-day multidien rhythm, as does the pig enamel rhythm. Metabolomics and genomics pathway analyses actually reveal two 5-day rhythms, one related to growth in which biological functions include cell proliferation, apoptosis, and transcription regulation/protein synthesis, and another 5-day rhythm related to degradative pathways that follows three days later. Our results provide experimental confirmation of a 5-day multidien rhythm in the domestic pig linking the periodic growth of enamel with oscillations of the metabolome and genome. This association reveals a new class of chronobiological rhythm and a snapshot of the biological bases that regulate mammalian growth, body size, and life history.