DENTINE ENAMEL

enamelprisms

ameloblastsat EFF

striae of Retzius (old EFFs)

Havers-Halberg Rhythms in Canis familiaris.Russell T. Hogg1, Timothy G. Bromage2, Bin Hu2

1Rehabilitation Sciences, FGCU; 2Basic Sciences and Biomaterials & Biomimetics, NYU College of Dentistry

Figure 2. Variation of RP (i.e., HHO) in mammals. The left image shows a histological section of an

eastern wooly lemur molar (Avahi laniger), whose RP = 3 days (yellow arrows = striae of Retzius, with 3

cross-striations visible between them, red arrows demarcate transition between striations). The right

image shows a section from an elephant molar (Elephas recki), where RP = 14 days (black arrows =

cross striations, blue lines = striae of Retzius).

Acknowledgments & References

HHO was quantified as the periodicity, in days, between successive striae of Retzius

(Retzius periodicity, RP) in 11 domestic dogs of different breeds (see Table 1). To obtain

this periodicity, 24-hour growth increments (cross-striations) were counted between

successive striae of Retzius on histological specimens. Data were gathered from

embedded thin sections of teeth, imaged using polarized light microscopy. For information

on the interpretation of RP from histological sections, see Figs. 1 and 2. Natural

logarithms (ln) of RP data were regressed against ln body mass and compared to prior

results obtained for primates (Hogg et al. 2015).

r2 = 0.8p < 0.01n = 48

r2 = 0.05p = .3n = 22

100 µm

Discussion

Introduction

Results

Materials & Methods

We aim to assess variation in Havers-Halberg oscillation (HHO) periodicities among

domestic dogs (Canis familiaris). The HHO is hypothesized to be a hypothalamus-

generated biorhythm that coordinates multiple life history variables including body size,

metabolic rate, and reproductive output (Bromage et al. 2009). The periodicity of this clock

varies among and within species, but not within individuals. In monkeys and apes, HHO

periodicity is strongly correlated with body mass, but in lemurs this is not the case. Lemurs

also have a very restricted range of HHO variation (Hogg et al. 2015). This raises the

question of how HHO rhythms and body size evolution can be decoupled. Domestic dogs

have high body mass variation but low variation in life history variables such as lifespan,

linked to intense artificial selection for IGF1 gene sequence variants (Sutter et al. 2007)

rather than neuroendocrine mechanisms such as the HHO. Based on this, we hypothesize

that HHO variation in dogs 1) will be narrow considering their body mass range, and 2) will

not be correlated with body mass; they will therefore resemble lemurs, providing potential

insight into lemur evolution.

Specimen Breed Sex RP ln RP Body Mass (kg) ln Body Mass2599 ? f 5 1.609 3.345 1.2083410 Spaniel m 5 1.609 11.350 2.4293474 ? f 5 1.609 31.780 3.4593475 ? m 5 1.609 15.770 2.7583515 St. Bernard m 5 1.609 90.710 4.5083532 ? ? 4 1.386 6.894 1.9313535 French Poodle f 6 1.792 20.259 3.0093544 Doberman m 6 1.792 17.187 2.8443545 Collie m 5 1.609 20.259 3.0093546 German Shepherd m 4 1.386 16.826 2.823"Harold" English Bulldog ? 4 1.386 27.240 3.305

Figure 1. Formation of striae

of Retzius,. An ameloblast

epithelium deposits enamel

matrix appositionally, moving

from the dentine toward the

future enamel surface (curved

black line to right). Over a

predetermined rhythmic

interval, a visible line forms in

enamel at successive positions

of the epithelium (enamel

formation front, or EFF). the

striae of Retzius. 24-hour

growth lines (cross-striations)

can between striae can be

summed to determine the RP

(see Fig. 2 & 3). Similar

growth lines appear in dentine.

The hypotheses are corroborated, in that 1) dogs have a narrow range of HHO variation,

and 2) dog HHO period is not significantly correlated with body mass. HHO periodicities

in dogs range between 4-6 days even though our sample spans nearly 2 orders of

magnitude in body mass. This may explain why dogs can have such a large size

variation, yet have a fairly consistent life history package in terms of lifespan and

reproductive output. I.e., IGF1 mutations explain the body size variation, but do not have

an impact on HHO biology and life history, which seems not to have been as affected by

artificial selection. Based on our results, we predict that similar physiological

mechanisms may be at play in lemurs.

Figure 3. HHO periodicities in sections from Canis familiaris. The left image is taken from dentine, the

right image from enamel. Large white arrows signify long-period growth lines (Andresen lines in dentine,

striae of Retzius in enamel), whereas small white arrows indicate one group of 24-hour growth increments

between two long period lines. In both cases, the RP = 4 days.

Table 1. Raw data included in study. Body mass data are taken from records for the individuals included.

RP

(H

HO

)

Group

ln body mass

lnR

P (

HH

O)

lnR

P (

HH

O)

ln body mass

r2 = 0.12p = 0.74n = 11

Group

ln b

od

y m

ass

Fig. 4. RP variation for the same body mass

range among all three groups. Dogs and lemurs

(purple and green) both exhibit much less

variation than monkeys and apes (blue).

Fig. 5. ln body mass across RP = 4, 5, and 6 (the

dog range). Both dogs have an overall larger body

mass for the same RP as monkeys and apes,

implying a faster life overall life history (t test p =

.007). For lemurs, n = 2 so no analysis was run.

This research funded by the 2010 Max Planck Research Award which is endowed by the German Federal Ministry of Education and Research to the Max Planck Society and the Alexander von Humboldt Foundation in respect of the Hard Tissue Research Program in Human Paleobiomics.

Bromage TG, Lacruz RS, Hogg RT, Goldmann HM, McFarlin SC, et al. (2009) Lamellar bone reconciles enamel rhythms, body size, and organismal life history. Calcif Tissue Int 84: 388-404.

Hogg RT, Godfrey LR, Schwartz GT, et al..(2015) Lemur biorhythms and life history evolution. PLOS One 10:e0134210. doi:10.1371/journal.pone.0134210.

Sutter NB, Bustamante CD, Chase K, Gray MM, Zhao K, et al. (2007) A single IGF1 allele is a major determinant of small size in dogs. Science 316: 112-115.

Fig. 6. Regression of ln RP against

ln body mass among domestic dog

sample. Results corroborate the

hypothesis that body mass and HHO

are not significantly correlated in

dogs.

Fig. 7. Regression of ln RP against

ln body mass among primates (from

Hogg et al. 2015). Lemurs have a

poor correlation and narrow range of

variation in RP relative to body size,

similar to dogs. D = Daubentonia.