Influences of Domestication and Island Evolution on Dental Growth in Sheep

Abstract

Domestication and island evolution can lead to changes of life history along the slow-fast gradient. Shifts of life history patterns, in turn, are potentially related to alterations of patterns and timing of tooth eruption. Schultz's rule predicts an earlier eruption of molars relative to premolars as fecundity increases during the domestication process. On the other hand, evolution on a predatorfree, resource limited island might lead to a generally slow life history and delayed tooth eruption, as in the Plio-Pleistocene Balearic caprine Myotragus. In this study, we investigate tooth eruption and its relation to life history in a unique sheep population that is an example of both domestication and island evolution: the ancient and feral Soay sheep (Ovis aries) of the St. Kilda archipelago, Scotland. Tooth eruption timing and sequence is investigated in a comparative framework featuring new data on other domestic sheep (O. aries), including European mouflon (O. a. musimon), as well as wild sheep (O. vignei, O. cycloceros, O. arkal, O. orientalis, O. ammon). These data indicate that the order of eruption is similar in wild and domestic sheep, despite the fundamental life history changes that came about with domestication. However, in contrast to other domestic sheep breeds, Soay sheep erupt their teeth at an absolute older age and also tend to grow more slowly, which resembles the evolutionary trend in island-adapted Myotragus. Despite these similarities, Soay sheep do not share the slow life history pattern inferred for Myotragus, highlighting the distinctive nature of tooth eruption in Soay sheep.

Dentoalveolar Defects of Hypophosphatasia are Recapitulated in a Sheep Knock-In Model

“…Sheep exfoliate their primary incisors and permanent incisors erupt into the oral cavity between 12 and 36 months, starting with central incisors and proceeding distally. ( 24 , 25 ) In both humans and sheep, odontoclastic resorption of tooth roots and loss of periodontal attachment leads to physiological exfoliation of primary teeth with substantially resorbed roots. However, cementum (and potentially alveolar bone) defects associated with HPP lead to poor periodontal attachment and premature primary tooth loss before roots have undergone extensive resorption, appearing as “fully rooted” teeth.…”

“…Sheep primary teeth sequentially erupt into the oral cavity after birth, with replacement between 12 and 18 months and full replacement by 2 to 3.5 years old. ( 24 , 25 ) The TNAP protein sequence is highly conserved in humans and sheep, with over 90% structural similarity, including conservation of the orthologous isoleucine among mammals. ( 19 ) The sheep model reproduced the broad spectrum of HPP craniofacial and dental manifestations, including reduced circulating ALP activity, hypomineralization, and metaphyseal flaring of long bones.…”

“…Sheep exfoliate their primary incisors and permanent incisors erupt into the oral cavity between 12 and 36 months, starting with central incisors and working distally. ( 24 , 25 ) Exfoliated or loosely attached and therefore extracted primary incisors were collected for high‐resolution μCT scanning and analysis of dental structures. When multiple teeth were collected from the same sheep, measurements from teeth were averaged to generate a single value for inclusion in graphs and statistical analysis.…”

A biomechanical perspective on molar emergence and primate life history

“…Primates, however, are not the only mammals for which these linked phenotypes exist. Recent work reveals a tight correlation between the same developmental parameter (later molar emergence ages) and the same orofacial anatomy (foreshortened jaw length) in ungulates ( 41 ). Future work should focus on revealing the gene regulatory networks that coordinate cranial and dental morphogenesis [e.g., ( 42 )].…”