Biology subjects

Loch, C.

Publications and source records attributed to Loch, C..

4 recordsLinked to original sources

bioRxiv2021

Variation in mechanical and structural properties of enamel in primate molars

Mechanical properties of enamel are known to vary across molar crowns in some primates, but the association of this variation with phylogeny, structural properties and tribological behaviour is not well understood. In this study, 20 molars from a range of primate taxa (n=15) were studied using nanoindentation, micro-CT scanning, and SEM imaging. After micro-CT scanning, teeth were sectioned in the lingual-buccal plane through the mesial cusps. Five positions (buccal lateral, buccal cuspal, occlusal middle, lingual cuspal, lingual lateral) were studied in three locations (inner, middle, outer enamel regions). The results show middle enamel had the highest hardness and elastic modulus values in all positions. Non-functional molar sides (lingual in lower molars and buccal in upper molars) had higher hardness values than their functional counterparts. Increase in prism size was associated with a decrease in hardness in some tooth positions, and mineral density showed a significant relationship with elastic modulus values. Variation in enamel structure variation (e.g., enamel Schmelzmuster, Hunter-Schreger band thickness), may also be crucial in explaining variation in mechanical properties, with decussation zones associated with higher mechanical properties values. Primate enamel is not a homogeneous material, with variation in mechanical and structural properties across the crown likely associated with functional differences and variation in force distribution. Overall structural and mechanical patterns were similar in the primate species studied despite substantial differences in diet, suggesting these properties are potentially evolutionary conserved.

evolutionary biology↗

bioRxiv2021

Dental caries in wild primates: interproximal cavities on anterior teeth

Dental caries has been reported in a variety of primates, although is still considered rare in wild populations. In this study, 11 catarrhine primates were studied for the presence of caries. A differential diagnosis of lesions found in interproximal regions of anterior teeth was undertaken, since they had been previously described as both carious and non-carious in origin. Each permanent tooth was examined macroscopically, with severity and position of lesions recorded. Two specimens were micro-CT scanned to assess demineralization. The differential diagnosis confirmed the cariogenic nature of interproximal cavities on anterior teeth (ICATs). Overall results show 3.3% of teeth are carious, with prevalence varying among species from 0% to over 7% of teeth affected. ICATs occurred in Pan troglodytes (9.8%), Gorilla gorilla gorilla (2.6%), Cercopithecus denti (22.4%), Presbytis femoralis (19.5%) and Cercopithecus mitis (18.3%). They make up 87.9% of carious lesions on anterior teeth. These results likely reflect dietary and food processing differences among species, but also between the sexes (e.g., 9.3% of teeth of female chimpanzees were carious vs. 1.8% in males). Processing cariogenic fruits and seeds with the anterior dentition (e.g., wadging) likely contributes to ICAT formation. Further research is needed on living populations to ascertain behavioral/dietary influences on caries occurrence in primates. Given the constancy of ICATs in frugivorous primates, their presence in archaeological and paleontological specimens may shed light on diet and food processing behaviors in fossil primates.

zoology↗

bioRxiv2021

Tooth chipping patterns in Paranthropus do not support regular hard food mastication

The paranthropines, including Paranthropus boisei and Paranthropus robustus, have often been considered hard-food specialists. The large post-canine teeth, thick enamel, and robust craniofacial features are often suggested to have evolved to cope with habitual mastication of hard foods. Yet, direct evidence for Paranthropus feeding behaviour often challenges these morphological interpretations. The main exception being antemortem tooth chipping which is still regularly used as evidence of habitual mastication of hard foods in this genus. In this study, data were compiled from the literature for six hominin species (including P. boisei and P. robustus) and 17 extant primate species, to analyse Paranthropus chipping patterns in a broad comparative framework. Severity of fractures, position on the dentition, and overall prevalence were compared among species. The results indicate that both Paranthropus species had a lower prevalence of tooth fractures compared to other fossil hominin species (P. boisei: 4%; P. robustus: 11%; Homo naledi: 37%; Australopithecus africanus: 17%; Homo neanderthalensis: 45%; Epipalaeolithic Homo sapiens: 29%); instead, their frequencies are similar to apes that masticate hard items in a non-regular frequency, including chimpanzees, gibbons, and gorillas (4%, 7% and 9% respectively). The prevalence is several times lower than in extant primates known to habitually consume hard items, such as sakis, mandrills, and sooty mangabeys (ranging from 28% to 48%). Comparative chipping analysis suggests that both Paranthropus species were unlikely habitual hard object eaters, at least compared to living durophage analogues.

paleontology↗

bioRxiv2020

Gene-tree Species-tree Discordance in the Eared Seals is best explained by Incomplete Lineage Sorting following Explosive Radiation in the Southern Hemisphere

AO_SCPLOWBSTRACTC_SCPLOWThe phylogeny and systematics of fur seals and sea lions (Otariidae) have long been studied with diverse data types, including an increasing amount of molecular data. However, only a few phylogenetic relationships have reached acceptance because of strong gene-tree species tree discordance. Divergence times estimates in the group also vary largely between studies. These uncertainties impeded the understanding of the biogeographical history of the group, such as when and how trans-equatorial dispersal and subsequent speciation events occurred. Here we used high-coverage genome-wide sequencing for 14 of the 15 species of Otariidae to elucidate the phylogeny of the family and its bearing on the taxonomy and biogeographical history. Despite extreme topological discordance among gene trees, we found a fully supported species tree that agrees with the few well-accepted relationships and establishes monophyly of the genus Arctocephalus. Our data support a relatively recent trans-hemispheric dispersal at the base of a southern clade, which rapidly diversified into six major lineages between 3 to 2.5 Ma. Otaria diverged first, followed by Phocarctos and then four major lineages within Arctocephalus. However, we found Zalophus to be non-monophyletic, with California (Z. californianus) and Steller sea lions (Eumetopias jubatus) grouping closer than the Galapagos sea lion (Z. wollebaeki) with evidence for introgression between the two genera. Overall, the high degree of genealogical discordance was best explained by incomplete lineage sorting resulting from quasi-simultaneous speciation within the southern clade with introgresssion playing a subordinate role in explaining the incongruence among and within prior phylogenetic studies of the family.

evolutionary biology↗