The phylogenetic signal in tooth wear: What does it mean?

Abstract

A new study by Fraser et al (2018) urges the use of phylogenetic comparative methods, whenever possible, in analyses of mammalian tooth wear. We are concerned about this for two reasons. First, this recommendation may mislead the research community into thinking that phylogenetic signal is an artifact of some sort rather than a fundamental outcome of the evolutionary process. Secondly, this recommendation may set a precedent for editors and reviewers to enforce phylogenetic adjustment where it may unnecessarily weaken or even directionally alter the results, shifting the emphasis of analysis from common patterns manifested by large clades to rare cases.

Phylogenetic signal in tooth wear dietary niche proxies: What it means for those in the field

“…This manifests as dietary shifts, say from a less gritty diet to a more gritty diet, but should rarely manifest as an intraspecific shift from herbivory to carnivory, for example (Price, Hopkins, Smith, & Roth, ). We further agree with DeSantis et al () that experimental diets can and do change the properties of mammal tooth wear (Hoffman, Fraser, & Clementz, ). However, our study refers only to the natural diet of mammals.…”

“…We subsequently make a recommendation that, when possible and necessary, appropriate phylogenetic comparative methods (PCMs) be applied, a recommendation that has been made time and time again in the ecology and evolution literature (Barr & Scott, ; Blomberg & Garland, ; Cooper, Jetz, & Freckleton, ; Freckleton, Harvey, & Pagel, ; Garland, Harvey, & Ives, ; Martins, ; Martins & Hansen, ; Pagel, ; Price, ). DeSantis et al (), however, express concern that (a) our study will cause editors to unnecessarily enforce the use of phylogenetic comparative methods during review and (b) that our study will mislead researchers into thinking phylogenetic signal is merely an artifact, rather than a result of the evolutionary process.…”

“…We have added to that vast literature an interesting observation that tooth wear may not in fact be “taxon‐free” and we do hope that editors will question (to a reasonable extent) this assertion in future studies of mammalian tooth wear. It is the onus of individual authors to determine and debate with individual editors for or against the use of PCMs, as DeSantis et al () indicate they have done successfully in the recent past.…”

“…In a further hypothetical example used by DeSantis et al (), families on their way to the airport tend to be either “knife carrying” or “knifeless.” We extend this example to suggest that, if the material from which the knives are made shows “phylogenetic signal” (e.g., some families carry ceramic knives that cannot be detected by magnetometers and others metal knives that can), airport security might overestimate the strength of the link between beeping magnetometer alarm and the presence of sharp cutting tools. While the beeping alarm is an honest signal of the presence of a knife, there are other equivalent knife‐wielders that are not detectable by this method.…”

“…DeSantis et al () further suggest that (a) convergence of diets among distantly related mammals and (b) intraspecific dietary differences negate the need to correct for phylogenetic signal in tooth wear. We consider the following example.…”