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  1. Abstract Objectives

    Human language represents an extreme form of communicative complexity. Primate facial display complexity, which depends upon facial mobility, can be used as a model for the study of the evolution of communicative complexity. The gelada (Theropithecus gelada) is the only primate that can produce a lip‐flip eversion. This study investigates the role of the lip‐flip relative to the bared‐teeth display to understand its role in generating communicative complexity.

    Materials and methods

    We reviewed videos of gelada social interactions. We utilized the facial action coding system (FACS) to define structural component action units (AUs) of each display. We inferred display motivation from the behaviors of the display sender.

    Results

    The lip‐flip was used only in combination with the essential AUs of the bared‐teeth display, serving as an optional structural element added to produce a structural variant. Both the bared‐teeth display with and without a lip‐flip occurred most frequently with nonaggressive, submissive behaviors. The lip‐flip was more frequently preceded by approach than the bared‐teeth display, especially in males. The lip‐flip was also present in the majority of structurally blended facial displays though the motivation of the non‐lip‐flip parent display often dominated.

    Discussion

    The lip‐flip may potentially function as an indicator of benign intent after an approach or as an intensifying component of nonaggressive intent. Adaptations to increase facial mobility in geladas via facilitating the lip‐flip may promote increased communicative complexity through increased conspicuousness and motivational signaling specification or intensification.

     
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  2. Abstract

    Understanding how ecology and phylogeny shape parasite communities can inform parasite control and wildlife conservation initiatives while contributing to the study of host species evolution.

    We tested the relative strengths of phylogeny and ecology in driving parasite community structure in a host whose ecology diverges significantly from that of its closest phylogenetic relatives.

    We characterized the gastrointestinal (GI) parasite community of wild geladasTheropithecus gelada, primates that are closely related to baboons but specialized to graminovory in the Ethiopian Highlands.

    Geladas exhibited very constrained GI parasite communities: only two genera (OesophagostomumandTrichostrongylus) were identified across 305 samples. This is far below the diversity reported for baboons (Papiospp.) and at the low end of the range of domestic grazers (e.g.Bos taurus,Ovis aries) inhabiting the same region and ecological niche.

    Using deep amplicon sequencing, we identified 15 amplicon sequence variants (ASVs) within the two genera, seven of which matched toOesophagostomumsp., seven toTrichostrongylussp., and one toT. vitrinus.

    Population was an important predictor of ASV richness. Geladas in the most ecologically disturbed area of the national park exhibited approximately four times higher ASV richness than geladas at a less disturbed location within the park.

    In this system, ecology was a stronger predictor of parasite community structure than was phylogeny, with geladas sharing more elements of their parasite communities with other grazers in the same area than with closely related sister taxa.

    A freePlain Language Summarycan be found within the Supporting Information of this article.

     
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