Mandibular shape variation in mainland and insular hylobatids. Issue 9 (22nd July 2020)

• Record Type: Journal Article
• Authors: Pitirri, M. Kathleen; Vermeulen, Erin; Komza, Klara; Begun, David R.
• Is Part Of: American journal of primatology. Volume 82:Issue 9(2020)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2020-07-22
• Subjects: geometric morphometrics -- Hylobates -- intraspecies variation -- island biogeography -- mandible; Primates -- Periodicals; Primates -- Périodiques; 599.8
• DOI: 10.1002/ajp.23175
• Languages: English
• ISSNs: 0275-2565

Abstract

Abstract: Although hylobatids are the most speciose of the living apes, their morphological interspecies and intraspecies variation remains poorly understood. Here, we assess mandibular shape variation in two species of Hylobates, white‐handed ( Hylobates lar ) and black‐handed ( Hylobates agilis ) gibbons. Using 71 three‐dimensional landmarks to quantify mandibular shape, interspecies and intraspecies variation and geographic patterns of mandibular shape are examined in a mixed sex sample of adult H. lar and H. agilis through generalized Procrustes analysis, Procrustes analysis of variance, and principal components analysis. We find that relative to H. agilis, H. lar exhibits a higher amount of variation in mandibular shape. Both species demonstrate similar allometric patterns in mandibular shape. We also highlight a geographic pattern in mandibular shape variation. Compared to mainland hylobatids, insular hylobatids have relatively lower, more posteriorly oriented, and anteroposteriorly wider mandibular condyles, with an increased distance between the condyles and the coronoid processes. This geographic pattern could reflect differences in functional demands on the mandible during mastication and/or could be driven by factors often associated with evolutionary pressures of island populations relative to mainland populations. The findings of this study highlight how little is known about Hylobates morphological variation and how important this is for using Hylobates to help interpret the primate fossil record. Understanding interspecific and intraspecific variation in extant primates is vital to interpreting variation in the primate fossil record. Abstract : Mean mandibular shape per taxon superimposed with the mean shape for the entire sample (dark blue) showing that insular gibbon species ( Hylobates lar vestitus and Hylobates agilis ) have similar mandibular shapes that are different from mainland gibbons ( Hylobates lar lar, Hylobates lar entelloides, and Hylobates lar carpenteri ). HIGHLIGHTS: Island‐dwelling gibbons are found to have significantly different mandibular shapes than mainland gibbons. These differences may be related to differences in masticatory loads resulting from differences in dietary regimes and/or be driven by factors often associated with evolutionary pressures of island populations relative to mainland populations. The findings of this study highlight how little is known about Hylobates morphological variation and how important this is for using Hylobates to help interpret the primate fossil record.