Interspecific Variation in the Bony Labyrinth (Inner Ear) of Anurans. Amber L
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Florida Museum of Natural History: Department of Herpetology Interspecific Variation in the Bony Labyrinth (Inner Ear) of Anurans. Amber L. Singh, Lauren A. Gonzales, Daniel J. Paluh, David C. Blackburn Introduction PCA Plot of PC1 vs. PC2 Grouping by Ecology and Clade PCA Plot of PC1 vs. PC2 with Labeled Specimens The semicircular canals of the inner ear sense positional information of the body and angular acceleration of the head during movement. It is widely accepted that birds Hyla boans and mammals with agile and spatially complex movements will have a canal Fig. 4. Same PCA as morphology that maximizes sensitivity to these behaviors. More specifically, agile 2∗ Nectophrynoides Fig. 2, but with animals have canals with larger radii of curvature and ipsilateral canal pairs that viviparus specimens labeled closely approximate 90os. However, it is not well understood if changes in canal 3∗ for identification functional morphology in mammals are broadly applicable across vertebrates, or if morphological responses to movement have evolved independently. Interestingly, and comparison recent documentation of inner ear variation in caecilians and fossorial snakes, a group PC 2 (17%) with Fig. 3 and of predominantly limbless vertebrates, indicates that both groups may have adopted Table 1. novel morphological traits thought to enhance sensitivity to movement below ground. We present a survey of the morphological diversity of the bony labyrinth of anurans, to further investigate the potential influence of habitat and phylogeny on inner ear morphology in the clade Lissamphibia. Using 3-dimensional endocasts generated 2 (17%) PC from high resolution CT scans, we document substantial variation in the size and shape of the semicircular canals and saccule across species. Implications regarding PC 1 (25%) locomotor behaviors and phylogeny are discussed. Allometry Methods Fig. 5. Bivariate plot of log centroid size regressed against Materials shape regression scores. A All specimens were housed at the Florida strong positive relationship is Museum of Natural History. CT scans were indicated. generated at the University of Florida’s Nanoscale Research Facility using a GE V TOME X M 240 ultra-high resolution CT Brachytarsophrys scanner. All specimens are listed in Table 1. Fig. 1a. carensis Data Collection PC 1 (25%) 4∗ VGStudio MAX 3.0 was used to gather 3D Shape (regression score) volumes of the right inner ear of each Fig. 2. PC 1 represents changes in the relative length of the semicircular canals with large canals having positive PC scores and specimen. Landmark data was then collected in small canals having negative PC scores. PC 2 represents changes in the arc of the anterior semicircular canal, with small arcs Rstudio (Figure 1a and 1b) and for the purpose having positive PC scores, and large arcs having negative PC scores. Most variation occurs on PC 1 (25%) which tends to of this study, only focused on the semicircular separate arboreal specimens from most other ecological categories. PC 2 exhibits 17% variance. Terrestrial taxa have the largest Limnonectes log(centroid size) canals. A total of 16 (9 fixed and 7 sliding) range of variation of any ecological category. macrocephalus Breviceps gibbosus landmarks were placed on each specimen. Anuran Inner Ear Anurans Studied5∗ 6∗ Table 1. Points shown in blue are fixed landmarks, Specimen Name: Clade: Ecology: Hemisus guineensis points shown in orange are sliding landmarks. Fig. 1b. 1 Limnomedusa macroglossa Hyloidea terrestrial 7∗ Fixed landmarks were chosen according to the 2 Arthroleptis bioko Ranoidea terrestrial most identifiable points consistent through 3 Ascaphus truei Archaeobatrachia aquatic each specimen. The sliding landmarks were 4 Barbourula busuangensis Archaeobatrachia aquatic then chosen to best show the range of curvature 5 Bombina maxima Archaeobatrachia aquatic of, and between, each of the semicircular Fig. 1c. 6 Balebreviceps hillimani Ranoidea terrestrial canals. 7 Breviceps gibbosus Ranoidea fossorial Conclusions: 8 Anaxyrus fowleri Hyloidea fossorial • Taxonomic relation appears to have very Analysis 9 Anaxyrus quercicus Hyloidea terrestrial little influence over specific morphological A Principal Component Analysis (PC) of semicircular 10 Anaxyrus terrestris Hyloidea terrestrial canal variation was performed using Procrustes 11 Nectophrynoides tornieri Hyloidea terrestrial variation of the semicircular canals. tangent coordinates (16 landmark variables corrected 12 Nectophrynoides viviparus Hyloidea terrestrial • Some ecological patterns exist particularly for variation in position, orientation, and size). The 13 Limnonectes blythii Ranoidea terrestrial for the arboreal ecological group as it is Procrustes-aligned specimens were plotted (Figure 2 14/15 Limnonectes macrocephalus Ranoidea terrestrial separated from most other ecological and 4) and grouped by ecological category (color) and 16/17 Gastrotheca peruana Hyloidea terrestrial clade membership (shape). Allometry was examined 18 Gastrotheca pseustes Hyloidea terrestrial categories. by assessing the multivariate regression between 19 Gastrotheca riobambae Hyloidea terrestrial • There appears to be significant correlation semicircular canal shape and canal centroid size based 20/21 Hemisus guineensis Ranoidea fossorial between the shape of the semicircular 22 Hyla andersonii Hyloidea arboreal on Procrustes distances. 23 Hyla boans Hyloidea arboreal canals and the relative size of the inner ear. 24 Hyla milaria Hyloidea arboreal 25 Pseudacris crucifer Hyloidea terrestrial Moving Forward: Images 26/27 Pseudacris nigrita Hyloidea terrestrial Each frog image ( with the exception of Pseudacris 28/29 Pseudacris ornata Hyloidea terrestrial • increase taxonomic breadth ornata) corresponds with one of the inner ears 30 Pseudacris triseriata Hyloidea terrestrial • Gather data on the variation seen in the expanded in either the PCA plot, or the allometry 31 Afrixalus orophilus Ranoidea arboreal sacculus plot. The image of P. ornata (right) corresponds 32 Afrixalus paradorsalis Ranoidea arboreal with the expanded image of the skull showing the 33 Callixalus pictus Ranoidea arboreal • Examine the effects on inner ear morphology placement of the inner ear. 34 Brachytarsophrys carensis Mesobatrachia terrestrial on hearing 35 Leptobrachium hasseltii Mesobatrachia terrestrial Photo credit: US Geological Survey; William 36 Pipa pipa Mesobatrachia aquatic 37 Rhinophrynus dorsalis Mesobatrachia fossorial Quatman; John1 W. Wilkinson; Thai2 National Park; 38 Scaphiopus holbrookii Mesobatrachia fossorial Merlijn 3Van Weerd; Mike Buckham4 ; Eigenes 39 Spea multiplicata Mesobatrachia fossorial Werk5 ; Ryan Photographic.6 7 40 Telmatobius halli Hyloidea aquatic Rhinophrynus dorsalis *All photos8 were altered from their original format. Pseudacris ornata Fig. 3. 41 Telmatobius thompsoni Hyloidea aquatic 8∗ 1∗ Florida Museum of Natural History: Department of Herpetology.