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Session Schedule & Abstracts




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Friday 1st July, 2016

GMM3
Geometric Morphometrics 3

Room: Salon C   2:30 pm–4:00 pm

Moderator(s): Bright JA, Close RA
GMM3-1  2:30 pm   Morphospace occupation and subclade disparity through time in monitor lizards. Ferrer EA *, American Museum of Natural History   eferrer@amnh.org
Abstract: Understanding the influences of morphological variation relative to other forms of diversity is a long-standing question in biology. To understand how phylogeny can affect measures of morphological variation, I quantified and compared levels of diversity regionally and temporally using a phylogenetic and non-phylogenetic framework in a morphologically conservative group, the monitor lizards. Monitor lizards are useful because they are morphologically conservative, but vary in size and regional diversity. I digitized a recent time calibrated molecular phylogeny of 39 species and ran a 2D geometric morphometric analysis on the snout of 313 skulls representing 29 species. All analyses were run in R, and morphological disparity through time was measured using both morphospace occupation (Procrustes variation) and average squared distance disparity-through-time (DTT) on size and shape (geomorph and geiger packages in R). Results indicate that monitor lizards may have explored large amounts of shape space early in their evolution. Discrepancies on patterns of morphospace size and DTT occurred when the shape of newly originating taxa fell within already occupied morphospace. Increased metrics of morphospace and DTT correlate with originations of clades like the dwarf monitors and the large Varanus komodoensis. Interestingly, regions of low taxic diversity show high morphological disparity and phylogenetic diversity. These results suggest that in order to understand the evolutionary consequences and causes of diversity shifts, we cannot just look at diversity with one metric alone. Origination, like extinction, can have disparate effects on measured morphological, taxic, and phylogenetic diversity. Trying to understand modern and past diversity without the power of a phylogenetic framework, in this case by accounting for when and where originations occurred across a phylogeny, may result in the loss of a wealth of information on underlying mechanisms.

GMM3-2  2:45 pm  Interspecific and intersexual morphometric variation in Darevskia lizards based on anal scale shape. Gabelaia M.*, Ghent University & Ilia State University; Adriaens D., Ghent University; Tarkhnishvili D., Ilia State University   mariam.gabelaia.1@iliauni.edu.ge
Abstract: Darevskia lizards are a highly diverse genus mostly found in the Greater and the Lesser Caucasus. Most of them are morphologically similar with variable but strongly overlapping scalation patterns across the species. They occupy the same type of habitats and their distribution often overlaps. We tried to identify sex and species specific morphological traits and test if the habitat is related to anal scale shape. Six species of Darevskia lizards have been studied throughout their range in Georgia. Phylogenetically D. mixta and D. derjugini belong to the same matrilineal (phylogeny based on mtDNA) clade (‘mixta clade’), whereas D. valentini, D. rudis and D. portschinskii belong to another one (‘rudis clade’). The phylogenetic position of D. parvula remains ambiguous. They have a very limited range, except for D. rudis and D. derjugini. All of them are rock dwelling, except for D. derjugini which is a ground dwelling species. In order to test if anal scale shape differed across the species, sex, and populations, a MANOVA was applied on the outline shape data. The analysis showed significant differences only between species that belong to different clades. D. derjugini, the only ground-dwelling species, has the most dissimilar shape from all the other species. At the intersexual level, anal scales of females have, on average, more circular scales compared to conspecific males, though are only sexually dimorphic in D. portschinskii and D. rudis. At the species level, scale shape variation is highest in D. rudis, which is also the species with the wider distributional range. At the population level, there are no significant differences in scale shape of specimens from different areas. As such, we did not find habitat related differences in anal scale shape.

GMM3-3  3:00 pm  Assessing levels of variation among parthenogenetic and bisexual whiptail lizard using geometric morphometrics. Tulga S*, University of Chicago; Ferrer E, American Museum of Natural History   stulga@uchicago.edu
Abstract: Determining baseline levels of morphological variation, within and among species, is difficult because of the influence of genetic, ontogenetic, environmental, and sexual differences. Parthenogenetic organisms are an ideal study system because new genetic variation is solely introduced through mutation. It might be expected that bisexual species should have a higher potential to produce genetic variation, resulting in higher levels of morphological variation. Using geometric morphometrics, we analyzed 121 skulls of 8 species of Aspidoscelis, a genus of whiptail lizard. Our study includes 7 bisexual and 1 parthenogenetic (A. velox) species from three regions in North and Central America, with sampling design to allow parsing of factors and controlling for habitat differences within regions. All skulls were measured and photographed in dorsal and lateral views. We statistically quantified variation across 67 landmarked points using Procrustes superimposition. Specimens were grouped according to species, sex, locality, and field-assessed age based on diagnostic characteristics. PCA, CVA, MANOVA, and disparity analyses were conducted using the geomorph and Morpho packages in R. Size had negligible impact on skull shape. A. velox significantly differed in shape to A. sexlineata (p<2e-16) a closely related bisexual species, but overall disparity between adult females was similar (respectively: 0.0012, 0.0014). Including males and juveniles created a negligible increase in disparity. Species from Mexico, New Mexico, and Florida significantly differ in shape (p<2e-16) with Mexico occupying a larger area of morphospace (M: 0.0028, F: 0.0017, NM: 0.0012). A velox overlaps in shape space with its parental taxon, A. inornata. There is a strong influence of environment and phylogenetic factors on morphological variation, and lower genetic diversity does not directly correspond to lower levels of morphological diversity.

GMM3-4  3:15 pm  The relationship between feeding ecology and phylogeny for Weberian ossicle and otolith morphology in the piranha and pacu family (Actinopterygii: Serrasalmidae). Boyle KS*, Muséum National d'Histoire Naturelle, UMR7179 Paris, France; Botton-Divet L, Muséum National d'Histoire Naturelle/CNRS, UMR7179 Paris, France; Couillaud P, Muséum National d'Histoire Naturelle, UMR7179 Paris, France; Herrel A, Muséum National d'Histoire Naturelle/CNRS, UMR7179 Paris, France   kboyle@mnhn.fr
Abstract: The Weberian apparatus is a synapomorphy for otophysan fishes, a diverse clade of approximately 7,900 species. This feature involves a chain of three bilateral vertebral elements (Weberian ossicles) that transduce sound pressure from the swim bladder to the ear. The Weberian apparatus and associated inner ear modifications provide increased sensitivity to sound pressure and a wider auditory bandwidth that are hypothesized to have facilitated the radiation of otophysans. Otophysans may use acute hearing to assess their environment, find prey, and detect feeding conspecifics. This hypothesis, however, remains speculative. In this context, we examined morphology of the Weberian apparatus, swim bladder, vertebrae 1-4, and ears within a Neotropical otophysan family (Serrasalmidae) with diverse feeding ecologies. We used µCT scans from 50 specimens (MNHN) from 19 species with broad ecologies: fruit and seed eaters, aquatic plant eating species associated with river rapids (rheophilic), and species that eat fish (parts or whole). 3D Geometric morphometrics with traditional and sliding landmarks were used to characterize shapes of Weberian ossicles (tripus, intercalarium, scaphium) and the lagenar otolith (asteriscus). Preliminary results indicate that Weberian apparatus and otolith morphologies are correlated with both phylogenetic association and ecology. Tripus and scaphium shapes were both found to be associated with ecology after accounting for phylogenetic history. In addition, after considering phylogeny, Lagenar otolith morphology differed between fish-eating taxa and plant-eating rheophilic taxa. In addition, some evidence of morphological integration was observed: tripus shape correlated with scaphium shape and scaphium shape correlated with lagenar shape. Tripus shape, however, was not found to correlate with lagenar shape. Future studies should examine how auditory sensitivity is associated with different morphologies and how sound influences feeding behaviors.

GMM3-5  3:30 pm  Probing the third dimension: are morphospaces of 2D and 3D fossil fish crania congruent? Close R A*, University of Birmingham; Friedman M, University of Oxford   roger.close@gmail.com
Abstract: Landmark-based geometric morphometric (GMM) studies of fossil fishes have overwhelmingly focused on 2D compression fossils. In addition to being less abundant, three-dimensionally preserved material presents technical challenges, and to date 3D GMM techniques have rarely been applied. Two-dimensional morphometric analyses of 3D biological structures are a common procedure in biology, using photographs taken in standardised orientations to record the features of interest in a two-dimensional coordinate plane. By contrast, researchers studying compression fossils are constrained to landmark specimens in their preserved orientations, and it remains unclear how faithfully compression fossils capture shape information present in specimens prior to taphonomic flattening. To assess potential discrepancies between shape information preserved in 2D and 3D fossils, we quantified shape variation in the skulls of Late Cretaceous to Paleogene teleost taxa that are known from both inflated specimens (drawn primarily from the English Chalk and London Clay) and compressed specimens (drawn from sites in Lebanon, Italy, USA and the former USSR). We find a significant but weak correlation between the relative positions of taxa within morphospaces derived from flattened and fully inflated skulls. This covariation appears to be driven almost exclusively by the second shape axis, corresponding to variation in skull elongation. However, differences in skull proportions associated with the third dimension (e.g., broad versus laterally compressed skulls) dominate over more subtle forms of morphological variation in 3D morphospace. This aspect of shape variation is lost or obscured in compression fossils preserved in lateral view. Thus, while some major axes of cranial variation are comparable in morphospaces derived from flattened and inflated fossils, three-dimensional landmark constellations capture substantial shape information that cannot otherwise be extracted from flattened specimens.

GMM3-6  3:45 pm  Diversification of the avian bill revealed with crowdsourced 3D geometric morphometrics. Bright JA*, University of Sheffield; Cooney CR, University of Sheffield; Capp EJR, University of Sheffield; Hughes EC, University of Sheffield; Moody CJA, University of Sheffield; Nouri LO, University of Sheffield; Varley ZK, University of Sheffield; Thomas GH, University of Sheffield   jen.bright@sheffield.ac.uk
Abstract: With nearly 10,000 species, birds represent a hugely diverse and disparate class within the Tetrapoda. How birds achieved this diversity has been of interest to biologists for centuries. Of particular interest is how phenotypic trait variation corresponds to changes in the rate of speciation. For instance, do rapid bursts of diversity necessarily entail rapid increases in morphological disparity? Crucial to this is understanding how phenotypes vary within and between lineages on a broad phylogenetic scale. We took 3D surface scans of beaks representing every bird genus, and landmarks for Geometric Morphometric analysis were then gathered using a specifically developed crowdsourcing website (www.markmybird.org), allowing for extremely rapid collection of beak shape data. Principal Components (PC) Analysis reveals that alterations in overall beak dimensions (length, width, and depth) account for approximately 90% of variation in shape, with specific clades or ecomorphs usually identified on lower ranking PCs. Analysis of evolutionary rates shows increased rates in several interesting parts of the tree, including the ducks and geese, and the split between swifts and hummingbirds. In particular, we note that several clades often identified as classic examples of adaptive island radiations (Madagascan vangas, Hawaiian honeycreepers, and the estrildid finches) display rapid rates of both phenotypic evolution and speciation. Despite accounting for half of avian diversity, passerines have more conservative beak morphologies than non-passerine birds. Non-passerines explored extremes of morphospace early in their evolutionary history revealing a pattern that is consistent with adaptive radiation playing out at a global scale. Our results highlight how the diversity of modern birds derives from a process of gradual phenotypic divergence interspersed with dramatic evolutionary bursts and slowdowns, affecting both clades and single lineages right across the avian phylogeny.



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