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Session Schedule & Abstracts

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Saturday 2nd July, 2016

Evo-Devo - Evolution of Developmental Processes 4

Room: Salon C   2:30 pm–4:00 pm

Moderator(s): Dial TR, Hirasawa T
EVD4-1  2:30 pm  The domestication of the neural crest – A developmental perspective on the origins of morphological variation in mammalian breeds and land races . Sánchez-Villagra M R*, University of Zurich; Geiger M, University of Zurich; Schneider R A, University of California San Francisco
Abstract: Studies on domestication are blooming, but the developmental bases for the generation of domestication traits and breed diversity remain largely unexplored. Some phenotypic patterns of human neurocristopathies are suggestive of those reported for domesticated mammals, and disrupting neural crest developmental programs have been argued to be the source of traits deemed the ‘domestication syndrome’. These character changes span multiple organ systems and morphological structures. But the distribution of such traits in the phylogeny of domesticated mammals is not universal, with canids being the only group showing a large set of predicted features. Modularity of traits tied to phylogeny characterizes domesticated mammals: through selective breeding, individual behavioral and morphological traits can be reordered, truncated, augmented, or deleted. Similarly, mammalian evolution on islands has resulted in suites of features much like those found in domesticated species. Some morphological features of domesticated mammals that were considered to be the result of juvenilesation have proven not to be so. This does not exclude the potential relevance of heterochrony in the evolution of domesticated species and breeds, as shown by new cranial and postcranial data on domesticated dogs and other species. There are many postnatal markers of growth, which together with morphometric studies of skull form, serve to examine local cases of developmental repatterning. Some features of breeds of domesticated mammals resemble abnormal conditions in humans (e.g., midfacial hypoplasia), but this has not been characterized from a developmental morphology perspective. Many domesticated mammals can serve as valuable models for conducting comparative studies on the evolutionary developmental biology of the neural crest given that series of their embryos are readily available and that their phylogenetic histories and genomes are well characterized.

EVD4-2  2:45 pm  Developmental basis behind the evolutionary origin of the diaphragm. Hirasawa T.*, Evolutionary Morphology Laboratory, RIKEN; Fujimoto S., Evolutionary Morphology Laboratory, RIKEN; Kuratani S., Evolutionary Morphology Laboratory, RIKEN
Abstract: The diaphragm, a skeletal muscle settled deep in the thorax, represents an evolutionary novelty of the mammalian lineage. In the embryonic development, the diaphragm is differentiated from somitic muscle precursor cells within the pleuroperitoneal fold (PPF), a paired medial protrusion of the lateral body wall. The other vertebrates do not possess muscles corresponding to the diaphragm, and, owing to this difficulty, the evolutionary origin of the diaphragm has not been fully proven yet. Based on comparative morphology of the brachial plexus, we inferred that the diaphragm was acquired through a duplication of the subscapular muscle concomitant with a caudad shift of the shoulder girdle during evolution. Here, we investigated the development of the cervico-pectoral region to elucidate the developmental basis behind the evolutionary origin of the diaphragm. First, we compared the transformation of the lateral body wall during development between mouse and chicken embryos. In the mouse, the PPF initially developed at the cervical level slightly cranial to the base of forelimb bud, and later became encapsulated within the thorax. An equivalent movement was observable in the chicken embryo. We demonstrated that the cells of the somatopleure at the cervical somite levels later become distributed within the thorax in the chicken embryo, through experiments of homotopic transplantation of the somatopleure of quail embryos into chicken embryos. Therefore, the novel developmental mechanism for the diaphragm was principally the repatterning of the muscle precursor cells in the cervical lateral body wall. From this perspective, we analyzed the difference in expression pattern of the Hox4–6 paralogous group genes between mouse and chicken embryos. Hoxc5 in particular expressed differently in the lateral body wall between these species, and its expression at the PPF and cranial part of the forelimb bud in the mouse potentially reflects the evolution of the diaphragm.

EVD4-3  3:00 pm  A cryptic sacral series that varies in count but not size defines the modular organization of the vertebral column in odontocete cetaceans. Buchholtz E A*, Wellesley College
Abstract: Almost all living mammals are terrestrial quadrupeds, and their vertebral columns resemble those of ancestral taxa in both organization and count. Mammals with extreme adaptations allow new insights into the possible range and developmental control of column transformation over evolutionary time. Odontocete cetaceans are unusual in the apparent lack of a sacral series. Vertebral counts of most taxa are extremely elevated, but increases are unequally distributed among series. Surprisingly, high-count taxa are not elongate, because counts vary inversely with vertebral centrum length. Following recent evidence that morphologically de-differentiated columns may be cryptically regionalized, we used spinal nerve origin, vertebral shape, and fetal ossification patterns to identify and characterize possible sacral vertebrae in odontocetes. We used the pudendal plexus, invariably located at S1 or S2 in quadrupeds, as a proxy for the axial location of the first sacral vertebra. This marker and the anterior boundary of the tail delimit a field within the lumbar series whose count increases directly with total column count. These vertebrae are also separable from anterior lumbars using geometric morphometrics, and ossify earlier in development than either anterior lumbar or caudal vertebrae. We conclude that the sacral series is still regionalized, and that lumbar, sacral, and anterior caudal vertebrae are integrated into a developmental module that undergoes a shared rate of somitogenesis distinct from that of other series. We propose that odontocete column reorganization occurred first by loss of primaxial : abaxial interaction at the sacrum, then by integration of lumbar, cryptic sacral, and anterior caudal vertebrae into a shared module, and finally by repeated, convergent increases to the count of this novel module. These data lend strong support to the currently debated hypothesis that vertebral count and identity assignment are independently regulated.

EVD4-4  3:15 pm  Anatomical tests of Hox gene function in a derived vertebrate body form: “Deregionalization” and the role of Hox10 in the evolution of snakes. Head J. J.*, University of Cambridge; Royle S. R., University of Cambridge
Abstract: The roles of Hox genes in regional patterning of the vertebrate A-P axis are well understood for model taxa and have been used to infer Hox modification in the evolution of novel body forms. The function of Hox10 paralogs to produce a distinct, ribless lumbar region of the presacral vertebral column is documented in Mus, and examination of Hox10 expression in snakes suggests that rib suppressing functions are secondarily inhibited, resulting in rib expression and loss of a lumbar region in the evolution of the snake body form. The ancestral presence of a ribless lumbar region in the lineages leading to snakes and the distribution of lumbar regions within Squamata have never been determined, however. To compare experimental results with evolutionary histories of lumbar regionalization, we characterized posterior presacral axial morphology as discrete characters (ribless lumbar, fused terminal ribs, free ribs) in 130 species of extant and fossil lepidosaurs and sauropterygians. We mapped morphologies onto comprehensive molecular and morphological phylogenies of Lepidosauria, and used Maximum Likelihood and Maximum Parsimony analyses to reconstruct ancestral node values for Squamata and constituent clades, including snakes. Lumbar regions occur in multiple clades; however, ancestral state reconstructions do not unambiguously support a hypothesis of secondary loss of a ribless lumbar region in the evolution of snakes, regardless of tree topology or reconstruction method. Instead, snakes are either nested deeply within a clade that lacks a lumbar region regardless of body form, or the ancestral condition for the clade is equivocal. Our results do not support evolutionary polarities of Hox10 function inferred from comparing Mus to snakes, and instead suggest more complicated histories for the roles of Hox10 in patterning the vertebral column. This research is funded by a Wellcome Trust ISSF Joint Grant to JJH.

EVD4-5  3:30 pm  Size, not age, predicts feeding morphology and kinematics among guppy offspring and juveniles. Dial T.R.*, Brown University; Hernandez L.P., George Washington University; Brainerd E.L., Brown University
Abstract: Large offspring size is routinely selected for in highly competitive environments, such as in low predation populations of the Trinidadian guppy (Poecilia reticulata). Low predation guppy environments have low predator density, large guppy biomass and limited supply of benthic algae encrusting the rocky floor. Large offspring are more successful than their smaller counterparts when competing for such limited resources, but the functional mechanisms underlying this advantage are unknown among guppy neonates. We measured cranial musculoskeletal morphologies and jaw kinematics during scraping in neonates and postnatal juveniles from two low-predation (LP) and three high-predation (HP) populations of Trinidadian guppy. Feeding morphology and jaw kinematics vary substantially with guppy neonatal size. Percentage of cranial elements ossified varies over 4-fold from smallest (20%) to largest (90%) neonates. The surface area of the jaw-closing muscle, the adductor mandibulae, scales with positive allometry relative to body length (L2.72) indicating growth of the muscle outpaces growth of the body. Maximum gape also scales with positive allometry (L1.20), indicating larger neonates are capable of greater jaw excursion. Rotation at the intramandibular joint, but not the quadratoarticular joint, increases with body length among guppy offspring. Average IMJ rotations of neonates range from 11.7° in the smallest HP neonates to 22.9° in the largest LP neonates. Additionally, we find that feeding morphology and kinematics continue to scale with size among juveniles, such that 10-day old juveniles from the highest predation populations are equivalent to newborn offspring from low predation populations. We show that larger LP offspring possess more mature feeding morphologies and kinematics at birth, and that HP juveniles acquire similar traits when grown postnatally to equivalent sizes of LP neonates.

EVD4-6  3:45 pm  Modelling human skull development. Libby J W*, University of Hull; Marghoub A, University College London; Khonsari R H, Hopital Universitaire Necker, Paris; Fagan M J, University of Hull; Moazen M, University College London
Abstract: Introduction: During the first year of life the human skull undergoes rapid morphological changes in both size and shape. Understanding the biomechanics of skull growth and in particular the relationship between forces induced by the growing brain during normal skull development would be useful. The aim of this study is to explore these relationships by developing a computational model of human calvarial growth. Methods: A 3D printed physical model and an equivalent finite element model (FEM) were developed from a micro-computed tomography scan of a newborn infant skull. Both models were created to investigate skull growth from birth by simulating brain volume expansion with the goal of replicating observed changes in in vivo head measurements. The physical model was used to validate the FEM at ages 0, 1 and 2 months, after which a second FEM was created which predicted growth from 0 to 12 months in an actual skull and compared to clinical CT scan data. Parameters considered included: skull width, skull length and circumference. Results: In both the physical model and FEM, cranial measurements increased gradually with age in line with reported in vivo measurements. For example, over 2 months the 1st FEM predicted an increase of 10%, 9.6% and 9.6% compared to 9.9%, 5.2% and 8.2% found in the physical model for width, length and circumference. The 2nd FEM predicted increases of 21.1%, 27.4%, 21.73% in width, length and circumference respectively, which was comparable to 23.3%, 24.2% and 25.9% reported in the literature. Over the 12-month growth period considered, the largest difference between the 2nd FEM’s predicted values and in vivo measurements was 11.4%. Conclusions: Despite the limitations of all three models, their predicted behaviours compare well with the available in vivo data. The next stage of the work involves an investigation into changes in skull development in patients affected by different forms of craniosynostosis.

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