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Session Schedule & Abstracts

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Saturday 2nd July, 2016

Evo-Devo - Evolution of Developmental Processes 3

Room: Salon C   11:30 am–1:00 pm

Moderator(s): Arenas Rodríguez A, Sessions SK
EVD3-1  11:30 am  Sample size artifacts in analyses of ontogenetic sequences. Colbert M. W.*, The University of Texas at Austin; Morris Z. S., Harvard University
Abstract: The resolution of hypothesized ontogenetic sequences within a taxon or population depends on the number of specimens and the number of included events. Simplistically, complete sequence resolution (i.e., every event’s position resolved relative to every other event) requires at least as many sampled individuals as ontogenetic events. In practical terms, one needs to include many more individuals than events because multiple individuals can represent the same transformation state. Furthermore, event-order can be variable, requiring large samples to establish the frequency of variant sequences. The negative effects of inadequate sampling are predictable, and include poor resolution and underestimation of sequence variation. Unfortunately, many studies assume that unresolved order between events indicates synchroneity, leading to a false equivalence of sequence position in comparative analyses. Underestimating sequence variation results in a false assertion of fixed sequence order for events, which also affects comparative analysis. While sample size artifacts are generally unavoidable, they need to be acknowledged. The Ontogenetic Sequence Analysis (OSA) method can identify the adequacy of sequence resolution - pinpointing under-sampled regions of ‘sequence-space’ (which generally correspond to particular maturity levels). Knowledge of under-sampled regions of sequence-space not only informs the suitability of sequence comparison between taxa, but presents a rationale for targeted sampling to address sampling biases. Accordingly, while attempts to establish ontogenetic sequences are encouraged, even with limited samples, it is imperative to consider and evaluate sampling effects – particularly with comparative analyses. Analysis of topological differences in ontogenetic sequence-space is considered the most promising avenue for development of a method that can interpret ontogenetic sequence evolution while accounting for sequence sampling artifacts.

EVD3-2  11:45 am  Variation in onset of ossification and conserved regions of bone contact in the bony skull development of marsupial mammals . Spiekman SNF*, Paläontologisches Institut und Museum der Universität Zürich; Werneburg I, Senckenberg Center for Human Evolution and Palaeoenvironment at Eberhard Karls Universität
Abstract: Among mammals, different life strategies can be observed ranging from altricial to precocial forms at birth. Development in marsupials is specialized towards an extremely short gestation resulting in highly altricial neonates. As a result, marsupial neonates display a number of morphological adaptations at birth related to functional constraints such as the crawling behavior to reach the mother’s teat directly after birth. The early fixation of marsupial neonates to the teats results in further constraints including the uniform construction of the skull in the pouch young. Little is known about the variability of marsupial skull development and how this relates to the variation observed in adult skull anatomy. We studied bony skull development in five marsupial species by µCT-scanning specimens of various ontogenetic stages. The relative timing of the very first onset of ossification was compared to literature data and the cranial ossification sequence of the marsupial ancestor was reconstructed using squared-change parsimony. The first appearance of ossification centers shows a high range of intra- and interspecific variation with little biological implications. However, for the first time, this study presents observations on the timing of the initial developmental contacts of cranial bones in later stages of development and their evolutionary and ecological implications. Although certain bone contacts display similar levels of variation compared to the initial onset of ossification, other connections are quite conserved. Bones that surround the oral cavity are generally the first to connect and the bones of the occipital region are among the last. The sequence of bone connections can be related to a size of the respective bones in adulthood. Overall, bone contact was shown to be more suitable for studying cranial bone diversity among species when compared to the onset of ossification.

EVD3-3  12:00 pm  Description and comparison of ossification sequences in Colombian species of frogs. Arenas Rodríguez A*, Pontificia Universidad Javeriana; Hoyos Hoyos JM, Pontificia Universidad Javeriana
Abstract: Colombia is one of the richest countries of the world in amphibian species, but there are very few studies about ossification sequences in Colombian species of frogs. Owing to skeleton transformations during metamorphosis in most anuran species involve ossification of structures, these data can contribute to carry on heterochrony analysis and to expand anuran phylogeny studies based on skeleton development. We describe and compare ossification sequences of chondrocranial and postcranial structures, from tadpoles to adults, of Neotropical frogs. Variability ossification ranges (ossification timing of different structures) in five hylid species and three leptodactylid ones were analyzed. Hylid species examined were Hypsiboas crepitans, Dendropsophus labialis, Dendropsophus minutus, Scinax ruber and Trachycephalus typhonius, and leptodactylid species examined were Leptodactylus colombiensis, Leptodactylus insularum and Engyostomops pustulosus. Our results show that there are differences in the timing of appearance of the first ossified elements among these species, such as the transverse processes of the vertebrae. It is remarkably that the early ossification of the chondrocranial elements (exoccipital, parasphenoid and frontoparietale) was common in Hylidae, while in leptodactylid species the ossification timing of these elements was in later stages. Ranges and number of ossified elements presented variability in all species: In leptodactylid frogs, we found three ranges for 11 ossified elements; in hylids, more than 15 ossified elements reached into more than five ranges. We made the first phylogenetic tree of Colombian species of frogs based on cranial ossification sequences in using Parsimov and PGi. There are near 2% of ossification sequences published of almost 6500 species of frogs, showing that we are far from having a comprehensive perspective of both the ossification sequences and the heterochrony of the development in frogs.

EVD3-4  12:15 pm  Breeding with and without water: What are the consequences of terrestrialization for embryonic morphology in anuran development? Schweiger S*, Department of Zoology and Evolutionary Biology; Mueller H, Department of Zoology and Evolutionary Biology
Abstract: In all three orders of Lissamphibia (Urodela, Gymnophiona and Anura), a high number of different reproductive modes exist including terrestrial forms of development where reproduction is independent from direct access to bodies of water. The steps towards complete independence from water are not well understood in amphibian evolution, but the presence of different developmental modes, with different degrees of terrestrialization, has the potential to inform us on how a terrestrial way of development could have evolved. In anurans, alternative reproductive strategies, where the ancestral requirement for aquatic reproduction is removed, have evolved several times independently and include terrestrial larval development and direct development. Several African taxa including Afrobatrachia and Pyxicephalidae show such alternative trends towards terrestrial reproduction, ranging from complete aquatic development to complete non-aquatic, terrestrial development (terrestrial larva and direct development). In this study, embryonic and post-embryonic development of terrestrial larval developing forms (Afrobatrachia: Brevicipitidae: Breviceps and Pyxicephalidae: Arthroleptella) and direct developing forms (Afrobatrachia: Arthroleptidae: Arthroleptis) are investigated and compared with the biphasic, aquatic and semi-aquatic development of close relatives within these two groups. In general we know little about the effects of such highly modified reproductive strategies on embryonic development, especially how it differs from closely related species with a ‘normal’, aquatic tadpole larva. We particularly focus on the extent as to how the ancestral larval developmental pathways have been altered in terrestrially breeding frogs. The tadpole larva has been proposed to represent a distinct developmental and evolutionary module in anurans. This idea is controversial and studying species that independently evolved apparently similar modes of reproduction will help in a critical appraisal of the ‘tadpole module hypothesis’.

EVD3-5  12:30 pm  Testis-ova and male gonad variability in the European blind cave salamander, Proteus anguinus (Amphibia: Urodela): consequence of sex-chromosome turnover? Bizjak Mali L.*, Department of Biology, Biotechnical Faculty, University of Ljubljana; Sessions S.K., Department of Biology, Hartwick College
Abstract: The reproductive biology of the blind cave salamander, Proteus anguinus, endemic to underground waters in the Dinaric karst of Southern Europe, is unique in many ways. Proteus matures late (14 years), and has a very extended reproductive period lasting at least 30 years with a life span of more than 70 years, with females laying eggs at intervals of 6 - 12.5 years. Unlike most other salamanders, Proteus males and females are morphologically indistinguishable. Furthermore, the embryonic mortality rates are quite high (> 50%), and they have a sex ratio (nearly 2:1) in favor of females. The objective of this study was to describe the detailed morphology of the testes of adult Proteus* and determine the maturation state of the gonads with respect to body size and seasonality. We found that testis morphology is highly variable and is independent of the size of the specimen. At least three testes morphologies were found: 1) a simple narrow testis with germ cells in early stage of spermatogenesis, 2) multi-lobed testis with spermatogonia and early spermatocytes, and 3) a broad, non-lobed, elongated testis with all stages of spermatogenesis including spermatozoa. Remarkably, testis-ova were found regardless of the morphology or meiotic condition of the testes. The testis-ova were located randomly among groups of spermatogonia and spermatocytes and corresponded mainly to primary oocytes in diplotene stage with lampbrush chromosomes. Testis-ova in other species of amphibians are usually associated with hormonal dysfunction or possible exposure to endocrine disruptors. In the case of the Proteus we think they might be related to current evidence that Proteus has undergone a sex-chromosome turnover involving X-Y translocation. *The testes were removed from preserved archived specimens collected for other research purposes with permission of the Ministry of the Environment and Spatial Planning of the Republic of Slovenia. (35701-81/2004-9 and 35601-1/2010-6).

EVD3-6  12:45 pm  The phoenix rises: reversal of cave adaptations in the blind cave salamander, Proteus anguinus (Amphibia: Urodela: Proteidae). Sessions SK*, Department of Biology, Hartwick College; Bizjak Mali L, Department of Biology, Biotechnical Faculty, University of Ljubljana
Abstract: The blind cave salamander, or olm, Proteus anguinus, inhabits caves in the Dinaric Karst of the Balkan region of Southern Europe. It is the largest cave-adapted (troglomorphic) vertebrate in the world, and the only troglomorphic vertebrate in Europe. Isolated populations of P. anguinus probably represent several species. Most of these are troglomorphic "white" forms, with little or no pigment and vestigial eyes, and are currently assigned to the subspecies P. a. anguinus. A single population of pigmented, non-troglomorphic "black" Proteus, with developed eyes and dark pigment, is currently assigned to a separate subspecies, P. a. parkelj, that is thought to resemble the common ancestor from which the troglomorphic olms evolved (Sket and Arntzen, 1994). Biochemical and molecular studies (Sket and Arntzen, 1994; Goriki and Trontelj, 2006), however, reveal that the "black olm" is more closely related to a geographically adjacent population of "white olm" than that population of white Proteus is to other populations of white Proteus. Thus, either a) the troglomorphic form has evolved multiple times independently, or, more parsimoniously, b) the black form evolved from a white ancestor (cf. Ivanovi et al., 2013). Recent research on the developmental genetics of cave adaptations in the Mexican Blind Cave Fish, Astyanax mexicanus (Jeffery, 2005), allows us to hypothesize the evolutionary developmental mechanism by which such transformations could have occurred in Proteus. Testing this idea could contribute to our understanding of how major transformations come about in morphological evolution but will require access to embryonic material of both subspecies of Proteus. Goricki, S, P Trontelj (2006) Gene 378:31-41. Ivanovic, A, G Aljancic, JW Arntzen (2013) Contributions to Zoology 82:107-114. Jeffery, WR (2005) J. of Heredity 96:185-196. Kos, M, B Bulog, ASP Roehlich (2001). Cell Tissue Res 303:15–25. Sket, B, JW Arntzen (1994). Bijdragen tot de Dierkunde 64:33-53.

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