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1. Embryonic development of a parthenogenetic vertebrate, the mourning gecko ( Lepidodactylus lugubris )

   https://doi.org/10.1002/dvdy.72  

   Griffing, Aaron H. ; Sanger, Thomas J. ; Daza, Juan D. ; Nielsen, Stuart V. ; Pinto, Brendan J. ; Stanley, Edward L. ; Gamble, Tony ( July 2019 , Developmental Dynamics)

   One goal of evolutionary developmental biology is to understand the role of development in the origin of phenotypic novelty and convergent evolution. Geckos are an ideal system to study this topic, as they are species‐rich and exhibit a suite of diverse morphologies—many of which have independently evolved multiple times within geckos.

   We characterized and discretized the embryonic development ofLepidodactylus lugubris—an all‐female, parthenogenetic gecko species. We also used soft‐tissue μCT to characterize the development of the brain and central nervous system, which is difficult to visualize using traditional microscopy techniques. Additionally, we sequenced and assembled a de novo transcriptome for a late‐stage embryo as a resource for generating future developmental tools. Herein, we describe the derived and conserved patterns ofL. lugubrisdevelopment in the context of squamate evolution and development.

   This embryonic staging series, μCT data, and transcriptome together serve as critical enabling resources to study morphological evolution and development, the evolution and development of parthenogenesis, and other questions concerning vertebrate evolution and development in an emerging gecko model.

    

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2. Hidden limbs in the “limbless skink” Brachymeles lukbani : Developmental observations

   https://doi.org/10.1111/joa.13447  

   Smith‐Paredes, Daniel ; Griffith, Oliver ; Fabbri, Matteo ; Yohe, Laurel ; Blackburn, Daniel G. ; Siler, Cameron D. ; Bhullar, Bhart‐Anjan S. ; Wagner, Günter P. ( April 2021 , Journal of Anatomy)

   Reduced limbs and limblessness have evolved independently in many lizard clades. Scincidae exhibit a wide range of limb‐reduced morphologies, but only some species have been used to study the embryology of limb reduction (e.g., digit reduction inChalcidesand limb reduction inScelotes). The genusBrachymeles, a Southeast Asian clade of skinks, includes species with a range of limb morphologies, from pentadactyl to functionally and structurally limbless species. Adults of the small, snake‐like speciesBrachymeles lukbanishow no sign of external limbs in the adult except for small depressions where they might be expected to occur. Here, we show that embryos ofB. lukbaniin early stages of development, on the other hand, show a truncated but well‐developed limb with a stylopod and a zeugopod, but no signs of an autopod. As development proceeds, the limb's small size persists even while the embryo elongates. These observations are made based on external morphology. We used florescent whole‐mount immunofluorescence to visualize the morphology of skeletal elements and muscles within the embryonic limb ofB. lukabni. Early stages have a humerus and separated ulna and radius cartilages; associated with these structures are dorsal and ventral muscle masses as those found in the embryos of other limbed species. While the limb remains small, the pectoral girdle grows in proportion to the rest of the body, with well‐developed skeletal elements and their associated muscles. In later stages of development, we find the small limb is still present under the skin, but there are few indications of its presence, save for the morphology of the scale covering it. By use of CT scanning, we find that the adult morphology consists of a well‐developed pectoral girdle, small humerus, extremely reduced ulna and radius, and well‐developed limb musculature connected to the pectoral girdle. These muscles form in association with a developing limb during embryonic stages, a hint that “limbless” lizards that possess these muscles may have or have had at least transient developing limbs, as we find inB. lukbani. Overall, this newly observed pattern of ontogenetic reduction leads to an externally limbless adult in which a limb rudiment is hidden and covered under the trunk skin, a situation calledcryptomelia. The results of this work add to our growing understanding of clade‐specific patterns of limb reduction and the convergent evolution of limbless phenotypes through different developmental processes.

    

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3. Embryonic development of a parthenogenetic vertebrate, the mourning gecko (Lepidodactylus lugubris)

   https://doi.org/DOI:10.1002/dvdy.72  

   Griffing, A. H. ; Sanger, T. J. ; Daza, J. D. ; Nielsen, S. V. ; Pinto, B. J. ; Stanley, E. L. ; Gamble, T. ( January 2019 , Developmental dynamics)

   Background: One goal of evolutionary developmental biology is to understand the role of development in the origin of phenotypic novelty and convergent evolution. Geckos are an ideal system to study this topic, as they are species-rich and exhibit a suite of diverse morphologies — many of which have independently evolved multiple times within geckos. Results: We characterized and discretized the embryonic development of Lepidodactylus lugubris - an all-female, parthenogenetic gecko species. We also used soft-tissue μCT to characterize the development of the brain and central nervous system, which is difficult to visualize using traditional microscopy techniques. Additionally, we sequenced and assembled a de novo transcriptome for a late-stage embryo as a resource for generating future developmental tools. Herein, we describe the derived and conserved patterns of L. lugubris development in the context of squamate evolution and development. Conclusions: This embryonic staging series, μCT data, and transcriptome together serve as critical enabling resources to study morphological evolution and development, the evolution and development of parthenogenesis, and other questions concerning vertebrate evolution and development in an emerging gecko model. 

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4. A GATA factor radiation in Caenorhabditis rewired the endoderm specification network

   https://doi.org/10.1101/2022.05.20.492851  

   Darragh, Antonia C ; Rifkin, Scott A ( May 2022 , bioRxiv)

   Although similar developmental regulatory networks can produce diverse phenotypes, different networks can also produce the same phenotype. In theory, as long as development can produce an acceptable end phenotype, the details of the process could be shielded from selection, leading to the possibility of developmental system drift, where the developmental mechanisms underlying a stable phenotype continue to evolve. Many examples exist of divergent developmental genetics underlying conserved traits. However, studies that elucidate how these differences arose and how other features of development accommodated them are rarer. InCaenorhabditis elegans, six GATA-type transcription factors (GATA factors) comprise the zygotic part of the endoderm specification network. Here we show that the core of this network - five of the genes - originated within the genus during a brief but explosive radiation of this gene family and that at least three of them evolved from a single ancestral gene with at least two different spatio-temporal expression patterns. Based on analyses of their evolutionary history, gene structure, expression, and sequence, we explain how these GATA factors were integrated into this network. Our results show how gene duplication fueled the developmental system drift of the endoderm network in a phylogenetically brief period in developmentally canalized worms.

    

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5. Developmental timing differences underlie armor loss across threespine stickleback populations

   https://doi.org/10.1111/ede.12242  

   Currey, Mark_C ; Bassham, Susan ; Perry, Stephen ; Cresko, William_A ( November 2017 , Evolution & Development)

   Comparing ontogenetic patterns within a well‐described evolutionary context aids in inferring mechanisms of change, including heterochronies or deletion of developmental pathways. Because selection acts on phenotypes throughout ontogeny, any within‐taxon developmental variation has implications for evolvability. We compare ontogenetic order and timing of locomotion and defensive traits in three populations of threespine stickleback that have evolutionarily divergent adult forms. This analysis adds to the growing understanding of developmental genetic mechanisms of adaptive change in this evolutionary model species by delineating when chondrogenesis and osteogenesis in two derived populations begin to deviate from the developmental pattern in their immediate ancestors. We found that differences in adult defensive morphologies arise through abolished or delayed initiation of these traits rather than via an overall heterochronic shift, that intra‐population ontogenetic variation is increased for some derived traits, and that altered armor developmental timing differentiates the derived populations from each other despite parallels in adult lateral plate armor phenotypes. We found that changes in ossified elements of the pelvic armor are linked to delayed and incomplete development of an early‐forming pelvic cartilage, and that this disruption likely presages the variable pelvic vestiges documented in many derived populations.

    

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