Convergent origins and rapid evolution of spliced leader trans-splicing in Metazoa: Insights from the Ctenophora and Hydrozoa

Replacement of mRNA 5′ UTR sequences by short sequences trans-spliced from specialized, noncoding, spliced leader (SL) RNAs is an enigmatic phenomenon, occurring in a set of distantly related animal groups including urochordates, nematodes, flatworms, and hydra, as well as in Euglenozoa and dinoflagellates. Whether SL trans-splicing has a common evolutionary origin and biological function among different organisms remains unclear. We have undertaken a systematic identification of SL exons in cDNA sequence data sets from non-bilaterian metazoan species and their closest unicellular relatives. SL exons were identified in ctenophores and in hydrozoan cnidarians, but not in other cnidarians, placozoans, or sponges, or in animal unicellular relatives. Mapping of SL absence/presence obtained from this and previous studies onto current phylogenetic trees favors an evolutionary scenario involving multiple origins for SLs during eumetazoan evolution rather than loss from a common ancestor. In both ctenophore and hydrozoan species, multiple SL sequences were identified, showing high sequence diversity. Detailed analysis of a large data set generated for the hydrozoan Clytia hemisphaerica revealed trans-splicing of given mRNAs by multiple alternative SLs. No evidence was found for a common identity of trans-spliced mRNAs between different hydrozoans. One feature found specifically to characterize SL-spliced mRNAs in hydrozoans, however, was a marked adenosine enrichment immediately 3′ of the SL acceptor splice site. Our findings of high sequence divergence and apparently indiscriminate use of SLs in hydrozoans, along with recent findings in other taxa, indicate that SL genes have evolved rapidly in parallel in diverse animal groups, with constraint on SL exon sequence evolution being apparently rare.     

Fossile Hydrozoen — Kenntnisstand und Probleme

A critical review on fossil Hydrozoa reveals the following questions and problems:

1. Microstructure, skeleton formation and morphology: According toKazmierczak’s morphogenetical model the formation of the ectodermal basal skeleton depends on a progressive folding of the coenosarc. Can this model be used for all polypoid hydrozoans? Another very important question deals with the possibility of distinctions between systematically important “primary” microstructures and taxonomically worthless “secondary” microstructures which are produced by diagenetical alteration effects.
2. Determination and classification: There is no general agreement on the morphological elements which can be used for the definition of Paleozoic and Mesozoic stromatoporoid genera and species, special problems refer to the taxonomical value of the astrorhizae and of quantitative criteria. About 2000 “species“ from the Paleozoic and about 500 “species“ from the Mesozoic have been described within the Stromatoporoidea but there exists no generally recognized classification system for this group.
3. Paleobiogeography: The oldest polypoid hydrozoans are known from Llanvirnian to Llandeiloverian reef- and shelf-carbonate-deposits; some species described from the Middle Cambrian of Western Sibiria may belong to Archaeocyatha. Tab. 3 shows the temporal distribution of hydrozoan groups. Stricking gaps of knowledge exist for Carboniferous and Permian, Lower Triassic, Liassic, Middle Jurassic and for Tertiary hydrozoan faunas.
4. Palecology: Main factors governing the distribution of polypoid hydrozoans seem to be consistence of substrate, different types of water movement, and eventually differences in salinity. These ecofactors may be recognized by the interpretation of growth forms and growth patterns together with investigations of hydrozoan associations and communities. According to the problems mentioned above no sound evolutionary scheme of all hydrozoan groups is possible just now. Questions dealing with the systematical position of Paleozoic and Mesozoic Chaetetida and with the relationships between Hydrozoa and Sclerospongia have to be studied first (see page 406).

     

Slow Mitochondrial COI Sequence Evolution at the Base of the Metazoan Tree and Its Implications for DNA Barcoding

The evolution rates of mtDNA in early metazoans hold important implications for DNA barcoding. Here, we present a comprehensive analysis of intra- and interspecific COI variabilities in Porifera and Cnidaria (separately as Anthozoa, Hydrozoa, and Scyphozoa) using a data set of 619 sequences from 224 species. We found variation within and between species to be much lower in Porifera and Anthozoa compared to Medusozoa (Hydrozoa and Scyphozoa), which has divergences similar to typical metazoans. Given that recent evidence has shown that fungi also exhibit limited COI divergence, slow-evolving mtDNA is likely to be plesiomorphic for the Metazoa. Higher rates of evolution could have originated independently in Medusozoa and Bilateria or been acquired in the Cnidaria + Bilateria clade and lost in the Anthozoa. Low identification success and substantial overlap between intra- and interspecific COI distances render the Anthozoa unsuitable for DNA barcoding. Caution is also advised for Porifera and Hydrozoa because of relatively low identification success rates as even threshold divergence that maximizes the “barcoding gap” does not improve identification success. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Shallow-water benthic hydroids from Tethys Bay (Terra Nova Bay, Ross Sea, Antarctica)

The shallow-water hydrozoan Antarctic fauna is still poorly studied, and available knowledge mostly refers to samples gathered by traditional ship-operated gears. By scuba diving in the coastal areas off the Italian Antarctic station “Mario Zucchelli” (Ross Sea, Terra Nova Bay), in the austral summer 2002–2003, a total of 20 hydrozoan species were found, belonging to 10 families and 13 genera. As hypothesized, Anthoathecata (11 species), usually under-represented in collections from indirect sampling gears, are common as also are Leptothecata (9 species). Hydractiniidae and Hydractinia are the dominant family and genus, followed by Haleciidae and Halecium. A new species to science, Halecium exaggeratum sp. nov. is also described. Most species are either endemic to Antarctic waters or restricted to Antarctic/sub-Antarctic areas; only two species have a wider distribution. Material reared in aquaria at the Italian Antarctic Base Mario Zucchelli facilitated knowledge of the life cycle and reproductive biology of several species. In particular, Opercularella belgicae was found to liberate a medusa stage referable to Phialella, and the species is assigned here to that genus, as Phialella belgicae. Also, extraordinary is the complete absence or scant representation of the most typical Antarctic benthic hydroid genera (Antarctoscyphus, Oswaldella, Schizotricha, Staurotheca, and Symplectoscyphus), likely related to the shallow limits of sampling (down to 48 m).     

Multiple origins of replication in archaea

Until recently, the only archaeon for which a bona fide origin of replication was reported was Pyrococcus abyssi, where a single origin was identified. Although several in silico analyses have suggested that some archaeal species might contain more than one origin, this has only been demonstrated recently. Two studies have shown that multiple origins of replication function in two archaeal species. One study identified two origins of replication in the archaeon Sulfolobus solfataricus, whereas a second study used a different technique to show that both S. solfataricus and Sulfolobus acidocaldarius have three functional origins. These are the first reports of archaea having multiple origins. This finding has implications for research on the mechanisms of DNA replication and evolution.     

Pseudomonad replication origins: a paradigm for bacterial origins?

Structural features of three analysed bacterial DNA replication origin classes (six enteric origins, three pseudomonad origins, and the Bacillus subtilis origin region) are compared in order to deduce characteristics common to all bacterial origins and characteristics that distinguish the three origin classes. The two Pseudomonas aeruginosa origins are shown to map within 10 kb of each other, and correlations are drawn with four potential origin regions in B. subtilis. The enteric origin class is further distinguished from the other two classes by its genetic organization, the presence of GATC sites, and the role of Dam methylation in enteric initiation. The pseudomonad origin class has the most features that are common to all of these bacterial origins, and hence may be the paradigm bacterial origin class.     

Die Cnidogenese der Octocorallia (Anthozoa,Cnidaria): II. Reifung,Wanderung und Zerfall von Cnidoblast und Nesselkapsel

Migration of cnidoblasts has never been observed in Anthozoa. In contrast to hydrozoans, anthozoans are repeatedly reported to develop nematocysts locally without migration in the entoderm as well as in the ectoderm. The majority of the nematocysts studied in different Octocorallia species (Alcyonaria:Alcyonarium digitatum, Parerythropodium coralloides; Gorgonaria:Pseudopterogorgia aerosa; Pennatularia:Veretillum cynomorium) originate from the ectoderm of the scapus, where, however, no mature nematocysts occur. Cnidoblasts containing immature nematocysts accumulate in the distal scapus, from where they migrate singly like amoebae into the pinnulae of the tentacles. The nematocysts mature during migration, during which the capsular matrix becomes completely electron-translucent. Only in the oral disc, where few nematocysts occur, do they mature locally without migration. In the Octocorallia, nematocyst development and maturation takes places only in the ectoderm. Development of nematocysts has never been observed in the entoderm, nor in the pharynx; this demonstrates its entodermal origin. The entoderm contains only degenerated or phagocytized nematocysts. Contrary to hydrozoans, the mature anthozoan cnidocyte is rounded and has no processes to the mesogloea. Instead of a cnidocil it has a ciliary cone consisting of a normal flagellum, stereocilia and macrovilli. The cnidocyte is characterised by abundant electron-translucent cytoplasm and nematocyst-anchoring structures made up of cross-striated, collagen-like fibrillae and a fibrous basal ring. The position of the cross-striated fibrillae is distally similar to that of the supportive rods in hydrozoan cnidoblasts. The present study clearly demonstrates that structure and, possibly, function of an octocorallian cnidocyte is much simpler than that of a hydrozoan cnidocyte. On the other hand, cnidoblast migration, occurring in Hydrozoa as well in Octocorallia, turned out to be a much older phylogenetic character than was formerly believed.     

The ocular skeleton through the eye of evo-devo

An evolutionary developmental (evo-devo) approach to understanding the evolution, homology, and development of structures has proved important for unraveling complex integrated skeletal systems through the use of modules, or modularity. An ocular skeleton, which consists of cartilage and sometimes bone, is present in many vertebrates; however, the origin of these two components remains elusive. Using both paleontological and developmental data, I propose that the vertebrate ocular skeleton is neural crest derived and that a single cranial neural crest module divided early in vertebrate evolution, possibly during the Ordovician, to give rise to an endoskeletal component and an exoskeletal component within the eye. These two components subsequently became uncoupled with respect to timing, placement within the sclera and inductive epithelia, enabling them to evolve independently and to diversify. In some extant groups, these two modules have become reassociated with one another. Furthermore, the data suggest that the endoskeletal component of the ocular skeleton was likely established and therefore evolved before the exoskeletal component. This study provides important insights into the evolution of the ocular skeleton, a region with a long evolutionary history among vertebrates.     

The development and evolution of hydrozoan polyp and colony form

Hydrozoans represent an extremely diverse group of mostly colonial forms. Despite this tremendous diversity, many of the morphological differences between hydrozoan species can be attributed to simple changes in the relative position of regions/structures along the axes of the polyp and the stolon or hydrocaulus from which polyps bud. Many genes have been implicated in the specification of positional information along the axis of the polyp. Knowledge from these studies in Hydra, and from comparative studies in Hydractinia polyp polymorphs, suggests that evolutionary changes in the regulation of axial patterning genes may be a prominent mechanism underlying hydrozoan evolution. Despite the paucity of interspecies comparative expression information, hypotheses can be formulated about the role of developmental regulatory genes in hydrozoan evolution from information available from Hydra.     

Cladistic analysis of Medusozoa and cnidarian evolution

Abstract. A cladistic analysis of 87 morphological and life history characters of medusozoan cnidarians, rooted with Anthozoa, results in the phylogenetic hypothesis (Anthozoa (Hydrozoa (Scyphozoa (Staurozoa, Cubozoa)))). Staurozoa is a new class of Cnidaria consisting of Stauromedusae and the fossil group Conulatae. Scyphozoa is redefined as including those medusozoans characterized by strobilation and ephyrae (Coronatae, Semaeostomeae, and Rhizostomeae). Within Hydrozoa, Limnomedusae is identified as either the earliest diverging hydrozoan lineage or as the basal group of either Trachylina (Actinulida (Trachymedusae (Narcomedusae, Laingiomedusae))) or Hydroidolina (Leptothecata (Siphonophorae, Anthoathecata)). Cladistic results are highly congruent with recently published phylogenetic analyses based on 18S molecular characters. We propose a phylogenetic classification of Medusozoa that is consistent with phylogenetic hypotheses based on our cladistic results, as well as those derived from 18S analyses. Optimization of the characters presented in this analysis are used to discuss evolutionary scenarios. The ancestral cnidarian probably had a sessile biradial polyp as an adult form. The medusa is inferred to be a synapomorphy of Medusozoa. However, the ancestral process (metamorphosis of the apical region of the polyp or lateral budding involving an entocodon) could not be inferred unequivocally. Similarly, character states for sense organs and nervous systems could not be inferred for the ancestral medusoid of Medusozoa.     

High-resolution analysis of four efficient yeast replication origins reveals new insights into the ORC and putative MCM binding elements

In budding yeast, the eukaryotic initiator protein ORC (origin recognition complex) binds to a bipartite sequence consisting of an 11 bp ACS element and an adjacent B1 element. However, the genome contains many more matches to this consensus than actually bind ORC or function as origins in vivo. Although ORC-dependent loading of the replicative MCM helicase at origins is enhanced by a distal B2 element, less is known about this element. Here, we analyzed four highly active origins (ARS309, ARS319, ARS606 and ARS607) by linker scanning mutagenesis and found that sequences adjacent to the ACS contributed substantially to origin activity and ORC binding. Using the sequences of four additional B2 elements we generated a B2 multiple sequence alignment and identified a shared, degenerate 8 bp sequence that was enriched within 228 known origins. In addition, our high-resolution analysis revealed that not all origins exist within nucleosome free regions: a class of Sir2-regulated origins has a stably positioned nucleosome overlapping or near B2. This study illustrates the conserved yet flexible nature of yeast origin architecture to promote ORC binding and origin activity, and helps explain why a strong match to the ORC binding site is insufficient to identify origins within the genome.     

The colonial ascidian <Emphasis Type="Italic">Diplosoma listerianum</Emphasis> enhances the occurrence of the hydrozoan <Emphasis Type="Italic">Obelia</Emphasis> sp. during early phases of succession

Recruitment patterns of sessile species often do not reflect the composition of the local propagule pool. This is, among other processes, attributed to the stimulation or inhibition of settlement by resident species. In an experimental study, we evaluated the effects of different densities of the ascidian Diplosoma listerianum on the settlement of the hydrozoan Obelia sp. For this, we monitored the cover of the dominant fouler Obelia sp. on vertically orientated PVC tiles, which were either bare or pre-seeded with two different densities (sparse or dense) of Diplosoma colonies, over the course of 8 weeks. The settlement tiles were deployed at two study sites in La Herradura Bay, Chile. The presence of D. listerianum enhanced the settlement or the growth or both of the colonial hydrozoan, but this effect disappeared within 4–8 weeks. Furthermore, we tested whether the initial enhancement of Obelia sp. by Diplosoma colonies goes back to the fact that larvae, which reject the ascidian tunic as a settlement substratum after a first contact, colonize nearby surfaces because of their limited mobility. However, we found no support for this assumption. We rather suggest that D. listerianum facilitated colonization indirectly by the accumulation of organic material in its vicinity and/or by its pumping activity. Initial resident-mediated enhancement of the hydrozoan was overridden by processes such as competition between later colonizers within the course of weeks and we could not detect any lasting effects of D. listerianum on the structure of the developing communities.     

Characterization of a novel EF-hand homologue, CnidEF, in the sea anemone Anthopleura elegantissima

The superfamily of EF-hand proteins is comprised of a large and diverse group of proteins that contain one or more characteristic EF-hand calcium-binding domains. This study describes and characterizes a novel EF-hand cDNA, CnidEF, from the sea anemone Anthopleura elegantissima (Phylum Cnidaria, Class Anthozoa). CnidEF was found to contain two EF-hand motifs near the C-terminus of the deduced amino acid sequence and two regions near the N-terminus that could represent degenerate EF-hand motifs. CnidEF homologues were also identified from two other sea anemone species. A combination of bioinformatic and molecular phylogenetic analyses was used to compare CnidEF to EF-hand proteins in other organisms. The closest homologues identified from these analyses were a luciferin binding protein (LBP) involved in the bioluminescence of the anthozoan Renilla reniformis, and a sarcoplasmic calcium-binding protein (SARC) involved in fluorescence of the annelid worm Nereis diversicolor. Predicted structure and folding analysis revealed a close association with bioluminescent aequorin (AEQ) proteins from the hydrozoan cnidarian Aequorea aequorea. Neighbor-joining analyses grouped CnidEF within the SARC lineage along with AEQ and other cnidarian bioluminescent proteins rather than in the lineage containing calmodulin (CAM) and troponin-C (TNC).     

Evolution of RAG-1 in polyploid clawed frogs

Possible genetic fates of a gene duplicate are silencing, redundancy, subfunctionalization, or novel function. These different fates can be realized at the DNA, RNA, or protein level, and their genetic determinants are poorly understood. We explored molecular evolution of duplicated RAG-1 genes in African clawed frogs (Xenopus and Silurana) (1) to examine the fate of paralogs of this gene at the DNA level in terms of recombination, positive selection, and gene degeneration and in the absence of extensive recombination among alleles at different paralogs, (2) to test phylogenetic hypotheses about the origins of polyploid species. We found that recombination between different RAG-1 paralogs is infrequent, that degeneration of some paralogs has occurred via stop codons and frameshift mutations, and that this degeneration occurred in paralogs inherited from only one diploid progenitor species. Simulations and phylogenetic analyses of RAG-1 and mitochondrial DNA support one origin of extant tetraploids in Xenopus and at least one origin in Silurana, five allopolyploid origins of extant octoploids, and two allopolyploid origins of extant dodecaploids. In allopolyploid species, which inherit a complete genome from two different ancestors, genes inherited from the same ancestor have a longer period of coevolution than genes inherited from different ancestors. Because of this, gene ancestry could potentially influence gene fate: interacting paralogs derived from the same lower ploidy ancestor might have similar genetic destinies.     

The Ocular Skeleton Through The Eye of Evo-devo

An evolutionary developmental (evo-devo) approach to understanding the evolution, homology and development of structures has proved important for unraveling complex integrated skeletal systems through the use of modules, or modularity. An ocular skeleton, which consists of cartilage and sometimes bone, is present in many vertebrates; however the origin of these two components remains elusive. Using both palaeontological and developmental data, I propose that the vertebrate ocular skeleton is neural crest derived and that a single cranial neural crest module divided early in vertebrate evolution, possibly during the Ordovician, to give rise to an endoskeletal component and an exoskeletal component within the eye. These two components subsequently became uncoupled with respect to timing, placement within the sclera and inductive epithelia, enabling them to evolve independently and to diversify. In some extant groups, these two modules have become reassociated with one another. Furthermore, the data suggests that the endoskeletal component of the ocular skeleton was likely established and therefore evolved before the exoskeletal component. This study provides important insights into the evolution of the ocular skeleton, a region with a long evolutionary history amongst vertebrates. J. Exp. Zool. (Mol. Dev. Evol.) 9999B: 1-9, 2012. ? 2012 Wiley Periodicals, Inc.     

Congruence between comparative morphology and molecular phylogenies: Evolution of the male genital skeletal/muscular system in the subtribe Polyommatina (Lepidoptera,Lycaenidae)

The skeleton and musculature of male genitalia were studied in species of a model butterfly group (subtribe Polyommatina, Lycaenidae). In total, we analyzed 45 species of the tribe Polyommatini most of which were previously used in the molecular phylogenetic study (Talavera et al., 2013). The studied morphological characters were mapped on the molecular trees, which allowed us to reveal trends of morphological changes and to estimate the age of their origin. As a result, chronology of evolution of skeleton and musculature traits was established. It was shown that periods of slow morphological evolution alternated in the subtribe Polyommatina with those of a high rate of origin of new traits. For example, topography of the intravalvar muscles has not changed for 26 MY preserving their initial fan-shaped attachment. The evolution of intravalvar muscles started 10 MYA, proceeded slowly during the first 5 MY, and then accelerated during the last 5 MY resulting in the extensive splitting of the musculature in most monophyletic lineages. Mapping the morphological characters on the phylogeny demonstrated that the rates of skeleton and muscle evolution within the skeleton/musculature apparatus were different. In most cases the intravalvar musculature evolved much faster than the skeleton. The cladistic interpretation of states of morphological traits was found to be consistent with phylogenetic reconstructions based on analysis of multiple molecular markers. Moreover, morphological synapomorphies were found for the lineages Alpherakya + Glabroculus and Aricia + (Alpherakya + Glabroculus), which had low statistical support in molecular phylogenetic analysis. Additionally, in some cases molecular studies helped to reveal trends in the evolution of morphological traits. For example, the unpaired uncus and the compact juxta are not plesiomorphic for Cupidina as previously thought; instead, they were shown to have evolved secondarily within this subtribe.     

Cloning of anthozoan fluorescent protein genes

Many cnidarians display vivid fluorescence under proper lighting conditions. In general, these colors are due to the presence of fluorescent proteins similar to the green fluorescent protein (GFP) originally isolated from the hydrozoan medusa Aequorea victoria (Cnidaria: Hydrozoa). To optimize the search for new fluorescent proteins (FPs), a technique was developed that allows for the rapid cloning and screening of FP genes without the need for a prior knowledge of gene sequence. Using this method, four new FP genes were cloned, a green from Montastraea cavernosa (Anthozoa: Scleractinia: Faviidae), a cyan from Pocillopora damicornis (Anthozoa: Scleractinia: Pocilloporidae), a cyan from Discosoma striata (Anthozoa: Corallimorpharia), and a red from a second Discosoma species. Two additional green FPs were cloned, one from M. cavernosa and one from its congener Montastraea faveolata, from purified cDNA using PCR primers designed for the first M. cavernosa green FP. Each FP has recognizable amino acid sequence motifs that place them conclusively in the GFP protein family. Mutation of these products using a low-stringency PCR protocol followed by screening of large numbers of bacterial colonies allowed rapid creation of mutants with a variety of characteristics, including changes in color, maturation time, and brightness. An enhanced version of the new red FP, DspR1+, matures faster at 30 degrees C than the commercially available DsRed but matures slower than DsRed at 37 degrees C. One of the M. cavernosa green FPs, McaG2, is highly resistant to photobleaching and has a fluorescence quantum yield approximately twice that of EGFP-1.     

Evolutionary diversification of banded tube-dwelling anemones (Cnidaria; Ceriantharia; Isarachnanthus) in the Atlantic Ocean

The use of molecular data for species delimitation in Anthozoa is still a very delicate issue. This is probably due to the low genetic variation found among the molecular markers (primarily mitochondrial) commonly used for Anthozoa. Ceriantharia is an anthozoan group that has not been tested for genetic divergence at the species level. Recently, all three Atlantic species described for the genus Isarachnanthus of Atlantic Ocean, were deemed synonyms based on morphological simmilarities of only one species: Isarachnanthus maderensis. Here, we aimed to verify whether genetic relationships (using COI, 16S, ITS1 and ITS2 molecular markers) confirmed morphological affinities among members of Isarachnanthus from different regions across the Atlantic Ocean. Results from four DNA markers were completely congruent and revealed that two different species exist in the Atlantic Ocean. The low identification success and substantial overlap between intra and interspecific COI distances render the Anthozoa unsuitable for DNA barcoding, which is not true for Ceriantharia. In addition, genetic divergence within and between Ceriantharia species is more similar to that found in Medusozoa (Hydrozoa and Scyphozoa) than Anthozoa and Porifera that have divergence rates similar to typical metazoans. The two genetic species could also be separated based on micromorphological characteristics of their cnidomes. Using a specimen of Isarachnanthus bandanensis from Pacific Ocean as an outgroup, it was possible to estimate the minimum date of divergence between the clades. The cladogenesis event that formed the species of the Atlantic Ocean is estimated to have occured around 8.5 million years ago (Miocene) and several possible speciation scenarios are discussed.     

WHY DOES A TRAIT EVOLVE MULTIPLE TIMES WITHIN A CLADE? REPEATED EVOLUTION OF SNAKELINE BODY FORM IN SQUAMATE REPTILES

Abstract Why does a trait evolve repeatedly within a clade? When examining the evolution of a trait, evolutionary biologists typically focus on the selective advantages it may confer and the genetic and developmental mechanisms that allow it to vary. Although these factors may be necessary to explain why a trait evolves in a particular instance, they may not be sufficient to explain phylogenetic patterns of repeated evolution or conservatism. Instead, other factors may also be important, such as biogeography and competitive interactions. In squamate reptiles (lizards and snakes) a dramatic transition in body form has occurred repeatedly, from a fully limbed, lizardlike body form to a limbreduced, elongate, snakelike body form. We analyze this trait in a phylogenetic and biogeographic context to address why this transition occurred so frequently. We included 261 species for which morphometric data and molecular phylogenetic information were available. Among the included species, snakelike body form has evolved about 25 times. Most lineages of snakelike squamates belong to one of two ecomorphs, either short‐tailed burrowers or long‐tailed surface dwellers. The repeated origins of snakelike squamates appear to be associated with the in situ evolution of these two ecomorphs on different continental regions (including multiple origins of the burrowing morph within most continents), with very little dispersal of most limb‐reduced lineages between continental regions. Overall, the number of repeated origins of snakelike morphology seems to depend on large‐scale biogeographic patterns and community ecology, in addition to more traditional explanations (e.g., selection, development).