Genetic structure and historic demography of endangered unarmoured threespine stickleback at southern latitudes signals a potential new management approach.

Habitat loss, flood control infrastructure, and drought have left most of southern California and northern Baja California's native freshwater fish near extinction, including the endangered unarmoured threespine stickleback (Gasterosteus aculeatus williamsoni). This subspecies, an unusual morph lacking the typical lateral bony plates of the G. aculeatus complex, occurs at arid southern latitudes in the eastern Pacific Ocean and survives in only three inland locations. Managers have lacked molecular data to answer basic questions about the ancestry and genetic distinctiveness of unarmoured populations. These data could be used to prioritize conservation efforts. We sampled G. aculeatus from 36 localities and used microsatellites and whole genome data to place unarmoured populations within the broader evolutionary context of G. aculeatus across southern California/northern Baja California. We identified three genetic groups with none consisting solely of unarmoured populations. Unlike G. aculeatus at northern latitudes, where Pleistocene glaciation has produced similar historical demographic profiles across populations, we found markedly different demographics depending on sampling location, with inland unarmoured populations showing steeper population declines and lower heterozygosity compared to low armoured populations in coastal lagoons. One exception involved the only high elevation population in the region, where the demography and alleles of unarmoured fish were similar to low armoured populations near the coast, exposing one of several cases of artificial translocation. Our results suggest that the current "management-by-phenotype" approach, based on lateral plates, is incidentally protecting the most imperilled populations; however, redirecting efforts toward evolutionary units, regardless of phenotype, may more effectively preserve adaptive potential.

First sequencing of ancient coral skeletal proteins.

Here we report the first recovery, sequencing, and identification of fossil biomineral proteins from a Pleistocene fossil invertebrate, the stony coral Orbicella annularis. This fossil retains total hydrolysable amino acids of a roughly similar composition to extracts from modern O. annularis skeletons, with the amino acid data rich in Asx (Asp + Asn) and Glx (Glu + Gln) typical of invertebrate skeletal proteins. It also retains several proteins, including a highly acidic protein, also known from modern coral skeletal proteomes that we sequenced by LC-MS/MS over multiple trials in the best-preserved fossil coral specimen. A combination of degradation or amino acid racemization inhibition of trypsin digestion appears to limit greater recovery. Nevertheless, our workflow determines optimal samples for effective sequencing of fossil coral proteins, allowing comparison of modern and fossil invertebrate protein sequences, and will likely lead to further improvements of the methods. Sequencing of endogenous organic molecules in fossil invertebrate biominerals provides an ancient record of composition, potentially clarifying evolutionary changes and biotic responses to paleoenvironments.

Mechanisms of cnidocyte development in the moon jellyfish Aurelia.

Stinging cells called cnidocytes are a defining trait of the cnidarians (sea anemones, corals, jellyfish, and their relatives). In hydrozoan cnidarians such as Hydra, cnidocytes develop from interstitial stem cells set aside in the ectoderm. It is less clear how cnidocytes develop outside the Hydrozoa, as other cnidarians appear to lack interstitial stem cells. We addressed this question by studying cnidogenesis in the moon jellyfish (Aurelia) through the visualization of minicollagen-a protein associated with cnidocyte development-as well as transmission electron microscopy. We discovered that developing cnidoblasts are rare or absent in feeding structures rich in mature cnidocytes, such as tentacles and lappets. Using transmission electron microscopy, we determined that the progenitors of cnidocytes have traits consistent with epitheliomuscular cells. Our data suggests a dynamic where cnidocytes develop at high concentrations in the epithelium of more proximal regions, and subsequently migrate to more distal regions where they exhibit high usage and turnover. Similar to some anthozoans, cnidocytes in Aurelia do not appear to be generated by interstitial stem cells; instead, epitheliomuscular cells appear to be the progenitor cell type. This observation polarizes the evolution of cnidogenesis, and raises the question of how interstitial stem cells came to regulate cnidogenesis in hydrozoans.

The genome of the jellyfish Aurelia and the evolution of animal complexity.

We present the genome of the moon jellyfish Aurelia, a genome from a cnidarian with a medusa life stage. Our analyses suggest that gene gain and loss in Aurelia is comparable to what has been found in its morphologically simpler relatives-the anthozoan corals and sea anemones. RNA sequencing analysis does not support the hypothesis that taxonomically restricted (orphan) genes play an oversized role in the development of the medusa stage. Instead, genes broadly conserved across animals and eukaryotes play comparable roles throughout the life cycle. All life stages of Aurelia are significantly enriched in the expression of genes that are hypothesized to interact in protein networks found in bilaterian animals. Collectively, our results suggest that increased life cycle complexity in Aurelia does not correlate with an increased number of genes. This leads to two possible evolutionary scenarios: either medusozoans evolved their complex medusa life stage (with concomitant shifts into new ecological niches) primarily by re-working genetic pathways already present in the last common ancestor of cnidarians, or the earliest cnidarians had a medusa life stage, which was subsequently lost in the anthozoans. While we favour the earlier hypothesis, the latter is consistent with growing evidence that many of the earliest animals were more physically complex than previously hypothesized.

How sea level change mediates genetic divergence in coastal species across regions with varying tectonic and sediment processes.

Plate tectonics and sediment processes control regional continental shelf topography. We examine the genetic consequences of how glacial-associated sea level change interacted with variable nearshore topography since the last glaciation. We reconstructed the size and distribution of areas suitable for tidal estuary formation from the last glacial maximum, ~20 thousand years ago, to present from San Francisco, California, USA (~38°N) to Reforma, Sinaloa, Mexico (~25°N). We assessed range-wide genetic structure and diversity of three codistributed tidal estuarine fishes (California Killifish, Shadow Goby, Longjaw Mudsucker) along ~4,600 km using mitochondrial control region and cytB sequence, and 16-20 microsatellite loci from a total of 524 individuals. Results show that glacial-associated sea level change limited estuarine habitat to few, widely separated refugia at glacial lowstand, and present-day genetic clades were sourced from specific refugia. Habitat increased during postglacial sea level rise and refugial populations admixed in newly formed habitats. Continental shelves with active tectonics and/or low sediment supply were steep and hosted fewer, smaller refugia with more genetically differentiated populations than on broader shelves. Approximate Bayesian computation favoured the refuge-recolonization scenarios from habitat models over isolation by distance and seaway alternatives, indicating isolation at lowstand is a major diversification mechanism among these estuarine (and perhaps other) coastal species. Because sea level change is a global phenomenon, we suggest this top-down physical control of extirpation-isolation-recolonization may be an important driver of genetic diversification in coastal taxa inhabiting other topographically complex coasts globally during the Mid- to Late Pleistocene and deeper timescales.

Mitogenomics supports an unexpected taxonomic relationship for the extinct diving duck Chendytes lawi and definitively places the extinct Labrador Duck.

Chendytes lawi, an extinct flightless diving anseriform from coastal California, was traditionally classified as a sea duck, tribe Mergini, based on similarities in osteological characters. We recover and analyze mitochondrial genomes of C. lawi and five additional Mergini species, including the extinct Labrador Duck, Camptorhynchus labradorius. Despite its diving morphology, C. lawi is reconstructed as an ancient relictual lineage basal to the dabbling ducks (tribe Anatini), revealing an additional example of convergent evolution of characters related to feeding behavior among ducks. The Labrador Duck is sister to Steller's Eider which may provide insights into the evolution and ecology of this poorly known extinct species. Our results demonstrate that inclusion of full length mitogenomes, from taxonomically distributed ancient and modern sources can improve phylogeny reconstruction of groups previously assessed with shorter single-gene mitochondrial sequences.

Introgression between ecologically distinct species following increased salinity in the Colorado Delta- Worldwide implications for impacted estuary diversity.

We investigate hybridization and introgression between ecologically distinct sister species of silverside fish in the Gulf of California through combined analysis of morphological, sequence, and genotypic data. Water diversions in the past century turned the Colorado River Delta from a normal estuary to a hypersaline inverse estuary, raising concerns for the local fauna, much of which is endangered. Salinity differences are known to generate ecological species pairs and we anticipated that loss of the fresher-water historic salinity regime could alter the adaptive factors maintaining distinction between the broadly distributed Gulf-endemic Colpichthys regis and the narrowly restricted Delta-endemic Colpichthys hubbsi, the species that experienced dramatic environmental change. In this altered environmental context, these long-isolated species (as revealed by Cytochrome b sequences) show genotypic (RAG1, microsatellites) evidence of active hybridization where the species ranges abut, as well as directional introgression from C. regis into the range center of C. hubbsi. Bayesian group assignment (STRUCTURE) on six microsatellite loci and multivariate analyses (DAPC) on both microsatellites and phenotypic data further support substantial recent admixture between the sister species. Although we find no evidence for recent population decline in C. hubbsi based on mitochondrial sequence, introgression may be placing an ancient ecological species at risk of extinction. Such introgressive extinction risk should also pertain to other ecological species historically sustained by the now changing Delta environment. More broadly, salinity gradient associated ecological speciation is evident in silverside species pairs in many estuarine systems around the world. Ecological species pairs among other taxa in such systems are likely poorly understood or cryptic. As water extraction accelerates in river systems worldwide, salinity gradients will necessarily be altered, impacting many more estuary and delta systems. Such alteration of habitats will place biodiversity at risk not only from direct effects of habitat destruction, but also from the potential for the breakdown of ecological species. Thus, evolutionary response to the anthropogenic alteration of salinity gradients in estuaries merits investigation as the number of impacted systems increases around the globe, permitting parallel study of multiple systems, while also permitting a conservation management response to help preserve this little championed component of biodiversity.

Sea-level driven glacial-age refugia and post-glacial mixing on subtropical coasts, a palaeohabitat and genetic study.

Using a novel combination of palaeohabitat modelling and genetic mixture analyses, we identify and assess a sea-level-driven recolonization process following the Last Glacial Maximum (LGM). Our palaeohabitat modelling reveals dramatic changes in estuarine habitat distribution along the coast of California (USA) and Baja California (Mexico). At the LGM (approx. 20 kya), when sea level was approximately 130 m lower, the palaeo-shoreline was too steep for tidal estuarine habitat formation, eliminating this habitat type from regions where it is currently most abundant, and limiting such estuaries to a northern and a southern refugium separated by 1000 km. We assess the recolonization of estuaries formed during post-LGM sea-level rise through examination of refugium-associated alleles and approximate Bayesian computation in three species of estuarine fishes. Results reveal sourcing of modern populations from both refugia, which admix in the newly formed habitat between the refuges. We infer a dramatic peak in habitat area between 15 and 10 kya with subsequent decline. Overall, this approach revealed a previously undocumented dynamic and integrated relationship between sea-level change, coastal processes and population genetics. These results extend glacial refugial dynamics to unglaciated subtropical coasts and have significant implications for biotic response to predicted sea-level rise.

Cell tracking supports secondary gastrulation in the moon jellyfish Aurelia.

The moon jellyfish Aurelia exhibits a dramatic reorganization of tissue during its metamorphosis from planula larva to polyp. There are currently two competing hypotheses regarding the fate of embryonic germ layers during this metamorphosis. In one scenario, the original endoderm undergoes apoptosis and is replaced by a secondary endoderm derived from ectodermal cells. In the second scenario, both ectoderm and endoderm remain intact through development. In this study, we performed a pulse-chase experiment to trace the fate of larval ectodermal cells. We observed that prior to metamorphosis, ectodermal cells that proliferated early in larval development concentrate at the future oral end of the polyp. During metamorphosis, these cells migrate into the endoderm, extending all the way to the aboral portion of the gut. We therefore reject the hypothesis that larval endoderm remains intact during metamorphosis and provide additional support for the "secondary gastrulation" hypothesis. Aurelia appears to offer the first and only described case where a cnidarian derives its endoderm twice during normal development, adding to a growing body of evidence that germ layers can be dramatically reorganized in cnidarian life cycles.

A New Species of the Bay Goby Genus Eucyclogobius, Endemic to Southern California: Evolution, Conservation, and Decline.

A geographically isolated set of southern localities of the formerly monotypic goby genus Eucyclogobius is known to be reciprocally monophyletic and substantially divergent in mitochondrial sequence and nuclear microsatellite-based phylogenies relative to populations to the north along the California coast. To clarify taxonomic and conservation status, we conducted a suite of analyses on a comprehensive set of morphological counts and measures from across the range of Eucyclogobius and describe the southern populations as a new species, the Southern Tidewater Goby, Eucyclogobius kristinae, now separate from the Northern Tidewater Goby Eucyclogobius newberryi (Girard 1856). In addition to molecular distinction, adults of E. kristinae are diagnosed by: 1) loss of the anterior supratemporal lateral-line canals resulting in higher neuromast counts, 2) lower pectoral and branched caudal ray counts, and 3) sets of measurements identified via discriminant analysis. These differences suggest ecological distinction of the two species. Previous studies estimated lineage separation at 2-4 million years ago, and mitochondrial sequence divergence exceeds that of other recognized fish species. Fish from Santa Monica Artesian Springs (Los Angeles County) northward belong to E. newberryi; those from Aliso Creek (Orange County) southward constitute E. kristinae. The lagoonal habitat of Eucyclogobius has been diminished or degraded, leading to special conservation status at state and federal levels beginning in 1980. Habitat of the newly described species has been impacted by a range of anthropogenic activities, including the conversion of closing lagoons to open tidal systems in the name of restoration. In the last 30 years, E. kristinae has only been observed in nine intermittently occupied lagoonal systems in northern San Diego County; it currently persists in only three sites. Thus, the new species is in imminent danger of extinction and will require ongoing active management.

Benefits of commercial weight-loss programs on blood pressure and lipids: a systematic review.

Our objective was to compare the effect of commercial weight-loss programs on blood pressure and lipids to control/education or counseling among individuals with overweight/obesity. We conducted a systematic review by searching MEDLINE and Cochrane Database of Systematic Reviews from inception to November 2014 and references identified by the programs. We included randomized, controlled trials ≥12weeks in duration. Two reviewers extracted information on study design, interventions, and mean change in systolic blood pressure (SBP), diastolic blood pressure (DBP), low-density lipoprotein cholesterol (LDL-c), high-density lipoprotein cholesterol (HDL-c), triglycerides, and total cholesterol and assessed risk of bias. We included 27 trials. Participants' blood pressure and lipids were normal at baseline in most trials. At 12months, Weight Watchers showed little change in blood pressure or lipid outcomes as compared to control/education (2 trials). At 12months, Atkins' participants had higher HDL-c and lower triglycerides than counseling (4 trials). Other programs had inconsistent effects or lacked long-term studies. Risk of bias was high for most trials of all programs. In conclusion, limited data exist regarding most commercial weight-loss programs' long-term effects on blood pressure and lipids. Clinicians should be aware that Weight Watchers has limited data that demonstrate CVD risk factor benefits relative to control/education. Atkins may be a reasonable option for patients with dyslipidemia. Additional well-designed, long-term trials are needed to confirm these conclusions and evaluate other commercial programs.

Direct comparisons of commercial weight-loss programs on weight, waist circumference, and blood pressure: a systematic review.

BACKGROUND: Obesity is common in the U.S. and many individuals turn to commercial programs to lose weight. Our objective was to directly compare weight loss, waist circumference, and systolic and diastolic blood pressure (SBP, DBP) outcomes between commercially available weight-loss programs. METHODS: We conducted a systematic review by searching MEDLINE and the Cochrane Database of Systematic Reviews from inception to November 2014 and by using references identified by commercial programs. We included randomized, controlled trials (RCTs) of at least 12 weeks duration that reported comparisons with other commercial weight-loss programs. Two reviewers extracted information on mean change in weight, waist circumference, SBP and DBP and assessed risk of bias. RESULTS: We included seven articles representing three RCTs. Curves participants lost 1.8 kg (95%CI: 0.1, 3.5 kg) more than Weight Watchers in one comparison. There was no statistically significant difference in waist circumference change among the included programs. The mean reduction in SBP for SlimFast participants was 4.5 mmHg (95%CI: 0.4, 8.6 mmHg) more than that of Atkins participants in one comparison. There was no significant difference in mean DBP changes among programs. CONCLUSIONS: There is limited evidence that any one of the commercial weight-loss programs has superior results for mean weight change, mean waist circumference change, or mean blood pressure change.

Ancestral state reconstruction of ontogeny supports a bilaterian affinity for Dickinsonia.

Despite numerous attempts, classification of the Precambrian fossil Dickinsonia has eluded scientific consensus. This is largely because Dickinsonia and its relatives are structurally simple, lacking morphological synapomorphies to clarify their relationship to modern taxa. However, there is increasing precedence for using ontogeny to constrain enigmatic fossils, and growth of the type species Dickinsonia costata is well understood. This study formalizes the connection between ontogeny in Dickinsonia-which grows by the addition of metameric units onto one end of its primary axis-with terminal addition, defined as growth and patterning from a posterior, subtermial growth zone. We employ ancestral state reconstruction and stochastic character mapping to conclude that terminal addition is a synapomorphy of bilaterian animals. Thus, terminal addition allies Dickinsonia with the bilaterians, providing evidence that large stem- or crown-group bilaterians made up a significant proportion of the Precambrian biota. This study also illustrates the potential for combining developmental and phylogenetic data in constraining the placement of ancient problematic fossil taxa on the evolutionary tree.

Temporal genetic analysis of the endangered tidewater goby: extinction-colonization dynamics or drift in isolation?

Extinction and colonization dynamics are critical to understanding the evolution and conservation of metapopulations. However, traditional field studies of extinction-colonization are potentially fraught with detection bias and have rarely been validated. Here, we provide a comparison of molecular and field-based approaches for assessment of the extinction-colonization dynamics of tidewater goby (Eucyclogobius newberryi) in northern California. Our analysis of temporal genetic variation across 14 northern California tidewater goby populations failed to recover genetic change expected with extinction-colonization cycles. Similarly, analysis of site occupancy data from field studies (94 sites) indicated that extinction and colonization are very infrequent for our study populations. Comparison of the approaches indicated field data were subject to imperfect detection, and falsely implied extinction-colonization cycles in several instances. For northern California populations of tidewater goby, we interpret the strong genetic differentiation between populations and high degree of within-site temporal stability as consistent with a model of drift in the absence of migration, at least over the past 20-30 years. Our findings show that tidewater goby exhibit different population structures across their geographic range (extinction-colonization dynamics in the south vs. drift in isolation in the north). For northern populations, natural dispersal is too infrequent to be considered a viable approach for recolonizing extirpated populations, suggesting that species recovery will likely depend on artificial translocation in this region. More broadly, this work illustrates that temporal genetic analysis can be used in combination with field data to strengthen inference of extinction-colonization dynamics or as a stand-alone tool when field data are lacking.

Structural and Developmental Disparity in the Tentacles of the Moon Jellyfish Aurelia sp.1.

Tentacles armed with stinging cells (cnidocytes) are a defining trait of the cnidarians, a phylum that includes sea anemones, corals, jellyfish, and hydras. While cnidarian tentacles are generally characterized as structures evolved for feeding and defense, significant variation exists between the tentacles of different species, and within the same species across different life stages and/or body regions. Such diversity suggests cryptic distinctions exist in tentacle function. In this paper, we use confocal and transmission electron microscopy to contrast the structure and development of tentacles in the moon jellyfish, Aurelia species 1. We show that polyp oral tentacles and medusa marginal tentacles display markedly different cellular and muscular architecture, as well as distinct patterns of cellular proliferation during growth. Many structural differences between these tentacle types may reflect biomechanical solutions to different feeding strategies, although further work would be required for a precise mechanistic understanding. However, differences in cell proliferation dynamics suggests that the two tentacle forms lack a conserved mechanism of development, challenging the textbook-notion that cnidarian tentacles can be homologized into a conserved bauplan.

Gene Expression Data from the Moon Jelly, Aurelia, Provide Insights into the Evolution of the Combinatorial Code Controlling Animal Sense Organ Development.

In Bilateria, Pax6, Six, Eya and Dach families of transcription factors underlie the development and evolution of morphologically and phyletically distinct eyes, including the compound eyes in Drosophila and the camera-type eyes in vertebrates, indicating that bilaterian eyes evolved under the strong influence of ancestral developmental gene regulation. However the conservation in eye developmental genetics deeper in the Eumetazoa, and the origin of the conserved gene regulatory apparatus controlling eye development remain unclear due to limited comparative developmental data from Cnidaria. Here we show in the eye-bearing scyphozoan cnidarian Aurelia that the ectodermal photosensory domain of the developing medusa sensory structure known as the rhopalium expresses sine oculis (so)/six1/2 and eyes absent/eya, but not optix/six3/6 or pax (A&B). In addition, the so and eya co-expression domain encompasses the region of active cell proliferation, neurogenesis, and mechanoreceptor development in rhopalia. Consistent with the role of so and eya in rhopalial development, developmental transcriptome data across Aurelia life cycle stages show upregulation of so and eya, but not optix or pax (A&B), during medusa formation. Moreover, pax6 and dach are absent in the Aurelia genome, and thus are not required for eye development in Aurelia. Our data are consistent with so and eya, but not optix, pax or dach, having conserved functions in sensory structure specification across Eumetazoa. The lability of developmental components including Pax genes relative to so-eya is consistent with a model of sense organ development and evolution that involved the lineage specific modification of a combinatorial code that specifies animal sense organs.

Efficacy of commercial weight-loss programs: an updated systematic review.

BACKGROUND: Commercial and proprietary weight-loss programs are popular obesity treatment options, but their efficacy is unclear. PURPOSE: To compare weight loss, adherence, and harms of commercial or proprietary weight-loss programs versus control/education (no intervention, printed materials only, health education curriculum, or <3 sessions with a provider) or behavioral counseling among overweight and obese adults. DATA SOURCES: MEDLINE and the Cochrane Database of Systematic Reviews from inception to November 2014; references identified by program staff. STUDY SELECTION: Randomized, controlled trials (RCTs) of at least 12 weeks' duration; prospective case series of at least 12 months' duration (harms only). DATA EXTRACTION: Two reviewers extracted information on study design, population characteristics, interventions, and mean percentage of weight change and assessed risk of bias. DATA SYNTHESIS: We included 45 studies, 39 of which were RCTs. At 12 months, Weight Watchers participants achieved at least 2.6% greater weight loss than those assigned to control/education. Jenny Craig resulted in at least 4.9% greater weight loss at 12 months than control/education and counseling. Nutrisystem resulted in at least 3.8% greater weight loss at 3 months than control/education and counseling. Very-low-calorie programs (Health Management Resources, Medifast, and OPTIFAST) resulted in at least 4.0% greater short-term weight loss than counseling, but some attenuation of effect occurred beyond 6 months when reported. Atkins resulted in 0.1% to 2.9% greater weight loss at 12 months than counseling. Results for SlimFast were mixed. We found limited evidence to evaluate adherence or harms for all programs and weight outcomes for other commercial programs. LIMITATION: Many trials were short (<12 months), had high attrition, and lacked blinding. CONCLUSION: Clinicians could consider referring overweight or obese patients to Weight Watchers or Jenny Craig. Other popular programs, such as Nutrisystem, show promising weight-loss results; however, additional studies evaluating long-term outcomes are needed. PRIMARY FUNDING SOURCE: None. ( PROSPERO: CRD4201-4007155).

The early expansion and evolutionary dynamics of POU class genes.

The POU genes represent a diverse class of animal-specific transcription factors that play important roles in neurogenesis, pluripotency, and cell-type specification. Although previous attempts have been made to reconstruct the evolution of the POU class, these studies have been limited by a small number of representative taxa, and a lack of sequences from basally branching organisms. In this study, we performed comparative analyses on available genomes and sequences recovered through "gene fishing" to better resolve the topology of the POU gene tree. We then used ancestral state reconstruction to map the most likely changes in amino acid evolution for the conserved domains. Our work suggests that four of the six POU families evolved before the last common ancestor of living animals-doubling previous estimates-and were followed by extensive clade-specific gene loss. Amino acid changes are distributed unequally across the gene tree, consistent with a neofunctionalization model of protein evolution. We consider our results in the context of early animal evolution, and the role of POU5 genes in maintaining stem cell pluripotency.

Attempted DNA extraction from a Rancho La Brea Columbian mammoth (Mammuthus columbi): prospects for ancient DNA from asphalt deposits.

Fossil-bearing asphalt deposits are an understudied and potentially significant source of ancient DNA. Previous attempts to extract DNA from skeletons preserved at the Rancho La Brea tar pits in Los Angeles, California, have proven unsuccessful, but it is unclear whether this is due to a lack of endogenous DNA, or if the problem is caused by asphalt-mediated inhibition. In an attempt to test these hypotheses, a recently recovered Columbian mammoth (Mammuthus columbi) skeleton with an unusual pattern of asphalt impregnation was studied. Ultimately, none of the bone samples tested successfully amplified M. columbi DNA. Our work suggests that reagents typically used to remove asphalt from ancient samples also inhibit DNA extraction. Ultimately, we conclude that the probability of recovering ancient DNA from fossils in asphalt deposits is strongly (perhaps fatally) hindered by the organic compounds that permeate the bones and that at the Rancho La Brea tar pits, environmental conditions might not have been ideal for the general preservation of genetic material.

Canopy flow analysis reveals the advantage of size in the oldest communities of multicellular eukaryotes.

VIDEO ABSTRACT: At Mistaken Point, Newfoundland, Canada, rangeomorph "fronds" dominate the earliest (579-565 million years ago) fossil communities of large (0.1 to 2 m height) multicellular benthic eukaryotes. They lived in low-flow environments, fueled by uptake [1-3] of dissolved reactants (osmotrophy). However, prokaryotes are effective osmotrophs, and the advantage of taller eukaryotic osmotrophs in this deep-water community context has not been addressed. We reconstructed flow-velocity profiles and vertical mixing using canopy flow models appropriate to the densities of the observed communities. Further modeling of processes at organismal surfaces documents increasing uptake with height in the community as a function of thinning of the diffusive boundary layer with increased velocity. The velocity profile, produced by canopy flow in the community, generates this advantage of upward growth. Alternative models of upward growth advantage based on redox/resource gradients fail, given the efficiency of vertical mixing. In benthic communities of osmotrophs of sufficient density, access to flow in low-flow settings provides an advantage to taller architecture, providing a selectional driver for communities of tall eukaryotes in contexts where phototropism cannot contribute to upward growth. These Ediacaran deep-sea fossils were preserved during the increasing oxygenation prior to the Cambrian radiation of animals and likely represent an important phase in the ecological and evolutionary transition to more complex eukaryotic forms.