Publications by authors named "Pincelli M Hull"

19 Publications

  • Page 1 of 1

Towards quantifying the mass extinction debt of the Anthropocene.

Proc Biol Sci 2021 Apr 28;288(1949):20202332. Epub 2021 Apr 28.

Department of Earth and Planetary Sciences, Yale University, New Haven, CT 06511, USA.

To make sense of our present biodiversity crises, the modern rate of species extinctions is commonly compared to a benchmark, or 'background,' rate derived from the fossil record. These estimates are critical for bounding the scale of modern diversity loss, but are yet to fully account for the fundamental structure of extinction rates through time. Namely, a substantial fraction of extinctions within the fossil record occurs within relatively short-lived extinction pulses, and not during intervals characterized by background rates of extinction. Accordingly, it is more appropriate to compare the modern event to these pulses than to the long-term average rate. Unfortunately, neither the duration of extinction pulses in the geological record nor the ultimate magnitude of the extinction pulse today is resolved, making assessments of their relative sizes difficult. In addition, the common metric used to compare current and past extinction rates does not correct for large differences in observation duration. Here, we propose a new predictive metric that may be used to ascertain the ultimate extent of the ongoing extinction threat, building on the observation that extinction magnitude in the marine fossil record is correlated to the magnitude of sedimentary turnover. Thus, we propose that the ultimate number of species destined for extinction today can be predicted by way of a quantitative appraisal of humanity's modification of ecosystems as recorded in sediments-that is, by comparing our future rock record with that of the past. The ubiquity of habitat disruption worldwide suggests that a profound mass extinction debt exists today, but one that might yet be averted by preserving and restoring ecosystems and their geological traces.
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http://dx.doi.org/10.1098/rspb.2020.2332DOI Listing
April 2021

The enigma of Oligocene climate and global surface temperature evolution.

Proc Natl Acad Sci U S A 2020 10 28;117(41):25302-25309. Epub 2020 Sep 28.

Department of Geology and Geophysics, Yale University, New Haven, CT 06511.

Falling atmospheric CO levels led to cooling through the Eocene and the expansion of Antarctic ice sheets close to their modern size near the beginning of the Oligocene, a period of poorly documented climate. Here, we present a record of climate evolution across the entire Oligocene (33.9 to 23.0 Ma) based on TEX sea surface temperature (SST) estimates from southwestern Atlantic Deep Sea Drilling Project Site 516 (paleolatitude ∼36°S) and western equatorial Atlantic Ocean Drilling Project Site 929 (paleolatitude ∼0°), combined with a compilation of existing SST records and climate modeling. In this relatively low CO Oligocene world (∼300 to 700 ppm), warm climates similar to those of the late Eocene continued with only brief interruptions, while the Antarctic ice sheet waxed and waned. SSTs are spatially heterogenous, but generally support late Oligocene warming coincident with declining atmospheric CO This Oligocene warmth, especially at high latitudes, belies a simple relationship between climate and atmospheric CO and/or ocean gateways, and is only partially explained by current climate models. Although the dominant climate drivers of this enigmatic Oligocene world remain unclear, our results help fill a gap in understanding past Cenozoic climates and the way long-term climate sensitivity responded to varying background climate states.
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http://dx.doi.org/10.1073/pnas.2003914117DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7568263PMC
October 2020

Extensive morphological variability in asexually produced planktic foraminifera.

Sci Adv 2020 Jul 10;6(28). Epub 2020 Jul 10.

School of the Earth, Ocean and Environment, University of South Carolina, Columbia, SC, USA.

Marine protists are integral to the structure and function of pelagic ecosystems and marine carbon cycling, with rhizarian biomass alone accounting for more than half of all mesozooplankton in the oligotrophic oceans. Yet, understanding how their environment shapes diversity within species and across taxa is limited by a paucity of observations of heritability and life history. Here, we present observations of asexual reproduction, morphologic plasticity, and ontogeny in the planktic foraminifer in laboratory culture. Our results demonstrate that planktic foraminifera reproduce both sexually and asexually and demonstrate extensive phenotypic plasticity in response to nonheritable factors. These two processes fundamentally explain the rapid spatial and temporal response of even imperceptibly low populations of planktic foraminifera to optimal conditions and the diversity and ubiquity of these species across the range of environmental conditions that occur in the ocean.
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http://dx.doi.org/10.1126/sciadv.abb8930DOI Listing
July 2020

Paleozoic ammonoid ecomorphometrics test ecospace availability as a driver of morphological diversification.

Sci Adv 2020 Sep 9;6(37). Epub 2020 Sep 9.

Department of Earth and Planetary Sciences, Yale University, 210 Whitney Ave., New Haven, CT 06511, USA.

The early burst model suggests that disparity rises rapidly to fill empty ecospace following clade origination or in the aftermath of a mass extinction. Early bursts are considered common features of fossil data, but neontological studies have struggled to identify them. Furthermore, tests have proven difficult because factors besides ecology can drive changes in morphology. Here, we document the ecomorphometric evolution of the extinct Ammonoidea at 1-million-year resolution, from their origination in the Early Devonian (Emsian) to the Early Triassic (Induan), over ~156 million years. This time interval encompasses six global extinction events, including two of the Big Five, and incorporates multiple ammonoid radiations. However, we find no evidence for early bursts of ecomorphological disparity. This contradicts arguments that the temporal scope, or traits measured in genomic data, conceal evidence of early bursts. Rather, early bursts may be less prevalent in fossil data than is often assumed.
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http://dx.doi.org/10.1126/sciadv.abc2365DOI Listing
September 2020

The evolution of complex life and the stabilization of the Earth system.

Interface Focus 2020 Aug 12;10(4):20190106. Epub 2020 Jun 12.

Department of Biology, University of Hawaii-Hilo, 200 West Kawili Street, Hilo, HI 96720, USA.

The half-billion-year history of animal evolution is characterized by decreasing rates of background extinction. Earth's increasing habitability for animals could result from several processes: (i) a decrease in the intensity of interactions among species that lead to extinctions; (ii) a decrease in the prevalence or intensity of geological triggers such as flood basalt eruptions and bolide impacts; (iii) a decrease in the sensitivity of animals to environmental disturbance; or (iv) an increase in the strength of stabilizing feedbacks within the climate system and biogeochemical cycles. There is no evidence that the prevalence or intensity of interactions among species or geological extinction triggers have decreased over time. There is, however, evidence from palaeontology, geochemistry and comparative physiology that animals have become more resilient to an environmental change and that the evolution of complex life has, on the whole, strengthened stabilizing feedbacks in the climate system. The differential success of certain phyla and classes appears to result, at least in part, from the anatomical solutions to the evolution of macroscopic size that were arrived at largely during Ediacaran and Cambrian time. Larger-bodied animals, enabled by increased anatomical complexity, were increasingly able to mix the marine sediment and water columns, thus promoting stability in biogeochemical cycles. In addition, body plans that also facilitated ecological differentiation have tended to be associated with lower rates of extinction. In this sense, Cambrian solutions to Cambrian problems have had a lasting impact on the trajectory of complex life and, in turn, fundamental properties of the Earth system.
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http://dx.doi.org/10.1098/rsfs.2019.0106DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7333899PMC
August 2020

Eggshell geochemistry reveals ancestral metabolic thermoregulation in Dinosauria.

Sci Adv 2020 02 14;6(7):eaax9361. Epub 2020 Feb 14.

Institute of Earth Sciences, The Hebrew University of Jerusalem, Jerusalem, Israel.

Studying the origin of avian thermoregulation is complicated by a lack of reliable methods for measuring body temperatures in extinct dinosaurs. Evidence from bone histology and stableisotopes often relies on uncertain assumptions about the relationship between growth rate and body temperature, or the isotopic composition (δO) of body water. Clumped isotope (Δ) paleothermometry, based on binding of C to O, provides a more robust tool, but has yet to be applied across a broad phylogenetic range of dinosaurs while accounting for paleoenvironmental conditions. Applying this method to well-preserved fossil eggshells demonstrates that the three major clades of dinosaurs, Ornithischia, Sauropodomorpha, and Theropoda, were characterized by warm body temperatures. Dwarf titanosaurs may have exhibited similar body temperatures to larger sauropods, although this conclusion isprovisional, given current uncertainties in taxonomic assignment of dwarf titanosaur eggshell. Our results nevertheless reveal that metabolically controlled thermoregulation was the ancestral condition for Dinosauria.
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http://dx.doi.org/10.1126/sciadv.aax9361DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7021498PMC
February 2020

On impact and volcanism across the Cretaceous-Paleogene boundary.

Science 2020 01;367(6475):266-272

Department of Stratigraphy, Geological Survey of Denmark and Greenland (GEUS), DK-1350 Copenhagen K, Denmark.

The cause of the end-Cretaceous mass extinction is vigorously debated, owing to the occurrence of a very large bolide impact and flood basalt volcanism near the boundary. Disentangling their relative importance is complicated by uncertainty regarding kill mechanisms and the relative timing of volcanogenic outgassing, impact, and extinction. We used carbon cycle modeling and paleotemperature records to constrain the timing of volcanogenic outgassing. We found support for major outgassing beginning and ending distinctly before the impact, with only the impact coinciding with mass extinction and biologically amplified carbon cycle change. Our models show that these extinction-related carbon cycle changes would have allowed the ocean to absorb massive amounts of carbon dioxide, thus limiting the global warming otherwise expected from postextinction volcanism.
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http://dx.doi.org/10.1126/science.aay5055DOI Listing
January 2020

Rapid ocean acidification and protracted Earth system recovery followed the end-Cretaceous Chicxulub impact.

Proc Natl Acad Sci U S A 2019 11 21;116(45):22500-22504. Epub 2019 Oct 21.

Department of Geology & Geophysics, Yale University, New Haven, CT 06520;

Mass extinction at the Cretaceous-Paleogene (K-Pg) boundary coincides with the Chicxulub bolide impact and also falls within the broader time frame of Deccan trap emplacement. Critically, though, empirical evidence as to how either of these factors could have driven observed extinction patterns and carbon cycle perturbations is still lacking. Here, using boron isotopes in foraminifera, we document a geologically rapid surface-ocean pH drop following the Chicxulub impact, supporting impact-induced ocean acidification as a mechanism for ecological collapse in the marine realm. Subsequently, surface water pH rebounded sharply with the extinction of marine calcifiers and the associated imbalance in the global carbon cycle. Our reconstructed water-column pH gradients, combined with Earth system modeling, indicate that a partial ∼50% reduction in global marine primary productivity is sufficient to explain observed marine carbon isotope patterns at the K-Pg, due to the underlying action of the solubility pump. While primary productivity recovered within a few tens of thousands of years, inefficiency in carbon export to the deep sea lasted much longer. This phased recovery scenario reconciles competing hypotheses previously put forward to explain the K-Pg carbon isotope records, and explains both spatially variable patterns of change in marine productivity across the event and a lack of extinction at the deep sea floor. In sum, we provide insights into the drivers of the last mass extinction, the recovery of marine carbon cycling in a postextinction world, and the way in which marine life imprints its isotopic signal onto the geological record.
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http://dx.doi.org/10.1073/pnas.1905989116DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6842625PMC
November 2019

Oxygen, temperature and the deep-marine stenothermal cradle of Ediacaran evolution.

Proc Biol Sci 2018 Dec;285(1893):20181724

1 Department of Geological Sciences, Stanford University , Stanford, CA 94305 , USA.

Ediacaran fossils document the early evolution of complex megascopic life, contemporaneous with geochemical evidence for widespread marine anoxia. These data suggest early animals experienced frequent hypoxia. Research has thus focused on the concentration of molecular oxygen (O) required by early animals, while also considering the impacts of climate. One model, the Cold Cradle hypothesis, proposed the Ediacaran biota originated in cold, shallow-water environments owing to increased O solubility. First, we demonstrate using principles of gas exchange that temperature does have a critical role in governing the bioavailability of O-but in cooler water the supply of O is actually lower. Second, the fossil record suggests the Ediacara biota initially occur approximately 571 Ma in deep-water facies, before appearing in shelf environments approximately 555 Ma. We propose an ecophysiological underpinning for this pattern. By combining oceanographic data with new respirometry experiments we show that in the shallow mixed layer where seasonal temperatures fluctuate widely, thermal and partial pressure ( pO) effects are highly synergistic. The result is that temperature change away from species-specific optima impairs tolerance to low pO. We hypothesize that deep and particularly stenothermal (narrow temperature range) environments in the Ediacaran ocean were a physiological refuge from the synergistic effects of temperature and low pO.
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http://dx.doi.org/10.1098/rspb.2018.1724DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6304043PMC
December 2018

Sixty-one thousand recent planktonic foraminifera from the Atlantic Ocean.

Sci Data 2018 08 28;5:180109. Epub 2018 Aug 28.

Department of Geology and Geophysics, Yale University, Yale 06520, USA.

Marine microfossils record the environmental, ecological, and evolutionary dynamics of past oceans in temporally expanded sedimentary archives. Rapid imaging approaches provide a means of exploiting the primary advantage of this archive, the vast number of fossils, for evolution and ecology. Here we provide the first large scale image and 2D and 3D shape dataset of modern planktonic foraminifera, a major microfossil group, from 34 Atlantic Ocean sediment samples. Information on more than 124,000 objects is provided, including general object classification for 4/5ths of the dataset (~ 99,000 objects). Of the ~ 99,000 classifications provided, more than 61,000 are complete or damaged planktonic foraminifera. Objects also include benthic foraminifera, ostracods, pteropods, spicules, and planktonic foraminifera test fragments, among others. This dataset is the first major microfossil output of a new high-throughput imaging method (AutoMorph) developed to extract 2D and 3D data from photographic images of fossils. Our sample preparation and imaging techniques are described in detail. The data provided here comprises the most extensive publically available archive of planktonic foraminiferal morphology and morphological variation to date.
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http://dx.doi.org/10.1038/sdata.2018.109DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6111889PMC
August 2018

Twelve thousand recent patellogastropods from a northeastern Pacific latitudinal gradient.

Sci Data 2018 01 9;5:170197. Epub 2018 Jan 9.

University of California, Department of Integrative Biology and Museum of Paleontology, Berkeley, CA 94720, USA.

Body size distributions can vary widely among communities, with important implications for ecological dynamics, energetics, and evolutionary history. Here we present a dataset of body size and shape for 12,035 extant Patellogastropoda (true limpet) specimens from the collections of the University of California Museum of Paleontology, compiled using a novel high-throughput morphometric imaging method. These specimens were collected over the past 150 years at 355 localities along a latitudinal gradient ranging from Alaska to Baja California, Mexico and are presented here with individual images, 2D outline coordinates, and 2D measurements of body size and shape. This dataset provides a resource for assemblage-scale macroecological questions and documents the size and diversity of recent patellogastropods in the northeastern Pacific.
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http://dx.doi.org/10.1038/sdata.2017.197DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5759373PMC
January 2018

Evolutionary history biases inferences of ecology and environment from δC but not δO values.

Nat Commun 2017 10 24;8(1):1106. Epub 2017 Oct 24.

Biological Sciences, University of Southampton, Life Sciences Building 85, Highfield Campus, Southampton, SO17 1BJ, UK.

Closely related taxa are, on average, more similar in terms of their physiology, morphology and ecology than distantly related ones. How this biological similarity affects geochemical signals, and their interpretations, has yet to be tested in an explicitly evolutionary framework. Here we compile and analyze planktonic foraminiferal size-specific stable carbon and oxygen isotope values (δC and δO, respectively) spanning the last 107 million years. After controlling for dominant drivers of size-δC and size-δO trends, such as geological preservation, presence of algal photosymbionts, and global environmental changes, we identify that shared evolutionary history has shaped the evolution of species-specific vital effects in δC, but not in δO. Our results lay the groundwork for using a phylogenetic approach to correct species δC vital effects through time, thereby reducing systematic biases in interpretations of long-term δC records-a key measure of holistic organismal biology and of the global carbon cycle.
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http://dx.doi.org/10.1038/s41467-017-01154-7DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5653665PMC
October 2017

A probabilistic assessment of the rapidity of PETM onset.

Nat Commun 2017 08 25;8(1):353. Epub 2017 Aug 25.

Department of Earth Sciences, University of California, Riverside, Riverside, CA, 92506, USA.

Knowledge of the onset duration of the Paleocene-Eocene Thermal Maximum-the largest known greenhouse-gas-driven global warming event of the Cenozoic-is central to drawing inferences for future climate change. Single-foraminifera measurements of the associated carbon isotope excursion from Maud Rise (South Atlantic Ocean) are controversial, as they seem to indicate geologically instantaneous carbon release and anomalously long ocean mixing. Here, we fundamentally reinterpret this record and extract the likely PETM onset duration. First, we employ an Earth system model to illustrate how the response of ocean circulation to warming does not support the interpretation of instantaneous carbon release. Instead, we use a novel sediment-mixing model to show how changes in the relative population sizes of calcareous plankton, combined with sediment mixing, can explain the observations. Furthermore, for any plausible PETM onset duration and sampling methodology, we place a probability on not sampling an intermediate, syn-excursion isotopic value. Assuming mixed-layer carbonate production continued at Maud Rise, we deduce the PETM onset was likely <5 kyr.Single-foraminifera measurements of the PETM carbon isotope excursion from Maud Rise have been interpreted as indicating geologically instantaneous carbon release. Here, the authors explain these records using an Earth system model and a sediment-mixing model and extract the likely PETM onset duration.
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http://dx.doi.org/10.1038/s41467-017-00292-2DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5572461PMC
August 2017

Emergence of modern marine ecosystems.

Authors:
Pincelli M Hull

Curr Biol 2017 Jun;27(11):R466-R469

Department of Geology & Geophysics, Yale University, PO Box 208109, New Haven, CT 06520-8109, USA. Electronic address:

The structure and function of marine ecosystems are not fixed. Instead, major innovations - from the origin of oxygenic photosynthesis, to the evolution of reefs or of deep bioturbation, to the rise of pelagic calcifiers - have changed biogeochemical cycles and ecosystem dynamics. As a result, modern marine ecosystems are fundamentally different from those in the distant past.
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http://dx.doi.org/10.1016/j.cub.2017.04.041DOI Listing
June 2017

Biogeochemical significance of pelagic ecosystem function: an end-Cretaceous case study.

Philos Trans R Soc Lond B Biol Sci 2016 05;371(1694)

Department of Earth Sciences, University of Bristol, Wills Memorial Building, Queens Road, Bristol BS8 1RJ, UK.

Pelagic ecosystem function is integral to global biogeochemical cycling, and plays a major role in modulating atmospheric CO2 concentrations (pCO2). Uncertainty as to the effects of human activities on marine ecosystem function hinders projection of future atmospheric pCO2 To this end, events in the geological past can provide informative case studies in the response of ecosystem function to environmental and ecological changes. Around the Cretaceous-Palaeogene (K-Pg) boundary, two such events occurred: Deccan large igneous province (LIP) eruptions and massive bolide impact at the Yucatan Peninsula. Both perturbed the environment, but only the impact coincided with marine mass extinction. As such, we use these events to directly contrast the response of marine biogeochemical cycling to environmental perturbation with and without changes in global species richness. We measure this biogeochemical response using records of deep-sea carbonate preservation. We find that Late Cretaceous Deccan volcanism prompted transient deep-sea carbonate dissolution of a larger magnitude and timescale than predicted by geochemical models. Even so, the effect of volcanism on carbonate preservation was slight compared with bolide impact. Empirical records and geochemical models support a pronounced increase in carbonate saturation state for more than 500 000 years following the mass extinction of pelagic carbonate producers at the K-Pg boundary. These examples highlight the importance of pelagic ecosystems in moderating climate and ocean chemistry.
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http://dx.doi.org/10.1098/rstb.2015.0510DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4843705PMC
May 2016

Towards a morphological metric of assemblage dynamics in the fossil record: a test case using planktonic foraminifera.

Philos Trans R Soc Lond B Biol Sci 2016 Apr;371(1691):20150227

Department of Geology and Geophysics, Yale University, P.O. Box 208109, New Haven, CT 06520-8109, USA

With a glance, even the novice naturalist can tell you something about the ecology of a given ecosystem. This is because the morphology of individuals reflects their evolutionary history and ecology, and imparts a distinct 'look' to communities--making it possible to immediately discern between deserts and forests, or coral reefs and abyssal plains. Once quantified, morphology can provide a common metric for characterizing communities across space and time and, if measured rapidly, serve as a powerful tool for quantifying biotic dynamics. Here, we present and test a new high-throughput approach for analysing community shape in the fossil record using semi-three-dimensional (3D) morphometrics from vertically stacked images (light microscopic or photogrammetric). We assess the potential informativeness of community morphology in a first analysis of the relationship between 3D morphology, ecology and phylogeny in 16 extant species of planktonic foraminifera--an abundant group in the marine fossil record--and in a preliminary comparison of four assemblages from the North Atlantic. In the species examined, phylogenetic relatedness was most closely correlated with ecology, with all three ecological traits examined (depth habitat, symbiont ecology and biogeography) showing significant phylogenetic signal. By contrast, morphological trees (based on 3D shape similarity) were relatively distantly related to both ecology and phylogeny. Although improvements are needed to realize the full utility of community morphometrics, our approach already provides robust volumetric measurements of assemblage size, a key ecological characteristic.
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http://dx.doi.org/10.1098/rstb.2015.0227DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4810820PMC
April 2016

Rarity in mass extinctions and the future of ecosystems.

Nature 2015 Dec;528(7582):345-51

Department of Paleobiology, National Museum of Natural History, Washington, DC 20013-7012, USA.

The fossil record provides striking case studies of biodiversity loss and global ecosystem upheaval. Because of this, many studies have sought to assess the magnitude of the current biodiversity crisis relative to past crises-a task greatly complicated by the need to extrapolate extinction rates. Here we challenge this approach by showing that the rarity of previously abundant taxa may be more important than extinction in the cascade of events leading to global changes in the biosphere. Mass rarity may provide the most robust measure of our current biodiversity crisis relative to those past, and new insights into the dynamics of mass extinction.
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http://dx.doi.org/10.1038/nature16160DOI Listing
December 2015

Parsing parallel evolution: ecological divergence and differential gene expression in the adaptive radiations of thick-lipped Midas cichlid fishes from Nicaragua.

Mol Ecol 2013 Feb 12;22(3):650-69. Epub 2012 Oct 12.

Lehrstuhl für Zoologie und Evolutionsbiologie, Department of Biology, University of Konstanz, Konstanz, Germany.

The study of parallel evolution facilitates the discovery of common rules of diversification. Here, we examine the repeated evolution of thick lips in Midas cichlid fishes (the Amphilophus citrinellus species complex)-from two Great Lakes and two crater lakes in Nicaragua-to assess whether similar changes in ecology, phenotypic trophic traits and gene expression accompany parallel trait evolution. Using next-generation sequencing technology, we characterize transcriptome-wide differential gene expression in the lips of wild-caught sympatric thick- and thin-lipped cichlids from all four instances of repeated thick-lip evolution. Six genes (apolipoprotein D, myelin-associated glycoprotein precursor, four-and-a-half LIM domain protein 2, calpain-9, GTPase IMAP family member 8-like and one hypothetical protein) are significantly underexpressed in the thick-lipped morph across all four lakes. However, other aspects of lips' gene expression in sympatric morphs differ in a lake-specific pattern, including the magnitude of differentially expressed genes (97-510). Generally, fewer genes are differentially expressed among morphs in the younger crater lakes than in those from the older Great Lakes. Body shape, lower pharyngeal jaw size and shape, and stable isotopes (δ(13)C and δ(15)N) differ between all sympatric morphs, with the greatest differentiation in the Great Lake Nicaragua. Some ecological traits evolve in parallel (those related to foraging ecology; e.g. lip size, body and head shape) but others, somewhat surprisingly, do not (those related to diet and food processing; e.g. jaw size and shape, stable isotopes). Taken together, this case of parallelism among thick- and thin-lipped cichlids shows a mosaic pattern of parallel and nonparallel evolution.
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http://dx.doi.org/10.1111/mec.12034DOI Listing
February 2013

Evidence for abrupt speciation in a classic case of gradual evolution.

Proc Natl Acad Sci U S A 2009 Dec 8;106(50):21224-9. Epub 2009 Dec 8.

Scripps Institution of Oceanography, University of California at San Diego, La Jolla, CA 92093, USA.

In contrast with speciation in terrestrial organisms, marine plankton frequently display gradual morphological change without lineage division (e.g., phyletic gradualism or gradual evolution), which has raised the possibility that a different mode of evolution dominates within pelagic environments. Here, we reexamine a classic case of putative gradual evolution within the Globorotalia plesiotumida-G. tumida lineage of planktonic foraminifera, and find both compelling evidence for the existence of a third cryptic species during the speciation event and the abrupt evolution of the descendant G. tumida. The third morphotype, not recognized in previous analyses, differs in shape and coiling direction from its ancestor, G. plesiotumida. This species dominates the globorotaliid population for 414,000 years just before the appearance of G. tumida. The first population of the descendant, G. tumida, evolves abruptly within a 44,000-year interval. A combination of morphological data and biostratigraphic evidence suggests that G. tumida evolved by cladogenesis. Our findings provide an unexpected twist on one of the best-documented cases of within-lineage phyletic gradualism and, in doing so, revisit the limitations and promise of the study of speciation in the fossil record.
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http://dx.doi.org/10.1073/pnas.0902887106DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2795541PMC
December 2009