Plio-Pleistocene environmental variability in Africa and its implications for mammalian evolution.

Understanding the climatic drivers of environmental variability (EV) during the Plio-Pleistocene and EV's influence on mammalian macroevolution are two outstanding foci of research in African paleoclimatology and evolutionary biology. The potential effects of EV are especially relevant for testing the variability selection hypothesis, which predicts a positive relationship between EV and speciation and extinction rates in fossil mammals. Addressing these questions is stymied, however, by 1) a lack of multiple comparable EV records of sufficient temporal resolution and duration, and 2) the incompleteness of the mammalian fossil record. Here, we first compile a composite history of Pan-African EV spanning the Plio-Pleistocene, which allows us to explore which climatic variables influenced EV. We find that EV exhibits 1) a long-term trend of increasing variability since ∼3.7 Ma, coincident with rising variability in global ice volume and sea surface temperatures around Africa, and 2) a 400-ky frequency correlated with seasonal insolation variability. We then estimate speciation and extinction rates for fossil mammals from eastern Africa using a method that accounts for sampling variation. We find no statistically significant relationship between EV and estimated speciation or extinction rates across multiple spatial scales. These findings are inconsistent with the variability selection hypothesis as applied to macroevolutionary processes.

Linking African herbivore community enamel isotopes and environments: challenges, opportunities, and paleoecological implications.

Paleoenvironmental reconstructions of fossil sites based on isotopic analyses of enamel typically rely on data from multiple herbivore taxa, with the assumption that this dietary spectrum represents the community's isotopic range and provides insights into local or regional vegetation patterns. However, it remains unclear how representative the sampled taxa are of the broader herbivore community and how well these data correspond to specific ecosystems. Verifying these underlying assumptions is essential to refining the utility of enamel isotopic values for paleoenvironmental reconstructions. This study explores potential links between modern herbivore community carbon isotopic enamel spectra, biome types, and climate in sub-Saharan Africa. This region is one of the most comprehensively isotopically sampled areas globally and is of particular relevance to hominin evolution. Our extensive data compilation reveals that published enamel isotopic data from sub-Saharan Africa typically sample only a small percentage of the taxa documented at most localities and that some biome types (e.g., subtropical savannas) are dramatically overrepresented relative to others (e.g., forests) in these modern data sets. Multiple statistical analyses, including linear models and cluster analyses, revealed weak relationships of associated mammalian herbivore enamel isotopic values, biome type, and climate parameters. These results confound any simple assumptions about how community isotopic profiles map onto specific environments, highlighting the need for more precise strategic approaches in extending isotopic frameworks into the past for paleoecological reconstructions. Developing more refined modern analogs will ultimately allow us to more accurately characterize the isotopic spectra of paleo-communities and link isotopic dietary signatures to specific ecosystems.

A chimpanzee enamel-diet δ13C enrichment factor and a refined enamel sampling strategy: Implications for dietary reconstructions.

Reconstructing diets from stable carbon isotopic signals in enamel bioapatite requires the application of a δ13C enamel-diet enrichment factor, or the isotopic offset between diet and enamel, which has not been empirically determined for any primate. In this study, an enamel-diet enrichment factor (ε∗enamel-diet) of 11.8 ± 0.3‰ is calculated for chimpanzees (Pan troglodytes) at Ngogo in Kibale National Park, Uganda, based on a comprehensive isotopic assessment of previously analyzed dietary plant data and new isotopic analyses of enamel apatite. Different enamel sampling methods are evaluated to determine the potential influence of weaning on isotopic enamel values and dietary interpretations. The new chimpanzee enrichment factor and a sampling strategy that excludes teeth that formed before weaning completion are applied to all known chimpanzee δ13Cenamel data, either previously published or newly derived in this study, resulting in a dietary range of almost 6‰ across all chimpanzees sampled. This new chimpanzee enamel-diet enrichment factor is then used to reassess dietary reconstructions of 12 fossil hominin species whose isotopic enamel signatures have been determined. Results reveal hominin diets that are isotopically more positive than previously reconstructed, highlighting the widespread contribution of 13C-enriched C4/crassulacean acid metabolism (CAM) resources in fossil hominin diets and emphasizing the broad use of these resources during human evolution. These findings stress the importance of ascertaining and employing an appropriate enrichment factor for dietary reconstructions of specific taxa as well as standardizing the sampling protocol for tooth enamel in isotopic paleodietary reconstructions.

Evidence for rapid faunal change in the early Miocene of East Africa based on revised biostratigraphic and radiometric dating of Bukwa, Uganda.

Field expeditions to Bukwa in the late 1960s and early 1970s established that the site had a small but diverse early Miocene fauna, including the catarrhine primate Limnopithecus legetet. Initial potassium-argon radiometric dating indicated that Bukwa was 22 Ma, making it the oldest of the East African early Miocene fossil localities known at the time. In contrast, the fauna collected from Bukwa was similar to other fossil localities in the region that were several million years younger. This discrepancy was never resolved, and due to the paucity of primate remains at the site, little subsequent research took place. We have collected new fossils at Bukwa, reanalyzed the existing fossil collections, and provided new radiometric dating. 40Ar/39Ar incremental heating ages on lavas bracketing the site indicate that the Bukwa fossils were deposited ∼19 Ma, roughly 3 Ma younger than the original radiometric age. Our radiometric dating results are corroborated by a thorough reanalysis of the faunal assemblage. Bukwa shares taxa with both stratigraphically older localities (Tinderet, Napak) and with stratigraphically younger localities (Kisingiri, Turkana Basin) perfectly corresponding to our revised radiometric age. This revised age for Bukwa is important because it indicates that significant faunal turnover may have occurred in East Africa between 20 and 19 Ma. Bukwa samples immigrant taxa such as large suids, large ruminants, and ochotonids that are absent from stratigraphically older but well-sampled localities in the region, such as Tinderet (∼20 Ma) and Napak (20 Ma). Further age refinements for Bukwa and the entire East African early Miocene sequence will help to constrain the timing of this faunal turnover event, of particular importance in paleoanthropology since this temporal sequence also provides us with what is currently our best window into the early evolution of cercopithecoid and hominoid primates.

Chimpanzee isotopic ecology: a closed canopy C3 template for hominin dietary reconstruction.

The most significant hominin adaptations, including features used to distinguish and/or classify taxa, are critically tied to the dietary environment. Stable isotopic analyses of tooth enamel from hominin fossils have provided intriguing evidence for significant C4/CAM (crassulacean acid metabolism) resource consumption in a number of Plio-Pleistocene hominin taxa. Relating isotopic tooth signatures to specific dietary items or proportions of C3 versus C4/CAM plants, however, remains difficult as there is an ongoing need to document and quantify isotopic variability in modern ecosystems. This study investigates the ecological variables responsible for carbon isotopic discrimination and variability within the C3-dominated dietary niche of a closed canopy East African hominoid, Pan troglodytes, from Ngogo, Kibale National Park, Uganda. δ(13)C values among C3 resources utilized by Ngogo chimpanzees were highly variable, ranging over 13‰. Infrequent foraging on papyrus (the only C4 plant consumed by chimpanzees at the site) further extended this isotopic range. Variation was ultimately most attributable to mode of photosynthesis (C3 versus C4), food type, and elevation, which together accounted for approximately 78% of the total sample variation. Among C3 food types, bulk carbon values ranged from -24.2‰ to -31.1‰ with intra-plant variability up to 12.1‰. Pith and sapling leaves were statistically more (13)C depleted than pulp, seeds, flowers, cambium, roots, leaf buds, and leaves from mature trees. The effect of elevation on carbon variation was highly significant and equivalent to an approximately 1‰ increase in δ(13)C for every 150 m of elevation gain, likely reflecting habitat variability associated with topography. These results indicate significant δ(13)C variation attributable to food type and elevation among C3 resources and provide important data for hominin dietary interpretations based on carbon isotopic analyses.

Oldest evidence of abundant C4 grasses and habitat heterogeneity in eastern Africa.

The assembly of Africa's iconic C4 grassland ecosystems is central to evolutionary interpretations of many mammal lineages, including hominins. C4 grasses are thought to have become ecologically dominant in Africa only after 10 million years ago (Ma). However, paleobotanical records older than 10 Ma are sparse, limiting assessment of the timing and nature of C4 biomass expansion. This study uses a multiproxy design to document vegetation structure from nine Early Miocene mammal site complexes across eastern Africa. Results demonstrate that between ~21 and 16 Ma, C4 grasses were locally abundant, contributing to heterogeneous habitats ranging from forests to wooded grasslands. These data push back the oldest evidence of C4 grass-dominated habitats in Africa-and globally-by more than 10 million years, calling for revised paleoecological interpretations of mammalian evolution.

The evolution of hominoid locomotor versatility: Evidence from Moroto, a 21 Ma site in Uganda.

Living hominoids are distinguished by upright torsos and versatile locomotion. It is hypothesized that these features evolved for feeding on fruit from terminal branches in forests. To investigate the evolutionary context of hominoid adaptive origins, we analyzed multiple paleoenvironmental proxies in conjunction with hominoid fossils from the Moroto II site in Uganda. The data indicate seasonally dry woodlands with the earliest evidence of abundant C4 grasses in Africa based on a confirmed age of 21 million years ago (Ma). We demonstrate that the leaf-eating hominoid Morotopithecus consumed water-stressed vegetation, and postcrania from the site indicate ape-like locomotor adaptations. These findings suggest that the origin of hominoid locomotor versatility is associated with foraging on leaves in heterogeneous, open woodlands rather than forests.

Partial skeleton of Theropithecus brumpti (Primates, Cercopithecidae) from the Chemeron Formation of the Tugen Hills, Kenya.

Here we describe a complete skull and partial skeleton of a large cercopithecoid monkey (KNM-TH 46700) discovered in the Chemeron Formation of the Tugen Hills at BPRP Site #152 (2.63 Ma). Associated with the skeleton was a mandible of an infant cercopithecoid (KNM-TH 48364), also described here. KNM-TH 46700 represents an aged adult female of Theropithecus brumpti, a successful Pliocene papionin taxon better known from the Omo Shungura Formation in Ethiopia and sites east and west of Lake Turkana, Kenya. While the morphology of male T. brumpti is well-documented, including a partial skeleton with both cranial and postcranial material, the female T. brumpti morphotype is not well-known. This skeleton represents some of the first associated evidence of cranial and postcranial female T. brumpti remains. In addition to the complete skull, postcranial material includes elements of the axial skeleton and lower limb. While aspects of the skeleton conform to those of specimens previously assigned to T. brumpti, other features on the femur and tibia appear to differ from those previously described for this species. It is unclear whether these differences represent general variation within the T. brumpti population, variation between the sexes in T. brumpti, or the incorrect assignment of previous isolated hindlimb specimens. In total, the observable morphological features of the hindlimb suggest that KNM-TH 46700 was a terrestrial quadruped similar to modern savannah baboons (Papio). From the available evidence, it is difficult to assess whether or not KNM-TH 46700 frequently engaged in the specialized squatting and shuffling behavior observed in extant geladas (Theropithecus gelada).

The origin and antiquity of syphilis revisited: an appraisal of Old World pre-Columbian evidence for treponemal infection.

For nearly 500 years, scholars have argued about the origin and antiquity of syphilis. Did Columbus bring the disease from the New World to the Old World? Or did syphilis exist in the Old World before 1493? Here, we evaluate all 54 published reports of pre-Columbian, Old World treponemal disease using a standardized, systematic approach. The certainty of diagnosis and dating of each case is considered, and novel information pertinent to the dating of these cases, including radiocarbon dates, is presented. Among the reports, we did not find a single case of Old World treponemal disease that has both a certain diagnosis and a secure pre-Columbian date. We also demonstrate that many of the reports use nonspecific indicators to diagnose treponemal disease, do not provide adequate information about the methods used to date specimens, and do not include high-quality photographs of the lesions of interest. Thus, despite an increasing number of published reports of pre-Columbian treponemal infection, it appears that solid evidence supporting an Old World origin for the disease remains absent.

Auditory contrast versus compensation for coarticulation: data from Japanese and English listeners.

English listeners categorize more of a [k-t] continuum as "t" after [character: see text] than [s] (Mann & Repp, 1981). This bias could be due to compensation for coarticulation (Mann & Repp, 1981) or auditory contrast between the fricatives and the stops (Lotto & Kluender, 1998). In Japanese, surface [[character: see text]k, [character: see text] t, sk, st] clusters arise via palatalization and vowel devoicing from /sik, sit, suk, sut/, and acoustic vestiges of the devoiced vowels remain in the fricative. On the one hand, compensation for coarticulation with the devoiced vowel would cancel out compensation for coarticulation with the fricative, and listeners would not show any response bias. On the other hand, if the stop contrasts spectrally with the fricative, listeners should respond "t" more often after [[character: see text] i] than [s[character: see text]]. Experiment I establishes that [k] and [t] coarticulate with preceding voiced [i, u], voiceless [[character: see text], [character: see text]], and [[character: see text], s]. Experiment 2 shows that both Japanese and English listeners respond "t" more often after [characters: see text] than [s[character: see text]], as predicted by auditory contrast. English listeners' "t" responses also varied after voiced vowels, but those of Japanese listeners did not. Experiment 3 shows that this difference reflects differences in their phonetic experience.

Regressive spectral assimilation bias in speech perception.

Speech perception presents a parsing problem: construing information from the acoustic input we receive as evidence for the speech sounds we recognize as language. Most work on segmental perception has focused on how listeners use differences between successive speech sounds to solve this problem. Prominent models either assume (a) that listeners attribute acoustics to the sounds whose articulation created them, or (b) that the auditory system exaggerates the changes in the auditory quality of the incoming speech signal. Both approaches predict contrast effects in that listeners will usually judge two successive phones to be distinct from each other. Few studies have examined cases in which listeners hear two sounds in a row as similar, apparently failing to differentiate them. We examine such under-studied cases. In a series of experiments, listeners were faced with ambiguity about the identity of the first of two successive phones. Listeners consistently heard the first sound as spectrally similar to the second sound in a manner suggesting that they construed the transitions between the two as evidence about the identity of the first. In these and previously reported studies, they seemed to default to this construal when the signal was not sufficiently informative for them to do otherwise. These effects go unaccounted for in the two prominent models of speech perception, but they parallel known domain-general effects in perceptual processing, and as such are likely a consequence of the structure of the human auditory system.

Shifting adaptive landscapes: progress and challenges in reconstructing early hominid environments.

Since Darwin situated humans in an evolutionary framework, much discussion has focused on environmental factors that may have shaped or influenced the course of human evolution. Developing adaptive or causal perspectives on the morphological and behavioral variability documented in the human fossil record requires establishing a comprehensive paleoenvironmental context. Reconstructing environments in the past, however, is a complex undertaking, requiring assimilation of diverse datasets of varying quality, scale, and relevance. In response to these difficulties, human evolution has traditionally been interpreted in a somewhat generalized framework, characterized primarily by increasing aridity and seasonality periodically punctuated by pulses or intervals of environmental change, inferred largely from global climatic records. Although these broad paradigms provide useful heuristic approaches for interpreting human evolution, the spatiotemporal resolution remains far too coarse to develop unambiguous causal links. This challenge has become more acute as the emerging paleoenvironmental evidence from equatorial Africa is revealing a complex pattern of habitat heterogeneity and persistent ecological flux throughout the interval of human evolution. In addition, recent discoveries have revealed significant taxonomic diversity and substantially increased the geographic and temporal range of early hominids. These findings raise further questions regarding the role of the environment in mediating or directing the course of human evolution. As a consequence, it is imperative to critically assess the environmental criteria on which many theories and hypotheses of human evolution hinge. The goals here are to 1) compile, review, and evaluate relevant paleoecological datasets from equatorial Africa spanning the last 10 Ma, 2) develop a hierarchical perspective for developing and evaluating hypotheses linking paleoecology to patterns and processes in early hominid evolution, and 3) suggest a conceptual framework for modeling and interpreting environmental data relevant to human evolution in equatorial Africa.

Maximum stability of a single spherical particle attached to an emulsion drop.

The stability of a single, solid, spherical particle attached to a liquid drop in an emulsion is discussed. Ignoring effects due to gravity and line tension, we calculate the energies required to either detach the particle from the drop or to engulf the particle within the drop. The stability of the attached particle is here defined as the smaller of these two energies. A simple formula is derived for the value of Young's angle which gives maximum stability for a given radius ratio of particle to detached drop. For maximum stability the particle should be preferentially wetted by the liquid forming the drop.

Eye movement evidence for an immediate Ganong effect.

Listeners tend to categorize an ambiguous speech sound so that it forms a word with its context (Ganong, 1980). This effect could reflect feedback from the lexicon to phonemic activation (McClelland & Elman, 1986), or the operation of a task-specific phonemic decision system (Norris, McQueen, & Cutler, 2000). Because the former account involves feedback between lexical and phonemic levels, it predicts that the lexicon's influence on phonemic decisions should be delayed and should gradually increase in strength. Previous response time experiments have not delivered a clear verdict as to whether this is the case, however. In 2 experiments, listeners' eye movements were tracked as they categorized phonemes using visually displayed response options. Lexically relevant information in the signal, the timing of which was confirmed by separate gating experiments, immediately increased eye movements toward the lexically supported response. This effect on eye movements then diminished over the course of the trial rather than continuing to increase. These results challenge the lexical feedback account. The present work also introduces a novel method for analyzing data from 'visual-world' type tasks, designed to assess when an experimental manipulation influences the probability of an eye movement toward the target. (PsycINFO Database Record

Definition of a Novel Feed-Forward Mechanism for Glycolysis-HIF1α Signaling in Hypoxic Tumors Highlights Aldolase A as a Therapeutic Target.

The hypoxia-inducible transcription factor HIF1α drives expression of many glycolytic enzymes. Here, we show that hypoxic glycolysis, in turn, increases HIF1α transcriptional activity and stimulates tumor growth, revealing a novel feed-forward mechanism of glycolysis-HIF1α signaling. Negative regulation of HIF1α by AMPK1 is bypassed in hypoxic cells, due to ATP elevation by increased glycolysis, thereby preventing phosphorylation and inactivation of the HIF1α transcriptional coactivator p300. Notably, of the HIF1α-activated glycolytic enzymes we evaluated by gene silencing, aldolase A (ALDOA) blockade produced the most robust decrease in glycolysis, HIF-1 activity, and cancer cell proliferation. Furthermore, either RNAi-mediated silencing of ALDOA or systemic treatment with a specific small-molecule inhibitor of aldolase A was sufficient to increase overall survival in a xenograft model of metastatic breast cancer. In establishing a novel glycolysis-HIF-1α feed-forward mechanism in hypoxic tumor cells, our results also provide a preclinical rationale to develop aldolase A inhibitors as a generalized strategy to treat intractable hypoxic cancer cells found widely in most solid tumors. Cancer Res; 76(14); 4259-69. ©2016 AACR.

Learning foreign vowels.

Two hypotheses have recently been put forward to account for listeners' ability to distinguish and learn contrasts between speech sounds in foreign languages. First, Best's Perceptual Assimilation Model and Flege's Speech Learning Model both predict that the ease with which a listener can tell one non-native phoneme from another varies directly with the extent to which these sounds assimilate to different native phonemes (Best, 1994; also Best, McRoberts, & Goodell, 2001; Flege, 1991). Second, Logan, Lively, & Pisoni (1991) have argued that training listeners to identify non-native phonemes teaches them sets of exemplars rather than more abstract distinctive feature values. I report here the results of three sets of experiments designed to test these hypotheses, in which American English listeners were trained to categorize German nonlow vowels. The first set of experiments show that some instances of the same contrast between German vowels are more easily discriminated than others, a result incompatible with the predictions of either Best's or Flege's models, but compatible with the alternative category recognition interpretation. The second set of experiments reveals effects of contextual and speaker variation on listeners' ability to learn [tense] but not [high] contrasts between foreign vowels, and are thus at least partly compatible with an exemplar model of foreign category learning (Pisoni, Lively, & Logan, 1994; also Nosofsky, 1986). The third set of experiments compares the predictions of Nosofsky's (1986) selective attention exemplar model of category learning with those of a feature learning model in tests of listeners' learning the natural classes to which the German vowels belong. The results are mixed: listeners learned the features that define the natural classes of [+/- high] and [+/- back] vowels, but could have learned either the feature that defines the natural classes of [+/- tense] vowels or sets of [+/- tense] exemplars. Natural classes defined by abstract distinctive feature values are thus learnable, even if their membership is phonetically polymorphous.

Context effects as auditory contrast.

Three experiments are reported that collectively show that listeners perceive speech sounds as contrasting auditorily with neighboring sounds. Experiment 1 replicates the well-established finding that listeners categorize more of a [d-g] continuum as [g] after [l] than after [r]. Experiments 2 and 3 show that listeners discriminate stimuli in which the energy concentrations differ in frequency between the spectra of neighboring sounds better than those in which they do not differ. In Experiment 2, [alga-arda] pairs, in which the energy concentrations in the liquid-stop sequences are H(igh) L(ow)-LH, were more discriminable than [alda-arga] pairs, in which they are HH-LL. In Experiment 3, [da] and [ga] syllables were more easily discriminated when they were preceded by lower and higher pure tones, respectively-that is, tones that differed from the stops' higher and lower F3 onset frequencies-than when they were preceded by H and L pure tones with similar frequencies. These discrimination results show that contrast with the target's context exaggerates its perceived value when energy concentrations differ in frequency between the target's spectrum and its context's spectrum. Because contrast with its context does more that merely shift the criterion for categorizing the target, it cannot be produced by neural adaptation. The finding that nonspeech contexts exaggerate the perceived values of speech targets also rules out compensation for coarticulation by showing that their values depend on the proximal auditory qualities evoked by the stimuli's acoustic properties, rather than the distal articulatory gestures.

Perceptual representations of phonotactically illegal syllables.

Listeners often categorize phonotactically illegal sequences (e.g., /dla/ in English) as phonemically similar legal ones (e.g., /gla/). In an earlier investigation of such an effect in Japanese, Dehaene-Lambertz, Dupoux, and Gout (2000) did not observe a mismatch negativity in response to deviant, illegal sequences, and therefore argued that phonotactics constrain early perceptual processing. In the present study, using a priming paradigm, we compared the event-related potentials elicited by Legal targets (e.g., /gla/) preceded by (1) phonemically distinct Control primes (e.g., /kla/), (2) different tokens of Identity primes (e.g., /gla/), and (3) phonotactically Illegal Test primes (e.g., /dla/). Targets elicited a larger positivity 200-350 ms after onset when preceded by Illegal Test primes or phonemically distinct Control primes, as compared to Identity primes. Later portions of the waveforms (350-600 ms) did not differ for targets preceded by Identity and Illegal Test primes, and the similarity ratings also did not differ in these conditions. These data support a model of speech perception in which veridical representations of phoneme sequences are not only generated during processing, but also are maintained in a manner that affects perceptual processing of subsequent speech sounds.

Scanning training in neurological vision loss: case studies.

The purpose of this paper is to describe the response of a Department of Veterans Affairs medical center's development of a rehabilitation program for patients with hemianopsia. Hemianopsia affects significant numbers of troops returning from Afghanistan and Iraq and their neurological vision loss presented unique challenges in developing an appropriate and effective rehabilitation program. A literature review indicated that existing therapies lacked supporting scientific evidence and that traumatic brain injury (TBI)-related vision loss affects large numbers of civilians. The increasing number of patients with TBI-related vision loss necessitated the development of an innovative program which combined elements of therapies that the literature suggested were most promising. In this paper we briefly review the literature, describe the rehabilitation program developed, and present case studies of two patients who incurred vision loss as a result of a motor vehicle accident and a gunshot wound. The intent of the article is to begin the documentation of our ongoing, evidence-based neurological vision loss rehabilitation program. We also encourage others who do not currently do so to assess the need for implementing vision rehabilitation programs for patients with TBI-related vision loss.

Comment on the paleoenvironment of Ardipithecus ramidus.

White and colleagues (Research Articles, 2 October 2009, pp. 65-67 and www.sciencemag.org/ardipithecus) characterized the paleoenvironment of Ardipithecus ramidus at Aramis, Ethiopia, which they described as containing habitats ranging from woodland to forest patches. In contrast, we find the environmental context of Ar. ramidus at Aramis to be represented by what is commonly referred to as tree- or bush-savanna, with 25% or less woody canopy cover.