Using multiple lines of evidence to assess recovery potential of a warm water fish population in a cold water impacted river

Introduction

Humans have substantially altered landscapes across the globe, generating novel ecosystems with varying states of modification. The principles of reconciliation ecology emphasise that such novel ecosystems must also be considered for conservation outcomes. This requires an understanding of how anthropogenic habitat alterations in a novel ecosystem may disrupt life cycle processes of key biota, thereby enabling the development of management strategies that may bypass or ameliorate potential bottlenecks in life history stages. We explore this by assessing Murray cod (Maccullochella peelii), a native fish species of considerable cultural, recreational and conservation significance in a severely altered river reach in south-eastern Australia. This species was considered to have disappeared in the reach following alterations to the river’s thermal profile (cold water pollution - CWP), but instead has persisted.

Methods

We examined the life cycle of Murray cod and use multiple lines of evidence to assess the impacts of CWP pollution on key processes such as adult migration, recruitment and juvenile survival. We also evaluated the potential for recovery and persistence of the species in this novel system using mitigation measures such as flow management and stocking and opportunistically tested their effectiveness.

Results

We found the key impact pathway of CWP on the Murray cod population is via its effects on the key processes influencing natural recruitment. Conversely, the effects of CWP on emigration and survival of larger juveniles and adults did not appear to be a major bottleneck for the population. Using a stochastic population model, we showed that the population could be sustained by stocking and opportunistic water management while still meeting irrigation demands. Monitoring to test our recommendations showed natural recruitment and improved survival of stocked fish during years with limited flow releases, thereby corroborating our predictions.

Discussion

Our use of multiple lines of evidence to assess a species’ responses to impacts of habitat alteration in a novel ecosystem enabled the formulation of recommendations for management that could then be tested. The success of such actions add to the growing body of literature that shows species of conservation significance can be maintained in novel ecosystems which should be specifically considered within the context of conservation planning across the landscape.

Tufas indicate prolonged periods of water availability linked to human occupation in the southern Kalahari

Detailed, well-dated palaeoclimate and archaeological records are critical for understanding the impact of environmental change on human evolution. Ga-Mohana Hill, in the southern Kalahari, South Africa, preserves a Pleistocene archaeological sequence. Relict tufas at the site are evidence of past flowing streams, waterfalls, and shallow pools. Here, we use laser ablation screening to target material suitable for uranium-thorium dating. We obtained 33 ages covering the last 110 thousand years (ka) and identify five tufa formation episodes at 114–100 ka, 73–48 ka, 44–32 ka, 15–6 ka, and ~3 ka. Three tufa episodes are coincident with the archaeological units at Ga-Mohana Hill dating to ~105 ka, ~31 ka, and ~15 ka. Based on our data and the coincidence of dated layers from other local records, we argue that in the southern Kalahari, from ~240 ka to ~71 ka wet phases and human occupation are coupled, but by ~20 ka during the Last Glacial Maximum (LGM), they are decoupled.

Magnesium in subaqueous speleothems as a potential palaeotemperature proxy

Few palaeoclimate archives beyond the polar regions preserve continuous and datable palaeotemperature proxy time series over multiple glacial-interglacial cycles. This hampers efforts to develop a more coherent picture of global patterns of past temperatures. Here we show that Mg concentrations in a subaqueous speleothem from an Italian cave track regional sea-surface temperatures over the last 350,000 years. The Mg shows higher values during warm climate intervals and converse patterns during cold climate stages. In contrast to previous studies, this implicates temperature, not rainfall, as the principal driver of Mg variability. The depositional setting of the speleothem gives rise to Mg partition coefficients that are more temperature dependent than other calcites, enabling the effect of temperature change on Mg partitioning to greatly exceed the effects of changes in source-water Mg/Ca. Subaqueous speleothems from similar deep-cave environments should be capable of providing palaeotemperature information over multiple glacial-interglacial cycles.

Few palaeoclimate archives beyond the polar regions preserve continuous and datable paleotemperature proxy time series over multiple glacial-interglacial cycles. Here, the authors show that Mg concentrations in a subaqueous speleothem from an Italian cave track regional sea-surface temperatures over the last 350,000 years.

Contemporaneity of Australopithecus, Paranthropus, and early Homo erectus in South Africa

Understanding the extinction of Australopithecus and origins of Paranthropus and Homo in South Africa has been hampered by the perceived complex geological context of hominin fossils, poor chronological resolution, and a lack of well-preserved early Homo specimens. We describe, date, and contextualize the discovery of two hominin crania from Drimolen Main Quarry in South Africa. At ~2.04 million to 1.95 million years old, DNH 152 represents the earliest definitive occurrence of Paranthropus robustus, and DNH 134 represents the earliest occurrence of a cranium with clear affinities to Homo erectus These crania also show that Homo, Paranthropus, and Australopithecus were contemporaneous at ~2 million years ago. This high taxonomic diversity is also reflected in non-hominin species and provides evidence of endemic evolution and dispersal during a period of climatic variability.

Kimberlites reveal 2.5-billion-year evolution of a deep, isolated mantle reservoir

The widely accepted paradigm of Earth's geochemical evolution states that the successive extraction of melts from the mantle over the past 4.5 billion years formed the continental crust, and produced at least one complementary melt-depleted reservoir that is now recognized as the upper-mantle source of mid-ocean-ridge basalts¹. However, geochemical modelling and the occurrence of high ³He/⁴He (that is, primordial) signatures in some volcanic rocks suggest that volumes of relatively undifferentiated mantle may reside in deeper, isolated regions². Some basalts from large igneous provinces may provide temporally restricted glimpses of the most primitive parts of the mantle^3,4, but key questions regarding the longevity of such sources on planetary timescales-and whether any survive today-remain unresolved. Kimberlites, small-volume volcanic rocks that are the source of most diamonds, offer rare insights into aspects of the composition of the Earth's deep mantle. The radiogenic isotope ratios of kimberlites of different ages enable us to map the evolution of this domain through time. Here we show that globally distributed kimberlites originate from a single homogeneous reservoir with an isotopic composition that is indicative of a uniform and pristine mantle source, which evolved in isolation over at least 2.5 billion years of Earth history-to our knowledge, the only such reservoir that has been identified to date. Around 200 million years ago, extensive volumes of the same source were perturbed, probably as a result of contamination by exogenic material. The distribution of affected kimberlites suggests that this event may be related to subduction along the margin of the Pangaea supercontinent. These results reveal a long-lived and globally extensive mantle reservoir that underwent subsequent disruption, possibly heralding a marked change to large-scale mantle-mixing regimes. These processes may explain why uncontaminated primordial mantle is so difficult to identify in recent mantle-derived melts.

Migration to freshwater increases growth rates in a facultatively catadromous tropical fish

Diadromy is a form of migration where aquatic organisms undergo regular movements between fresh and marine waters for the purposes of feeding and reproduction. Despite having arisen in independent lineages of fish, gastropod molluscs and crustaceans, the evolutionary drivers of diadromous migration remain contentious. We test a key aspect of the 'productivity hypothesis', which proposes that diadromy arises in response to primary productivity differentials between marine and freshwater habitats. Otolith chemistry and biochronology data are analysed in a facultatively catadromous tropical fish (barramundi, Lates calcarifer) to determine the effect of freshwater residence on growth rates. Individuals that accessed freshwater grew ~ 25% faster on average than estuarine residents in the year following migration, suggesting that catadromy provides a potential fitness advantage over non-catadromous (marine/estuarine) life histories, as predicted by the productivity hypothesis. Although diadromous barramundi exhibited faster growth than non-diadromous fish, we suggest that the relative reproductive success of diadromous and non-diadromous contingents is likely to be strongly influenced by local environmental variability such as temporal differences in river discharge, and that this may facilitate the persistence of diverse life history strategies within populations.

The age of Homo naledi and associated sediments in the Rising Star Cave, South Africa

New ages for flowstone, sediments and fossil bones from the Dinaledi Chamber are presented. We combined optically stimulated luminescence dating of sediments with U-Th and palaeomagnetic analyses of flowstones to establish that all sediments containing Homo naledi fossils can be allocated to a single stratigraphic entity (sub-unit 3b), interpreted to be deposited between 236 ka and 414 ka. This result has been confirmed independently by dating three H. naledi teeth with combined U-series and electron spin resonance (US-ESR) dating. Two dating scenarios for the fossils were tested by varying the assumed levels of ²²²Rn loss in the encasing sediments: a maximum age scenario provides an average age for the two least altered fossil teeth of 253 +82/–70 ka, whilst a minimum age scenario yields an average age of 200 +70/–61 ka. We consider the maximum age scenario to more closely reflect conditions in the cave, and therefore, the true age of the fossils. By combining the US-ESR maximum age estimate obtained from the teeth, with the U-Th age for the oldest flowstone overlying Homo naledi fossils, we have constrained the depositional age of Homo naledi to a period between 236 ka and 335 ka. These age results demonstrate that a morphologically primitive hominin, Homo naledi, survived into the later parts of the Pleistocene in Africa, and indicate a much younger age for the Homo naledi fossils than have previously been hypothesized based on their morphology.

DOI:http://dx.doi.org/10.7554/eLife.24231.001

Species of ancient humans and the extinct relatives of our ancestors are typically described from a limited number of fossils. However, this was not the case with Homo naledi. More than 1500 fossils representing at least 15 individuals of this species were unearthed from the Rising Star cave system in South Africa between 2013 and 2014. Found deep underground in the Dinaledi Chamber, the H. naledi fossils are the largest collection of a single species of an ancient human-relative discovered in Africa.

After the discovery was reported, a number of questions still remained. Not least among these questions was: how old were the fossils? The material was undated, and predictions ranged from anywhere between 2 million years old and 100,000 years old. H. naledi shared several traits with the most primitive of our ancient relatives, including its small brain. As a result, many scientists guessed that H. naledi was an old species in our family tree, and possibly one of the earliest species to evolve in the genus Homo.

Now, Dirks et al. – who include many of the researchers who were involved in the discovery of H. naledi – report that the fossils are most likely between 236,000 and 335,000 years old. These dates are based on measuring the concentration of radioactive elements, and the damage caused by these elements (which accumulates over time), in three fossilized teeth, plus surrounding rock and sediments from the cave chamber. Importantly, the most crucial tests were carried out at independent laboratories around the world, and the scientists conducted the tests without knowing the results of the other laboratories. Dirks et al. took these extra steps to make sure that the results obtained were reproducible and unbiased.

The estimated dates are much more recent than many had predicted, and mean that H. naledi was alive at the same time as the earliest members of our own species – which most likely evolved between 300,000 and 200,000 years ago. These new findings demonstrate why it can be unwise to try to predict the age of a fossil based only on its appearance, and emphasize the importance of dating specimens via independent tests. Finally in two related reports, Berger et al. suggest how a primitive-looking species like H. naledi survived more recently than many would have predicted, while Hawks et al. describe the discovery of more H. naledi fossils from a separate chamber in the same cave system.

DOI:http://dx.doi.org/10.7554/eLife.24231.002

Calcium-dependent structural changes in scallop heavy meromyosin

The mechanism of calcium regulation of scallop myosin is not understood, although it is known that both myosin heads are required. We have explored possible interactions between the heads of heavy meromyosin (HMM) in the presence and absence of calcium and nucleotides by sedimentation and electron microscope studies. The ATPase activity of the HMM preparation was activated over tenfold by calcium, indicating that the preparation contained mostly regulated molecules. In the presence of ADP or ATP analogs, calcium increased the asymmetry of the HMM molecule as judged by its slower sedimentation velocity compared with that in EGTA. In the absence of nucleotide the asymmetry was high even in EGTA. The shift in sedimentation occurred with a sharp midpoint at a calcium level of about 0.5 microM. Sedimentation of subfragment 1 was not dependent on calcium or on nucleotides. Modeling accounted for the observed sedimentation behavior by assuming that both HMM heads bent toward the tail in the absence of calcium, while in its presence the heads had random positions. The sedimentation pattern showed a single peak at all calcium concentrations, indicating equilibration between the two forms with a t(1/2) less than 70 seconds. Electron micrographs of crosslinked, rotary shadowed specimens indicated that 81 % of HMM molecules in the presence of nucleotide had both heads pointing back towards the tail in the absence of calcium, as compared with 41 % in its presence. This is consistent with the sedimentation data. We conclude that in the "off" state, scallop myosin heads interact with each other, forming a rigid structure with low ATPase activity. When molecules are switched "on" by binding of calcium, communication between the heads is lost, allowing them to flex randomly about the junction with the tail; this could facilitate their interaction with actin in contracting muscle.

A national general pediatric clerkship curriculum: the process of development and implementation

OBJECTIVE

To describe a new national general pediatrics clerkship curriculum, the development process that built national support for its use, and current progress in implementing the curriculum in pediatric clerkships at US allopathic medical schools. CURRICULUM DEVELOPMENT: A curriculum project team of pediatric clerkship directors and an advisory committee representing professional organizations invested in pediatric student education developed the format and content in collaboration with pediatric educators from the Council on Medical Student Education in Pediatrics (COMSEP) and the Ambulatory Pediatric Association (APA). An iterative process or review by clerkship directors, pediatric departmental chairs, and students finalized the content and built support for the final product. The national dissemination process resulted in consensus among pediatric educators that this curriculum should be used as the national curricular guideline for clerkships. MONITORING IMPLEMENTATION: Surveys were mailed to all pediatric clerkship directors before dissemination (November 1994), and in the first and third academic years after national dissemination (March 1996 and September 1997). The 3 surveys assessed schools' implementation of specific components of the curriculum. The final survey also assessed ways the curriculum was used and barriers to implementation.

OUTCOMES

The final curriculum provided objectives and competencies for attitudes, skills, and 18 knowledge areas of general pediatrics. A total of 216 short clinical cases were also provided as an alternative learning method. An accompanying resource manual provided suggested strategies for implementation, teaching, and evaluation. A total of 103 schools responded to survey 1; 84 schools to survey 2; and 85 schools responded to survey 3 from the 125 medical schools surveyed. Before dissemination, 16% of schools were already using the clinical cases. In the 1995-1996 academic year, 70% of schools were using some or all of the curricular objectives/competencies, and 45% were using the clinical cases. Two years later, 90% of schools surveyed were using the curricular objectives, 88% were using the competencies, 66% were using the clinical cases. The extent of curriculum use also increased. Schools using 11 or more of the 18 curriculum's knowledge areas increased from 50% (1995-1996) to 73% (1996-1997).

CONCLUSION

This new national general pediatric clerkship curriculum developed broad support during its development and has been implemented very rapidly nationwide. During this period the COMSEP and the APA have strongly supported its implementation with a variety of activities. This development and implementation process can be a model for other national curricula.

Pectoralis major flaps: functional aspects of the repair of oral and oropharyngeal resections

The use of pectoralis major flaps for reconstruction after oral and oropharyngeal resection in a series of seventeen patients is reported. The applications and complications are described. A post-operative assessment of speech, chewing and swallowing in ten of the patients is reported. The functional aspects of such surgery are discussed.

Caries resistance in children with chronic renal failure: plaque pH, salivary pH, and salivary composition

We studied properties of saliva and of dental plaque which affect the caries process in an effort to understand the low prevalence of caries in patients with chronic renal failure. Plaque pH, before and following carbohydrate exposure, saliva pH, and saliva composition were evaluated in children and adolescents with chronic renal failure (n = 10) and successful renal transplantation (n = 11), and in two comparison groups of healthy children with few caries (n = 15) and numerous caries (n = 15). Salivary urea nitrogen concentration was elevated in all subjects with elevated serum urea nitrogen concentration. Chronic renal failure subjects had significantly higher salivary urea nitrogen concentration than transplanted subjects. Plaque pH correlated directly with salivary urea nitrogen concentration and was significantly more alkaline in chronic renal failure than transplant or comparison groups. Salivary urea nitrogen concentration accounted for the majority of variability in plaque pH; salivary pH and salivary phosphorous contributed negligibly. Absolute pH drop following carbohydrate exposure did not differ among groups, but because baseline plaque pH was elevated for chronic renal failure subjects, minimum pH did not attain cariogenic levels. Our data support the hypothesis that the relative paucity of caries in patients with chronic renal failure results from alteration of plaque by metabolic end products of urea metabolism. Our data further suggest that transplanted patients whose renal function is normal may be at increased risk of caries, especially if enamel hypoplasia is present and oral hygiene is poor.