Hypoxia and male behaviour in an African cichlid Pseudocrenilabrus multicolor victoriae

This study tested the prediction that hypoxia may reduce the frequency of energetically expensive behaviours by quantifying male mating and aggressive displays in the cichlid Pseudocrenilabrus multicolor victoriae after long-term acclimation (5 months) to either high dissolved oxygen (DO) or low DO. Regardless of DO treatment, males engaged in more aggressive displays than mating displays; however, males acclimated to low DO reduced their total number of displays compared to high DO-acclimated males.     

Hypoxia and life‐history traits in a eurytopic African cichlid

This study quantified variation in key life‐history traits of the widespread African mouth‐brooding cichlid Pseudocrenilabrus multicolor victoriae. Egg size, number, batch reproductive effort, size at maturity and brooding efficiency were compared among field populations across a wide range of dissolved oxygen (DO) concentrations from extreme hypoxia to normoxia. In the laboratory, a similar suite of characters was quantified in F1 of low‐ and high‐DO origin reared under low or high DO. In general, females from low‐DO habitats and females reared under low DO were characterized by a smaller size at maturity and no difference in batch reproductive effort when compared with females from high‐DO habitats or females reared under normoxia. A trade‐off between egg size and number was evident in the field and in the laboratory‐rearing experiment, but the direction of the trade‐off differed. Egg size was negatively correlated with egg number across field populations; females collected from low‐DO sites generally had more, smaller eggs relative to females from high‐DO sites. In the laboratory‐rearing experiment, F1 females of high‐DO origin produced larger, fewer eggs than F1 females of low‐DO origin, lending support to the field results and suggesting a heritable component to these traits. There was also an element of developmental plasticity, F1 females raised under low DO produced larger, fewer eggs compared with F1 females raised under high DO (regardless of population) suggesting that DO may interact with other variables to determine egg size in the field.     

Hypoxia and interdemic variation in Poecilia latipinna

Variation in respiratory traits was quantified between two populations of the sailfin molly Poecilia latipinna (one from a periodically hypoxic salt marsh, Cedar Key, and one from a chronically normoxic river site, Santa Fe River). Two suites of characters were selected: traits that may show both short‐term acclimation response and interdemic variation in acclimation response (metabolic rate, critical oxygen tension and respiratory behaviour), and those that are not likely to respond to short‐term acclimation but may vary among populations (gill morphometric characters). Sailfin mollies from the salt marsh, acclimated to hypoxia (1 mg l⁻¹, c . 20 mmHg) for 6 weeks, spent less time conducting aquatic surface respiration and had lower gill ventilation rates than hypoxia‐acclimated conspecifics from the well‐oxygenated river site. Poecilia latipinna acclimated to hypoxia exhibited a lower critical oxygen tension ( P _c) than fish acclimated to normoxia; however, there was also a significant population effect. Poecilia latipinna from Cedar Key exhibited a lower P _c than fish from the Santa Fe River, regardless of acclimation. Cedar Key fish had a 14% higher mean gill surface area relative to fish from the Santa Fe River, a character that could account, at least in part, for their greater tolerance to hypoxia.     

Hypoxia tolerance of the mummichog: the role of access to the water surface

Low dissolved oxygen (DO) had a significant effect on specific growth rate (G_S), length increment (I_L) and haematocrit (Hct) of the mummichog Fundulus heteroclitus. Regardless of access to the water surface, F. heteroclitus maintained high growth rates (G_S and I_L) at DO concentrations as low as 3 mg O₂ l^?1. With access to the water surface, both G_S and I_L of F. heteroclitus decreased by c. 60% at 1·0 mg O₂ l^?1 compared to all higher DO treatments. When denied access to the water surface, a further decrease in G_S (c. 90%) and I_L (c. 75%) was observed at 1 mg O₂ l^?1. There was no effect of diel‐cycling DO (1–11 mg O₂ l^?1) with or without surface access on G_S, I_L or Hct of F. heteroclitus. Similar trends between G_S and faecal production across DO treatments suggest that decreased feeding contributed significantly to the observed decrease in growth rate. Haematocrit was significantly elevated at 1 mg O₂ l^?1 for fish with and without access to the water surface. Increased Hct, however, was not sufficient to maintain high G_S or I_L at severely low DO. When permitted to respire in the surface layer, however, F. heteroclitus was capable of maintaining moderate growth rates at DO concentrations of 1 mg O₂ l^?1 (c. 15% saturation). Although aquatic surface respiration (ASR) was not quantified in this study, F. heteroclitus routinely swam in contact with the water surface and performed ASR at DO concentrations ≤3 mg O₂ l^?1. No hypoxia‐related mortality was observed in any DO or surface access treatment for as long as 9 days. This study demonstrates that surface access, and thus potential for ASR, plays an important role in providing F. heteroclitus substantial independence of growth rate over a wide range of low DO conditions commonly encountered in shallow estuarine environments.     

Larval damselflies in extreme environments: behavioral and physiological response to hypoxic stress

The extensive papyrus (Cyperus papyrus) swamps of East and Central Africa form a habitat of great ecological importance due to their extent, the extreme and chronic hypoxia of the interior swamp, and the unique assemblages of water-breathing insects that characterize these communities, including zygopteran (damselfly) larvae. The major goal of this study was to quantify physiological and behavioral responses of gilled and gill-less damselfly larvae of a papyrus swamp specialist, Proischnura subfurcatum, to low-oxygen conditions. Gill autotomization was common in P. subfurcatum of the Rwembaita Swamp in Kibale National Park, Uganda, with one to three gills missing from 56% of the specimens surveyed. We examined behavioral (ventilation activity and vertical migration) and physiological (metabolic rate) response to hypoxia in gilled and gill-less P. subfurcatum. Behavioral response to progressive hypoxia indicated that gill-less individuals rely more on use of wing sheaths (lifting and spreading) than gilled P. subfurcatum larvae. However, both morphs migrated to the surface to gain contact with atmospheric air under extreme hypoxia. On average, the rate of oxygen consumption of gill-less individuals was 51% lower than that of gilled individuals. This observed metabolic depression in gill-less P. subfurcatum may be attributed to the loss of major respiratory appendages. However, the apparent ability of both gilled and gill-less individuals to maintain their metabolic rates to a similar critical tension suggests other mechanisms may compensate for loss of gills, though not enough to mediate metabolic depression.     

At the tipping point: Differential influences of warming and deoxygenation on the survival,emergence, and respiration of cosmopolitan clams

Although warming and low dissolved oxygen (DO) levels are co‐occurring significant climatic stressors in the ocean, the combined effects of these stressors on marine benthic animals have not been well established. Here, we tested the effects of elevated temperatures and low dissolved oxygen levels on the survival, emerging behavior from sediment, and the respiration of juvenile cosmopolitan Manila clams (Venerupis philippinarum) by exposing them to two temperatures (20 and 23.5°C) and DO levels (3.5 and 6–7 mg/L). Although within previously described tolerable ranges of temperature and DO, this 3.5°C increase in temperature combined with a 50% decrease in DO had a devastating effect on the survival of clams (85% mortality after 8 days). The mortality of clams under normoxia at 23.5°C appeared to be higher than under the low DO condition at 20°C. On the other hand, more clams emerged from sediment under the low DO condition at 20°C than under any other conditions. Oxygen consumption rates were not significantly affected by different conditions. Our results suggest temperature elevation combined with low oxygen additively increases stress on Manila clams and that warming is at least as stressful as low DO in terms of mortality. However, low DO poses another threat as it may induce emergence from sediment, and, thus increase predation risk. This is the first evidence that a combination of warming and deoxygenation stressors should reduce population survival of clams much more so than changes in a single stressor.     

Potential effects of three antibiotics on community respiration and production measurements

The effects of three commonly available antibiotics (tetracycline hydrochloride, streptomycin and neomycin sulfate) on the micro-Winkler and D.O. probe oxygen techniques and on the pH method of CO₂ determination were investigated in the laboratory to assess potential effects on community metabolism measurements.All three antibiotics significantly altered O₂ and CO₂ concentrations through time. The results demonstrate that the use of the three antibiotics as bacterial respiratory inhibitors in community metabolism studies could cause significant overestimations of community respiration when measured as CO₂, and significant underestimation of primary productivity and overestimation of respiration when measured as O₂.     

The Effects of Hypoxia on Three Sympatric Shark Species: Physiological and Behavioral Responses

Behavioral and physiological responses to hypoxia were examined in three sympatric species of sharks: bonnethead shark Sphyrna tiburo, blacknose shark, Carcharhinus acronotus, and Florida smoothhound shark, Mustelus norrisi, using closed system respirometry. Sharks were exposed to normoxic and three levels of hypoxic conditions. Under normoxic conditions (5.5–6.4mg l^–1), shark routine swimming speed averaged 25.5 and 31.0cm s^–1 for obligate ram-ventilating S. tiburo and C. acronotus respectively, and 25.0cm s^–1 for buccal-ventilating M. norrisi. Routine oxygen consumption averaged about 234.6 mg O₂kg^–1h^–1 for S. tiburo, 437.2mg O₂kg^–1h^–1 for C. acronotus, and 161.4mg O₂ kg^–1 h^–1 for M. norrisi. For ram-ventilating sharks, mouth gape averaged 1.0cm whereas M. norrisi gillbeats averaged 56.0 beats min^–1. Swimming speeds, mouth gape, and oxygen consumption rate of S. tiburo and C. acronotus increased to a maximum of 37–39cm s^–1, 2.5–3.0cm and 496 and 599mg O₂ kg^–1 h^–1 under hypoxic conditions (2.5–3.4mg l^–1), respectively. M. norrisi decreased swimming speeds to 16cm s^–1 and oxygen consumption rate remained similar. Results support the hypothesis that obligate ram-ventilating sharks respond to hypoxia by increasing swimming speed and mouth gape while buccal-ventilating smoothhound sharks reduce activity.     

Hypoxia tolerance of two centrarchid sunfishes and an introduced cichlid from karstic Everglades wetlands of southern Florida, U.S.A.

In this study, the hypoxia tolerance of three Everglades fishes, two native centrarchids ( Lepomis gulosus and Lepomis marginatus ) and a recently introduced cichlid ( Hemichromis letourneuxi ), were documented. Aquatic surface respiration (ASR) thresholds were lowest for H. letourneuxi , followed by L. gulosus , then L. marginatus . The ASR thresholds for L. marginatus were within ranges reported for small, freshwater tropical fishes, while those for L. gulosus were similar to swamp-adapted fishes. For H. letourneuxi , ASR thresholds were some of the lowest reported. All three species showed excellent tolerance of low dissolved oxygen levels when allowed access to the surface. When denied surface access, L. marginatus lost equilibrium at a higher oxygen tension than the other species. Overall, although all species easily tolerated hypoxia, H. letourneuxi appeared to be best equipped to deal with hypoxia, followed by L. gulosus , then L. marginatus . Hemichromis letourneuxi also exhibited more aggressive behaviours than the centrarchids. These results suggest that hypoxia is not likely to prevent H. letourneuxi from exploiting the seasonally inundated wetlands of south Florida while expanding its range there.     

Phenotypic plasticity and the possible role of genetic assimilation: Hypoxia-induced trade-offs in the morphological traits of an African cichlid

In this study we investigate the possible role of phenotypic plasticity and genetic assimilation in the process of adaptation and evolutionary change in the cichlid Pseudocrenilabrus multicolor victoriae . In the field we compared a population of a stable hypoxic habitat with one of a stable well-oxygenated habitat. In the laboratory, we compared individuals from the same mother raised under hypoxic or well-oxygenated conditions to examine phenotypic plasticity. Morphological parameters of three categories were measured: (a) the gill apparatus, (b) the surrounding structural elements, and (c) the outer shape of the fish. Swamp-dwelling fish had a 29% greater total gill surface area than fish from the well-oxygenated habitat due to their larger gill filament length and greater lamellar area. In the plasticity experiment, total gill surface area was 18% greater in the hypoxia group due to a larger number of longer filaments. Surrounding elements and outer shape also differed between the field populations and between fish grown under hypoxic and well-oxygenated conditions, but there was disparity between the field results and the plasticity experiment. The disparity between field and experimental fish may be due to: (a) differences in selection pressures between populations, (b) different constraints for genetic and plasticity changes, or (c) selection against plastic responses to hypoxia. Our results suggest that both (a) and (c) are involved.     

Paleogeographic variations of pedogenic carbonate delta13C values from Koobi Fora, Kenya: implications for floral compositions of Plio-Pleistocene hominin environments

Plio-Pleistocene East African grassland expansion and faunal macroevolution, including that of our own lineage, are attributed to global climate change. To further understand environmental factors of early hominin evolution, we reconstruct the paleogeographic distribution of vegetation (C(3)-C(4) pathways) by stable carbon isotope (delta(13)C) analysis of pedogenic carbonates from the Plio-Pleistocene Koobi Fora region, northeast Lake Turkana Basin, Kenya. We analyzed 202 nodules (530 measurements) from ten paleontological/archaeological collecting areas spanning environments over a 50-km(2) area. We compared results across subregions in evolving fluviolacustrine depositional environments in the Koobi Fora Formation from 2.0-1.5 Ma, a stratigraphic interval that temporally brackets grassland ascendancy in East Africa. Significant differences in delta(13)C values between subregions are explained by paleogeographic controls on floral composition and distribution. Our results indicate grassland expansion between 2.0 and 1.75 Ma, coincident with major shifts in basin-wide sedimentation and hydrology. Hypotheses may be correct in linking Plio-Pleistocene hominin evolution to environmental changes from global climate; however, based on our results, we interpret complexity from proximate forces that mitigated basin evolution. An approximately 2.5 Ma tectonic event in southern Ethiopia and northern Kenya exerted strong effects on paleography in the Turkana Basin from 2.0-1.5 Ma, contributing to the shift from a closed, lacustrine basin to one dominated by open, fluvial conditions. We propose basin transformation decreased residence time for Omo River water and expanded subaerial floodplain landscapes, ultimately leading to reduced proportions of wooded floras and the establishment of habitats suitable for grassland communities.     

The life and death of a street boy in East Africa: everyday violence in the time of AIDS

This article focuses on the life history of a single street boy in northwestern Tanzania, whom I name Juma. I suggest that Juma's experiences and the life trajectory of himself and of significant individuals around him (particularly his mother) were structured by everyday violence. I describe everyday violence in terms of a conjuncture between macrostructural forces in East Africa (including a history of failed development schemes and the contemporary political economy of neoliberalism) and the lived experience of individuals as they negotiate local, contextual factors (including land-tenure practices, the power dynamics between immediate and extended kin, life on the streets, and constructions of gender and sexuality). I suggest that AIDS and its many impacts on Juma's life course can only be understood in a broader context of everyday violence. From this basis, I draw several general conclusions regarding AIDS prevention and intervention strategies.     

Drought and recovery: Livestock dynamics among the Ngisonyoka Turkana of Kenya

From 1980–1985, the Turkana District of Kenya experienced both drought and above average rainfall. The effects of a 2-year drought on the livestock population of the nomadic pastoral Ngisonyoka are discussed. Detailed data on mortality rates and offtake are presented for the animals of four herd owners, and the recovery process is followed for the 5-year period for one herd owner. It is concluded that during the drought, 63% of the cattle, 45% of the camels, and 55% of the small stock left the sample herds. The livestock population of one herd had recovered to pre-drought levels 3 years after the drought.     

A critique of the chronometric evidence for hominid fossils: I. Africa and the Near East 500-50 ka

The chronometric dating evidence for all hominid fossils from Africa and the Near East that have previously been dated to 500-50 ka is critically assessed using the concept of chronometric hygiene, and these dates are revised using Bayesian statistical analyses where possible. Sixteen relevant hominid sites lacking chronometric evidence are briefly discussed. Chronometric evidence from 37 sites is assessed in detail. The dates for many hominid fossils are poorly constrained, with a number dated by comparisons of faunal assemblages-a method that does not have good chronological resolution for much of the last million years. For sites with stratigraphic sequences of dates, it is generally possible to refine the dating, but in some cases, the revised chronology is less precise than previous chronologies. Fossils over 200 ka in age tend to be poorly dated, but for the last 200 kyr, dating is better due to the availability of electron-spin-resonance and thermoluminescence dating. Consideration of the chronologies favored by the proponents of the out-of-Africa and multiregional hypotheses of human evolution shows their selectivity. The chronological assessment of the fossils here is compatible with either hypothesis. If evolutionary schemes that do not rely on the morphology of the hominid fossils to decide the sequence of fossils are to be built, then further dating is required, alongside full publication of existing dates.     

Photosynthesis and UV-B Tolerance of the Marine Alga Fucus vesiculosus at Different Sea Water Salinities

The marine algal species in the Baltic Sea are few due to the low sea water salinity. One of the few species that can be found is Fucus vesiculosus. Even this species is affected by the low salinity and becomes smaller in size in the Baltic. In present work the photosynthesis of F. vesiculosus in the northern Baltic (Bothnian Sea) was compared to the photosynthesis of F. vesiculosus in the Atlantic. Oxygen evolution was measured before and after exposure to 2.3 W of UV-B (280–320 nm) radiation for 5 h, as well as after 48 h recovery in low light. The plants were kept in their own sea water salinity as well as in a changed salinity, this to examine possible correlations between salinity and photosynthesis. The results show a significant higher initial maximal photosynthesis (P _max) for Atlantic plants (10.3 nmol O₂ g⁻¹ FW s⁻¹) compared to Baltic plants (4.0 nmol O₂ g⁻¹ FW s⁻¹). The Baltic plants were found more sensitive to UV-B with a 40–50% decrease of P _max as well as a lower degree of recovery (60–70% compared to 75–95% for the Atlantic plants). The higher salinity (35 psu) had a positive effect on the Baltic F. vesiculosus with increased P _max as well as increased tolerance to UV-B. The lower salinity (5 psu) had a negative effect on the Atlantic plants with a decreased P _max as well as a lower tolerance to UV-B. Pigment content was found higher in Atlantic F. vesiculosus. The pigment content decreased then the Atlantic plants were transferred to 5 psu. The concentration of Chl a as well as the total content of violaxanthin, diadinoxanthin and zeaxanthin in Baltic plants increased when transferred to 35 psu. The Atlantic F. vesiculosus can not survive the low salinity in the northern Baltic (died within 8 weeks). It is likely that a long time acclimation or adaptation to low salinity has taken place for F. vesiculosus in northern Baltic. If this is an ecotypic or genotypic development it is too early to say.     

Evaluation and use of a diffusion-controlled sampler for determining chemical and dissolved oxygen gradients at the sediment-water interface

Field and laboratory evaluations were made of a simple, inexpensive diffusion-controlled sampler with ports on two sides at each interval which incorporates 0.2-m polycarbonate membrane to filter samples in situ. Monovalent and divalent ions reached 90% of equilibrium between sampler contents and the external solution within 3 and 6 hours, respectively. Sediment interstitial water chemical gradients to depths of tens of centimeters were obtained within several days after placement. Gradients were consistent with those determined from interstitial water obtained by centrifugation of adjacent sediment. Ten milliliter sample volumes were collected at 1-cm intervals to determine chemical gradients and dissolved oxygen profiles at depth and at the interface between the sediment and water column. The flux of dissolved species, including oxygen, across the sediment-water interface can be assessed more accurately using this sampler than by using data collected from benthic cores.     

New ages for Middle and Later Stone Age deposits at Mumba rockshelter, Tanzania: optically stimulated luminescence dating of quartz and feldspar grains

The archaeological deposits at Mumba rockshelter, northern Tanzania, have been excavated for more than 70 years, starting with Margit and Ludwig Köhl-Larsen in the 1930s. The assemblages of Middle Stone Age (MSA) and Later Stone Age (LSA) artefacts collected from this site constitute the type sequences for these cultural phases in East Africa. Despite its archaeological importance, however, the chronology of the site is poorly constrained, despite the application since the 1980s of several dating methods (radiocarbon, uranium-series and amino acid racemisation) to a variety of materials recovered from the deposits. Here, we review these previous chronologies for Mumba and report new ages obtained from optically stimulated luminescence (OSL) and infrared stimulated luminescence (IRSL) measurements on single grains of quartz and multi-grain aliquots of potassium (K) feldspar from the MSA and LSA deposits. Measurements of single grains of quartz allowed the rejection of unrepresentative grains and the application of appropriate statistical models to obtain the most reliable age estimates, while measurements of K-feldspars allowed the chronology to be extended to older deposits. The seven quartz ages and four K-feldspar ages provide improved temporal constraints on the archaeological sequence at Mumba. The deposits associated with the latest Kisele Industry (Bed VI-A) and the earliest Mumba Industry (Bed V) are dated to 63.4 ± 5.7 and 56.9 ± 4.8 ka (thousands of years ago), respectively, thus constraining the time of transition between these two archaeological phases to ∼60 ka. An age of 49.1 ± 4.3 ka has been obtained for the latest deposits associated with the Mumba Industry, which show no evidence for post-depositional mixing and contain ostrich eggshell (OES) beads and abundant microlithics. The Nasera Industry deposits (Bed III) contain large quantities of OES beads and date to 36.8 ± 3.4 ka. We compare the luminescence ages with the previous chronologies for Mumba, and briefly discuss how the revised chronology fits in the context of existing archaeological records and palaeoclimatic reconstructions for East Africa.