Production dynamics of some arctic Chironomus larvae

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/110095/1/lno19822740728.pd

Effects of Crude Oil on Aquatic Insects of Tundra Ponds

Aquatic insects are numerous and important in the ecology of tundra thaw ponds, comprising most of the biomass and production. The most common types are the caddisflies Asynarchus and Micrasema, the stonefly Nemoura, the beetle Agabus and especially larvae of the fly family Chironomidae. Studies in vitro showed no detectable mortality of these insects at doses of oil up to 1.5 l/m² Prudhoe Bay crude oil. However, field experiments on two ponds with application rates of about 10 l/m² (Pond E, 1970) and 0.24 l/m² (Pond Omega, 1975) both indicated that selective elimination of Asynarchus and Nemoura had occurred. Chironomidae in Pond Omega displayed much lower rates of adult emergence in 1976 and 1977 than in 1975, immediately before and after oil treatment, with several species in the tribe Tanytarsini most reduced. Pond E did not show low emergence rates, but the proportion of Orthocladiinae was much higher than in reference ponds. Trichotanypus was severely reduced in Pond Omega but unusually abundant in Pond E in 1976 and 1977. Effects of oil seem to be different for different species, and occur at some point during the late larval stages of insects or at metamorphosis, but toxicity experiments did not confirm this. Oil may also interfere with reproduction in insect species which remain mainly on or near the pond surface as adults. Apparent effects in field experiments are not entirely consistent with observations of Canadian researchers. Nevertheless there were several similarities and both followed patterns like those observed in marine benthic communities, such as greater effects on shore fauna, greater effects of low-molecular-weight hydrocarbons, and species-specificity of effects. There is no indication of recovery of Nemoura, Asynarchus or Tanytarsini in Pond E seven years after the spill, but biomass and abundance of the other aquatic insects remains high. We recommend that clean-up measures avoid introducing solvents or dispersants, which might be toxic to insects in the pond

Growing-Season Temperature Change across Four Decades in an Arctic Tundra Pond

We examined temperature dynamics across a 42-year period in a low-centered tundra polygon pond on the Arctic Coastal Plain of northern Alaska to assess potential changes in thermal dynamics for ponds of this type. Using water temperature data from a pond near Barrow (now Utqiaġvik), Alaska, studied intensively during 1971 – 73 and again in 2007 – 12, we built an empirical model coupling historical air temperatures to measured pond temperatures for four summers. We then used the model to predict summer pond temperatures over a 42-year span, including 1974 – 2008, for which direct aquatic temperature records do not exist. Average pond temperatures during the growing season (1 May through 31 October) increased by 0.5˚C decade-1 or 2.2˚C over the 42-year period. Our simulations predicted the average date of spring thaw for the pond as 2 June (± 3 d), which did not change over the 42-year time period. However, average pond temperature during the first 30 days of the growing season increased from 1971 to 2012, suggesting that recently, ponds are warmer in early spring. The average date of pond sediment freeze over the 42 years shifted later by 15 days, from 28 September in 1971 to 13 October in 2012. These changes correspond to a growing season that has increased in length by 14 days, from 118 days in 1971 to 132 days in 2012. Contemporary temperature measurements in other shallow tundra ponds in northern Alaska show a high degree of temporal coherence (r = 0.93 – 0.99), which warrants the general conclusion that tundra ponds on Alaska’s Arctic Coastal Plain have undergone a significant change in thermal dynamics over the past four decades. Our results provide a means to incorporate these pond types into larger-scale simulations of Arctic climate change.Nous avons examiné la dynamique des températures sur une période de 42 ans dans un étang de polygone de toundra concave sur la plaine côtière arctique du nord de l’Alaska dans le but d’évaluer les changements potentiels sur le plan de la dynamique thermique des étangs de ce type. À l’aide des données de la température de l’eau provenant d’un étang situé près de Barrow (maintenant Utqiaġvik), en Alaska, étang ayant fait l’objet d’études intensives de 1971 à 1973 et de 2007 à 2012, nous avons construit un modèle empirique en couplant les températures de l’air historiques aux températures de quatre étés observées à l’étang. Ensuite, nous nous sommes servis de ce modèle pour prévoir les températures estivales de l’étang sur une période de 42 ans, incluant la période allant de 1974 à 2008, pour lesquelles il n’existe pas de données de températures aquatiques directes. Pendant la saison de croissance (du 1er mai au 31 octobre), les températures moyennes de l’étang ont augmenté de 0,5 ˚C par décennie-1 ou de 2,2 ˚C sur la période de 42 ans. Nos simulations ont permis de prévoir une date moyenne pour le dégel du printemps (± 3 j), ce qui n’a pas changé pendant la période de 42 ans. Cependant, la température moyenne de l’étang au cours des 30 premiers jours de la saison de croissance a augmenté entre 1971 et 2012, ce qui laisse entendre que depuis récemment, les étangs sont plus chauds au début du printemps. Sur la période de 42 ans, la date moyenne de gel des sédiments de l’étang a été retardée de 15 jours, passant ainsi du 28 septembre en 1971 au 13 octobre en 2012. Ces changements correspondent à une saison de croissance dont la durée a rallongé de 14 jours, passant de 118 jours en 1971 à 132 jours en 2012. Les mesures de températures contemporaines d’autres étangs de toundra peu profonds du nord de l’Alaska affichent un haut degré de cohérence temporelle (r = 0,93 – 0,99), ce qui permet de tirer la conclusion générale que les étangs de toundra de la plaine côtière arctique de l’Alaska ont connu un important changement sur le plan de la dynamique thermique au cours des quatre dernières décennies. Nos résultats permettent d’incorporer ces types d’étangs à des simulations à plus grande échelle du changement climatique de l’Arctique

Breaking the rule: Five larval instars in the podonomine midge Trichotanypus alaskensis Brundin from Barrow, Alaska

Except for one unconfirmed case, chironomid larvae have been reported to pass through four larval instars between egg and pupal stages. We have observed a fifth larval instar to be a standard life-cycle feature of the podonomine Trichotanypus alaskensis Brundin 1966 in tundra ponds on the Arctic Coastal Plain near Barrow, Alaska. T. alaskensis has a one-year life cycle in these arctic ponds. Adults emerge in June ~2-3 weeks after pond thaw, then mate and oviposit; most newly-hatched larvae reach instar IV by October when pond sediments freeze. Overwintering larvae complete instar IV within a few days of thaw, then molt again to a fifth larval instar. Imaginal discs, normally seen only during instar IV in Chironomidae, develop across both instars IV & V prior to pupation and adult emergence. While monitoring larval development post-thaw in 2014, we noticed freshly-molted T. alaskensis larval exuviae a week or more prior to any pupation by that species. In 2015-16 we reared overwintering instar IV larvae from single pond sources, individually with daily monitoring, through molts to instar V, pupa, and adult. Some overwintering instar II and III larvae were reared as well, but were few in number. During 2016 we also reared T. alaskensis progeny (from eggs) through instar II, thus documenting head capsule size ranges for all five instars in a single pond’s population. Without individual rearings, the fifth larval instar was not readily apparent for two reasons: 1) The molt itself occurs immediately after thaw and is so synchronous it is difficult to discern in daily field samples. 2) The head capsule size increment between instars IV-V is much lower than the ratio predicted by the Brooks-Dyar Rule. Up through instar IV, the Brooks-Dyar ratio for T. alaskensis ranged 1.30-1.61, but during the IV-V molt head capsule dimensions (sexes pooled) increased by a ratio of 1.09 – comparable to the magnitude of sexual dimorphism in head capsule size within each of the final two larval instars. Individual rearings coupled with 2014-2016 field surveys in nine other ponds suggest that five larval instars is an obligatory trait of this species at this location. As this is the first confirmed case of five larval instars in a chironomid, the phylogenetic uniqueness of this trait needs further investigation

Pre-emergence growth and development in the arctic midge Trichotanypus alaskensis Brundin

Developing at low mean temperatures, arctic chironomids often have prolonged larval growth yet adult emergence is typically a brief and highly synchronous event. How does a midge population achieve synchronous emergence? Under the Absolute Spring Species Hypothesis (AbSS), adult eclosion by early-emerging species may be synchronized by overwintering as fully mature larvae. Such prepupal larvae would neither feed nor grow after spring thaw, only pupate and emerge. The podonomine Trichotanypus alaskensis Brundin is an abundant midge in tundra ponds on Alaska’s Arctic Coastal Plain, and one of the earliest-emerging species in this chironomid-dominated insect community. T. alaskensis is univoltine in these arctic ponds, with most emergence from any one pond occurring within less than a one-week span during late June, typically about three weeks after pond thaw. We evaluated T. alaskensis for conformity to the AbSS model by documenting the overwintering state of this species in a tundra pond near Barrow, Alaska, then monitoring larval growth and development of the population from spring thaw to pupation. Most T. alaskensis were immature instar IV larvae when collected in late September of both 2010 and 2011, with 10-30% still in late instar III. Immediately after pond thaw in 2011, all collected larvae had imaginal disc primordia showing early stages of instar IV development. Within the first two weeks following pond thaw, most larvae had doubled their dry mass and developed into mature (prepupal) final-instar larvae. Highly synchronized emergence by T.  alaskensis is not a consequence of a population overwintering as fully-mature larvae, as per the Absolute Spring Species Hypothesis. Rather, larvae in a given tundra pond appear to develop synchronously throughout the life cycle, including a period of substantial growth and rapid prepupal development between spring thaw and early-summer emergence

Electromagnetic Moments of the Baryon Decuplet

We compute the leading contributions to the magnetic dipole and electric quadrupole moments of the baryon decuplet in chiral perturbation theory. The measured value for the magnetic moment of the $\Omega^-$ is used to determine the local counterterm for the magnetic moments. We compare the chiral perturbation theory predictions for the magnetic moments of the decuplet with those of the baryon octet and find reasonable agreement with the predictions of the large--$N_c$ limit of QCD. The leading contribution to the quadrupole moment of the $\Delta$ and other members of the decuplet comes from one--loop graphs. The pionic contribution is shown to be proportional to $I_z$ (and so will not contribute to the quadrupole moment of $I=0$ nuclei), while the contribution from kaons has both isovector and isoscalar components. The chiral logarithmic enhancement of both pion and kaon loops has a coefficient that vanishes in the $SU(6)$ limit. The third allowed moment, the magnetic octupole, is shown to be dominated by a local counterterm with corrections arising at two loops. We briefly mention the strange counterparts of these moments.Comment: Uses harvmac.tex, 15 pages with 3 PostScript figures packed using uufiles. UCSD/PTH 93-22, QUSTH-93-05, Duke-TH-93-5

Mallard Duckling Growth and Survival in Relation to Aquatic Invertebrates

Identification and assessment of the relative importance of factors affecting duckling growth and survival are essential for effective management of mallards on breeding areas. For each of 3 years (1993-95), we placed Fl-generation wild mallard (Anas platyrhynchos) females on experimental wetlands and allowed them to mate, nest, and rear broods for 17 days. We manipulated invertebrate densities by introducing fathead minnows (Pimephales promelas) at high densities in half of the wetlands on which broods were confined. Day- 17 body mass of surviving ducklings (n = 183) was greater for ducklings that were heavier at hatch; the difference averaged 1.7 g at day 17 for each 1.0 g at hatch (P = 0.047). Growth ratio (the proportion of body mass attained by ducklings when they were last measured relative to that predicted for wild female mallard ducklings) also was positively related to body mass at hatch (P = 0.004). Mean day-17 body mass and mean growth ratio of ducklings per brood (each adjusted for body mass at hatch) were positively related to numbers of aquatic invertebrates (Ps \u3c 0.001) and negatively related to variance in the daily minimum air temperature during the exposure period (Ps \u3c 0.020). Early growth of mallards was more sensitive to variation in numbers of invertebrates than to air temperature or biomass of invertebrates. Duckling survival was positively related to growth ratio (P \u3c 0.001). Our study provides parameter estimates that are essential for modeling growth and survival of mallard ducklings. We emphasize the need for conserving brood-rearing wetlands in the Prairie Pothole Region that are capable of supporting high densities of aquatic invertebrates

Dating of the oldest continental sediments from the Himalayan foreland basin

A detailed knowledge of Himalayan development is important for our wider understanding of several global processes, ranging from models of plateau uplift to changes in oceanic chemistry and climate(1-4). Continental sediments 55 Myr old found in a foreland basin in Pakistan(5) are, by more than 20 Myr, the oldest deposits thought to have been eroded from the Himalayan metamorphic mountain belt. This constraint on when erosion began has influenced models of the timing and diachrony of the India-Eurasia collision(6-8), timing and mechanisms of exhumation(9,10) and uplift(11), as well as our general understanding of foreland basin dynamics(12). But the depositional age of these basin sediments was based on biostratigraphy from four intercalated marl units(5). Here we present dates of 257 detrital grains of white mica from this succession, using the Ar-40-(39) Ar method, and find that the largest concentration of ages are at 36-40 Myr. These dates are incompatible with the biostratigraphy unless the mineral ages have been reset, a possibility that we reject on the basis of a number of lines of evidence. A more detailed mapping of this formation suggests that the marl units are structurally intercalated with the continental sediments and accordingly that biostratigraphy cannot be used to date the clastic succession. The oldest continental foreland basin sediments containing metamorphic detritus eroded from the Himalaya orogeny therefore seem to be at least 15-20 Myr younger than previously believed, and models based on the older age must be re-evaluated

Neutrino-Deuteron Scattering in Effective Field Theory at Next-to-Next-to Leading Order

We study the four channels associated with neutrino-deuteron breakup reactions at next-to-next to leading order in effective field theory. We find that the total cross-section is indeed converging for neutrino energies up to 20 MeV, and thus our calculations can provide constraints on theoretical uncertainties for the Sudbury Neutrino Observatory. We stress the importance of a direct experimental measurement to high precision in at least one channel, in order to fix an axial two-body counterterm.Comment: 32 pages, 14 figures (eps