ASPECTS OF COMPARATIVE PLANKTON ECOLOGY IN CASCADING MGENI RIVER RESERVOIRS (MIDMAR,ALBERT FALLS,AND NAGLE): AN OVERVIEW

Summary

An overview of a three year study of abundance, community structure and succession of zooplankton and phytoplankton in relation to physical limnological conditions in Lakes Midmar and Albert Falls is presented, along with findings on zooplankton from a nine month study of Lake Nagle. Physical stability increased between Midmar (mean summer N² = 6.55 × 10⁴ s²) and Albert Falls (N² = 8.70 × 10⁴ s²), in line with elevations in water temperature. Phytoplankton richness and diversity was similar in these reservoirs, although zooplankton species richness increased downstream. Abundance levels of both phyto- and zoo-plankton were broadly comparable in these two reservoirs. In Midmar and Albert Falls, overall mean (± SD) chlorophyll levels were 3.60 ± 1.54 and 3.41 ± 1.41 μg 1¹, with corresponding overall average zooplankton standing stocks of 0.85 and 0.76 g m² dry mass, dropping to 0.54 g m² in Nagle (for which spring to midsummer data are missing).

Ruderal and colonist phytoplankters were persistently dominant both in Midmar and Albert Falls, in keeping with the continuous (if incomplete) mixing patterns evident in these reservoirs. Few stress tolerant algae occurred. The summer ruderal assemblage was unexpectedly dominated by diatoms in the physically more stable conditions of Albert Falls, but not Midmar. Mean zooplankton grazer-induced instantaneous mortality rates for planktonic algae for the whole study were estimated (by regression predictions) as 0.17 d¹ in both lakes. Phytoplankton was not studied in Nagle.

Changes in zooplankton community structure between Midmar and Nagle largely involved progressive increases in the contribution of smaller-bodied cladocerans (comprising both sequentially smaller species of Daphnia (D. pulex, D. longispina, D. laevis), and additional genera such as Diaphanosoma, Ceriodapnia, Moina and Bosmina). As with a parallel progressive switch between Metadiaptomus meridianus and Tropodiaptomus spectabilis over this series of reservoirs, (and the temporal separation of “co-existing” populations in Albert Falls), which has been shown experimentally to be strongly temperature-linked, changes in absolute temperature are implicated as a primary causal factor in the shifts in cladoceran species composition. Temporal occurrences of these species also indicate the primacy of temperature.     

Cave-adapted evolution in the North American amblyopsid fishes inferred using phylogenomics and geometric morphometrics

Cave adaptation has evolved repeatedly across the Tree of Life, famously leading to pigmentation and eye degeneration and loss, yet its macroevolutionary implications remain poorly understood. We use the North American amblyopsid fishes, a family spanning a wide degree of cave adaptation, to examine the impact of cave specialization on the modes and tempo of evolution. We reconstruct evolutionary relationships using ultraconserved element loci, estimate the ancestral histories of eye-state, and examine the impact of cave adaptation on body shape evolution. Our phylogenomic analyses provide a well-supported hypothesis for amblyopsid evolutionary relationships. The obligate blind cavefishes form a clade and the cave-facultative eyed spring cavefishes are nested within the obligate cavefishes. Using ancestral state reconstruction, we find support for at least two independent subterranean colonization events within the Amblyopsidae. Eyed and blind fishes have different body shapes, but not different rates of body shape evolution. North American amblyopsids highlight the complex nature of cave-adaptive evolution and the necessity to include multiple lines of evidence to uncover the underlying processes involved in the loss of complex traits.     

Effect of Chronic Caloric Restriction on the Circadian Regulation of Physiological and Behavioral Variables in Old Male B6C3F1 Mice

The circadian rhythms of food and water consumption, the number of feeding and drinking episodes, oxygen consumption, carbon dioxide production, respiratory quotient, gross motor activity, and body temperature were measured in male B6C3F, mice that were fed ad libitum (AL) or fed a caloric-restricted diet (CR). The CR regimen (60% of the normal AL consumption) was fed to mice during the daytime (5 hr after lights on). CR animals exhibited fewer feeding episodes but consumed more food per feeding bout and spent more total time feeding than AL mice. It appears that CR caused mice to change from their normal “nibbling behavior” to meal feeding. Compared to AL animals, the mean body temperature was reduced in CR animals, while the amplitude of the body temperature rhythm was increased. Spans of reduced activity, metabolism, and body temperature (torpor) occurred in CR mice for several hours immediately before feeding, during times of high fatty acid metabolism (low RQ). The acute availability of exogenous substrates (energy supplies) seemed to modulate metabolism shifting metabolic pathways to promote energy efficiency. CR was also associated with lower DNA damage, higher DNA repair, and decreased proto-oncogene expression. Most of the circadian rhythms studied seemed to be synchronized primarily to the feeding rather than the photoperiod cycle. Night-time CR feeding was found to be better than daytime feeding because the circadian rhythms for AL and CR animals were highly synchronized when this regimen was used.     

Can temperate insects take the heat? A case study of the physiological and behavioural responses in a common ant, Iridomyrmex purpureus (Formicidae), with potential climate change

Insects in temperate regions are predicted to be at low risk of climate change relative to tropical species. However, these assumptions have generally been poorly examined in all regions, and such forecasting fails to account for microclimatic variation and behavioural optimisation. Here, we test how a population of the dominant ant species, Iridomyrmex purpureus, from temperate Australia responds to thermal stress. We show that ants regularly forage for short periods (minutes) at soil temperatures well above their upper thermal limits (upper lethal temperature = 45.8 ± 1.3 °C; CT_max = 46.1 °C) determined over slightly longer periods (hours) and do not show any signs of a classic thermal performance curve in voluntary locomotion across soil surface temperatures of 18.6–57°C (equating to a body temperature of 24.5–43.1 °C). Although ants were present all year round, and dynamically altered several aspects of their thermal biology to cope with low temperatures and seasonal variation, temperature-dependence of running speed remained invariant and ants were unable to elevate high temperature tolerance using plastic responses. Measurements of microclimate temperature were higher than ant body temperatures during the hottest part of the day, but exhibited a stronger relationship with each other than air temperatures from the closest weather station. Generally close associations of ant activity and performance with microclimatic conditions, possibly to maximise foraging times, suggest I. purpureus displays highly opportunistic thermal responses and readily adjusts behaviour to cope with high trail temperatures. Increasing frequency or duration of high temperatures is therefore likely to result in an immediate reduction in foraging efficiency. In summary, these results suggest that (1) soil-dwelling temperate insect populations may be at higher risks of thermal stress with increased frequency or duration of high temperatures resulting from climate change than previously thought, however, behavioural cues may be able to compensate to some extent; and (2) indices of climate change-related thermal stress, warming tolerance and thermal safety margin, are strongly influenced by the scale of climate metrics employed.     

Cattle as capital

Livestock have been seen either as a source of subsistence or as commodities in a process of capital accumulation. Is the association of cattle with capital just a poetic metaphor or the grounds for a serious analysis of third world herding communities? Economists are divided between an orthodox notion of capital as physical equipment and a Marxist emphasis on social relations dominated by money. Nevertheless, some anthropologists assert that herders should be conceptualised as capitalists. The key elements in the Western folk concept of capital are: increase, money, physical stock and preoccupation with future time. Despite the plausible link between herding and some of these ideas, we conclude that, as an analytical category, ‘capital’ is too loaded and diffuse for fruitful application to the analysis of pastoralist production.     

Copper complexing capacity in fresh-waters using the catechol-cathodic stripping voltammetric method

Abstract

The catechol-cathodic stripping voltammetric (CSV) method for measurement of the copper complexing capacity of marine and estuarine waters, has been modified and applied to fresh-waters. The optimum catechol concentration needed was the major difference between the two methods. It was found necessary to separately optimise the catechol concentration for each of the three fresh-water samples tested, presumably because of the much greater differences in the concentration of complexing ligands in fresh-water compared with marine or estuarine waters. This limits the usefulness of the CSV method for the determination of the complexing capacity of fresh-waters.

The total ligand concentration ([L_t]) and conditional stability constants (*K) derived for the three fresh-waters are compared with similar data obtained using an anodic stripping voltammetric (ASV) method. The set of copper-binding ligands determined using the CSV method were slightly lower in concentration, but stronger binding, than those obtained using the ASV method (CSV: [L_t] 0.04–0.06 μM, log K(pH 6) 8.9–9.4; ASV: [L_t] 0.11–0.17 μM, log *K(pH 6) 7.9–8.1).     

Foraging area fidelity for Kemp's ridleys in the Gulf of Mexico

For many marine species, locations of key foraging areas are not well defined. We used satellite telemetry and switching state‐space modeling (SSM) to identify distinct foraging areas used by Kemp's ridley turtles (Lepidochelys kempii) tagged after nesting during 1998–2011 at Padre Island National Seashore, Texas, USA (PAIS; N = 22), and Rancho Nuevo, Tamaulipas, Mexico (RN; N = 9). Overall, turtles traveled a mean distance of 793.1 km (±347.8 SD) to foraging sites, where 24 of 31 turtles showed foraging area fidelity (FAF) over time (N = 22 in USA, N = 2 in Mexico). Multiple turtles foraged along their migratory route, prior to arrival at their “final” foraging sites. We identified new foraging “hotspots” where adult female Kemp's ridley turtles spent 44% of their time during tracking (i.e., 2641/6009 tracking days in foraging mode). Nearshore Gulf of Mexico waters served as foraging habitat for all turtles tracked in this study; final foraging sites were located in water <68 m deep and a mean distance of 33.2 km (±25.3 SD) from the nearest mainland coast. Distance to release site, distance to mainland shore, annual mean sea surface temperature, bathymetry, and net primary production were significant predictors of sites where turtles spent large numbers of days in foraging mode. Spatial similarity of particular foraging sites selected by different turtles over the 13‐year tracking period indicates that these areas represent critical foraging habitat, particularly in waters off Louisiana. Furthermore, the wide distribution of foraging sites indicates that a foraging corridor exists for Kemp's ridleys in the Gulf. Our results highlight the need for further study of environmental and bathymetric components of foraging sites and prey resources contained therein, as well as international cooperation to protect essential at‐sea foraging habitats for this imperiled species.     

Stand-replacing wildfires alter the community structure of wood-inhabiting fungi in southwestern ponderosa pine forests of the USA

Increases in stand-replacing wildfires in the western USA have widespread implications for ecosystem carbon (C) cycling, in part because the decomposition of trees killed by fire can be a long-term source of CO₂ to the atmosphere. Knowledge of the composition and function of decay fungi communities may be important to understanding how wildfire alters C cycles. We assessed the effects of stand-replacing wildfires on the community structure of wood-inhabiting fungi along a 32-yr wildfire chronosequence. Fire was associated with low species richness for up to 4 yr and altered species composition relative to unburned forest for the length of the chronosequence. A laboratory incubation demonstrated that species varied in their capacity to decompose wood; Hypocrea lixii, an indicator of the most recent burn, caused the lowest decomposition rate. Our results show that stand-replacing wildfires have long-term effects on fungal communities, which may have consequences for wood decomposition and C cycling.