Instream habitat use by blue duck (Hymenolaimus malacorhynchos) in a New Zealand river

1. The feeding habitat of a river specialist, blue duck (Hymenolaimus malacorhynchos (Gmelin 1789): Anatidae), was characterized in terms of water depth and velocity on eight occasions over a 13-month period in a river in the central North Island of New Zealand using video to record activity and relocate feeding sites. 2. Of the five feeding activities identified (‘pecking’, ‘grazing’, ‘head-dipping’, up-ending’ and ‘diving’), adult blue duck used mostly head-dipping (> 60% of feeding events on all dates), although diving or grazing from submerged surfaces of exposed boulders comprised major proportions of feeding behaviour (up to 33%) on occasions. Variations in feeding behaviour between dates partly reflected changes in antecedent flow conditions and the annual cycle of the birds. 3. Grazing and diving occurred in significantly faster water (mostly 0.3–0.45 m s^–1) and at significantly different depths (mean = 0.10 and 0.55 m, respectively) than head-dipping (0.20 m depth and 0.28 m s^–1 velocity). Adult feeding depths and velocities at four sites on different dates averaged 0.20 m and 0.31 m s^–1, respectively. Most feeding by 3–4-week-old ducklings occurred over a similar distribution of water velocities to adults but over a wider range of depths. 4. Adult birds fed in significantly shallower and lower velocity water than was available on the two dates that comparisons could be made. Ducklings also fed over a slower range of water velocities but were not selective in terms of water depth. 5. Energetically more expensive search methods were employed at times of high apparent energy demand to access flow microhabitats where larger bodied prey were more likely to be encountered. 6. These data indicate that, like other aquatic organisms, river birds can be influenced by basic hydraulic elements of river flow, but show at the same time that adult blue duck can accommodate variable lotic environments efficiently.     

The relationship between geographic area and the latitudinal gradient in species richness in New World birds

One hypothesis for the latitudinal gradient in species richness observed in most animal taxa is that the richness of a region is determined by its geographic area. However, the relationship between geographic area and species richness across regions is generally weak. It has been suggested that this is because species from the tropics spill out of this region of high richness, artificially inflating the richness of other regions. This generates the interesting prediction that the area and richness of extra-tropical regions should be more strongly correlated if tropical species are excluded. We test this prediction using the avifauna of the New World. We find that there is indeed a relationship between the land area and species richness of a region once tropical species are excluded. This relationship is independent of the latitude and productivity of regions. Both latitude and productivity can explain variance in richness unexplained by land area. There is no relationship between land area and species richness if tropical species are not excluded from the analysis, suggesting that tropical species do indeed mask the relationship between richness and area. We conclude that our results generally support the geographic area hypothesis, although tests of its other predictions and on other land masses are required.     

Host size selection and sex allocation behaviour among parasitoid trophic levels

Abstract.

• 1 Sex ratio in the ectoparasitoid Chrysocharis nephereus, when attacking larvae of the lepidopteran leafminer Cameraria jacintoensis inhabiting the scrub oak Quercus dumosa, varies as a function of host size.
• 2 Female progeny are overproduced on large hosts and male progeny are overproduced on small hosts. Whether a host is perceived as large or small depends on the distribution of sizes of hosts encountered. Lastly, the primary sex ratio is consistently male biased. These patterns are not due to variation in progeny sex specific mortality, but are probably a result of maternal choice.
• 3 Female wasp size increases at a greater rate than does male wasp size with an equivalent increase in C.jacintoensis larval size. Although the average adult longevity of female C.nephereus is significantly greater than the average longevity of male C.nephereus, male wasp longevity increases at a greater rate than does female wasp longevity with an equivalent increase in C.jacintoensis larval size.
• 4 Chrysocharis nephereus developing on large C.jacintoensis are more likely to be hyperparasitized by Closterocerus sp. than are C.nephereus developing on smaller sized C.jacintoensis. Closterocerus sp. hyperparasitize female C.nephereus progeny with significantly greater frequency than male progeny.
• 5 Female C.nephereus overproducing daughters on large hosts and sons on small hosts may experience fitness trade-offs between the benefits associated with producing offspring on large hosts and costs associated with these offspring becoming hyperparasitized.

     

In situ localization of the sites of paraquat action

Abstract. Effects of paraquat were monitored by electron microscopic, cytochemical, and in vivo spectrophotometric procedures. Electron microscopy of paraquat-treated pea leaf discs indicates that the chloroplasts are affected primarily with both thylakoid dilation and apparent lamellar fusions, resulting in a 'honeycomb' of lamellae. No ultra-structural effects were noted when leaf discs were incubated in both DCMU and paraquat. Paraquat-induced peroxide was located cytochemically along the stroma lamellae, on the ends of the grana stack and in the dilated thylakoids. Less destruction was noted in those samples where peroxide was precipitated by cerium chloride, indicating that peroxide or one of its products is one of the major causes of paraquat toxicily. In C₄ plants mesophyll plastids exhibited much more peroxide deposition than was detected in bundle sheath plastids. No plastid peroxide depositions were noted in a photobleaching mutant that is resistant to paraquat. In situ cytochrome f oxidation-reduction was followed during paraquat treatments and resulted in a hastening of the dark re-reduction of cytochrome f after only 1 h of treatment. This effect was prevented by DCMU or CeCI₃. Electron transport, as measured by cytochrome f oxidation-reduction, was completely obliterated by a 24 h paraquat treatment. These in situ studies on paraquat confirm previous studies that the primary effect in the light is on the plastid and involves peroxide or further products generated by peroxide.     

DNA probes for species identification of mosquitoes in the Anopheles gambiae complex

Abstract. Identification of species within the Anopheles gambiae Giles species complex is essential for the correct evaluation of malaria vector ecology studies and control programmes. The development of DNA probes to distinguish species of the An.gambiae complex is described. Genomic libraries were prepared for four members of the An.gambiae complex. These were screened using radiolabeled DNA from different species of An. gambiae sensu lato and a number of clones selected on the basis of their species specificity. These clones could be divided into two groups, each containing homologous sequences. Sequences homologous to group 1 inserts are highly reiterated in the genomes of Anopheles arabiensis Patton and Anopheles merus Dönitz, present in low copy number in Anopheles melas Theobald, but were not detected in Anopheles gambiae sensu stricto. Studies on the organization of this sequence in the genome of An.arabiensis show that homologous sequences are male specific and interspersed within the chromatin. Sequences homologous to group 2 inserts are highly repeated in the genomes of An.merus and An.melas, but present in low copy number in An.gambiae s.s. and An.arabiensis. Group 2 homologous sequences are not sex-specific in the species tested and appear to be tandemly repeated. When used as hybridization probes, these sequences provide a sensitive means for the identification of species within the Anopheles gambiae complex.     

PATTERNS IN THE GEOGRAPHICAL RANGES OF SPECIES

1. A growing number of studies have documented patterns in species geographic ranges relevant to the study of community structure. These include patterns in the frequency of geographic ranges of different sizes, and in the interaction of range sizes with population abundances and variabilities, body sizes, trophic characteristics and extinction probabilities.
2. Agreement between hypothesized and observed relationships is reasonably good, but we do not know how general the patterns are. Analysis of patterns has focused upon a few taxonomic groups, a bias largely resulting from a lack of information on the geographic distributions of most taxa.
3. Many of the patterns are interrelated, and although theoretical bases to all the patterns can be suggested, it is possible that some are artifacts.
4. Taylor power plots give us a means of making predictions about population behaviour as it pertains to geographic ranges. Some of these predictions suggest that previous conceptions of such interactions have been too narrow, but empirical analyses of these patterns will be hampered by the difficulty of measuring population variability.
5. In general, our knowledge of the structure, and spatial and temporal behaviour, of species geographic ranges remains poor.     

Ultrastructure of the Erythrocytic Stages of Plasmodium malariae1

This report describes the fine structure of the erythrocytic stages of Plasmodium malariae. Erythrocytic parasites from a naturally acquired human infection and an experimentally infected chimpanzee were morphologically indistinguishable and structurally similar to other primate malarias. New findings included observations of highly structured arrays of merozoite surface coat proteins in the cytoplasm of early schizonts and on the surface of budding merozoites and the presence of knobs in the membranes of Maurer's clefts. Morphological evidence is presented suggesting that proteins are transported between the erythrocyte surface and intracellular parasites via two routes: one associated with Maurer's clefts for transport of membrane-associated knob material and a second associated with caveolae in the host cell membrane for the import or export of host- or parasite-derived substances through the erythrocyte cytoplasm.