Turbulence,displacement, death and worms: a day in the life of a fluvial Carboniferous bivalve

Kane, I.A. 2010: Turbulence, displacement, death and worms: a day in the life of a fluvial Carboniferous bivalve. Lethaia, Vol. 43, pp. 381–395. In the Pennsylvanian Rough Rock Flags and Rough Rock of northern England trace fossils attributed to the non‐marine bivalve Carbonicola are found. Carbonicola, recorded by Lockeia and associated trace fossils, lived a semi‐infaunal lifestyle and thus were influenced by both the sediment in which they were hosted, and the currents which supplied their nutrients and oxygen. A number of palaeocurrent indictors are commonly associated with Lockeia: (1) downstream inclination of vertical burrows; (2) palaeoflow‐parallel orientation of long axes; (3) steeper scouring and higher sediment surface on the upstream side; and (4) diffuse lamination downstream of the trace or more widespread downstream erosion. Semi‐infaunal, Carbonicola bivalves were partly exposed to the prevailing flow and acted as bed defects; flow separation and acceleration enhanced flow turbulence around the bivalve leading to erosion and the development of a variably developed fan‐shaped zone of scour immediately downstream. Disturbance and destabilization of sediment in this way may have affected bivalves immediately downstream, plausibly explaining the relatively regular spacing pattern of individual or clustered Lockeia, exposed on bedding planes and revealed by nearest neighbour analyses. Bivalves that did not survive high‐energy flow events were either trapped within the sediment, or transported downstream and deposited in lower energy environments within the otherwise high‐energy deposits of the Rough Rock.     

Linkage disequilibrium and natural selection for mimicry in the Batesian mimic Hypolimnas misippus (L.) (Lepidoptera: Nymphalidae) in the Afrotropics

On two occasions, on opposite sides of the African continent (Cape Coast, Ghana, and Dar es Salaam, Tanzania), high adult population densities in the polymorphic butterfly Hypolimnas misippus (a presumed mimic of Danaus chrysippus) were followed by linkage disequilibrium in combinations of fore‐ and hindwing colour patterns. On both occasions, disequilibrium was caused by significant changes in morph frequencies favouring rarer and more mimetic forms. Recaptures were too few for analysis at Dar, although the changes there took place within a single generation and must have been the result of differential survival. Recapture rate data and survival rate estimates at Cape Coast support the hypothesis that selective predation was responsible, as does the observation of synchronous linkage disequilibrium at Dar in the model D. chrysippus, indicating parasitic mimicry. There was clear selection for the perfection of mimicry for forewings at Dar and for hindwings at Cape Coast. Disequilibrium is also reported for two other sites, Legon (Ghana) and Boksburg (South Africa) and, in all four sites, it was associated with an increase in the most mimetic forms. New chemical evidence is presented to support the contention that D. chrysippus is a defended model. Although all the evidence leads to the conclusion that H. misippus is a Batesian mimic of D. chrysippus, many questions remain, particularly with regard to the identity of predators, the episodic nature of selective predation events, and their apparent lack of lasting and significant impact on overall gene frequencies. We conclude that H. misippus presents both challenges and opportunities for studies on mimicry, and we suggest that linkage disequilibrium can be a useful generic indicator for Gestalt predation on polymorphic prey. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 100 , 180–194.     

The influence of male age on within‐pair and extra‐pair paternity in passerines

Although male age has often been found to predict success in gaining extra‐pair paternity, it is unclear whether this gain is associated with an individual’s success in avoiding cuckoldry. We examined the relationship between male age and both within‐ and extra‐pair paternity in passerines using a meta‐analytical approach. There was a positive correlation between male age and success in extra‐pair paternity but little evidence for an association between male age and within‐pair paternity. In addition, effect sizes for male within‐pair paternity and male extra‐pair paternity were not significantly correlated. Thus, factors that predict success in obtaining extra‐pair paternity, such as male age, may not necessarily predict success in avoiding cuckoldry.     

Features of the underwater light climate just below the surface in some New Zealand inland waters

1. Using sampling rates of 8–64 Hz we found clear indications of extensive and high frequency fluctuations of underwater photosynthetically active radiation (PAR) just below the surface (0.016–1.1 m) in some New Zealand water bodies. High variability and flashing occurred down to at least 3 m depth.
2. PAR variability increased under the influence of bright sunshine if wind roughening of the surface took place. Concomitantly, the average PAR levels declined by about 10%. However, even when the surface was shaded, high variability of PAR persisted.
3. Under a calm surface, PAR irradiance followed a log normal distribution. This occurred independently of the presence of direct sunlight. However, when the surface was roughened by wind in sunshine, PAR immediately switched to a Gumbel (extreme value type EV1) distribution.
4. Neither wave action nor wave focusing of incident irradiance would explain the wide range of PAR close to the water surface, although both factors add to the PAR variability.
5. The data indicate that transmittance through the surface is highly variable at the temporal and spatial scales studied, and that the irregularity of the air–water interface is instrumental in bringing about the observed fluctuations of PAR just below the surface.     

Movement patterns of Common Crossbills Loxia curvirostra in Europe

Over much of Europe, Common Crossbills Loxia curvirostra depend primarily on the seeds of Norway Spruce Picea abies , and their breeding and movement patterns are governed largely by the cropping patterns of this tree species. Good cone crops occur only every few years in particular areas, but in different years in different areas. The main period of movement is in summer, when the previous year's crop is coming to an end, and a new crop is forming in different areas. In years when the Norway Spruce crop is poor over a wide area, and when Common Crossbills are abundant, they leave the boreal forest in large numbers, and appear as irruptive migrants in southwest Europe, with at least 40 invasions reaching Britain in the 120-year period 1881–2000. On irruptions the main migration axis is from northeast to southwest or west. Recoveries of birds ringed mainly in Germany confirm that these birds do not return to the boreal forest in northern Russia in the same calendar year as their irruption, but do so only in a later calendar year, when a new Norway Spruce crop is becoming available. The findings agree with an earlier interpretation of Common Crossbill movements, but not with an alternative hypothesis that irrupting Common Crossbills return to their region of origin in the same calendar year as the outward movement. Recoveries also suggest that some individual Common Crossbills may have bred in widely separated localities in different years (records up to 3170 km apart), and sometimes in localities far removed from their natal sites (records up to 2950 km apart).     

Flow- and substratum-mediated movement by a stream insect

1. In streams subject to frequent hydrologic disturbance, the ability of benthic invertebrates to disperse within the channel is key to understanding the mechanisms of flow refugium use and population persistence. This study focuses on crawling invertebrates, the effects on movement of abiotic factors (specifically, flow near the stream bed and bed micro‐topography) and the consequences for dispersal. 2. In a large flume, we observed individual cased caddisflies, Potamophylax latipennis, moving in fully turbulent flows over a precise replica of a water‐worked surface. From maps of movement paths, we quantified crawling behaviour and entrainment, and the influence of bed micro‐topography. We manipulated discharge and tested its effect on movement, linear displacement and areal dispersal. The highest discharge treatment was a disturbance to the caddis; the lowest discharge was not. Crawling behaviours were used to parameterise random walk models and estimate population dispersal, and to test the effects of abiotic factors on movement. 3. Bed micro‐topography influenced crawling in several ways. Caddis spent most of their time at the junctions between proud particles and the adjacent plane bed. The frequency distribution of turn angles was bimodal, with modal values approximating the angle required to travel around median‐sized particles. Larvae generally crawled downstream, but crawling direction relative to the flow was skewed by bed micro‐topography and was not directly downstream, unlike drift. 4. Caddis crawled for most of the time and discharge affected almost every aspect of their movement. As discharge increased, caddis crawled less often, more slowly and over shorter distances; they also became entrained more frequently and over greater distances. With increased discharge, caddis spent proportionately less time at the junctions between proud particles and the adjacent plane bed, and more time on the tops and sides of proud clasts. This is curious as most entrainment occurred from the tops and sides of clasts and entrainment is generally considered to be disadvantageous during disturbances. 5. Linear displacement (drift and entrainment combined) was downstream, but the relation between total displacement and discharge was complex. Total displacement decreased at intermediate discharge as crawling decreased, but increased at high discharge as entrainment and drift played a greater role in movement. 6. Within‐stream dispersal via crawling contained elements of both a correlated random walk (we observed directional persistence in turn angles) and a biased random walk (we observed downstream bias in move direction angles) and was best described as a biased correlated random walk. Dispersal was inversely related to discharge, suggesting that the ability of P. latipennis to crawl into flow refugia on the streambed is reduced at high flow.     

Seasonal variation in the migration strategies of the green lacewing Chrysoperla carnea species complex

Abstract.  1. Insect migration strategies are generally poorly understood due to the propensity for high-altitude flight of many insect species, and the technical difficulties associated with observing these movements. While some progress has been made in the study of the migration of important insect pests, the migration strategies of insect natural enemies are often unknown.
2. Suction trapping, radar monitoring, and high-altitude aerial netting were used to characterise the seasonal migrations in the U.K. of an assemblage of aphid predators: three green lacewings in the Chrysoperla carnea species complex.
3. Chrysoperla carnea sens. str . was found to be very abundant at high altitudes during their summer migration, and some individuals were capable of migrating distances of ≈ 300 km during their pre-ovipositional period. In contrast, high-altitude flights were absent in the autumn migration period, probably due to a behavioural adaptation that increases the probability that migrants will encounter their over-wintering sites. The other two species in the complex, C. lucasina and C. pallida , were much rarer, making up ≈ 3% of the total airborne populations throughout the study period.
4. The summer migration of C. carnea sens. str . was not directly temporally associated with the summer migration of its cereal aphid prey, but lagged behind by about 4 weeks. There was also no evidence of spatial association between aphid and lacewing populations.
5. The results show that to understand the population ecology of highly mobile insect species, it is necessary to characterise fully all aspects of their migration behaviour, including the role of high-altitude flights.