Influence of food‐web structure on the biodegradability of lake sediment

1. Sediment plays a key role in internal nutrient cycling and eutrophication in lakes. However, studies focusing on the efficiency of the biomanipulation techniques for improving the control of primary producers have rarely examined the effects of changes in food‐web structure on the sediment biochemical composition and biodegradability. 2. In a 1‐year experiment conducted in large replicated mesocosms, we tested how the absence or presence of a zooplanktivorous fish (roach, Rutilus rutilus) affected the elemental composition and the potential biodegradability of recently deposited sediment in a eutrophic system. The potential biodegradability of these sediments was assessed in laboratory microcosms by measuring the production of CO₂ during 44‐day incubations. 3. The potential biodegradability of recently deposited sediment from the fish treatment was 60% higher than that from the fishless treatment. This higher biodegradability was corroborated by a higher annual loss of sediment in fish enclosures (36%) than in fishless ones (16%). Annual losses of carbon, nitrogen and organic phosphorous were higher for sediment from fish enclosures. 4. Carbon and nitrogen contents of sediment were higher for the fish treatment. In contrast, the sediment C/N ratio, one of the proxies used to estimate sediment biodegradability, did not differ between treatments. No relationship was observed between elemental composition of sediment and its potential biodegradability. This latter appeared to be more probably dependent on the biochemical composition of the sediment and especially on the content of labile compounds such as proteins, sugars and polyunsaturated fatty acids. The use of sterols as biomarkers revealed an important degradation by microorganisms of 1‐year‐old sediment from both fish and fishless treatments. 5. Our results revealed that fish biomanipulations might favour clear water states not only through a stronger top–down control on phytoplankton but also through a lower biodegradability of sediment reducing internal nutrient cycling.     

Developmental instability: measures of resistance and resilience using pumpkin (Cucurbita pepo L.)

Fluctuating asymmetry measures random deviations from bilateral symmetry, and thus estimates developmental instability, the loss of ability by an organism to regulate its development. There have been few rigorous tests of this proposition. Regulation of bilateral symmetry must involve either feedback between the sides or independent regulation toward a symmetric set point. Either kind of regulation should decrease asymmetry over time, but only right–left feedback produces compensatory growth across sides, seen as antipersistent growth following perturbation. Here, we describe the developmental trajectories of perturbed and unperturbed leaves of pumpkin, Cucurbita pepo L., grown at three densities. Covering one side of a leaf with aluminium foil for 24 h perturbed leaf growth. Reduced growth on the perturbed side caused leaves to become more asymmetrical than unperturbed controls. After the treatment the size-corrected asymmetry decreased over time. In addition, rescaled range analysis showed that asymmetry was antipersistent rather than random, i.e. fluctuation in one direction was likely to be followed by fluctuations in the opposite direction. Development involves right–left feedback. This feedback reduced size-corrected asymmetry over time most strongly in the lowest density treatment suggesting that developmental instability results from a lack of resilience rather than resistance.   © 2003 The Linnean Society of London, Biological Journal of the Linnean Society , 2003, 78, 27–41.     

Psychosurgery; present indications and future prospects

Although the advent and widespread use of ataractic drugs has more or less eclipsed lobotomy as a method of dealing with severe psychotic states, variations and adaptations of the operation still can be used with benefit in certain pretty well defined circumstances."Chemical lobotomy" and regressive electroshock bring about alterations in behavior superficially resembling those of lobotomy, but without the changes in personality that are the object of lobotomy. These desirable changes consist in increased extraversion, decreased preoccupation with self and decreased sensitivity to the opinions of others. With restricted operations, undesirable changes-the "frontal lobe syndrome"-do not occur. OPERATIVE FAILURES ARE DUE TO THREE MAIN CAUSES: (a) Preoperative emotional deterioration; (b) progress of the underlying disease; (c) relapse, possibly due to inadequate operation. Lobotomy is advisable if the patient does not show sustained improvement after a year of active treatment by other indicated means. The operation often represents the turning point in effective treatment. After the first year of ineffective treatment valuable time is being lost, with danger of fixation and deterioration. Then it is safer to operate than to wait. The future of psychosurgery lies in prompt application, in favorable patients, of selective operations that will reverse the trend of illness. There is particular need for further exploration of the temporal lobes in the hope of finding some procedure that will suppress hallucinations. Some 90 per cent of patients remaining in hospitals after psychosurgery are experiencing hallucinations. If these phenomena can be eliminated without producing serious personality defects, another large field for the application of psychosurgery will be opened.     

The comparative distribution and population dynamics in Trinidad of Sceliphron fistularium (Dahlbom) and S. asiaticum (L.) (Hymenoptera: Sphecidae)

Two sphecid wasps, Sceliphron asiaticum (L.) and S. fistularium (Dahlbom), which build mud nests and capture spider prey, had overlapping but distinctly different distributions in Trinidad. Sceliphron asiaticum was associated with drier (<2000 mm mean annual precipitation) and less forested areas. The analysis of existing data on these species revealed a similar differential distribution throughout the neotropics. Based on the dissection of their old nests collected at 42 sites in Trinidad, retrospective life tables were constructed and estimates of fecundity made. Sceliphron asiaticum tended to form denser nesting associations and, while most of the common parasitoids were shared, had overall higher developmental mortality. Although such mortality was density-dependent in both species, where the two wasps nested together mortality from Melittobia (Eulophidae, Chalcidoidea) was higher in S. asiaticum . Both species were protarrhenotokous and had similar field fecundities (7–8/♀), but the rate of oviposition may be greater in S. asiaticum since far less mud was used in the construction of its cells. Both species had >50° mortality of the females between emergence and starting to nest. The regulation of numbers of these wasps in relation to that of S. assimile (Dahlbom) in Jamaica is discussed.