Terrigenous sediment-dominated reef platform infilling: an unexpected precursor to reef island formation and a test of the reef platform size–island age model in the Pacific

Low-lying coral reef islands are considered highly vulnerable to climate change, necessitating an improved understanding of when and why they form, and how the timing of formation varies within and among regions. Several testable models have been proposed that explain inter-regional variability as a function of sea-level history and, more recently, a reef platform size model has been proposed from the Maldives (central Indian Ocean) to explain intra-regional (intra-atoll) variability. Here we present chronostratigraphic data from Pipon Island, northern Great Barrier Reef (GBR), enabling us to test the applicability of existing regional island evolution models, and the platform size control hypothesis in a Pacific context. We show that reef platform infilling occurred rapidly (~4–5 mm yr⁻¹) under a “bucket-fill” type scenario. Unusually, this infilling was dominated by terrigenous sedimentation, with platform filling and subsequent reef flat formation complete by ~5000 calibrated years BP (cal BP). Reef flat exposure as sea levels slowly fell post highstand facilitated a shift towards intertidal and subaerial-dominated sedimentation. Our data suggest, however, a lag of ~1500 yr before island initiation (at ~3200 cal BP), i.e. later than that reported from smaller and more evolutionarily mature reef platforms in the region. Our data thus support: (1) the hypothesis that platform size acts to influence the timing of platform filling and subsequent island development at intra-regional scales; and (2) the hypothesis that the low wooded islands of the northern GBR conform to a model of island formation above an elevated reef flat under falling sea levels.

     

Quantification of Bt-endotoxin exposure pathways in carabid food webs across multiple transgenic events

Despite the reported specificity of Bacillus thuringiensis proteins against target pests, a number of studies have indicated that the uptake of Bt-endotoxins from bioengineered crops could have negative effects on natural enemies. It is therefore essential to quantify exposure pathways in non-target arthropod food webs across multiple transgenic events. Adult ground beetles (Coleoptera: Carabidae) were collected from transgenic corn fields expressing lepidopteran-specific Cry1Ab, coleopteran-specific Cry3Bb1, and both Cry1Ab and Cry3Bb1 (stacked event), as well as a non-transgenic isoline. Carabid gut-contents were screened for Cry1Ab Bt-endotoxin using enzyme-linked immunosorbent assay. Significant numbers of carabids tested positive for Cry1Ab from the lepidopteran-specific field: Harpalus pensylvanicus (39%, 25 of 64), Stenolophus comma (4%, 6 of 136), Cratacanthus dubius (50%, 1 of 2), Clivina bipustulata (50%, 1 of 2), and Cyclotrachelus sodalis (20%, 1 of 5). The highest proportion of Bt-endotoxin uptake was 4–6 weeks post-anthesis. Only one species, H. pensylvanicus (5%, 4 of 75), screened positive for Cry1Ab from the stacked line, despite similar expression of this endotoxin in plant tissue harvested from both lines. This difference in Cry1Ab uptake could be due to changes in the non-target food web or differential rates of Bt-endotoxin decay between genetic events. This study has quantified the differential uptake of Cry1Ab Bt-endotoxin by the carabid community across multiple transgenic events, thus forming the framework for future risk-assessment of transgenic crops.     

Demographic analysis of reproduction in Nearctic and Palearctic populations of Coccinella septempunctataand Propylea quatuordecimpunctata

Coccinella septempunctata and Propylea quatuordecimpunctata in North America have documented invasive capacity. Studies are needed to identify relevant life-history parameters responsible for their successful spatial spread. This study is a detailed analysis of phenotypic variation in reproductive traits of several Nearctic and Palearctic populations of these two coccinellid species. From 47 to 61% of C. septempunctata females laid their first batch of eggs within the first two weeks of their adult life. Within P. quatuordecimpunctatapopulations, 56 to 83% of females initiated oviposition within 2 weeks. The remaining females either had preoviposition periods > 2 weeks or never laid eggs during a 60-day observation period. Analysis of daily fecundity revealed differences in oviposition strategies among females within each population. Repeatability estimates of daily parity for C. septempunctata populations were 0.32 for Iowa (USA), 0.35 for Delaware (USA), 0.28 for France, and 0.33 for Ukraine. Repeatability estimates for P. quatuordecimpunctata populations were 0.35 for Canada, 0.25 for France, and 0.33 for Turkey. The within-female component accounted for most of the variation in daily parity; this was due to female variability in their daily oviposition rates. This revised version was published online in July 2006 with corrections to the Cover Date.     

Ecology and management of mahogany (Swietenia macrophylla King) in the Chimanes Forest, Bed, Bolivia

Mahogany ( Swietenia macrophylla King) regenerates in areas of erosion on high terraces and in forest killed by flooding and deposition of alluvial sediments in the Chimanes Forest, Bolivia. These hydrological disturbances are patchy, and only one of five stands of mahogany that we inventoried was regenerating. Mahogany survives these disturbances significantly better than the common tree species. The long time between disturbances appears to favour late maturation. Mahogany trees allocate little photosynthates to reproduction until they are very large emergents, at least 80 cm in diameter. The episodic nature of the regeneration sites means that mahogany stands are composed of one or a few cohorts, which are vulnerable to overharvesting, particularly with the current use of a minimum cutting diameter to regulate harvest. The delayed onset of fecundity means that the small trees that escape harvest are not very fecund, resulting in minimal seed input to logged forest. Only 7–9% of the gaps created by logging contain natural regeneration after 20 + yr. A successful management plan for mahogany would entail a monocyclic harvest, with a rotation age of 100 + years, the estimated time that it takes for trees to achieve commercial size in natural forest. Since the number of seed trees that will be left is small, they should be concentrated in sites that are likely to be conducive to natural regeneration, such as near rivers and flood damaged forest. Seed production will be maximized for a given basal area (opportunity cost to loggers) if trees c. 110 cm dbh are selected as seed trees. The mahogany stocks in the Chimanes Forest are nearly exhausted, but the findings of this study could be used to help rebuild the mahogany populations, or to design management plans for the commercial species that have similar ecologies to mahogany.     

Comparative Prey Suitability ofOstrinia nubilalisEggs andAcyrthosiphon pisumforColeomegilla maculata

The effects ofOstrinia nubilalis(Hübner) (Lepidoptera: Pyralidae) eggs andAcyrthosiphon pisum(Harris) (Homoptera: Aphididae), when provided as single prey species and in combination, on life history characteristics ofColeomegilla maculataDeGeer (Coleoptera: Coccinellidae) larvae and adults were quantified. Preimaginal development was not influenced by the larval prey regime; development at 26 ± 1°C was completed in approximately 13.5 days onO. nubilaliseggs,A. pisum,orA. pisumalternated daily withO. nubilaliseggs. The resulting adults weighed 13.0, 10.7, and 12.5 mg when reared onO. nubilaliseggs,A. pisum,andA. pisumalternated daily withO. nubilaliseggs, respectively. Eighteen percent of the individuals died when reared onA. pisum,28% died when reared onO. nubilaliseggs, and 22% died when fedA. pisumalternated daily withO. nubilaliseggs. Seven adult diet combinations, based on diet regimes of larvae and adults, did not cause significant differences in preoviposition period, interoviposition period, and the number of days on which eggs were laid. Total fecundity was influenced both by larval and adult diet. The diet that resulted in highly fecund females wasA. pisumalternated daily withO. nubilaliseggs for larvae andO. nubilaliseggs for adults. FemaleC. maculatafedO. nubilaliseggs had the highest intrinsic rate of increase and net reproductive rate.