An adaptive annual rhythm in the sex of first pigeon eggs

When the reproductive value of male and female offspring varies differentially, parents are predicted to adjust the sex ratio of their offspring to maximize their fitness (Trivers and Willard, Science 179:90–92, 1973). Two factors have been repeatedly linked to skews in avian offspring sex ratio. First, laying date can affect offspring sex ratio when the sexes differ in age of first reproduction, such that the more slowly maturing sex is overproduced early in the season. Second, position of the egg in the laying sequence of a clutch may affect sex ratio bias since manipulating the sex of the first eggs may be least costly to the mother. We studied both factors in two non-domesticated pigeon species. Both the Wood pigeon (Columba palumbus) and the Rock pigeon (Columba livia) have long breeding seasons and lay two-egg clutches. In the field, we determined the sex of Wood pigeon nestlings. In Rock pigeons, housed in captivity outdoors, we determined embryo sex after 3 days of incubation. On the basis of their sex-specific age of first reproduction, we predicted that males, maturing at older age than females, should be produced in majority early and females later in the year. This was confirmed for both species. The bias was restricted to first eggs. Rock pigeons produced clutches throughout the year and show that the sex of the first egg followed an annual cycle. To our knowledge, this study presents the first evidence of a full annual rhythm in adaptive sex allocation in birds. We suggest that this reflects an endogenous seasonal program in primary sex ratio controlled by a preovulatory mechanism.     

Reconstructing human contributions to accidents: the new view on error and performance

PROBLEM: How can human contributions to accidents be reconstructed? Investigators can easily take the position a of retrospective outsider, looking back on a sequence of events that seems to lead to an inevitable outcome, and pointing out where people went wrong. This does not explain much, however, and may not help prevent recurrence. METHOD AND RESULTS: This paper examines how investigators can reconstruct the role that people contribute to accidents in light of what has recently become known as the new view of human error. The commitment of the new view is to move controversial human assessments and actions back into the flow of events of which they were part and which helped bring them forth, to see why assessments and actions made sense to people at the time. The second half of the paper addresses one way in which investigators can begin to reconstruct people's unfolding mindsets. IMPACT ON INDUSTRY: In an era where a large portion of accidents are attributed to human error, it is critical to understand why people did what they did, rather than judging them for not doing what we now know they should have done. This paper helps investigators avoid the traps of hindsight by presenting a method with which investigators can begin to see how people's actions and assessments actually made sense at the time.     

Macroglomeruli for fruit odors change blend preference in Drosophila

The olfactory circuitry of Drosophila melanogaster is becoming increasingly clear. However, how olfactory processing translates into appropriate behavioral responses is still poorly understood. Using a sibling species approach, we tested how a perturbation in the olfactory circuitry affects odor preference. In a previous study, we found that the sibling species of D. melanogaster, the specialist D. sechellia, overrepresents a sensillum, ab3, the A neuron of which is sensitive to hexanoate esters, characteristic of the species’ sole host, the Morinda citrifolia fruit. Concordantly, the corresponding glomerulus, DM2, is enlarged. In this study, we found that the ab3B neuron, the expansion of which was previously assumed to be pleiotropic and of no ecological significance, is in fact tuned to another morinda fruit volatile, 2-heptanone (HP). Axons of this neuron type arborize in a second enlarged glomerulus. In behavioral experiments we tested how this has affected the fly’s odor preference. We demonstrate that D. sechellia has a reversed preference for the key ligands of these macroglomeruli, especially at high concentrations. Whereas D. melanogaster was repelled by high concentrations of these odors, D. sechellia was highly attracted. This was the case for odors presented singly, but more notably for blends thereof. Our study indicates that relatively simple changes, such as a shift in sensillar abundance, and concordant shifts in glomerular size, can distort the resulting olfactory code, and can lead to saltatory shifts in odor preference. D. sechellia has exploited this to align its olfactory preference with its ecological niche.     

The complexity of failure: Implications of complexity theory for safety investigations

Complexity theory suggests that we see performance as an emergent property, the result of complex interactions and relationships. This can clash, however, with what stakeholders see as legitimate and normal in accident investigations. When systems fail, it is still common to blame components (e.g. human errors) and when they succeed spectacularly, to think in terms of individual heroism (e.g. the A320 Hudson River landing). In this paper, we lay out the contrast between a Newtonian analysis of failure that can be recognized in many efforts at safety analysis and improvement. It makes particular assumptions about the relationship between cause and effect, foreseeability of harm, time-reversibility and the ability to produce the “true story” of an accident. With inspiration from complexity theory, failures are seen as an emergent property of complexity. We explore what that means for safety science and work towards a post-Newtonian analysis of failure in complex systems.     

Little effect of excessive biofouling on the uptake of organic contaminants by semipermeable membrane devices

The effects of water flow rate and antifouling agents on the extent of biofouling and on the uptake of non-polar organic contaminants by semipermeable membrane devices (SPMDs) were studied during four field experiments in the Western Wadden Sea. Biofouling densities on the sampler surface ranged from 0.3 to 16 g dry weight dm⁻². Water sampling rates were estimated from the dissipation rates of performance reference compounds (PRCs). The antifouling agents Irgarol and capsaicin (33 mg per ml triolein) had no noticeable effect on the extent of fouling, and caused only a 5–10% increase in the absorbed amounts. Enhanced flow rates had only a minimal effect on the amount of biofouling, but caused the water sampling rates to increase by a factor of 1.2–2. Increases in PRC-derived sampling rates were reflected by increases in the absorbed amounts for compounds that were in the linear uptake stage of the sampling process. The results imply (1) that extreme biofouling does not always result in reduced sampling rates, (2) that extreme biofouling does not preclude the existence of flow effects on the sampling rates, and (3) that differences in uptake rates are quantitatively reflected by the dissipation rates of PRCs.