Physiological adaptations to climate change in pro-ovigenic parasitoids.

Temperature increase can affect physiological and behavioural constraints. Here, we use a stochastic dynamic modelling approach to predict changes in physiological adaptations and behaviour in response to temperature increase of pro-ovigenic parasitoids (i.e., parasitoids that mature all of their eggs before emergence). Adults of most species of parasitoids, are not capable of de novo lipogenesis. The allocation of lipids accumulated during the larval stage determines adult lifespan and fecundity. In females, lipids can be allocated either to egg production or to adult lipid reserves leading to a trade-off between fecundity and lifespan. Our results show that selection by an increase in ambient temperature, favours a smaller initial egg load and a larger amount of lipids for maintenance. The cost of habitat exploitation increases with temperature because the rate of lipid consumption increases. Hence, lifetime reproductive success decreases. When the optimal activity rate shifts to match the higher ambient temperature, these effects become less pronounced.

Acute exacerbation of idiopathic pulmonary fibrosis: outcome and prognostic factors.

BACKGROUND: Acute exacerbation is a substantial cause of death in patients with idiopathic pulmonary fibrosis with poorly described prognostic factors. OBJECTIVES: To review the features associated with acute exacerbation of idiopathic pulmonary fibrosis and assess its prognostic factors. METHODS: Thirty-seven occurrences of acute exacerbation of idiopathic pulmonary fibrosis were retrospectively reviewed in the medical records of 27 patients. Clinical presentation, radiographic studies, pulmonary function tests, laboratory data, treatment, and outcome were analyzed. RESULTS: Acute exacerbation of idiopathic pulmonary fibrosis occurred more frequently between December and May (75.7%) than between June and November (24.3%) (p = 0.01). In-hospital mortality was 27% and median survival was 4.2 months (range 0.2-36.6). Significant differences between nonsurvivors and survivors included the time elapsed between their admission and the initiation of treatment for acute exacerbation (6 vs. 3.1 days, p = 0.04), lactate dehydrogenase levels at admission (801 vs. 544.6 IU/l, p = 0.002), impairment of the prior forced vital capacity (51.2 vs. 65%, p = 0.01) and diffusing capacity for carbon monoxide (21.7 vs. 34%, p = 0.01). Furthermore, the evolution of gas exchange in the first 10 days after the initiation of treatment was associated with in-hospital and long-term mortality. CONCLUSIONS: Acute exacerbations of idiopathic pulmonary fibrosis are more frequent during winter and spring. The time between admission and initiation of treatment is a new reported prognostic factor that should be investigated further. This finding highlights the need for a fast diagnostic approach that should probably be standardized. Early gas exchange modifications reflect the response to treatment and predict the prognosis.

Feeding and stocking up: radio-labelled food reveals exchange patterns in ants.

Food sharing is vital for a large number of species, either solitary or social, and is of particular importance within highly integrated societies, such as in colonial organisms and in social insects. Nevertheless, the mechanisms that govern the distribution of food inside a complex organizational system remain unknown. Using scintigraphy, a method developed for medical imaging, we were able to describe the dynamics of food-flow inside an ant colony. We monitored the sharing process of a radio-labelled sucrose solution inside a nest of Formica fusca. Our results show that, from the very first load that enters the nest, food present within the colony acts as negative feedback to entering food. After one hour of the experiments, 70% of the final harvest has already entered the nest. The total foraged quantity is almost four times smaller than the expected storage capacity. A finer study of the spatial distribution of food shows that although all ants have been fed rapidly (within 30 minutes), a small area representing on average 8% of the radioactive surface holds more than 25% of the stored food. Even in rather homogeneous nests, we observed a strong concentration of food in few workers. Examining the position of these workers inside the nest, we found heavily loaded ants in the centre of the aggregate. The position of the centre of this high-intensity radioactive surface remained stable for the three consecutive hours of the experiments. We demonstrate that the colony simultaneously managed to rapidly feed all workers (200 ants fed within 30 minutes) and build up food stocks to prevent food shortage, something that occurs rather often in changing environments. Though we expected the colony to forage to its maximum capacity, the flow of food entering the colony is finely tuned to the colony's needs. Indeed the food-flow decreases proportionally to the food that has already been harvested, liberating the work-force for other tasks.

How an ant manages to display individual and colonial signals by using the same channel.

Cuticular hydrocarbons are used by some ants to discriminate nestmates from nonnestmates. Every member of the colony bears the same pattern because they are continuously exchanged among nestmates. The postpharyngeal gland (PPG) stores the blend of hydrocarbons and is involved in the distribution of this common mixture. However, some individuals might display individual information on the cuticle (such as a chemical signal of fertility) that must not be mixed within the common pool. We investigated how this paradox is solved in the ant Pachycondyla goeldii by analyzing the nature and localization of colonial and fertility signals. Workers in a queenless condition showed a dominance hierarchy that was correlated with ovarian development. Hydrocarbons from the cuticle and the PPG analyzed by gas chromatography (GC) and identified by GC-mass spectrometry showed a clear discrimination among colonies, supporting the involvement of the PPG in the colonial identity signal. We identified and selected 11 cuticular hydrocarbons that permitted us to discriminate ovarian development classes and that might function as a fertility signal. They allowed clear colony discrimination as well, which suggests that the two signals (the individual signal of fertility and the common signal of colony identity) can be conveyed by the same compounds. However, the hydrocarbons in the PPG did not discriminate among ovarian developmental classes, suggesting that the portion of variation in the cuticular hydrocarbons constituting the fertility signal is superimposed on the signal of colony identity.

Queen movement during colony emigration in the facultatively polygynous ant Pachycondyla obscuricornis.

In ants, nest relocations are frequent but nevertheless perilous, especially for the reproductive caste. During emigrations, queens are exposed to predation and face the risk of becoming lost. Therefore the optimal strategy should be to move the queen(s) swiftly to a better location, while maintaining maximum worker protection at all times in the new and old nests. The timing of that event is a crucial strategic issue for the colony and may depend on queen number. In monogynous colonies, the queen is vital for colony survival, whereas in polygynous colonies a queen is less essential, if not dispensable. We tested the null hypothesis that queen movement occurs at random within the sequence of emigration events in both monogynous and polygynous colonies of the ponerine ant Pachycondyla obscuricornis. Our study, based on 16 monogynous and 16 polygynous colony emigrations, demonstrates for the first time that regardless of the number of queens per colony, the emigration serial number of a queen occurs in the middle of all emigration events and adult ant emigration events, but not during brood transport events. It therefore appears that the number of workers in both nests plays an essential role in the timing of queen movement. Our results correspond to a robust colony-level strategy since queen emigration is related neither to colony size nor to queen number. Such an optimal strategy is characteristic of ant societies working as highly integrated units and represents a new instance of group-level adaptive behaviors in social insect colonies.