Biopolymers, nanoparticles and surfactants: short stories in building-up gels from self- assembly

Hydrogels obtained from the chemical and physical association of macromolecules, surfactants and nanoparticles, are a huge area of materials science and have found numerous applications in food, personal care products and biomedicine. The macroscopic properties of hydrogels are a complex interplay between the microscopic and mesoscopic supramolecular organization; thus, both their dynamics and structure are dictated by the interactions between the constituents, the fabrication pathway and resulting spatial organization over different length scales. Work in our group has explored various approaches to make gels from non-covalent interactions, spanning biopolymers1-4, wormlike micelles5,6 or host-guest interactions with cyclodextrins7-9. Biopolymers offer a number of advantages over their synthetic counterparts, but suffer from a lack of characterization. This talk will describe our approach to make cheap, functional materials based on widely available biopolymers obtained from natural sources, such as gelatin, or polysaccharides.1-4,10 We will describe the impact of using a hybrid gelation process, combining physical gelling and chemical cross-linking, as well as gels made from hydrophobic interactions between modified biopolymers (dextran or gellan gum) with surfactant micelles.10 Time allowing, I will report on some recent work involving surfactants and laponite architectures, leading to pH- and temperature-responsive gels. The nanoscale morphology of these gels is characterized by small-angle neutron scattering, which is correlated to the rheology of the gels to extract useful structure-function relationships. [1] M.A. da Silva et al. Biomacromolecules (2015) 16, 1401-1409 [2] M.A. da Silva et al. Macromolecular Bioscience (2014) 14, 817-830. [3] F. Bode et al. Soft Matter (2013) 9, 6986-6999 [4] F. Bode et al. Biomacromolecules (2011) 12, 3741-3752 [5] C. A. Dreiss Soft Matter (2007) 2, 956-970 [6] C. Zonglin et al. Chem. Soc. Rev. (2013) 42, 7174-7203 [7] G. González-Gaitano et al. Langmuir (2015) 31, 5645-5655 [8] A.G. Peréz et al. Langmuir (2014) 30, 11552-11562 [9] M.A. da Silva et al. Langmuir (2013) 29, 7697-7708 [10] H. Afifi et al. Soft Matter (2011) 7, 4888-489

Divorce in the barn owl: securing a compatible or better mate entails the cost of re-pairing with a less ornamented female mate.

Two nonmutually exclusive hypotheses can explain why divorce is an adaptive strategy to improve reproductive success. Under the 'better option hypothesis', only one of the two partners initiates divorce to secure a higher-quality partner and increases reproductive success after divorce. Under the 'incompatibility hypothesis', partners are incompatible and hence they may both increase reproductive success after divorce. In a long-term study of the barn owl (Tyto alba), we address the question of whether one or the two partners derive fitness benefits by divorcing. Our results support the hypothesis that divorce is adaptive: after a poor reproductive season, at least one of the two divorcees increase breeding success up to the level of faithful pairs. By breeding more often together, faithful pairs improve coordination and thereby gain in their efficiency to produce successful fledglings. Males would divorce to obtain a compatible mate rather than a mate of higher quality: a heritable melanin-based signal of female quality did not predict divorce (indicating that female absolute quality may not be the cause of divorce), but the new mate of divorced males was less melanic than their previous mate. This suggests that, at least for males, a cost of divorce may be to secure a lower-quality but compatible mate. The better option hypothesis could not be formally rejected, as only one of the two divorcing partners commonly succeeded in obtaining a higher reproductive success after divorce. In conclusion, incompatible partners divorce to restore reproductive success, and by breeding more often together, faithful partners improve coordination

Dynamic covalent surfactants and their uses in the development of smart materials

Dynamic covalent chemistry, which leverages the dynamic nature of reversible covalent bonds controlled by the conditions of reaction equilibrium, has demonstrated great potential in diverse applications related to both the stability of covalent bonds and the possibility of exchanging building blocks, imparting to the systems the possibility of “error checking” and “proof-reading”. By incorporating dynamic covalent bonds into surfactant molecular architectures, combinatorial libraries of surfactants with bespoke functionalities can be readily fabricated through a facile strategy, with minimum effort in organic synthesis. Consequently, a multidisciplinary field of research involving the creation and application of dynamic covalent surfactants has recently emerged, which has aroused great attention in surfactant and colloid science, supramolecular chemistry, self-assembly, smart materials, drug delivery, and nanotechnology. This review reports results in this field published over recent years, discusses the possibilities presented by dynamic covalent surfactants and their applications in developing smart self-assembled materials, and outlines some future perspectives

Social rules govern vocal competition in the barn owl

To resolve the share of limited resources, animals often compete through exchange of signals about their relative motivation to compete. When two competitors are similarly motivated, the resolution of conflicts may be achieved in the course of an interactive process. In barn owls, Tyto alba, in which siblings vocally compete during the prolonged absence of parents over access to the next delivered food item, we investigated what governs the decision to leave or enter a contest, and at which level. Siblings alternated periods during which one of the two individuals vocalized more than the other. Individuals followed turn-taking rules to interrupt each other and momentarily dominate the vocal competition. These social rules were weakly sensitive to hunger level and age hierarchy. Hence, the investment in a conflict is determined not only by need and resource-holding potential, but also by social interactions. The use of turn-taking rules governing individual vocal investment has rarely been shown in a competitive context. We hypothesized that these rules would allow individuals to remain alert to one another's motivation while maintaining the cost of vocalizing at the lowest level

Information retention during competitive interactions : siblings need to constantly repeat vocal displays

Memory is essential to adjust behaviour according to past experience. In societies where animals interact on numerous occasions, memory of previous social interactions may help optimise investment in competition. How long information about the resource holding potential and motivation to compete of conspecifics is retained depends on how fast the value of this information fades, but also on the cost and benefit of retaining information. Information retention has never been investigated in the context of interactions prevailing within the family and more specifically sibling competition. In the absence of parents, barn owl (Tyto alba) nestlings vocally compete for priority of access to the next indivisible food item brought by a parent. The finding that owlets eavesdrop on vocal interactions between siblings to adjust investment in vocalization once competing with them suggests that they memorize siblings' vocal interactions. Playback experiments showed that owlets take into account the past siblings' vocal performance that signals hunger for at least 15 min, but only if the performance was witnessed during a sufficiently long period of time (30 min). Moreover, using natural vocal exchanges in another set of individuals, we showed that sibling signalling was no more taken into account after a few minutes. This suggests that young barn owls need to continuously display their motivation to trigger siblings' withdrawal from the current competition. Repeating a vocal display may ensure its honesty. Studying the extent to which individuals retain past information is important to understand how individuals adjust their competitive investment over resources

Prosody Predicts Contest Outcome in Non-Verbal Dialogs.

Non-verbal communication has important implications for inter-individual relationships and negotiation success. However, to what extent humans can spontaneously use rhythm and prosody as a sole communication tool is largely unknown. We analysed human ability to resolve a conflict without verbal dialogs, independently of semantics. We invited pairs of subjects to communicate non-verbally using whistle sounds. Along with the production of more whistles, participants unwittingly used a subtle prosodic feature to compete over a resource (ice-cream scoops). Winners can be identified by their propensity to accentuate the first whistles blown when replying to their partner, compared to the following whistles. Naive listeners correctly identified this prosodic feature as a key determinant of which whistler won the interaction. These results suggest that in the absence of other communication channels, individuals spontaneously use a subtle variation of sound accentuation (prosody), instead of merely producing exuberant sounds, to impose themselves in a conflict of interest. We discuss the biological and cultural bases of this ability and their link with verbal communication. Our results highlight the human ability to use non-verbal communication in a negotiation process

Sleep and vigilance linked to melanism in wild barn owls.

Understanding the function of variation in sleep requires studies in the natural ecological conditions in which sleep evolved. Sleep has an impact on individual performance and hence may integrate the costs and benefits of investing in processes that are sensitive to sleep, such as immunity or coping with stress. Because dark and pale melanic animals differentially regulate energy homeostasis, immunity and stress hormone levels, the amount and/or organization of sleep may covary with melanin-based colour. We show here that wild, cross-fostered nestling barn owls (Tyto alba) born from mothers displaying more black spots had shorter non-REM (rapid eye movement) sleep bouts, a shorter latency until the occurrence of REM sleep after a bout of wakefulness and more wakefulness bouts. In male nestlings, the same sleep traits also correlated with their own level of spotting. Because heavily spotted male nestlings and the offspring of heavily spotted biological mothers switched sleep-wakefulness states more frequently, we propose the hypothesis that they could be also behaviourally more vigilant. Accordingly, nestlings from mothers displaying many black spots looked more often towards the nest entrance where their parents bring food and towards their sibling against whom they compete. Owlets from heavily spotted mothers might invest more in vigilance, thereby possibly increasing associated costs due to sleep fragmentation. We conclude that different strategies of the regulation of brain activity have evolved and are correlated with melanin-based coloration

Vocal communication regulates sibling competition over food stock

Animals resolve conflicts over the share of resources by competing physically or signalling motivation with honest signals of need. In some species, young siblings vocally signal to each other their hunger level and the most vocal individual deters its siblings from competing for the non-divisible food item delivered at the next parental visit. This so-called sibling negotiation for forthcoming food has been studied only in this context. It therefore remains unclear whether siblings could also negotiate access to a pool of divisible resources, a situation that is similar to a group of individuals competing for an accessible food resource. To tackle this issue, we placed barn owl (Tyto alba) nestlings singly in artificial nests containing several mice, and we simulated the presence of a sibling calling at low or high rate using playback experiments. If nestling barn owls vocally negotiate over a divisible food stock, we propose the following two predictions. First, nestlings would vocally signal before eating from this stock of food, and second, numerous playback vocalizations would inhibit feeding. Accordingly, singleton nestlings vocalized just before consuming food stored in their artificial nest and they delayed the consumption of the food stock if hearing many playback calls. The production of such food-associated vocalizations has been observed in foraging adults in various birds and mammals, but never in young animals and when resource is divisible and easily accessible. Our study raises the possibility that vocal communication could evolve in a variety of competitive contexts. We present here the first experimental evidence that sibling barn owls use food-associated vocalizations to compete over the preys stored in the nest. Owlets emit calls just before consuming an available food item and broadcasting calls induces nestlings to temporarily refrain from eating from the food stock. This raises the possibility that vocal communication can mediate the share of a food stock accessible to all competitors

Big brother is watching you: eavesdropping to resolve family conflicts

Adult animals can eavesdrop on behavioral interactions between potential opponents to assess their competitive ability and motivation to contest resources without interacting directly with them. Surprisingly, eavesdropping is not yet considered as an important factor used to resolve conflicts between family members. In this study, we show that nestling barn owls (Tyto alba) competing for food eavesdrop on nestmates' vocal interactions to assess the dominance status and food needs of opponents. During a first training playback session, we broadcasted to singleton bystander nestlings a simulated vocal interaction between 2 prerecorded individuals, 1 relatively old (i.e., senior) and 1 younger nestling (i.e., junior). One playback individual, the "responder,” called systematically just after the "initiator” playback individual, hence displaying a higher hunger level. To test whether nestlings have eavesdropped on this interaction, we broadcasted the same prerecorded individuals separately in a subsequent playback test session. Nestlings vocalized more rapidly after former initiators' than responders' calls and they produced more calls when the broadcasted individual was formerly a junior initiator. They chiefly challenged vocally juniors and initiators against whom the likelihood of winning a vocal contest is higher. Owlets, therefore, identified the age hierarchy between 2 competitors based on their vocalizations. They also memorized the dynamics of competitors' previous vocal interactions, and used this information to optimally adjust signaling level once interacting with only 1 of the competitor. We conclude that siblings eavesdrop on one another to resolve conflicts over parental resource