Quantitative Matching of Clutch Size in Reciprocating Hermaphroditic Worms.

Reciprocity [1] is one of the most controversial evolutionary explanations of cooperation among non-kin [2, 3]. For some authors, cognitive capacity of non-human organisms is limiting, and more parsimonious mechanisms should apply [3-5]; for others, the debate is mainly semantic [2, 6], and empirical evidence can be found in a wide range of taxa [7]. However, while the ability to alternate cooperative behaviors does not settle the reciprocity controversy, the capacity to adjust cooperative behavior to the value of received help could prove decisive. Marine polychaete worms Ophryotrocha diadema, as several simultaneous hermaphrodites, do not self-fertilize and have unilateral mating (i.e., they behave either as females or as males during each mating event). They are also external fertilizers and thus cannot store allosperm, which contribute to make them ideal model organisms to investigate reciprocity, since partners usually alternate sexual roles with each other, repeatedly exchanging egg clutch of variable size [8-12]. However, whether the alternation of sexual roles is the result of conditional reciprocity rather than by-product reciprocity has never been tested [13]. Here, we show that O. diadema worms reciprocate eggs conditionally to the partner's behavior and adjust the quality of cooperation according to that of their partners. Moreover, only egg reciprocation offers similar fitness returns via both the female and the male function with respect to non-reciprocating laying strategies. These results document that fine-tuned forms of conditional reciprocity can emerge in cognitively unsophisticated animals, broadening the criteria to recognize conditional reciprocity among animals.

Social networks dynamics revealed by temporal analysis: An example in a non-human primate (Macaca sylvanus) in "La Forêt des Singes".

This study applied a temporal social network analysis model to describe three affiliative social networks (allogrooming, sleep in contact, and triadic interaction) in a non-human primate species, Macaca sylvanus. Three main social mechanisms were examined to determine interactional patterns among group members, namely preferential attachment (i.e., highly connected individuals are more likely to form new connections), triadic closure (new connections occur via previous close connections), and homophily (individuals interact preferably with others with similar attributes). Preferential attachment was only observed for triadic interaction network. Triadic closure was significant in allogrooming and triadic interaction networks. Finally, gender homophily was seasonal for allogrooming and sleep in contact networks, and observed in each period for triadic interaction network. These individual-based behaviors are based on individual reactions, and their analysis can shed light on the formation of the affiliative networks determining ultimate coalition networks, and how these networks may evolve over time. A focus on individual behaviors is necessary for a global interactional approach to understanding social behavior rules and strategies. When combined, these social processes could make animal social networks more resilient, thus enabling them to face drastic environmental changes. This is the first study to pinpoint some of the processes underlying the formation of a social structure in a non-human primate species, and identify common mechanisms with humans. The approach used in this study provides an ideal tool for further research seeking to answer long-standing questions about social network dynamics.

Anarchy Is a Molecular Signature of Worker Sterility in the Honey Bee.

Worker sterility is a defining characteristic of eusociality. The existence of the sterile worker caste remains a fundamental question for evolutionary biology as it requires the existence of genes that reduce personal reproduction. Currently, little is known about the proximate mechanisms underpinning worker sterility. Studies into a mutant "anarchistic" strain (in which workers can activate their ovaries) of honey bee, Apis mellifera, identified a list of candidate genes that regulate ovary activation. We quantified the expression of the four most promising candidate genes (Anarchy, Pdk1, S6k, and Ulk3) in nonactivated and activated ovaries of wild-type workers. Ovarian expression of Anarchy, a peroxisomal membrane protein, predicts the ovary state of workers with 88.2% accuracy. Increased expression of Anarchy in the ovary is strongly associated with suppression of oogenesis and its expression is sensitive to the presence of the queen. Therefore, Anarchy satisfies key criteria for a "gene underlying altruism". When we knocked down expression of Anarchy in the ovary using RNA interference (RNAi) we altered the expression of Buffy, a gene that regulates programmed cell death. Whole-mount multiplex fluorescent in situ hybridization (mFISH) shows Anarchy transcripts localize to degenerating oocytes within the ovary. Our results suggest that Anarchy is involved in the regulation of oogenesis through programmed cell death. The evolution of facultative worker sterility most likely occurred when the conserved mechanism of programmed cell death was co-opted to regulate ovary activation. Anarchy may therefore be the first example of a gene that has evolved through kin selection to regulate worker sterility.

Effects of natural mating and CO2 narcosis on biogenic amine receptor gene expression in the ovaries and brain of queen honey bees, Apis mellifera.

A queen honey bee mates at ∼6 days of age, storing the sperm in her spermatheca for life. Mating is associated with profound changes in the behaviour and physiology of the queen but the mechanisms underlying these changes are poorly understood. What is known is that the presence of semen in the oviducts and spermatheca is insufficient to initiate laying, and that copulation or CO(2) narcosis is necessary for ovary activation. In this study we use real-time quantitative PCR to investigate the expression of biogenic amine receptor genes in the brain and ovarian tissue of queens in relation to their reproductive status. We show that dopamine, octopamine and serotonin receptor genes are expressed in the ovaries of queens, and that natural mating, CO(2) narcosis, and the presence of semen in the spermatheca differentially affect their expression. We suggest that these changes may be central to the hormonal cascades that are necessary to initiate oogenesis.

Enriched topological learning for cluster detection and visualization.

The exponential growth of data generates terabytes of very large databases. The growing number of data dimensions and data objects presents tremendous challenges for effective data analysis and data exploration methods and tools. Thus, it becomes crucial to have methods able to construct a condensed description of the properties and structure of data, as well as visualization tools capable of representing the data structure from these condensed descriptions. The purpose of our work described in this paper is to develop a method of describing data from enriched and segmented prototypes using a topological clustering algorithm. We then introduce a visualization tool that can enhance the structure within and between groups in data. We show, using some artificial and real databases, the relevance of the proposed approach.

Boys and girls on the playground: sex differences in social development are not stable across early childhood.

Sex differences in human social behaviors and abilities have long been a question of public and scientific interest. Females are usually assumed to be more socially oriented and skillful than males. However, despite an extensive literature, the very existence of sex differences remains a matter of discussion while some studies found no sex differences whereas others reported differences that were either congruent or not with gender stereotypes. Moreover, the magnitude, consistency and stability across time of the differences remain an open question, especially during childhood. As play provides an excellent window into children's social development, we investigated whether and how sex differences change in social play across early childhood. Following a cross-sectional design, 164 children aged from 2 to 6 years old, divided into four age groups, were observed during outdoor free play at nursery school. We showed that sex differences are not stable over time evidencing a developmental gap between girls and boys. Social and structured forms of play emerge systematically earlier in girls than in boys leading to subsequent sex differences in favor of girls at some ages, successively in associative play at 3-4 years, cooperative play at 4-5 years, and social interactions with peers at 5-6 years. Preschool boys also display more solitary play than preschool girls, especially when young. Nevertheless, while boys catch up and girls move on towards more complex play, sex differences in social play patterns are reversed in favor of boys at the following ages, such as in associative play at 4-5 years and cooperative play at 5-6 years. This developmental perspective contributes to resolve apparent discrepancies between single-snapshot studies. A better understanding of the dynamics of sex differences in typical social development should also provide insights into atypical social developments which exhibit sex differences in prevalence, such as autism.