Laureano Castro

Inter‐ and intraspecific sexual discrimination in the flour beetles Tribolium castaneum and Tribolium confusum

In Tribolium castaneum (CS) and T. confusum (CF), intra- and interspecific rates of homosexual mounting have been measured. The intraspecific results are compatible with the hypothesis of both species being sexually indiscriminate. However, the CF intraspecific rates were very high (35%–53% of mountings were homosexual), suggesting a lower sexual attractiveness, or a stronger rejection to being mounted, of CF females relative to conspecific males. CS males discriminate between species but, in interspecific contacts, preferentially mounted CF males rather than CF females. CF males do not discriminate between species, but the loss of sexual attractiveness of CF females, or their rejection to being mounted, may act as a precopulatory isolation mechanism.

Human evolution and the capacity to categorize

Abstract We have studied—with the help of a mathematical model of cultural transmission—evolutionary effects which may derive from the appearance of a conceptual capacity to categorize behavior (approving or disapproving of it) in one of our hominid ancestors. We consider acquisition of behavior through individual learning and rudimentary cultural transmission. The ability to categorize behavior produces an increase in the efficiency and the flexibility of the cultural transmission process. Moreover, the capacity to categorize allows the acquisition, through cultural transmission, of information about behavior, similar to that provided by individual learning (i.e., an individuals interaction with the environment, in contrast to the receipt of lessons learned by others) but avoids unnecessary costs by not having to resort to experience. An analysis of the model reveals that the advantage in terms of fitness in individuals capable of categorizing compared to individuals without this ability increases the greater the difference in the intensity of cultural transmission between them and declines the greater the probability that behavior with adaptive importance can be developed without the need of culture, that is, solely through individual learning. Finally, we suggest that intelligence has developed, within this framework of the cultural transmission, as a new system, outside the limbic-hypothalamic system, capable of generating values and showing preferences between different kinds of behavior.

The genetic properties of homosexual copulation behavior in Tribolium castaneum : diallel analysis

The rate of homosexual copulation has been defined as the ratio between the number of homosexual mountings and the total number of mountings (homo and heterosexual) performed by aTribolium castaneum male during a period of 30 min. In a laboratory population, the average rate when a number of males (m) and females (k×m) are tested together has been estimated in each of the six situations defined by m=2 and 10 and k=0.5, 1, and 2, k being the sex ratio among scored individuals. Good agreement was found between the observed rates of homosexual copulation and those expected assuming random contacts between pairs of individuals totally indiscriminate with respect to sex. The genetic properties of the trait have been investigated by means of a diallel analysis of six highly inbred lines derived from the same population and their F1 crosses. Significant general and specific combining ability effects were detected. When noninbred females were used for testing, the rate of homosexual copulation is expected to be higher for inbred than for noninbred males. This prediction, implying the existence of inbreeding depression for the trait, also was confirmed by the data.

Cumulative cultural evolution: The role of teaching

In humans, cultural transmission occurs usually by cumulative inheritance, generating complex adaptive behavioral features. Cumulative culture requires key psychological processes (fundamentally imitation and teaching) that are absent or impoverished in non-human primates. In this paper we analyze the role that teaching has played in human cumulative cultural evolution. We assume that a system of cumulative culture generates increasingly adaptive behaviors, that are also more complex and difficult to imitate. Our thesis is that, as cultural traits become more complex, cumulative cultural transmission requires teaching to ensure accurate transmission from one generation to the next. In an increasingly complex cultural environment, we consider that individuals commit errors in imitation. We develop a model of cumulative cultural evolution in a changing environment and show that these errors hamper the process of cultural accumulation. We also show that a system of teaching between parents and offspring that increases the fidelity of imitation unblocks the accumulation and becomes adaptive whenever the gain in fitness compensates the cost of teaching.

Iterated prisoner's dilemma in an asocial world dominated by loners, not by defectors.

Cooperation among genetically unrelated individuals can arise when pairs of individuals interact repeatedly in the Prisoners Dilemma. However, the conditions allowing the evolution of reciprocal cooperation become extremely restrictive as the size of the cooperative group increases, because defectors can exploit cooperators more efficiently in larger groups. Here we consider three strategies: Tit for Tat, defector, and loner. Loner beats defector in a non-cooperative world. However, a cooperative strategy Tit for Tat (TFT(0)) that stops cooperation after the first iteration when there is at least one defector in the group, can invade a world of loners, even in sizable groups, if both the TFT(0) and the defector strategies arise at the same frequency by mutation.

Imitation or innovation? Unselective mixed strategies can provide a better solution

Current theory about the evolution of social learning in a changing environment predicts the emergence of mixed strategies that rely on some selective combination of social and asocial learning. However, the results of a recent tournament of social learning strategies [Rendell et al. Science 328(5975):208–213, 2010] suggest that the success relies almost entirely on copying to learn behavior. Those authors conclude that mixed strategies are vulnerable to invasion by individuals using social learning strategies alone. Here we perform a competition using unselective strategies that differ only in the degree of social versus asocial learning. We show that, under the same conditions of the aforementioned tournament, a pure social learning strategy can be invaded by an unselectively mixed strategy and attain an equilibrium where the latter is majority. Although existing theory suggests that copying other individuals unselectively is not adaptive, we show that, at this equilibrium, the average individual fitness of the population is higher than for a population of pure asocial learners, overcoming Rogers’ paradox in finite populations.

To be or not to be a good social partner

Cooperation based in mutual benefit provides a perfect scenario to start selfish behaviors aimed to obtain greater benefit at the expense of the partner. Here we investigate if mutual benefit cooperation can be stable between individuals that cooperate with kindness (good partners) or if they will be displaced by other individuals that try to obtain more benefit with less cost (bad partners). Our model assumes an asymmetry between partners in such a way that one of them (actor) proposes the cooperation whereas the other (receiver) always accepts the offer. It also assumes that actors can choose the partner on the basis of their past experiences with the potential partners. With the help of a simple two-locus mathematical model we show that not only the gene that conditions the actor preference to choose good partners can increase in frequency but also the gene responsible of the good partner behavior.