Bullying as an advertisement of social dominance in common waxbills.

Bullying consists of preferentially attacking individuals lowest in the dominance hierarchy, and its functions are unclear because the most subordinate individuals do not pose social challenges to the aggressor. Instead, conflict is expected mostly between individuals of similar dominance rank or socially distant (i.e. weakly associated), among whom dominance relationships may not be well established. A possible function of bullying is that it may be used as a low-risk strategy of showing-off dominance to relevant third parties. To study this hypothesis, we monitored aggressions during feeding, the composition of audiences, dominance hierarchy and social network of common waxbills (Estrilda astrild) in an open-air mesocosm, and tested (i) whether their aggressions show a pattern of bullying, and (ii) whether audience effects influence aggressiveness. Waxbills showed bullying, most often attacking the lowest ranking individuals rather than socially distant individuals or those of similar dominance rank, and aggressions increased when the audience included socially distant individuals, indicating a signalling function of bullying. Showing-off dominance in the presence of socially distant individuals may be a strategy to manage dominance hierarchies, avoiding direct fights with potentially dangerous opponents in the audience. We suggest that bullying is a safe manner of managing dominance hierarchies, by signalling dominance status to potential opponents.

Cleaner blues: Condition-dependent colour and cleaner fish service quality.

While vivid colours in sexual signals can provide information on individual quality, vivid colours in interspecific signals have been interpreted mostly as indicating species identity and maximizing signal detection. Here we investigate if colour differences in an interspecific signal could also indicate relevant aspects of individual quality because, similarly to sexual signalling, in interspecific communication it could sometimes be advantageous to assess individual quality. For example when interacting with cleaner species, clients should benefit from assessing which individual cleaners provide better service. Since oxidative stress commonly influence condition-dependent colour signals, we oxidized the diet of cleaner wrasses (Labroides dimidiatus) in laboratory conditions to test if this affects their vivid blue skin colour and the quality of their cleaning service. Compared to controls, experimental cleaners decreased blue colour saturation after the oxidized diet treatment, decreased the quality of their cleaning service by performing less tactile stimulation and, although clients in the laboratory were de-parasitized, also tended to decrease the touching the client with the mouth. We used visual modelling, based on the spectral sensitivity of vision in various client species, to show that some client species can perceive these changes in cleaner blue colour saturation, while other client species not. We suggest that, similarly to sexual signals, some vivid colours used in interspecific communication may convey information on aspects of individual quality that are relevant to heterospecifics.

The lag-time constraint for behavioural plasticity.

Environmental instability (i.e. environments changing often) can select fixed phenotypes because of the lag time of plastically adapting to environmental changes, known as the lag-time constraint. Because behaviour can change rapidly (e.g. switching between foraging strategies), the lag-time constraint is not considered important for behavioural plasticity. Instead, it is often argued that responsive behaviour (i.e. behaviour that changes according to the environment) evolves to cope with unstable environments. But proficiently performing certain behaviours may require time for learning, for practising or, in social animals, for the group to adjust to one's behaviour. Conversely, not using certain behaviours for a period of time can reduce their level of performance. Here, using individual-based evolutionary simulations, we show that environmental instability selects for fixed behaviour when the ratio between the rates of increase and reduction in behavioural performance is below a certain threshold; only above this threshold does responsive behaviour evolve in unstable environments. Thus, the lag-time constraint can apply to behaviours that attain high performance either slowly or rapidly, depending on the relative rate with which their performance decreases when not used. We discuss these results in the context of the evolution of reduced behavioural plasticity, as seen in fixed personality differences.

Choice of high-quality mates versus avoidance of low-quality mates.

Research in sexual selection assumes that individuals attempt to choose high-quality mates, and that sexual signals evolve to indicate high quality. But it may often be more important to instead discriminate and avoid low-quality mates, thus reducing the likelihood of large penalties in fitness. We show, using simulations, that avoidance of low-quality mates (i.e., rejecting low-quality and accepting either high- or medium-quality mates) evolves in socio-ecological circumstances such as monogamy with moderate opportunities for choice, costly choice, or abundant low-quality mates. We also show that this strategy is qualitatively different from choosing high-quality mates (i.e., preferring high-quality over medium- and low-quality mates). Rather than selecting signals that distinguish high- from low- and medium-quality mates, avoiding low-quality mates selects for signals or cues attuned at discriminating low-quality mates from the remaining (e.g., low-cost signals, absence of signaling mistakes). This may help explain the high diversity of sexual signals in nature, and their high evolutionary turnover with frequent losses and replacements (rather than reductions/increases of the same signal) over evolutionary time.

Speciation is associated with changing ornamentation rather than stronger sexual selection.

Although sexual ornamentation mediates reproductive isolation, comparative evidence does not support the hypothesis that stronger sexual selection promotes speciation. Prior analyses have neglected the possibility that decreases in ornamentation may also promote speciation, such that both increases and decreases in the strength of sexual selection and associated changes in ornamentation promote speciation. To test this hypothesis, we studied color ornamentation in one of the largest and fastest avian radiations, the estrildid finches. We show that more ornamented lineages do not speciate more, even though they tend to have faster rates of ornamental evolution, whereas changes in ornamentation (i.e., increases or decreases) are associated with speciation. This indicates that divergence in sexually selected ornamentation, rather than stronger sexual selection, promotes or is otherwise associated with speciation. We also show that gregariousness and investment in reproduction are related to the elaboration of some ornamental traits, suggesting ecological influences on speciation mediated by ornamentation. We conclude that past work focusing specifically on the strength of sexual selection may have greatly underestimated the importance of sexual ornamentation for speciation.

Morfologia do lateral superior: conhecimento de suas faces / Morphology of the lateral superior: knowledge of their faces

O incisivo lateral superior é um dos dentes mais variáveis da arcada humana apresentando uma morfologia muito semelhante ao do dente incisivo central, porém o incisivo lateral tem uma coroa mais estreita no sentido mésio-distal. O segmento distal deste dente é mais inclinado, aproximando-se da morfologia do dente canino.São dentes cuneiformes (forma de cunha).Também são classificados em: Oval, triangular ou retangular.A dimensão vertical é bastante preponderante sobre a horizontal