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The magnitude of the e¡ect of good genes as a viability bene¢t accruing to choosy females remains a controversial theoretical and empirical issue. We collected all available data from the literature to estimate the magnitude of good-genes viability e¡ects, while adjusting for sample size. The average correlation coe¤cient between male traits and o¡spring survival in 22 studies was 0.122, which di¡ered highly signi¢cantly from zero. This implies that male characters chosen by females reveal on average 1.5% of the variance in viability. The studies demonstrated considerable heterogeneity in e¡ect size; some of this heterogeneity could be accounted for by di¡erences among taxa (birds demonstrating stronger e¡ects), and by di¡erences in the degree of mating skew in the species (high skew re£ecting stronger e¡ects). Although these results suggest that viability-based sexual selection is widespread across taxa, they indicate that the e¡ect is relatively minor. Finally, there was also an e¡ect of publication year in that the more recent studies reported reduced e¡ects. This may re£ect publication biases during paradigm shifts of this debated issue, but it should also be recalled that the studies have only partly estimated the full ¢tness consequences of mate choice for o¡spring.

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Understanding the early evolution of aposematic (warning) coloration has been a challenge for scientists, as a new conspicuous morph in a population of cryptic insects would have a high predation risk and would probably die out before local predators learnt to avoid it. Fisher presented the idea of aggregation benefit through the survival of related individuals; however, his theory has been strongly debated as the mechanisms that favour grouping have never been explored experimentally with the incorporation of detectability costs. Here we create a comprehensive 'novel world' experiment with the great tit (Parus major) as a predator to explore simultaneously the predation-related benefits and costs for aposematic aggregated prey, manipulating both group size and signal strength. Our results show that grouping would have been highly beneficial for the first aposematic prey individuals surrounded by naive predators, because (1) detectability risk increased only asymptotically with group size; (2) additional detectability costs due to conspicuous signals were marginal in groups; (3) even naive predators deserted the group after detecting unpalatability (dilution effect); and (4) avoidance learning of signal was faster in groups. None of these mechanisms require kin selection.

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SUMMARYBatesian mimicry is the resemblance between unpalatable models and palatable mimics. The widely accepted idea is that the frequency and the unprofitability of the model are crucial for the introduction of a Batesian mimic into the prey population. However, experimental evidence is limited and furthermore, previous studies have considered mainly perfect mimicry (automimicry). We investigated imperfect Batesian mimicry by varying the frequency of an aposematic model at two levels of distastefulness. The predator encountered prey in a random order, one prey item at a time. The prey were thus presented realistically in a sequential way. Great tits (Parus major) were used as predators. This experiment, with a novel signal, supports the idea that Batesian mimics gain most when the models outnumber them. The mortalities of the mimics as well as the models were significantly dependent on the frequency of the model. Both prey types survived better the fewer mimics there were confusing the predator. There were also indications that the degree of distastefulness of the model had an effect on the survival of the Batesian mimic : the models survived significantly better the more distasteful they were. The experiment supports the most classical predictions in the theories of the origin and maintenance of Batesian mimicry.