Summary1. Anthropogenic noise is known to affect acoustic signal production in birds, frogs and mammals. These animals use different mechanisms to adjust their signals to elevated background noise levels (increase in signal amplitude, shift to higher frequencies, etc.). Previous studies have concentrated on behaviourally plastic changes in signal production as a result of elevated background noise levels. To our knowledge, long-term effects of anthropogenic noise on signal production have not yet been investigated. Moreover, strategies of invertebrate species to ensure acoustic signal transmission under anthropogenic noise have not been examined, so far. 2. We tested whether and how male Chorthippus biguttulus grasshoppers from noisy roadside habitats may adjust acoustic courtship signals to elevated background noise levels, compared with conspecifics from quiet control habitats. In this species, sexually selected male courtship signals serve to attract potential mating partners, which make the undisturbed transmission of signals in habitats with increased background noise levels crucial for male reproductive success. 3. Compared to males from control populations, males from roadside habitats produced songs with a significantly higher local frequency maximum under standardized, quiet recording conditions. This local frequency maximum (in the range of c. 6-9 kHz) overlaps with low-frequent road noise that has the potential to degrade or mask this part of the signals' frequency spectrum. 4. To our knowledge, this is the first evidence that insects from noisy habitats produce different acoustic signals than conspecifics from quiet habitats, possibly using a more permanent mechanism for signal adjustment than behavioural plasticity, which was found in different bird species adjusting to high background noise levels. Such an effect of anthropogenic noise has not been shown for any invertebrate species before, and our results suggest that similar strategies to avoid degradation or masking by noise (i.e. increase in carrier frequency) are used over a wide range of taxa, including both, vertebrates and invertebrates.

The hypothesis that females of socially monogamous species obtain indirect benefits (good or compatible genes) from extra-pair mating behaviour has received enormous attention but much less generally accepted support. Here we ask whether selection for adult survival and fecundity or sexual selection contribute to indirect selection of the extra-pair mating behaviour in socially monogamous coal tits (Periparus ater). We tracked locally recruited individuals with known paternity status through their lives predicting that the extra-pair offspring (EPO) would outperform the within-pair offspring (WPO). No differences between the WPO and EPO recruits were detected in lifespan or age of first reproduction. However, the male WPO had a higher lifetime number of broods and higher lifetime number of social offspring compared with male EPO recruits, while no such differences were evident for female recruits. Male EPO recruits did not compensate for their lower social reproductive success by higher fertilization success within their social pair bonds. Thus, our results do not support the idea that enhanced adult survival, fecundity or within-pair fertilization success are manifestations of the genetic benefits of extra-pair matings. But we emphasize that a crucial fitness component, the extra-pair fertilization success of male recruits, has yet to be taken into account to fully appreciate the fitness consequences of extra-pair matings.

Summary1. Increasing levels of anthropogenic noise have the potential to mask signals of acoustically communicating species in their natural habitats. Animals in noise-polluted habitats typically adjust their signals away from high background noise levels to ensure successful signal transmission under challenging environmental conditions. Earlier we demonstrated that male Chorthippus biguttulus grasshoppers from roadside habitats produce courtship signals with elevated frequency components compared to conspecifics from non-roadside habitats.2. Here, we use a common garden approach to study the mechanisms underlying this response. We transferred grasshopper nymphs from seven roadside as well as five non-roadside habitats to the laboratory to rear half of them under noisy and the other half under quiet conditions in a full factorial two-by-two design. Courtship songs of adult males were later recorded under standardized quiet conditions. 3. Males exposed to road noise as nymphs produced signals with higher frequency components compared to males reared under quiet conditions, indicating developmental plasticity as a mechanism underlying the signal adjustment to anthropogenic noise in grasshoppers. 4. In addition, males originating from roadside habitats produced signals with higher frequency components and an increased syllable to pause ratio -a sexually selected signal trait -compared to males from non-roadside habitats. 5. Our results demonstrate for the first time that developmental plasticity may play an important role in song trait modifications in response to anthropogenic noise. Furthermore, they suggest that multiple roadside populations may have diverged in parallel, possibly in response to selection for minimizing signal masking by road noise.

Avian extrapair mating systems provide an interesting model to assess the role of genetic benefits in the evolution of female multiple mating behavior, as potentially confounding nongenetic benefits of extrapair mate choice are seen to be of minor importance. Genetic benefit models of extrapair mating behavior predict that females engage in extrapair copulations with males of higher genetic quality compared to their social mates, thereby improving offspring reproductive value. The most straightforward test of such good genes models of extrapair mating implies pairwise comparisons of maternal half-siblings raised in the same environment, which permits direct assessment of paternal genetic effects on offspring traits. But genetic benefits of mate choice may be difficult to detect. Furthermore, the extent of genetic benefits (in terms of increased offspring viability or fecundity) may depend on the environmental context such that the proposed differences between extrapair offspring (EPO) and within-pair offspring (WPO) only appear under comparatively poor environmental conditions. We tested the hypothesis that genetic benefits of female extrapair mate choice are context dependent by analyzing offspring fitness-related traits in the coal tit (Parus ater) in relation to seasonal variation in environmental conditions. Paternal genetic effects on offspring fitness were context dependent, as shown by a significant interaction effect of differential paternal genetic contribution and offspring hatching date. EPO showed a higher local recruitment probability than their maternal half-siblings if born comparatively late in the season (i.e., when overall performance had significantly declined), while WPO performed better early in the season. The same general pattern of context dependence was evident when using the number of grandchildren born to a cuckolding female via her female WPO or EPO progeny as the respective fitness measure. However, we were unable to demonstrate that cuckolding females obtained a general genetic fitness benefit from extrapair fertilizations in terms of offspring viability or fecundity. Thus, another type of benefit could be responsible for maintaining female extrapair mating preferences in the study population. Our results suggest that more than a single selective pressure may have shaped the evolution of female extrapair mating behavior in socially monogamous passerines.

Whether female birds choose extra-pair mating partners to obtain genetic fitness benefits is intensely debated. The most straightforward and crucial test of 'good genes' models of female extra-pair mating is the comparison of naturally 'cross-fostered' maternal half-siblings sharing the same rearing environment as any systematic differences in performance between the two categories of offspring phenotype can be attributed to differential paternal genetic contribution. We analysed local recruitment and first-year reproductive performance of maternal half-siblings in the coal tit (Parus ater), a passerine bird with high levels of extra-pair paternity. We provide a highly comprehensive measure of the long-term fitness consequences of female extra-pair matings based on a large sample of 736 within-pair offspring (WPO) and 368 extrapair offspring (EPO) from 91 first and 55 second broods, from which 132 breeders recruited into the study population. In contrast to predictions derived from 'good genes' models, we found no differences in local recruitment and seven parameters of first-year reproductive performance when comparing WPO and EPO. These results question the universal validity of findings in other bird species supporting 'good genes' models, particularly as they are based on the best approximation to female fitness obtained so far.