Ecological variation along the salinity gradient in the Baltic Sea Area and its consequences for reproduction in the common goby

Although it has become clear that sexual selection may shape mating systems and drive speciation, the potential constraints of environmental factors on processes and outcomes of sexual selection are largely unexplored. Here, we investigate the geographic variation of such environmental factors, more precisely the quality and quantity of nest resources (bivalve shells) along a salinity gradient in the Baltic Sea Area (Baltic Sea, Sounds and Belts, and Kattegat). We further test whether we find any salinity-associated morphological differences in body size between populations of common gobies Pomatoschistus microps, a small marine fish with a resource-based mating system. In a geographically expansive field study, we sampled 5 populations of P. microps occurring along the salinity gradient (decreasing from West to East) in the Baltic Sea Area over 3 consecutive years. Nest resource quantity and quality decreased from West to East, and a correlation between mussel size and male body size was detected. Population density, sex ratios, mating- and reproductive success as well as brood characteristics also differed between populations but with a less clear relation to salinity. With this field study we shed light on geographic variation of distinct environmental parameters possibly acting on population differentiation. We provide insights on relevant ecological variation, and draw attention to its importance in the framework of context-dependent plasticity of sexual selection.Peer reviewe

Noise Affects Multimodal Communication During Courtship in a Marine Fish

Selection pressures on signals can be substantially modified by a changing environment, but we know little about how modified selection pressures act on multimodal signals. The currently increasing levels of anthropogenic noise in the ocean may affect the use of acoustic signaling relative to other modalities. In the Painted Goby (Pomatoschistus pictus), visual and acoustic signals are associated during courtship behavior, but females usually rely more heavily on acoustic signals than on visual signals in mate choice. In an aquarium experiment, we compared male courtship behavior and female spawning decisions between silent treatments and treatments with additional noise. We found that the relationships between male characteristics, male visual and acoustic courtship, and spawning success were affected by noise. A path analysis revealed that females pay more attention to visual courtship in noisy circumstances compared to control. We conclude that environmental stressors can cause shifts in the use of different signaling modalities for spawning decisions and discuss how selection pressures on multimodal signals may change with increasing noise-levels

Egg density and salinity influence filial cannibalism in common gobies

Filial cannibalism, i.e. the consumption of own offspring, has fascinated animal ecologists for many decades but is still not fully understood. Often assumed to happen primarily due to energetic needs of the cannibalizing parents, we here address a more recent notion that suggests an interplay between egg density, salinity, egg infections and filial cannibalism in fish. Previous evidence indicates that (a) filial cannibalism may be related to egg density that (b) egg pathogens such as water moulds spread more easily on high density clutches and are (c) generally suppressed in high salinity conditions and that (d) parents selectively cannibalize infected eggs, suggesting cannibalism to maximise in high density clutches in low salinity as a response to egg infections. We thus tested if egg density, salinity and their interaction directly affect filial cannibalism using the common goby (Pomatoschistus microps) as a model system. We additionally recorded male brood care behaviour and weight to account for other potentially salinity-related effects. While males unexpectedly cannibalized more eggs in low density instead of high density clutches, we found that egg consumption was higher in low salinity conditions in agreement with our prediction. Neither male behaviour nor metabolism did adequately explain this finding, indicating that variation in filial cannibalism under different environmental conditions such as salinity may indeed be driven by a differential prevalence of egg infections. Significance statement During parental care, parents may forgo taking care of their offspring but rather invest in future reproduction. Filial cannibalism, the consumption of one's own offspring, has often been considered to occur for energetic reasons or as a strategy to reduce investment in less valuable offspring. In this study we specifically test how male brood care behaviour, i.e. egg fanning and filial cannibalism is affected by salinity and egg density (how tightly females decide to place their eggs) in a small marine fish. Our experimental approach is to assess environmental influences and to show their relevance for the evolution and persistence of such a seemingly maladaptive behavioural trait with drastic consequences for fish reproduction. We conclude that variation in filial cannibalism under different environmental conditions such as salinity may indeed be driven by a differential prevalence of egg infections

Data from: Water mold infection but not paternity induces selective filial cannibalism in a goby

Many animals heavily invest in parental care but still reject at least some of their offspring. Although seemingly paradoxical, selection can favor parents to neglect offspring of particularly low reproductive value, for example, because of small survival chances. We here assess whether filial cannibalism (FC), where parents routinely eat some of their own young, is selective in response to individual offspring reproductive value. We performed two independent laboratory experiments in the common goby (Pomatoschistus microps) to test whether caring fathers preferentially cannibalize eggs of a given infection history and paternity. While males did not discriminate kin from nonkin eggs, they consumed significantly more eggs previously exposed to water mold compared to uninfected eggs. Our findings clearly show that parents differentiate between eggs based on differences in egg condition, and thus complement the prevailing view that FC arises for energetic reasons. By preventing the spread of microbial infections, the removal of molded eggs can constitute an important component of parental care and may represent a key driver of selective FC in a wide array of parental fish

Data from: The noise egg: a cheap and simple device to produce low-frequency underwater noise for laboratory and field experiments

Studying the effect of anthropogenic noise on animal behaviour and physiology is a field of growing scientific and management interest. Anthropogenic noise is internationally seen as major environmental concern, but knowledge of the response of animals to noise and its ecological and evolutionary consequences is disparate. Even though fish and invertebrates form the majority of aquatic taxa, the effects of noise on these taxa are largely understudied. Especially the consequences of noise for short-range communication and behavioural interactions are yet unknown. While experimental studies on this subject are thus greatly needed, the expense of the equipment can be a main factor limiting data generation. Speakers that produce low-frequency sounds under water are currently either too large or too expensive to allow for sufficient replication in many research set-ups. Here, we describe a device that can produce a low-frequency sound, which can be used as an experimental source of noise both in aquaria and in the field. The device is completely self-contained and costs around 10 euros per ‘noise egg’. The sound created consists of frequency bands (harmonics), which has the advantage that broadband and pulsed sounds, such as sounds produced by vocal fish, are easily detected in a spectrogram. Because the sound from the egg attenuates quickly, it can be used in aquaria and in the field to target certain study species or individuals without affecting a large part of the surrounding area. We have developed the device to study the effects of noise on communication and behaviour in small aquatic animals; however, it could be used for other purposes, such as testing the propagation of certain frequencies in shallow-water habitats. We hope the described method will facilitate the generation of experimental data on the effect of noise on behaviour and communication in aquatic animals in a wide variety of study systems and study areas

The noise egg: a cheap and simple device to produce low-frequency underwater noise for laboratory and field experiments

1. Studying the effect of anthropogenic noise on animal behaviour and physiology is a field of growing scientific and management interest. Anthropogenic noise is internationally seen as major environmental concern, but knowledge of the response of animals to noise and its ecological and evolutionary consequences is disparate. Even though fish and invertebrates form the majority of aquatic taxa, the effects of noise on these taxa are largely understudied. Especially the consequences of noise for short-range communication and behavioural interactions are yet unknown. While experimental studies on this subject are thus greatly needed, the expense of the equipment can be a main factor limiting data generation. Speakers that produce low-frequency sounds under water are currently either too large or too expensive to allow for sufficient replication in many research set-ups. Here, we describe a device that can produce a low-frequency sound, which can be used as an experimental source of noise both in aquaria and in the field. The device is completely self-contained and costs around 10 euros per noise egg'. The sound created consists of frequency bands (harmonics), which has the advantage that broadband and pulsed sounds, such as sounds produced by vocal fish, are easily detected in a spectrogram. Because the sound from the egg attenuates quickly, it can be used in aquaria and in the field to target certain study species or individuals without affecting a large part of the surrounding area. We have developed the device to study the effects of noise on communication and behaviour in small aquatic animals; however, it could be used for other purposes, such as testing the propagation of certain frequencies in shallow-water habitats. We hope the described method will facilitate the generation of experimental data on the effect of noise on behaviour and communication in aquatic animals in a wide variety of study systems and study areas

Male personality and female spawning consistency in a goby with exclusive male care

Consistent inter-individual behavioral differences in animals, or animal personalities, are increasingly recognized as an important component of sexual selection. Despite growing evidence for personality-mediated effects on reproductive success in species with biparental care, the link between personality and intrasexual competition or mate choice in species with uniparental care remains largely unexplored. Here, the non-caring sex in particular should seek partners with personality traits that promise high quality care. Therefore, we investigated effects of male personality in the common goby, a well-established model species for sexual selection under exclusive male care. Using competitive trials, we investigated how personality affects male ability to monopolize either of two central reproductive resources, nesting sites (male-male competition) and ready-to-spawn females (female choice). Personalities were scored in a feeding context and thus independent of reproduction. We found that slow-feeding individuals better succeeded in monopolizing nests, but that female spawning decisions were independent of the foraging personality of two male competitors. Instead, females showed a remarkably consistent between-female spawning preference for slightly heavier males and males with more elaborate nests. Our findings indicate that fitness benefits of the male personality type only materialize via male-male competition in environments where nesting sites are a limiting resource, whereas female choice favors large males with elaborate nests independent of male personality. Animal personality can strongly affect reproductive success in species with parental care. We studied this link in the common goby, a fish where males build nests and solely take care of the brood until hatching. Hence, females should choose a male whose personality traits promise high quality care. We scored male personalities and conducted nest-competition and mate-choice trials. We found that male personality had an effect on nest monopolization, but not on female mating preferences. Instead, females agreed remarkably well in their mating decisions and consistently favored large males with elaborate nests. Our results show that male personality is important for nest allocation, which is crucial in environments where nesting sites are rare

Females increase current reproductive effort when future access to males is uncertain

Trade-offs between current and future reproduction shape life histories of organisms, e.g. increased mortality selects for earlier reproductive effort, and mate limitation has been shown to shape male life histories. Here, we show that female life histories respond adaptively to mate limitation. Female common gobies (Pomatoschistus microps) respond to a female-biased operational sex ratio by strongly increasing the size of their first clutch. The plastic response is predicted by a model that assumes that females use the current competitive situation to predict future difficulties of securing a mating. Because female clutch size decisions are much more closely linked to population dynamics than male life-history traits, plastic responses to mate-finding limitations may be an underappreciated force in population dynamics

Noise Affects Multimodal Communication During Courtship in a Marine Fish

Selection pressures on signals can be substantially modified by a changing environment, but we know little about how modified selection pressures act on multimodal signals. The currently increasing levels of anthropogenic noise in the ocean may affect the use of acoustic signaling relative to other modalities. In the Painted Goby (Pomatoschistus pictus), visual and acoustic signals are associated during courtship behavior, but females usually rely more heavily on acoustic signals than on visual signals in mate choice. In an aquarium experiment, we compared male courtship behavior and female spawning decisions between silent treatments and treatments with additional noise. We found that the relationships between male characteristics, male visual and acoustic courtship, and spawning success were affected by noise. A path analysis revealed that females pay more attention to visual courtship in noisy circumstances compared to control. We conclude that environmental stressors can cause shifts in the use of different signaling modalities for spawning decisions and discuss how selection pressures on multimodal signals may change with increasing noise-levels