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In externally fertilizing species, the gametes of both males and females are exposed to the influences of the environment into which they are released. Sperm are sensitive to abiotic factors such as salinity, but they are also affected by biotic factors such as sperm competition. In this study, the authors compared the performance of sperm of three goby species, the painted goby, Pomatoschistus pictus, the two-spotted goby, Pomatoschistus flavescens, and the sand goby, Pomatoschistus minutus. These species differ in their distributions, with painted goby having the narrowest salinity range and sand goby the widest. Moreover, data from paternity show that the two-spotted goby experiences the least sperm competition, whereas in the sand goby sperm competition is ubiquitous. The authors took sperm samples from dissected males and exposed them to high salinity water (31 PSU) representing the North Sea and low salinity water (6 PSU) representing the brackish Baltic Sea Proper. They then used computer-assisted sperm analysis to measure the proportion of motile sperm and sperm swimming speed 10 min and 20 h after sperm activation. The authors found that sperm performance depended on salinity, but there seemed to be no relationship to the species' geographical distribution in relation to salinity range. The species differed in the proportion of motile sperm, but there was no significant decrease in sperm motility during 20 h. The sand goby was the only species with motile sperm after 72 h., (© 2021 The Authors. Journal of Fish Biology published by John Wiley & Sons Ltd on behalf of Fisheries Society of the British Isles.)

Studies of colonization of new habitats that appear from rapidly changing environments are interesting and highly relevant to our understanding of divergence and speciation. Here, we analyse phenotypic and genetic variation involved in the successful establishment of a marine fish (sand goby, Pomatoschistus minutus) over a steep salinity drop from 35 PSU in the North Sea (NE Atlantic) to two PSU in the inner parts of the post-glacial Baltic Sea. We first show that populations are adapted to local salinity in a key reproductive trait, the proportion of motile sperm. Thereafter, we show that genome variation at 22,190 single nucleotide polymorphisms (SNPs) shows strong differentiation among populations along the gradient. Sequences containing outlier SNPs and transcriptome sequences, mapped to a draft genome, reveal associations with genes with relevant functions for adaptation in this environment but without overall evidence of functional enrichment. The many contigs involved suggest polygenic differentiation. We trace the origin of this differentiation using demographic modelling and find the most likely scenario is that at least part of the genetic differentiation is older than the Baltic Sea and is a result of isolation of two lineages prior to the current contact over the North Sea-Baltic Sea transition zone., (© 2020 The Authors. Journal of Evolutionary Biology published by John Wiley & Sons Ltd on behalf of European Society for Evolutionary Biology.)

Body size, social setting, and the physical environment can all influence reproductive behaviours, but their interactions are not well understood. Here, we investigated how male body size, male-male competition, and water turbidity influence nest-building behaviour in the sand goby (Pomatoschistus minutus), a marine fish with exclusive paternal care. We found that environmental and social factors affected the nest characteristics of small and large males differently. In particular, association between male size and the level of nest elaboration (i.e. the amount of sand piled on top of the nest) was positive only under clear water conditions. Similarly, male size and nest entrance size were positively associated only in the absence of competition. Such interactions may, in turn, help to explain the persistence of variation in reproductive behaviours, which-due to their importance in offspring survival-are otherwise expected to be under strong balancing selection.

This study aims to characterize the estrogen receptor (er) in sand goby (Pomatoschistus minutus) and determine the temporal effects of 17α-ethinyl estradiol (EE2) on erα and vitellogenin (vtg) gene expression in males. Two partial cDNA sequences (erα and erβ1) are presented showing conserved structural features with ers of other species. Transcript levels for both ers were low in control fish but EE2 exposure (11 ng/L, for 29 days) increased both to a pattern similar to vitellogenic females. The relative expression of three vtg genes (vtga, vtgb and vtgc) along with erα was determined in control and male fish exposed to EE2 (11 ng/L) at multiple time-points over 29 days. All four transcripts were significantly induced due to exposure and expression rose during the time course with distinct temporal patterns and vtga reached a substantially higher level at the end of the time course coinciding with rapid elevation in erα expression., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

To date, mate choice studies have mostly focused on establishing which mates are chosen or how the choices are performed. Here, we combined these two approaches by empirically testing how latency to mate is affected by various search costs, variation in mate quality and female quality in the sand goby (Pomatoschistus minutus). Our results show that females adjust their mating behaviour according to the costs and benefits of the choice situation. Specifically, they mated sooner when access to males was delayed and when the presence of other females presented a mate sampling cost. We also found a positive link between size variation among potential mating partners and spawning delay in some (but not all) experimental conditions. By contrast, we did not find the number of available males or the females' own body size ('quality') to affect mating latency. Finally, female mating behaviour varied significantly between years. These findings are notable for demonstrating that (i) mate sampling time is particularly sensitive to costs and, to a lesser degree, to variation among mate candidates, (ii) females' mating behaviour is sensitive to qualitative rather than to quantitative variation in their environment, and (iii) a snapshot view may describe mate sampling behaviour unreliably.

In many animals acquiring limited reproductive opportunities involves competition for resources, mates and opposite-sex gametes. There is ambiguity in which competitive steps are included in measures of sexual selection: individuals who fail to obtain resources necessary for reproduction are often excluded. We illustrate the implications of variation in who is included in measures of selection. We quantified selection on male length and the opportunity for selection associated with nest acquisition, mate acquisition, and fertility of mates at two levels of density and two levels of nest availability in the sand goby. Both measures varied significantly across the three episodes of selection. Nest and mate acquisition contributed substantially to the overall opportunity for selection and selection on male size. Focusing only on males with nests led to lower estimates of selection. The effects of density and nest availability depended on the selective episodes considered. While there is nothing wrong with focusing on particular episodes of interest, inconsistency in who is included in measures of sexual selection across studies will make it difficult to answer broad research questions.

Endocrine disrupting chemicals (EDCs) are a diverse group of compounds that can mimic, block or modulate the synthesis of natural hormones. They are known to cause impairment of reproduction of aquatic organisms at very low concentrations. The aim of this study was to examine how exposure from 10 to 31 days to 17alpha-ethinyl estradiol (EE2, 41 ng L(-1)) affects the courtship and parental care behaviour of male sand gobies (Pomatoschistus minutus). The sand goby exhibits a polygynous mating system, where males compete for females and provide paternal care. First, male courtship performance towards a stimulus female was recorded with video camera. Secondly, after the male had received eggs his parental care behaviour was video recorded. In addition to behavioural endpoints, we measured the expression of hepatic vitellogenin (Vtg) and zona radiata protein (Zrp) mRNA, as well as common somatic indices. Our study shows that exposure to EE2 affected male fanning behaviour during both courtship and parental care. Interestingly, small exposed males increased their courtship fanning to similar levels as larger control males. However, during parental care egg fanning was not related to male size, and all exposed males fanned more than control males. The EE2-exposure induced Vtg and Zrp mRNA expression in males and decreased hepatosomatic index (HSI), and increased gonadosomatic index (GSI). Females prefer males that fan more, which will favour the small EDC exposed males. This may lead to mating that favours males that are not strong enough to tend the eggs until they hatch, thus decreasing the reproductive success of individuals., (2009 Elsevier B.V. All rights reserved.)

Endocrine disrupting chemicals (EDCs), natural or manmade, are known to interfere with the endocrinology of organisms and also cause behavioural changes. The aim of this study was to test how 1-4weeks exposure to 17alpha-ethinyl estradiol (EE2, 11ngL(-1)) affects nest building, courtship and aggressive behaviour of male fish. Our study species, the sand goby (Pomatoschistus minutus) exhibits a polygynous mating system, in which males compete for females and defend their nest against intruders. Nest takeovers are common in their nest-constrained habitat. In our experiment, control and EE2-exposed males were first allowed to build a nest and mate with non-exposed females. When the males had received eggs in their nest, three rival males were introduced into the test aquarium, and the males were left to compete for the nest site overnight. Courtship and aggressive defence behaviour were recorded using a video camera. In addition to behavioural endpoints we measured the expression of hepatic vitellogenin (Vtg) and zona radiata protein (Zrp) mRNA, and several common somatic indices. Our study showed that exposure to EE2 delays nest building and decreases male courtship and leading behaviour. Additionally, EE2-exposed males were significantly less aggressive than control males. Nest takeover rate was not affected by EE2 exposure: an equal percent of males in both treatments lost their nest to competitors. EE2 exposure also induced Vtg and Zrp mRNA expression in males and decreased the hepatosomatic index. The observed changes in nest building, courtship and aggressive behaviour of EE2-exposed males are likely to have negative implications for male reproductive success.

According to theory, directional female choice for male sexual ornaments is expected to erode underlying genetic variation. Considerable attention, in this regard, has been given to understanding the ubiquity of heritable genetic variation in both female choice and male sexual traits. One intriguing possibility emerging from this work is that persistent genetic variation could be maintained, over time, by variation in female mate preferences. Here, we report the results of a four-year study showing significant year-to-year fluctuations in mate preferences in a small marine fish, the sand goby, Pomatoschistus minutus. Although the average size of mature fish varied across years, we were unable to find direct evidence linking this variation to differences in female preferences among years. Our results, nevertheless, underscore the importance of temporal fluctuations in female mate preferences, as these can have important consequences for understanding variation in sexual traits and the intensity of sexual selection.

Reproductive activities are often conspicuous and can increase the risk of predation. Evidence suggests that individuals are capable of responding to predators in a risk-sensitive manner. However, most studies tend to consider only the predator-mediated responses of males and females in isolation and with little regard to differences in local environmental conditions. Here, we experimentally investigate the effects of environmental visibility (turbidity) and predation risk on reproductive decisions in the sand goby, Pomatoschistus minutus, when exposed to a visually oriented predator, the European perch, Perca fluviatilis. We found that gobies were more reluctant to spawn in the predator's presence, although larger males spawned sooner than smaller males. Interestingly, latency to spawning was unaffected by the visual environment, suggesting that gobies may be relying on non-visual cues under turbid conditions.

Endocrine disrupting chemicals (EDCs) are a widely studied group of chemicals that interfere with the endocrinology of organisms. So far, few studies have demonstrated the effect of EDCs on the reproductive behavior of aquatic wildlife. Here we show that sand goby males' (Pomatoschistus minutus) success in mating competition greatly decreases after an exposure for 7 to 24 days to 17alpha-ethinyl estradiol (EE2, measured concentration 4 ng L(-1)). The sand goby exhibits a polygynous mating system with male parental care, in which males compete for nest sites and females. The aim of this study was to test how EE2 exposure affects the ability of males to compete for breeding resources, i.e. nest sites and mates. First, EE2 exposed males competed over a nest site against a non-exposed, control male of the same size. Secondly, we examined male courtship behavior and female mate preferences for EE2 exposed males and similar-sized non-exposed, control males. In addition to the behavioral experiments we determined the zona radiata protein (Zrp) mRNA gene expression and measured morphometric indicators of sexual maturation. Our study revealed that EE2 treated males were not able to acquire or defend a nest site. Additionally, EE2 treated males spent significantly less time in active courtship and nest leading behavior than control males. As a result, females clearly preferred to mate with control males. However, we found no significant differences in Zrp mRNA expression or the morphometric indicators between treatments. Our study illustrates that exposure to this EDC can greatly reduce the chances of an individual reproducing successfully. Moreover, it demonstrates that severe behavioral effects can be seen before any effects are detectable at the molecular or morphometric level.

In aquatic environments, endocrine disrupting chemicals (EDCs) that interfere with the reproductive physiology of males form a threat to the reproduction of populations. This is often manifested as decreased sexual performance or sterility among males. We show that exposure to EDCs can directly affect the mating system of a marine fish, the sand goby (Pomatoschistus minutus). We exposed males for 1 to 4 weeks to two different concentrations (5 ng L(-1) and 24 ng L(-1)) of 17alpha-ethinyl estradiol (EE2); a synthetic compound mimicking estrogen and a water control. The sand goby exhibits a polygynous mating system, in which male mating success is typically skewed towards the largest males, resulting in strong sexual selection for increased male size. Our experiment shows that when males have been exposed to EE2, male size has a smaller effect on mating success, resulting in weaker sexual selection on male size as compared to the control. There was an interaction between treatment and exposure time on the expression of vitellogenin and zona radiata protein mRNAs. Males exposed to high EE2 reached much higher expression levels than males exposed to low EE2. Of the somatic markers, the hepatosomatic index was lower in males exposed to high EE2 than in the low EE2 and control males. Our results suggest that exposure to EDCs can have effects on the mating system before physiological changes are observable. These effects can be of profound nature as they interfere with sexual selection, and may in the long run lead to the loss of traits maintained through sexual selection.

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.

Filial cannibalism (the consumption of one's own offspring) is thought to represent an adaptive strategy in many animals. However, little is known about the details of which offspring are consumed when a parent cannibalizes. Here, we examined patterns of within-brood filial cannibalism in the sand goby (Pomatoschistus minutus). Males spawned sequentially with two females, and we asked whether males cannibalized selectively with regard to egg size or the order in which eggs were received. Males preferentially consumed the larger eggs of the second female they spawned with. Because larger eggs took longer to hatch, and because female 2's eggs were up to 1 day behind those of female 1, such preferential cannibalism might allow males to decrease the time spent caring for the current brood and re-enter the mating pool sooner. More work is needed to understand the fitness consequences of such selective cannibalism.

Why should animals knowingly consume their own young? It is difficult to imagine many circumstances in which eating one's own young (i.e., filial cannibalism) actually increases an individual's fitness; however, filial cannibalism commonly co-occurs with parental care in fishes. The evolutionary significance of filial cannibalism remains unclear. The most commonly accepted explanation is that filial cannibalism is a mechanism by which caring males gain energy or nutrients that they reinvest into future reproduction, thereby increasing net reproductive success. There is mixed support for this hypothesis and, at best, it can only explain filial cannibalism in some species. A recent alternative hypothesis suggests that filial cannibalism improves the survivorship of remaining eggs by increasing oxygen availability, and thus increases current reproductive success. This theory has received little attention as of yet. We evaluated the hypothesis of oxygen-mediated filial cannibalism in the sand goby by examining the effect of oxygen and egg density on the occurrence of filial cannibalism, evaluating the effects of partial clutch cannibalism on the survivorship of remaining eggs, and comparing potential costs and benefits of filial cannibalism related to the net number of eggs surviving. Indeed, we found that oxygen level and egg density affected the occurrence of cannibalism and that simulated partial clutch cannibalism improved survivorship of the remaining eggs. Additionally, because increased egg survivorship, stemming from partial egg removal, compensated for the cost of cannibalism (i.e., number of eggs removed) at a range of cannibalism levels, filial cannibalism potentially results in no net losses in reproductive success. However, oxygen did not affect egg survivorship. Thus, we suggest a more general hypothesis of filial cannibalism mediated by density-dependent egg survivorship.

Pomatoschistus minutus show paternal care in a resource defence mating system. We investigated the effect of nest-site availability on parasitic spawning. Each experimental pool contained four potentially nest-building males, four females and nests-sites in shortage (2) or excess (6). Both treatments were conducted in two populations; one with natural nest-sites in excess, one with a nest-site shortage. Microsatellite-DNA revealed that all nest-holders had fertilized most of the eggs they tended. Yet, 35% of the nests contained eggs fertilized by another male and 14.4% of the males had performed parasitic spawning. There was no site or treatment effect. Several females spawned in two nests, which coincided with parasitic spawnings, suggesting a cost to the nest-holder in terms of lost mating success. Nest-holders with and without eggs and non-nesting males all spawned parasitically, generating a significantly lower opportunity for sexual selection compared to if there had been no parasitic spawning.

Eutrophication as a result of human activity has resulted in increased algal blooms and turbidity in aquatic environments. We investigated experimentally the effect of algal turbidity on the mating system and sexual selection in the sand goby, Pomatoschistus minutus (Pallas), a marine fish with a resource-defence mating system and paternal care. Owing to male-male competition and female choice, large males can monopolize multiple mates, while some males do not achieve mating at all. We show that the number of eggs laid was the same in both turbid and clear tanks but that mating success was more evenly distributed among males in turbid than in clear water. The opportunity for sexual selection was lower in turbid conditions. In turbid conditions mating success was less skewed towards large males. Our results suggest that increased turbidity can change mating systems and decrease the opportunity for sexual selection as well as selection intensity.