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In animals, colorful and conspicuous ornaments enhance individual attractiveness to potential mates, but are typically tempered by natural selection for crypsis and predator protection. In species where males compete for females, this can lead to highly ornamented males competing for mating opportunities with choosy females, and vice versa. However, even where males compete for mating opportunities, females may exhibit conspicuous displays. These female displays are often poorly understood and it may be unclear whether they declare mating intent, signal intrasexual aggression or form a target for male mate preference. We examined the function of the conspicuous dark eyes that female sand gobies temporarily display during courtship by experimentally testing if males preferred to associate with females with artificially darkened eyes and if dark eyes are displayed during female aggression. By observing interactions between a male and two females freely associating in an aquarium we also investigated in which context females naturally displayed dark eyes. We found that dark eyes were more likely to be displayed by more gravid females than less gravid females and possibly ahead of spawning, but that males did not respond behaviorally to dark eyes or prefer dark-eyed females. Females behaving aggressively did not display dark eyes. We suggest that dark eyes are not a signal per se but may be an aspect of female mate choice, possibly related to vision.

In viviparous species, a conflict over maternal resource allocation may arise between mothers and embryos, between siblings, and between maternal and paternal genes within an embryo due to relatedness asymmetries. We performed two experiments to study the effects of polyandry and brood relatedness on offspring growth in a placental fish (Heterandria formosa). Polyandry was beneficial as it increased the probability of pregnancy, possibly to avoid genetic incompatibility. However, females mated to four males produced offspring that had a longer maturation time than those of monandrous females. When within-brood relatedness was manipulated, the size of the newborn offspring decreased with time in low-relatedness treatment, whereas in highly related broods, offspring size was constant. Low within-brood relatedness may lead to less cooperative offspring in terms of resource extraction from the mother, which may lead to impaired development during gestation. Offspring conflict may thus reduce the benefits of polyandry in viviparous species., (© 2011 The Authors. Journal of Evolutionary Biology © 2011 European Society For Evolutionary Biology.)

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.)

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.

The magnitude of inbreeding depression is often larger in traits closely related to fitness, such as survival and fecundity, compared to morphological traits. Reproductive behaviour is also closely associated with fitness, and therefore expected to show strong inbreeding depression. Despite this, little is known about how reproductive behaviour is affected by inbreeding. Here we show that one generation of full-sib mating results in a decrease in male reproductive performance in the least killifish (Heterandria formosa). Inbred males performed less gonopodial thrusts and thrust attempts than outbred males (delta = 0.38). We show that this behaviour is closely linked with fitness as gonopodial performance correlates with paternity success. Other traits that show inbreeding depression are offspring viability (delta = 0.06) and maturation time of males (delta = 0.19) and females (delta = 0.14). Outbred matings produced a female biased sex ratio whereas inbred matings produced an even sex ratio.

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.

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.

Social costs are often important in promoting the honesty of sexually selected traits. What happens, then, when social costs are relaxed? In species that breed in shallow coastal waters, increases in the frequency and severity of phytoplankton blooms may undermine the value of visual signals by reducing visibility and, in so doing, lead to dishonest signaling by relaxing the social consequences of high signaling effort for poor-quality individuals. Here, we experimentally test the effects of algally induced water turbidity on the role of male-male competition in facilitating reliable sexual displays in three-spined sticklebacks. We found that males in poor condition reduced their courtship effort in the presence of competition in turbid water. This reduction, however, was to a much lesser extent than that observed in clear water. Thus, courtship under conditions of algal turbidity did not reflect male condition as honestly as courtship in clear water. Algal turbidity also influenced breeding coloration, with males in poor condition reducing their area of red nuptial coloration in turbid conditions. Our findings suggest that anthropogenic disturbance to the signaling environment can potentially reduce the evolutionary potential of sexual selection by diminishing the efficacy of visual displays and weakening socially enforced signals of male quality.

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.

Alternative mating strategies are common in nature and are generally thought to increase the intensity of sexual selection. However, cuckoldry can theoretically decrease the opportunity for sexual selection, particularly in highly polygamous species. We address here the influence of sneaking (fertilization thievery) on the opportunity for sexual selection in the sand goby Pomatoschistus minutus, a marine fish species in which males build and defend nests. Our microsatellite-based analysis of the mating system in a natural sand goby population shows high rates of sneaking and multiple mating by males. Sneaker males had fertilized eggs in approximately 50% of the assayed nests, and multiple sneakers sometimes fertilized eggs from a single female. Successful males had received eggs from 2 to 6 females per nest (mean = 3.4). We developed a simple mathematical model showing that sneaking in this polygynous sand goby population almost certainly decreases the opportunity for sexual selection, an outcome that contrasts with the usual effects of cuckoldry in socially monogamous animals. These results highlight a more complex and interesting relationship between cuckoldry rates and the intensity of sexual selection than previously assumed in much of the literature on animal mating systems.

Molecular markers have proved extremely useful in resolving mating patterns within individual populations of a number of species, but little is known about how genetic mating systems might vary geographically within a species. Here we use microsatellite markers to compare patterns of sneaked fertilization and mating success in two populations of sand goby (Pomatoschistus minutus) that differ dramatically with respect to nest-site density and the documented nature and intensity of sexual selection. At the Tvärminne site in the Baltic Sea, the microsatellite genotypes of 17 nest-tending males and mean samples of more than 50 progeny per nest indicated that approximately 35% of the nests contained eggs that had been fertilized by sneaker males. Successful nest holders mated with an average of 3.0 females, and the distribution of mate numbers for these males did not differ significantly from the Poisson expectation. These genetically deduced mating-system parameters in the Tvärminne population are remarkably similar to those in sand gobies at a distant site adjoining the North Sea. Thus, pronounced differences in the ecological setting and sexual selection regimes in these two populations have not translated into evident differences in cuckoldry rates or other monitored patterns of male mating success. In this case, the ecological setting appears not to be predictive of alternative male mating strategies, a finding of relevance to sexual selection theory.

Filial cannibalism (the consumption of one's own viable offspring) is common among fish with paternal care. In this study, I use a computer simulation to study simultaneous evolution of male filial cannibalism and female mate choice. Under certain conditions, selection on parental males favors filial cannibalism. When filial cannibalism increases a male's probability to raise the current brood successfully, filial cannibalism also benefits the female. However, when egg eating is a male investment into future reproduction, a conflict between female and male interests emerges. Here I investigate how female discrimination against filial cannibals affects evolution of filial cannibalism and how different female choice criteria perform against filial cannibalism. The introduction of discriminating females makes the fixation of filial cannibalism less likely. I introduced three different female choice criteria: (1) females who could discern a male's genotype, that is, whether the male was going to eat eggs as an investment in future reproductive events; (2) energy-choosing females that preferred to mate with males who had enough energy reserves to live through the current brood cycle without consuming eggs; and (3) females that preferred to mate with already mated males, that is, males with eggs in their nest. Genotype choice never coexisted with filial cannibals at fixation and filial cannibals were unable to invade a population with genotype-choosing females. Energy choice was successful only when males had high energy reserves and were less dependent on filial cannibalism as an alternative energy source. The egg choosers frequently coexisted with the cannibals at fixation. When the female strategies were entered simultaneously, the most frequent outcome for low mate sampling costs was that both the cannibals and the egg choice was fixed and all other strategies went extinct. These results suggest that sexual conflicts may not always evolve toward a resolution of the conflict, but sometimes the stable state retains the conflict. In the present case, this was because the egg-preference strategy had a higher fitness than the other female strategies. The outcome of this simulation is similar to empirical findings. In fish with paternal care, male filial cannibalism and female preference for mates with eggs commonly co-occur.