Sand Goby Pomatoschistus Minutus Research Articles

Spatial and temporal patterns of nest distribution influence sexual selection in a marine fish

In many species, the natural distribution of material resources important for reproduction can profoundly impact reproductive success among individuals and, hence, the opportunity and intensity of sexual selection. Here, we report on a field‐based experiment investigating the effects of nest aggregation on sexual selection in a fish, the sand goby Pomatoschistus minutus. We found that the distribution of potential nests (sparse versus aggregated nest treatments) affected patterns of nest colonization and reproductive success. Specifically, in the treatment with aggregated nesting resources, a greater proportion of nests remained unoccupied by sand goby males. Although the size of nesting males did not differ between treatments, eggs accumulated more rapidly when nests were sparsely distributed. We found that the opportunity for selection decreased over time with the accumulation of eggs in the nests in both the aggregated and sparse treatments. Moreover, the effect of male size on reproductive success was influenced by an interaction between nest distribution and time, with the selection gradient being highest right after nest colonization when nests were aggregated, while the opposite pattern was observed in the sparse nest treatment. Such findings highlight the vital role that environmental and social factors can play in determining the importance of male phenotypic traits (in this case, male size). More broadly, our results also underscore how the natural distribution of resources, both in space and time, can impact the strength of sexual selection acting on wild animal populations.

Genetic analysis reveals the diversity of larval Gobiidae in a temperate estuary

Using molecular tools to examine Gobiidae, the second most abundant taxon in ichthyoplankton samples in the Gulf of Riga (Baltic Sea), the sand goby Pomatoschistus minutus was the most abundant taxon (82% of all individuals analysed), the common goby Pomatoschistus microps constituted 12% and the black goby Gobius niger 6%. The spatiotemporal distribution of P. microps and G. niger indicated a preference for habitats closer to the river inlet and their abundances increased slightly towards the end of the sampling period in summer. The species composition was interpreted in the context of the prevailing habitat conditions, characterized by extremely low water transparency, low salinity, limited spread of vegetated area and dominance of sandy-muddy substrata.

Trophic niche partitioning of littoral fish species from the rocky intertidal of Helgoland, Germany

During a 3-year field study, interspecific and interannual differences in the trophic ecology of littoral fish species were investigated in the rocky intertidal of Helgoland island (North Sea). We investigated trophic niche partitioning of common coexisting littoral fish species based on a multi-tracer approach using stable isotope and fatty acids in order to show differences and similarities in resource use and feeding modes. The results of the dual-tracer approach showed clear trophic niche partitioning of the five target fish species, the goldsinny wrasse Ctenolabrus rupestris, the sand goby Pomatoschistus minutus, the painted goby Pomatoschistus pictus, the short-spined sea scorpion Myoxocephalus scorpius and the long-spined sea scorpion Taurulus bubalis. Both stable isotopes and fatty acids showed distinct differences in the trophic ecology of the studied fish species. However, the combined use of the two techniques added an additional resolution on the interannual scale. The sand goby P. minutus showed the largest trophic plasticity with a pronounced variability between years. The present data analysis provides valuable information on trophic niche partitioning of fish species in the littoral zones of Helgoland and on complex benthic food webs in general.

Odour cues from suitors' nests determine mating success in a fish.

Animals use a range of sensory cues for finding food, avoiding predators and choosing mates. In this regard, the aquatic environment is particularly suitable for the use of olfactory and other chemical cues. Nevertheless, mate choice research, even on aquatic organisms, has focused on visual signals, while chemical cues relevant in sexual selection have been assumed to be 'intrinsic' excretions of mate candidates. Here, using the sand goby Pomatoschistus minutus, a small fish with paternal egg care, we investigated the possibility that 'extrinsic' chemical cues in the males' nests could also have a significant contribution to mating success. We found that females strongly avoided laying eggs into nests subject to the odour of Saprolegnia water moulds (an egg infection) and that this effect was independent of the females' initial, visually based preference for males. To the best of our knowledge, this is the first study to show that chemical cues related to parental failure can play a large role in sexual selection.

Filial cannibalism in a nest-guarding fish: females prefer to spawn in nests with few eggs over many

In fish, fecundity correlates with female body size and egg-tending males often eat small broods. Therefore, small females may prefer to spawn in nests that already contain many eggs, to ensure the brood is as large as possible. In contrast, large females may prefer nests with few eggs, if high egg number or density has a negative effect on egg survival, or if there are drawbacks of spawning last in a nest. To test the hypothesis that female body size affects nest (and male mate) choice, using the sand goby (Pomatoschistus minutus), we allowed small and large females to choose between two males that were matched in size — one guarding a small clutch and the other a large clutch, respectively. We recorded where females spawned (measure of female preference), the combined brood size, male courtship, egg care and nest building. We also quantified the effect of brood size and egg density on egg survival in a separate data set. Although the combined broods did not exceed the small brood sizes that are at risk of being eaten, both small and large females preferred to spawn in nests with smaller clutch sizes. This preference could not be explained by more courtship or male parental effort, nor by reduced survival of larger or denser broods. Instead, our result might be explained by females avoiding the danger of cannibalism of young eggs by males or the risk of reduced egg health associated with being near the nest periphery.

Population structure, production and feeding habit of the sand goby Pomatoschistus minutus (Actinopterygii: Gobiidae) in the Minho estuary (NW Iberian Peninsula)

Estuaries are highly productive and heterogeneous ecosystems, and hence they provide an excellent opportunity to study the population structure and feeding patterns of euryhaline species like the sand goby Pomatoschistus minutus. In this context the population dynamics of the sand goby was investigated during 18 months in the Minho estuary (NW Iberian Peninsula). The fish density varied significantly among estuarine areas and seasons, with most of the individuals being caught near the river mouth during the autumn (38 % of the total). Males, females and juveniles were not spatially segregated, as well as fishes belonging to different size classes. The sand goby fed mostly on crustaceans (Frequency of Occurrence - FO) = 35 %; Relative Abundance - RA = 40 %), detritus (FO = 27 %; RA = 23 %) and annelids (FO = 15 %; RA = 14 %), with no obvious difference between the diet of males and females. The density (up to 20 times) and the secondary production (up to 16 times) of the sand goby were substantially higher than in other southern European estuaries. Our results highlighted that the population dynamics of the sand goby can vary considerably among nearby systems and that the Minho estuary, probably due to the lower temperature and salinity values and also the different water circulation regime found in this system when compared to other Iberian estuaries, promotes noticeable differences on the P. minutus population dynamics.

Courtship Sounds Advertise Species Identity and Male Quality in Sympatric Pomatoschistus spp. Gobies

Acoustic signals can encode crucial information about species identity and individual quality. We recorded and compared male courtship drum sounds of the sand goby Pomatoschistus minutus and the painted goby P. pictus and examined if they can function in species recognition within sympatric populations. We also examined which acoustic features are related to male quality and the factors that affect female courtship in the sand goby, to determine whether vocalisations potentially play a role in mate assessment. Drums produced by the painted goby showed significantly higher dominant frequencies, higher sound pulse repetition rates and longer intervals between sounds than those of the sand goby. In the sand goby, male quality was predicted by visual and acoustic courtship signals. Regression analyses showed that sound amplitude was a good predictor of male length, whereas the duration of nest behaviour and active calling rate (i.e. excluding silent periods) were good predictors of male condition factor and fat reserves respectively. In addition, the level of female courtship was predicted by male nest behaviour. The results suggest that the frequency and temporal patterns of sounds can encode species identity, whereas sound amplitude and calling activity reflects male size and fat reserves. Visual courtship duration (nest-related behaviour) also seems relevant to mate choice, since it reflects male condition and is related to female courtship. Our work suggests that acoustic communication can contribute to mate choice in the sand goby group, and invites further study.

Characterization of polymorphic microsatellite markers for the bearded goby Sufflogobius bibarbatus

Fourteen polymorphic microsatellite markers with tetranucleotide repeats were developed for the bearded goby (Sufflogobius bibarbatus) from partial genomic DNA libraries using a repeat enrichment protocol, and characterized using two putative populations from the northern Benguela. The average number of alleles per locus ranged from 4 to 34, and the observed heterozygosities across loci were between 0.237 and 0.983. We also tested the utility of these markers in two other marine gobies; sand goby Pomatoschistus minutus and two-spotted goby Gobiusculus flavescens. These polymorphic markers can be employed to investigate population structure and related questions of the bearded goby.

Food conditions of the sand goby Pomatoschistus minutus in shallow waters: An analysis in the context of Dynamic Energy Budget theory

Several epibenthic species aggregate in large numbers in shallow waters during summer, feeding on the available benthic meio- and macrofauna. Whether this concentration leads to periods of food limitation affecting habitat quality for some of these species is not clear at present. In this study we applied the Dynamic Energy Budget (DEB) theory as a framework to analyze growth, in order to investigate the food conditions of the sand goby Pomatoschistus minutus in estuarine and coastal Atlantic waters. Average food conditions over the entire lifespan were determined based on maximum sizes of sand gobies reported in various areas. In addition, seasonal growth trajectories in the field were compared to model simulations with unlimited food conditions. Results showed that growth of sand gobies in the field is at the same level or even above model simulations. Our findings suggest that sand gobies' growth is not food-limited across their distributional range and that growth variability between areas is mainly related to environmental temperature conditions. Limitations of the present approach are discussed.

Sand goby males trade off between defence against egg predators and sneak intrusions

According to life-history theory, a care-taking parent should balance investment in current and future reproduction in such a way that it maximizes lifetime reproductive success. In the sand goby Pomatoschistus minutus, a small marine fish with paternal care, nest-guarding males may lose current reproductive success to both parasitically fertilizing males and egg predators. Here, we observed sand gobies at a marine and a brackish site, two geographically distant and ecologically different habitats. In a field experiment, we found that sand gobies at the marine site suffered from severe egg predation by netted dogwhelks Nassarius nitidus, which are lacking at the brackish site. Because egg laying takes hours and several females often lay eggs sequentially in one nest, the risk of parasitic spawnings and egg predation overlaps in time during breeding activities. Hypothesizing that egg predators might influence the success of parasitic spawnings, we then simulated these natural conditions in a laboratory experiment with the presence or absence of egg predators, combined with the presence of sneaker males. As expected, in the egg predator treatment, egg-guarding males had to compromise between defence behaviours and thus had less time to devote to defence against sneaker males. Sneaker males took advantage of the situation and approached the nests more actively than in the predator-free treatment. However, the increase in approaches did not result in more successful parasitic fertilizations by sneaker males, as determined using microsatellite DNA. Nevertheless, in nature the adjustment of time budgets by the egg-guarding male are likely to have serious fitness consequences, both if the male fails to defend his paternity and if he fails to defend his offspring.

Investment in testes, sperm‐duct glands and lipid reserves differs between male morphs but not between early and late breeding season in Pomatoschistus minutus

This study of the sand goby Pomatoschistus minutus, a nest-holding fish with paternal care, focused on gonadal investment among males of different sizes collected early and late in the breeding season. All males caught at the nest had breeding colour, whereas trawl-caught fish consisted of males both with and without colour. The absence or presence of breeding colour was a good predictor of testes investment. Compared to males with breeding colour, males without colour were smaller in body size but had extraordinarily large testes. In absolute terms, testes mass of males without breeding colour was on average 3.4 times greater than those of males with breeding colour. Since small colourless males are known to reproduce as sneaker males, this heavy investment in testes probably reflects that they are forced to spawn under sperm competition. Contrary to testes size, sperm-duct glands were largest among males with breeding colour. These glands produce mucins used for making sperm-containing mucous trails that males place in the nest before and during spawning. Since both sneakers and nest-holders potentially could benefit from having large glands, this result is intriguing. Yet, high mucus production may be more important for nest-holders, because it also protects developing embryos from infections. There was no significant effect of season on body size, testes or sperm-duct glands size, but colourless males tended to be less common late in the season. Possibly this may indicate that individual small colourless males develop into their more colourful counterparts within the breeding season.

Differential modes of selection on the rhodopsin gene in coastal Baltic and North Sea populations of the sand goby, Pomatoschistus minutus

An excellent model to elucidate the mechanisms and importance of evolution in the marine environment is the spectral tuning mechanism of the visual pigment in vertebrates. In the sand goby Pomatoschistus minutus (Teleostei; Gobiidae), a distribution-wide study showed that spatial variation at the rhodopsin gene (RH1) matches the characteristics of specific light environments. This match suggests that populations are locally adapted to selective light regimes targeting the RH1 gene. If so, then the direction of selection should depend on the regional spatial and temporal stability of the light conditions. We tested this prediction by comparing goby populations from two regions: the Baltic Sea, characterized by divergent, but temporally stable light conditions, and the North Sea, characterized by locally heterogeneous and temporally variable light conditions. RH1 sequences of 491 Pomatoschistus minutus individuals from 15 locations were analysed. We found that variation at the RH1 gene in the Baltic populations showed signatures of diversifying selection, whereas the RH1 gene in the North Sea showed signatures of stabilizing selection. These different modes of selection are consistent with the regional light conditions and hence support our predictions, but may also be influenced by migration between the open sea and more turbid estuarine environments. An interesting observation is that within one gene, synonymous and non-synonymous SNPs show a totally different pattern between populations. Population differentiation based on non-synonymous SNPs of the RH1 gene correlated with spectral variation of the local environment of the sand goby populations. In contrast, the differentiation based on synonymous SNPs of RH1 reflects more the neutral historical pattern of the species.

Offspring recognition and the influence of clutch size on nest fostering among male sand gobies, Pomatoschistus minutus

When parental care is costly, parents should avoid caring for unrelated young. Therefore, it is an advantage to discriminate between related and unrelated offspring so that parents can make informed decisions about parental care. In the present study, we test the hypothesis that male sand gobies (Pomatoschistus minutus) recognize and differentially care for their own offspring when given a choice between a nest with sired eggs and a second nest with eggs sired by an unrelated male. The sand goby is a species with exclusive and costly paternal care. Male parasitic spawnings (e.g., sneaking) as well as nest takeovers by other males are common. Our results show that nests containing sired eggs were preferred and received significantly more care, as measured by nest building and nest occupancy, than nests with foreign eggs even when males cared for both nests. These findings suggest that males respond to paternity cues and recognize their own clutches. Relative clutch size also had a significant effect on male parental care. When sired clutches were larger than foreign clutches, males preferred to care for their own nest. In the few cases where males chose to take care of foreign nests, the foreign clutch was larger than their own clutch. Taken together, our results provide evidence that both paternity cues and clutch size influence parenting decisions among male sand gobies.

Mito-nuclear discordance in the degree of population differentiation in a marine goby

An increasing number of phylogeographic studies on marine species shows discordant patterns in the degree of population differentiation between nuclear and mitochondrial markers. To understand better which factors have the potential to cause these patterns of discordance in marine organisms, a population genetic study was realized on the sand goby Pomatoschistus minutus (Pallas 1770; Gobiidae, Teleostei). Sand gobies from eight European locations were genotyped at eight microsatellite markers. Microsatellites confirmed the global phylogeographical pattern of P. minutus observed with mitochondrial DNA (mtDNA) markers and nuclear allozyme markers. Three groups consistent with the mitochondrial lineages were defined (the Mediterranean, Iberian and North Atlantic groups) and indications of a recent founder event in the northern Baltic Sea were found. Nevertheless, differences in the degree of population differentiation between the nuclear and mitochondrial markers were large (global F(ST)-values for microsatellites=0.0121; for allozymes=0.00831; for mtDNA=0.4293). Selection, sex-biased dispersal, homoplasy and a high effective population size are generally accepted as explanations for this mitonuclear discrepancy in the degree of population differentiation. In this study, selection on mtDNA and microsatellites, male-biased dispersal and homoplasy on microsatellite markers are unlikely to be a main cause for this discrepancy. The most likely reason for the discordant pattern is a recent demographical expansion of the sand goby, resulting in high effective population sizes slowing down the differentiation of nuclear DNA.

Estuarine recruitment of a marine goby reconstructed with an isotopic clock

Information on movement patterns of marine fishes between estuarine populations and stocks at sea is fundamental to understanding their population dynamics, life history tactics and behavior. Furthermore, understanding estuarine habitat use by marine fishes is crucial for their effective conservation and integrated estuarine management. Although large numbers of young marine fish make use of temperate estuaries in highly predictable abundance patterns, very little is known about how estuarine populations interact with the populations at sea. Recruitment of sand goby Pomatoschistus minutus (Pallas, 1770) into the low salinity zone of the Scheldt estuary (Belgium) was reconstructed over an entire year by means of an isotopic clock. These results were combined with a growth model to yield age and length at immigration. Sand gobies entered the upper Scheldt estuary almost continuously from May onwards, except in July when they appeared to avoid the estuary due to warm summer temperatures. About 70% of the fish caught in the upper estuary resided there for less than 1 month, which indicates a strong temporal overlap of immigration and emigration. This complex migration pattern suggests that estuarine residence is caused by trade-offs made at the individual level, whereby migration is probably triggered by temperature. The high turnover of individuals in the estuarine population leads us to question the functional role of the estuary for marine fishes. Sand gobies entering the upper estuary had a wide range of ages and body sizes, although they were at least 2 months old and had a minimum standard length of approximately 20 mm. This study shows that the use of an isotopic clock strongly complements catch data and is useful to describe the connectivity between populations.

Effect of digestion on the δ13C and δ15N of fish‐gut contents

Gut contents of sand goby Pomatoschistus minutus showed higher C and N isotope values than the food before consumption. This enrichment was more pronounced in the hindgut than in the foregut, probably because of preferential assimilation of 12C and 14N along the gastro‐intestinal tract. The results indicated that the shift towards higher values in the alimentary canal occurs in the first 2 h after feeding.

Mate compatibility, parental allocation and fitness consequences of mate choice in the sand goby Pomatoschistus minutus

Recent theory and empirical work suggests that there may be variation among females in mate preferences that is adaptive. One of the possible mechanisms maintaining variability in preferences and preferred traits is that the benefits of mate choice may depend on compatibility with potential mating partners. We examined fitness consequences of mate choice in a species of fish, the sand goby, Pomatoschistus minutus with a special focus on mate compatibility. Females were given the opportunity to establish their mate preferences in a dichotomous mate choice experiment. This information was then applied by mating the focal or control female with either the preferred or the non-preferred male. The parental performance of the males of these four mating combinations was then measured. In a separate experiment, we assessed the female differential allocation by determining the residual gonad weight of spawned females as a measure of the proportion of eggs spawned. We also estimated the amount of filial cannibalism separately for both sexes. Our results show that preferred males provided benefits in the form of an increased number of hatching eggs. This benefit was the same when the male was mated with a focal or a control female. Hence, we found no support for benefits that depend on mate compatibility. Neither did we find support for the hypothesis that females would lay a different number of eggs depending on the male status. The results also indicate that male filial cannibalism has a strong role in determining hatching success in this species.

Changes in δ13C and δ15N in different tissues of juvenile sand goby Pomatoschistus minutus: a laboratory diet-switch experiment

Studies on diet or migration of organisms based on stable isotopes require precise estimates of how quickly stable isotope ratios change in the investigated tissues. Isotopic turnover rates in fish, however, are poorly understood. Prior to field applications of the stable isotope technique for investigating sand goby Pomatoschistus minutus migrations, a laboratory diet-switch experiment was conducted to (1) determine C and N isotopic turnover rates in sand goby muscle, liver and heart tissue, and (2) evaluate the relative contribution of growth and metabolic replacement to the total change in isotopic composition. Both time-based and growth-based models adequately described the carbon and nitrogen isotopic change in each tissue. The variation in isotopic turnover rates among the tissues and elements could be attributed to differences in metabolic activity. Muscle tissue had the slowest turnover rates, with half-lives of approximately 25 and 28 d for δ13C and δ15N, respectively. The shortest half-life value for δ15N was in liver tissue (3 d) and for δ13C in heart tissue (6 d). The rate of isotopic change in goby muscle tissue was mainly regulated by somatic growth, but metabolic replacement significantly accelerated the turnover rate for δ13C. In liver and heart tissue, basal metabolism contributed considerably to the isotopic shift. As a result, effects of short-term food deprivation were only found in liver and heart tissue. Although the observed trophic fractionation factors were within reported ranges, they were exceptionally large for δ13C in muscle and liver tissue.

Urogenital papilla feminization in male Pomatoschistus minutus from two estuaries in northwestern Iberian Peninsula

Recently, male urogenital papilla feminization (UGPF) in the sand goby Pomatoschistus minutus was reported in several UK estuaries with high levels of estrogenic compounds. The fact that this species is also common in southern European estuaries, together with its life-cycle characteristics, prompted us to investigate P. minutus UGPF in the northwestern of Iberian Peninsula. Specimens of P. minutus were periodically sampled during 2004 at several locations in two estuaries (Minho and Lima). Evidence for UGPF was recorded in both estuaries, the highest incidence being observed in the Lima estuary (50%). Estrogen levels (17beta-estradiol and estrone) above 100 pg/l were observed in both estuaries, the higher concentrations being found in the Lima estuary. Overall, the results suggest a relationship between the feminization of male P. minutus urogenital papilla and the presence of estrogenic compounds. In the future, more in-depth studies are required in order to use P. minutus as a sentinel species for estrogenic compound monitoring in estuaries.

Seasonal Variations of Selected Biomarkers in Sand Gobies Pomatoschistus minutus from the Guadalquivir Estuary, Southwest Spain

Sand gobies, Pomatoschistus minutus, were collected monthly from September 2002 to August 2003 at a station situated 8 km upstream from the mouth of the Guadalquivir estuary (southwest Spain). Physical parameters of the water and selected biomarkers of organic pollution were recorded in the fish to discuss its potential as a sentinel species in estuaries. The biomarkers selected were the activities of catalase (CAT), 7-ethoxyresorufin-O-deethylase (EROD), and glutathione S-transferase (GST) in the liver and acetylcholinesterase (AChE) and lipid peroxidation (LP) in the head. The results showed an increase in total protein synthesis in late spring and early summer coinciding with the reproductive period as well as the release of fresh water from a dam situated 110 km upstream. During the same period, a significant depletion of hepatic GST and head AChE but higher LP levels in this tissue suggest exposure to pesticides such as those applied to crops established along the course of the river and reaching the estuary mostly when the freshwater discharges occur. Changes in CAT and EROD activities fluctuated randomly and were not noted as seasonally dependent. Biomarker fluctuations in sand goby are discussed as normal seasonal variations, but other variables-such as potential local pollution inputs-cannot be disregarded.