Aquarius Remigis Research Articles

Tests for associations between sexual dimorphism and patterns of quantitative genetic variation in the water strider, Aquarius remigis

The evolution of sexual dimorphisms requires divergence between sexes in the evolutionary trajectories of the traits involved. Discerning how genetic architecture could facilitate such divergence has proven challenging because of the difficulty in estimating non-additive and sex-linked genetic variances using traditional quantitative genetic designs. Here we use a three-generation, double-first-cousin pedigree design to estimate additive, sex-linked and dominance (co)variances for 12 traits in the water strider, Aquarius remigis. Comparisons among these traits, which have size ratios ranging from 1 to 5 (larger/smaller), allow us to ask if sexual dimorphisms are associated with characteristic patterns of quantitative genetic variation. We frame our analysis around three main questions, derived from existing theory and empirical evidence: Are sexual dimorphisms associated with (1) lower additive inter-sex genetic correlations, (2) higher proportions of sex-linked variance, or (3) differences between sexes in autosomal additive and dominance genetic variances? For questions (1) and (2), we find weak and non-significant trends in the expected directions, which preclude definitive conclusions. However, in answer to question (3), we find strong evidence for a positive relationship between sexual dimorphism and differences between sexes in proportions of autosomal dominance variance. We also find strong interactions among the three genetic components indicating that their relative influence differs among traits and between sexes. These results highlight the need to include all three components of genetic (co)variance in both theoretical evolutionary models and empirical estimations of the genetic architecture of dimorphic traits.

Anthropogenic impact on environmental variables and macroinvertebrates community of River Eme, South-East, Nigeria

Macroinvertebrates are good bioindicators of water quality and ecosystem health and are often used to study anthropogenic effect on aquatic ecosystems. Consequently, some environmental variables and macroinvertebrates of Eme river were studied to understand the impact of human activities on this socio-economically important ecosystem. Six stations (reflecting different anthropogenic activities) along the reaches of the river were sampled and analyzed monthly from December, 2017 to November, 2018 using standard methods. The results showed that water temperature varied from 22.00, station 1 to 28.5oC, station 6, turbidity (0.50-9.40 NTU, station 4), flow velocity (0.21, station 1-0.85m/s, station 3), pH (4.30, station 2-6.30, station 1), electrical conductivity (45.20, station 2-168.40µS/cm, station 5), dissolved oxygen (1.60, station 4-6.10mg/l, stations 3 and 4), biochemical oxygen demand (0.80-4.30mg/l, station 4), nitrate (1.10, station 3-5.6mg/l, station 4) and phosphate (0.40, station 3-4.6mg/l, station 4). Flow velocity, electrical conductivity, biochemical oxygen demand, nitrate and phosphate varied significantly between stations (p<0.05). A total of 584 individuals from 5 taxonomic groups and 23 species of macroinvertebrates were recorded. Aquarius remigis was the most abundant species (8.7%). The macroinvertebrate community was dominated by tolerant and very tolerant species, such as Aquarius remigis, Caridina africana, Pseudocloen sp. nymph, Hydrometra sp and Belostoma sp. The dominance of tolerant species, high turbidity, biochemical oxygen demand, nitrate and phosphate values and low dissolved oxygen values are strong indications of anthropogenic effect. It is suggested that adequate management attention should be paid to the river in order to prevent further deterioration.

Male social plasticity influences transient dynamics in the emergence of alternative mating systems in water striders

AbstractAnimal mating systems are often studied with the goal of understanding why species, populations, or groups vary from one another in the system they display. Although these differences are often treated as basically stable, it is also known that mating systems may shift over time (e.g., from one breeding season to the next). There has been some study of how ecological factors correlate with these changes; however, few, if any, studies have investigated how the phenotypic composition of a group governs the timing and probability of these mating system transitions. Groups of stream water striders (Aquarius remigis) can experience rapid changes in mating system dynamics, with small groups often transitioning into a system in which a single, large male monopolizes mating opportunities. We asked if variation in individual- and group-level traits associated with morphology and behavior (e.g., size of the largest individual, average activity behavioral type in the group) could partially explain the variability in how rapidly groups make this transition, if they make it at all. We show that groups with males that exhibit higher social plasticity tended to take longer to transition to a mating system dominated by a single male. Our results, therefore, suggest that groups in identical ecological conditions can diverge in their mating systems based on how much individuals in the group change their behavior in response to the behavior of other members of the group.

Plasticity of Mating Duration in Response to Slightly Biased Operational Sex Ratios in the Water Strider (Aquarius remigis): The Effect of Cohabitation Under Standard Laboratory Conditions

In polygynandrous species, males face the trade-off between the pursuit of increased mating opportunities and securing paternity. Within such systems, males need to accurately assess the social composition of the local environment to maximize fitness. Here, we investigated this capability in the water strider (Aquarius remigis), a semi-aquatic insect known to exhibit a broad spectrum of mating behaviors and inhabit a socially diverse and changing environment. Using a combination of methodological designs to track both within- and between-subject effects, individuals remained in same-sex housing prior to being exposed to slightly biased operational sex ratios (2:1 vs. 1:2) with or without prior cohabitation to determine the effects on mating duration. Results show that males were sensitive to these subtle differences in social conditions, mating for longer periods within male-biased environments, but this was true only under conditions with prior cohabitation. In particular, when individuals could acclimate to the testing environment, mating duration dropped precipitously in female-biased conditions. These findings do not support the view that male water striders have consistent behavioral syndromes, and instead show that individuals are able to differentiate between, and adaptively respond to, small changes in the local sex ratio. In addition to improving our understanding of the plasticity of male mating behavior in this species, this study offers new insights for future laboratory research studying reproductive competition across a diverse range of polygynandrous animals.

Variation in Zn, C, and N isotope ratios in three stream insects

Total Zn concentrations and Zn isotope ratios were measured, using multicollector inductively coupled plasma (ICP)-mass spectrometry (MS), in three species of aquatic insects collected from a stream in Peterborough, Ontario, Canada. Total Zn levels averaged 193 ± 88 μg/g dry weight (dw) in water striders (Heteroptera: Gerridae, Aquarius remigis) and were significantly higher than the concentrations measured in stonefly nymphs (Plecoptera: Perlidae, Acroneuria abnormis) and caddisfly larvae (Trichoptera: Limnephilidae, Pycnopsyche guttifer), i.e., 136 ± 34 μg/g dw and 125 ± 26 μg/g dw, respectively. Average delta values for 66Zn/64Zn in the water striders were approximately 0.7‰ lighter (−1.2‰ ± 1.0‰) and were significantly different than those measured for stoneflies (−0.45‰ ± 0.62‰) and caddisflies (−0.51‰ ± 0.54‰). Nitrogen isotope ratios were significantly different ( P < 0.05) among the three species suggesting differences in trophic positioning. Similar to the Zn isotope ratios, δ 13C values for the water striders (−28.61‰ ± 0.98‰) were significantly different than those of the stoneflies and caddisflies, i.e., −30.75‰ ± 1.33‰ and −30.68‰ ± 1.01‰, respectively. The data suggest that the differences observed in Zn ratios relate to food source for these insects. Similar to their carbon sources, Zn in water striders appears to be primarily of terrestrial origin, and of aquatic origin for the other two species.

Correlational selection on personality and social plasticity: morphology and social context determine behavioural effects on mating success.

Despite a central line of research aimed at quantifying relationships between mating success and sexually dimorphic traits (e.g., ornaments), individual variation in sexually selected traits often explains only a modest portion of the variation in mating success. Another line of research suggests that a significant portion of the variation in mating success observed in animal populations could be explained by correlational selection, where the fitness advantage of a given trait depends on other components of an individual's phenotype and/or its environment. We tested the hypothesis that interactions between multiple traits within an individual (phenotype dependence) or between an individual's phenotype and its social environment (context dependence) can select for individual differences in behaviour (i.e., personality) and social plasticity. To quantify the importance of phenotype- and context-dependent selection on mating success, we repeatedly measured the behaviour, social environment and mating success of about 300 male stream water striders, Aquarius remigis. Rather than explaining individual differences in long-term mating success, we instead quantified how the combination of a male's phenotype interacted with the immediate social context to explain variation in hour-by-hour mating decisions. We suggest that this analysis captures more of the mechanisms leading to differences in mating success. Males differed consistently in activity, aggressiveness and social plasticity. The mating advantage of these behavioural traits depended on male morphology and varied with the number of rival males in the pool, suggesting mechanisms selecting for consistent differences in behaviour and social plasticity. Accounting for phenotype and context dependence improved the amount of variation in male mating success we explained statistically by 30-274%. Our analysis of the determinants of male mating success provides important insights into the evolutionary forces that shape phenotypic variation. In particular, our results suggest that sexual selection is likely to favour individual differences in behaviour, social plasticity (i.e., individuals adjusting their behaviour), niche preference (i.e., individuals dispersing to particular social conditions) or social niche construction (i.e., individuals modifying the social environment). The true effect of sexual traits can only be understood in interaction with the individual's phenotype and environment.

Escape jumping by three age-classes of water striders from smooth, wavy and bubbling water surfaces.

Surface roughness is a ubiquitous phenomenon in both oceanic and terrestrial waters. For insects that live at the air-water interface, such as water striders, non-linear and multi-scale perturbations produce dynamic surface deformations which may impair locomotion. We studied escape jumps of adults, juveniles and first-instar larvae of the water strider Aquarius remigis on smooth, wave-dominated and bubble-dominated water surfaces. Effects of substrate on takeoff jumps were substantial, with significant reductions in takeoff angles, peak translational speeds, attained heights and power expenditure on more perturbed water surfaces. Age effects were similarly pronounced, with the first-instar larvae experiencing the greatest degradation in performance; age-by-treatment effects were also significant for many kinematic variables. Although commonplace in nature, perturbed water surfaces thus have significant and age-dependent effects on water strider locomotion, and on behavior more generally of surface-dwelling insects.

Occurrence of Orthetrum abbotti Calvert (1892) (Odonata, Libellulidae) and intraguild predation on Clarias gareipinus Burchell, 1822 (Suliformes, Clariidae) and Oreochromis niloticus L., 1758 (Perciformes, Cichlidae) fry in Lagos fish farms

Intraguild predation occurs when species competing for the same resource prey upon or parasitize one another. This may result in economic losses under commercial circumstances. A survey of the insect species of fish farms in Badagry and Ojo Areas of Lagos State, Nigeria was carried out followed by an evaluation of the predatory ability of Orthetrum abbotti nymphs on fish fry. Nymph predation was evaluated in the laboratory against fry of Clarias gariepinus and Oreochromis niloticus . Samples of insects were randomly collected from 10 earthen ponds, 10 concrete ponds and the vegetation surrounding the ponds and identified over a period of 12 weeks from three study fish farms. Six species of insects belonging to four orders namely Notonecta unifasciata , Gerris remigis , O. abbotti , Aedes aegypti , Dysticus marginalis and Acentria ephemerella syn. niveus were collected from the ponds. Studies on feeding preference of 5th nymphal instar of O. abbotti on fry of C. gariepinus and O. niloticus over other food types revealed that the dragonfly preferred to feed more on C. gariepinus fry than on O. niloticus although there was no significant difference in the number of O. niloticus and C. gariepinus fry preyed upon by O. abbotti nymphs.

Variation in chromosome numbers and the sex determination system in the Gerromorpha with special reference to the family Gerridae (Hemiptera)

ABSTRACTWe assess karyotypic variation in the heteropteran infraorder Gerromorpha. Counts of autosomes, m-chromosomes and sex chromosomes are obtained from literature reports for 51 species, including 35 in the family Gerridae. Placing these data on recently derived phylogenies reveals that XX/X0 sex determination is ancestral to the clade containing the Gerridae and Veliidae, but that XX/XY sex determination has been secondarily derived several times. Our results confirm the absence of m-chromosomes in the Gerromorpha, but contrary to previous reviews, we find intermediate levels of variation in chromosome counts and sex-determining systems when compared to other Heteropteran clades. A new karyological analysis reveals that the X chromosome of Aquarius remigis Say, 1832 is the largest chromosome, which contrasts with A. najas De Geer, 1773 in which it the X chromosome is the smallest. This karyotypic difference supports molecular evidence that the A. remigis group of species is not closely related to other species in the genus Aquarius Schellenburg, 1800.

Multiple mating reveals complex patterns of assortative mating by personality and body size.

Understanding patterns of non-random mating is central to predicting the consequences of sexual selection. Most studies quantifying assortative mating focus on testing for correlations among partners' phenotypes in mated pairs. Few studies have distinguished between assortative mating arising from preferences for similar partners (expressed by all or a subset of the population) vs. from phenotypic segregation in the environment. Also, few studies have assessed the robustness of assortative mating against temporal changes in social conditions. We tracked multiple matings by stream water striders (Aquarius remigis) across variable social conditions to investigate mating patterns by both body size and behavioural type (personality). We documented temporal changes in partner availability and used a mixed model approach to analyse individual behaviours and changes in mating status recorded on an hourly basis. We assessed whether all or only a subset of individuals in the population expressed a tendency to mate with similar phenotypes. Our analyses took into account variation in the level of competition and in the phenotypes of available partners. Males and females exhibited significant assortative mating by body size: the largest males and females, and the smallest males and females mated together more often than random. However, individuals of intermediate size were equally likely to mate with small, intermediate or large partners. Individuals also displayed two contrasting patterns of assortative mating by personality (activity level). Individuals generally mated preferentially with partners of similar activity level. However, beyond that general trend, individuals with more extreme personalities tended to exhibit disassortative mating: the most active males mated disproportionately with less active females and the least active males tended to mate with more active females. Our analyses thus revealed multiple, distinct patterns of nonrandom mating. These mating patterns did not arise from differences in partner availability among individuals and were robust to temporal changes in social conditions. Hence, mating patterns likely reflect mate preferences or arise from male-male competition coupled with sexual conflict. Our study also stresses the importance of accounting for variation in partner availability and demonstrates the influence of behavioural variation on mating patterns.

An interommatidial exocrine gland with a “nail-headed” structure in the water strider Aquarius remigis (Hemiptera, Gerridae)

The fine structure of the interommatidial exocrine glands, found in the compound eyes of the water strider Aquarius remigis, is described using light, scanning, and transmission electron microscopy. The glandular pores of the glands are specialized into minute “nail-headed” structures (NS), which are described for the first time in arthropod compound eyes. Each NS is composed of two components: a rod-like stalk and a cup-like depression. The TEM study shows that the glands are class 3 epidermal glands as defined by Noirot and Quennedey (1974, 1991). Each gland consists of 3 cells: a gland cell, an intermediary cell, and a duct (canal) cell. The gland cell contains abundant electron-lucent vesicles, while the intermediary cell contains a large number of osmiophilic secretory granules. These two cells might secrete different substances which mix together in the dilated sac-like portion of the conducting canal before final release. The possible functions of the secretions released from these glands are discussed.

Characterization of plasma membrane associated type II α-d-mannosidase and β-N-acetylglucosaminidase of Aquarius remigis sperm

For successful fertilization to occur, molecules on the surface of male and female gametes must recognize each other in a complementary manner. In some organisms, sperm possess a glycosidase on the plasma membrane overlying the head while eggs have glycoproteins that are recognized by those glycosidases resulting in sperm-egg recognition. In this study, two glycosidases, mannosidase and β-N-acetylglucosaminidase, were identified and biochemically characterized in Aquarius remigis sperm. The mannosidase had a Km of 2.36 ± 0.19 mM, a Vmax of 27.49 ± 0.88 pmol/min and a Hill coefficient of 0.94 ± 0.18 at its optimal pH of 7.0. The mannosidase was extracted most efficiently with CHAPSO but was also efficiently extracted with sodium chloride. Mannosidase activity was effectively inhibited by swainsonine, but not by kifunesine, and was significantly reduced in the presence of Mn2+ and Mg2+, but not Zn2+. N-acetylglucosaminidase had a Km of 0.093 ± 0.01 mM, a Vmax of 153.80 ± 2.97 pmol/min and a Hill coefficient of 0.96 ± 0.63 at its optimal pH of 7.0. N-acetylglucosaminidase was extracted most efficiently with potassium iodide but was also efficiently extracted with Triton X-100 and Zn2+, but not Ca2+, Co2+, Mn2+ or Mg2+, significantly inhibited its activity. Taken together, these results indicate that the A. remigis sperm surface contains at least two glycosidases that may recognize complementary glycoconjugates on the surface of water strider eggs.

Germ-cell hub position in a heteropteran testis correlates with the sequence and location of spermatogenesis and production of elaborate sperm bundles.

In insects, spermatogonial cells undergo several mitotic divisions with incomplete cytokinesis, and then proceed through meiosis and spermatogenesis in synchrony. The cells derived from a single spermatogonial cell are referred to as a cyst. In the water strider Aquarius remigis, spermiogenesis occurs within two bi-lobed testes. In contrast to most insects, in which the germ-cell hub is located apically and sequential stages of spermatogenesis can be seen moving toward the base of the testis, each lobe of the water strider testis contains a single germ-cell hub located medially opposite to the efferent duct of the lobe; the developing cysts are displaced toward the distal ends of the lobe as spermiogenesis proceeds. Water strider sperm have both a long flagellum and an unusually long acrosome. The water strider spermatids elongate most of the flagellum prior to morphogenesis of the acrosome, and exhibit several stages of nuclear remodeling before the final, mature sperm nucleus is formed. The maturing sperm are aligned in register in the cyst, and the flagella fold into a coiled bundle while their acrosomes form a rigid helical process that extends from the cyst toward the efferent duct.

Linking short-term behavior and personalities to feeding and mating rates in female water striders

In systems of strong sexual conflict, male harassment can constrain female feeding, which can limit fecundity. Female responses to harassment can depend on the social context or differ between individuals, and could be based on social or intrinsic behavioral cues at different spatio-temporal scales. Using experimental groupings of stream water striders (Aquarius remigis), we examined individual behavioral differences and effects of sex ratio on 4 aspects of female behavior: 1) habitat use and 2) activity, which lead to differences in 3) feeding rates and 4) mating rates. We compared effects of the immediate social environment, immediate female habitat use and activity, and consistent female behavioral tendencies (personalities) on feeding and mating probabilities, and asked if population sex ratio affected the relationships among these behaviors. We found that individual females did differ significantly in all 4 behaviors. Population sex ratio strongly influenced average female habitat use, feeding, and mating behaviors, and female feeding and mating behaviors were predicted by a combination of moment-to-moment female behavioral state, moment-to-moment social factors, and consistent individual female behavioral differences. Furthermore, habitat use tendencies correlated significantly with activity tendencies, and habitat use and activity tendencies predicted mating probabilities, but not feeding probabilities. Our study elucidates the specific individual-level behavioral mechanisms that lead to observed population-level patterns and emphasizes the benefits of studying behavior at multiple spatial and temporal scales.

Personalities and presence of hyperaggressive males influence male mating exclusivity and effective mating in stream water striders

Male expected reproductive success can be enhanced by increased mating success (mate number) or, when females can mate multiply, by increased mating exclusivity (i.e., reduced partner promiscuity). A positive or negative covariance between these two mating outcomes could substantially increase or decrease overall variation in male expected reproductive success, yet the relationship between these mating outcomes is relatively understudied. We examined this relationship and the influence of male personality traits, female personality traits, and the social environment on mating outcomes in stream water striders, Aquarius remigis, at two experimental sex ratios: equal and 2:1 male-biased. To our knowledge, this study is the first to quantify this full set of effects. We found that mating frequency (mating success) and mating exclusivity were positively correlated in the male-biased treatment, but were not related at equal sex ratios. At both sex ratios, males that were more active and aggressive had both higher mating frequency and higher mating exclusivity. A male’s effective mating (the product of mating frequency and mating exclusivity) was also higher if on average he mated with females that tended to hide in refuges (and were presumably less available for future matings). Finally, males that were more often in pools with extremely aggressive (“hyperaggressive”) males actually had increased mating exclusivity, potentially because hyperaggression reduced average female promiscuity. This study highlights the importance of considering mating outcomes beyond mating success and examining the simultaneous contribution of male behaviours, female behaviours and social factors to mating dynamics.

Variation in terrestrial and aquatic sources of methylmercury in stream predators as revealed by stable mercury isotopes.

Mercury (Hg) is widely distributed in the environment, and its organic form, methylmercury (MeHg), can extensively bioaccumulate and biomagnify in aquatic and terrestrial food webs. Concentrations of MeHg in organisms are highly variable, and the sources in natural food webs are often not well understood. This study examined stable isotope ratios of MeHg (mass-dependent fractionation, as δ(202)HgMeHg; and mass-independent fractionation, as Δ(199)HgMeHg) in benthic invertebrates, juvenile steelhead trout (Oncorhynchus mykiss), and water striders (Gerris remigis) along a stream productivity gradient, as well as carnivorous terrestrial invertebrates, in a forested watershed at the headwater of South Fork Eel River in northern California. Throughout the sampling sites, δ(202)HgMeHg (after correction due to the effect of MeHg photodegradation) was significantly different between benthic (median = -1.40‰; range, -2.34 to -0.78‰; total number of samples = 29) and terrestrial invertebrates (median = +0.51‰; range, -0.37 to +1.40‰; total number of samples = 9), but no major difference between these two groups was found for Δ(199)HgMeHg. Steelhead trout (52 individual fishes) have MeHg of predominantly aquatic origins, with a few exceptions at the upstream locations (e.g., 1 fish collected in a tributary had a purely terrestrial MeHg source and 4 fishes had mixed aquatic and terrestrial MeHg sources). Water striders (seven pooled samples) derive MeHg largely from terrestrial sources throughout headwater sections. These data suggest that direct terrestrial subsidy (e.g., terrestrial invertebrates falling into water) can be important for some stream predators in headwater streams and could represent an important means of transfer of terrestrially derived MeHg (e.g., in situ methylation within forests, atmospheric sources) to aquatic ecosystems. Moreover, these findings show that terrestrial subsidies can enhance MeHg bioaccumulation of consumers in headwater streams where aqueous MeHg levels are very low.

Effects of behavioural type, social skill and the social environment on male mating success in water striders

We examined the relative importance of individual differences in personality (activity and aggressiveness), social skill and the social environment (average activity and aggressiveness of the group, presence of hyperaggressive males) in determining the behaviour and mating success of males of the stream water strider, Aquarius remigis. Males that had a consistently more active–aggressive behavioural type had, on average, higher mating success largely because they spent more time active in microhabitats associated with acquiring mates. Some active–aggressive males, however, showed hyperaggressive behaviour, apparently attempting to mate forcibly with other males, or forcibly separate pairs, which was rarely successful. A higher tendency to be hyperaggressive was associated with reduced mating success (i.e. being hyperaggressive represents low social skill). The overall effect was thus stabilizing sexual selection on male activity and aggression. The social environment also had large effects on male behaviour and mating success. In particular, the presence of a keystone hyperaggressive male had strong negative effects on the mating success and general activity of other males in the pool. Notably, males with a more active–aggressive behavioural type maintained higher mating success than less active–aggressive males in the presence of a hyperaggressive male. Social plasticity (change in behaviour in response to changing social conditions) also depended on the male's behavioural type; males with a more active–aggressive behavioural type were more plastic.

Mate disruption in the water strider Aquaris remigis Say, 1832 (Hemiptera: Gerridae)

This report describes the behaviour of a previously uncharacterised mating tactic amongst male water striders (Aquarius remigis Say, 1832), involving the physical break up of existing mating pairs. Using data from four separate laboratory observations on the water strider mating system, we show that this behaviour represents roughly 12.6% of all mating attempts by males. Furthermore, we demonstrate that males are successful in breaking up the existing mating pair in 15.6% of the cases, resulting in secure matings with the disrupted female 6.2% of time. We suspect that mate disruption may serve as an alternative means for acquiring mates by males with low mating success using conventional behaviours. Further research should be performed to determine the prevalence of this behaviour in various natural populations and the specific contexts in which this behaviour occurs.

Multilevel selection and effects of keystone hyperaggressive males on mating success and behavior in stream water striders

Aggression is a behavioral trait that has important implications for many issues in behavioral ecology at both the individual and group level, including variation in individual fitness, mating patterns, social dynamics, and group fitness. Here, we examine the effects of aggression and hyperaggression (the tendency of some males to aggressively attempt to mate with other males or with pairs) on male and female behavior and group and individual mating success in stream water striders (Aquarius remigis). Our results showed that males displaying hyperaggressive behavior play a keystone role in reducing group mating by reducing the activity, aggression, and use of open microhabitats by other males who share a pool with hyperaggressive males; that is, group selection acted against hyperaggressiveness. In contrast, the presence of hyperaggressive males had little detectable effect on the behavior of females. This was likely due to offsetting effects where negative effects of hyperaggressive males on female activity or use of open microhabitats were countered by hyperaggressive males reducing harassment of females by non-hyperaggressive males. On average, hyperaggressive males gained little or no mating benefit from their behavior although there was a trend for the most hyperaggressive males to gain higher mating success than other males in the same pool.

Aquatic and terrestrial organic matter in the diet of stream consumers: implications for mercury bioaccumulation

The relative contribution of aquatic vs. terrestrial organic matter to the diet of consumers in fluvial environments and its effects on bioaccumulation of contaminants such as mercury (Hg) remain poorly understood. We used stable isotopes of carbon and nitrogen in a gradient approach (consumer isotope ratio vs. periphyton isotope ratio) across temperate streams that range in their pH to assess consumer reliance on aquatic (periphyton) vs. terrestrial (riparian vegetation) organic matter, and whether Hg concentrations in fish and their prey were related to these energy sources. Taxa varied in their use of the two sources, with grazing mayflies (Heptageniidae), predatory stoneflies (Perlidae), one species of water strider (Metrobates hesperius), and the fish blacknose dace (Rhinichthys atratulus) showing strong connections to aquatic sources, while Aquarius remigis water striders and brook trout (Salvelinus fontinalis) showed a weak link to in-stream production. The aquatic food source for consumers, periphyton, had higher Hg concentrations in low-pH waters, and pH was a much better predictor of Hg in predatory invertebrates that relied mainly on this food source vs. those that used terrestrial C. These findings suggest that stream biota relying mainly on dietary inputs from the riparian zone will be partially insulated from the effects of water chemistry on Hg availability. This has implications for the development of a whole-system understanding of nutrient and material cycling in streams, the choice of taxa in contaminant monitoring studies, and in understanding the fate of Hg in stream food webs.