On the relationship between ontogenetic and static allometry.

Ontogenetic and static allometries describe how a character changes in size when the size of the organism changes during ontogeny and among individuals measured at the same developmental stage, respectively. Understanding the relationship between these two types of allometry is crucial to understanding the evolution of allometry and, more generally, the evolution of shape. However, the effects of ontogenetic allometry on static allometry remain largely unexplored. Here, we first show analytically how individual variation in ontogenetic allometry and body size affect static allometry. Using two longitudinal data sets on ontogenetic and static allometry, we then estimate variances and covariances for the different parameters of the ontogenetic allometry defined in our model and assess their relative contribution to the static allometric slope. The mean ontogenetic allometry is the main parameter that determines the static allometric slope, while the covariance between the ontogenetic allometric slope and body size generates most of the discrepancies between ontogenetic and static allometry. These results suggest that the apparent evolutionary stasis of the static allometric slope is not generated by internal (developmental) constraints but more likely results from external constraints imposed by selection.

Methane emissions from macrophyte beach wrack on Baltic seashores.

Beach wrack of marine macrophytes is a natural component of many beaches. To test if such wrack emits the potent greenhouse gas methane, field measurements were made at different seasons on beach wrack depositions of different ages, exposure, and distance from the water. Methane emissions varied greatly, from 0 to 176 mg CH4-C m-2 day-1, with a clear positive correlation between emission and temperature. Dry wrack had lower emissions than wet. Using temperature data from 2016 to 2020, seasonal changes in fluxes were calculated for a natural wrack accumulation area. Such calculated average emissions were close to zero during winter, but peaked in summer, with very high emissions when daily temperatures exceeded 20 °C. We conclude that waterlogged beach wrack significantly contributes to greenhouse gas emissions and that emissions might drastically increase with increasing global temperatures. When beach wrack is collected into heaps away from the water, the emissions are however close to zero.

Reduced sexual size dimorphism in a pipefish population where males do not prefer larger females.

Within a species' distribution, populations are often exposed to diverse environments and may thus experience different sources of both natural and sexual selection. These differences are likely to impact the balance between costs and benefits to individuals seeking reproduction, thus entailing evolutionary repercussions. Here, we look into an unusual population (Baltic Sea) of the broadnosed pipefish, Syngnathus typhle, where males do not seem to select females based on size and hypothesize that this pattern may derive from a reduction in direct benefits to the male. We further hypothesize that if larger females do not persistently secure a higher reproductive success, either through pre- or postcopulatory sexual selection, a decrease in sexual size dimorphism in the Baltic population should be apparent, especially when contrasted with a well-studied population, inhabiting similar latitudes (Swedish west coast), where males prefer larger females. We found that, in the Baltic population, variation in female quality is low. We were unable to find differences in abortion rates or protein concentration in oocytes produced by females of contrasting sizes. Direct benefits from mating with large partners seem, thus, reduced in the Baltic population. We also found no evidence of any postcopulatory mechanism that could favor larger mothers as embryo development was unrelated to female size. While female size can still be selected through intrasexual competition or fecundity selection, the pressure for large female body size seems to be lower in the Baltic. Accordingly, we found a noticeable decrease in sexual size dimorphism in the Baltic population. We conclude that, although far from negating the significance of other selective processes, sexual selection seems to have a decisive role in supporting pipefish sexual size asymmetries.

Sex in murky waters: algal-induced turbidity increases sexual selection in pipefish.

ABSTRACT: Algal-induced turbidity has been shown to alter several important aspects of reproduction and sexual selection. However, while turbidity has been shown to negatively affect reproduction and sexually selected traits in some species, it may instead enhance reproductive success in others, implying that the impact of eutrophication is far more complex than originally believed. In this study, we aimed to provide more insight into these inconsistent findings. We used molecular tools to investigate the impact of algal turbidity on reproductive success and sexual selection on males in controlled laboratory experiments, allowing mate choice, mating competition, and mate encounter rates to affect reproduction. As study species, we used the broad-nosed pipefish, Syngnathus typhle, a species practicing male pregnancy and where we have previously shown that male mate choice is impaired by turbidity. Here, turbidity instead enhanced sexual selection on male size and mating success as well as reproductive success. Effects from mating competition and mate encounter rates may thus override effects from mate choice based on visual cues, producing an overall stronger sexual selection in turbid waters. Hence, seemingly inconsistent effects of turbidity on sexual selection may depend on which mechanisms of sexual selection that have been under study. SIGNIFICANCE STATEMENT: Algal blooms are becoming increasingly more common due to eutrophication of freshwater and marine environments. The high density of algae lowers water transparency and reduces the possibility for fish and other aquatic animals to perform behaviors dependent on vision. We have previously shown that pipefish are unable to select the best partner in mate choice trials when water transparency was reduced. However, fish might use other senses than vision to compensate for the reduction in water transparency. In this study, we found that when fish were allowed to freely interact, thereby allowing competition between partners and direct contact between the fish, the best partner was indeed chosen. Hence, the negative effects of reduced water visibility due to algal blooms may be counteracted by the use of other senses in fish.

Effects of manganese on chemically induced food search behaviour of the Norway lobster, Nephrops norvegicus (L.).

The decapod Norway lobster, Nephrops norvegicus (L.), lives on muddy sediments rich in manganese (Mn). In hypoxic conditions, manganese is reduced and released from the sediment, so increased concentrations of dissolved Mn(2+) become bioavailable. In excess, manganese acts as a neurotoxin and may inhibit vital functions of benthic organisms, such as muscle contraction. We investigated in a laboratory flume experiment, the effect of environmentally realistic concentrations of manganese (0.1 and 0.2mM for 12 days) on the food search behaviour of N. norvegicus. We found that lobsters exposed to manganese had a more than doubled reaction time to food odour stimuli compared to the controls (p<0.05). In addition, manganese exposure reduced the number of N. norvegicus reaching the food stimuli source. Compared to the controls where 86% reached the stimuli source, only about half of the lobsters exposed to 0.1mM Mn and one-third of the lobsters exposed to 0.2mM Mn reached the stimuli source (p<0.05 and 0.001, respectively). There was no significant difference between treatments in the number of lobsters leaving their shelter or in the time from reaction until leaving the shelter and there was no difference in search time for those animals that eventually did locate the stimuli source. This study shows that environmentally realistic manganese concentrations affect parts of the food search behaviour of N. norvegicus, likely due to impaired chemosensory ability or reduced motivation for feeding. Thus, the ability of N. norvegicus to detect and find food can be reduced in areas with high manganese concentrations, with possible consequences on individual and population levels.

Effects of an Offshore Wind Farm (OWF) on the Common Shore Crab Carcinus maenas: Tagging Pilot Experiments in the Lillgrund Offshore Wind Farm (Sweden).

Worldwide growth of offshore renewable energy production will provide marine organisms with new hard substrate for colonization in terms of artificial reefs. The artificial reef effect is important when planning offshore installations since it can create habitat enhancement. Wind power is the most advanced technology within offshore renewable energy sources and there is an urgent need to study its impacts on the marine environment. To test the hypothesis that offshore wind power increases the abundance of reef species relative to a reference area, we conduct an experiment on the model species common shore crab (Carcinus maenas).Overall, 3962 crabs were captured, observed, marked and released in 2011 and 1995 crabs in 2012. Additionally, carapace size, sex distribution, color morphs and body condition was recorded from captured crabs. We observed very low recapture rates at all sites during both years which made evaluating differences in population sizes very difficult. However, we were able to estimate population densities from the capture record for all three sites. There was no obvious artificial reef effect in the Lillgrund wind farm, but a spill-over effect to nearby habitats cannot be excluded. We could not find any effect of the wind farm on either, morphs, sex distribution or condition of the common shore crab. Our study found no evidence that Lillgrund wind farm has a negative effect on populations of the common shore crab. This study provides the first quantitative and experimental data on the common shore crab in relation to offshore wind farms.

Sex ratio and density affect sexual selection in a sex-role reversed fish.

Understanding how demographic processes influence mating systems is important to decode ecological influences on sexual selection in nature. We manipulated sex ratio and density in experimental populations of the sex-role reversed pipefish Syngnathus typhle. We quantified sexual selection using the Bateman gradient (ßss'), the opportunity for selection (I), and sexual selection (Is), and the maximum standardized sexual selection differential (smax'). We also measured selection on body length using standardized selection differentials (s') and mating differentials (m'), and tested whether the observed I and Is differ from values obtained by simulating random mating. We found that I, Is, and s'max, but not ßss', were higher for females under female than male bias and the opposite for males, but density did not affect these measures. However, higher density decreased sexual selection (m' but not s') on female length, but selection on body length was not affected by sex ratio. Finally, Is but not I was higher than expected from random mating, and only for females under female bias. This study demonstrates that both sex ratio and density affect sexual selection and that disentangling interrelated demographic processes is essential to a more complete understanding of mating behavior and the evolution of mating systems.

The effect of purging on sexually selected traits through antagonistic pleiotropy with survival.

Sexually selected traits are expected to evolve to a point where their positive effect on reproductive success is counterbalanced by their negative effect on survival. At the genetic level, such a trade-off implies antagonistic pleiotropy between survival and the expression of sexually selected traits. Yet, the consequences of such a genetic architecture have been largely overlooked in studies examining how inbreeding influences sexually selected traits. These studies have solely interpreted their results as an effect of increased homozygosity. An alternative, however, is that purging of recessive alleles deleterious for survival when inbreeding increases can negatively affect the expression of sexually selected traits through antagonistic pleiotropy. We tested this hypothesis by analyzing the effects of inbreeding on several male ornaments and life-history traits across 20 captive populations of guppies (Poecilia reticulata) with varying levels of inbreeding. Only one ornament, orange area, decreased in its expression with an increasing level of inbreeding. This was most likely due to purging because we found no within-population relationship between orange area and the inbreeding coefficient. We further tested this hypothesis by crossing unrelated individuals from the four most inbred populations, creating a group of individuals with purged genomes but restored heterozygosity. Restoration of heterozygosity only slightly increased orange area, confirming that the decrease in orange area in the inbred populations most likely resulted from purging. These results support previous studies suggesting the existence of antagonistic pleiotropy between ornament expression and survival.

The Measurement of Sexual Selection Using Bateman's Principles: An Experimental Test in the Sex-Role-Reversed Pipefish Syngnathus typhle.

Angus J. Bateman's classic study of sexual selection in Drosophila melanogaster has had a major influence on the development of sexual selection theory. In some ways, Bateman's study has served a catalytic role by stimulating debate on sex roles, sexual conflict and other topics in sexual selection. However, there is still considerable disagreement regarding whether or not "Bateman's principles" are helpful in the study of sexual selection. Here, we test the idea that Bateman's principles provide the basis for a useful method to quantify and compare mating systems. In this study, we focus on the sex-role-reversed pipefish Syngnathus typhle as a model system to study the measurement of sexual selection. We set up artificial breeding assemblages of pipefish in the laboratory and used microsatellite markers to resolve parentage. Three different sex-ratio treatments (female-biased, even and male-biased) were used to manipulate the expected intensity of sexual selection. Measures of the mating system based on Bateman's principles were calculated and compared to the expected changes in the intensity of sexual selection. We also compare the results of this study to the results of a similar study of Bateman's principles in the rough-skinned newt, a species with conventional sex roles. The results of this experiment show that measures of the mating system based on Bateman's principles do accurately capture the relative intensities of sexual selection in the different treatments and species. Thus, widespread use of Bateman's principles to quantify mating systems in nature would facilitate comparative studies of sexual selection and mating system evolution.

Variation in plasma steroids and reproductive traits in dimorphic males of corkwing wrasse (Symphodus melops L.).

Differences in plasma steroid levels may reflect behavioral, gonadal, or morphological specializations that characterize different male reproductive phenotypes in teleost fishes. In the present study, we investigated whether differences in plasma steroid levels exist between two distinct male morphs shown in the corkwing wrasse Symphodus melops. In addition, we examined differences in male reproductive traits, including gonad mass, sperm motility, and sperm concentration, between the two male types. Possible associations between plasma steroid levels and reproductive traits were also investigated. The results indicated that males with typical male secondary sexual characters (territorial males) had higher plasma levels of 11-ketotestosterone (11kT) compared to smaller males with female secondary sexual characters (female mimics). The female mimics in turn had higher plasma levels of both testosterone (T) and 17beta-estradiol. In addition, female mimics had relatively larger gonads and longer-lived sperm than territorial males. Relative gonad mass covaried significantly with the plasma levels of 11kT and T among the morphs, indicating that the relative gonad size correlates positively with the plasma level of these two steroids. However, there was no significant covariance between sperm traits and plasma steroids for the two male morphs. Hence, our results do not indicate any causal link between sperm quality and hormones.

Disruption of male reproductive behavior in threespine stickleback Gasterosteus aculeatus exposed to 17 beta-estradiol.

In past years we have witnessed decreased reproductive capacity in many wildlife species due to exposure to chemicals with endocrine-disrupting properties. In this laboratory experiment male threespine sticklebacks Gasterosteus aculeatus exposed to 17 beta-estradiol (2.0 micrograms/g) dispersed in peanut oil, on days 1, 7, 14, and 21, showed impaired paternal care compared to control fish that were exposed to peanut oil only. There were no differences between the two groups in number of males that built nests or in courtship displays. However, exposed males started nest building significantly later than control males. This study suggests that some but not all essential traits of male reproductive behavior may be altered as a result of exposure to 17 beta-estradiol. To reveal harmful effects of chemicals with suggested reproductive-disrupting properties it is thus important to take a wide variety of variables related to reproductive behavior into consideration.

Postexposure effects of DDE and butylbenzylphthalate on feeding behavior in threespine stickleback.

In a laboratory experiment we documented effects of sublethal concentrations of p,p'-2,2-bis(p-chlorophenyl)-1,1-dichloroethylene (DDE) and butylbenzylphthalate (BBP) on feeding behavior in threespine stickleback Gasterosteus aculeatus. The fish were exposed for 31 days to either BBP (10 or 100 microg/L) or DDE (5 or 50 microg/L) or to a mixture of BBP and DDE in the corresponding concentrations. Five weeks after exposure termination, we showed that fish that had been exposed to the higher concentrations of DDE and/or BBP initiated feeding more often than control fish. The latency time to feeding (ranging from 0.25 to 5.0 min) differed between control fish and fish exposed to mixtures of DDE and BBP. This experiment shows that feeding behavior may be used as a suitable behavioral variable in the detection of effects of pollutants even long time after the termination of exposure.

Butyl benzyl phthalate affects shoaling behavior and bottom-dwelling behavior in threespine stickleback.

In this laboratory experiment, the effects on fish behavior caused by butyl benzyl phthalate (BBP) were of interest. We showed that shoaling behavior and bottom-dwelling behavior in threespine stickleback, Gasterosteus aculeatus, were altered as a result of exposure to 0.1 mg/L BBP. Threespine sticklebacks, collected from a freshwater population in central Norway, were exposed to BBP for 26 days. BBP was administered daily through the water. We found that exposed fish aggregated more into one single shoal than control fish. Further, the exposed fish spent more time at the bottom of the test aquarium than the control fish. From these results we conclude that the behavior traits aggregation and bottom-dwelling activity may be suitable and sensitive in detecting effects of BBP in threespine stickleback.