How do different populations of three‐spined sticklebacks Gasterosteus aculeatus combine spatial information?

Populations of three‐spined sticklebacks Gasterosteus aculeatus originating from contrasting habitats were studied to determine if habitat can affect the ability to combine spatial cues. Previous work has shown that different species combine spatial cues in different ways, and this study showed these differences also arose within a species: all fish were able to use geometrical cues to locate a maze exit, but only fish collected from river populations combined geometric cues with a non‐geometric global landmark cue.     

Local adaptation to salinity in the three‐spined stickleback?

Different lines of evidence suggest that the occurrence and extent of local adaptation in high gene flow marine environments – even in mobile and long‐lived vertebrates with complex life cycles – may be more widespread than earlier thought. We conducted a common garden experiment to test for local adaptation to salinity in Baltic Sea sticklebacks (Gasterosteus aculeatus). Fish from three different native salinity regimes (high, mid and low) were subjected to three salinity treatments (high, mid and low) in a full‐factorial experimental design. Irrespective of their origin, fish subjected to low (and mid) salinity treatments exhibited higher juvenile survival, grew to largest sizes and were in better condition than fish subjected to the high salinity treatment. However, a significant interaction between native and treatment salinities – resulting mainly from the poor performance of fish native to low salinity in the high salinity treatment – provided clear cut evidence for adaptation to local variation in salinity. Additional support for this inference was provided by the fact that the results concur with an earlier demonstration of significant differentiation in a number of genes with osmoregulatory functions across the same populations and that the population‐specific responses to salinity treatments exceeded that to be expected by random genetic drift.     

Male three‐spined sticklebacks Gasterosteus aculeatus make antibiotic nests: a novel form of parental protection?

The egg nest of male three‐spined sticklebacks Gasterosteus aculeatus is constructed with a glue‐like secretion that this study demonstrates has antimicrobial properties. Glue collected from reproductively active males decreased the growth rate of bacteria and opportunistic fungi, and eggs were more likely to mature and hatch after exposure to their father’s glue. This phenomenon may represent a direct physiological contribution from a male towards protecting his offspring from pathogens, and if so is a novel form of parental protection.     

Does predation drive morphological differentiation among Adriatic populations of the three‐spined stickleback?

Morphometric differentiation among freshwater fish populations is a commonplace occurrence, although the underlying causes for this divergence often remain elusive. We analysed the degree and patterns of morphological differentiation among nine freshwater three‐spined stickleback (Gasterosteus aculeatus) populations inhabiting isolated karst rivers of the Adriatic Sea basin, to characterise the phenotypic diversity and differentiation in these populations. The analyses revealed marked and significant morphometric differentiation – especially in traits related to predator defence amongst most populations – even among those located within close geographic proximity in the same catchment system. Accordingly, the degree of morphometric and neutral genetic differentiation, as assessed from variability in 15 microsatellite loci from a parallel study, were uncorrelated across the populations. However, P_ST/F_ST comparisons revealed that the degree of phenotypic differentiation (P_ST) among populations exceeded that to be expected from genetic drift alone, suggesting a possible adaptive basis for the observed differentiation. In fact, avian predation pressure and several physiochemical environmental variables were identified as the main putative drivers of the observed differentiation, particularly in the dorsal spines, ascending process and lateral plates. Hence, the high degree of morphometric differentiation among Adriatic three‐spined stickleback populations appears to reflect adaptation to local ecological conditions. © 2015 The Linnean Society of London, Biological Journal of the Linnean Society, 2015, 115 , 219–240.     

Morphological anti‐predator defences in the nine‐spined stickleback: constitutive,induced or both?

Environmental differences among populations are expected to lead to local adaptation, while spatial or temporal environmental variation within a population will favour evolution of phenotypic plasticity. As plasticity itself can be under selection, locally adapted populations can vary in levels of plasticity. Nine‐spined stickleback (Pungitius pungitius) originating from isolated ponds (low piscine predation risk, high competition) vs. lake and marine populations (high piscine predation risk, low competition) are known to be morphologically adapted to their respective environments. However, nothing is known about their ability to express phenotypic plasticity in morphology in response to perceived predation risk or food availability/competition. We studied predator‐induced phenotypic plasticity in body shape and armour of marine and pond nine‐spined stickleback in a factorial common garden experiment with two predator treatments (present vs. absent) and two feeding regimes (low vs. high). The predation treatment did not induce any morphological shifts in fish from either habitat or food regime. However, strong habitat‐dependent differences between populations as well as strong sexual dimorphism in both body shape and armour were found. The lack of predator‐induced plasticity in development of the defence traits (viz. body armour and body depth) suggests that morphological anti‐predator traits in nine‐spined stickleback are strictly constitutive, rather than inducible. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, ??, ??–??.     

Pelvic anti-predator armour reduction in Norwegian populations of the threespine stickleback: a rare phenomenon with adaptive implications?

In order to search for armour reductions in the anti-predator armour apparatus of the threespine stickleback Gasterosteus aculeatus , we studied populations from 200 coastal lakes and 32 marine and estuarine sites in Norway. We scored the presence of reductions in the pelvic apparatus in these populations, measured the length of the second dorsal fin and pelvic spine and counted lateral plates in a subset of 96 populations. Then we looked for the relation between pelvic reduction and number of lateral plates and lengths of the second dorsal spine and pelvic spine. We also observed whether pelvic reduced fish had asymmetric development on the right or the left side of the pelvis. Pelvic reduction was not found in marine and estuarine sticklebacks (with one single exception), but in freshwater it occurred in four out of 200 lakes. The amount of pelvic reduction differed from 5% to 68% in the four populations. There appears to be a correlation between pelvic reduction and spine lengths at the population level, but not plate number. Further, it appears to be difficult to explain the occurrence of pelvic reduction in Norway with the factors proposed to be responsible for pelvic reduction in other regions.     

Do competing males cooperate? Familiarity and its effect on cooperation during predator inspection in male three‐spined sticklebacks (Gasterosteus aculeatus)

We investigated the trade‐off between conflict and cooperation, using predator inspection behaviour in sticklebacks as a model system. Male three‐spined sticklebacks ( Gasterosteus aculeatus ) compete for territories during the breeding season and it has been demonstrated that the level of aggression between territorial neighbours declines with time, a phenomenon known as the dear enemy effect. In this experiment we examine whether this increase in familiarity between territorial neighbours can facilitate an increase in cooperation during predator inspection events. This was analyzed using male sticklebacks from four pond populations, two with and two without predatory rainbow trout ( Oncorhyncus mykiss ). Males were each exposed to five different treatments: (1) the presentation of a live rainbow trout when alone; (2) with a newly revealed territorial neighbour; (3) with this neighbour after two days of familiarization; (4) with another unfamiliar neighbour (termed a 'floater'); and (5) a second solitary trial (to provide controls at the start and end of the experiment). As predicted, fish from predator‐sympatric populations showed higher levels of predator inspection and lower rates of misdirected territorial aggression towards the predator throughout. However, familiarity between neighbouring males did not facilitate an increase in predator inspection behaviour. Instead, predator inspection behaviour decreased throughout treatments involving the presence of any sort of neighbouring male. Familiarity between neighbours did not influence their ability to cooperatively inspect, but only the nature of any aggressive territorial behaviours, all of which detracted equally from individual inspection effort.     

Genotoxic damage in field-collected three-spined sticklebacks (Gasterosteus aculeatus L.): a suitable biomonitoring tool?

Three-spined sticklebacks (Gasterosteus aculeatus L.) were collected during different sampling trails from three locations in Northern Germany, which differ in the amount of sewage-treatment effluent that they receive. Due to natural population developments, the size of the specimens caught decreased significantly from April to August. The fish were examined for DNA damage in their blood cells by means of the comet (single-cell gel electrophoresis, SCGE) assay and the micronucleus test (MT). The suitability of stickleback erythrocytes as indicators for genotoxic substances in water was assessed. The median level of strand breakage ranged from 5.23 to 9.67%, and decreased significantly from April to August. The difference between the locations was marginally significant. The amount of micronuclei was more variable (ranging from 0.40 to 4.35%), but appears to better reflect the pollution state of the sampling location. Significant differences between the locations were found. The relatively strong micronucleus induction found in this study may be related to the fish species selected. Contrary to the SCGE results, a significant increase in the number of micronuclei from April to August was observed. A significant negative correlation between strand breakage and micronuclei was found for the sticklebacks from the most polluted location and for the pooled data of all locations. The length of the fish was positively correlated with results of the SCGE and negatively with those of the MT, whereby males show a clearer relation between size and the amount of genotoxic damage. The test results are predominantly affected by seasonal impacts. This study indicates that the outcome of the SCGE and MT applied to sticklebacks is determined by multiple factors, which need to be identified first before these tests can be applied routinely. Because of the profound negative correlation between SCGE and MT results, we recommend to apply both tests for the evaluation of the genotoxic potential of surface waters.     

Carotenoids‐based reddish pelvic spines in nonreproducing female and male sticklebacks (Gasterosteus aculeatus) – Signalling social dominance?

Conspicuous ornaments are often considered a result of evolution by sexual selection. According to the social selection hypothesis, such conspicuous traits may also evolve as badges of status associated with increased boldness or aggression toward conspecifics in conflicts about ecological resources. This study tested predictions from the social selection hypothesis to explain evolution of conspicuous red color of the pelvic spines of the three‐spine stickleback (Gasterosteus aculeatus). Wild nonreproducing sticklebacks were presented to pairs of dummies which differed at their pelvic spines, having either (i) normal‐sized gray or red pelvic spines or (ii) normal‐sized gray or large red pelvic spines. The experimental tank was illuminated by white or green light, since green light impedes the sticklebacks’ ability to detect red color. The dummies moved slowly around in circles at each end of the experimental tank. We quantified the parameters (i) which of the two dummies was visited first, (ii) time taken before the first visit to a dummy, (iii) distribution of the focal sticklebacks in the two zones close to each of the two dummies and in the neutral zone of the tank, (iv) close to which of the two dummies did the focal fish eat its first food‐piece, and (v) time spent until the first piece of food was eaten. This was carried out for 22 females and 29 males sticklebacks. The results suggested no effect of the color or size of the dummies’ pelvic spines, on none of the five behavioral parameters. Moreover, neither the color of the pelvic spines of the focal sticklebacks themselves (as opposed to redness of the dummies’ spines) nor their body length was associated with behavior toward the dummies. Thus, this study did not support predictions from the social selection hypothesis to explain evolution of red pelvic spines in sticklebacks.     

To be,or not to be,a non‐native freshwater fish?

We examine the evolving concept of what constitutes a non‐native (or alien) freshwater fish. In an attempt to distinguish between biogeographical and socio‐political perspectives, we review the patterns in the introduction and dispersal of non‐native fishes in Europe and North America, and especially the recent expansion of Ponto‐Caspian gobies in Europe. We assess patterns in the development of national policy and legislation in response to the perceived threat of non‐native fish introductions to native species and ecosystems. We review, and provide a glossary of, the terms and definitions associated with non‐native species. Finally, we discuss perspectives as regards the future treatment of naturalized species.     

Does freshwater macroinvertebrate diversity along a pH‐gradient reflect adaptation to low pH?

1. The impacts of anthropogenic surface water acidification are much better known than those of natural acidity. Recent studies have indicated biodiversity is not degraded and species composition unaltered in naturally acidic compared to circumneutral watercourses.
2. Here, we use a geographically extensive dataset comprising sites in more than 200 Swedish streams to test whether the lack of effects on macroinvertebrate species diversity is due to exaptation and adaptation to natural acidity.
3. To this end, we modelled pH associated with spring flood episodes, which inflict the most challenging hydrochemical conditions to the biota. We compared taxonomic richness and species composition along the modelled pH gradient in northern Sweden, where acidity is largely natural, with southern Sweden, a region influenced by significant anthropogenic acidification.
4. We found Plecoptera richness did not respond to varying pH either in northern or southern Sweden. Ephemeroptera richness was sensitive to pH in both regions, while that of Trichoptera increased with increasing pH in southern Sweden, but decreased in the north. The taxonomic composition of Plecoptera changed along the pH gradient in both regions, whereas that of Ephemeroptera and Trichoptera changed more strongly with pH in southern Sweden.
5. Our results support the hypothesis that stream invertebrates are able to tolerate low pH through exaptation or adaptation, but that this capability varies among taxonomic groups.     

Is size‐assortative mating important for rapid pigment differentiation in a freshwater isopod?

Identifying mechanisms behind assortative mating is central to the understanding of ecological divergence and speciation. Recent studies show that populations of the freshwater isopod Asellus aquaticus can rapidly become locally differentiated when submerged Chara vegetation expands in lakes. In the novel Chara habitat, isopods have become lighter pigmented and smaller than in ancestral reed stands. In this study, we used a laboratory multiple-choice experiment to investigate assortative mating as a possible prezygotic reproductive barrier between Chara and reed isopods. Mating was assortative when Chara isopods were experimentally mixed with isopods from an adjacent reed site with large-size individuals, suggesting a partial prezygotic reproductive barrier. No deviation from random mating could, however, be detected when Chara isopods were mixed with smaller sized isopods from another reed site. In both experiments, assortative mating was apparently based on size, as Chara isopods were larger and reed isopods smaller in mixed pairs than in assortative pairs. Pigmentation did not have any clear influence on mating. We suggest that divergence in pigmentation evolved through natural selection in conjunction with size-assortative mating indirectly causing assortative mating between Chara and reed isopods. Size-assortative mating is likely a by-product of natural selection, but its importance may hypothetically be transient, if selection erodes the correlation between pigmentation and size over time.     

The three-dimensional flight of red-footed boobies: adaptations to foraging in a tropical environment?

In seabirds a broad variety of morphologies, flight styles and feeding methods exist as an adaptation to optimal foraging in contrasted marine environments for a wide variety of prey types. Because of the low productivity of tropical waters it is expected that specific flight and foraging techniques have been selected there, but very few data are available. By using five different types of high-precision miniaturized logger (global positioning systems, accelerometers, time depth recorders, activity recorders, altimeters) we studied the way a seabird is foraging over tropical waters. Red-footed boobies are foraging in the day, never foraging at night, probably as a result of predation risks. They make extensive use of wind conditions, flying preferentially with crosswinds at median speed of 38 km h(-1), reaching highest speeds with tail winds. They spent 66% of the foraging trip in flight, using a flap-glide flight, and gliding 68% of the flight. Travelling at low costs was regularly interrupted by extremely active foraging periods where birds are very frequently touching water for landing, plunge diving or surface diving (30 landings h(-1)). Dives were shallow (maximum 2.4 m) but frequent (4.5 dives h(-1)), most being plunge dives. While chasing for very mobile prey like flying fishes, boobies have adopted a very active and specific hunting behaviour, but the use of wind allows them to reduce travelling cost by their extensive use of gliding. During the foraging and travelling phases birds climb regularly to altitudes of 20-50 m to spot prey or congeners. During the final phase of the flight, they climb to high altitudes, up to 500 m, probably to avoid attacks by frigatebirds along the coasts. This study demonstrates the use by boobies of a series of very specific flight and activity patterns that have probably been selected as adaptations to the conditions of tropical waters.     

Distance decay of similarity in freshwater communities: do macro‐ and microorganisms follow the same rules?

Aim An intensively debated issue in macroecology is whether unicellular organisms show biogeographic patterns different from those of macroorganisms. One aspect of this debate addresses beta diversity, that is, do microbial organisms exhibit distance‐decay patterns similar to those of macroorganisms? And if so, is the decay of community similarity caused by spatially limited dispersal or by niche‐related factors? We studied the community similarity of stream diatoms, macroinvertebrates and bryophytes across the same set of sites in relation to environmental and geographic distance. Location A geographical gradient of c. 1100 km in Finland. Methods We first identified the subset of environmental variables that produced the highest correlation with community similarities for each taxonomic group. Based on these variables, we used partial Mantel tests to separate the independent influences of environmental and geographical distance for distance decay of community similarity, separately for diatoms, bryophytes and macroinvertebrates. Finally, macroinvertebrates were divided into three groups based on their different dispersal categories and a partial Mantel test was used to assess whether each of these groups were differently affected by environmental versus geographic distance, i.e. is dispersal a key factor in tests of niche versus neutral models. Results The level of environmental control was by far the strongest for diatoms; however, all groups were controlled more by environmental factors than by limited dispersal. Macroinvertebrate species with low dispersal ability were significantly related to geographic distance, while more effective dispersers showed no relationship to geography but were instead strongly related to environmental distance. Main conclusions Our results suggest that patterns between macro‐ and microorganisms are not fundamentally different, but the level of environmental control varies according to dispersal ability. The relative importance of niche versus dispersal processes is not simply a function of organism size but other traits (e.g. life‐history type, dispersal capacity) may obscure this relationship.     

Chloride uptake and base secretion in freshwater fish: a transepithelial ion-transport metabolon?

Despite all the efforts and technological advances during the last few decades, the cellular mechanisms for branchial chloride uptake in freshwater (FW) fish are still unclear. Although a tight 1 : 1 link with HCO-3 secretion has been established, not much is known about the identity of the ion-transporting proteins involved or the energizing steps that allow for the inward transport of Cl- against the concentration gradient. We propose a new model for Cl- uptake in FW fish whereby the combined action of an apical anion exchanger, cytoplasmic carbonic anhydrase, and basolateral V-type H+ -ATPase creates a local [HCO-3] high enough to energize Cl- uptake. Our model is based on analyses of structure-function relationships, reinterpretation of previous results, and novel observations about gill cell subtypes and immunolocalization of the V-H+ -ATPase.     

Non‐consumptive effects of predation: does perceived risk strengthen the genetic integration of behaviour and morphology in stickleback?

Predators can shape genetic correlations in prey by altering prey perception of risk. We manipulated perceived risk to test whether such non‐consumptive effects tightened behavioural trait correlations in wild‐caught stickleback from high‐ compared to low‐risk environments due to genetic variation in plasticity. We expected tighter genetic correlations within perceived risk treatments than across them, and tighter genetic correlations in high‐risk than in low‐risk treatments. We identified genetic variation in plasticity, with genetic correlations between boldness, sociality, and antipredator morphology, as expected, being tighter within treatments than across them, for both of two populations. By contrast, genetic correlations did not tighten with exposure to risk. Tighter phenotypic correlations in wild stickleback may thus arise because predators induce correlational selection on environmental components of these traits, or because predators tighten residual correlations by causing environmental heterogeneity that is controlled in the laboratory. Our study places phenotypic integration firmly into an ecological context.     

Periostin: a putative mediator involved in tumour resistance to anti‐angiogenic therapy?

Despite advances in the development of anti-angiogenic agents for cancer treatment, the increase in the survival duration of cancer patients is still rather modest. One major obstacle in anti-angiogenic therapy is the emergence of drug resistance. Understanding the molecular mechanisms that enable a tumour to evade anti-angiogenic treatment is valuable to improve therapeutic efficacy. Targeting blood supply usually causes hypoxic responses of tumours that trigger a series of adaptive changes leading to a resistant phenotype. Periostin, a secreted ECM (extracellular matrix) protein, is mainly produced by CAFs (cancer-associated fibroblasts) on hypoxic stress. As CAFs have been casually linked to tumour resistance to angiogenesis blockade and periostin can influence many aspects of tumour biology, we hypothesized that periostin might be a crucial mediator involved anti-angiogenic resistance in cancer treatment. This hypothesis is indirectly supported by the following facts: (a) high levels of periostin promote tumour angiogenesis; (b) periostin improves cancer cell survival under hypoxic conditions; and (c) genetic modulation of periostin induces EMT (epithelial-mesenchymal transition) and enhances cancer cell invasion and metastasis, which represents an escape mechanism from anticancer treatment. Testing and confirmation of this hypothesis will give more insight into the resistance mechanisms and provide the rationale for improvement of therapeutic outcome of anti-angiogenic therapy.