Shoaling behaviour of sticklebacks infected with the microsporidian parasite, <Emphasis Type="Italic">Glugea anomala</Emphasis>

We compared the shoaling behaviour of three-spined sticklebacks, Gasterosteus aculeatus, infected with the microsporidian, Glugea anomala, to that of non-infected conspecifics. Infected fish lost significantly more weight than non-infected fish during a period of food deprivation, suggesting a metabolic cost to parasitism. In binary shoal choice tests, non-infected test fish showed an association preference for a shoal of non-infected over a shoal of infected conspecifics; infected test fish displayed no preference. Infected fish, however, showed a higher overall tendency to shoal than non-parasitised fish. Furthermore, infected fish occupied front positions within a mixed school. We consider the behavioural differences between infected and uninfected fish in the context of their potential benefits to the fish hosts and the parasites.     

Handling does not affect reproductive signals of male threespine stickleback

We examined the affect of handling on reproductive signal expression in male threespine stickleback, Gasterosteus aculeatus. Spectrophotometric techniques have become popular methods for measuring fish color, but the measurements require handling of the subjects in order to make measurements. Fish can undergo rapid physiological color change in response to stress. As such, handling fish may induce color changes and measured colour may not be representative of signal appearance under non-stressful conditions. We measured the reflectance characteristics of the opercular, ventro-lateral and dorso-lateral areas of 41 reproductive males from Hotel Lake, BC, Canada using spectroradiometry immediately upon capture and again at 2, 3, 4, 5, 10, 15, and 20 min post-capture. Repeated measures ANOVA revealed that post-capture handling did not affect opercular or ventro-lateral reflectance characteristics over the 20 min period. However, we did observe a change in dorso-lateral reflectance characteristics of parental males over the experiment. The results of our study show that handling does not influence reflective properties of two key components of stickleback reproductive signals during a time frame that is reasonable for taking field measurements of signal color.     

Geographical and Temporal FA Variation in Threespine Stickleback Populations from Galicia (NW Spain)

Subtle departures from bilateral symmetry (FA) in morphological traits has been used as a measure of developmental stability in populations subjected to genetic and environmental processes as inbreeding, pollution or parasitic infection. Geographic variation of FA was assessed in 19 threespine stickleback (Gasterosteus aculeatus) populations from Miño and Limia rivers, from Galicia (NW Spain). This variation was evaluated using four FA indices on five meristic and one morphometric traits. Temporal variation of FA was also assessed using several samples through time in only one population. Significant geographical variation was detected for pectoral fin rays, lateral forks, lateral plates and spine length. Lateral plates, upper gillrakers, pectoral fin rays and spine length showed significant variation through the time. The variation of FA through the time showed a common performance for all characters during the period considered: a slight increase in the intermediate months with a decrease at the end of the period. Symmetric and asymmetric sticklebacks exhibited similar infection, with one exception: symmetric sticklebacks for lower gillrakers of Antela populations exhibited increased parasite infection relative to asymmetric ones. Sticklebacks with extreme phenotypes exhibited much higher levels of asymmetry than modal ones in all samples for all traits.     

Food selection in juvenile three-spined sticklebacks studied in relation to size,abundance and biomass of prey

The food selection and diet of juvenile three-spined sticklebacks (Gasterosteus aculeatus L.) was studied in the littoral of a brackish-water sea area. The sampling stations were located in a eutrophicated area, where the plankton was characterized by rotifers, in a noneutrophicated zone, where copepods predominated, and in the intermediate zone, characterized by cladocerans. In all areas the fish preferred microcrustaceans to rotifers, but they did not feed strictly according to the size-selection hypothesis. Nor did they take the most abundant prey species. With some exceptions the species chiefly eaten by and also selected by fish, were those which had the largest biomass in the plankton.     

The breeding colouration of male three-spined sticklebacks (Gasterosteus aculeatus) as an indicator of energy investment in vigour

Summary A necessary condition of most models of intersexual selection requires that secondary sexual traits are costly so that cheating is prevented. If the conspicuous breeding colouration of male three-spined sticklebacks (Gasterosteus aculeatus L.) is such a handicap, it must involve costs. I examined the energetic costs of the breeding colouration by varying the energy contents of the daily food supply among five groups of sticklebacks over a 10 week period. The nutritional carotenoid level, i.e. the colour pigment used in the breeding colouration, was constant for all fish. Both the increase of their condition factor and the condition level they finally achieved correlated positively with the food ration of the groups. Individuals whose condition increased during the experiment developed a more intensive red colouration. However, a direct correlation between food quantity and the red breeding colouration reached at the end of the experiment did not exist. Nevertheless, given the limitation of pigment availability, there was still variation in the breeding colouration and the costs for the metabolism of the colouration were sufficient to render it an honest signal: a female stickleback can assess a male's condition and condition change over the past few weeks by the intensity of the colour of his blue eyes (which is not based on carotenoids and whose pigments were therefore not controlled in the food) and his red jaw, respectively. How much an individual male fish invests in increase of length and increase of condition (which correlate negatively with each other) seems to be, at least partly, his own strategic decision, which could have important consequences in the competition for female mates. It is eventually this decision that a male stickleback seems to signal with his red jaw.     

Expression of gonadotropin subunits in roach (Rutilus rutilus, Cyprinidae) infected with plerocercoids of the tapeworm Ligula intestinalis (Cestoda)

Plerocercoids of the tapeworm Ligula intestinalis (Cestoda: Bothriocephalidea) have been reported to inhibit gametogenesis of their intermediate fish hosts. However, mechanistic studies are rare and the proximate cues leading to impaired reproduction still remain unknown. In the present study we investigated the effects of infection by L. intestinalis on reproductive parameters of roach (Rutilus rutilus, Cyprinidae), a common fish host of this parasite. Field studies on roach demonstrated that in both genders infection prevented gonad development. As revealed by quantitative PCR, infection was accompanied by essentially lower pituitary expression of follicle-stimulating hormone β-subunit (FSHβ) and luteinizing hormone β-subunit (LHβ) mRNA compared with uninfected roach, providing clear evidence for gonadotropin-insufficiency as the cause of arrested gametogenesis. Under controlled laboratory conditions infected roach showed lower mRNA levels of FSHβ but not of LHβ, despite histology revealing similar gonad stages as in uninfected conspecifics. These findings indicate the involvement of FSH rather than LH in mediating effects of infection early during gonad development in roach. Moreover, the impact of L. intestinalis on reproductive parameters of roach appeared to be independent of the parasite burden. Together, these data provide valuable information on the role of FSH and LH as mediators of parasite-induced sterilization in a vertebrate and implicate the selective inhibition of host reproduction by L. intestinalis as a natural source of endocrine disruption in fish.     

Innate versus adaptive immunity in sticklebacks: evidence for trade-offs from a selection experiment

In vertebrates, the immune system consists of two arms of different characteristics: the innate and the acquired immune response. Parasites that are only shortly exposed to the immune system are most efficiently attacked by fast, constitutive innate immune mechanisms. Here, we experimentally selected within four fish families for high innate resistance versus susceptibility of three-spined sticklebacks (Gasterosteus aculeatus) against infection with the eye-fluke (Diplostomum pseudospathacaeum), a parasite whose metacercariae are protected from the immune system within the eye lens. We predicted that in families with high susceptibility, the adaptive immune system would be upregulated when challenged with infection. In accordance, we found that MHC class IIB expression is increased by approximately 50% in those lines selected for higher parasite load (i.e. low innate response). This suggests extensive genetic correlations between innate and adaptive immune system and/or crosstalk between both lines of defense. An efficient, specific innate immune response might reduce overall activation of the immune system and potentially alleviate associated effects of immunopathology.     

Changes in the reproductive biology of Biomphalaria glabrata experimentally infected with the nematode Angiostrongylus cantonensis

This study showed for the first time changes in the reproductive biology of Biomphalaria glabrata experimentally infected with Angiostrongylus cantonensis. The values of all the parameters analyzed (total number of eggs, number of egg masses, number of eggs/mass, number of eggs/snail, percentage of viable eggs and galactogen content in albumen gland) changed with progressive infection. The results indicate the occurrence of partial parasitic castration of B. glabrata by A. cantonensis larvae, probably in response to the depletion of energy reserves, with no injuries to the gonadal tissues.     

Who is in control of the stickleback immune system: interactions between Schistocephalus solidus and its specific vertebrate host

The cestode Schistocephalus solidus is a frequent parasite of three-spined sticklebacks and has a large impact on its host's fitness. Selection pressure should therefore be high on stickleback defence mechanisms, like an efficient immune system, and also on parasite strategies to overcome these. Even though there are indications for manipulation of the immune system of its specific second intermediate host by the cestode, nothing is yet known about the chronology of specific interactions of S. solidus with the stickleback immune system. We here expected sticklebacks to first mount an innate immune response directly post-exposure to the parasite to clear the infection at an early stage and after an initial lag phase to upregulate adaptive immunity. Most interestingly, we did not find any upregulation of the specific lymphocyte-mediated immune response. Also, the pattern of activation of the innate immune system did not match our expectations: the proliferation of monocytes followed fluctuating kinetics suggesting that the parasite repeatedly installs a new surface coat not immunogenic to the host. Furthermore, the respiratory burst activity, which has the potential to clear an early S. solidus infection, was upregulated very late during infection, when the parasite was too big to be cleared but ready for transmission to its final host. We here suggest that the late activation of the innate immune system interferes with the neuroendocrine system, which mediates reduced predation avoidance behaviour and so facilitates the transmission to the final host.     

A new model of lateral plate morph inheritance in the threespine stickleback,Gasterosteus aculeatus

The threespine stickleback,Gasterosteus aculeatus, is polymorphic for the arrangement of lateral bony plates. It is confirmed in this paper that four morphs (not three) should be distinguished in this species: low plated, low plated with a keel, partially plated and completely plated. A new model is proposed to explain the inheritance of these morphs which involves one major gene with three alleles displaying a dominance hierarchy withA (completely plated) dominant toa (low plated) which is dominant toa _k (low plated with keel). The dominance of theA allele is modified to semidominance by a dominant alleleC at a second locus. This scheme explains all the results of relevant breeding experiments published so far. Field data also fulfill predictions derived from this model.     

Responsivenes of total content changes of magnesium and zinc status in patients infected with Giardia intestinalis

The aim of the study was to investigate the changes of total content of the essential elements of zinc and magnesium levels in patients infected with Giardia intestinalis. Zinc and magnesium concentrations were measured in 64 patients who were positive for the intestinal parasite G. intestinalis. Scores were obtained for the positives and their 60 age- and sex-matched G. intestinalis-negative healthy controls. The mean concentration of magnesium in blood was significantly lower in G. intestinalis-positive patients than in their controls both in females (p<0.05) and males (p<0.05). The average zinc concentration in G. intestinalis-positive female patients was 0.76±0.3 mg/L and it was 0.60±0.2 mg/L in controls (p>0.05). The mean values of the zinc in blood were 0.73±0.2 mg/L in G. intestinalis-positive male patients and 0.82±0.1 mg/L in controls (p>0.05). No correlation could be demonstrated between age and mean values of zinc and magnesium in both G. intestinalis-positive females/males and controls (p>0.05). No significant correlation could be found between blood zinc and magnesium levels in G. intestinalis-positive female/male patients and controls (p>0.05). Magnesium levels were found to be clearly decreased, whereas no change was observed in zinc level in the patients infected with G. intestinalis compared to controls.     

Variation in reproductive investment among and within populations of the scorpion Centruroides vittatus

Although information concerning variation among and within populations is essential to understanding an organism's life history, little is known of such variation in any species of scorpion. We show that reproductive investment by the scorpion Centruroides vittatus varied among three Texas populations during one reproductive season. Females from the Kickapoo population produced smaller offspring and larger litters than females from the Independence Creek or Decatur populations; this pattern remained when adjusting for among population variation in either female mass or total litter mass. Relative clutch mass (RCM) and within-litter variability in offspring mass (V*) did not differ among populations. Among-population variation may result from genetic differences or from phenotypically plastic responses to differing environments. Within populations, the interrelationships among reproductive variables were similar for Decatur and Independence Creek: females investing more in reproduction (measured by total litter mass, TLM) produced larger litters and larger offspring, and V* decreased with increased mean offspring mass (and with decreased litter size at Decatur). At Kickapoo, larger females produced larger litters and had larger TLM; females investing more in reproduction produced larger litters but not larger offspring. Within litter variability in offspring mass was not correlated with any reproductive variables in this latter population. These patterns may be explained by the fractional clutch hypothesis, the inability of females precisely to control investment among offspring or morphological constraints on reproduction.     

Natural variation in stress response is related to post-stress parental effort in male house sparrows

The central life-history trade-off between current and future reproductive effort seems to be mediated by corticosterone in birds. However, still little is known about how naturally occurring corticosterone levels during an acute stress may influence subsequent parental behavior. In this study we observed the parental behavior of free-living male house sparrows (Passer domesticus) both before and after they were subjected to a standard capture–handling stress. We investigated the relationships between corticosterone levels, pre- and post-stress parental behavior, while we statistically controlled for a number of other variables using a multivariate regression method, the path analysis. We found that males' baseline feeding rate predicted the body mass of the nestlings, indicating that male parental care is directly linked to fitness. Corticosterone levels were not explained by baseline feeding rate, but both baseline and stress-induced corticosterone levels had a negative influence on the males' post-stress feeding behavior. Moreover, males with large bib size had a stronger stress response and lower post-stress feeding rate than small bibbed males. These results indicate that naturally occurring variation in baseline and stress-induced corticosterone levels may influence subsequent parental decisions: individuals mounting a robust stress response are likely to reduce their parental commitment. Parental effort may be regulated in a complex manner, with corticosterone mediating the life-history trade-off between current reproduction and survival. However, different resolutions of this trade-off were apparent only following the stress, therefore the ability to modulate the stress response and maintain parental care in stressful situations may be important in life-history evolution.