Differential effects of the severe winter of 1995/96 on the intertidal bivalves Mytilus edulis, Cerastoderma edule and Mya arenaria in the Northern Wadden Sea

Intertidal mussel beds were severely damaged by scouring ice floes during the winter of 1995/96. Aerial surveys before and after the winter showed that more clusters of mussel beds vanished in a region with a higher areal share of tidal flats and a lower salinity, suggesting that the amount of ice present determined the magnitude of the disturbance on beds of Mytilus edulis. Nehls and Thiel [(1993) Neth J Sea Res 31:181–187] observed a strikingly similar spatial pattern of disturbances caused by severe storms in the Wadden Sea. Areas on mussel beds mechanically undisturbed by ice showed no reduced abundance and biomass of mussels, indicating that temperature alone was of little importance as a lethal factor. Conversely, Cerastoderma edule was strongly affected by low temperature. On average 80% died during the winter with extinctions up to 100% in the high tidal zone. At the lowest tidal level, surviving cockles were larger than those killed by the frost. A reinvestigation of sampled sites in autumn revealed that substantial further mortality had occurred during spring and summer which may constitute a time-lag effect of the preceding winter. There was no increased mortality in juvenile and adult Mya arenaria during the winter of 1995/96, confirming that this clam is a hard-winter species like Macoma balthica. Received in revised form: 7 May 2001 Electronic Publication     

Effect of dietary polyunsaturated fatty acids on reproductive output and larval growth of bivalves

The pre-spawning condition of adult bivalves is influenced by quantity and quality of available food. For bivalves, the essential polyunsaturated fatty acids (PUFAs) eicosapentaenoic acid (EPA) 20:5(n-3) and docosahexaenoic acid (DHA) 22:6(n-3) are presumed to determine the nutritional value of algae. Macoma balthica kept on a broodstock diet supplemented with PUFAs spawned a larger number of eggs (average 22220) per female and larger sized eggs (106.7 μm) compared to adults kept on a diet without PUFA supplementation (962.5 eggs with average size 99.8 μm).Larvae of M. balthica from the same parental pool however did not profit from a diet where a part was replaced with PUFA spheres. Instead, larvae reared on Isochrysis sp. showed lower mortality and higher growth rates than larvae fed on the same algae supplemented with lipid spheres. Crassostrea gigas larvae showed no clear response to a PUFA supplemented diet.     

Selective settlement of the barnacle Semibalanus balanoides (L.) facilitates its growth and reproduction on mussel beds in the Wadden Sea

On the unstable sedimentary tidal flats of the Wadden Sea, a suitable attachment substrate for sessile organisms is generally lacking. Epibenthic mussel beds (Mytilus edulis L.) provide the only and strongly limited settlement sites available for the barnacle, Semibalanus balanoides (L.). Field investigations showed that barnacles were non-randomly distributed within a mussel bed. They preferentially occurred near the siphonal apertures of living mussels but rarely grew on dead mussels or shell fragments. Field experiments revealed that this was due to selective settlement of barnacle cyprid larvae. Growth of barnacles was significantly higher upon living mussels than on empty mussel shells. Moreover, a higher reproductive output was obtained by individuals on living mussels which produced twice as many nauplii larvae than barnacles attached to empty shells. This study shows that selective settlement of S. balanoides cyprid larvae on living mussels is adaptive with respect to individual fitness. Received in revised form: 15 January 2001 Electronic Publication     

Population density, phenotype and reproductive output in the grasshopper Chorthippus brunneus

ABSTRACT. 1. The effects of population density on the reproductive output of individual female grasshoppers ( Chorthippus brunneus Thunberg) and the relationships between reproductive output and component elements of each female's phenotype, were investigated.
2. Reproductive output was primarily determined by the rate of egg-pod production. Increased density led to significant reductions in the rate of egg-pod production and reproductive output.
3. Exoskeleton size (reflecting nymphal experience) was positively correlated with clutch size at both high and low densities, but condition (reflecting adult experience) showed no such correlation. At high density, exoskeleton size was more strongly correlated with the rate of egg-pod production and reproductive output than condition. It is concluded that the nymphal aspects of size are more important than the adult aspects.
4. At low density, females with small exoskeletons compensated for their smaller clutches by producing egg-pods at a faster rate. Thus, there was no overall relationship between reproductive output and any of the phenotypic characteristics.
5. The effects of competition were weakly asymmetric in high density populations. The weakness of the asymmetry suggests scramble-like interactions for resources. It is concluded that not only are the effects of competition influenced by individual differences, but also that competition may reveal differences that would not otherwise be apparent.     

Maternal body-volume as a constraint on reproductive output in lizards: evidence from the evolution of viviparity

A few species of squamate reptiles contain both oviparous (egg-laying) and viviparous (live-bearing) populations, and thus offer exceptional opportunities to test adaptationist hypotheses on the determinants of reproductive output. We focus on the hypothesis that maternal body-volume constrains reproductive output in squamate reptiles. If females are “full” of eggs, what happens when viviparity evolves within a lineage? Eggs increase in volume and mass during development, primarily due to the uptake of water, so how can they be accommodated within the mother's abdomen? We predict that the resultant increase in relative clutch mass (RCM) will be lessened by (1) a decrease in reproductive output (by reducing the number or size of offspring), and/or (2) an increase in maternal body-volume (via modifications of size or shape of adult females). Our comparisons of conspecific oviparous and viviparous lizards (Lerista bougainvillii) confirm that live-bearers carry heavier clutches (in both absolute and relative terms) and show the predicted shifts in body size and shape of reproductive females. However, offspring size and number were unaffected by the evolution of viviparity, and the shifts in maternal morphology were too small to fully offset the increase in clutch mass. Thus, RCMs increased by 50%, indicating that viviparous females produced clutches which more completely filled the space available in the abdominal cavity. We conclude that maternal body-volume does play a role in determining reproductive output, but that the observed clutch masses may be optimized, rather than maximized, with respect to the abdominal space available.     

Effects of temperature on reproductive output, egg provisioning, juvenile hormone and vitellogenin titres in the butterfly Bicyclus anynana

Environmentally induced phenotypic plasticity is common in nature. Hormones, affecting multiple traits and signaling to a variety of distant target tissues, provide a mechanistic link between environments, genes and trait expression, and may therefore well be involved in the regulation phenotypic plasticity. Here, we investigate whether in the tropical butterfly Bicyclus anynana temperature-mediated plasticity in egg size and number, with fewer but larger eggs produced at lower temperatures and vice versa, is under control of juvenile hormone, and whether different temperatures cause differences in egg composition. Female B. anynana butterflies showed the expected response to temperature, however, we found no evidence for an involvement of juvenile hormone. Neither haemolymph JH II and JH III titres nor vitellogenin levels differed across temperatures. The smaller eggs produced at the higher temperature contained relatively higher amounts of water, free carbohydrates and proteins, but relatively lower amounts of lipids. While these smaller eggs had a lower absolute energy content, total reproductive investment was higher at the higher temperature (due to a higher fecundity). Overall, our study indicates that temperature-mediated plasticity in reproduction in B. anynana is mechanistically related to a biophysical model, with oocyte production (differentiation) and oocyte growth (vitellogenesis) having differential temperature sensitivities.     

Interactive effects of food availability and aerial body temperature on the survival of two intertidal Mytilus species

Intertidal organisms must episodically contend with the rigors of both the terrestrial and the marine environments. While body temperatures during high tide are driven primarily by water temperature, aerial body temperatures are driven by multiple environmental factors such that temperature of an organism during low tide is usually quite different from air temperature. Thus, whereas decades of research have investigated the effects of water temperature on intertidal species, considerably less is known about the physiological impacts of temperature during aerial exposure at low tide, especially with regard to the interaction of aerial body temperature with other stressors. We examined the interactive effects of aerial body temperature and food supply on the survival of two intertidal blue mussels, Mytilus galloprovincialis and Mytilus trossulus. Survival was monitored for nine weeks using a simulated tidal cycle, with two levels of food and three levels of aerial body temperature (30, 25, and 20 °C). Decreased food supply significantly reduced the survival of mussels, but only under the 30 °C treatment. In the other two thermal regimes there were no significant effect of food on survival. When aerial body temperatures are high, food availability may have a greater effect on intertidal organisms. Decreases in ocean productivity have been linked to increased in ocean temperatures, thus intertidal organisms may become more susceptible to thermal stress as climates shift.     

Late Pleistocene and Holocene distribution of Mytilus edulis in the Barents Sea region and its palaeoclimatic implications

Aim For decades, subfossil shells of the bivalve Mytilus edulis Linnaeus, 1758 in Svalbard have been taken as evidence of higher surface temperatures during the early Holocene because the modern northern occurrence of this mollusc was, until recently, in the southern Barents Sea. Here, we elucidate and discuss the spatial and temporal Late Pleistocene and Holocene distribution of the species within the entire Barents Sea region. Location The Barents Sea region. Methods Radiocarbon dates of Mytilus shells from the Barents Sea region and information about the present distribution of the species were compiled, including two new radiocarbon dates from north‐eastern Spitsbergen. The dataset was divided into time slices, each covering 1000 years, and compared with Holocene temperature variations, ocean current systems and present‐day temperature patterns. Results Maps show the Late Pleistocene and Holocene spatial and temporal distribution of Mytilus edulis in the Barents Sea region. M. edulis was already present in northern Norway about 14,000 cal. yr bp . It appeared at western Spitsbergen about 11,000 cal. yr bp , and slowly spread to the rest of the archipelago. The maximum distribution in the region was reached 10,000–7000 cal. yr bp , coinciding with the Holocene climatic optimum. The species gradually disappeared in the late Holocene and became absent from the northern and eastern parts of the region 3000–1000 cal. yr bp . Today, M. edulis lives in the southern part and has begun to recolonize the northern parts. Main conclusions The time slices illustrate strong connections between the ocean current regimes, the climate and the distribution of M. edulis. The species settled in the southern part of the Barents Sea region several thousand years before it spread to the northern part during the Holocene climatic optimum. It may even have been completely absent from the region for a short time during the late Holocene cold period. The Holocene distribution of Mytilus implies that the underlying pattern of coastal sea surface temperatures in the region was very stable.     

Recent changes in the contributions of river Rhine and North Sea to the eutrophication of the western Dutch Wadden Sea

From 1955 to the mid 1980s the loads of both nitrogen and phosphorus from the river Rhine to the Dutch coastal area, the Wadden Sea included, increased. Since 1985 the phosphorus loads has decreased significantly, while the nitrogen load remained about the same.Annual primary production in the western Dutch Wadden Sea has increased fromc. 40 g C m^–2 (1950) to 150 (mid 1960s) and over 500 g C m^–2 (1986). The biomass of macrozoobenthos has more than doubled since 1970. Simultaneously, the meat yield of cultured blue mussels (Mytilus edulis), has increased since the 1960s. Previously, it was indicated that the increase in primary production of the phytoplankton over the period 1950 to 1986 was stimulated by the load of dissolved inorganic phosphate from Lake IJssel, a reservoir supplied by Rhine water. Since 1990, however, primary production has been higher than was expected from decreased phosphate loads from Lake IJssel. It is argued that this lack of response may have been caused by increased concentrations of dissolved inorganic phosphate at sea originating from increased inflow from a.o. the Strait of Dover, which compensate for the decrease in phosphate from the rivers, possibly in combination with a significant improvement of the light conditions of the water in the Wadden Sea.     

Effects of lairage temperature and holding time on pig behaviour and on carcass and meat quality

Twenty three groups of about 30 pigs each were kept in an environmentally controlled room in lairage, at temperatures of 20 or 35°C for periods of 0.5 or 3 h, to establish the effects of these parameters on animal behaviour and meat quality. Following initial exploration, 50% of pigs kept at 35°C but only 5% kept at 20°C lay down before the end of the 0.5 h period. Seven percent of pigs fought in both temperature conditions. When held in lairage for 0.5 h there was no difference in meat quality or skin damage at either temperature. When held for 3 h, about 95% of pigs were lying down after 2 h in the pens. Again, the percentage of animals fighting was similar for both temperatures, the number of encounters increasing during the first 30–40 min. The more intense initial fighting within the group held at 35°C resulted in the pigs lying down slightly earlier. Irrespective of the lairage time, the frequency of sexual activity decreased with temperature. The proportion of carcasses with skin damage increased with lairage time due, perhaps, to the longer duration of aggressive encounters. Increased lairage time at 20°C reduced the incidence of PSE meat, but at 35°C the longer lairage time showed no benefit to animal welfare or meat quality.     

滑鼠蛇的繁殖输出及孵化热环境对孵出幼体表型特征的影响

用15条2002年6月中旬捕自浙江丽水的怀卵滑鼠蛇研究繁殖输出及孵化热环境对孵出幼体表型特征的影响。母体在捕后3周内各产一窝柔性卵。窝卵数、窝卵重和卵大小均随母体体长增加而增大,平均值分别为13．3(枚卵)、332．4g和24．8g。窝卵数和卵大小的变异系数分别为0．18和0．13。窝卵数与产后母体状态呈正相关,卵数量和大小无关。每窝部分可孵卵分别用恒温(24、27、30、33℃)和21．0-39．0℃(平均28．3℃)范围内的波动温度孵化,每隔5d记录恒温孵化卵的重量。孵化热环境对卵与环境之间的水分交换有显著影响,并影响孵化卵重量的时间变化。24、27、30、33℃和波动温度的平均孵化期分别为105．4、78．0、57．8、51．3和58．6d。不同热环境下的孵化成功率和幼体畸形率有一定差别,但统计上不显著。24℃和30℃孵出幼体雄性比例较高,27℃、33℃和波动温度孵出幼体雌性比例较高,但没有证据表明孵化温度能决定滑鼠蛇性别。除孵出幼体灰分含量外,孵化温度对其它幼体特征均有显著影响。33℃孵出幼体SVL较小,但剩余卵黄和其中的灰分含量大于其它温度孵出的幼体。24℃和30℃孵出幼体的总干重、总能量、躯干干重、脂肪体干重总体上小于27℃和波动温度孵出幼体。24℃孵出幼体特征性具有最小的剩余卵黄,33℃孵出幼体则特征性地具有最大的剩余卵黄。24℃和30℃孵出幼体特征较为接近,27℃和波动温度孵出幼体较为接近。对9个幼体特征变量做主成分分析发现,第一和第二主成分共解释81．2％的变异。幼体SVL、湿重、干重、脂肪含量、能量、躯干干重和脂肪体干重在第一主成分有较高的正负载系数(解释56．9％变异),剩余卵黄干重在第二主成分有较高的正负载系数(解释24．3％变异),第一和第二主成分的分值均差异显著。主成分分析进一步显示,24、30和33℃孵出幼体总体上小于27℃和波动温度孵出幼体[动物学报50(4)：541-550,2004]。     

Effects of ectoparasite infestation during pregnancy on physiological stress and reproductive output in a rodent-flea system

Biotic and abiotic stressors impose various fitness costs on individuals across a variety of taxa. In vertebrates, these stressors typically trigger complex neuroendocrine responses that stimulate glucocorticoid (GC) secretion from the adrenal cortex. Short-term elevation of GCs can be adaptive as it shifts energy toward physiological processes that cope with acute stressors; however, chronic increases in GC levels could have detrimental effects on fitness. Parasitism can be considered an important biotic stressor in nature and a possible cause of reproductive failure that could substantially affect an individual’s fitness. Thus, we aimed to test the effects of parasitism and maternal stress, as measured by GCs, during pregnancy and the relationship between these variables and measures of reproductive output using a rodent-flea system. Female Egyptian spiny mice (Acomys cahirinus) were randomly assigned to flea (Parapulex chephrenis) infested or uninfested treatments before and during pregnancy. The offspring of these females were flea-free. Feces were collected at five time points during the experiment to determine maternal fecal glucocorticoid metabolite (FGCM) concentrations. Overall, infested females had lower FGCM levels during gestation but higher FGCM levels post-parturition and larger mass changes than uninfested females. Additionally, models related to pup quality and quantity often included some measure of maternal investment or body condition moderating relationships between infestation and stress. This suggests that flea parasitism or high GC levels alone might not significantly impact host reproduction but rather females can experience different effects depending on their level of investment, which could be limited by body condition and/or the number of pups present in a litter.     

高体重布氏田鼠产仔数较多但繁殖输出及氧化损伤不受影响

体重可影响动物几乎所有的生物学变量。高体重双亲通常产生较大胎仔数。繁殖过程代价很高,可能伴随着氧化损伤。为比较双亲体重对繁殖期能量学特征、繁殖输出和氧化损伤的影响,检测了高体重组(雌性:51. 5 g ± 1. 6 g;雄性:60. 4 g ±2. 5 g)和低体重组(雌性:35. 5 g ± 1. 2 g;雄性:49. 6 g ± 2. 8 g)布氏田鼠繁殖过程中母体的体重和摄食量,分娩时的胎仔数和胎仔总重,及后代断乳时母体的身体成分、激素含量(血清瘦素和催乳素)和氧化损伤(血清丙二醛、蛋白质羰基和肝脏丙二醛含量)。结果显示:(1)高体重组妊娠末期的母体体重增量显著高于低体重组;(2)高体重组母体的出生胎仔数显著高于低体重组,但出生及断乳时的平均胎仔重、胎仔总重和母体繁殖期间的能量摄入无显著差异; (3)血清激素含量、身体成分、身体脂肪重量及氧化损伤指标均无组间差异。结果表明,高体重布氏田鼠可产生较多的出生胎仔数,但母体并不通过摄入更多的能量来保证其繁殖输出,对氧化损伤也没有影响。这些结果对于理解不同体重的动物在繁殖期间的能量策略以及繁殖与生存之间的权衡等生活史理论具有重要意义。     

Macroclimatic and maternal effects on the evolution of reproductive traits in lizards

Much of life‐history theory rests on fundamental assumptions about constraints on the acquisition and allocation of energy to growth and reproduction. In general, the allocation of energy to reproduction depends on maternal size, which in turn depends on environmental factors experienced throughout the life of the mother. Here, we used phylogenetic path analyses to evaluate competing hypotheses about the environmental and maternal drivers of reproductive traits in lizards. In doing so, we discovered that precipitation, rather than temperature, has shaped the evolution of the life history. Specifically, environments with greater rainfall have enabled the evolution of larger maternal size. In turn, these larger mothers produce larger clutches of larger offspring. However, annual precipitation has a negative direct effect on offspring size, despite the positive indirect effect mediated by maternal size. Possibly, the evolution of offspring size was driven by the need to conserve water in dry environments, because small organisms are particularly sensitive to water loss. Since we found that body size variation among lizards is related to a combination of climatic factors, mainly precipitation and perhaps primary production, our study challenges previous generalizations (e.g., temperature‐size rule and Bergmann''s rule) and suggests alternative mechanisms underlying the evolution of body size.     

The effect of temperature on the development time and brood size of diaptomus pallidus herrick

Diaptomus pallidus individuals were raised in the laboratory at three temperatures (15, 20, and 25°C) and fed an alfalfa and trout-food diet ad libitum. Data were taken on the development times of the egg, naupliar, and each copepodid stage and the brood sizes of field animals acclimated to the test conditions.The results indicated D. pallidus does not have a temperature range over which its development rate is nearly constant as earlier reported. Rather, the development rate is temperature dependent within the experimental range. Broods produced at 20°C and 25°C were significantly smaller than those produced at 15°C but not significantly different from each other.     

Interactive effects of time and vegetation on reproduction of redshanks (Tringa totanus) breeding in Wadden Sea salt marshes

As shown for various species, nesting waders are non-randomly distributed on wetlands and preferentially select riparian nest-sites adjacent to limnic or marine waterbodies. Studying the redshank Tringa totanus, we tested the hypotheses that, in a coastal wader species which conceals its clutch in vegetation, predation and hatching success are affected by vegetation zonation, and that breeding in lower salt marsh areas has negative consequences for reproduction. We further predicted effects of timing of breeding and breeding experience/age of adults potentially reflected by egg biometrics both on nest-site selection and reproduction. Effects of vegetation, space, time and individual quality on hatching success of redshanks were studied in the German part of the Wadden Sea. Dominant plant species, vertical vegetation structure and nest concealment varied significantly between nests. Variation in nest concealment was relatively low: about 90% of clutches were classified as being well concealed. This variation was explainable by vegetation structure but not by vegetation composition at the nest-site, distance to shoreline, and time of clutch initiation. Vertical vegetation structure varied by dominant plant species but not by distance to shoreline and time of clutch initiation. Hatching success of clutches was low (10.6%) due to high predation (daily predation rate: 7.4%). Hatching success and duration of clutch survival were negatively and predation positively related to the date of clutch initiation. Furthermore, negative relationships were found between egg size and predation and duration of survival, respectively. We assume that concealed nests, early breeding and breeding experience diminish predation in salt marsh breeding redshanks. Thus, redshank reproduction appears to be affected by interactive effects of timing of breeding and vegetation facilitating early breeding. In contrast to open-nesting species, breeding in riparian habitats next to waterbodies may be disadvantageous for species breeding concealed in vegetation if these are covered by less structured vegetation.     

High survival and growth rates of introduced Pacific oysters may cause restrictions on habitat use by native mussels in the Wadden Sea

Pacific oysters Crassostrea gigas (Thunberg, 1793) were introduced to the northern Wadden Sea (North Sea, Germany) by aquaculture in 1986 and finally became established. Even though at first recruitment success was rare, three consecutive warm summers led to a massive increase in oyster abundances and to the overgrowth of native mussel beds (Mytilus edulis L.). These mussels constitute biogenic reefs on the sand and mud flats in this area. Survival and growth of the invading C. gigas were investigated and compared with the native mussels in order to predict the further development of the oyster population and the scope for coexistence of both species. Field experiments revealed high survival of juvenile C. gigas (approximately 70%) during the first three months after settlement. Survival during the first winter varied between > 90% during a mild and 25% during a cold winter and was independent of substrate (i.e., mussels or oysters) and tide level. Within their first year C. gigas reached a mean length of 35-53 mm, and within two years they grew to 68-82 mm, which is about twice the size native mussels would attain during that time. Growth of juvenile oysters was not affected by substrate (i.e., sand, mussels, and other oysters), barnacle epibionts and tide level, but was facilitated by fucoid algae. By contrast, growth of juvenile mussels was significantly higher on sand flats than on mussel or oyster beds and higher in the subtidal compared to intertidal locations. Cover with fucoid algae increased mussel growth but decreased their condition expressed as dry flesh weight versus shell weight. High survival and growth rates may compensate for years with low recruitment, and may therefore allow a fast population increase. This may lead to restrictions on habitat use by native mussels in the Wadden Sea.     

Lack of anti-androgenic effects of equol on reproductive neuroendocrine function in the adult male rat

Equol (EQ), a metabolite of the soy isoflavone daidzein, has well known estrogenic properties. Data from animal studies suggested that EQ may act also as an anti-androgen. However, data regarding how EQ may affect brain functions like the regulation of neuroendocrine activity and reproductive outcomes in adult male rats are still lacking. We therefore investigated the effects of EQ on sex-steroid regulated gene expression in the brain [medial preoptic area/anterior hypothalamus (MPOA/AH) and medial basal hypothalamus/median eminence (MBH/ME)], pituitary, and prostate as a reference androgen-dependent organ. Furthermore reproductive outcomes were evaluated. The anti-androgen flutamide (FLUT) served as reference compound. Male rats (n = 12 per group) were treated by gavage for 5 days with either EQ (100 or 250 mg/kg BW/day), or FLUT 100 mg/kg BW/day. All vehicle- and EQ-treated males showed successful reproductive outcomes, whereas FLUT-exposed males had severe reproductive impairments resulted in infertility. FLUT decreased relative weights of prostate, seminal vesicles and epididymides, and increased serum levels of luteinizing hormone, follicle-stimulating hormone, testosterone and 5α-dihydrotestosterone without altering prolactin levels, whereas EQ exerted opposite effects. Both EQ and FLUT decreased gonadotropin releasing hormone (GnRH) expression in the MPOA/AH. Only FLUT upregulated levels of GnRH receptor expression both in the MBH/ME and pituitary. While EQ downregulated the hypothalamic ERα and ERβ expressions, but FLUT did not. In the prostate, only FLUT upregulated both ERα and AR mRNA expression levels. Taken together, our findings are the first data that EQ did not induce anti-androgenic effects on brain, prostate and male reproductive parameters, however, estrogenic neuroendocrine and reproductive effects of EQ were observed.