Responsiveness of selected condition measures of herring, Clupea harengus, larvae to starvation in relation to ontogeny and temperature

A laboratory experiment was performed to study the responsiveness of selected condition measures to starvation in herring, Clupea harengus, larvae in relation to temperature and ontogeny. The larvae at two intervals of development, i.e. stage 1 larvae with initial exogenous feeding and stage 2 larvae with established feeding prior to notochord flexion, were reared at three temperatures (5, 8 and 11°C) and subjected to sub-lethal durations of starvation. Temporal changes in standard length, dry weight, DNA concentration (% of dry weight), RNA concentration (% of dry weight), Fulton's condition factor (CF) and RNA/DNA were assessed and compared with fed controls. Starvation led to decreases in dry weight, CF, RNA concentration and RNA/DNA, while it led to an increase in DNA concentration. Higher responsiveness to starvation was observed at higher temperatures, and the magnitude of the changes was higher in stage 2 larvae. The shortest latency in starvation response was found with respect to RNA/DNA which was length independent in the size range studied. RNA/DNA was also significantly related to average DNA growth rate, and the model for DNA growth rate was, SGRDNA=4.49 RNA/DNA + 7.14 T – 0.42 T2 – 37.5 ; n=32, r2=0.85, p < 0.001). While the model seemed to adequately represent the average temperature dependent DNA growth, a relatively low classification success made it unsuitable for depicting individually starving larvae. Critical levels in DNA concentration can be used (2.2% for stage 1 larvae, 2.9% for stage 2 larvae) to differentiate starving larvae (after 3 – 5 days) from feeding larvae. RNA/DNA was the most sensitive and suitable condition index studied in detecting early starvation of herring larvae.     

The effect of maternal and paternal immune challenge on offspring immunity and reproduction in a cricket

Trans‐generational immune priming is the transmission of enhanced immunity to offspring following a parental immune challenge. Although within‐generation increased investment into immunity demonstrates clear costs on reproductive investment in a number of taxa, the potential for immune priming to impact on offspring reproductive investment has not been thoroughly investigated. We explored the reproductive costs of immune priming in a field cricket, Teleogryllus oceanicus. To assess the relative importance of maternal and paternal immune status, mothers and fathers were immune‐challenged with live bacteria or a control solution and assigned to one of four treatments in which one parent, neither or both parents were immune‐challenged. Families of offspring were reared to adulthood under a food‐restricted diet, and approximately 10 offspring in each family were assayed for two measures of immunocompetence. We additionally quantified offspring reproductive investment using sperm viability for males and ovary mass for females. We demonstrate that parental immune challenge has significant consequences for the immunocompetence and, in turn, reproductive investment of their male offspring. A complex interaction between maternal and paternal immune status increased the antibacterial immune response of male offspring. This increased immune response was associated with a reduction in son's sperm viability, implicating a trans‐generational resource trade‐off between investment into immunocompetence and reproduction. Our data also show that these costs are sexually dimorphic, as daughters did not demonstrate a similar increase in immunity, despite showing a reduction in ovary mass.     

Feeding and growth of larval herring,Clupea harengus,in relation to density of copepod nauplii

Synopsis Feeding and growth rates of 1–3 wk old herring larvae from four different stocks were compared in laboratory experiments (8°C). For most of the larval groups, feeding rate was saturated at nauplii (Acartia tonsa, nauplii stages 3–5) densities over 301^–1 (5 g d.w. 1^–1). Specific growth rate increased asymptotically with nauplii density, and reached about 6% d^–1 at densities over 120 nauplii 1^–1. The growth rates attained in the laboratory were similar to field measured growth rates of similarly aged herring larvae at comparable food densities. Since food particles were homogenously distributed in the laboratory tanks, patches of dense plankton concentrations are, thus, apparently not necessary for larval growth and survival in the sea. Growth efficiency differed between larval groups, with large sized larvae being the most efficient in transforming ingested matter into growth. The difference probably relates to different sizes rather than to the different geographical origins of the larvae.     

Senescence and costs of reproduction in the life history of a small precocial species

Species following a fast life history are expected to express fitness costs mainly as increased mortality, while slow‐lived species should suffer fertility costs. Because observational studies have limited power to disentangle intrinsic and extrinsic factors influencing senescence, we manipulated reproductive effort experimentally in the cavy (Cavia aperea) which produces extremely precocial young. We created two experimental groups: One was allowed continuous reproduction (CR) and the other intermittent reproduction (IR) by removing males at regular intervals. We predicted that the CR females should senesce (and die) earlier and produce either fewer and/or smaller, slower growing offspring per litter than those of the IR group. CR females had 16% more litters during three years than IR females. CR females increased mass and body condition more steeply and both remained higher until the experiment ended. Female survival showed no group difference. Reproductive senescence in litter size, litter mass, and reproductive effort (litter mass/maternal mass) began after about 600 days and was slightly stronger in CR than IR females. Litter size, litter mass, and offspring survival declined with maternal age and were influenced by seasonality. IR females decreased reproductive effort less during cold seasons and only at higher age than CR females. Nevertheless, offspring winter mortality was higher in IR females. Our results show small costs of reproduction despite high reproductive effort, suggesting that under ad libitum food conditions costs depend largely on internal regulation of allocation decisions.     

Determination of the cost of worker reproduction via diminished life span in the ant Diacamma sp

Workers of social Hymenoptera can usually produce male offspring, but rarely do so in the presence of a queen despite the potential individual fitness benefit. Various mechanisms have been hypothesized to regulate worker reproduction, including avoiding the colony-level cost of worker reproduction. However, firm quantitative evidence is lacking to support that hypothesis. Here, we accurately quantified this cost by studying an ant species (Diacamma sp.) in which worker reproduction is rare in the presence of the gamergate (the functional queen). A series of experiments to manipulate worker-gamergate contact revealed that short-term brood-production efficiency is not changed by the presence of worker reproduction. However, when workers reproduce, their average life span is reduced to between 74% and 88% of that in the absence of reproduction, indicating a long-term cost to the colony. In theory, this cost can explain the policing of worker reproduction under a queen-single mating system, but the cost does not appear to be high enough to stop worker reproduction. When contact with the gamergate is lost, it is only the nonreproductive workers whose life span was reduced; the reproductive workers lived as long as nonorphaned workers. We suggest that an increased workload can account for the reduction in life span better than a trade-off between reproduction and longevity.     

School density affects the strength of collective avoidance responses in wild‐caught Atlantic herring Clupea harengus: a simulated predator encounter experiment

An experimental study in a semi‐controlled environment was conducted to examine whether school density in wild‐caught Atlantic herring Clupea harengus affects the strength of their collective escape behaviours. Using acoustics, the anti‐predator diving responses of C. harengus in two schools that differed in density were quantified by exposing them to a simulated threat. Due to logistical restrictions, the first fish was tested in a low‐density school condition (four trials; packing density = 1·5 fish m^?3; c. 6000 fish) followed by fish in a high‐density school condition (five trials; packing density = 16 fish m^?3; c. 60 000 fish). The C. harengus in a high‐density school exhibited stronger collective diving avoidance responses to the simulated predators than fish in the lower‐density school. The findings suggest that the density (and thus the internal organization) of a fish school affects the strength of collective anti‐predatory responses, and the extent to which information about predation risk is transferred through the C. harengus school. Therefore, the results challenge the common notion that information transfer within animal groups may not depend on group size and density.     

Investment in survival and reproduction along a semelparity–iteroparity gradient in the Beta species complex

The Beta species complex shows a gradient of life histories from pronounced semelparity (big‐bang reproduction) to pronounced iteroparity (repeated reproduction). Models assume a trade‐off between investment in reproduction and survival. Reproductive effort is thought to increase with decreasing life span, and to be invariable in semelparous plants and susceptible to environmental conditions in iteroparous plants. These assumptions and hypotheses were verified by a greenhouse experiment testing six different life cycles at three contrasting nutrient levels. This study suggests that reproductive effort is negatively correlated with mean life span along the life‐cycle gradient. Unlike semelparous beets, reproductive effort in iteroparous beets is extremely sensitive to nutrient level. Phenotypic correlation between allocation to reproduction and allocation to survival generally appeared significantly negative in the longest‐lived iteroparous beets, nonsignificant in intermediate life histories and obviously positive in semelparous beets (no trade‐off control).     

Norwegian spring‐spawning herring as the test case of piecewise linear regression method for detecting maturation from growth patterns

Data from Norwegian spring‐spawning herring Clupea harengus, were used empirically to assess the performance of a regression method aimed at detecting the time of the onset of maturation from growth trajectories. At the level of the whole dataset, the piecewise linear‐regression method was accurate and showed only a minor bias (?0·17 years) relative to age at maturation visually read from scales. The method, however, was relatively imprecise and provided an estimate of age at maturation equal to the one read from the scale in less than half of the cases (47·6%). Moreover, bias was strongly dependent on age at maturation: the age at maturation of early maturing fish was often overestimated, whereas the opposite was true for late‐maturing fish. Accuracy and precision of the regression method relative to visual readings also depended on the growth type (determined by the nursery area of young C. harengus) and cohort but not on sex. Modifying the original regression method enabled marginally improving the precision of the approach but a strong maturation age‐dependent bias persisted. The results with C. harengus suggested that age‐at‐maturation estimates from the piecewise linear regression method should be treated with caution.     

Outcrossing hermaphroditic polychaete worms adjust their sex allocation to social conditions

Sex allocation theory predicts that simultaneous hermaphrodites shift sex allocation facultatively in response to variation in local group size. This study was performed to evaluate the relative investment in each sex function by the simultaneously hermaphroditic polychaete worm Ophryotrocha diadema and to test whether allocation to each sex depends on the number of reproductive competitors. Four experimental groups were set up (in a 2 x 2 factorial design) with small or large group size and with small or large enclosures to control for potential confounding effects of density. We measured the proportion of female and male investment in focal individuals. Results revealed that individuals regulated their reproductive output so that when reproductive competitors were present, the number of female gametes was strongly reduced and the male function increased. In contrast, under monogamy, individuals in small groups produced lower numbers of sperm but had a higher egg output than worms in large groups. Density did not affect sex allocation in our experiment. Our findings provide qualitative support for Local Mate Competition theory, but also show that the pattern of sex allocation specific to this species is more complex than expected by current theory.     

Separating two herring stocks from growth data: long‐term changes in survey indices for Western Baltic Spring Spawning Herring (Clupea harengus) after application of a stock separation function

In the Baltic Sea, herring stocks are surveyed and managed according to a spatial allocation based on ICES (International Council for the Exploration of the Sea) subdivisions. In the western Baltic, the distribution areas of two stocks overlap: the Western Baltic Spring Spawning Herring (WBSSH) and the Central Baltic Herring (CBH). Survey results of length‐at‐age data indicate in Subdivision (SD) 24, which is a part of the WBSSH management area, that a considerable fraction of CBH is present and correspondingly erroneously allocated to WBSSH stock indices. Accordingly, a stock Separation Function (SF) based on growth parameters was established to identify the fraction of CBH in the WBSSH area. In the present study, the SF was applied to 8 years of data from the GERman Acoustic Survey (GERAS), which is conducted annually in autumn in ICES subdivisions 21‐24. Results showed a distinct fraction of CBH in SD 24, and exclusion of the CBH greatly improved the quality of the GERAS index used in the assessment of the WBSSH stock.     

The influence of nuptial feeding and sperm transfer on the immunological cost of reproduction in the ground cricket Allonemobius socius

Mating is often accompanied by decreased female immune function across numerous animals systems, suggesting that immune suppression is a widespread reproductive cost. However, the trade‐off between immunity and reproduction can be minimized when females have access to abundant nutrient resources. This observation suggests that the nuptial gifts provided by males in many insect systems may help to offset the common immunological cost to reproduction. In the present study, this hypothesis is tested in the ground cricket Allonemobius socius (Scudder), whose females receive a sizeable haemolymph‐based gift. Accordingly, male gift donation is controlled by covering the tibial spur (the source of the gift) of randomly chosen males with clear nail polish. The influence of sperm transfer on female immunity is disentangled from that of the nuptial gift by also examining females who fail to receive sperm during mating (spermatophore transfer has a 40% failure rate in virgin males). It is predicted that females who receive a nuptial gift will exhibit superior immune function compared with those who receive no gift. The results show that sperm transfer reduces female immune function, which is an expected immunological cost of reproduction. By contrast to the prediction, nuptial gifts do not minimize the immunological cost of reproduction in this system. Unexpectedly, the receipt of a gift appears to decrease female immune function independent of sperm transfer. The findings suggest that the nuptial gift, similar to sperm, signals the female to begin her reproductive investment, causing limited resources to be reallocated from immune function.     

Plasticity in reproduction and growth among 52 range‐wide populations of a Mediterranean conifer: adaptive responses to environmental stress

A plastic response towards enhanced reproduction is expected in stressful environments, but it is assumed to trade off against vegetative growth and efficiency in the use of available resources deployed in reproduction [reproductive efficiency (RE)]. Evidence supporting this expectation is scarce for plants, particularly for long‐lived species. Forest trees such as Mediterranean pines provide ideal models to study the adaptive value of allocation to reproduction vs. vegetative growth given their among‐population differentiation for adaptive traits and their remarkable capacity to cope with dry and low‐fertility environments. We studied 52 range‐wide Pinus halepensis populations planted into two environmentally contrasting sites during their initial reproductive stage. We investigated the effect of site, population and their interaction on vegetative growth, threshold size for female reproduction, reproductive–vegetative size relationships and RE. We quantified correlations among traits and environmental variables to identify allocation trade‐offs and ecotypic trends. Genetic variation for plasticity was high for vegetative growth, whereas it was nonsignificant for reproduction. Size‐corrected reproduction was enhanced in the more stressful site supporting the expectation for adverse conditions to elicit plastic responses in reproductive allometry. However, RE was unrelated with early reproductive investment. Our results followed theoretical predictions and support that phenotypic plasticity for reproduction is adaptive under stressful environments. Considering expectations of increased drought in the Mediterranean, we hypothesize that phenotypic plasticity together with natural selection on reproductive traits will play a relevant role in the future adaptation of forest tree species.     

Flight dimorphism is related to survival,reproduction and mating success in the leaf beetle Oreina cacaliae

1. Alternative life histories may be maintained in populations due to variation in the costs and benefits of the underlying strategies. In this study, potential costs of dispersal by flight were investigated as an alternative life‐history strategy in the mountain‐living chrysomelid beetle Oreina cacaliae. 2. In this species, previous mark–recapture studies showed a dispersal dimorphism in both males and females. While a fraction of the population engages in flight in autumn and spring (in the following referred to as ‘flyers’), the other part does not fly (non‐flyers). Flyers emerge earlier than non‐flyers and feed on a spring host plant before the emergence of the main host plant. 3. In this study, the overwintering and dispersal locations were recorded over 7 years in the field, flyers from the spring host plant were collected, and morphology and lifetime reproductive output and survival of collected flyers and non‐flyers were compared. 4. A potential trade‐off between flight and life‐history traits was observed: flyers were smaller in size, lighter in body mass, had a lower lifetime fecundity and a higher mortality. 5. Mating experiments of field‐caught beetles in the laboratory showed that larger beetles had a higher (multiple) mating success, but there was no evidence for size‐assortative mating. It is hypothesized that one reason for small beetles to disperse by flight might be to escape competition for mates with larger non‐flyers. 6. The overwhelming quantity of beetles found on the spring host every year reveals that the flying strategy is successful, despite the costs and risks.     

Genetic covariance between components of male reproductive success: within‐pair vs. extra‐pair paternity in song sparrows

The evolutionary trajectories of reproductive systems, including both male and female multiple mating and hence polygyny and polyandry, are expected to depend on the additive genetic variances and covariances in and among components of male reproductive success achieved through different reproductive tactics. However, genetic covariances among key components of male reproductive success have not been estimated in wild populations. We used comprehensive paternity data from socially monogamous but genetically polygynandrous song sparrows (Melospiza melodia) to estimate additive genetic variance and covariance in the total number of offspring a male sired per year outside his social pairings (i.e. his total extra‐pair reproductive success achieved through multiple mating) and his liability to sire offspring produced by his socially paired female (i.e. his success in defending within‐pair paternity). Both components of male fitness showed nonzero additive genetic variance, and the estimated genetic covariance was positive, implying that males with high additive genetic value for extra‐pair reproduction also have high additive genetic propensity to sire their socially paired female's offspring. There was consequently no evidence of a genetic or phenotypic trade‐off between male within‐pair paternity success and extra‐pair reproductive success. Such positive genetic covariance might be expected to facilitate ongoing evolution of polygyny and could also shape the ongoing evolution of polyandry through indirect selection.     

No direct selection to increase offspring number of bet-hedging strategies in large populations: Simons' model revisited

In mixed or 'bet-hedging' strategies, offspring phenotypes are taken randomly from a distribution determined by the genotype and shaped by evolution. Offspring of a single parent represent a finite sample from this distribution, and therefore are subject to variability because of sampling. Contrary to a recent article by A.M. Simons (2007; J. Evol. Biol.20: 813-817), I show that selection does not favour the production of many offspring just to reduce sampling variability when such mixed strategies are used in large populations.     

Differences in temperature conditions and somatic growth rate of larval and early juvenile spring-spawned herring from the Vistula Lagoon, Baltic Sea manifested in the otolith to fish size relationship

Larval and juvenile herring Clupea harengus collected in the Polish part of the Vistula Lagoon in May-July 1997 had hatched between 17 April and 9 June and originated from three cohorts. The spawning season began on 1 March at 3·8° C and was completed on 3 June at 12·7° C. Mortality among larvae was high in the first 2 weeks of April, probably associated with significant temperature decrease at the beginning of the spawning season. The growth of 10–48 mm L _S herring was linear, highest for larvae and juveniles from the first cohort (0·58 mm mm^-1 day^-1), slower for the second cohort (0·55 mm mm^-1 day^-1) and the slowest for the third cohort (0·45 mm mm day^-1). Temperature effects on the growth were inconclusive and potentially unfavourable feeding conditions in June might have been responsible for the relatively slow growth of third cohort larvae and juveniles.
Relationships between otolith size (perimeter, length, width, area, and weight) and fish size ( L _S) differed among the three cohorts, related mostly to the positive temperature effect on otolith growth, individuals growing in warmer water had larger otoliths. Although a negative growth rate effect was observed as well, it was less significant.     

High sexual reproduction and limited contemporary dispersal in the ectomycorrhizal fungus Tricholoma scalpturatum: new insights from population genetics and spatial autocorrelation analysis

Dispersal and establishment are fundamental processes influencing the response of species to environmental changes, and the long-term persistence of populations. A previous study on the symbiotic ectomycorrhizal fungus Tricholoma scalpturatum revealed strong genetic differentiations between populations in Western Europe, suggesting restricted dispersal for this wind-dispersed cosmopolitan fungus. Two distinct genetic groups (genetic groups 1 and 2), co-occurring in some locations, were also identified and could correspond to cryptic species. In the present work, we examine the reproductive strategy and dispersal biology of the two T. scalpturatum's genetic groups. Variable molecular markers (intersimple sequence repeats and intergenic spacer 2-restriction fragment length polymorphisms) and spatial autocorrelation analyses were used to examine fine-scale patterns (< 140 m) of genetic structure, in an effort to determine the physical scale at which genetic structure exists. A total of 473 fruit bodies were mapped and collected over 3 years from two plots located in the south of France, including 219 and 254 samples from group 1 and group 2, respectively. High genetic diversity and the presence of numerous small genets were observed in both groups. Autocorrelation analyses revealed significant positive spatial genetic structures of genets at close distances (up to few metres for both groups). Mantel tests confirmed this isolation-by-distance pattern. These results clearly demonstrate high sexual reproduction and spatial structuring of genets at very small geographical scales in this wind-dispersed ectomycorrhizal fungal species, a pattern consistent with restricted contemporary dispersal of spores.     

Examining growth rate and starvation endurance in pit‐building antlions from Mediterranean and desert regions

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