The effect of temperature and somatic growth on otolith growth: the discrepancy between two clupeid species from a similar environment

Otolith growth rates of the early life stages of herring Clupea harengus ( n = 472) and smelt Osmerus eperlanus ( n = 348) collected in the Vistula Lagoon (Baltic Sea) during 1997–1999 were analysed. The larvae and early juveniles were not only collected in the same geographical area they were also of the same size (range 15–43 mm standard length, L _S), similar ages and were collected during the same seasons (May to July). Although the two clupeid species experienced very similar environmental conditions, there were significant discrepancies in the analysed relationships. The otolith growth of larval and juvenile smelt was very strongly related to somatic growth while temperature had a minor effect. In herring, the effect of somatic growth, although clearly visible and statistically highly significant, was of less importance than temperature. Furthermore, variation in the otolith size and L _S relationship was affected by temperature and somatic growth in both species, but the variance of otolith size at L _S was higher for herring than for smelt. Although growth backcalculation from otoliths can presently be recommended as an appropriate method for use with both smelt and herring (despite possibly lower precision and accuracy with the latter), other methods referring directly to short-term increment width changes ( e.g. marginal increment analysis) are recommended for smelt but not for herring.     

Parental effects on fertilization and hatching success and development of Atlantic halibut (Hippoglossus hippoglossus L.) embryos and larvae

The parental effects on fertilization and early life history traits were studied in Atlantic halibut, Hippoglossus hippoglossus L. Sperm from 12 different males were used to fertilize eggs of two females in separate crosses. The fertilization success were generally high, above 80% of developing embryos at 16-cell stage in 20 of 24 crosses with an average of 85.9+/-17.6% and 87.2+/-16.5% for female A and female B, respectively. Corresponding hatching success was 74.8+/-17.7% and 41.6+/-20.1%, respectively. The relationship between fertilization success and hatching success was positive. The parental influence on hatching was dominated by a strong and significant (p<0.001) maternal effect; however, the paternal effect was also significant (p<0.001). Furthermore, there was no relationship between fertilization success, hatching success and larvae viability as a high number of larvae developed locked jaws (i.e., were not functional). There was a significant (p<0.01) difference in yield of functional larvae of female A (43%) and female B (56%), and also between crosses sired by different males. The standard length of offspring of female A (12.4+/-0.5 mm) and B (12.6+/-0.6 mm) were significantly (p<0.001) different, and also significantly influenced by both the female (p<0.001) and the male (p<0.001). The present paper provides strong indications that not only the female, but also the male parent influences quantitative features of early development of their offspring.     

Susceptibility of Atlantic herring and plaice larvae to predation by juvenile cod and herring at two constant temperatures

Predation encounters were staged in the laboratory to compare prey responsiveness, predator error rate, and predator capture success for juvenile cod Gadus morhua (a suction feeder) and herring Clupea harengus (a biting predator) preying on herring and plaice Pleuronectes platessa larvae. Trials were conducted at near natural temperature extremes for the larvae (8 and 13°C) to assess the importance of water temperature to the interaction. Herring larvae were significantly more responsive to attacks by herring than were plaice larvae (5·7 vs 0'0%). The two prey species were equally responsive to attacks by cod (2–6 vs 10%). Cod caught 91% of herring larvae attacked and juvenile herring caught 87%. Cod were successful in 96% of attacks on plaice, but juvenile herring caught significantly fewer (83%) plaice larvae. For each predator species, capture success did not vary significantly with prey species. Overall capture success for herring was significantly lower than that for cod. Responsiveness of herring larvae to attacks by juvenile herring increased with temperature, but predator error rate and capture success were not altered by water temperature.     

Drinking and water absorption by the larvae of herring (Clupea harengus) and turbot (Scophthalmus maximus)

The efficiencies of water absorption from the guts of the larvae of herring ( Clupea harengus L.) and turbot ( Scophthalmus maximus L.) were estimated by two methods, The first method was based on the differences in the rates of accumulation, by drinking, and clearance from the gut of radiolabelled inert markers. The second method used the equilibrium level of radioactivity in the larvae to measure the concentration of the markers in the gut above background as water is absorbed from the gut. Water absorption efficiencies for herring larvae drinking sea water were estimated to be 77% using both methods. When external salinity was reduced to 50% sea water, drinking rates and water absorption efficiency in herring larvae fell substantially.
Estimates of water absorption efficiency of seawater-adapted turbot larvae were similar (71–84%) to that of herring using both methods. Although temperature had a marked effect on both the rate of drinking and water absorption, there was no significant thermal effect on the efficiency of absorption from the guts of turbot larvae. The limitations of the techniques and the implications of the estimates in terms of water balance in fish larvae are discussed.     

The relationships between host selection and subsequent larval performance in three free-living graminivorous sawflies

1. Selection of host plants for oviposition by females of three graminivorous sawfly species, Dolerus puncticollis C. G. Thomson, Dolerus picipes Klug. and Pachynematus clitellatus Lepeletier, was investigated experimentally using three grass species, Lolium perenne L., Festuca rubra L. and wheat, Triticum aestivum L. cv. Hunter.
2. Both species of Dolerus showed significant preferences for one grass over the other two, D. puncticollis preferring L. perenne and D. picipes selecting F. rubra. P. clitellatus females used L. perenne and F. rubra equally for oviposition, but avoided wheat.
3. The results correlated closely with larval performance trials, with D. puncticollis larvae having maximal survival and growth rates on L. perenne , and D. picipes larval performance being maximized on F. rubra. P. clitellatus larvae survived well on both grasses, but had a high level of mortality on wheat.
4. P. clitellatus larval growth rates were significantly higher on L. perenne than on F . rubra . Individual P. clitellatus adult females developing from larvae reared on L. perenne reached a significantly greater dry weight than those reared on F. rubra , but there was no significant difference in weight between males reared on the two hosts. There was some evidence that this disproportionate effect of host plant quality on the weight gain of the two sexes was translated into a bias in sex ratio of the eggs laid towards a greater proportion of females on L. perenne than on F. rubra . This manipulation of sex ratio would have a potential benefit for ovipositing females through disproportionate fecundity gains for female offspring.     

Run timing of pelagic fishes in Gulf of St Lawrence: area and species effects

Run timings of four ubiquitous pelagic fishes in the Gulf of St Lawrence were compared for area and year effects. Run timing of alewife, Alosa pseudoharengus (Wilson), smelt, Osmerus mordax (Mitchill), and Atlantic salmon, Salmo salar L., was estimated at index rivers, and time of arrival of herring, Clupea harengus L., on spawning grounds was estimated from gillnet fisheries located around the Gulf, 1978–87. Time of pelagic fish migrations had strong species and area effects, but weak year effects. The species had their own unique migration times and durations, and could be divided into two groups: herring and smelt, which arrived in all areas of the Gulf at the same time; and alewife and salmon, which had significant area effects. Environmental data were not correlated with run timing. There was little annual variation in run timing among early-run species; only alewife had significant year effects. There was annual variation in the timing of late-run species, but it was not correlated with proximate environmental factors. Because run timing is an easily defined stock characteristic, observations over large areas and many years might be useful for understanding the impact of large-scale environmental changes on natural populations.     

The question of fluctuating asymmetry in the blacklegged tick Ixodes scapularis (Acari: Ixodidae)

An analysis of fluctuating asymmetry was conducted on populations of the blacklegged tick Ixodes scapularis. The eight groups used in this study consisted of larvae and nymphs and males and females from the states of Minnesota, Massachusetts, Maryland, Missouri, North Carolina and Georgia and the F1 progenies of reciprocal crosses between ticks from Massachusetts and Georgia. Measurements included 16 larval, 19 nymphal, ten female and 12 male bilateral characters. Only five differences between the right and left bilateral characters had normal distributions with means of zero and differences in variances between the groups. These five characters included three setal lengths of the larvae, the spiracular plate length of females and the coxa I internal spur widths of males. Bivariate plots of character size ((R+L)/2) and asymmetry (R-L) showed no correlation. In the spiracular plate lengths of females and one of the setal lengths, ticks from Massachusetts had significantly less within-group variance than all the other groups. The only character in which fluctuating asymmetry was observed was the coxa I internal spur width of males, in which ticks from Minnesota, Missouri and North Carolina had significantly greater variance than the remaining groups; fluctuating asymmetry in this character may be explained by sexual selection. The cross progeny did not demonstrate any fluctuating asymmetry, as would be expected if the northern and southern forms of I. scapularis were true species. The virtual lack of fluctuating asymmetry in the characters used in this study further supports the conclusions of other studies which concluded that I. scapularis is a species with clinal variation and a broad geographic distribution.     

Genetic variation among females affects paternity in a dioecious plant

Flowering plants rely on vectors for pollen transfer, and cannot choose their mates. Although recipient plants are unable to choose which pollen they receive, post‐pollination selection (acting pre‐ or post‐zygotically) may modify the outcome of pollination. Here we show that genetic variation among pollen recipients can predict the outcome of pollen competition (seed paternity) in the dioecious white campion. To investigate whether genetic variation among pollen recipients affects paternity, we applied the same pollen mixture from two males to three females, two of which full sisters and the third one chosen at random (unrelated). To control for maternal environmental effects, the plants used for these crosses were greenhouse‐reared F₁. We replicated this in two populations, for a total of 51 crosses, and genotyped a total of 772 offspring to assign paternity. If genetic variation affects paternity, we expected greater similarity of paternity success of the focal male with the sisters, compared to the unrelated female. Paternity of the focal male was significantly more repeatable over sisters, compared to repeatability over the mean of sisters and the unrelated females. When populations were analyzed separately, this was significant in one of the two populations. Paternity was not significantly correlated with stigma size. This provides evidence that in at least one population, genetic variation among individual plants influences the donors’ paternity success, as assessed through genetic analysis of the seedling. Since due to gravity‐dispersed seeds natural patches may often consist of related plants, the observed effect may contribute to variation in male reproductive success.     

A stereological method for estimating fish fecundity

This paper describes the application and evaluation of a stereological method for counting fish oocytes. The method has been applied to herring, Clupea harengus L., Dover sole, Solea solea L., and mackerel, Scomber scombrus L., and compared with existing volumetric and/or automated particle counter methods. The stereological method has been shown to given similar results and to have a number of distinct advantages over the other methods.     

Influence of temperature on evasive responses of Atlantic herring larvae attacked by yearling herring, Clupea harengus L.

Predation encounters were staged in the laboratory between yearling herring, Clupea harengus L., 66 to 104 mm t.l. , and herring larvae, 8 to 30 mm t.l. ., at 8,11 and 14 o C. Video records were used to quantify prey behaviour. Prey responsiveness, reactive distance, response latency, and apparent looming threshold were not affected by temperature. Response speeds increased with temperature. Predator error rate and capture success showed no consistent thermal effects. Although the experiments could not fully evaluate the influence of temperature on the predators, results suggest that the predator's performance largely governs the outcome of an attack on a larva and that higher temperatures favour the predator by increasing the frequency of its encounter with prey.     

Potential predation pressure of littoral mysids on herring (Clupea harengus membras L.) eggs and yolk-sac larvae

The predation potential of littoral mysid shrimps (Mysidacea) on Baltic herring (Clupea harengus membras L.) eggs and yolk-sac larvae was studied experimentally. The results showed that littoral mysids feed actively on both eggs and yolk-sac larvae. It was shown that Neomysis integer preys on eggs, which are not attached to the substrate. Alternative food (yolk-sac larvae or zooplankton) did not decrease feeding rate on eggs. Only gravel as a bottom material lowered the ingestion rate to nearly zero. The largest of the mysid species Praunus flexuosus ate yolk-sac larvae more than other mysids and most efficiently. Mysids switched to feed on eggs when larvae and eggs were offered simultaneously, thus predation focused on eggs. It is possible that hydrodynamic signals of moving larvae induced mysids to prey and eggs were easier prey to catch as well as more numerous. In addition egg size is optimal and the nutritive value (measured as C:N ratio) is better compared with larvae. The results indicate that mysids may have local effects on populations of Baltic herring by eating the early life stages, mostly eggs. Especially when large swarms of N. integer shoal in the spawning areas. However, the effect on recruitment of herring is still hard to evaluate.     

Population genetics of the fissiparous holothurian Stichopus chloronotus (Aspidochirotida) on the Great Barrier Reef, Australia

 Population genetic structure was studied in one nearshore and two offshore populations of Stichopus chloronotus, a common holothurian species on Indo-Pacific coral reefs. Genetic variation at five polymorphic loci was examined using allozyme electrophoresis. The nearshore population consisted almost exclusively of male individuals, and more males than females were found in all populations studied. Deviations of heterozygosity from that predicted under Hardy-Weinberg equilibrium indicated that asexual reproduction occurred in all populations. Estimates of the level of asexual reproduction using the ratios of the number of sexually produced individuals to sample size, observed genotypic diversity to expected genotypic diversity, and number of genotypes to sample size confirmed that this reproductive mode was more important at the nearshore reef compared to the two offshore reefs. There were large differences in genotypic frequencies between males and females. F-statistics on clonal genotypic frequencies were not statistically significant between populations for neither females or males, suggesting high dispersal of larvae between reefs. A higher mortality of females during larval or early post-settlement stages, or reduced dispersal capability of female larvae are the most likely reasons for biased sex ratios. Accepted: 23 November 1998     

Developmental plasticity in Macrophiothrix brittlestars: are morphologically convergent larvae also convergently plastic?

The pluteus larval forms of sea urchins (echinoids) and brittlestars (ophiuroids) use an internal skeleton to project arms that bear a long ciliated band used in swimming and feeding. The length of this ciliated band influences rates of maximum food clearance for larvae of both echinoderm classes and affects rates of growth and development in the plankton. Phylogenetic and morphological evidence, however, tend to support the view that the pluteus morphologies of the two classes are independently derived. Studies with echinoplutei have shown that investment in skeletal growth and ciliated band length changes in response to food conditions, with poorly fed larvae investing more in growth of the larval skeleton and arms either absolutely or in relation to other larval or developing postlarval structures. We present evidence for similar plasticity of skeletal growth in ophioplutei. We examined four species in the brittlestar genus Macrophiothrix that spanned a 3.8-fold range in egg size. Sibling larvae in 14 male-female crosses were reared with high (H) or low (L) food rations, and measurements were recorded for five skeletal arm rods and three non-arm body dimensions. The expression of adaptive plasticity (significantly longer arms in L versus H cultures on a given day) was apparent for most crosses in M. koehleri, the species with the smallest egg size. In the single cross for M. longipeda, larvae from L cultures had longer arms for their body length or stomach width than did larvae from H cultures. In these cases, plasticity was similar in timing, persistence, and magnitude to previously published results from echinoplutei. If internal skeletons are independently derived in the two classes, then plasticity in the expression of this homoplastic trait may itself be homoplastic.     

Maternal nutritional condition and genetic differentiation affect brood size and offspring body size in Nicrophorus

In most animal species, brood size and body size exhibit some variation within and between populations. This is also true for burying beetles (genus Nicrophorus), a group in which the body size of offspring depends critically on the number of offspring competing for food due to the discrete nature of resource used for larval nutrition (vertebrate carcasses). In one species, brood size and body size are correlated with population density, and appear to be phenotypically plastic. We investigated potential proximate causes of between-population variation in brood size and body size in two species, Nicrophorus vespilloides and Nicrophorus defodiens. Our first experiment supported the notion that brood size is phenotypically plastic, because it was affected by environmental variation in adult nutritional condition. We found that the pre-breeding nutritional status of female N. vespilloides affected the number of eggs they laid, the number of surviving larvae in their broods, and the body size of their offspring. We do not know whether this plasticity is adaptive because greater offspring body size confers an advantage in contests over breeding resources, or whether starved females are constrained to produce smaller clutches because they cannot fully compensate for their poor pre-breeding nutritional status by feeding from the carcass. Our second experiment documents that brood size, specifically the infanticidal brood-size adjustment behavior, has undergone genetic differentiation between two populations of N. defodiens. Even under identical breeding conditions with identical numbers of first-instar larvae, females descended from the two populations produced broods of different size with corresponding differences in offspring body size.     

Interactions between an entomopathogenic microsporidium and the endoparasitoid Glyptapanteles liparidis within their host, the gypsy moth larva

Interactions in the host-parasitoid-pathogen system, Lymantria dispar L. (Lep., Lymantriidae)-Glyptapanteles liparidis (Bouché) (Hym., Braconidae)-Vairimorpha sp. (Protista, Microspora), were investigated. Host selection experiments revealed that G. liparidis females did not discriminate between infected and uninfected host larvae for oviposition. Transmission of the microsporidium from infected to uninfected hosts by stinging female wasps could not be ascertained. Females that developed in infected L. dispar larvae did not transmit the pathogen via oviposition. Vairimorpha infection of the host negatively affected the performance of the braconid, when inoculation took place either before or after parasitization. Microsporidiosis of the host caused delayed development, reduced pupation and adult eclosion, reduction in size and weight, and reduction of adult longevity of G. liparidis. Parasitoids themselves were not systemically infected by Vairimorpha sp., but braconid larvae did ingest microsporidian spores at the end of their endoparasitic development and accumulated the undigested and ungerminated spores in the blind midgut. Negative effects of host infection on parasitoid larvae were detectable from the beginning of parasitoid larval development. Lethal time was reduced when L. dispar larvae were infected and parasitized, often at the expense of the parasitoid when G. liparidis were unable to complete endoparasitic development before the host died. Intensity of infection, measured as number of spores produced per milligram fresh weight of L. dispar larva, was slightly higher in parasitized and infected hosts than in unparasitized and infected hosts.     

The influence of male and female body size on copulation duration and fecundity in Drosophila melanogaster

We studied two components of the mating system, copulation duration and early fecundity, in relation to body size in Drosophila melanogaster. Body size variation was created experimentally by varying the degree of crowding (starvation) among larvae from an inbred strain, keeping the genetics and temperature as constant as possible. Hence, in contrast to most previous studies, where genetic and environmental variation have been confounded, we aimed at investigating how much pure phenotypic variation could influence copulation duration and early fecundity. It is shown that copulation duration and fecundity both strongly dependent on female body size, but either not or much less so on male body size. Small females mate faster than medium or large females and small females have the lowest fecundity. Among males, medium-size males are more fecund than smaller or larger males, resulting in stabilising selection for intermediate male size. These results are in contrast with previous findings.     

Growth and emigration of third-stage larvae of Hysterothylacium aduncum (Nematoda: Anisakidae) in larval herring Clupea harengus

The growth and emigration of Hystherothylacium aduncum in laboratory-reared herring larvae Clupea harengus was studied. Experimental infections of 36-day-old herring larvae resulted in 126 hosts infected with 306 H. aduncum larvae. Regression analyses showed a significant worm emigration from the rectum to the head of the fish, accompanied by an increase in worm body length. The emigration was independent of worm intensity, which suggests an ontogenetic process. Some worms departed from this pattern by moving posteriorly or by penetrating into the muscle, and in 5 cases, the larvae were observed to leave living fish. This individual variation has not been observed in previous studies and might be explained by host signals related to condition or development stage. Indirect evidence suggested parasite-induced mortality in the tanks due to the emigrations because only 4 of the 126 infected fish survived 8 days postinfection; the emigration of H. aduncum affected vital organs, such as the heart and brain, and the larvae penetrating or leaving the host's tissues can cause extensive damage to the delicate herring larvae.     

Feeding ability and survival during starvation of marine fish larvae reared in the laboratory

The larvae of Clyde and Baltic herring (Clupea harengus L.), cod (Gadus morhua L.) and flounder (Platichthys flesus L.) were reared and fed to examine the changes in feeding ability and survival during progressive starvation. The time to initial feeding for yolk-sac larvae and to the point-of-no-return (PNR, when 50% of the larvae, although still alive, are no longer strong enough to feed) for both yolk-sac and older larvae were determined. The yolk-sac larvae of Clyde and Baltic herring, cod and flounder begin to feed on days 6, 3, 5 and 6 post-hatching at rearing temperatures of 7.5, 9.2, 6.9 and 9.5°C, respectively. The time to reach the PNR for yolk-sac larvae of these species is only 3–5 days after yolk resorption. From the onset of starvation in older larvae the time to reach the PNR is 6–7 days for 36-and 60-day-old Clyde herring at 9.6 and 10.5°C and for 46-day-old Baltic herring at 13.1°C but it is 23 days for 32-day-old flounder at 12.3°C. In yolk-sac larvae the peak of feeding rate and intensity usually occurred on the day that the yolk became exhausted, or 1 day later. Older larvae could withstand longer periods without food than yolk-sac larvae, especially in flounder. While the feeding rate during starvation of older larvae slowly decreased the feeding intensity first increased significantly and then decreased. Survival of larvae remained high up to the PNR.     

Genetic control of geographic variation for cannibalism in the southwestern corn borer,Diatraea grandiosella

The southwestern corn borer,Diatraea grandiosella Dyar, is a subtropical insect whose range has expanded northward within this century. Geographic variation exists between populations at the extremes of the range for a suite of morphological and behavioral characters, including cannibalism. Laboratory colonies established from a Missouri population (37°N lat.) with a high cannibalism rate and a Mexican population (19° N lat.) with a low cannibalism rate were used to examine the genetic basis of cannibalism by means of a controlled breeding design. When larvae were held in pairs on artificial diet in 30 ml plastic cups at 30° C 16L:8D, the highest incidence of cannibalism in both Missouri and Mexican populations was found in larvae 15 to 18 days-of-age (5th and 6th instars). Under these conditions, cannibalism was expressed in 33% of the pairs formed from Missouri larvae and 11% of the pairs formed from Mexican larvae. First and second generation crosses between Missouri and Mexican populations showed an intermediate level of cannibalism, whereas backcrosses to the parental generations showed a regression to the parental phenotypes. These results indicate that cannibalism is under additive genetic control. Larvae from the Missouri parental population were more likely to consume their victim (i.e., cannibalize) once intraspecific killing had occurred than were larvae from the Mexican parental population or from any of the crosses, and female larvae were cannibals more often than were males. Under the conditions employed, no advantage was detected for cannibalism over instraspecific killing for larval weight gain or growth rate.     

Diel differences in avoidance of three vertical profile sampling gears by herring larvae

Three plankton sampling systems [pump, Longhurst-Hardy PlanktonRecorder (LHPR) and MOCNESS] were used to obtain vertical profilesof herring larvae off the north-east coast of England in October1986 during the International Herring Larval Survey (IHLS).A factorial sampling design allowed a comparison of the numberof herring larvae caught by depth (four levels), time of day(three levels) and gear (three levels). The size compositionof herring larvae taken in the different gears has also beenexamined. Catches taken at night were greater than those takenduring the day throughout the water column, particularly withlarger larvae. This indicates that visual avoidance of all gearsis an important factor, which increases as the larvae grow bigger.LHPR night catches were greater than in the MOCNESS and fargreater than in the pump, which indicates that avoidance isalso due to senses other than vision. Examination of the 1981–1986International Herring Larvae Survey catch data showed that night-timecatches were similar to daytime catches for herring larvae <10mm long, but night time catches caught progressively more asthe length of the larvae increased to 24 mm.