Natural variability in size and condition at settlement of 3 species of marine invertebrates

Experimental studies have demonstrated that for many marineinvertebrate species, variability in larval condition or qualityat settlement may have important effects on post-settlement,early juvenile performance. Relatively few studies, however,explicitly examine natural variability in larval condition atsettlement. This study examines natural variability in larvalattributes (size and lipid index) at settlement for terminal-stagelarvae of intertidal mussels (Mytilus sp.) and barnacles (Pollicipespolymerus and Chthamalus dalli) from southern California. Despitesignificant differences among cohorts in larval attributes,for all 3 species a greater percentage of the variance in larvallength (80–100%) and lipids (58–83%) occurred amongindividuals within a cohort, rather than among cohorts. Forall 3 species, coefficients of variation within a cohort forlength were much smaller (3–8%) than those for lipid index(30–93%), suggesting that lipid storage is a much moreplastic attribute than size for larvae. For mussels, settlementintensity and larval attributes were decoupled, such that averagelarval condition of a cohort was not related to the number oflarvae that settled. At the cohort level, Mytilus and Pollicipessettling together across 3 dates showed similar trends of decreasinglipid index over time, suggesting that environmental conditionsmay influence co-occurring planktonic larvae similarly acrossspecies. This work highlights the need for further experimentsin the field on the effects of larval history on recruitmentsuccess in natural populations, and further studies to determinewhat factors influence larval attributes for planktonic larvaein the field.     

Growth and otolith microstructure of cod (Gadus morhua L.) larvae

Cod larvae from Irish Sea stocks were reared under differentgrowth conditions, and the otolith growth and increment formationexamined in sagittae and lapilli. Otolith increments were firstdeposited around the time of hatching and increment counts,on average, reflected larval age. The growth rate of fish larvaereared in different sized tanks was significantly different(P < 0.001), but there was no detectable effect on incrementformation. Otolith size was independent of larval size for individuals<5 mm in length. In larvae >6 mm, larger, faster growingindividuals had larger and faster growing otoliths.     

Consequences of variable larval dispersal pathways and resulting phenotypic mixtures to the dynamics of marine metapopulations

Larval dispersal can connect distant subpopulations, with important implications for marine population dynamics and persistence, biodiversity conservation and fisheries management. However, different dispersal pathways may affect the final phenotypes, and thus the performance and fitness of individuals that settle into subpopulations. Using otolith microchemical signatures that are indicative of ‘dispersive’ larvae (oceanic signatures) and ‘non-dispersive’ larvae (coastal signatures), we explore the population-level consequences of dispersal-induced variability in phenotypic mixtures for the common triplefin (a small reef fish). We evaluate lipid concentration and otolith microstructure and find that ‘non-dispersive’ larvae (i) have greater and less variable lipid reserves at settlement (and this variability attenuates at a slower rate), (ii) grow faster after settlement, and (iii) experience similar carry-over benefits of lipid reserves on post-settlement growth relative to ‘dispersive’ larvae. We then explore the consequences of phenotypic mixtures in a metapopulation model with two identical subpopulations replenished by variable contributions of ‘dispersive’ and ‘non-dispersive’ larvae and find that the resulting phenotypic mixtures can have profound effects on the size of the metapopulation. We show that, depending upon the patterns of connectivity, phenotypic mixtures can lead to larger metapopulations, suggesting dispersal-induced demographic heterogeneity may facilitate metapopulation persistence.     

Body size variation in aquatic consumers causes pervasive community effects,independent of mean body size

Intraspecific phenotypic variation is a significant component of biodiversity. Body size, for example, is variable and critical for structuring communities. We need to understand how homogenous and variably sized populations differ in their ecological responses or effects if we are to have a robust understanding of communities. We manipulated body size variation in consumer (tadpole) populations in mesocosms (both with and without predators), keeping mean size and density of these consumers constant. Size‐variable consumer populations exhibited stronger antipredator responses (reduced activity), which had a cascading effect of increasing the biomass of the consumer's resources. Predators foraged less when consumers were variable in size, and this may have mediated the differential effects of predators on the community composition of alternative prey (zooplankton). All trophic levels responded to differences in consumer size variation, demonstrating that intrapopulation phenotypic variability can significantly alter interspecific ecological interactions. Furthermore, we identify a key mechanism (size thresholds for predation risk) that may mediate impacts of size variation in natural communities. Together, our results suggest that phenotypic variability plays a significant role in structuring ecological communities.     

Variation in larval properties of the Atlantic brooding coral <Emphasis Type="Italic">Porites astreoides</Emphasis> between different reef sites in Bermuda

Recent research has documented phenotypic differences among larvae released from corals with a brooding reproductive mode, both among species and within broods from a single species. We studied larvae released from the common Atlantic coral Porites astreoides in Bermuda to further evaluate phenotypic variability. Inter-site differences were investigated in larvae from conspecifics at a rim and patch reef site. Larvae were collected daily for one lunar cycle from several colonies per site each year over 5 yr. Larval volume varied with reef site of origin, with colonies from the rim reef site producing larger larvae than colonies from the patch reef site. This inter-site variation in larval size could not be explained by corallite size and may be a response to different environmental conditions at the sites. Larvae from both reef sites also varied in size depending on lunar day of release over 4 yr of study. Regardless of site of origin, smaller larvae were released earlier in the lunar cycle. Over 1 yr of study, lipid and zooxanthellae content and settlement success after 48 h covaried with larval size. However, there may be a trade-off between larger larvae and reduced fecundity. Overall, larvae released from colonies from the rim reef site were larger and had greater settlement success than those from colonies from the patch reef site. This study documents larval phenotypic variability and a distinct inter-site difference in larval ecology among conspecifics within the same geographic area, which may have implications for recruitment success, population dynamics, and resilience.     

Behavioral syndrome over the boundaries of life--carryovers from larvae to adult damselfly

Activity is an important behavioral trait that mediates a trade-offbetween obtaining food for growth and avoiding predation. Activeindividuals usually experience a higher encounter rate withfood items and suffer higher predation pressure than less activeindividuals. I investigated how activity of the damselfly Lestescongener is affected by larval state and predator presence andif larval behavioral type (BT) can be used to predict larvalboldness, foraging success, and adult BT. Activity level ofindividual larvae was studied without predator at 2 differentphysiological states (hungry and fed) and in 2 predator treatments:familiar predator cues and unfamiliar predator cues. Larvaedid not adjust their activity depending on state or when subjectedto unfamiliar predator cues, but a general reduction in activitywas seen in the familiar predator treatment. Hence, active individualsremained active compared with their conspecifics, independentof state or predator treatment. Active individuals were alsobolder and more efficient foragers than their less active conspecifics.Furthermore, both adult activity and boldness were correlatedwith larval BT. The results illustrate that BT of a larvae iscarried over many different situations keeping active larvaeactive even in maladaptive situations, demonstrating how a behavioralsyndrome may constrain behavioral plasticity. Furthermore, resultsshowed that behavioral syndromes can carry over from larvaethrough metamorphosis and dictate the BT of the adult.     

Development of size structure in tiger salamanders: the role of intraspecific interference

Cannibalism affects patterns of density-dependent mortality and may regulate population size. In many cases, rates of cannibalism depend on size structure, the frequency distribution of body sizes in the population, because cannibals can often only capture and consume smaller individuals. Size differences within single-age groups can be caused by a variety of factors. In this research we tested the hypothesis that size variation among larval tiger salamanders is due, in part, to interference interactions among individuals of different sizes. We found that size variation was greater when we raised larvae in groups rather than in isolation. This increase in size variation was due more to a relative deceleration of growth among smaller individuals rather than acceleration among larger individuals. We also found that smaller larvae had lower feeding rates than larger larvae when in groups, but not when isolated. Including spatial structure to limit physical interactions did not affect the size specificity of feeding rate, although it reduced feeding rates overall. We argue that these results are consistent with the hypothesis that larger larvae interfere, probably indirectly, with the feeding behavior of small individuals and this contributes to increases in size variation over time. We hypothesize that this indirect interference is caused by a behavioral response of smaller larvae to the risk of predation (cannibalism) by larger individuals. Received: 18 May 1998 / Accepted: 29 April 1999     

Effects of temporary food limitation on survival and development of brachyuran crab larvae

As a consequence of the combined effects of prey patchinessand diel or tidal vertical migrations in the water column, decapodcrustacean larvae may experience temporal or spatial variabilityin the availability of planktonic food. In a laboratory study,we evaluated effects of temporarily limited access to prey onthe larvae of three species of brachyuran crabs, Chasmagnathusgranulata, Cancer pagurus and Carcinus maenas. Stage-I zoeaewere fed ad libitum for 4 or 6 h per day (20 or 25% treatments;6 h tested in C. pagurus only), and rates of larval survivaland development were compared with those observed in continuouslyfed control groups (24 h, 100%). In C. granulata, we also testedif intraspecific variability in initial biomass of freshly hatchedlarvae originating from different broods has an influence onearly larval tolerance of food limitation. Moreover, we exposedembryos and larvae of this estuarine species to moderately decreasedsalinities to identify possible interactions of osmotic andnutritional stress. Finally, we evaluated in this species theeffect of food limitation on survival from hatching throughall larval instars to metamorphosis. In all three species, limitedaccess to prey had only weak or insignificant negative effectson survival through the Zoea-I stage. The strength of the effectsof temporary food limitation varied in C. granulata significantlyamong broods. However, no significant relationships were foundbetween initial larval biomass (C content) and either survivalor development duration. Strongly decreased survival to metamorphosiswas found when food limitation continued throughout larval development.Thus, early brachyuran crab larvae are well adapted to transitorylack of planktonic food. The capability of the Zoea-I stageof C. granulata to withstand nutritional stress also under conditionsof concomitant salinity stress allows them to exploit variousbrackish environments within estuarine gradients. However, continuedexposure to limited access to planktonic prey may exceed thenutritional flexibility of C. granulata larvae.     

Intraspecific competition of Glyptotendipes paripes (Diptera: Chironomidae) larvae under laboratory conditions

Glyptotendipes paripes larvae were reared in wells of tissue culture plates, in groups of 2, 4, 8, 16, and 32 (representing densities of about 1,300, 2,600, 5,200, 10,400, and 20,800 larvae per m², respectively). Larval groups were supplied with one of two concentrations (low or high) of food and larvae were individually observed to evaluate the effects of density on mortality, growth, development, behavior, and adult body size. Increased larval densities resulted in higher mortality, as well as slower larval growth and development. The distribution of developmental time became flatter at higher density, with a wider range of values, or even became bimodal. This was a consequence of the most rapidly developing individuals at higher densities emerging as adults sooner than the fastest developing individuals at lower densities, although overall mean developmental time was longer at higher densities. At higher densities, growth and development of smaller larvae were slowed, based on the relative difference in body length between competitors. When larger competitors emerged as adults or died, the growth of smaller larvae may have accelerated, resulting in increased variability of developmental times. The effect of larval density on adult body size was complex, with the largest body size found at the lowest density and a second peak of adult size at high-middle densities, with smaller adult body sizes found at low-middle, and high densities. Similarly, as with developmental time, the range of body size increased with increasing density. Examined food concentrations had no effect on larval mortality, but significantly affected developmental time, growth rate, and adult body size. At higher densities, larvae spent more time gathering food and were engaged in aggressive or antagonistic behaviors.     

QUANTIFYING EVOLUTIONARY POTENTIAL OF MARINE FISH LARVAE: HERITABILITY,SELECTION, AND EVOLUTIONARY CONSTRAINTS

For many marine fish, intense larval mortality may provide considerable opportunity for selection, yet much less is known about the evolutionary potential of larval traits. We combined field demographic studies and manipulative experiments to estimate quantitative genetic parameters for both larval size and swimming performance for a natural population of a common coral‐reef fish, the bicolor damselfish (Stegastes partitus). We also examined selection on larval size by synthesizing information from published estimates of selective mortality. We introduce a method that uses the Lande–Arnold framework for examining selection on quantitative traits to empirically reconstruct adaptive landscapes. This method allows the relationship between phenotypic value and fitness components to be described across a broad range of trait values. Our results suggested that despite strong viability selection for large larvae and moderate heritability (h²= 0.29), evolutionary responses of larvae would likely be balanced by reproductive selection favoring mothers that produce more, smaller offspring. Although long‐term evolutionary responses of larval traits may be constrained by size‐number trade‐offs, our results suggest that phenotypic variation in larval size may be an ecologically important source of variability in population dynamics through effects on larval survival and recruitment to benthic populations.     

Aggregation as a cost-reducing strategy for lycaenid larvae

If a mutualistic relationship entails providing services ata cost, selection will favor individuals that maximize the netbenefits of the interaction and minimize the costs. Larvae ofmany species of lycaenid butterflies secrete nutritious foodrewards to attending ants and, in return, receive protectionagainst predators and parasitoids. Because ants typically recruitmore workers to larger resources, by forming groups the larvaemay ensure more reliable access to ants and thereby gain betterprotection. A further consequence of aggregating should be achange of the cost-benefit relationship for individual larvae.The larger the group, the smaller a single larva's influencewill be on total ant density, which could lead to a smallerinvestment in secretion, thus reducing the per capita cost ofcooperation. In this study, die influence of ant attendance,group size, and companion quality on larval investment was investigated.The interaction between the obligately ant-dependent lycaenid,Jalmanus evagoras, and its attendant Iridomyrmax ants was manipulatedand the effect on larval secretion measured. As the level ofant attendance increased, the delivery of food rewards increased,bodi for solitary and for aggregated larvae. When aggregated,larvae provided less food rewards to ants dun when solitary,and secretion rate decreased with increasing group size. Furthermore,larvae had lower secretion rates when paired with a bigger,more attractive larva than when paired with a smaller one. Theconsiderable reduction in secretion rates for larvae in groupssuggests that gaining protection at a lower secretion cost couldbe one factor that promotes aggregation in myrmecophilous lycaenids.     

Temperature dependent larval resource allocation shaping adult body size in Drosophila melanogaster

Geographical variation in Drosophila melanogaster body size is a long-standing problem of life-history evolution. Adaptation to a cold climate invariably produces large individuals, whereas evolution in tropical regions result in small individuals. The proximate mechanism was suggested to involve thermal evolution of resource processing by the developing larvae. In this study an attempt is made to merge proximate explanations, featuring temperature sensitivity of larval resource processing, and ultimate approaches focusing on adult and pre-adult life-history traits. To address the issue of temperature dependent resource allocation to adult size vs. larval survival, feeding was stopped at several stages during the larval development. Under these conditions of food deprivation, two temperate and two tropical populations reared at high and low temperatures produced different adult body sizes coinciding with different probabilities to reach the adult stage. In all cases a phenotypic trade-off between larval survival and adult size was observed. However, the underlying pattern of larval resource allocation differed between the geographical populations. In the temperate populations larval age but not weight predicted survival. Temperate larvae did not invest accumulated resources in survival, instead they preserved larval biomass to benefit adult weight. In other words, larvae from temperate populations failed to re-allocate accumulated resources to facilitate their survival. A low percentage of the larvae survived to adulthood but produced relatively large flies. Conversely, in tropical populations larval weight but not age determined the probability to reach adulthood. Tropical larvae did not invest in adult size, but facilitated their own survival. Most larvae succeeded in pupating but then produced small adults. The underlying physiological mechanism seemed to be an evolved difference in the accessibility of glycogen reserves as a result of thermal adaptation. At low rearing temperatures and in the temperate populations, glycogen levels tended to correlate positively with adult size but negatively with pupation probability. The data presented here offer an explanation of geographical variation in body size by showing that thermal evolution of resource allocation, specifically the ability to access glycogen storage, is the proximate mechanism responsible for the life-history trade-off between larval survival and adult size.     

大小等级和大小组合差异对盆养安吉小鲵幼体同种相残率的影响

用改变安吉小鲵 (Hynobiusamjiensis)幼体大小等级、盆养密度和饵料投放量的实验方法 ,研究这些生态要素对同种相残 (撕咬和吞吃 )的影响 ;同时结合Fuetal (2 0 0 3)的研究 ,比较了大小组合的差异对同种相残的影响。结果表明 ,①大小等级、密度与饵料量均显著地影响幼体的被吞吃率 :较小个体易被较大个体攻击 ;低饵料×高密度水平下 ,3个等级大小幼体的同种相残率都最高。②大小组合的差异显著影响幼体间的同种相残率 :不同大小组合的幼体间被吞吃率均显著大于相同大小组合 ,而被撕咬率反之。这证实了体形大小决定种群同种相残率的理论预测。     

Genetic variability in the diapause response of the burnet moth Zygaena trifolii (Lepidoptera: Zygaenidae)

A high degree of phenotypic variability was observed in the diapause response of the burnet moth Zygaena trifolii. In this study, we show that the observed variability is partly based on genetic differences between individuals. In a selection experiment, the larval instar at which diapause occurs was changed within six generations. Diapause instars were dependent on the time of pre-diapause development of larvae, which varied considerably between larvae. A heritability analysis indicates that a part of the variability in development time is based on additive genetic variance. The maintenance of genetic variability in the development time and the diapause response of Z. trifolii is discussed in the context of spatially and temporally changing selection pressures.     

Recruitment of marine species: Is the bandwagon rolling in the right direction?

A highly variable rate of recruitment from pelagic larval to demersal or sessile juvenile and adult stage is characteristic of marine organisms. At present it is a major subject of attention by ecologists interested in population or community processes. Several factors conspire to ensure this variability, but in studying them it will be important to focus on the behavioral capabilities of marine larvae, and on the very small proportion of (perhaps lucky) larvae destined to be successful.     

Morphogenesis and phenotypic divergence in two developmental morphs of Streblospio benedicti (Annelida,Spionidae)

Abstract. The morphology of marine invertebrate larvae is strongly correlated with egg size and larval feeding mode. Planktotrophic larvae typically have suites of morphological traits that support a planktonic, feeding life style, while lecithotrophic larvae often have larger, yolkier bodies, and in some cases, a reduced expression of larval traits. Poecilogonous species provide interesting cases for the analysis of early morphogenesis, as two morphs of larvae are produced by a single species. We compared morphogenesis in planktotrophic and lecithotrophic morphs of the poecilogonous annelid Streblospio benedicti from the trochophore stage through metamorphosis, using observations of individuals that were observed alive, with scanning electron microscopy, or in serial sections. Offspring of alternate developmental morphs of this species are well known to have divergent morphologies in terms of size, yolk content, and the presence of larval bristles. We found that some phenotypic differences between morphs occur as traits that are present in only one morph (e.g., larval bristles, bacillary cells on the prostomium and pygidium), but that much of the phenotypic divergence is based on heterochronic changes in the differentiation of shared traits (e.g., gut and coelom). Tissue and organ development are compared in both morphs in terms of their structure and ontogenetic change throughout early development and metamorphosis.     

Maternal effects on offspring growth and development depend on environmental quality in the frogBombina orientalis

Summary Differences in maternal investment and initial offspring size can have important consequences for offspring growth and development. To examine the effects of initial size variability in the frogBombina orientalis, we reared larvae (N=360) in one of two treatments representing different levels of environmental quality. We used snout-vent length at the feeding stage (stage 25, Gosner 1960) as a measure of maternal investment. In a “low quality” treatment, larvae were reared with two conspecific tadpoles and food was limited, whereas in a “high quality” treatment, larvae were reared individually and were fed ad libitum. Among tadpoles reared in the low quality treatment, individuals that were initially small had smaller body sizes through metamorphosis and longer larval periods than individuals that were initially large. Among tadpoles reared in the high quality treatment, initial size had only a weak influence on later larval size, and did not significantly affect metamorphic size of the duration of the larval period. This interaction between maternal investment and rearing conditions suggests that production of initially small offspring could be advantageous if these offspring develop in relatively benign environments, but disadvantageous if environments are more severe. These findings are discussed in light of previous studies that have demonstrated such interactions in organisms with complex life cycles.     

Seasonal and tidal abundance patterns of decapod crustacean larvae in a shallow inlet (SW Spain)

Planktonic larvae of decapod crustaceans were collected monthlyfrom July 1991 to June 1992 by pumping during nocturnal floodand ebb tides to establish seasonal larval abundance patternsin an inlet of the Bay of Cdiz. Additional 24 h series of sampleswere collected seasonally (July 1991, October 1991, January1992 and May/June 1992) during spring and neap tides to analyselarval abundance in relation to the main environmental cycles(diel, tidal and lunar phases) and vertical position in thewater column. First zoeae were the most abundant stage for mostspecies, representing 97.6% of all individuals collected. ZoeaI abundance was higher in spring and swmner and, on most samplingoccasions, there was a net output from the inlet to the bay.Five species (Liocarcinus arcuatus and Liocarcinus vernalis,Uca tangeri, Diogenes pugilator and Panopeus africanus) represented60% of total individuals caught. The seasonal occurrence offirst zoeae of the most abundant species indicated two differentreproductive patterns: species with a short reproductive periodand species spawning year round. Zoea I of several species (Panopeusafricanus, Uca tangeri, Pachygrap sus marmoratus, Processa spp.)were significantly more abundant during ebb tides and theirlater larval stages were scarcely collected, suggesting thatthese larvae are released in the inlet and exported to the bay.Conversely, a net input of first zoeae was observed for otherspecies (D.pugilator and Pinnotheres pinnotheres), but theirlater larval stages were also scarcely collected. Such importationcould be a larval rhythm artifact due to release of larvae inthe bay that drifted into the inlet by tidal currents. The crabIlia nucleus, whose later larval stages were collected frequently,was the only species that seemed to complete its life cyclewithin the bay. These results suggest that the studied inletwas primarily used by decapods as an adult habitat and spawningground, while larval development occurred in open sea. Sincevertical migration was not observed for exported larvae, thetidal synchronization of female release seemed to be the mostprobable mechanism of larval exportation. There were no significantdifferences between larval release during spring and neap tides.     

The influence of competition between foragers on clutch size decisions in an insect parasitoid with scramble larval competition

The effect of competition between ovipositing females on theirclutch size decisions is studied in animals that lay their eggsin discrete units of larval food (hosts). In such species theeffect of competition depends on the form of the larval competitionwithin such units. In insect parasitoids, there might eitherbe contest (solitary parasitoids) or scramble competition (gregariousparasitoids) between larvae within a host For gregarious parasitoids,a decreasing clutch size with increasing competition betweenforagers is predicted. This prediction is tested in experimentsusing the parasitoid Aphaertta minuta. Parasitoids were eitherkept alone or in groups of four before the experiment, in whichthey were introduced singly in a patch containing unparasitizedhosts. Animals kept together laid on average clutches of 0.74eggs smaller than females kept alone (average clutch is 5.3),thereby confirming the prediction. Clutch size decreased withencounter number, which might be due to the adjustment of thefemale's estimate of the encounter rate with hosts. Finally,the results are compared with those reported for solitary parasitoids(that have scramble larval competition), for which it is predictedthat the clutch size will increase with increasing levels ofcompetition between females.     

Behavioral, ecological, and molecular genetic analyses of reproductive strategies in the Amazonian dart-poison frog, Dendrobates ventrimaculatus

We report the first field and genetic studies of the reproductivestrategies of the Amazonian dart-poison frog Dendrobates ventrimaculatus,a species with biparental care. Neither males nor females arestrictly monogamous. Males are aggressively territorial, butsome females interact without aggression. Monitoring of breedingpools revealed high rates of multiple clutch deposition andhigh levels of larval cannibalism. Laboratory experiments confirmedlarval cannibalism and suggested a benefit to cannibals in increasedgrowth rate. Genetic analyses indicate that offspring from differentclutches in or above the same pool vary in relatedness and areon average intermediate in relatedness between individuals fromthe same clutch and unrelated individuals (from different pools).These data suggest that reproductive parasitism may be commonin this species