Substrate selection by saprophagous wood‐borer larvae within highly variable hosts

In insects completing their larval development within a single host, oviposition site is seen as a major determinant of offspring performance. However, in previous studies, the saprophagous wood‐borer Anthophylax attenuatus (Haldeman) (Coleoptera: Cerambycidae) showed no strong response to between‐host variations in nutritional factors influencing larval growth and survival. To explain such weak selection in adults, we hypothesized that substrate selection occurs at a smaller scale by larvae within hosts showing high variability in substrate quality. In this study, we described within‐host variability in wood density and determined whether wood‐boring larvae were found more often than expected in specific decay types. We characterized the variability of decay in 24 snags by producing wood density profiles for each. We then collected larvae from the same snags through wood dissection, and associated a wood density value to each by taking a wood sample around each larva found. We then compared ratios of available and used substrate types defined by wood density. We observed substantial within‐snag variation in wood density. Middle decay class (0.275–0.375 g cm^?3) was significantly overused by larvae, whereas more decayed wood was clearly avoided. High within‐host variability in substrate quality and active or passive selection by larvae of specific substrate types suggest that selection pressures on adult behaviour could be lower than expected for a parasitic species, and might be linked with the weak selection observed at a larger scale by ovipositing adults.     

Laboratory studies on the larval food habits of the ground beetle Amara (Curtonotus) gigantea (Motschulsky) (Coleoptera: Carabidae: Zabrini)

Ground beetles (Coleoptera: Carabidae) are important components of soil ecosystems in temperate zones, but our knowledge regarding the ecology of many species is limited. This study examined larval food habits in the ground beetle Amara (Curtonotus) gigantea (Motschulsky) using laboratory‐rearing experiments. Because this beetle is a member of the tribe Zabrini, which includes several species that exhibit granivory during larval and/or adult stages, three diet types were tested, with starvation as a control: Tenebrio larvae, mixed seeds (Bidens pilosa (Asteraceae), Setaria spp., Digitaria ciliaris (both Poaceae), and Humulus scandens (Moraceae)), and Tenebrio larvae + mixed seeds. Because of high larval mortality during overwintering under laboratory‐rearing conditions, survival and the duration of development through pre‐overwintering stages (first and second instars) were compared. Larvae fed the diet of Tenebrio larvae + mixed seeds showed the highest survival (89%), followed by the diet of Tenebrio larvae (83%), but the difference between the two treatments was not significant; similarly, developmental durations did not differ between these two diets. Larvae fed the mixed‐seeds diet showed markedly lower survival, and no larvae reached the second instar. Therefore, for A. gigantea larvae, animal food results in high larval performance, whereas seeds provide a low value diet; animal food is essential for larval development, but seeds provide no benefit, even as a dietary supplement. Overall, the present results suggest that A. gigantea larvae are omnivorous but with a mainly carnivorous food habit.     

Density‐dependent polyphenism and baculovirus resistance in teak defoliator,Hyblaea puera (Cramer)

1. Field populations of the teak defoliator larvae, Hyblaea puera Cramer exhibit colour polyphenism under different population densities: greyish‐green with black‐ and orange‐coloured dorsal bands in low‐density endemic populations and uniformly black or intermediate colour during high‐density population. 2. The density dependence of colour polyphenism was confirmed by field monitoring of H. puera populations during 2008–2010. 3. The above findings were later substantiated by rearing H. puera larvae under different densities (i.e. solitary and crowded in the laboratory). Ninety one per cent of the solitary reared laboratory population developed bright coloration whereas, 92% of the group reared larvae turned to black. Eight per cent of larvae from both the rearing densities were of intermediate colour. 4. Density‐dependent resistance build‐up against H. puera nucleopolyhedrovirus by H. puera were tested using the fifth instar larvae. The results showed three‐fold increase of median lethal dose (LD₅₀) value for the group reared larvae (5332 polyhedral occlusion bodies/larvae) compared to the solitary reared ones (1727 polyhedral occlusion bodies/larva) and also significant difference for the mean time to death (3.6 and 3.3 days, respectively). 5. The study revealed the strong influence of larval density on H. puera larval melanism and resistance build‐up against H. puera nucleopolyhedrovirus.     

Spatial Distribution,Food and Activity of Gomphus pulchellus SELYS 1840 (Insecta; Odonata; Gomphidae) from a Still Water Habitat

Distribution patterns of Gomphus pulchellus larvae in different sediments with different density of prey organisms were studied in the field in a small gravel pit lake in the south of Germany. Larval burrowing behaviour at different temperatures as well as food preference, consumption rates and activity were studied in laboratory experiments. In the study lake G. pulchellus larvae lived exclusively in places where macrophytes were present and in fine sediments (mean grain size <3 mm) with detritus cover. There was a significant positive correlation between larval density and density of food organisms suggesting that abundance of food is one of the determinants of larval distribution. In late autumn larvae migrated to deeper places probably to survive the winter. Low temperatures simulated in laboratory experiments did not induce larvae to burrow deeper. Larvae were always found in a sediment depth of 0.59–0.74 cm. Experiments with mixed prey showed that G. pulchellus larvae preferred tubificid worms and chironomid larvae over gammarids and ephemerid larvae. However, chironomid larvae which stayed in their tubes had a higher survival rate than those outside of tubes. Single-prey experiments showed that G. pulchellus larvae can prey not only on benthic species but also on Daphnia from the open water. Functional-response experiments showed that one G. pulchellus larva consumes a maximum of 2 to 3 tubificid worms or chironomid larvae per day, which corresponds to a maximum biomass (freshweight) of 5 to 30 mg per day. Video recordings of activity showed that G. pulchellus larvae cover long distances of up to 52 m per night on the substrate surface and that activity on the substrate surface started after midnight and ceased before sunrise. Consumption of Zooplankton prey and high activity above the substrate is interpreted as an adaptation of G. pulchellus larvae to the life in still water habitats.     

How predacious are predators? A study on Ocypus similis,a rove beetle of cereal fields

It is attempted determine the diet breadth and to quantify the predator pressure by Ocypus similis (F.) (Coleoptera: Staphylinidae), a dominant species of the rove beetle fauna in a winter wheat field. Laboratory and field experiments were conducted to determine the range of prey taxa and the consumption of a whole predator generation (including larvae) during its activity in the field. In laboratory experiments, adults and larvae of O. similis fed on a variety of prey except spiders and larvae of soldier beetles (Cantharidae), but they preferred millipedes as food (Diplopoda: Julidae, Polydesmidae). This preference could also be observed in the field. Although the predator population reached its maximum density in April, highest predator pressure occurred in June because of high consumption rates during the second larval stage. Adult beetles and the individuals of the second larval stage contributed both about 1/3 to total population consumption. Predation by adult beetles was mainly restricted to early spring and summer while larval consumption was highest from April to July. The staphylinids reduced the population density of diplopods by 7–35%. Because millipedes are an important part of the decomposer community, predator activity may lead to a decrease of decomposition rates.     

Oviposition habitat selection by container‐dwelling mosquitoes: responses to cues of larval and detritus abundances in the field

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Gregariousness does not vary with geography,developmental stage,or group relatedness in feeding redheaded pine sawfly larvae

Aggregations are widespread across the animal kingdom, yet the underlying proximate and ultimate causes are still largely unknown. An ideal system to investigate this simple, social behavior is the pine sawfly genus Neodiprion, which is experimentally tractable and exhibits interspecific variation in larval gregariousness. To assess intraspecific variation in this trait, we characterized aggregative tendency within a single widespread species, the redheaded pine sawfly (N. lecontei). To do so, we developed a quantitative assay in which we measured interindividual distances over a 90‐min video. This assay revealed minimal behavioral differences: (1) between early‐feeding and late‐feeding larval instars, (2) among larvae derived from different latitudes, and (3) between groups composed of kin and those composed of nonkin. Together, these results suggest that, during the larval feeding period, the benefits individuals derive from aggregating outweigh the costs and that this cost‐to‐benefit ratio does not vary dramatically across space (geography) or ontogeny (developmental stage). In contrast to the feeding larvae, our assay revealed a striking reduction in gregariousness following the final larval molt in N. lecontei. We also found some intriguing interspecific variation: While N. lecontei and N. maurus feeding larvae exhibit significant aggregative tendencies, feeding N. compar larvae do not aggregate at all. These results set the stage for future work investigating the proximate and ultimate mechanisms underlying developmental and interspecific variation in larval gregariousness across Neodiprion.     

MicroRNA Let‐7 targets the ecdysone signaling pathway E75 gene to control larval–pupal development in Bactrocera dorsalis

MicroRNAs (miRNAs) regulate various biological processes during insect developme nt;however, their role in larval-pupal development in oriental fruit fly, Bactrocera dorsalis (Hendel) remains unknown. In the current study, we address the biological function of a conserved miRNA, Bdo-Let-7 in the regulation of BdE75 gene, which belongs to the ecdysone signaling pathway and participates in the larval-pupal development in B. dorsalis. Using dual luciferase reporter assay in HEK293T cells we show that Bdo-Let-7 miRNA interacts with the 3' untranslated region of BdE75 gene and suppresses its expression. The Bdo-Let?7 and BdE75 are also co-expressed in the larval-pupal stages and in different tissues of B. dorsalis .In in vivo experiments, the injectio n of Bdo-Let-7 agomir and antagomir in third instar larvae down- and up-regulated the expression of BdE75、 respectively. The 20-hydroxyecdysone (20E) injection assay shows that 20E up-regulated the expression of Bdo-Let-7 on the 5th day of the larvae. Moreover, abnormal pupation and eclosion were observed after larval Bdo-Let-7 antagomir injection. Based on these results, we show that Bdo-Let-7 regulates the ecdysone signaling pathway through the exact dose of BdE75 gene, and is indispensable for normal larval-pupal development in B. dorsalis.     

Expression of trypsin-like serine peptidases in pre-imaginal stages of Aedes aegypti (Diptera: Culicidae)

This study reports the biochemical characterization and comparative analyses of highly active serine proteases in the larval and pupal developmental stages of Aedes aegypti (Linnaeus) using substrate‐SDS‐PAGE. Zymographic analysis of larval stadia detected proteolytic activity in 6–8 bands with apparent molecular masses ranging from 20 to 250 kDa, with activity observed from pH 5.5 to 10.0. The pupal stage showed a complex proteolytic activity in at least 11 bands with apparent Mr ranging from 25 to 250 kDa, and pH optimum at 10.0. The proteolytic activities of both larval and pupal stages were strongly inhibited by phenyl‐methyl sulfonyl‐fluoride and N‐α‐Tosyl‐L ‐lysine chloromethyl ketone hydrochloride, indicating that the main proteases expressed by these developmental stages are trypsin‐like serine proteases. The enzymes were active at temperatures ranging from 4 to 85°C, with optimal activity between 37 and 60°C, and low activity at 85°C. Comparative analysis between the proteolytic enzymes expressed by larvae and pupae showed that substantial changes in the expression of active trypsin‐like serine proteases occur during the developmental cycle of A. aegypti. © 2011 Wiley Periodicals, Inc.     

Reproductive Physiology of Fishes

Atlantic cod Gadus morhua larvae reached four‐fold (at low larval density) to 11 fold higher body mass (high larval density) at 50 days post hatch (dph) when fed zooplankton rather than enriched rotifers. A short period (22–36 dph) of dietary change affected larval growth positively if changed from enriched rotifers to natural zooplankton and negatively if prey type changed vice versa. Overall survival did not differ between the two larval groups at low larval density, but at high density the rotifer group had a higher overall survival (10·8% v. 8·9%). Long‐term growth was affected significantly by larval diet in favour of the zooplankton diet; juveniles reached a 23% higher mass in a 12 week growth period. No difference in growth performance was found between juveniles fed natural zooplankton during the larval period for 36, 22 or 14 days, but all these juveniles performed significantly better compared with the rotifer‐fed group. These findings suggest that optimal diet during a short period in the larval period can result in improved growth in both the larval and juvenile period. Improved rotifer quality may, therefore, hold a large potential for growth improvement in this species.     

How do food quality and larval crowding affect performance of the autumnal moth,Epirrita autumnata?

Outbreak densities of autumnal moth, Epirrita autumnata (Borkhausen) (Lepidoptera: Geometridae), lead to high larval crowding. Phenotypic responses of E. autumnata to larval crowding and to food quality were studied by measuring growth and consumption as well as pupal weight and fecundity. Crowding may trigger increased consumption and faster development to avoid impending food shortage on good quality food. This is suggested by the result that on a good‐quality diet, the growth of crowded larvae was better than that of solitary larvae, though they did not consume more food than solitary larvae. Crowded larvae also completed the last instar earlier than solitary larvae. The fecundity of crowded autumnal moths was not lower than the fecundity of solitarily grown autumnal moths. This may provide conditions for extra rapid population build‐up of E. autumnata. During the population increase phase the crowding effect may facilitate larval performance; however, at peak density the crowding starts to have negative effects on the performance of larvae. On a poor‐quality diet, the performance of crowded and solitary larvae did not differ. The growth of larvae was better on a good‐quality diet than on a poor‐quality diet, due to higher efficiency in food utilization. Larvae feeding on low‐quality diet did not prolong their development time, but pupated at smaller size; this resulted in lower fecundity. A decrease in food quality can be seen as a cue of oncoming food shortage and resource depletion; it may be advantageous to pupate at a smaller size and ensure survival till reproduction, rather than risk prolonging development to achieve larger size and higher fecundity.     

Black soldier fly (Diptera: Stratiomyidae) larval heat generation and management

Mass production of black soldier fly, Hermetia illucens (L.) (Diptera: Stratiomyidae), larvae results in massive heat generation, which impacts facility management, waste conversion, and larval production. We tested daily substrate temperatures with different population densities (i.e., 0, 500, 1000, 5000, and 10 000 larvae/pan), different population sizes (i.e., 166, 1000, and 10 000 larvae at a fixed feed ratio) and air temperatures (i.e., 20 and 30 °C) on various production parameters. Impacts of shifting larvae from 30 to 20 °C on either day 9 or 11 were also determined. Larval activity increased substrate temperatures significantly (i.e., at least 10 °C above air temperatures). Low air temperature favored growth with the higher population sizes while high temperature favored growth with low population sizes. The greatest average individual larval weights (e.g., 0.126 and 0.124 g) and feed conversion ratios (e.g., 1.92 and 2.08 g/g) were recorded for either 10 000 larvae reared at 20 °C or 100 larvae reared at 30 °C. Shifting temperatures from high (30 °C) to low (20 °C) in between (∼10-d-old larvae) impacted larval production weights (16% increases) and feed conversion ratios (increased 14%). Facilities should consider the impact of larval density, population size, and air temperature during black soldier fly mass production as these factors impact overall larval production.     

Fenoxycarb,a potent contaminant of the silkworm,Bombyx mori L., does not influence its juvenile hormone titer

Fenoxycarb (FC) effects were studied on juvenile hormone (JH) titers and JH‐esterase activities in the silkworm, B. Mori. In the literature, FC was observed to induce high JH titers but also to act without corpora allata (CA). These contradictory results did not permit us to conclude whether FC was a potent JH mimic or it was acting through the enhancement of JH titers in the hemolymph. Analysis of hemolymph JH‐esterase activities during the last larval instar reveals that FC was not a JH‐esterase inhibitor. Considering JHs, only JH II was detected in the European hybrid 200×300. Furthermore, JH titer was exactly identical in control and FC‐treated larvae, i.e., it dropped during the first 2 days of the last larval instar and became undetectable after day 2. This result is important since it contradicts the generally admitted concept that FC was acting by increasing the titer of JH. On the contrary, it was found that, despite its non‐terpenoid chemical structure, FC might be a JH mimic. In addition, FC suspected contamination of mulberry leaves was analyzed from a physiological viewpoint. We observed that "contaminated" mulberry leaves‐fed larvae became permanent larvae through the inhibition of their prothoracic glands (PG) activity and without any modification of their JH titers, i.e., exactly as for FC‐treated larvae. This last point adds information concerning the suspected implication of FC in the induction of the non‐spinning syndrome. Arch. Insect Biochem. Physiol. 40:141–149, 1999. © 1999 Wiley‐Liss, Inc.     

Reproductive performance of carp, Catla catla (Ham.), reared on a formulated diet with PUFA supplementation

Effect of dietary supplementation of n‐3 and n‐6 polyunsaturated fatty acids (PUFA) on reproductive performances in both sexes of an Indian major carp, Catla catla (Ham.), were investigated in terms of sperm quality, spawning response, fecundity and spawn recovery over a consecutive 2‐year period. Sperm count and spermatocrit value were in the range of 3.2–3.8 × 10⁷ ml⁻¹ and 80–82%, respectively, in fish fed the PUFA‐enriched test diet, and significantly higher (P < 0.01) than in fish fed control diet (2.3–2.5 × 10⁷ ml⁻¹ and 64–70%). Spawning response in the test diet group was quite high (96%) compared to 76% in the control. Egg and larval quality were superior in the test diet group as evidenced by the significantly higher fertilization rate and larval survival in the range of 91–92% and 93.3%, respectively. Fatty acid profile of fertilized eggs and larvae showed that the quantities of 18:3 (n‐3), 20:5 (n‐3) and 22:6 (n‐3) were significantly (P < 0.01) increased in the test group while 18:1, 18:2 (n‐6) and 20:4 (n‐6) remained at higher levels in control. The results indicated that enrichment of n‐3 PUFA in the broodfish diet not only improved the quality of eggs and larvae in terms of recovery, but also enhanced the physiological response of broodfish to induced spawning. Oil enrichment in the broodfish diet should therefore be mandatory to ensure the optimum n‐3 PUFA content for warmwater carp for quality seed production.     

Allee effect in larval resource exploitation in Drosophila: an interaction among density of adults, larvae, and micro-organisms

Abstract 1. Aggregation pheromones can evolve when individuals benefit from clustering. Such a situation can arise with an Allee effect, i.e. a positive relationship between individual fitness and density of conspecifics. Aggregation pheromone in Drosophila induces aggregated oviposition. The aim of the work reported here was to identify an Allee effect in the larval resource exploitation by Drosophila melanogaster, which could explain the evolution of aggregation pheromone in this species. 2. It is hypothesised that an Allee effect in D. melanogaster larvae arises from an increased efficiency of a group of larvae to temper fungal growth on their feeding substrate. To test this hypothesis, standard apple substrates were infested with specified numbers of larvae, and their survival and development were monitored. A potential beneficial effect of the presence of adult flies was also investigated by incubating a varying number of adults on the substrate before introducing the larvae. Adults inoculate substrates with yeast, on which the larvae feed. 3. Fungal growth was related negatively to larval survival and the size of the emerging flies. Although the fungal growth on the substrate was largely reduced at increased larval densities, the measurements of fitness components indicated no Allee effect between larval densities and larval fitness, but rather indicated larval competition. 4. In contrast, increased adult densities on the substrates prior to larval development yielded higher survival of the larvae, larger emerging flies, and also reduced fungal growth on the substrates. Hence, adults enhanced the quality of the larval substrate and significant benefits of aggregated oviposition in fruit flies were shown. Experiments with synthetic pheromone indicated that the aggregation pheromone itself did not contribute directly to the quality of the larval resource. 5. The interaction among adults, micro‐organisms, and larval growth is discussed in relation to the consequences for total fitness.     

Blood feeding of Ornithodoros turicata larvae using an artificial membrane system

An artificial membrane system was adapted to feed Ornithodoros turicata (Ixodida: Argasidae) larvae from a laboratory colony using defibrinated swine blood. Aspects related to larval feeding and moulting to the first nymphal instar were evaluated. A total of 55.6% of all larvae exposed to the artificial membrane in two experimental groups fed to repletion and 98.0% of all fed larvae moulted. Mortality rates of first instar nymphs differed significantly depending on the sorting tools used to handle engorged larvae (χ² = 35.578, P < 0.0001): engorged larvae handled with featherweight forceps showed significantly higher mortality (odds ratio = 4.441) than those handled with a camel‐hair brush. Differences in the physical properties of the forceps and camel‐hair brush may affect the viability of fragile soft tick larvae even when care and the same technique are used to sort them during experimental manipulations. The current results represent those of the first study to quantify successful feeding to repletion, moulting and post‐moulting mortality rates in O. turicata larvae using an artificial membrane feeding system. Applications of the artificial membrane feeding system to fill gaps in current knowledge of soft tick biology and the study of soft tick–pathogen interactions are discussed.     

Group size in a gregarious tortoise beetle: patterns of oviposition vs. larval behaviour

In laboratory and garden experiments, we tested for the existence of adaptive patterns of oviposition and larval behaviour regarding group size in the gregarious tortoise beetle Chelymorpha varians Blanchard (Coleoptera: Chrysomelidae: Cassidinae) on its host plant Calystegia sepium L. (Convolvulaceae). Specifically, we addressed the following questions: (i) Which is the more frequent egg cluster size? (ii) Does cluster size fully predict larval group size? (iii) Are newborn larvae attracted or repelled to conspecific groupings? and (iv) Which is the group size associated with enhanced larval development and adult mass? We found that the mean cluster size was 21.4 eggs. Egg hatch time was significantly shorter in larger clusters. A regression analysis of larval group size against cluster size showed non‐significant results. Thus, original cluster size did not totally determine the larval group size. The mean larval group size was 17.1. Choice tests in an experimental arena showed that larvae clearly preferred leaves of a host plant rather than moistened papers, and that larvae preferred a small group of conspecifics (four larvae per leaf) over larger groups (12 or 20 larvae). Empty leaves of the host plant showed an intermediate level of preference. Development time and beetle performance (adult mass) were affected by larval group size. Larvae in the smallest group (one per leaf) took four more days to attain adulthood than larvae in the larger groups (12 and 20 larvae). Adult C. varians reared in the 12‐larvae group were significantly larger than those reared at the other densities. Comparison of patterns across experimental groups, excluding the 12‐larvae group, showed a tendency for a greater final mass with slower developmental rate.     

Peptidases in Drosophila melanogaster. I. Characterization of dipeptidase and leucine aminopeptidase activities

Four major peptidases of Drosophila melanogaster have been described and distinguished by their electrophoretic mobilities, molecular weights, net electrical charges, and substrate specificities. The previously described leucine aminopeptidase, LAP D, consists of at least two isozymes, designated here LAP P and LAP G. In pupae most LAP activity results from LAP P (pupal); in larvae and adults, in contrast, most LAP activity results from LAP G (gut). These two LAPs may be separated by electrophoresis in the presence of the nonionic detergent Triton X-100. A specific assay for LAP P, which exploits the large difference between the net electrical charge of LAP P and that of LAP G, is described. The activity levels of two dipeptidases, Dip A and Dip B, were high in all the postembryonic stages examined. Specific assays for Dip A and Dip B were used to show that for each of these isozymes, the activity in an adult is proportional to gene dosage.     

First estimates of metabolic rate in Atlantic bluefin tuna larvae

Atlantic bluefin tuna is an iconic scombrid species with a high commercial and ecological value. Despite their importance, many physiological aspects, especially during the larval stages, are still unknown. Metabolic rates are one of the understudied aspects in scombrid larvae, likely due to challenges associated to larval handling before and during respirometry trials. Gaining reliable estimates of metabolic rates is essential to understand how larvae balance their high growth needs and activity and other physiological functions, which can be very useful for fisheries ecology and aquaculture. This is the first study to (a) estimate the relationship between routine metabolic rate (RMR) and larval dry weight (DW) (mass scaling exponent) at a constant temperature of 26°C, (b) measure the RMR under light and darkness and (c) test whether the interindividual differences in the RMR are related to larval nutritional status (RNA/DNA and DNA/DW). The RMR scaled nearly isometrically with body size (b = 0.99, 0.60–31.56 mg DW) in contrast to the allometric relationship observed in most fish larvae (average b = 0.87). The results show no significant differences in larval RMR under light and darkness, suggesting similar larval activity levels in both conditions. The size explained most of the variability in RMR (97%), and nutritional condition was unrelated to the interindividual differences in routine metabolism. This is the first study to report the metabolic rates of Atlantic bluefin tuna larvae and discuss the challenges of performing bioenergetic studies with early life stages of scombrids.     

Reconstructing larval growth and habitat use in an amphidromous goby using otolith increments and microchemistry

High‐resolution analysis of growth increments, trace element chemistry and oxygen isotope ratios (δ¹⁸O) in otoliths were combined to assess larval and post‐larval habitat use and growth of Awaous stamineus, an amphidromous goby native to Hawai‘i. Otolith increment widths indicate that all individuals experience a brief period of rapid growth during early life as larvae and that the duration of this growth anomaly is negatively correlated with larval duration. A protracted high‐growth period early in larval life is associated with a lower ratio of Sr:Ca, which may reflect low salinity conditions in nearshore habitats. A distinct shift in δ¹⁸O (range: 4–5‰) is closely associated with the metamorphic mark in otoliths, indicating that larval metamorphosis occurs promptly upon return to fresh water. Strontium and other trace elements are not as tightly coupled to the metamorphosis mark, but confirm the marine‐to‐freshwater transition. Integration of microstructural and microchemical approaches reveals that larvae vary substantially in growth rate, possibly in association with habitat differences. Although time and financial costs make it difficult to achieve large sample sizes, present results show that examining even a small number of individuals can lead to novel inferences about early life history in diadromous fishes and illustrates the value of integrating analyses.