Effect of lamellae autotomy on survival and foraging success of the damselfly Lestes sponsa (Odonata: Lestidae)

Damselfly larvae can autotomize their caudal lamellae to escape predation. Costs of caudal lamellae autotomy were investigated by directly manipulating lamellae condition of Lestes sponsa in laboratory experiments. Larvae without lamellae had higher predation mortality in the presence of Notonecta. Both lamellae loss and larval density increased the probability of being cannibalized. The results suggest that the increased vulnerability after lamellae loss resulted from a reduced escape performance. Larvae were less mobile after lamellae loss or in the presence of a predator, but the decrease was no longer significant when both factors were combined. This indicates that larvae compensate for the increased predation risk with a fixed response. Both lamellae loss and predator presence reduced hunting success, but the decrease after lamellae loss was only significant in the absence of a predator. The fitness consequences of these effects for both the larval and adult stages are discussed. In general, the data strongly suggest that lamellae autotomy plays a role in population regulation of damselflies. Received: 1 April 1998 / Accepted: 28 August 1998     

Do damselfly larvae recognize and differentially respond to distinct categories of macroinvertebrates?

Zygopteran larvae normally encounter other aquatic macroinvertebrates that are predators, competitors, and prey and should therefore demonstrate varied responses when faced with different categories of opponent. In a laboratory experiment individual final-instarIschnura posita (Hagen) larvae were observed in interactions with six categories of invertebrate opponents. The opponent categories were a nonconspecific damselfly and a small crayfish, which represented threatening opponents because they were larger than theI. posita subject larva, and a mayfly and a stonefly, which constituted nonthreatening opponents because they were smaller than the subject larva. The levels of threat posed by conspecific larvae of final and penultimate instar were inferred by comparison to the other opponent categories. Multivariate analysis showedI. posita's response differed between the two larger opponents, but responses were statistically indistinguishable between the two smaller opponents. Larvae retreated, moved around the stalk, and struck their opponents with their lamellae more often in the presence of a crayfish than the nonconspecific zygopteran. In contrast, they assumed an S-bend posture frequently with the zygopteran. Responses toward final-instar conspecifics differed from responses toward the larger opponents. Effectively, larvae wagged their abdomens only in the presence of final-instar conspecifics and retreated and moved around the stalk less frequently in these trials. Responses toward the smaller conspecifics differed from the responses to the small opponents. Larvae struck penultimate-instar conspecifics with their lamellae more frequently than the other small opponents. Our results suggest that larval zygopteran behaviors (such as S-bend and SCS) that have previously been described as intraspecific displays are of a more general nature and used toward a variety of opponents, whereas wag is unique to intraspecific interactions inI. posita.     

An experimental study of population regulation in the salamander,Notophthalmus viridescens dorsalis (Urodela: Salamandridae)

Summary The roles of density-dependent larval survival and cannibalism of larvae as potential mechanisms of population regulation in the newt (Notophthalmus viridescens dorsalis) were evaluated in laboratory and field experiments. In laboratory containers, adults cannibalized larvae and large larvae cannibalized smaller larvae. In artificial ponds, larval survival did not depend on initial larval density. No cannibalism could be demonstrated in the complex environment, although the experiment was powerful enough to detect an ecologically relevant difference in survival. Adult growth was negatively correlated with the final biomass of larval newts, suggesting that the two life stages competed for resources. Larval growth rates were negatively correlated with final larval density, suggesting that larvae competed with each other. The proportion of larvae that became sexually mature at age 7 months (paedomorphs and adults that skipped the eft stage) varied inversely with larval density. Therefore, the potential regulatory mechanisms identified in this study are competition within and between life stages.     

Mass breeding larvae of the critically endangered diving beetles Dytiscus sharpi sharpi and Dytiscus sharpi validus (Coleoptera: Dytiscidae)

For conservation purposes, and to supply critically endangered insects for laboratory use, a system for artificial breeding is crucial. However, in the case of carnivorous insects such as diving beetles, the larvae must be isolated because they are cannibalistic. We developed a method for mass breeding the larvae of two diving beetles, Dytiscus sharpi sharpi (Wehncke) and Dytiscus sharpi validus (Régimbart) (Coleoptera: Dytiscidae), which are designated critically endangered species in Japan. Ten to twenty larvae were raised in a small tank (35 cm × 25 cm × 10 cm; water depth 7 cm) with Rana ornativentris (Werner) tadpoles as prey. At low prey density, ~80 % of the larvae were cannibalized. At moderate prey density, 50–60 % were cannibalized. However, at high prey density, <3 % were cannibalized. Well-fed mass-bred adults were larger than individually bred and field-collected adults. This mass breeding method can be used for the conservation and breeding of these rare diving beetles in a manageable number of aquaria.     

Functional responses during the early larval stages of the charal fish Chirostoma riojai (Pisces: Atherinidae) fed rotifers and cladocerans

Survival during early fish larval stages depends largely upon the availability of appropriate prey. Studied were the functional responses from hatching to 6 weeks of age of whitefish (Charal) (Chirostoma riojai) larvae that were offered selected rotifers (Brachionus rotundiformis and B. rubens) and cladocerans (Moina macrocopa and Ceriodaphnia dubia). The experiments were conducted in a 50 ml medium at a salinity of 2 g L^?1. Each treatment used four replicates. Rotifers were introduced at densities of 0.5, 1, 2, 4, 8 and 16 individuals ml^?1 and cladocerans at 0.1, 0.2, 0.4, 0.8, 1.6, 3.2, 4.8 and 6.4 individuals ml^?1. Two larvae, previously starved for 2 h, were introduced into each test jar and allowed to feed for 45 min. The difference between the initial and final zooplankton density represented prey consumption. C. riojai larvae showed Type II functional response curves, i.e. they consumed more zooplankton with increasing prey availability; above a certain prey density (8–16 individuals ml^?1 in rotifers and 3.2–6.4 individuals ml^?1 in cladocerans) the consumption rate tended to stabilize in most trials. Results are discussed in relation to aquaculture.     

Extra molting,cannibalism and pupal diapause under unfavorable growth conditions in Atrophaneura alcinous (Lepidoptera: Papilionidae)

Atrophaneura alcinous adopt multiple strategies such as extra molting, cannibalism and pupal diapause under unfavorable growth conditions. The conditions under which these strategies are adopted have been separately verified, but their relationship has often been overlooked. We examined which strategy A. alcinous adopted and the relative advantages of strategies using four experimental groups under different food quantity and individual density conditions. Our results indicated that A. alcinous often extra‐molted, prolonged the larval period, and larval and pupal weights were lighter under food shortage. Cannibalism and disease often occurred under the high density and food shortage condition. We also showed that individuals cannibalized during the prepupal or pupal period were less likely to extra molt before they were killed. Extra molting tended to occur more frequently in females than in males under a shortage of food. In addition, we showed that, when food was insufficient, A. alcinous might initiate pupal diapause under low densities, but not under high densities. These results suggest that A. alcinous prolongs the larval period by engaging in extra molting during times of unfavorable food conditions. This strategy might decrease the risk of cannibalization because surrounding larvae who could potentially cannibalize others pupate before larvae who prolong the larval period pupate. Our results also suggest that diapausing pupae under a shortage of food can only survive when there are few surrounding conspecifics, due to a lower cannibalization risk. In conclusion, there is a complex interaction between extra molting, cannibalism and pupal diapause strategies.     

Structure and swimming behavior of the larva of Halichondria melanadocia (Porifera: Demospongiae)

Larvae of the sponge Halichondria melanadocia are of the parenchymella type and, during swimming, can change shape rapidly from cigar-like to ovoid. Larvae collected in Hawaii displayed neither qualitative nor quantitative differences in behavior or structure from those collected in Florida. Floridian larvae were examined at 2, 28, 48, and 72 hr after release to assess anatomical changes correlated with duration of the free-swimming period. Although 2 hr larvae were significantly longer than 48 or 72 hr larvae, other differences were not observed. Positively phototactic throughout the free-swimming period, the larvae eventually begin to swim on or near the bottom of dishes, settle temporarily, but can resume swimming before permanent settlement is achieved. The larva is extensively flagellated and a band of long flagella separates the lateral and posterior regions. The epidermis is a tall, simple columnar epithelium composed of highly polarized, monoflagellated cells. The interior contains at least two distinct amoeboid cell types that intermesh with the basal ends of epidermal cells within a loosely defined cavity. No spicules are present. Choanocyte chambers, found within 3 of the 50 larvae that were serially sectioned, varied in size and complexity, but were not associated with canals. This report is the-first of such chambers in Halichondria larvae. Spicules and choanocyte chambers are somatic structures associated with adults, and their appearance in larvae is presumably a consequence of a heterochronic event, most likely acceleration. The evolutionary significance of the occurrence of these traits in Halichondria larvae awaits further developmental analysis and greater phylogenetic resolution.     

Egg cannibalism by larvae and adults of the milkweed leaf beetle (Labidomera clivicollis, Coleoptera: Chrysomelidae)

Abstract.

• 1 Egg cannibalism is a form of infanticide that has been implicated in the evolution of guarding of eggs and immatures in some species of insects. The milkweed leaf beetle, Labidomera clivicollis (Coleoptera: Chrysomelidae), exhibits three types of egg cannibalism in the field: siblicide, cannibalism of eggs by older larvae from earlier hatching egg clutches, and cannibalism of eggs by adult females. Unlike their close relative, L.suterella (Choe, 1989), female L.clivicollis do not guard their eggs or immatures. They move slowly about a patch of milkweeds laying multiple egg clutches.
• 2 First instar and older larvae cannibalized eggs in two geographically separated study populations (subspecies) in Austin, Texas, and Bridgeport, New York, U.S.A. Although adult females of both populations cannibalized eggs in the laboratory, only the Texas subspecies, L.c.rogersii, exhibited such cannibalism in the field.
• 3 In the field, correlates of siblicide varied both temporally (within subspecies) and spatially (between subspecies) in terms of whether they were statistically significant, but trends were all in the same direction. Group size was positively correlated with hatching success and siblicide, but negatively correlated with other types of predation. Siblicide was also positively correlated with egg density in a laboratory study of the Texas subspecies, L.c.rogersii.
• 4 In the laboratory, an average of 15–17% of L.c.clivicollis eggs never developed embryos. Although these were almost always cannibalized, some viable eggs were also eaten and there is no evidence that females increased the proportion of infertile eggs they laid to increase siblicide.
• 5 Field data and laboratory experiments showed that adult female L. c.rogersii cannibalized eggs while males rarely did. Females preferentially ate the eggs of other females over their own eggs in an experiment that removed spatial cues.
• 6 Although the selective context of cannibalism is not demonstrated here, I suggest that females may increase siblicide by increasing egg density and may cannibalize eggs to protect their own eggs from being eaten by second and third instar larvae produced by other females.

     

Effects of size structure and habitat complexity on predator–prey interactions

1. A predator's ability to suppress its prey depends on the level of interference among predators. While interference typically decreases with increasing habitat complexity, it often increases with increasing size differences among individuals. However, little is known about how variation in intrinsic factors such as population size structure alters predator–prey interactions and how this intrinsic variation interacts with extrinsic variation. 2. By experimentally varying the level of vegetation cover and the size structure of the predatory damselfly Ischnura posita Hagen, we examined the individual and interactive effects of variation in habitat complexity and predator size structure on prey mortality. 3. Copepod prey survival linearly increased as the I. posita size ratio decreased and differed by up to 31% among different predator size structures. Size classes had an additive effect on prey survival, most likely because intraspecific aggression appeared size‐independent and size classes differed in microhabitat preference: large I. posita spent 14% more time foraging on the floor than small larvae and spent more time in the vegetation with increasing habitat complexity. Despite this difference in microhabitat use among size classes, habitat structure did not influence predation rates or interference among size classes. 4. In general, results suggest that seasonal and spatial variation in the size structure of populations could drive some of the discrepancies in predator‐mediated prey suppression observed in nature, and this variation could exceed the effects of variation in habitat structure.     

Ontogeny of critical and prolonged swimming performance for the larvae of six Australian freshwater fish species

Critical (<30 min) and prolonged (>60 min) swimming speeds in laboratory chambers were determined for larvae of six species of Australian freshwater fishes: trout cod Maccullochella macquariensis, Murray cod Maccullochella peelii, golden perch Macquaria ambigua, silver perch Bidyanus bidyanus, carp gudgeon Hypseleotris spp. and Murray River rainbowfish Melanotaenia fluviatilis. Developmental stage (preflexion, flexion, postflexion and metalarva) better explained swimming ability than did length, size or age (days after hatch). Critical speed increased with larval development, and metalarvae were the fastest swimmers for all species. Maccullochella macquariensis larvae had the highest critical [maximum absolute 46·4 cm s^?1 and 44·6 relative body lengths (L_B) s^?1] and prolonged (maximum 15·4 cm s^?1, 15·6 L_B s^?1) swimming speeds and B. bidyanus larvae the lowest critical (minimum 0·1 cm s^?1, 0·3 L_B s^?1) and prolonged swimming speeds (minimum 1·1 cm s^?1, 1·0 L_B s^?1). Prolonged swimming trials determined that the larvae of some species could not swim for 60 min at any speed, whereas the larvae of the best swimming species, M. macquariensis, could swim for 60 min at 44% of the critical speed. The swimming performance of species with precocial life‐history strategies, with well‐developed larvae at hatch, was comparatively better and potentially had greater ability to influence their dispersal by actively swimming than species with altricial life‐history strategies, with poorly developed larvae at hatch.     

The impact of a small, alien invertebrate on a sub-Antarctic terrestrial ecosystem: Limnophyes minimus (Diptera, Chironomidae) at Marion Island

Density and biomass of the larvae of a small, alien chironomid midge, Limnophyes minimus, whose parthenogenetic adult females do not feed, were quantified for ten major lowland plant communities at sub-Antarctic Marion Island (46°52′S 37°51′E) and compared with the density and biomass of indigenous macro-invertebrates in the same communities. An estimate of litter consumption by larvae of this midge was also made. L. minimus reached high densities in most of the plant communities sampled, with the highest density being recorded in the Cotula plumosa biotically influenced community (annual mean of 4,365 individuals m⁻²) and the lowest in the Crassula moschata salt spray community (annual mean of 41 individuals m⁻²). Estimates of litter ingestion indicated that L. minimus larvae are capable of consuming between 0.07 and 8.54 g_{(dry mass)} m⁻² per year, depending on the community. In some communities this litter consumption amounted to an order of magnitude more than that consumed by Pringleophaga marioni (Lepidoptera, Tineidae). Although the larvae of this moth species are thought to represent the bottleneck to nutrient recycling on the island, this study showed that midge larvae may also contribute substantially to this process. As a consequence, the considerable changes that have been predicted to occur in Marion Island's terrestrial ecosystem as a consequence of enhanced predation by mice on P. marioni larvae may be retarded or obscured by the contribution of the midge larvae to nutrient cycling. Hence, it is suggested that greater attention be given to the small and inconspicuous elements of the alien sub-Antarctic faunas because such species may have profound consequences for ecosystem functioning on these islands. Received: 17 November 1997 / Accepted: 23 February 1998     

Effect of food availability on larval cannibalism by foundresses of the paper wasp <Emphasis Type="Italic">Polistes chinensis antennalis</Emphasis>

Cannibalism is a behavioral trait seen in a number of species and can be favored when the fitness gain outweighs the cost. In social wasps, field studies have suggested that food limitation causes larval cannibalism as a compensation of a meal for adult wasp and/or earlier production of the first workers, but experimental studies for the effect of food availability on larval cannibalism have been very scarce. Hence we examined whether Polistes chinensis antennalis foundresses exhibit a higher level of larval cannibalization under food-limited conditions than under food-available conditions. Larval cannibalization occurred frequently under both prey- and honey-limited conditions; however, young larvae were more frequently cannibalized than old larvae in the prey-limited colonies, while old larvae were more frequently cannibalized than young larvae in the honey-limited colonies. The number of days between colony initiation and the emergence of the first workers was not significantly different between the prey-limited and prey-available colonies, suggesting that under prey-limited conditions P. chinensis antennalis foundresses tend to cannibalize their young larvae and feed probably the flesh of these cannibalized larvae to old larvae in order to ensure the rapid production of the first workers. On the other hand, the number of days between colony initiation and the emergence of the first workers was longer in the honey-limited colonies than in the honey-available colonies. We propose explanations for the first time for why the foundresses in the honey-limited conditions cannibalized their old larvae more frequently than their young larvae in spite of this resulting in the delayed emergence of the first workers.     

Effects of Bacillus thuringiensis Cry1C toxin on the metabolic rate of Cry1C resistant and susceptible Spodoptera exigua (Lepidoptera: Noctuidae)

Abstract. The effects of Bacillus thuringiensis (Bt) Cry1C toxin on the metabolic rate of Cry1C resistant and susceptible Spodoptera exigua (Hübner) (Lepidoptera: Noctuidae) are investigated using closed‐system respirometry. Mechanisms of resistance to the Bt toxin may be associated with an energetic cost that can be measured as an increase in metabolic rate compared with Bt‐susceptible insects. This hypothesis is tested using third‐ and fifth‐instar larvae and 1–7‐day‐old pupae. Metabolic rate is measured as the amount of O₂ consumed and CO₂ produced. V?_O2 and V?_CO2 (mL g^?1 h^?1) of third‐instar Cry1C resistant larvae reared continuously on a diet containing 320 µg Cry1C toxin per g diet (CryonT) are significantly greater than third‐instar Cry1C resistant larvae reared on toxin for 5 days and reared thereafter on untreated diet (Cry5dT), Cry1C resistant larvae reared on untreated diet (CryReg) and the susceptible parental strain (SeA) reared on untreated diet. There are no differences in V?_O2 and V?_CO2 (mL g^?1 h^?1) among treatment groups for fifth‐instar larvae. CryonT larvae and pupae weigh significantly less than larvae and pupae receiving other treatments. Smaller body mass may be an important biological cost to individuals exposed continuously to Bt toxin. One‐day‐old pupae of all treatment groups exhibit a high V?_O2 (mean approximately 0.174 mL g^?1 h^?1) with CryonT having a significantly greater value than all other treatments; there are no differences among the other treatments. Pupal metabolic rates of all treatment groups decline to a minimum between days 2 and 4 then increase linearly between days 4 and 7 until adult emergence. These results demonstrate no difference in metabolic rates, and possibly fitness costs, between resistant (CryReg and Cry5dT) and susceptible (SeA) S. exigua except when larvae were reared continuously on toxin (CryonT).     

Benthic ctenophores (Platyctenida: Coeloplanidae) in South Florida: predator–prey interactions

The primary goal of this study was to demonstrate, from field observations and laboratory experiments, some key trophic roles of benthic ctenophores as predators and prey in subtropical communities. We examined individuals of two benthic platyctenid species: Coeloplana waltoni, a minute epibiont on octocorals in exposed, open‐water settings; and Vallicula multiformis, an associate of calm‐water biofouling communities and floating Sargassum spp. Laboratory observations of individuals of both ctenophore species revealed frequent capture and ingestion of diverse zooplankton taxa, especially crustaceans. Laboratory predation trials demonstrated the capture of dolphinfish (Coryphaena hippurus) eggs and larvae by both ctenophore species. Dolphinfish eggs and larvae larger than individuals of C. waltoni were captured but not ingested during 2‐h trial periods. These prey items were sometimes purloined and ingested by polyps of the ctenophore's octocoral host. Ingestion of dolphinfish eggs and larvae by individuals of C. waltoni was observed, however, after longer periods of exposure to prey. In predation trials, dolphinfish eggs and larvae were both captured and ingested by larger individuals of the ctenophore species V. multiformis. Field and laboratory observations revealed diverse invertebrate and fish taxa that prey on both ctenophore species. In the laboratory, the mean daily per capita consumption of individuals of C. waltoni by a pomacanthid fish ranged 0.5–2.8 individuals, and ranged 2.6–3.6 individuals for predation by an ovulid mollusc. Field population densities of these predators ranged 0.1–0.7 individuals per m² for the pomacanthid, and 0.2–1.1 individuals per m² for the mollusc. Laboratory feeding observations demonstrated frequent consumption of individuals of V. multiformis by a sea anemone, and by three species of brachyuran crabs. Field observations revealed eight fishes that probably feed incidentally on individuals of V. multiformis. These findings add to the limited knowledge base of predator–prey dynamics in both C. waltoni and V. multiformis.     

Long-term movements of self-marked caddisfly larvae (Trichoptera: Sericostomatidae) in a California coastal mountain stream

1. Over 140 000 larvae of the case-building caddisfly Gumaga nigricula were self-marked as they incorporated glitter into small portions of their cases while reared in streamside troughs. These marked individuals were released into stream pools and their movements monitored in the dry season, when base flow was low and no spates occurred, and in the wet season when base flow was high and several spates occurred. 2. Of the 9,000–10 000 larvae released in each of two stream pools in the dry season, 4–20% (i.e. 377–1817 marked individuals) were observed on three sampling dates (4, 11 and 24 d after release). Most larvae (87–93%) remained within 4 m up- or downstream of the release line after 24 d. No larvae were found outside of the release pools, even after 37 d. 3. Of the > 120 000 larvae released in one stream pool near the beginning of the wet season, 408 larvae were recaptured 130–167 d later, a period that included 30 days of high flow associated with six spates. Estimated survivorship over this period was 0.7–6.2%; there was no relationship between survival and larval size at release. Most (75%) recaptured larvae were found in the pool where they were originally released. The remaining larvae were found downstream of the release pool. Larvae had generally dispersed only a short distance downstream of the release pool (median = 18 m, maximum = 222 m). In addition, four marked pupae were later found 436 m downstream of the release pool. 4. These results illustrate the sedentary nature of larval G. nigricula as well as the important role that high flow events play in larval mortality and dispersal. These case-building larvae move very little during low flow periods, even when food resources appear limiting. In contrast, the frequency and distance of larval dispersal are much greater during periods with high flow. 5. Our observations for G. nigricula support previously published inferences that larval dispersal within a stream can be limited for some aquatic insects. However, our observations also suggest that, even for a relatively sedentary species like G. nigricula, larval dispersal during periods with high flow may contribute significantly to gene flow within a stream reach.     

Discovery of swimming larvae in Elmidae (Coleoptera: Byrrhoidea)

The aquatic larvae of the family Elmidae (Coleoptera) have been considered unable to swim because they lack swimming setae on their body and legs. We discovered that riffle beetle larvae (Leptelmis gracilis Sharp) are in fact able to swim. After opening the tuft‐like gills on the last abdominal segment they swim by repeatedly bending the abdomen into a U‐shape very quickly and in a wavy manner, while their head and thorax move anteriorly, resulting in a sigmoidal body shape. The flat bodies of L. gracilis larvae could be advantageous for swimming compared to the cylindrical or semicylindrical bodies of larvae in related genera.     

Submergence tolerance in immature stages of the stalk-eyed fly Sphyracephala detrahens (Diptera: Diopsidae)

Sphyracephala detrahens (Walker, 1860) (Diptera: Diopsidae) inhabits the riparian zones of streams and rivers. Because of the limited dispersal ability of S. detrahens during egg, larval, and pupal stages, immature individuals are at risk of being submerged by floodwater after heavy rain. In this study, I evaluated the submergence tolerances of immatures of S. detrahens by comparing them to immatures of Drosophila melanogaster, which also feed on rotten fruits but are not restricted to the riparian zone. The results showed that S. detrahens eggs were susceptible to desiccation, but more than 80% of eggs hatched after full submergence. Later instar larvae were more resistant to full submergence than earlier instar larvae. The duration of submergence causing 50% pupation (PD₅₀) in the first, second, and third-instar larvae of S. detrahens were 15.88, 58.46, and 91.74 h, respectively. The PD₅₀ of the third-instar larvae of D. melanogaster was 20.01 h. Third-instar S. detrahens larvae continued to develop in water for a longer duration than D. melanogaster larvae of the same instar. In the pupal stages, late pupae tended to remain afloat longer than early pupae. The duration of submergence causing 50% emergence (ED₅₀) of adults from early and late pupae were 40.70 and 104.74 h, respectively. In the larval and pupal stages, individuals in the later developmental phases tended to be more tolerant to full submergence. The submergence tolerance of the immature stages of S. detrahens may reflect adaptation to an environment with fluctuating water levels.     

Experimental analysis of the evolutionary potential of hybridization in leopard frogs (Anura: Ranidae)

Artificial crossing using Rana blairi and R. sphenocephala frogs produced conspecific, interspecific and F₁ backcross hybrid genotypes. Although hybrid males used in the crosses were sterile, crosses using hybrid females produced viable larvae. The larval performance of resultant parental and hybrid genotypes was measured in experimental ponds at two densities. Density significantly affected survival, body mass at metamorphosis, larval period length and metamorphosis for all genotypes. Survival was the same among genotypes, but decreased with increasing density. Body mass at metamorphosis was the same among genotypes, but decreased with increasing density. Larval period increased with increasing density. Among genotypes, larvae from the conspecific R. sphenocephala cross had the shortest larval period while larvae from the conspecific R. blairi cross had the longest larval period. All hybrid genotypes had larval periods longer than R. sphenocephala, but shorter than R. blairi. The percentage of individuals metamorphosing was highest for R. sphenocephala ponds and lowest for R. blairi ponds across densities. Ponds with hybrid larvae produced a greater proportion of metamorphs than those with R. blairi larvae, but a smaller proportion than R. sphenocephala ponds. Equivalent or increased relative larval performance of hybrid genotypes under the conditions of our experiment suggests that hybrid genotypes may possess similar or higher fitnesses relative to their progenitors in some environments. Reduced fertility of adult hybrid males is a powerful selective force against natural hybridization. Nevertheless, because of the successful reproduction by female hybrids, natural hybridization has the potential to serve as a mechanism for the introgression of novel genetic variation that can benefit both R. blairi and R. sphenocephala in fluctuating and unpredictable larval environments. Experimental determination of the fitness of parental and hybrid genotypes is crucial for a comprehensive understanding of the effects of hybridization on organismal evolution.     

Morphological development of the swim bladder in hatchery-reared striped trumpeter Latris lineata

This study examined swim bladder morphogenesis in three cohorts of striped trumpeter (Latris lineata), a euphysoclist species with physostomous larvae. The swim bladder was first discernible 1–2 days after hatching as an evagination on the dorsal surface of the incipient digestive tract. It comprised a cluster of mesenchymal cells surrounding an inner primordium of epithelial cells. At mouth opening in larvae of 5.3 mm standard length (SL), the swim bladder was noticeably enlarged. Histologically, the swim bladder lumen was dilated and liquid filled. The pneumatic duct was first seen during the dilation stage and the rete mirabile began forming among the connective tissue surrounding the swim bladder. Initial swim bladder inflation occurred on day 11 post‐hatching in Cohort 1, at 14°C, and day 9 post‐hatching, in Cohorts 2 and 3, at 16°C. Histologically, the lumens of inflated swim bladders were ellipsoid and the epithelium was squamous, except for cuboidal gas gland cells at the anterio‐ventral and anterio‐lateral regions of the swim bladder. During the initial inflation interval the pneumatic duct was dilated in larvae both with and without swim bladder inflation. The pneumatic duct began to regress in some larvae over 7.5 mm SL. The swim bladder of striped trumpeter was similar to larvae of other altricial perciform marine fish in respect to organ derivation, tissue differentiation, luminal dilation and initial gaseous inflation. However, variations, particularly the delay in initial swim bladder inflation until after the start of feeding, were observed that could be fundamental to problems encountered during larval rearing.     

Synthesis and luminescence properties of a blue-emitting Sr(3.5) Y(6.5) O(2) (PO(4) )(1.5) (SiO(4) )(4.5) :Eu(2+) phosphor

A novel blue‐emitting Sr_3.5Y_6.5O₂(PO₄)_1.5(SiO₄)_4.5:Eu²⁺ phosphor was synthesized via a solid‐state reaction. Powder X‐ray diffraction (XRD) analysis demonstrated that the Sr_3.5Y_6.5O₂(PO₄)_1.5(SiO₄)_4.5 host had a hexagonal crystal structure in the space group P6₃/m and unit cell parameters a = 9.418 Å, c = 6.900 Å. The as‐prepared phosphor showed a blue emission and all the main emission peaks were located at around 466 nm for different excitation wavelengths of 297, 333 and 391 nm. The temperature dependence of the photoluminescence property was investigated in the range 20–250 °C, and the emission intensity decreased to 71% of the initial value at room temperature on increasing the temperature to 150 °C. According to the classical theory of fluorescent thermal quenching, the activation energy (ΔE) for the thermal quenching luminescence of the as‐prepared Sr_3.45Y_6.5O₂(PO₄)_1.5(SiO₄)_4.5:0.05Eu²⁺ phosphor was determined to be 0.20 eV. Copyright © 2011 John Wiley & Sons, Ltd.