Flash kinetics and spatial patterns of bioluminescence in the copepodGaussia princeps

Kinetics and local spatial patterns of bioluminescence in the mesopelagic copepodGaussia princeps (T. Scott), collected by net off the coast of southern California, USA, were investigated from 1986 to 1989. Luminescence elicited by single electrical stimuli began as a localized secretion from any of 16 widely distributed sites on the body. Appendage or body movements swept the particulate luminescent exudate away from the cuticle. Three types of single flashes were identified in response to single electrical stimuli, including a fast flash of ca. 2 s duration, a long flash of 7 s duration, and a 17 s slow flash. In addition, in 20% of the tests a fourth, two-component flash consisting of a fast or long component followed by a slow component was elicited. Frequency of the four flash types was dependent on the recovery time after collection. Shorter, less intense fast and long flashes occurred early in the recovery period, and longer, brighter slow and compound flashes became more common as recovery progressed. The laboratory handling protocol strongly affected total stimulable light (TSL). Strong handling resulted in a reduced TSL, which recovered to the original level upon termination of the stimulation. TSL and flash kinetics in the laboratory were highly dependent on the chronic laboratory stimulation protocol and represent an equilibrium between recovery of luminous reserves and re-stimulation. Flash kinetics and TSL were also affected by the frequency of stimulation. Higher stimulation rates resulted in greater temporal summation of the flashes, a decreased response duration, and a lower TSL. Stimulus frequency and duration therefore determine the nature of the bioluminescent response. Flash kinetics and TSL made with either in situ bathyphotometric measurements of laboratory measurements strongly depend on the extent of prestimulation, depletion of bioluminescent reserves, and the level of stimulation inherent with the particular device.     

Flash competition in male Photinus macdermotti fireflies

Summary The courtship of Photinus macdermotti fireflies involves a flash code in which the male emits a pair of flashes about two seconds apart and the female responds with a flash about 1.2 s after the second flash of the male pair. The male repeats his pair of courting flashes at varying intervals of four seconds or more. Lloyd (1979, 1981 a, b) observed that rival males in Florida sometimes interject flashes between the courtship flashes of the courting male. We have found that the competitive behavior of males of the same species on Long Island, New York, was somewhat different. Rival males timed their competing flashes from either the first or second of the original males's courting flashes. When a competing flash from the rival male was timed from the first courting flash it was synchronized with the original male's second courting flash. When a competing flash was timed from the second courting flash, a delayed flash resulted which appeared after the female's response. In either case the male's display period was preserved, insuring that the female would continue to respond. Either of these rival male flashes could sometimes induce the female to respond in his direction.     

Diel patterns of planktonic bioluminescence in the northern Sargasso Sea

Day-night changes in the vertical distribution, intensity, and size of bioluminescence flashes were investigated during a series of cruises to the northern Sargasso Sea in 1987 and 1988. Overall, depth integrated bioluminescence potential and flash density estimated from in situ measurements with a pumping bathyphotometer were 2 to 5 x higher at midnight than at midday. Depths from 50 to 100 m exhibited the most substantial day to night increases in bioluminescence potential and flash density. When classified by flash size (photon output per flash event), the increase from day to night was significant for all flash sizes, but was most dramatic for small flashes producing <7 x 10⁸ photons flash^-1. Bioluminescence potential and flash density increased 2 to 3 x during bathyphotometer measurements made at dusk. Bioluminescent light budgets estimated from day and night net collections in May and August 1987 also predicted 2.5 x higher nighttime than daytime mesoplankton bioluminescence. However, large bioluminescent taxa (mesoplankton) capable of significant vertical migrations only contributed on the order of 15% of the total bioluminescence in surface waters. Our results do not support the idea that most of the nightly increase in bioluminescence potential and flash density are due to vertical migration of bioluminescent organisms; rather they are consistent with an alternate view that photoinhibition of bioluminescent flashing by dinoflagellates may be primarily responsible for the diel patterns.     

Counterillumination in the Hawaiian bobtail squid,<Emphasis Type="Italic"> Euprymna scolopes</Emphasis> Berry (Mollusca: Cephalopoda)

The mutualism between the Hawaiian bobtail squid Euprymna scolopes and the luminescent symbiont Vibrio fischeri has been used extensively as a model system for studies ranging from co-speciation and biogeography to gene regulation and the evolution of pathogenesis. In this association, the luminescent bacterium V. fischeri is housed in a complex light organ within the mantle cavity of E. scolopes. Prior hypotheses have assumed that sepiolid squids in general utilize the bioluminescence produced by their V. fischeri symbionts for counterillumination, a behavior that helps squid camouflage themselves by matching down-welling moonlight via silhouette reduction. This assumption, based solely on the morphology of the squid light organ, has never been empirically tested for Euprymna in the laboratory. Here, we present data demonstrating that E. scolopes can modify the intensity of light produced by V. fischeri in the light organ as down-welling light intensity changes. Bacterial bioluminescence from the light organ is directly correlated with down-welling light intensity, suggesting that E. scolopes individuals utilize and control V. fischeri luminescence for counterillumination.Communicated by P.W. Sammarco, Chauvin     

Bioluminescence of deep-sea coronate medusae (Cnidaria: Scyphozoa)

Bioluminescence is the production of visible light by a living organism. The light commonly appears as flashes from point sources (involving one or more cells, usually described as photocytes) or as a glandular secretion. A visible flash usually involves synchronous light emission from a group of cells or, if from a single-celled organism such as a dinoflagellate, from a group of organelles. The number of cells (or organelles) responding synchronously is the main determinant of the flash intensity. Bioluminescence is a common phenomenon in many deep-sea animals and is widespread among the Cnidaria. In this paper, we compare and contrast in situ and laboratory recordings of the bioluminescent responses of specimens of the deep-sea scyphozoans Atolla wyvillei, Atolla vanhoffeni, Atolla parva, Nausithoe rubra, Paraphyllina intermedia, Periphyllopsis braueri and Periphylla periphylla. Displays in all seven species consist of localised flashes and propagated waves of light in the surface epithelium. The first few single waves propagate at rates of up to 60 cm s^-1 but subsequent ones in any sequence of stimuli gradually decrease in speed. After several single wave responses, a subsequent stimulus may elicit multiple waves that persist for several seconds. Following such a frenzy, the specimen becomes temporarily refractory to further stimuli, but if rested will recover its normal responses and may produce further frenzies. The dome area, situated above the coronal groove, of the genera Paraphyllina, Periphylla, and Nausithoe is covered with luminescent point sources. Such point sources are generally absent from the dome of species of Atolla. Captured specimens of A. parva also produce secretory bioluminescence, corroborating prior in situ observations of this ability. Secretory bioluminescence in P. periphylla takes the form of scintillating particles released from the lappet margins. We did not observe secretory displays in specimens of any other species in the laboratory, but one instance of apparent secretory luminescence was recorded in situ in a specimen of A. wyvillei.Communicated by J. P. Thorpe, Port Erin     

Three new modes of luminescence in the leiognathid fish Gazza minuta: Discrete projected luminescence,ventral body flash,and buccal luminescence

Three new modes of luminescence are described for Gazza minuta (Bloch) (Perciformes: Leiognathidae) as observed in specimens collected in the Philippines in April and May, 1982: discrete projected luminescence (DPL), ventral body flash, and buccal luminescence. DPL sharply contrasts with previously reported modes of diffuse luminescence in leiognathids (counterillumination and opercular flash) in being a pair of bright collimated beams of light emanating from the fish in an anteroventral direction. The brightness, coherence, directionality, and control of DPL suggest striking similarities to luminescence in anomalopid (flashlight) and monocentrid (pinecone) fishes and perhaps in certain apogonids (cardinalfishes). The structural correlate for DPL is a small clear patch of skin lying at the posterior margin of each opercular cavity. Luminescence from the internally located light organ traverses transparent bone and translucent muscle before passing through the clear skin of the patch area. Behavioral and anatomical observations of ventral body flash and buccal luminescence are also presented. These new modes of luminescence indicate a much greater than expected diversity of luminescent behaviors in leiognathids, perhaps greater than that of any other organism yet studied. The internal location of the light organ is recognised as providing the potential for this diversity.     

Trophic relations of the cephalopod Martialia hyadesi (Teuthoidea: Ommastrephidae) at the Antarctic Polar Front,Scotia Sea

Samples of the squid Martialia hyadesi were collected aboard two Japanese squid-jigging vessels carrying out commercial fishing trials at the Antarctic Polar Frontal Zone, north Scotia Sea, in February 1989. The dissected stomachs of 61 specimens were classified according to fullness and the contents were examined visually. Identifiable food items included fish sagittal otoliths, crustacean eyes, the lappets on euphausiid first antennule segments and cephalopod sucker rings. The most frequent items in the squid's diet were the myctophid fishes Krefftichthys anderssoni and Electrona carlsbergi, the euphausiid Euphausia superba and a hyperiid amphipod, probably Themisto gaudichaudi. A small proportion of the sample had been feeding cannibalistically. Total lengths of the fish prey were estimated from sagittal otolith size using published relationships. All fish were relatively small; 7 to 35% of squid mantle-length. However, it is possible that some heads of larger fish are discarded by the squid and so are not represented by otoliths in the stomach contents. Over the size range of squid in the sample there was no relationship between size of fish prey and size of squid. Similarly, when the squid sample was divided into groups according to prey categories: crustaceans, crustaceans+fish, fish, cephalopod, there was no evidence that dietary preference was related to squid size. The prevalence of copepod-feeding myctophids in the diet of this squid, which is itself a major prey item of some higher predators in the Scotia Sea, suggests that a previously unrecognised food chain: copepod-myctophid-M. hyadesi-higher predator, may be an important component of the Antarctic oceanic ecosystem.     

Sperm storage and mating in the deep-sea squid Taningia danae Joubin, 1931 (Oegopsida: Octopoteuthidae)

Spermatangium implantation is reported in the large oceanic squid Taningia danae, based on ten mated females from the stomachs of sperm whales. Implanted spermatangia were located in the mantle, head and neck (on both sides) or above the nuchal cartilage, under the neck collar and were often associated with incisions. These cuts ranged from 30 to 65 mm in length and were probably made by males, using the beak or arm hooks. This is the first time wounds facilitating spermatangium storage have been observed in the internal muscle layers (rather than external, as observed in some other species of squid). The implications of these observations for the mating behavior of the rarely encountered squid T. danae are discussed.     

Ontogeny of dispersal distances in young Spanish imperial eagles

Summary I studied factors influencing dispersal distances in 30 young Spanish imperial eagles (Aquila adalberti) radio-tagged in southwestern Spain in 1986–1990. The mean dispersal distance between the natal nest and the settling area was 138 km. Every young bird reached its maximum dispersal distance within 4 months of its departure from the natal population. No significant differences between the sexes were detected in maximum dispersal distance, but females spent more time in the more distant settling areas. Dispersal distance was not related to the date of departure from the natal population. Dispersal distance was significantly longer for birds that hatched earlier and that had lower blood urea levels, indicating that better-nourished young had longer displacements. These results are not in accordance with the competitive displacement hypothesis.     

Are behavioral syndromes invariant? Spatiotemporal variation in shy/bold behavior in squid

Behavioral syndromes are correlated suites of behavior, analogous to human personality traits. Most work to date has been taken from limited “snapshots” in space and time, with the implicit assumption that a behavioral syndrome is an invariant property, fixed by evolutionary constraints or adaptations. However, directional selection on two mechanistically independent traits (selective covariance) could also result in correlated behaviors. Previously, we have shown that shy/bold behavior in Southern dumpling squid (Euprymna tasmanica) across predator encounter and feeding risk contexts is genetically and phenotypically uncoupled, and hence potentially free to vary independently. Here, we collected data on shy/bold behaviors from two independent wild populations of squid in two different years to test whether behavioral correlations across these same two functional contexts vary through time and space. We detected significant influences of population, sex, and body size on the expression of boldness in squid within each functional context, and this was coupled with significant differences in relative population density and adult sex ratio. Despite these changes in behavior and demographic parameters, we found that correlations between boldness scores across the two functional contexts were largely absent in both wild populations of squid in both years. Our work suggests that some animal groups may be largely characterized by context-specific behavioral expression. A theoretical framework which conceptualizes behavioral syndromes resulting from context-specific behavioral rules may be needed to fully understand why behaviors are sometimes correlated, and why sometimes they are not.     

Photosynthesis and carbon storage between tides in a brown alga, Fucus vesiculosus

Intertidal macroalgae may spend a significant part of their lives in air. During photosynthesis in air, they encounter much lower concentrations of inorganic carbon than in seawater. Because they accumulate inorganic carbon from seawater, we investigated whether they similarly accumulate it from air. We measured photosynthesis in the intertidal species Fucus vesiculosus L. during 1990 and 1991 with a gas-phase O₂ electrode or CO₂-exchange apparatus in air and with a liquid-phase O₂ electrode in seawater. Maximum rates were rapid and similar in air and seawater regardless of the method. Tissue from seawater could carry on photosynthesis in CO₂-free air, indicating that carbon was stored in the tissue. After 2 h, this store was depleted and photosynthesis ceased. Supplying CO₂ in air replenished the store. Under identical conditions, terrestrial C₃ and C₄ species showed no evidence of this store, but a CAM (crassulacean acid metabolism) species did. However, in contrast to the CAM behavior, F. vesiculosus did not store CO₂ significantly in the dark. We found a small acid-releasable pool of carbon in the tissue that disappeared as photosynthesis depleted the carbon store. However, the pool was too small to account for the total carbon stored. While CO₂ was being acquired or released from the store in the light, photosynthesis was not inhibited by 21% O₂. These results indicate that there are two parallel paths for the supply of CO₂ to photosynthesis. The first depends on inorganic carbon in seawater or in air and supports rapid photosynthesis. The second involves CO₂ slowly released from an organic intermediate. The release protects CO₂ fixation from the inhibitory effects of 21% O₂. Photosynthesis in F. vesiculosus thus appears to be C₃-like in its rapid fixation of CO₂ from a small inorganic pool into phosphoglycerate. However, it is C₄-like in its pre-fixation of carbon in an organic pool in the light, and is CAM-like in its ability to slowly use this pool as a sole source of CO₂. The organic pool may serve to protect photosynthetic CO₂ fixation against the inhibitory effects of O₂ in air and in the boundary layer in seawater. Received: 6 March 1998 / Accepted: 16 October 1998     

Spatial and temporal variation in growth rates and maturity in the Indo-Pacific squid <Emphasis Type="Italic">Sepioteuthis lessoniana</Emphasis> (Cephalopoda: Loliginidae)

Age, growth and maturity parameters are described for the Indo-Pacific squid Sepioteuthis lessoniana both temporally and spatially (equatorial, tropical and subtropical). Tropical squid that grew through periods of warming water temperatures grew 9% faster than squid that grew through periods of cool water temperatures. The tropical spring-hatched and equatorial squid had similar growth rates (3.24, 3.18 g/day) and these were significantly faster than the tropical summer/autumn hatched squid (2.89 g/day). The oldest squid aged was 224 days, but the majority of individuals were <200 days. Subtropical squid were larger, older and matured later than equatorial and tropical spring-hatched squid. The mean weight of subtropical squid aged between 100 and 150 days was >400 g, 85% greater than tropical and equatorial squid. Geographical differences revealed that subtropical mature winter females and males had mean ages >150 days, respectively 17% and 23% older than their tropical mature winter counterparts. Temporal differences in age at maturity were also evident with tropical winter females and males having a mean age of ~140 days, respectively 41% and 25% older than their summer counterparts. Cooler subtropical and winter tropical squid had the heaviest gonads (>15 g ovaries, >1.5 g testes) compared to summer tropical and equatorial squid. However, relative gonad investment (GSI) values of the cooler squid were significantly lower with cool subtropical and winter tropical females having GSI values <3, which was about half the value of the warmer water females. This study revealed considerable plasticity in the size-at-age of this species. The tropical population had growth parameters that fluctuated between an equatorial strategy (fast growth, small body size, and small gonads) and a subtropical strategy (large body size, slower growth, and large gonads) depending on season.     

Temporal life history plasticity of the Southern Ocean squid <Emphasis Type="Italic">Todarodes filippovae</Emphasis> from waters off Tasmania,Australia

Population dynamics and maturity parameters were analysed for seasonal samples of the oceanic ommastrephid squid Todarodes filippovae from off the coast of Tasmania Australia from 2002 to 2004. Based on assumed daily periodicity in statolith increments, T. filippovae had a life cycle of about a year with the sexually dimorphic females reaching their larger size by predominantly growing faster than males. Due to the small sample size of males, analysis was undertaken on female individuals only. Growth in all samples was best described by a power curve and varied annually, with significantly faster growth in 2001 compared to the subsequent 2 years. Seasonal growth rates also varied with autumn- and winter-hatched squid significantly faster than summer-hatched squid. Spring growth rates were intermediate but not significantly different to the other three seasons. Peak hatching periods occurred in late autumn and early winter. ANOVA revealed a season × year interaction for mantle length and total body weight. Pairwise comparisons showed that the annual differences were likely driven by smaller squid in autumn 2002 compared to autumn samples in the other 2 years. Pairwise comparisons also revealed seasonal differences with winter-caught squid smaller than those from the majority of other samples. There were no seasonal effects on mature female gonad weights but females caught in 2002 had significantly lighter gonad weights than females from the following 2 years. There were no consistent trends among seasons or years in the age structure of mature females. This study revealed the plasticity and flexibility in growth and maturity parameters in this species, with a preference for faster growth during cooler periods.     

Eyes and extraocular photoreceptors in midwater cephalopods and fishes: Their roles in detecting downwelling light for counterillumination

The means of detecting downwelling light for counterillumination in several midwater animals has been examined. Eyes and extraocular photoreceptors (drosal photosensitive vesicles in the enoploteuthid squid Abraliopsis sp. B and pineal organs in the myctophid fish Myctophum spinosum) were alternately exposed to overhead light or covered by a small opaque shield above the animal and the bioluminescent response of the animal was monitored. Covering either the eyes or the extraocular photoreceptors resulted in a reduction in the intensity of counterillumination. Preliminary experiments examining the bioluminescent feedback mechanism for monitoring intensity of bioluminescence during counterillumination in the midwater squid Abralia trigonura indicated that the ventral photosensitive vesicles are responsible for bioluminescent feedback.     

Genetic variation in the neritic squid Loligo forbesi (Myopsida: Loliginidae) in the northeast Atlantic Ocean

Horizontal starch gel electrophoresis was employed to investigate levels of genetic differentiation between 13 samples of the neritic squid species Loligo forbesi Steenstrup obtained from throughout the majority of its known geographical range. Six enzyme loci identified in a preliminary study as being polymorphic were screened for variation between samples. No significant differences in allele distribution were detected between any of the samples obtained from the Faroe Bank in the north to Lisbon in the south, suggesting that squid throughout this range in the vicinity of the continental shelf are able to maintain panmixia, and effectively belong to a single population sharing a common gene pool. No clinal variation in allele distribution was detected throughout this range, a result which complements the findings of a detailed morphological companion study of the same individuals. Comparison of this homogenous European continental shelf population with squid from the Azores revealed highly significant (P<0.01) differences in allele distribution at five of the six polymorphic enzyme loci studied. A genetic identity value (I) equivalent to 0.93 over 33 loci was obtained. Analysis of F-statistics suggested migration rates between sites to be as low as one individual per five generations, a rate deemed insufficient under most models to prevent divergence by random genetic drift. The large distance and oceanic depths separating the Azores from continental Europe seem to present an effective barrier to gene flow to L. forbesi, a squid belonging to a family considered to be confined in distribution to relatively shallow, near coastal waters. The two populations of squid in the Azores and along the European continental shelf currently both ascribed to L. forbesi should therefore probably best be regarded as relative subspecies.     

Dinoflagellate luminescence increases susceptibility of zooplankton to teleost predation

The burglar alarm theory of bioluminescence was investigated by determining predation rates of a nocturnal teleost predator,Porichthys notatus, on nonluminescent kelp mysids illuminated by dinoflagellate flashes, between the fall and spring of 1989/1990. Mysids (Holmesimysis costata) were placed in aquaria containing varying concentrations (0 to 40 cells/ml) of the dinoflagellatePyrocystis fusiformis and a single midshipman fish. Controls usedP. fusiformis during their luminescence-inhibited day phase. Mysid swimming movements readily stimulated dinoflagellate luminescence. Flashes and prey strikes were observed simultaneously by image-intensifying and infrared video cameras on a splitscreen monitor. Predation rates increased at dinoflagellate concentrations of 3 to 15 cells/ml and decreased below controls at levels>20 cells/ml. Videotape analysis showed that at low concentrations (2 to 5 cells/ml), strike success rates exceeded 75% if prey were previously illuminated by a flash, but dropped below 50% at higher cell densities. Increased predation was attributed to luminescence revealing prey position. The decrease at higher concentrations was considered to be due to greater flash frequency providing a more diffuse and confusing target. The study demonstrates the effects of secondary luminescence on zooplankton predation at normally encountered dinoflagellate concentrations.     

Geographic variation in Loligo forbesi in the Northeast Atlantic Ocean: analysis of morphometric data and tests of causal hypotheses

Geographic variation in the squid Loligo forbesi was investigated using multivariate analysis of morphometric and meristic characters in samples of squid taken from 13 localities in the Northeast Atlantic Ocean. Two character sets, body morphometrics and beak morphometrics, indicated similar patterns of variation, with squid from the Azores differing markedly from those on the continental shelf. No consistent pattern was apparent in meristic data. Partial Mantel tests indicated that similarity matrices for morphological data were significantly correlated with distance matrices for (a) geographic proximity, (b) whether the capture site was on the continental shelf or the Azorean bank, and (c) (beak data only) average seasurface temperature at site of capture. Partial Mantel tests on allozyme data for the same individuals support hypothesis (b). The results suggest that L. forbesi in the Azores may reasonably be regarded as a distinct stock, differing significantly from L. forbesi on the continental shelf.     

Disparate forms of bioluminescence from the amphipodsCyphocaris faurei,Scina crassicornis andS. borealis

Bioluminescence from the gammarid amphipodCyphocaris faurei Barnard and the hyperiid amphipodsScina crassicornis (Fabricius) andScina borealis (Sars) was measured with a photomultiplier coupled to an integrating sphere, and with a video camera.C. faurei andS. crassicornis were collected in July 1986 and 1987 off Oahu, Hawaii;S. crassicornis was also collected in May 1987 in the northern Sargasso Sea, and in October 1988 north of Hawaii, andS. borealis was obtained in September 1989 off the southern California coast. Emission spectra were obtained with an optical multichannel analyzer. Bioluminescence ofC. faurei appeared as a secretion through integumentary pores on the telson and uropods, and as a glow from a single location on the cephalothorax. The emission spectrum was bimodal or unimodal, with distinct blue-green and orange peaks. In contrast, the bioluminescence ofS. crassicornis andS. borealis was internal and of significantly shorter duration and lower quantum emission, with a unimodal, bluegreen emission spectrum. Appropriate repetitive stimulation in all species induced temporally summated flashes with greater rise times, durations, and total quantum emission than luminescence induced by a single stimulus. The emission spectrum, flash kinetics, quantum emission, and mode of luminescence ofC. faurei are unique compared with those of all other previously investigated amphipod species.     

Fatty acid signatures of stomach contents reflect inter- and intra-annual changes in diet of a small pelagic seabird,the Thin-billed prion <Emphasis Type="Italic">Pachyptila belcheri</Emphasis>

In diet analyses of seabirds, fatty acid signatures (FAS) can be used to overcome biases due to differential digestion of prey and enable the analysis of very digested diet samples. We applied FAS analysis to stomach contents of a small sub-Antarctic seabird, the Thin-billed Prion Pachyptila belcheri, which feeds mainly on squid during incubation and on crustacea during chick rearing. This seasonal dietary switch of Thin-billed prions was reflected in differences in FAS in regurgitates, as were inter-annual differences in diet composition. A discriminant function analysis correctly classified 93.4% of cases with respect to year (2006–2008) and stage of the breeding cycle (incubation versus chick rearing). The dominant types of crustacea in the diet of Thin-billed prions (amphipods Themisto gaudichaudii, euphausiids, decapods Munida gregaria, and calanoid copepods) were distinguished well by characteristic FAS patterns. However, the FAS of the two main types of prey by volume, amphipods T. gaudichaudii and squid Gonatus antarcticus, were similar to each other. Although FAS were successfully applied in the analysis of prey in stomach contents of prions, FAS of some prey species were similar and may not be distinguishable from each other if used in quantitative diet analyses.     

Effects of ownership status,weight asymmetry,and case fit on the outcome of case contests in two populations of Agrypnia pagetana (Trichoptera : Phryganeidae) larvae

Summary The contest behavior of larvae from a dense and a sparse population of the caddisfly Agrypnia pagetana was studied in the laboratory. Fights were generally of short duration, and most fights were won by owners in both populations. Take-over contests lasted longer than non-takeover ones, indicating that owners in general used a more persistent strategy. Ownership was more important in the sparse population than in the dense population, but contest duration did not differ between the two populations. Effect of weight asymmetry was most pronounced in the dense population, and here the larger larvae usually won. However, when the intruding larvae were much larger than the owner, a low number of take-over contests were probably related to the inferior fit (low resource value) of small cases to the intruding larvae. In both populations the frequency of case takeover contests was low when the case fit to the intruder was low. We conclude that A. pagetana larvae use fighting strategies typical for contests over resources of low value relative to contest costs.