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Sexual mimicry among animals is widespread, but does it impart a fertilization advantage in the widely accepted 'sneak-guard' model of sperm competition? Here we describe field results in which a dramatic facultative switch in sexual phenotype by sneaker-male cuttlefish leads to immediate fertilization success, even in the presence of the consort male. These results are surprising, given the high rate at which females reject copulation attempts by males, the strong mate-guarding behaviour of consort males, and the high level of sperm competition in this complex mating system.

Acoustic telemetry has emerged as a leading approach to infer diel, tidal and lunar rhythmicity in the movements of aquatic organisms in a range of taxa. Typically, studies examine the relative frequency of detections from individuals tagged with acoustic transmitters, and then infer patterns in the species’ behaviour, but studies to date have not controlled for factors that may influence tag detection patterns in the absence of animal behaviour. We compared patterns in acoustic detections from tagged cuttlefishSepia apamaand several fixed-location control tags, and used these data to highlight the danger of misinterpreting patterns in the absence of adequate controls. Cuttlefish and control tags displayed similar detection patterns, and correcting cuttlefish-detection data for the influence of environmental factors resulted in the opposite pattern of cuttlefish activity displayed prior to correction. This study highlights the danger of using acoustic data to infer animal behaviour in the absence of adequate controls.

Incremental refinements were made to a generic Nordmøre-grid to minimise bycatches of blue swimmer crabs Portunus armatus and giant cuttlefish Sepia apama, while maintaining catches of western king prawns Melicertus latisulcatus in the Spencer Gulf penaeid-trawl fishery. These refinements involved varying bar spaces, escape-exit areas and guiding-panel lengths, and were compared against a conventional trawl. Catches of teleosts and M. latisulcatus largely remained unaffected by the changes. Maximum reductions in P. armatus and S. apama bycatches (both ~90%) were achieved with a Nordmøre-grid comprising 38-mm bar spaces, 0.81- or 1.05-m(2) escape exits and a 2.7-m guiding panel. Catching fewer P. armatus should reduce abrasion and crushing of M. latisulcatus in the codend and so increase the value of this targeted species. While noting some unresolved operational concerns, these results demonstrate the potential improvements in selectivity in this fishery using a Nordmøre-grid, primarily by mechanical separation.

1. Estimating the metabolic rate of animals in nature is central to understanding the physiological, behavioural and evolutionary ecology of animals. Doubly labelled water and heart-rate methods are the most commonly used approaches, but both have limitations that preclude their application to some systems. 2. Accelerometry has emerged as a powerful tool for estimating energy expenditure in a range of animals, but is yet to be used to estimate field metabolic rate in aquatic taxa. We combined two-dimensional accelerometry and swim-tunnel respirometry to estimate patterns of energy expenditure in giant Australian cuttlefish Sepia apama during breeding. 3. Both oxygen consumption rate () and swimming speed showed strong positive associations with body acceleration, with coefficients of determination comparable to those using similar accelerometers on terrestrial vertebrates. Despite increased activity during the day, field metabolic rate rarely approached , and night-time was similar to that at rest. 4. These results are consistent with the life-history strategy of this species, which has a poor capacity to exercise anaerobically, and a mating strategy that is visually based. With the logistical difficulties associated with observation in aquatic environments, accelerometry is likely to prove a valuable tool for estimating energy expenditure in aquatic animals.

It might seem obvious that a camouflaged animal must generally match its background whereas to be conspicuous an organism must differ from the background. However, the image parameters (or statistics) that evaluate the conspicuousness of patterns and textures are seldom well defined, and animal coloration patterns are rarely compared quantitatively with their respective backgrounds. Here we examine this issue in the Australian giant cuttlefish Sepia apama. We confine our analysis to the best-known and simplest image statistic, the correlation in intensity between neighboring pixels. Sepia apama can rapidly change their body patterns from assumed conspicuous signaling to assumed camouflage, thus providing an excellent and unique opportunity to investigate how such patterns differ in a single visual habitat. We describe the intensity variance and spatial frequency power spectra of these differing body patterns and compare these patterns with the backgrounds against which they are viewed. The measured image statistics of camouflaged animals closely resemble their backgrounds, while signaling animals differ significantly from their backgrounds. Our findings may provide the basis for a set of general rules for crypsis and signals. Furthermore, our methods may be widely applicable to the quantitative study of animal coloration.

Living under intense predation pressure, octopuses evolved an effective and impressive camouflaging ability that exploits features of their surroundings to enable them to \"blend in.\" To achieve such background matching, an animal may use general resemblance and reproduce characteristics of its entire surroundings, or it may imitate a specific object in its immediate environment. Using image analysis algorithms, we examined correlations between octopuses and their backgrounds. Field experiments show that when camouflaging, Octopus cyanea and O. vulgaris base their body patterns on selected features of nearby objects rather than attempting to match a large field of view. Such an approach enables the octopus to camouflage in partly occluded environments and to solve the problem of differences in appearance as a function of the viewing inclination of the observer.

While a suite of approaches have been developed to describe the scale, rate and spatial structure of exchange among populations, a lack of mechanistic understanding will invariably compromise predictions of population-level responses to ecosystem modification. In this study, we measured the energetics and sustained swimming capacity of giant Australian cuttlefish Sepia apama and combined these data with information on the life-history strategy, behaviour and circulation patterns experienced by the species to predict scales of connectivity throughout parts of their range. The swimming capacity of adult and juvenile S. apama was poor compared to most other cephalopods, with most individuals incapable of maintaining swimming above 15 cm s-1. Our estimate of optimal swimming speed (6-7 cm s-1) and dispersal potential were consistent with the observed fine-scale population structure of the species. By comparing observed and predicted population connectivity, we identified several mechanisms that are likely to have driven fine-scale population structure in this species, which will assist in the interpretation of future population declines.

Many animals produce multiple displays during agonistic interactions, but the roles of these displays often remain ambiguous. The hierarchical signaling hypothesis has been proposed to explain their occurrence and posits that different displays convey different levels of aggressive intent, allowing signalers to communicate graded series of threats. This hypothesis suggests that low-risk signals, typically performed at the beginning stages of an interaction, are strong predictors of high-risk signals but weak predictors of physical aggression. High-risk signals, typically produced at later stages of an interaction, are strong predictors of physical aggression. We used giant Australian cuttlefish, Sepia apama, to test these predictions. We combined field observations and laboratory video playback experiments to determine whether (i) male cuttlefish produce specific sequences of displays, (ii) displays in early stages of an interaction predict displays in later stages of an interaction, and (iii) displays produced in later stages of an interaction provide reliable predictors of physical aggression. Field observations suggested that males progressed from low-risk to high-risk signals (i.e., visual signaling to physical aggression). Video playback results zrevealed that the low-risk frontal display, produced during early stages of an interaction, conveys reliable information about the cuttlefish's intent to escalate to later stages of visual signaling. Both the shovel and lateral displays were produced during the later stages of signaling and were reliable predictors of subsequent physical aggression. Our study supports the hierarchical signaling hypothesis and provides new empirical insights into how cuttlefish use progressive visual signaling to convey increasing levels of threat.

Animals attempt to maximize their reproductive fitness by employing discrimination tactics that increase their fertilization success. Semelparous species are faced with high energy and time constraints. These constraints are predicted to affect the extent of discrimination tactics that may be employed. The semelparous giant Australian cuttlefish, Sepia apama, seek multiple mates during their single breeding season, yet the discrimination tactics used to assess mates remain ambiguous. We combined field observations and laboratory-controlled mating experiments to determine (i) the relationship between the female signal (i.e., white lateral stripe) and mating outcome and (ii) the effects of the white lateral stripe, receptive postures, mating history, and familiarity on mating behavior. Females were less likely to mate when they expressed the white lateral stripe, suggesting that this signal conveys non-receptivity. Female mating history appeared to predict their likelihood of mating because females that had not recently mated were more likely to perform receptive postures and less likely to express the white lateral stripe. Familiarity with the males did not affect female expression of the white lateral stripe nor receptive postures. In males, mating behavior was not affected by the females’ expression of the white lateral stripe nor female receptive postures; however, familiarity with the female did affect male mating behavior. Males exerted a strong preference for unfamiliar females, providing evidence for familiarity discrimination. This research suggests that distinct selection pressures may be driving different discrimination capabilities in the sexes and provides the first empirical evidence of familiarity discrimination in a cephalopod species.

While a suite of approaches have been developed to describe the scale, rate and spatial structure of exchange among populations, a lack of mechanistic understanding will invariably compromise predictions of population-level responses to ecosystem modification. In this study, we measured the energetics and sustained swimming capacity of giant Australian cuttlefish Sepia apama and combined these data with information on the life-history strategy, behaviour and circulation patterns experienced by the species to predict scales of connectivity throughout parts of their range. The swimming capacity of adult and juvenile S. apama was poor compared to most other cephalopods, with most individuals incapable of maintaining swimming above 15 cm s(-1). Our estimate of optimal swimming speed (6-7 cm s(-1)) and dispersal potential were consistent with the observed fine-scale population structure of the species. By comparing observed and predicted population connectivity, we identified several mechanisms that are likely to have driven fine-scale population structure in this species, which will assist in the interpretation of future population declines.