Cephalopod dynamic camouflage: bridging the continuum between background matching and disruptive coloration

Individual cuttlefish, octopus and squid have the versatile capability to use body patterns for background matching and disruptive coloration. We define—qualitatively and quantitatively—the chief characteristics of the three major body pattern types used for camouflage by cephalopods: uniform and mottle patterns for background matching, and disruptive patterns that primarily enhance disruptiveness but aid background matching as well. There is great variation within each of the three body pattern types, but by defining their chief characteristics we lay the groundwork to test camouflage concepts by correlating background statistics with those of the body pattern. We describe at least three ways in which background matching can be achieved in cephalopods. Disruptive patterns in cuttlefish possess all four of the basic components of ‘disruptiveness’, supporting Cott''s hypotheses, and we provide field examples of disruptive coloration in which the body pattern contrast exceeds that of the immediate surrounds. Based upon laboratory testing as well as thousands of images of camouflaged cephalopods in the field (a sample is provided on a web archive), we note that size, contrast and edges of background objects are key visual cues that guide cephalopod camouflage patterning. Mottle and disruptive patterns are frequently mixed, suggesting that background matching and disruptive mechanisms are often used in the same pattern.     

Cephalopod and Groundfish Landings: Evidence for Ecological Change in Global Fisheries?

Cephalopod fisheries are among the few still with some local potential for expansion; in fact, as groundfish landings have declined globally, cephalopod landings have increased. We propose the hypothesis that, although increased cephalopod landings may partly reflect increased market demand, overfishing groundfish stocks has positively affected cephalopod populations. Data from 15 key FAO areas reveal that, with the exception of the north- east Atlantic, cephalopod landings have increased significantly over the last 25 years while groundfish have risen more slowly, remained stable, or declined. In terms of volume, cephalopods have not replaced groundfish. This is hypothesized as owing to the shorter life cycle of cephalopods, and rapid turnover and lower standing stocks than for longer-lived finfish species. Under high fishing pressure, groundfish are probably poor competitors, having less opportunity for spawning and replacement. In West Africa, the Gulf of Thailand and Adriatic there is strong circumstantial evidence that fishing pressure has changed ecological conditions and cephalopod stocks have increased as predatory fish have declined. We recommend that this hypothesis be tested thoroughly in other areas where suitable data exist. Most coastal and shelf cephalopod fisheries are likely to be fully exploited or overexploited, and current annual fluctuations in cephalopod landings are probably largely environmentally-driven.     

Extraction of chromatophores from Rhodospirillum rubrum in aqueous two-phase systems: A method for large-scale isolation of membrane particles

Chromatophores, membrane vesicles with the capacity of cyclic photophosphorylation, have been isolated from Rhodospirillum rubrum cells on a pilot plant scale. Results of disintegration in a glass bead mill and in a high pressure homogenizer were compared. The chromatophores were isolated from the crude extract by extraction in aqueous two-phase systems. In systems of polyethylene glycol (PEG) and dextran the chromatophores were partitioned to the upper PEG phase by the addition of PEG-palmitate. Most of the proteins and nucleic acids were forced to the bottom phase by addition of sodium chloride. Methods to prevent precipitation of the chromatophores were studied.     

The dual function of barred plumage in birds: camouflage and communication

A commonly held principle in visual ecology is that communication compromises camouflage: while visual signals are often conspicuous, camouflage provides concealment. However, some traits may have evolved for communication and camouflage simultaneously, thereby overcoming this functional compromise. Visual patterns generally provide camouflage, but it was suggested that a particular type of visual pattern – avian barred plumage – could also be a signal of individual quality. Here, we test if the evolution of sexual dimorphism in barred plumage, as well as differences between juvenile and adult plumage, indicate camouflage and/or signalling functions across the class Aves. We found a higher frequency of female- rather than male-biased sexual dimorphism in barred plumage, indicating that camouflage is its most common function. But we also found that, compared to other pigmentation patterns, barred plumage is more frequently biased towards males and its expression more frequently restricted to adulthood, suggesting that barred plumage often evolves or is maintained as a sexual communication signal. This illustrates how visual traits can accommodate the apparently incompatible functions of camouflage and communication, which has implications for our understanding of avian visual ecology and sexual ornamentation.     

On the psychology of cooperation in humans and other primates: combining the natural history and experimental evidence of prosociality

In any given species, cooperation involves prosocial acts that usually return a fitness benefit to the actor. These acts are produced by a set of psychological rules, which will be similar in related species if they have a similar natural history of cooperation. Prosocial acts can be (i) reactive, i.e. in response to specific stimuli, or (ii) proactive, i.e. occur in the absence of such stimuli. We propose that reactive prosocial acts reflect sensitivity to (i) signals or signs of need and (ii) the presence and size of an audience, as modified by (iii) social distance to the partner or partners. We examine the evidence for these elements in humans and other animals, especially non-human primates, based on the natural history of cooperation, quantified in the context of food sharing, and various experimental paradigms. The comparison suggests that humans share with their closest living relatives reactive responses to signals of need, but differ in sensitivity to signs of need and cues of being watched, as well as in the presence of proactive prosociality. We discuss ultimate explanations for these derived features, in particular the adoption of cooperative breeding as well as concern for reputation and costly signalling during human evolution.     

Cone visual pigments in two marsupial species: the fat-tailed dunnart (Sminthopsis crassicaudata) and the honey possum (Tarsipes rostratus)

Uniquely for non-primate mammals, three classes of cone photoreceptors have been previously identified by microspectrophotometry in two marsupial species: the polyprotodont fat-tailed dunnart (Sminthopsis crassicaudata) and the diprotodont honey possum (Tarsipes rostratus). This report focuses on the genetic basis for these three pigments. Two cone pigments were amplified from retinal cDNA of both species and identified by phylogenetics as members of the short wavelength-sensitive 1 (SWS1) and long wavelength-sensitive (LWS) opsin classes. In vitro expression of the two sequences from the fat-tailed dunnart confirmed the peak absorbances at 363 nm in the UV for the SWS1 pigment and 533 nm for the LWS pigment. No additional expressed cone opsin sequences that could account for the middle wavelength cones could be amplified. However, amplification from the fat-tailed dunnart genomic DNA with RH1 (rod) opsin primer pairs identified two genes with identical coding regions but sequence differences in introns 2 and 3. Uniquely therefore for a mammal, the fat-tailed dunnart has two copies of an RH1 opsin gene. This raises the possibility that the middle wavelength cones express a rod rather than a cone pigment.     

Plant signalling: the opportunities and dangers of chemical communication

The notion of chemical communication between plants and other organisms has gone from being viewed as a fringe idea to an accepted ecological phenomenon only recently. An Organized Oral Session at the August 2010 Ecological Society of America meeting in Pittsburgh examined the role of plant signalling both within and between plants, with speakers addressing the remarkably wide array of effects that plant signals have on plant physiology, species interactions and entire communities. In addition to the familiar way that plants communicate with mutualists like pollinators and fruit dispersers through both chemical and visual cues, speakers at this session described how plants communicate with themselves, with each other, with herbivores and with predators of those herbivores. These plant signals create a complex odour web superimposed upon the more classical food web itself, with its own dynamics in the face of exotic species and rapid community assembly and disassembly.     

The origins of gestures and language: history,current advances and proposed theories

Investigating in depth the mechanisms underlying human and non‐human primate intentional communication systems (involving gestures, vocalisations, facial expressions and eye behaviours) can shed light on the evolutionary roots of language. Reports on non‐human primates, particularly great apes, suggest that gestural communication would have been a crucial prerequisite for the emergence of language, mainly based on the evidence of large communication repertoires and their associated multifaceted nature of intentionality that are key properties of language. Such research fuels important debates on the origins of gestures and language. We review here three non‐mutually exclusive processes that can explain mainly great apes' gestural acquisition and development: phylogenetic ritualisation, ontogenetic ritualisation, and learning via social negotiation. We hypothesise the following scenario for the evolutionary origins of gestures: gestures would have appeared gradually through evolution via signal ritualisation following the principle of derived activities, with the key involvement of emotional expression and processing. The increasing level of complexity of socioecological lifestyles and associated daily manipulative activities might then have enabled the acquisition and development of different interactional strategies throughout the life cycle. Many studies support a multimodal origin of language. However, we stress that the origins of language are not only multimodal, but more broadly multicausal. We propose a multicausal theory of language origins which better explains current findings. It postulates that primates' communicative signalling is a complex trait continually shaped by a cost–benefit trade‐off of signal production and processing of interactants in relation to four closely interlinked categories of evolutionary and life cycle factors: species, individual and context‐related characteristics as well as behaviour and its characteristics. We conclude by suggesting directions for future research to improve our understanding of the evolutionary roots of gestures and language.     

Oviposition preference and life history traits in cactophilic Drosophila koepferae and D. buzzatii in association with their natural hosts

Drosophila koepferae and D. buzzatii are two closely related cactophilic species inhabiting the arid lands of southern South America. Previous studies have shown that D. buzzatii breeds primarily on the necrotic cladodes of several Opuntia cacti and D. koepferae on the rotting stems of columnar cacti of the genera Trichocereus and Cereus. In this paper, we analyze the patterns of host plant utilization in a locality where both Drosophila species are sympatric. Field studies showed an absence of differential attraction of adult flies to the rots of two major host cacti: O. sulphurea and T. terschekii. However, the proportion of D. buzzatii flies emerged from the rotting cladodes of O. sulphurea was significantly higher than in T. terschekii. In laboratory experiments, egg to adult viability in single species cultures varied when both Drosophila species were reared in media prepared with O. sulphurea or T. terschekii. In addition, between-species comparisons of flies emerged from single species cultures showed that D. buzzatii adults were smaller and developed faster than D. koepferae. Furthermore, analysis of flies emerged in mixed species cultures showed differences in oviposition preference and oviposition behavior. We discuss the observed between-species differences and suggest that these traits are the result of adaptation to specific patterns of spatial and temporal predictability of their respective preferred host plants: columnar are less dense and less ephemeral resources, whereas the opuntias are more abundant, and fast rotting cacti. This revised version was published online in July 2006 with corrections to the Cover Date.     

The relationship between body weight and natural mortality in juvenile and adult fish: a comparison of natural ecosystems and aquaculture

The relationship between body weight and natural mortality in juvenile and adult fish was analysed for different aquatic ecosystems: lakes, rivers, the ocean, and pond, cage and tank aquaculture systems. Mortality was modelled as a power function of weight, and the parameters b (exponent) and M_u (mortality at the unit weight of 1 g) estimated for fish in the six ecosystems, as well as within selected populations, species and families. At the ecosystem level, no significant differences in parameters were found between lakes, rivers and the ocean and a joint mortality-weight relationship for all natural ecosystems was estimated with parameters b=?0.288 (90% CL[?0.315, ?0.261]) and M_u=3.00 (90% CL[2.70, 3.30]) year^?1. Among the culture systems, mortality-weight relationships in ponds and cages were not significantly different and a joint relationship was estimated. The weight exponents of mortality in ponds/cages and tanks were very similar at about b=?0.43, and significantly more negative than in natural ecosystems. Mortalities at unit weight were significantly lower in tanks (0.91 year^?1) than in ponds/cages (2.24 year^?1), and both were significantly lower than in natural ecosystems. No systematic differences were found between the mortality-weight relationships determined for individual populations, species or families, and fish in the respective ecosystems. It is hypothesized that aquaculture mortality-weight relationships indicate the allometric scaling of non-predation mortality, which is therefore more strongly size dependent than predation mortality. If non predation mortality in natural ecosystems shows a similar scaling with body weight, then the allometric exponent of predation mortality must be less negative than that observed for total natural mortality. Implications of the established mortality-weight relationships for aquaculture and culture-based fisheries are discussed.     

运动对时距知觉的影响及其神经机制

在运动过程中,时距知觉的能力非常重要,能帮助个体对时长进行判断及对事件的发生做出预测和准备.近年来,越来越多的研究发现运动本身会直接影响个体的时距知觉.本文分别从运动参数、运动阶段、视觉运动刺激和运动有关的个体因素四个方面梳理了运动对时距知觉产生影响的行为学证据.目前已经有大量研究从不同角度证明,大脑运动系统组成了支持...     

Ultraviolet reflectance and cryptic sexual dichromatism in the ocellated lizard, Lacerta (Timon) lepida (Squamata: Lacertidae)

Ultraviolet (UV) colorations have garnered extensive theoretical and empirical treatment in recent years, although the majority of studies have concerned themselves with avian taxa. However, many lizards have acute visual systems with retinal photoreceptors that are sensitive to UV wavelengths, and also display UV-reflecting colour patches. In the present study, we used UV photography and full-spectrum reflectance spectrophotometry to describe intra- and intersexual colour variation in adult ocellated lizards Lacerta ( Timon ) lepida and to obtain evidence of UV-based ornamentation. We also investigated whether any colour traits correlate with morphological traits potentially related to individual quality. The results obtained show that the prominent eyespots and blue outer ventral scales (OVS) that ocellated lizards have on their flanks reflect strongly in the UV range and are best described as UV/blue in coloration. The eyespots of males are larger and cover a larger surface area than those of females. However, these differences can be entirely accounted for by sex differences in body size, with males being generally larger than females. We also found differences in the shape of reflectance curves from males and females, with the eyespots and blue OVS of males being more UV-shifted than those of females. Other body regions have extremely low UV reflectance and are not sexually dichromatic. Eyespot size and the total surface area covered by eyespots increases with body size in males but not in females, suggesting that they may be signalling an intrinsic individual characteristic such as body size or male fighting ability. We also discuss the alternative and non-exclusive hypothesis that eyespots may function in lizards of both sexes as protective markings against predators.  © 2009 The Linnean Society of London, Biological Journal of the Linnean Society , 2009, 97 , 766–780.     

Explaining the global biodiversity gradient: energy, area, history and natural selection

Hubbell's neutral theory of biodiversity is used to investigate the decline in species richness from the tropics to the poles. On this basis, biodiversity should correlate with productivity or climate (there is strong statistical evidence for this), with the latitudinal width of the continents (insufficiently investigated as yet), and with the speciation rate (which may not vary in such a way as to produce a planetary gradient). According to the neutral, model biodiversity will vary with the area of the “metacommunity”: it is suggested that at higher latitudes species disperse most readily east–west, within their climatic belt, but that the relatively uniform temperature across the intertropical belt allows isotropic dispersal there. Metacommunities within the tropics may therefore be an order of magnitude larger than those at other latitudes. This could explain the extra bulge in the gradient in the tropics. It is further possible that long-term and cyclical climate change generates a tropic-pole gradient. Niche assembly models will also explain tropical biodiversity, but the enhanced division of habitat may be the result, not the cause, of the species richness. The neutrality–competition debate in ecology closely parallels the neutrality–natural selection debate in evolution and may be equally hard to resolve.

Zusammenfassung

Hubbells neutrale Theorie der Biodiversität wird genutzt um den Rückgang des Artenreichtums von den Tropen zu den Polen zu untersuchen. Auf dieser Basis sollte die Biodiversität mit der Produktivität oder dem Klima (es gibt überzeugende statistische Beweise dafür) korrelieren, mit der Ausdehnung der Kontinente in geografischer Breite (bisher unzureichend untersucht) und mit der Artbildungsrate (welche möglicherweise nicht in der Weise variiert, als dass sie einen planetarischen Gradienten erzeugen kann).Dem neutralen Model entsprechend wird die Biodiversität mit dem Areal der “Metagemeinschaft” variieren. Es wird behauptet, dass sich Arten in höheren Breiten am leichtesten innerhalb ihres klimatischen Gürtels in Ost–West-Richtung ausbreiten, dass aber die relativ gleichmäßige Temperatur des innertropischen Gürtels dort eine isotrope Ausbreitung erlaubt.Metagemeinschaften in den Tropen können daher um eine Größenordnung größer sein als in anderen Breiten. Dies könnte die zusätzliche Ausdehnung des Gradienten in den Tropen erklären. Es ist darüber hinaus möglich, dass langfristige und zyklische Klimaveränderungen einen Gradienten von den Tropen zu den Polen generieren. Modelle der Nischenanordnung erklären ebenfalls tropische Biodiversität. Die verstärkte Habitataufteilung könnte jedoch das Ergebnis und nicht der Grund des Artenreichtums sein. Die Neutralitäts–Konkurrenz-Debatte in der Ökologie ähnelt sehr der Neutralitäts–Selektions-Debatte in der Evolution und mag ähnlich schwer zu lösen sein.     

The natural history of a monogamous coral-reef fish, Valenciennea strigata (Gobiidae): 2. behavior, mate fidelity and reproductive success

This study examined the behavior and reproduction of a monogamous coral-reef fish, Valenciennea strigata, to determine mate fidelity and the proximate causes of monogamy. Most fish were found in monogamous pairs that remained together over several rounds of reproduction. Pairs stayed within close proximity to each other and their burrows. Females fed at a higher rate than their mates, while males spent more time maintaining burrows. Females spawned every 13 days; males guarded eggs in the burrow for 2–3 days. Although females limited the RS of males, males did not mate polygynously under natural conditions. Reproductive success (RS) was affected primarily by survival, and secondarily by size. Both sexes enforced monogamy by guarding their mates. Three factors facilitated mate guarding: (1) all males were able to hold a nest site, (2) both sexes showed strong site fidelity, and (3) residents had an advantage in contests over mates. Thus, mates were economically defensible. Additionally, females formed a crescent of dark pigments on their abdomen that resembled a gravid condition; these marks may enhance continuation of the pair bond. Both sexes preferred large mates, and pairs were positively assorted by size. Males benefited from guarding large females because fecundity increased with size. Females may benefit from the burrowing of males, and larger males should be better burrowers.     

Evolution of life history traits in Leporidae: a test of nest predation and seasonality hypotheses

Recently, it has been proposed that adult mortality schedules may be responsible for latitudinal patterns of life history variation in passerine birds, whereas nest predation only could explain within latitude patterns. Unfortunately, no independent test has been performed regarding the importance of nest predation with different taxa. In the present study, seasonality and nest predation hypotheses explaining variations in gestation time and litter size in 17 lagomorph species were tested. Among latitude patterns were analysed using the phylogenetic independent contrast method of Felsenstein and within latitude patterns were analysed by the pairwise comparative method. The results obtained indicate that latitudinal patterns observed in both variables are explained by different factors: seasonality for litter size and nest predation for gestation time. Litter size variations within latitudes are also explained by differences in nest predation, supporting previous hypotheses. In conclusion, the present study suggests that, when compared among latitudes, different life history traits (e.g. litter size and gestation time) may be shaped by different selective forces and that the effects of nest predation may be high both within and between latitudes.  © 2006 The Linnean Society of London, Biological Journal of the Linnean Society , 2006, 88 , 603–610.     

The austral cordgrass Spartina densiflora Brong.: its taxonomy, biogeography and natural history

Aim During the last 20 years, the austral cordgrass Spartina densiflora has been recorded aggressively invading estuarine environments in the USA, Spain and Morocco. Whereas this species is one of the three most widely distributed worldwide, it is among the least studied within the genus. The objective of this work is to integrate baseline information about the taxonomy, global distribution, centre of origin, and general ecology of S. densiflora in native and invaded marshes worldwide in order to help to strengthen management efforts currently directed at controlling or eradicating it from locations where it has been introduced. Location World‐wide. Methods I review, update and discuss relevant information about S. densiflora published in peer‐reviewed papers, including those in journals with limited international distribution. I also review theses and major technical reports containing critical up‐to‐date information. Results This work indicates that, although S. densiflora remains in need of thorough scientific attention, key information on its taxonomy, distribution and invasive biology has been overlooked because it was published in languages other than English, and/or in journals with restricted distribution. Main conclusions Spartina densiflora seems to have originated along the east coast of South America; today, however, many other regions worldwide serve as donors for this invasive species, including Chile, the USA, Spain and Morocco. Spartina densiflora is a bioengineer organism, tolerant of a broad spectrum of environmental conditions and able to re‐shape the structure of invaded communities not just in mudflats, but also on sandy, muddy, and rocky shores as well as on cobble beaches. Only by integrating local‐scale research conducted in different geographical regions will we be able to understand the between‐site variations of its biological cycle, which in turn will aid in the design of more effective conservation strategies.