Experimental support for the cost–benefit model of lizard thermoregulation

According to Huey and Slatkin’s [Q Rev Biol 51:363–384, 1976] cost–benefit model of behavioural thermoregulation, lizards should adjust their thermoregulatory strategy between active thermoregulation and thermoconformity (no thermoregulation) according to the costs (time and energy spent thermoregulating, exposure to predators), benefits (optimised physiological performance) and thermal quality of environment associated with a given situation. However, Gilchrist’s [Am Nat 146:252–270, 1995] model of thermal specialisation suggests that apparently costly mechanisms of behavioural thermoregulation can greatly increase fitness if the optimal body temperature is achieved. Field studies of ectotherm thermoregulatory strategies under extreme cold conditions and experiments testing the effects of cool environments on thermoregulatory behaviour are surprisingly scarce. We conducted laboratory experiments to test if common lizards Zootoca vivipara (an active thermoregulator in the field) are able to switch between active thermoregulation and thermoconformity in response to different thermal environments. We found that lizards in treatments with an opportunity to reach their preferred body temperature thermoregulated accurately, maintained their level of daily activity and improved their body condition considerably. In contrast, lizards in the treatment where the preferred body temperature could not be reached became thermoconformers, decreased their daily activity (except for gravid females) and did not increase their body condition. Our results show that lizards can indeed change their thermoregulatory strategy but stress that maintaining the preferred body temperature and, thus, optimising the physiological performance have high priority in lizard behaviour.     

The role of size and aggression in intrasexual male competition in a social lizard species, Egernia whitii

Competition between males is a key component of the agonistic intrasexual interactions that influence resource acquisition, social system dynamics, and ultimately reproductive success. Sexual selection theory predicts that traits that enhance success in intrasexual competition (particularly male–male competition) should be favored. In vertebrates, this often includes body size and aggression, with larger and/or more aggressive males outcompeting smaller or less aggressive conspecifics. The majority of studies consider aggression as a flexible trait which responds to local social or environmental conditions. However, aggression frequently shows considerable within-individual consistency (i.e., individuals have identifiable aggressive behavioral types). Little is known about how such consistency in aggression may influence competition outcomes. We integrated a detailed field study with a laboratory experiment to examine how a male’s aggressive phenotype and his size influence competitive interactions in Egernia whitii, a social lizard species which exhibits strong competition over resources (limited permanent shelter sites and basking sites). Individual aggression and size did not predict competition outcome in the laboratory nor did they predict home range size, overlap, or reproductive success in the field. However, winners of laboratory trial contests maintained consistent aggressive phenotypes while consistency in aggression was lost in losers. We suggest that aggression may be important in other functional contexts, such as parental care, and that alternative traits, such as fighting experience, may be important in determining competition outcome in this species.     

The role of learning in the mating biology of a sweat bee Lasioglossum zephyrum (Hymenoptera: Halictidae)

Summary Results from experiments on the role of learning in the mating biology of a sweat bee, Lasioglossum zephyrum (Hymenoptera: Halictidae), are described in this paper. Male learning of individual female odors is important in natural populations (Table 1), as has been shown in the laboratory. Four other hypotheses are unlikely to account for the observed behavior: (1) Female odors dissipate rapidly; (2) Males learn and then avoid the study area; (3) Males or females produce repellents which are effective against other males; or (4) males recognize their own odor on previously-contacted females, which they subsequently avoid. Regarding questions of male preference and optimal outbreeding, Tables 2 and 3 show there are no consistent preferences for more novel or less novel female odors.     

Marine biology: the role of accommodation in shaping marine biodiversity

A review of evidence from two kinds of studies conducted in the marine environment suggests a species relationship not previously recognized as being consistent and widespread. In the first instance, observations on species invading from a more diverse ecosystem into a less diverse ecosystem indicate that successful colonizations take place because space is yielded by their ecological equivalents. In the second instance, widespread studies show that any community, rich or poor, located in tropical or cold waters, is vulnerable to invasions by species from a larger, more diverse region. Furthermore, the species richness of a community apparently depends upon that of the region to which it belongs. Together, these observations indicate the existence of a general rule which states that if an invader becomes established, it is permitted to do so by an accommodation on the part of the species that occupies the preferred ecological space. Paleontological data on invasions provide evidence of speciation following accommodation. This leads to the recognition of a three-step process: invasion to accommodation to speciation (IAS). This process, which may be called the IAS mechanism, may have contributed to historical rises of global biodiversity.     

The functional biology and trophic role of krill (Thysanoessa raschii) in a Greenlandic fjord

Despite being a key zooplankton group, knowledge on krill biology from the Arctic is inadequate. The present study examine the functional biology and evaluate the trophic role of krill in the Godth?bsfjord (64°N, 51°W) SW Greenland, through a combination of fieldwork and laboratory experiments. Krill biomass was highest in the middle fjord and inner fjord, whereas no krill was found offshore. The dominating species Thysanoessa raschii revealed a type III functional response when fed with the diatom Thalassiosira weissflogii. At food saturation, T. raschii exhibited a daily ration of 1% body C d^?1. Furthermore, T. raschii was capable of exploiting plankton cells from 5 to 400???m, covering several trophic levels of the pelagic food web. The calculated grazing impact by T. raschii on the fjord plankton community was negligible. However, the schooling and migratory behaviour of krill will concentrate and elevate the grazing in specific areas of the euphotic zone.     

Shouting the odds: vocalization signals status in a lizard

Many species possess multiple sexually dimorphic traits, which incorporate different sensory modalities (e.g., acoustic, olfactory and visual), although their relative roles in sexual selection and in determining reproductive success are still poorly understood for most taxa. We assessed the role of multiple male traits, including one acoustic (dominant call frequency) and one visual (yellow throat patch) trait, in residency advertisement, contest behavior, and breeding success in barking geckos (Ptenopus garrulus garrulus). We show that male barking geckos maintain largely exclusive home ranges, with a trend for larger males to maintain larger home ranges. We also show that larger males have a lower dominant calling frequency. When aggressive behavior was elicited in the field using a recorded call of average frequency, resident males with low frequency calls were more likely to respond aggressively and charge the speaker compared to males with high frequency calls. However, body size and small relative throat patch size, rather than call frequency, were the best predictors of overall aggressiveness. Body size was also the best predictor of whether males bred. We suggest that call frequency in this crepuscular species constitutes an effective long-range signal of body size, used by males for remote rival assessment and to advertise home range boundaries in low-light environments.     

Dominance and reproduction in a parthenogenetic lizard

Summary In most vertebrates, males and females are believed to differ in terms of their investment in offspring. Dominance theory suggests that one way individuals of the sex with lower parental investment can increase reproductive success would be to dominate others of the same sex. The dominant competitors are thought to achieve preferred access to mates, and thus, have greater reproductive success than subordinates.Reproduction in parthenogenetic Cnemidophorus uniparens normally proceeds without males, but individuals exhibit mounting behaviors in captivity that are typical of closely related Cnemidophorus species that reproduce sexually. Thus, these animals provide an unusual opportunity to study the effects of behavior on reproduction apart from copulation and fertilization. In this study relationships between dominance and reproduction were investigated in the unisexual lizard species, C. uniparens. Dominance hierarchies were rapidly established and maintained in the laboratory by agonistic encounters among individuals. The number of times an individual charged its cagemates was positively correlated with the number of clutches and eggs laid. Also, dominant animals who charged their cagemates were likely to win agonistic encounters; recipients of charges usually fled. Hierarchies based on different behaviors were not all related to reproduction. Charges as a predictor of dominance was unrelated to body length, percent increase in body length and time spent in the basking site. However, individuals with a high percent increase in body length spent more time basking. This is likely a result of the increased energy demands of growth in addition to reproduction. Physiological stress as measured by plasma corticosterone titers was unrelated to dominance. We suggest that dominance is an important factor affecting reproduction in C. uniparens.     

Influence of animal manures on the biology of temperate earthworm, Eisenia fetida in tropical semiarid climate

For understanding the potential utility in field scale production of vermicompost and vermiprotein economically, Eisenia fetida was cultured to establish the influence of (i) prevailing tropical semiarid (North-East region of Karnataka, India) environmental factors and (ii) different animal manures (cattle, horse and 1:1 mixture of cattle and horse) (on its growth, reproduction and life span. In three forms of diet, growth (mg/d/g live weight of worm) was almost similar, but the biomass in cattle manure (565.7 +/- 15.3) was significantly more than horse manure (494.9 +/- 22.8) and 1:1 mixture (470.3 +/- 22.0). Mean cocoon production (per worm/week) in horse manure (0.16) was significantly (P<0.001) lower than that in cattle manure (1.6) and in 1:1 mixed manure (1.4). Cattle favoured biomass, growth and cocoon production. Horse manure inhibited cocoon production and the conserved energy in this process might have been added to the body weight almost equal to that in cattle manure. In 1:1 mixed manure, the biomass was less due to moderate cocoon production (presumably due to the stimulatory influence of 50% cattle manure) under semifavorable nutrients and environmental conditions. Fecundity of the worms declined with aging, despite favourable nutrients and environmental conditions. Worms survived up to 92, 68 and 66 weeks in cattle manure, 1:1 mixed manure and horse manure respectively.     

Defensive secretion of a flightless grasshopper: Failure to prevent lizard attack

Summary We tested the role of a grasshopper defensive secretion in deterring lizard predation. Adults, but not young larvae, of the chemically defended lubber grasshopperRomalea guttata (=microptera) froth a volatile secretion when attacked by predators. The lizardAnolis carolinensis failed to strike juvenile lubbers (which lack secretion) in laboratory trials. Survivorship of palatable crickets loaded with secretion offered toA. carolinensis was not significantly different from survivorship of control crickets. In experiments designed to investigate if lizards learn an aversion to the secretion, striking times forSceloporus undulatus fed wax worms coated with secretion were not significantly different over three days of trials. Three primary conclusions are drawn from these data. First, the secretion may not be necessary for lubber protection from lizards. Second, lubber secretion does not appear to deter lizards from attacking or eating prey items. Third, lizards do not appear to develop an aversion to the secretion.     

Combining motions into complex displays: playbacks with a robotic lizard

Complex displays composed of multiple, seemingly independent, units can result from sexual selection for increasingly variable, but redundant, displays and from potentially opposing selective pressures imposed by use of the display in multiple contexts. Our playback results support the latter, multireceiver hypothesis by confirming that two aspects of the sagebrush lizard headbob display (number of headbobs and use of display-specific body postures) are independently-meaningful components that are interpreted differently by different receivers. Male receivers use species-typical body postures to distinguish between aggressive and broadcast forms of the display, whereas female receivers are more attentive to the number of headbob motions, using these to distinguish male courtship from a challenge from a female competitor. Thus, display components are likely subject to different selective pressures and the display as a whole is evolving in response to a complex selective regime. Our example differs from other complex signals that have been considered in that both display elements involve dynamic motions (turned on and off by the display producer) as opposed to static signal elements (e.g., color, size). In addition, we found evidence that display structure is highly malleable, and that lizards both produce and respond to artificial displays that violate syntactic rules identified from field observations. Finally, our experiments demonstrate that a robotic lizard can be used effectively in playback studies of visual display behavior in lizards.Electronic Supplementary Material: S1. Movie clip of the robotic lizard producing a species-typical headbob display as in Fig. 1a.     

Re-evaluating the role of energy efficiency standards: A behavioral economics approach

The economic models that prescribe Pigovian taxation as the first-best means of reducing energy-related externalities are typically based on the neoclassical model of rational consumer choice. Yet, consumer behavior in markets for energy-using durables is generally thought to be far from efficient, giving rise to the concept of the “energy-efficiency gap.” This paper presents a welfare analysis of energy policies that is based on a behavioral model of temptation and self-control, introduced by Gul and Pesendorfer 23 and 24. We find that, in the presence of temptation, (i) Pigovian taxes alone do not yield a first-best outcome, (ii) when viewed as substitutes, energy efficiency standards can dominate Pigovian taxes, and (iii) a policy combining standards with a Pigovian tax can yield higher social welfare than a Pigovian tax alone, implying that the two instruments should be viewed as complements rather than substitutes.     

Nitrogen effects on decomposition: a five-year experiment in eight temperate sites

The influence of inorganic nitrogen (N) inputs on decomposition is poorly understood. Some prior studies suggest that N may reduce the decomposition of substrates with high concentrations of lignin via inhibitory effects on the activity of lignin-degrading enzymes, although such inhibition has not always been demonstrated. I studied the effects of N addition on decomposition of seven substrates ranging in initial lignin concentrations (from 7.4% to 25.6%) over five years in eight different grassland and forest sites in central Minnesota, USA. I predicted that N would stimulate the decomposition of lignin-poor substrates but retard the decomposition of lignin-rich substrates. Across these sites, N had neutral or negative effects on decomposition rates. However, in contrast to my hypothesis, effects of N on decomposition were independent of substrate initial lignin concentrations, and decomposition of the lignin fraction was unaffected by N fertilization. Rather, substrate-site combinations that exhibited more rapid decomposition rates in the control treatment were affected more negatively by addition of N fertilization. Taken together, these results suggest that decreased decomposition with added N did not result from inhibition of lignin-degrading enzyme activity, but may have resulted from abiotic interactions between N fertilizer and products of microbial degradation or synthesis or from N effects on the decomposer community. Low initial substrate N concentrations and N fertilization both stimulated N immobilization, but the differences among substrates were generally much larger than the effects of fertilization. This study suggests that atmospheric N addition could stimulate ecosystem carbon sequestration in some ecosystems as a result of reduced rates of forest floor decomposition.     

Homing behaviour in the sleepy lizard (Tiliqua rugosa): the role of visual cues and the parietal eye

To investigate how visual cues are integrated into a navigational strategy for homing in the Australian sleepy lizard (Tiliqua rugosa), lizards were displaced beyond their home range, either with full access to visual cues or with no access to visual cues during the displacement. Homeward orientation was significantly worse when lizards were denied visual cues during the displacement than when they were not. However when lizards were displaced with their field of view restricted to the sky, their homeward orientation was equally as good as that of lizards displaced with no visual restriction. These experiments suggest that sleepy lizards use celestial cues to determine the compass bearing of the outward journey, and reverse this bearing to orient in the homeward direction (course reversal). In a subsequent experiment, lizards oriented randomly with respect to home when the parietal eye was entirely covered with a patch during the displacement and return, while control lizards fitted with a sham parietal eye patch were well oriented towards home. In both groups, the lateral eyes were unobstructed and had complete access to visual cues including celestial cues and landmarks. These results suggest that the parietal eye plays a highly significant role in sleepy lizard homing, perhaps mediating a sky polarization compass sense.     

Predatory behavior and prey selection by army ants in a desert-grassland habitat

Summary Colonies of Neivamyrmex nigrescens conduct extensive nocturnal raids on other ants and termites in the desert-grassland of Arizona-New Mexico. We collected quantitative data on several aspects of raiding to pinpoint differences due to colony size and behavioral phase. In the nomadic phase, colonies began raiding at sunset and continued until dawn. Larger colonies covered more area, discovered more prey sites, and collected more booty than smaller colonies, but there were no systematic changes in raid intensity over the course of the nomadic phase. In the statary phase, raiding occurred less frequently and was less intense when it occurred; however, at the end of this phase, raiding was similar to nomadic phase raids in extent, duration, and booty captured. N. nigrescens preyed exclusively on termites and ants, and appeared to select certain species of Pheidole in preference to other ants. Pheidole was the most abundant genus, but was preyed upon twice as often as expected based on relative colony density. Pheidole attempted to avoid predation by fleeing or defending their nest, but rarely succeeded. Because they are about the same size as army ants and lack defensive chemicals, Pheidole made comparatively easy prey. N. nigrescens ignored or was repelled by other ants (Pogonomyrmex, Novomessor, Iridomyrmex, Myrmecocystus) during the early summer, when Pheidole was abundant; however, in late summer when Pheidole was less available, the army ants preyed upon Novomessor cockerelli. N. harrisi raided in close proximity to N. nigrescens, but preyed exclusively on Solenopsis xyloni. Selection of prey and partitioning of resources are now indicated in several army ant species; these processes have probably been important factors in the evolution of the ants' predatory behavior.     

The response of temperate aquatic ecosystems to global warming: novel insights from a multidisciplinary project

This article serves as an introduction to this special issue of Marine Biology, but also as a review of the key findings of the AQUASHIFT research program which is the source of the articles published in this issue. AQUASHIFT is an interdisciplinary research program targeted to analyze the response of temperate zone aquatic ecosystems (both marine and freshwater) to global warming. The main conclusions of AQUASHIFT relate to (a) shifts in geographic distribution, (b) shifts in seasonality, (c) temporal mismatch in food chains, (d) biomass responses to warming, (e) responses of body size, (f) harmful bloom intensity, (f), changes of biodiversity, and (g) the dependence of shifts to temperature changes during critical seasonal windows.     

Biogeochemistry of a temperate forest nitrogen gradient

Wide natural gradients of soil nitrogen (N) can be used to examine fundamental relationships between plant-soil-microbial N cycling and hydrologic N loss, and to test N-saturation theory as a general framework for understanding ecosystem N dynamics. We characterized plant production, N uptake and return in litterfall, soil gross and net N mineralization rates, and hydrologic N losses of nine Douglas-fir (Pseudotsuga menziesii) forests across a wide soil N gradient in the Oregon Coast Range (U.S.A.). Surface mineral soil N (0-10 cm) ranged nearly three-fold from 0.29% to 0.78% N, and in contrast to predictions of N-saturation theory, was linearly related to 10-fold variation in net N mineralization, from 8 to 82 kg N.ha(-1) x yr(-1). Net N mineralization was unrelated to soil C:N, soil texture, precipitation, and temperature differences among sites. Net nitrification was negatively related to soil pH, and accounted for <20% of net N mineralization at low-N sites, increasing to 85-100% of net N mineralization at intermediate- and high-N sites. The ratio of net: gross N mineralization and nitrification increased along the gradient, indicating progressive saturation of microbial N demands at high soil N. Aboveground N uptake by plants increased asymptotically with net N mineralization to a peak of approximately 35 kg N.ha(-1) x yr(-1). Aboveground net primary production per unit net N mineralization varied inversely with soil N, suggesting progressive saturation of plant N demands at high soil N. Hydrologic N losses were dominated by dissolved organic N at low-N sites, with increased nitrate loss causing a shift to dominance by nitrate at high-N sites, particularly where net nitrification exceeded plant N demands. With the exception of N mineralization patterns, our results broadly support the application of the N-saturation model developed from studies of anthropogenic N deposition to understand N cycling and saturation of plant and microbial sinks along natural soil N gradients. This convergence of behavior in unpolluted and polluted forest N cycles suggests that where future reductions in deposition to polluted sites do occur, symptoms of N saturation are most likely to persist where soil N content remains elevated.     

The swimming crab Charybdis smithii: distribution, biology and trophic role in the pelagic ecosystem of the western Indian Ocean

Surface “swarms” of the swimming crabs Charybdis smithii are still considered as an unusual phenomenon in the open Indian Ocean, although their dense pelagic aggregations were already reported in waters off the Indian coast and in the northern Arabian Sea. Based on an extensive large-scale data series taken over 45 years, we demonstrate that C. smithii is common in the pelagic provinces of the western Indian Ocean driven by the wind monsoon regime. Swimming crabs are dispersed by the monsoon currents throughout the equatorial Indian Ocean. They aggregate at night in the upper 150-m layer, where their estimated biomass derived from pelagic trawling data can exceed 130 kg km⁻². Abundance of C. smithii can reach >15,000 ind. km⁻² in July (i.e. the peak of the south-west monsoon), declines by 50-fold in March and is negligible in May. C. smithii is an important prey for more than 30 species of abundant epipelagic top predators. In turn, it feeds on mesopelagic species. This swimming crab is a major species of the intermediate trophic levels and represents a crucial seasonal trophic link in the open ocean ecosystem of the western Indian Ocean. Outbursts in pelagic waters of huge biomasses of ordinarily benthic crustaceans (C. smithii and Natosquilla investigatoris) are a remarkable feature of the Indian Ocean, although similar, but smaller, events are reported in the Pacific and Atlantic Oceans.

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