Plasticity in male courtship behaviour as a function of light intensity in guppies

The environment is profoundly important in shaping many aspects of animal phenotype, including courtship and mating behaviours. Courtship displays rely upon the transmission of visual information from the signaller to the receiver, which means they are likely to be less effective in visually poor conditions such as at low light or in turbid ecosystems. One might therefore predict that in visually poor environments it would be beneficial for individuals to plastically adjust their mating behaviour to maximise mating success. Here, we investigate the impact of the developmental and current visual environment (light intensity) upon male mating behaviour in the Trinidadian guppy Poecilia reticulata. Male guppies have two different mating tactics: They can court females with a visual sigmoid display or attempt to circumvent female choice by attempting a non-consensual copulation (gonapodium thrust). We reared juvenile guppies in low light and relatively high light intensities for 5 months before observing individual males for mating behaviour in both light conditions. We found that the current light environment is important in determining the frequency of both sigmoidal courtship displays and non-consensual copulation attempts. Males increase the frequency of sigmoidal displays at relatively high light and increase non-consensual mating attempts at low light, suggesting that males compensate for poor visual conditions via an adjustment in tactics. We also find a significant correlation in courtship effort between the different light environments, suggesting that there is individual consistency across time and context for this trait. Developmental environment was less important. However, we found that fish reared at lower light intensities continued to employ sigmoidal displays despite the poor current visual environment. Our data show that male mating behaviour is phenotypically plastic in response to recent light environment. This may have implications for understanding how animals cope with anthropogenic environmental change.     

Bats aloft: variability in echolocation call structure at high altitudes

Bats alter their echolocation in response to changes in ecological and behavioral conditions, but little is known about how they adjust call structure in response to changes in altitude. We examined altitudinal variation in the echolocation of Brazilian free-tailed bats, Tadarida brasiliensis, a species known to fly to altitudes of 3,000 m above the ground. From 50.2 h of recordings, we analyzed 113 high-quality echolocation call sequences recorded from 0 to 862 m above ground level. Bats flying near the ground used shorter, higher-frequency, broader-bandwidth calls compared to bats at higher altitudes, an effect likely due to the greater levels of echo-producing clutter (i.e., vegetation, buildings) found near the ground. When ground-level recordings are excluded, bats continue to shift towards the use of longer-duration, lower-frequency, narrower-bandwidth calls with increasing altitude. We propose that the observed high-altitude changes in call structure are a response to changing acoustic attenuation rates and/or decreasing insect densities at higher altitudes.     

In vivo and in vitro differences in chloroplast functionality in the two north Atlantic sacoglossans (Gastropoda,Opisthobranchia) <Emphasis Type="Italic">Placida dendritica</Emphasis> and <Emphasis Type="Italic">Elysia viridis</Emphasis>

The photosynthetic functionality in chloroplasts in the two sacoglossan molluscs Placida dendritica and Elysia viridis from the Trondheim fjord in Norway was studied. P. dendritica and E. viridis with no functional chloroplasts in their digestive system were introduced to the green macroalgae Codium fragile. Our results showed that P. dendritica was not able to retain functional (photosynthetic) chloroplasts. Transmission electron microscopy (TEM) showed that chloroplasts were directly digested when phagocytosed into the digestive cells. Four stages of chloroplast degradation were observed. A corresponding operational quantum yield of chl a fluorescence (Φ_PSII ~ 0) indicated autofluorescence, and the presence of highly degraded chl a supported these observations. In contrast, E. viridis was able to retain functional chloroplasts. For this species it took only 1 week for the chloroplasts inside the digestive cells to acquire the same Φ_PSII and light utilisation coefficient (α) as C. fragile kept under the same light conditions. Data for 8 days showed a 2–6-fold increase in the maximum photosynthetic rate (P _max) and light saturation index (E _k) relative to C. fragile. This increase in available light was probably caused by a reduced package effect in the digestive gland of E. viridis relative to C. fragile, resulting in a partial photoacclimation response by reducing the turnover time of electrons (τ). Isolated pigments from C. fragile compared to E. viridis showed the same levels of photosynthetic pigments (chl a and b, neoxanthin, violaxanthin, siphonaxanthin, siphonein and β,ε-carotene) relative to μg chl a (w:w), indicating that the chloroplasts in E. viridis did not synthesise any new pigments. After 73 days of starvation, it was estimated that chloroplasts in E. viridis were able to stay photosynthetic 5–9 months relative to the size of the slugs, corresponding to an RFC of level 8 (a retention ability to retain functional chloroplasts (RFC) for more than 3 months). The reduction in Φ_PSII, P _max and α as a function of time was caused by a reduction in chloroplast health and number (chloroplast thylakoid membranes and PSII are degraded). These observations therefore conclude that chloroplasts from C. fragile cannot divide or synthesise new pigments when retained by E. viridis, but are able to partially photoacclimate by decreasing τ as a response to more light. This study also points to the importance of siphonaxanthin and siphonein as chemotaxonomic markers for the identification of algal sources of functional chloroplasts.     

Predicted impact of ocean acidification on a marine invertebrate: elevated CO<Subscript>2</Subscript> alters response to thermal stress in sea urchin larvae

Ocean acidification (OA) and the biological consequences of altered seawater chemistry have emerged as a significant environmental threat to healthy marine ecosystems. Because a more acidic ocean interferes with fixation of calcium carbonate to form shells or calcified skeletons, future ocean chemistry may significantly alter the physiology of calcifying marine organisms. These alterations may manifest themselves directly in the calcification process, or have synergistic effects with other environmental factors such as elevated temperatures. New tools permit us to explore subtle changes in gene expression patterns in response to environmental conditions. We raised sea urchins (Strongylocentrotus franciscanus) under conditions simulating future atmospheric CO₂ levels of 540 and 970 ppm. When larvae raised under elevated CO₂ conditions were subjected to 1-h acute temperature stress, their ability to mount a physiological response (as measured by expression of the molecular chaperone hsp70) was reduced relative to those raised under ambient CO₂ conditions. These results represent the first use of gene expression assays to study the effects of OA on sea urchin development. They highlight the importance of looking at multiple environmental factors simultaneously as this approach may reveal previously unsuspected biological impacts of atmospheric changes.     

Quantification of copepod gut content by differential length amplification quantitative PCR (dla-qPCR)

Quantification of feeding rates and selectivity of zooplankton is vital for understanding the mechanisms structuring marine ecosystems. However, methodological limitations have made many of these studies difficult. Recently, molecular based methods have demonstrated that DNA from prey species can be used to identify zooplankton gut contents, and further, quantitative gut content estimates by quantitative PCR (qPCR) assays targeted to the 18S rRNA gene have been used to estimate feeding rates in appendicularians and copepods. However, while standard single primer based qPCR assays were quantitative for the filter feeding appendicularian Oikopleura dioica, feeding rates were consistently underestimated in the copepod Calanus finmarchicus. In this study, we test the hypothesis that prey DNA is rapidly digested after ingestion by copepods and describe a qPCR-based assay, differential length amplification qPCR (dla-qPCR), to account for DNA digestion. The assay utilizes multiple primer sets that amplify different sized fragments of the prey 18S rRNA gene and, based on the differential amplification of these fragments, the degree of digestion is estimated and corrected for. Application of this approach to C. finmarchicus fed Rhodomonas marina significantly improved quantitative feeding estimates compared to standard qPCR. The development of dla-qPCR represents a significant advancement towards a quantitative method for assessing in situ copepod feeding rates without involving cultivation-based manipulation.     

Delayed ontogenic dietary shift and high levels of omnivory in green turtles (<Emphasis Type="Italic">Chelonia mydas</Emphasis>) from the NW coast of Africa

Young green turtles (Chelonia mydas) spend their early lives as oceanic omnivores with a prevalence of animal prey. Once they settle into neritic habitats (recruitment), they are thought to shift rapidly to an herbivorous diet, as revealed by studies in the Greater Caribbean. However, the precise timing of the ontogenic dietary shift and the actual relevance of animal prey in the diet of neritic green turtles are poorly known elsewhere. Stable isotopes of carbon, sulfur and nitrogen in the carapace scutes of 19 green turtles from Mauritania (NW Africa), ranging from 26 to 102 cm in curved carapace length (CCLmin), were analyzed to test the hypothesis of a rapid dietary shift after recruitment. Although the length of residence time in neritic habitats increased with turtle length, as revealed by a significant correlation between turtle length and the δ¹³C and the δ³⁴S of the scutes, comparison of the δ¹⁵N of the innermost and outermost layers of carapace scutes demonstrated that consumption of macrophytes did not always start immediately after recruitment, and turtles often resumed an animal-based diet after starting to graze on seagrasses. As a consequence, seagrass consumption did not increase gradually with turtle size and animal prey largely contributed to the diet of turtles within the range 29–59 cm CCLmin (76–99% of assimilated nutrients). Seagrass consumption by turtles larger than 59 cm CCLmin was higher, but they still relied largely on animal prey (53–76% of assimilated nutrients). Thus, throughout most of their neritic juvenile life, green turtles from NW Africa would be better classified as omnivores rather than herbivores. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Going deep: common murres dive into frigid water for aggregated,persistent and slow-moving capelin

Owing to the necessity of delivering food to offspring at colonies, breeding seabirds are highly constrained in their foraging options. To minimize constraints imposed by central-place foraging and to optimize foraging behavior, many species exhibit flexible foraging tactics. Here we document the behavioral flexibility of pursuit-diving common murres Uria aalge when foraging on female capelin Mallotus villosus in the northwest Atlantic. Quite unexpectedly, being visual foragers, we found that common murres dived throughout the day and night. Twenty-one percent of recorded dives (n = 272 of 1,308 dives) were deep (≥50 m; maximum depth = 152 m, maximum duration = 212 s), bringing murres into sub-0°C water in the Cold Intermediate Layer (CIL; 40–180 m) of the Labrador Current. Deep dives occurred almost exclusively during the day when murres would have encountered spatially predictable aggregations of capelin between 100 and 150 m in the water column. Temperatures within the CIL shaped trophic interactions and involved trade-offs for both predators and prey. Sub-0°C temperatures limit a fish’s ability to escape from endothermic predators by reducing burst/escape speeds and also lengthening the time needed to recover from burst-type activity. Thus, while deep diving may be energetically costly, it likely increases certainty of prey capture. Decreased murre foraging efficiency at night (indicated by an increase in the number of dives per bout) reflects both lower light conditions and changing prey behavior, as capelin migrate to warmer surface waters at night where their potential to escape from avian predators could increase.     

Interactions among bacterial-feeding nematode species at different levels of food availability

Accurate prediction of the biodiversity–ecosystem functioning relationship requires adequate understanding of the interactions among species in a community. Effects of species diversity on ecosystem functioning are usually considered more pronounced with increasing functional dissimilarity, although species within functional groups may also perform non-identical functions and interact with each other. Here we present results of a laboratory experimental study aimed at elucidating whether interspecific interactions among species within a single nematode trophic group, bacterivores, (1) affect population development and community structure, and (2) depend on food availability. We studied the population growth of Rhabditis (Pellioditis) marina, a rhabditid nematode known to favour very high food densities when in monoculture, and of Diplolaimelloides meyli and D. oschei, congeneric Monhysteridae known to perform better in monocultures at intermediate food availability. Both Diplolaimelloides species showed significantly different patterns of food-density dependence in combination culture compared to monoculture. At very high food availability, the rhabditid nematode facilitated growth of both monhysterid species, probably as a result of down-regulation of bacterial density. At the lowest food availabilities, the presence of even low numbers of monhysterid nematodes lead to exclusion of the rhabditid, which at such low food availability has a very inefficient food uptake. At intermediate food availabilities, abundances of both Diplolaimelloides species were strongly depressed in the combination culture, as a result of food depletion by the rhabditid, indirect inhibitory interactions between the two congeneric species, or both. The complexity of the species interactions render predictions on the outcome and functional consequences of changes in within-trophic-group diversity highly problematic.     

The effect of size and cheliped autotomy on sexual competition between males of the mud crab <Emphasis Type="Italic">Cyrtograpsus angulatus</Emphasis> Dana

Size advantage in male–male competition over mates, combined with male preference over large females, is a common feature that can drive to size assortative mating and, eventually, sexual selection. In crabs, appendage autotomy can affect assortative mating and opportunity for sexual selection by affecting size advantage in mating contests. In this work, we evaluate the effect of size and appendage autotomy in generating assortative mating in the mud crab Cyrtograpsus angulatus. Field observations of guarding pairs in two different populations show a positive correlation between carapace width of males and females in both the populations. In one of the populations, incidence of appendage autotomy was low and the variability in the size of reproductive males was lower than the variability in the size of randomly collected males (i.e. only larger males were successful in getting a female), whereas there was no differences in the other population (i.e. most male sizes were successful) where the incidence of appendage autotomy was very high, indicating that the importance of size is higher when the incidence of autotomy is low. In this context, experiments (in both populations) show that, in contests for a female, larger males outcompete smaller ones only when they had intact appendages. When males had missing chelipeds, winning or loosing against smaller males was random. This may lead to a decrease in the importance of male size in populations with high incidence of cheliped autotomy, affecting assortative mating and opportunity for selection and, thus, affecting selective pressures.