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Article Summaries

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Host plant finding and recognition by visual and olfactory floral cues in an oligolectic bee
Hannah Burger, Stefan Dötterl, Manfred Ayasse
The sweet smell (and colour) of success; Bees use both visual and olfactory senses to find food
Most of us have walked through a grassy field and noticed the buzzing of bees around colourful flowers. But how do bees distinguish between the many kinds of flowers when they leave their nests each morning? A recent study published in the journal Functional Ecology helps explain this mystery. Previous work on bees demonstrated that bees use a variety of cues such as odour, colour, size and shape to discriminate and recognise flowers, but exactly how social and solitary bees use these cues is poorly understood. Researchers from the University of Bayreuth and the University of Ulm in Germany studied a bee species (Hoplitis adunca) that collects pollen exclusively from flowers of Viper's Bugloss (Echium, Boraginaceae). They showed that these bees use a combination of visual and olfactory cues to distinguish Viper's Bugloss’s flowers from other similar flowers for which the bees are not well suited. They also showed that the blue colour of the plants first attracts the bees, while the olfactory cues, which are specific to the plant species, are used by the bees to recognise their host plant and discriminate it from non-host plants. In other words, color is the first cue that attracts bees to the plant, with odor being a secondary cue that helps bees choose among alternatives. This research thus indicates that to understand how bees, and potentially other insects that consume specific plants, one must consider how an integrative use of the sensory system enables insects to literally find a needle in a haystack.  

Grass snakes exploit anthropogenic heat sources to overcome distributional limits imposed by oviparity
Kristin Löwenborg, Richard Shine, Simon Kärvemo, Mattias Hagman
Human activities have made life more difficult for many animals, with vulnerable species often disappearing from the local area when forests are converted to agricultural land. However, some species have proven adept at taking advantage of the new environments created by humans. New research shows that grass snakes in Sweden have found a use for a habitat type that wouldn't generally be seen as offering too many advantages: the manure heaps that farmers create from the droppings of farm animals. Those piles are distinctive habitats not only in terms of their odour, but also their temperature: the mixture of straw and decomposing faeces is much warmer than any other site in the surrounding landscape. Grass snakes lay their eggs in these manure piles, allowing the eggs to be kept warm all the way through the (often cool) Swedish summer. Incubation trials showed that baby snakes hatching from eggs kept in these warm conditions were likely to hatch earlier, and were faster than their brothers and sisters that had incubated under cooler conditions. As a result of exploiting these hot-but-smelly nest-sites, grass snakes have been able to colonise areas with much colder climates than can support other types of egg-laying reptiles.

Maternal effects in an insect herbivore as a mechanism to adapt to host plant phenology
Margriet van Asch, Riita Julkunen-Tiito & Marcel Visser
Mothers may shape their offspring’s life history not only via the genes she passes on but also by non-genetic effects, so-called maternal effects. These are especially important as a way to prepare the offspring for specific environmental conditions that can be forecasted from the mother’s own environment. We show, using an insect herbivore, the winter moth (Operophtera brumata) feeding on oak (Quercus robur), that maternal effects can affect seasonal timing of egg hatching in an adaptive way. Winter moth egg-hatching needs to coincide with oak bud opening, as only freshly emerged leaves are suitable as food for the caterpillars. However, there is spatial variation in the timing of bud opening among oaks to which the winter moth needs to adapt. We show experimentally that the generation time between the mother’s and her offsprings’ hatching dates was shorter for mothers who hatched late relative to bud opening of the tree they had to feed on (and hence had to feed on older leaves) than for mothers’ who hatched on time. Maternal feeding conditions affected both the larval and the pupal development time of the mother as well as the egg development time of her offspring: at all three stages developmental time was shorter for the mistimed treatment. We thus show that adaptation to spatial variation may be achieved via maternal effects. While this is a mechanism selected to adapt to spatial variation, it may now also play a role in adaptation to climate change induced shifts in host phenology.

Elevated CO2 effects on semiarid grassland plants in relation to water availability and competition
Feike A. Dijkstra, Dana Blumenthal, Jack A. Morgan, Daniel R. LeCain, and Ronald F. Follett
Semiarid grasslands have shown large increases in productivity, shifts in species composition, and altered carbon (C) and nitrogen (N) cycling in response to increased atmospheric CO2 concentration. Because an increase in atmospheric CO2 also resulted in increased soil moisture (because plants transpire less water through their leaves under elevated CO2), it has been suggested that much of the elevated CO2 effects on semiarid grasslands are related to this increase in soil moisture. It is unclear how important these CO2-induced soil water improvements are compared to more direct effects of elevated CO2 on plant productivity and N cycling in this system. A greenhouse experiment was conducted to test for effects of elevated CO2 and soil moisture on plant productivity and plant N uptake in five semiarid grassland species common in northern Colorado. Species were grown as monocultures and as a mixture of all five species. Species showed mostly greater productivity (particularly for C3 grasses), but not greater plant N uptake, under elevated CO2. On the other hand, both plant productivity and plant N uptake increased with increased soil moisture. This suggests that soil water improvement under elevated CO2 in field observations is a critical factor in stimulating plant productivity and plant N uptake. When grown in mixtures, species responses to elevated CO2 and increased soil moisture showed large differences compared to their responses when grown as monocultures. Thus, the responses of these species to elevated CO2 and water availability depend on competition for resources with other species.

Iridescent hindwing patches in the pipevine swallowtail: differences in dorsal and ventral surfaces relate to signal function and context 
Ronald Rutowski, Alexandra Nahm & Joseph Macedonia
Bright colorations in animals are intriguing, especially the bright iridescent color signals of butterflies. Iridescent signals are directional by definition and produced by structural phenomena both of which present interesting problems in terms of their function, production, and perception. We studied brilliant blue iridescent patches on the dorsal and ventral hindwings of the Pipevine Swallowtail butterfly. Evidence suggests that the ventral iridescent blue patch is a component of the warning coloration of this distasteful species that is displayed mostly in the early evening and early morning when the animals are at their nocturnal perches and ambient light levels are low. In contrast, the iridescent blue hindwing surface is proposed to be a sexual signal displayed by males to females during courtship courting females in the middle of the day under bright sunlight. As expected to enhance signal brightness in low light, the reflectance of the ventral iridescence area is much more intense than that of the dorsal hindwing. Also, in studies of the variation in signal brightness the dorsal iridescence was more condition dependent than that of the ventral hindwing. Results of this study suggest that properties of iridescent coloration such as that on the hindwing of the Pipevine Swallowtail have been fine-tuned by evolution in response to prevailing ambient light conditions and viewing perspectives of signal receivers. 

Associations between over-winter survival and resting metabolic rate in juvenile North American red squirrels
Meghan L. Larivée, Stan Boutin, John R. Speakman, Andrew G. McAdam, Murray M. Humphries
North American red squirrels are territorial, food hoarding rodents that remain active throughout winter. Squirrels in Kluane, Yukon rely primarily on hoarded white spruce cones for food during 5-6 months of cold winter conditions. An animal’s resting metabolic rate (RMR) is the minimum amount of energy necessary for survival. Energy expenditure for a squirrel occupying a winter nest is similar to its RMR, yet during autumn cone hoarding, metabolism may reach 3.8 times RMR, a measure approaching the limit for mammals. We hypothesized that a lower RMR may enhance survival by reducing winter expenditure costs and conserving food. Moreover, a lower RMR minimizes maintenance costs and may allow more energy to be allocated towards hoarding. A higher RMR, on the other hand, may enhance survival if it allows individuals to increase the throughput of energy available for investment in hoarding activities. In autumn, we obtained estimates of RMR, of free-living metabolic rate, and of the size of larder hoards. A spring census was used to access survival. We found that squirrels with both a larger body mass and a lower RMR were more likely to survive over-winter. Survivors also tended to have more food stored within their hoard. A larger body mass can be advantages as it reduces heat loss by increasing thermal inertia, however, normally a this would also entail an increase in RMR. Survivors may have had the best of both worlds: a low RMR and a larger body mass to minimize expenditure costs, while maximizing thermal inertia.

Tree Transpiration varies spatially in response to atmospheric but edaphic conditions
Elizabeth Traver, Brent Ewers, David Mackay and Michael Loranty
Many studies have now shown that tree water loss during photosynthesis (transpiration) is mainly a result of the dryness of the soil and atmosphere. This body of work has led to models that predict how transpiration varies in time. However, there is insufficient knowledge to predict how transpiration varies in space even within a forested stand. To help alleviate this knowledge gap, this study quantified the amount of transpiration in more than 100 trees each from a stand of mature aspen dominated trees that are smaller than another stand of maple dominated trees. In each stand we tested whether spatial transpiration could be explained by light or atmospheric dryness and soil moisture, texture and nutrients. We found that only atmospheric dryness explained spatial variation in transpiration as it changed in time. When atmospheric dryness was low (during cloudy days or mornings and evenings) transpiration from trees in the aspen stand was very similar to each other when trees were closer together than 50 m and 80 m in the maple stand. When atmospheric dryness was high (in the middle of sunny days with high temperatures and low relative humidity), the result changed to 35 m in the aspen stand and 25 m in the maple stand. This change in the relatedness of tree transpiration with atmospheric dryness provides an explanation for spatial variability in tree transpiration and will improve future predictions of water loss from forested areas.

Interaction effect among maternal environment, maternal investment and progeny genotype on life history traits in Callosobruchus chinensis
Shin-ichi Yanagi & Midori Tuda
Although maternal effects are often treated as being independent of progeny genotype, this assumption has rarely been tested. Mothers are known to reduce egg mass at high larval density and this often leads to the decrease of progeny fitness. Genotypes that can increase fitness of progeny even under low maternal investment might be selected for. Because laboratory populations tend to be reared at and adapt to high population density, relative to natural populations, it is possible that an interaction among progeny genotype (G), egg mass (E) and maternal rearing environment (preE) contributes to the difference between natural and laboratory populations.
To eliminate the influence of the genetic correlation between egg mass and other life history traits, we employed inbred-isofemale-line approach to evaluate the contribution of maternal nongenetic resource to progeny traits in the adzuki bean beetle, Callosobruchus chinensis. The females propagated from one female of an inbred line were reared at either high or low densities and crossed with males from either laboratory or wild strains.
In the offspring of mothers reared at low density, the negative correlation between egg mass and development time was higher with lab strain fathers, whereas in the offspring of mothers reared at high density, the negative correlation was higher with the wild strain fathers. The highly negative egg mass-development time relation in the progeny with a maternal density condition new to (therefore adverse for) a paternal strains indicates a nongenetic maternal effect overrides genotypic effects (therefore, G × E × preE effect).

Resource partitioning and niche hyper-volume overlap in free-living Pygoscelid penguins
Rory P. Wilson
Species that occur together and take the same food are considered to compete for this resource unless there is some mechanism by which they can avoid competition. This study looks at 3 penguin species, Adélies, chinstraps and gentoos, all breeding at one island in Antarctica, and all eating the same prey, Antarctic krill, which implies, therefore, that they should be competing. Using special technology attached to 49 individuals, I found that birds ostensibly avoided competition by foraging at different depths, in different sea areas and at different times of the day. However, krill is highly mobile and able to move between depths and areas over periods of just a few hours so, although the three penguin species conform to a classic scenario for avoiding competition by foraging in different ways, they may be competing for exactly the same food anyway.

Lipid metabolism, begging behaviour and nestling obesity in a pelagic seabird
Samuel Riou & Keith Hamer
Chicks of Procellariiform seabirds accumulate large quantities of fat during their development, the functional significance of which remains poorly understood. By measuring levels of lipid metabolites in the blood, we show here that Manx shearwater chicks made use of these fat reserves during periods of parental absence throughout their development. Yet chicks did not run out of reserves during the main period of growth, which suggested that a safeguard against variability in parental attendance at the colony could not, alone, explain the extent of these lipid reserves. We find that chicks begged more vigorously during the period of mass loss at the end of the nestling period than at any previous stage of their development, and that mobilization of fat stores was also at a maximum during this period in well-fed chicks, coinciding with a decrease in food provisioning by parents. These results therefore mainly support the hypothesis that fat stores fuel chicks through a period of several weeks of reduced food provisioning prior to fledging, when parents are unable or unwilling to maintain earlier levels of food provisioning, despite increased solicitation from chicks.

Effects of morphology on swimming performance in wild and laboratory crosses of brook trout ecotypes
Sébastien Rouleau, Hélène Glémet & Pierre Magnan
Individuals of same fish species can differ in their habitat use, food preference and morphology. It is thought that morphological differences arise to enable specific use of certain habitats, but the relationship between the two has never been explicitly tested. We examined the swimming performance of two forms of brook trout; littoral ones that use areas close to lake shore and pelagic ones that use mostly open waters. To evaluate swimming performance and morphological differences, trout were either raised in the laboratory for one year or captured in the wild were forced to swim in respirometers, then measured for 16 morphological characters. The critical swimming speed (Ucrit) revealed that pelagic trout reared in the wild are better swimmers than littoral ones. High Ucrit. was associated with shorter fins as well as to high body width and height. These results only partially support our original prediction that Ucrit of pelagic individuals should be higher than that of littoral ones due to their shorter fins and streamlined body shape; high Ucrit was associated to short fins but not to a streamlined body shape. Additionally, wild littoral individuals had a higher energy expenditure due to swimming than pelagic ones; however, this was compensated by a lower metabolic rate, resulting in comparable cost between forms. This confirms that a lower performance can be compensated by a low metabolic rate, a phenomenon that could apply to all species where morphological differentiation is present among individuals.

When sea-ice clock is ahead of Adélie penguins' clock
Michael Beaulieu,  Antoine Dervaux, Anne Mathilde Thierry, David Lazin, Yvon Le Maho, Yan Ropert-Coudert, Marion Spée, Thierry Raclot, & André Ancel
In Polar Regions, the extent and dynamics of sea-ice are changing. This affects the whole food web including polar top predators like penguins. Here we monitored the response of Adélie penguin pairs during two seasons of contrasting timing of sea-ice retreat. We measured foraging trip duration, body mass and reproductive success as well as food-related stress (via the measurement of the stress hormone "corticosterone") and the use of penguins' habitat. Body mass and reproductive success remained unchanged but foraging trips were shorter when sea-ice retreated earlier. Constant concentrations of corticosterone indicated that none of the feeding conditions resulted in a food-related stress. In addition, coastal prey like fish contributed slightly more to the penguins' diet when sea-ice retreated prematurely. In the present study, even though the timing of sea-ice retreat differed drastically between the two years, Adélie penguins were not severely affected because they were able to adjust their at-sea behavior and thus maintained their body condition and reproductive success unchanged. This suggests that, even though sea-ice is retreating earlier and earlier in Antarctica, the timing of sea-ice retreat does not represent an important threat to populations of Adélie penguins at least as long as alternative resources are still available and other environmental parameters like winter sea-ice are not dramatically altered.

 

 

 

 

 


 


 

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