Functional EcologyBritish Ecological Society
 

Article Summaries

The below summaries are provided by our authors to help put their research paper into context for the wider scientific community and the general public. These summaries are for paper where our editors considered the work to be particularly novel and interesting.  We hope you enjoy reading them!

 

You'll catch a cold out there! …or will you?

Dana Hawley, Sarah DuRant, Amanda Wilson, James Adelman and William Hopkins

Despite what your mother told you about bundling up on cold days so you won't catch a cold, we still know surprisingly little about how ambient temperature influences susceptibility to disease. Perhaps that advice to stay warm stemmed from an assumption that staying warm requires so much energy, you won't have any left to fight off infection. We examined this assumption in a common North American songbird, the house finch, that regularly visits backyard feeders. House finches catch their own version of the common cold - in their case, Mycoplasmal conjunctivitis - a bacterial infection that causes debilitating eye inflammation. This disease shows seasonal patterns akin to cold and flu in humans, with annual outbreaks occurring in the fall and winter in eastern North American finches. Therefore, house finches are fighting off infection with this pathogen at the same time of year they are expending significant amounts of energy to keep warm.

We tested whether house finches infected with this pathogen expend more energy than their healthy counterparts, and whether the energetic costs of infection are even higher at colder temperatures where house finches are forced to expend energy to stay warm. We hypothesized that the simultaneous energetic demands of fighting infection and staying warm would make house finches more susceptible to this illness in colder weather. We found that house finches fighting infection do expend significantly more energy than their healthy counterparts. However, the energy needed to fight infection was the same regardless of whether or not house finches also had to work hard to stay warm. Despite the high energetic demands of staying warm, house finches were not more susceptible to infection at cooler temperatures - in fact, much to our surprise, they showed less severe disease symptoms and higher circulating levels of an immune messenger at the cooler temperature. Perhaps mom's concerns about bundling up to avoid catching a cold weren't founded after all?

 

Seasonal stage differences overwhelm environmental and individual factors as determinants of energy expenditure in free-ranging red squirrels

Quinn Fletcher, John Speakman, Stan Boutin, Andrew McAdam, Sarah Woods and Murray Humphries

All animals must obtain energy from the environment and use this energy to survive and reproduce. The amount of energy that animals expend can be influenced by the characteristics of individuals, by what individuals are doing, and by what environmental conditions they are exposed to. It has recently become possible to determine the amount of energy free-living animals expend in the wild over multiple-day periods. In this article, we quantified the amount of energy expended by wild female North American red squirrels in Yukon, Canada, at different times of the year, over an eight year period. We found that female squirrels pass through seasonal and reproductive stages during the year when energy is either spent or saved. Lactating female squirrels spend high levels of energy when they are the sole providers for their developing offspring. During lactation, we also found that levels of energy expenditure were higher when females had more access to food. Squirrels also spend comparably high levels of energy during the fall when they hoard mature spruce cones that they feed on to survive winter and reproduce the next spring. Our finding that levels of energy expenditure during food hoarding were similar to levels during lactation was surprising, because lactation has traditionally been considered the most energetically demanding time of the year for females. At this time they must obtain enough energy to support themselves and their developing offspring. During winter, squirrels are exposed to extremely cold ambient temperatures. Squirrels are non-hibernators, but they are extremely good at saving energy at this time, using about half as much energy as they do during lactation and hoarding. Squirrels can save energy during winter presumably because they have stored food nearby their warm nests and their winter coats are well-insulated. Interestingly, winter was the only time of the year when the characteristics of individuals influenced levels of energy expenditure, with larger individuals spending more energy. Overall, even though squirrels face a range of energetic challenges throughout the year, they have an amazing ability to adjust their levels of energy expenditure to survive and reproduce.

Photo: Red squirrel in winter with bracts from white spruce cones. White spruce cones contain seeds, which are the primary food item of squirrels at our study site by Ryan W. Taylor

 

How much carbon dioxide do Arctic mosses soak up?

Lorna Street, Paul Stoy, Martin Sommerkorn, Benjamin Fletcher, Victoria Sloan, Timothy Hill and Mathew Williams

For just a few months in the summer, much of the land within the Arctic circle is green with plant life. Within this short window of opportunity, Arctic plants grow, take up carbon dioxide from the atmosphere, and transform the carbon into leaves, stems and roots. When eventually these plant parts die, they decay slowly because the cold wet ground slows the work of decomposing microorganisms. As a consequence, over thousands of years, partly decomposed plants have accumulated in the soil of cold northern regions, storing vast amounts of carbon.

As the Arctic climate changes, and temperatures rise, decomposition may speed up. If this happens, the extra carbon dioxide released from decaying plant materials will enter the atmosphere, adding to the CO2 emissions caused by humans. However, when it's warmer, plants grow better and take up more carbon dioxide. To find out if these changes will add to or reduce climate change, we need to know how much extra carbon dioxide will be released from soils versus that taken up by plants - in other words, we need to forecast the 'carbon balance' of the Arctic. To do this, we need mathematical 'models' of plant growth, just as to make a weather forecast we use mathematical models of winds and air pressure.

At the moment, our forecasting abilities are limited because we don't fully understand how changes in the environment affect the uptake of carbon dioxide by plants. This is especially true for mosses. We suspected however that changes affecting mosses may have large effects on carbon balance, because mosses are abundant in the Arctic, and have tough leaves and stems that resist decay.

This study measures the carbon dioxide uptake of mosses and compares it to that of common tundra shrubs. The paper also presents a mathematical model of moss growth, of the kind required to forecast carbon balance. We show that some moss species can take up almost as much carbon dioxide as shrubs, and that mosses take up lots of carbon dioxide in spring, when it is too cold for other plants to grow. This means that changes in climate that affect mosses will have a big effect on the carbon balance, especially in spring.

 

Antioxidant supplementation during early development reduces parasite load but does not affect sexual ornament expression in adult ring-necked pheasants

Josephine M. Orledge, Jonathan D. Blount, Andrew N. Hoodless and Nick J. Royle

Males of many species of bird often have bright, colourful sexual ornaments, such as the fleshy facial wattles of pheasants or the combs of cockerels. One possible reason for this may be that these exaggerated, brightly-coloured features of males provides an indication of his ability to resist infection by parasites and therefore his quality to potential mates. The colour of many of these sexual ornaments is determined by carotenoid pigments, which are obtained from the diet and also have other important functions as antioxidants and in immune defence. As a result carotenoids that are used as antioxidants or in immune defence (e.g. when exposed to parasite infection) are not available for use in sexual display, so individuals that are less able to resist parasite infection are expected to have duller and/or less exaggerated sexual ornaments. However, this prediction has proved difficult to test experimentally, most probably because most studies do not take into account early life-history effects: the environmental conditions that individuals experience during growth and development affect the expression of traits, such as sexual ornaments, in adulthood. If the brightness and size of sexual ornaments reflects the ability of individuals to resist parasites in the long-term (i.e. their 'quality') then individuals that have reduced exposure to infection during early development, either directly (lower parasite burden) or indirectly (increased availability of non-pigmentary antioxidants) are expected to have brighter sexual ornaments in adulthood. We tested this prediction by providing an antioxidant supplement and manipulating the parasite burden of male pheasants during early development (the first 8 weeks of life) and then measured the size and brightness of sexual ornaments at adulthood. Supplementation of individuals with vitamin E reduced the amount of parasites they had both during early life and in adulthood. However, despite this neither the growth, size and immune function, nor the intensity of sexual display of individuals was affected by either the antioxidant supplementation or the intensity of parasite infection experienced during development. Consequently there was no evidence that the expression of sexual ornaments provided information on the ability of males to resist infection from parasites.

 

Fish mediated trait compensation in zooplankton

Samuel Hylander, Sol Souza, Esteban Balseiro, Beatriz Modenutti and Lars-Anders Hansson

Lakes and oceans contain large numbers of small crustaceans called zooplankton (~1 mm). These animals are crucial for the ecosystem in that they eat phytoplankton and are themselves important food items for fish. A common type of zooplankton are called copepods and they are able to accumulate red pigments when exposed to sun light. This "sun tan",which is very similar to the red pigment in carrots, reduces the damage to DNA and other cellular structures that can result from exposure to ultraviolet radiation (UVR). The red pigmentation is however dangerous for the animals since they become more visible and hence more easily eaten by fish (predation). This puts the animals in a difficult situation where getting sun protection comes at a cost of higher predation risk.

We exposed zooplankton to fish cues (i.e. the smell of a fish) and observed that they reduced their pigmentation by approximately 30%. Interestingly, this reduction did not lead to the expected increase in UVR damage even though they had lost some of their protective pigmentation. Instead, zooplankton were able to offset the reduction in pigmentation by increasing their antioxidant enzymes. These enzymes protect the cells from damage by detoxifying reactive molecules that are produced when the copepods are exposed to UVR.We therefore conclude that zooplankton pigmentation and antioxidants are flexible defence systems which can be up- or down-regulated in accordance to the prevailing fish and UVR threat levels. These results add new knowledge to the fascinating set of defence mechanisms that animals have evolved to counteract detrimental effects of radiation from the sun.

 

How the ladybird got its spots

Jonathan Blount, Hannah Rowland, Falko Drijfhout, John Endler, Richard Inger, John Sloggett, Gregory Hurst, David Hodgson and Michael Speed

Prey species often possess defences (e.g. toxins) coupled with eye-catching colours and patterns to deter predators. Such warning signals have traditionally been thought to convey relatively little information, functioning only to inform predators that prey are defended (rather than undefended). Rather like a red traffic light, warning signals should be clear and simple so that the message is readily understood. Recently, however, it has become clear that warning colouration often varies within species, and correlates with the strength of defences. This has led to speculation that warning signals may be honest signals of defensive capability, with signal reliability ensured by the costliness of producing the display. However, evidence that warning signals are costly to produce has been lacking.

We reared seven-spot ladybirds on either a Low or a High aphid diet, and measured the effects on warning signals, levels of defensive chemicals, and relationships between signals and defences. Our main finding was that ladybirds fed abundant aphids (High diet) had increased body levels of one defensive chemical (precoccinelline), and their wing cases were redder and more conspicuous at adulthood. Furthermore, wing case pigmentation correlated positively with levels of precoccinelline in both diet groups, suggesting that the familiar red colouration of the seven-spot ladybird is an honest signal of defensive capability. We also found that the size of black spots and body levels of a different toxin, coccinelline, correlated positively in Low diet ladybirds but negatively in High diet ladybirds.

Our findings confirm that producing warning signals, and chemical defences, is costly for ladybirds. When individuals lacked access to an abundant supply of food they produced relatively weak chemical defences and this was revealed to predators through the expression of relatively inconspicuous signals. However, when resources were abundant, ladybirds produced stronger chemical defences and more conspicuous signals. Therefore, it appears that warning signals are far more information-rich than has previously been thought likely.

 

Acceleration data reveals the energy management strategy of a marine ectotherm during reproduction

Sabrina Fossette, Gail Schofield, Martin Lilley, Adrian Gleiss and Graeme Hays

Female ectotherms (i.e. animals whose body temperature varies with the environment) need to maintain warm body temperatures during the reproductive season to boost embryonic development. On land, many ectotherms (e.g. lizards and snakes) do so by basking in the sun, but the strategy used by marine species, such as sea turtles, is less obvious.

To study the strategy that female sea turtles use to keep warm, and help egg development during the weeks before their first nest, we equipped six loggerhead turtles with accelerometers (i.e. devices recording three dimensional movements) for six weeks, at the important breeding site of Laganas Bay, Zakynthos, Greece. There, sea temperatures vary seasonally, and are generally cool at the start of the season. The deployed accelerometers measured turtle activity and the temperature they experienced when in the shallow waters of Laganas Bay.

The data we collected show that at the beginning of the season, female turtles did not stay inactive for long periods, in the same manner as basking snakes or lizards, perhaps because the ambient temperature in shallow waters may vary rapidly with wind conditions. Therefore, the turtles probably had to constantly seek out new warm water patches along the shoreline. In addition, strong competition with other females for access to these warm patches may also explain the high level of activity observed at the start of the breeding season.

As sea temperatures in the bay warmed up, female activity levels dramatically decreased; the turtles spent more time resting and reduced any unnecessary movements. They notably spend long periods of time (up to 90 minutes) resting on the sea bed. This behaviour may help females save energy before eventually crawling up the beach to lay their eggs.

We compared our field results with a theoretical model and found that actively maintaining a high and stable body temperature during the first few weeks of the breeding season, before decreasing activity levels for the rest of the season, seems to be of clear benefit to female turtles at temperate breeding sites, and may help maximise the number of eggs they can lay over a season.

 

Elevated haemocyte number is associated with infection and low fitness potential in wild Daphnia magna.

Stuart K. J. R. Auld, Andrea L. Graham, Philip J. Wilson and Tom J. Little

You might think that being able to mount a strong immune response is a good thing - animals with stronger immune responses should be healthier because they are better at preventing infections. However, it's not always that simple. We studied the immune responses and health of the pond-dwelling crustacean Daphnia magna (water flea) and its sterilizing parasite Pasteuria ramosa, both in the wild and in the lab. Daphnia with the strongest cellular immune responses were most likely to develop infection with the parasite, and sick Daphnia had the most circulating immune cells. What is more, sick Daphnia were sterile - they permanently lost the ability to have offspring. Here, a strong immune response was a symptom of infection and not a cause of immunity; a desperate and futile attempt to stay healthy.

The image is of two genetically identical (clones) of Daphnia magna. The female on the left is healthy and carrying a clutch of offspring; the female on the right has been sterilized by an infection with Pasteuria ramosa (note the empty brood pouch).

 

Stem xylem conductivity is key to plant water balance across Australian angiosperm species

Sean M Gleason, Don W Butler, Kasia Ziemiska, Pawe Waryszak and Mark Westoby

Differences in plant size and shape are conspicuous aspects of Earth's vegetation. Some differences are obvious, such as plant height or canopy leafiness. Other differences remain unseen, such as the capacity of trunks and branches to transport water from soil to leaves, or the depth to which roots explore the soil. Plant traits, both seen and unseen, affect how well a plant species will survive and compete in habitats ranging from wet rain forests to arid deserts.

We measured traits affecting the transport of water in woody plants across a broad range of temperature and aridity in eastern Australia. A plant's demand for water increases as its canopy becomes leafier or as the air becomes drier. Resistance to water transport also increases as the soil becomes drier or as the plant becomes taller. Plants have various options for satisfying their canopy's demand for water as the resistance to water transport becomes greater (increasing height or drier soils). Plants can grow deeper roots to access deeper water sources. Plants can become shorter. Plants can become less leafy or reduce the water loss from their leaves. Plants can also increase the capacity of their roots and stems to transport water. The question we asked was, out of all these possible ways to deal with water scarcity, which accounted for most of the variation across the species and habitats in this study?

Reduced leafiness turned out not to be a common response. Indeed as plant height increased across species (impeding water transport), plants actually became more leafy. Increasing height and leafiness may have evolved to achieve better access to light where competition for light was significant. The main plant trait offsetting height and leafiness was increased water transport capacity in stems. This enables plants to supply tall, leafy canopies with water. Our study is the first to quantify the importance of water transport capacity in maintaining water balance across such a large range of species and habitats.

 

Shrinking Crustaceans in a Warming World: It's Strictly for Grown-Ups

Jack Forster and Andrew Hirst

We have been investigating an unusual phenomenon in cold-blooded organisms: when individuals from a single species are reared at warmer temperatures, they grow up to be smaller adults than those reared at colder temperatures. This effect, known as the "temperature-size rule" (TSR), affects more than 80% of cold-blooded species.

The impact of the TSR is substantial, with adult size decreasing by an average of 2.5% for every 1°C increase in temperature. Given the predicted increases in global temperature, it is vital that we understand how these size changes are brought about. In particular, we do not when in the life cycle these size changes occur, and whether they are maintained across many generations. To answer these questions, we used the brine shrimp Artemia franciscana, a close relative of the children's pet the "sea monkey". These make a good test species as they have clearly-identifiable life stages (egg and 17 larval stages).

We grew these shrimp over a range of temperature for two generations, to see how and when size changes occurred. We found that egg and early larval sizes were not significantly affected by temperature; it was only later in life (from larval stage 12) that sizes became temperature sensitive in line with the TSR. Further, the second generation of shrimps followed exactly the same pattern: even though their parents followed the TSR, young were the same size at all temperatures. This means temperature-size effects are "reset" at the beginning of each generation. We also show that the underlying cause of the TSR is that growth (increase in weight) is less temperature-sensitive than development (increase in life-stage).

As brine shrimp are primitive crustaceans, we put together similar data available for other crustacean species, to see if there were any commonalities in this group. We found the same pattern in these species: early life stages were not temperature-sensitive but later life stages were. This is not the case for all cold-blooded organisms, suggesting different mechanisms exist for bringing about temperature-size changes.

 

 

Spatial scale influences the outcome of the predator-prey space race between tadpoles and predatory dragonflies

John Hammond, Barney Luttbeg, Tomas Brodin and Andrew Sih

Predator prey interactions are often a daily occurrence for animals, including humans. We act as predators when we harvest food, prey when we combat diseases, and even play both roles for fun in games of tag and hide-and -seek. In these interactions how predators and prey use space has large consequences for their growth and survival. Traditionally, most research has focused on the response of one species while keeping the other species fixed in space. Not surprisingly, research has found that predators try to be in areas with more prey and prey try to be in areas with fewer predators. When predators and prey can freely interact though, the resulting distribution is inherently a product of both their responses.

We expect the species with an advantage either in movement, perception, or better utilization of the environment to be more able to dictate the joint spatial distribution. We predict that food patch size also inherently favors one species, but switches between favoring the prey at smaller scales to favoring the predators at larger. To test this question, we examined groups of tadpole prey and larval dragonfly predators in experimental arenas consisting of four patches of the prey's resources divided into two spatial scales.

Our results generally match our predictions, with predators near more prey than expected at larger scales and prey near fewer predators than expected at smaller scales. We also examined what conditions influence an individual to leave a patch. At the smaller scale, prey generally left areas with less food and higher densities of prey. At the larger scale, prey still left areas with low food, but tended to remain in patches with more predators.

Understanding how spatial patterns of predators and prey are formed will be critical in our changing world. As natural habitats are increasingly destroyed by humans, the habitats of predators and prey have become more fragmented. To predict how predators and prey will fare in their new environments we need to know how they will use space and how their relative spatial distributions affect their interactions.

 

 

 

Competition through pollen loss to foreign flowers among plants that share bat pollinators

Nathan Muchhala and James Thomson

Competition for pollination is often thought to be central to the evolution of flowers. Such competition occurs when pollinators switch between different species of flowers in their foraging routes, thus transferring pollen between species. When foreign pollen is delivered to a flower, it can inhibit the pollination process, blocking same-species pollen from reaching ovules or usurping these ovules. Such negative affects on female fitness have been well-studied. The complementary negative affects on male fitness, when switching between flowers reduces pollen successfully delivered by male flowers to female flowers, have received less attention.

Here we quantify the amount of pollen transferred by nectar bats between bat-pollinated focal flowers (Aphelandra acanthus) with and without intervening visits to one of two competitor species. One competitor (Centropogon nigricans) places its pollen in the same region of bats' heads as the focal species, while the other (Burmeistera sodiroana) places its pollen farther forward. We found that 1) any intervening visit caused some reduction in the number of pollen grains transferred, 2) competitor flowers with similar pollen-placement locations caused greater reductions in pollen transfer, and 3) of these competitors, those in male-phase (dispensing pollen) caused greater pollen loss than those in female-phase (without pollen). This study provides rare empirical support for the detrimental effects of competition for pollination on male fitness via pollen loss, and is the first to show an added cost imposed by male-phase competitors. Although this competition is especially strong when competitors overlap in pollen placement, placing pollen in different regions of pollinator's bodies will not completely eliminate pollen loss during visits to foreign flowers, simply because pollen sheds or is groomed from their bodies at some background rate over time. This suggests that any flowering plants that share pollinators face pervasive selection through male fitness to diverge in floral traits, alleviating competition by evolving differences that attract different pollinators or alter when flowers open. This diversifying selection in response to competition may help to explain why plants have evolved such a spectacular diversity of flower shapes, colors, and odors.

Search the Site

Search

Site Adverts

 
 
Virtual Issue on Evolutionary Ecology of MutualismsEcological ImmunologySpecial Feature on Plant Defences