Energetic Benefits of Sociality Offset the Costs of Parasitism in a Cooperative Mammal

Sociality and particularly advanced forms of sociality such as cooperative breeding (living in permanent groups with reproductive division of labour) is relatively rare among vertebrates. A suggested constraint on the evolution of sociality is the elevated transmission rate of parasites between group members. Despite such apparent costs, sociality has evolved independently in a number of vertebrate taxa including humans. However, how the costs of parasitism are overcome in such cases remains uncertain. We evaluated the potential role of parasites in the evolution of sociality in a member of the African mole-rats, the only mammal family that exhibits the entire range of social systems from solitary to eusocial. Here we show that resting metabolic rates decrease whilst daily energy expenditure and energy stores (i.e. body fat) increase with group size in social Natal mole rats (Cryptomys hottentotus natalensis). Critically, larger groups also had reduced parasite abundance and infested individuals only showed measurable increases in energy metabolism at high parasite abundance. Thus, in some circumstances, sociality appears to provide energetic benefits that may be diverted into parasite defence. This mechanism is likely to be self-reinforcing and an important factor in the evolution of sociality.     

Sociality in the Australian Allodapine Bee Brevineura elongata: Small Colony Sizes Despite Large Benefits to Group Living

Allodapine bees (family Apidae, subfamily Xylocopinae) provide substantial material for investigating the evolution of sociality because of their wide variation in colony size, life history traits, and caste differentiation. Two recent studies have shown that the Australian allodapine genus Brevineura exhibits a strong increase in per capita brood production (PCBP) in social colonies compared to single-female nests. However both species previously examined, B. xanthoclypeata and B. froggatti, show relatively few multi-female nests, which is puzzling considering the apparently large advantages for group-living in these species. Here we show that in a third species, B. elongata, there are also substantial benefits for group living, involving increased PCBP and a greatly reduced likelihood of nests without brood. As expected from these observations, we also found strongly female biased sex allocation. Nevertheless only a small percentage of nests contained more than one adult female, similar to the other two Brevineura species, raising the question of why multifemale colonies are not more common in this genus. Solving this puzzle will throw light on conditions that constrain sociality when group living apparently provides major advantages.     

Aphid Wing Induction and Ecological Costs of Alarm Pheromone Emission under Field Conditions

The pea aphid, Acyrthosiphon pisum Harris, (Homoptera: Aphididae) releases the volatile sesquiterpene (E)-β-farnesene (EBF) when attacked by a predator, triggering escape responses in the aphid colony. Recently, it was shown that this alarm pheromone also mediates the production of the winged dispersal morph under laboratory conditions. The present work tested the wing-inducing effect of EBF under field conditions. Aphid colonies were exposed to two treatments (control and EBF) and tested in two different environmental conditions (field and laboratory). As in previous experiments aphids produced higher proportion of winged morphs among their offspring when exposed to EBF in the laboratory but even under field conditions the proportion of winged offspring was higher after EBF application (6.84±0.98%) compared to the hexane control (1.54±0.25%). In the field, the proportion of adult aphids found on the plant at the end of the experiment was lower in the EBF treatment (58.1±5.5%) than in the control (66.9±4.6%), in contrast to the climate chamber test where the numbers of adult aphids found on the plant at the end of the experiment were, in both treatments, similar to the numbers put on the plant initially. Our results show that the role of EBF in aphid wing induction is also apparent under field conditions and they may indicate a potential cost of EBF emission. They also emphasize the importance of investigating the ecological role of induced defences under field conditions.     

Female‐Biased Helping in a Cooperatively Breeding Bird: Female Benefits or Male Costs?

There is often a sex bias in helping effort in cooperatively breeding species with both male and female helpers, and yet this phenomenon is still poorly understood. Although sex‐biased helping is often assumed to be correlated with sex‐specific benefits, sex‐specific costs could also be responsible for sex‐biased helping. Cooperatively breeding brown jays (Cyanocorax morio) in Monteverde, Costa Rica have helpers of both sexes and dispersal is male‐biased, a rare reversal of the female‐biased dispersal pattern often seen in birds. We quantified helper contributions to nestling care and analyzed whether there was sex‐biased helping and if so, whether it was correlated with known benefits derived via helping. Brown jay helpers provided over 70% of all nestling feedings, but they did not appear to decrease the workload of breeders across the range of observed group sizes. Female helpers fed nestlings and engaged in vigilance at significantly higher levels than male helpers. Nonetheless, female helpers did not appear to gain direct benefits, either through current reproduction or group augmentation, or indirect fitness benefits from helping during the nestling stage. While it is possible that females could be accruing subtle future direct benefits such as breeding experience or alliance formation from helping, future studies should focus on whether the observed sex bias in helping is because males decrease their care relative to females in order to pursue extra‐territorial forays. Explanations for sex‐biased helping in cooperative breeders are proving to be as varied as those proposed for helping behavior in general, suggesting that it will often be necessary to quantify a wide range of benefits and costs when seeking explanations for sex‐biased helping.     

蜜蜂肠道微生物与其社会性的关系

蜜蜂是一种典型的营群居生活的社会性昆虫,相比独居生活的昆虫,其肠道微生物具有独特的区系结构。这种独特肠道微生物与其社会性之间的关系是一个重要的科学问题。现有研究显示,蜜蜂肠道的优势菌包括9大类群。消化道不同区段的优势菌种类和丰度存在差异。主要表现为前肠种类少、丰度低、后肠种类多、数量大,占了全消化道微生物的99%以上。不同社会分工的蜜蜂肠道微生物区系结构存在差异,肠道微生物会通过影响胰岛素信号的传导、保幼激素和卵黄原蛋白的合成以及蜜蜂抗氧化应激的能力等对蜜蜂的级型分化、社会分工、摄食行为及寿命长短产生调节作用。除此之外,蜜蜂肠道微生物还具有激活免疫、抑制病原菌生长、降解食物、促进养分吸收、解毒、发酵蜂蜜和蜂粮等作用。主要针对蜜蜂肠道微生物的基本特征及其与蜜蜂社会性的关系作一简要综述。     

Cultivars of Hexaploid Wheat of Contrasting Stature and Chlorophyll Retention Differ in Cytokinin Content and Responsiveness

The work reported here compared cytokinin content and sensitivityin a selection of hexaploid wheat (Triticum aestivum L.) cultivarsusing the following measurements: leaf cytokinins at three timepoints during light-growth and at four 24 h intervals afterlight-grown plants were transferred to darkness; sensitivityof root growth to direct applications of isopentenyl adenosine([9R]iP); and, sensitivity of germination and subsequent rootand shoot growth to 18 h imbibition of seeds in benzyladenine(BA). Accumulation of zeatin riboside-type cultivars was greatestduring light-growth in Tibet Dwarf, a wheat with an extremedwarf phenotype, intermediate in Omar standard and dwarf cultivars,and lowest in the standard and dwarf versions of Itana. Cytokininlevels were otherwise not directly correlated to plant staturein these wheats. There were no cultivar-associated qualitativedifferences in the types of cytokinins detected in this study.During the 16 h light period, the content of zeatin riboside-typecytokinins increased up to tenfold and then declined to basallevels during dark growth. Chlorophyll retention during dark-growthwas correlated with leaf cytokinin content. Data collected ata restricted number of sampling points during dark-growth suggesteda cyclic accumulation of [9R]iP-type cytokinins and the apparentcycle in Tibet Dwarf was offset by 24 h. Tibet Dwarf showedthe greatest root growth inhibition after exposure of seedlingroots to [9R]iP or imbibition of seeds in BA. Neither of thesetreatments affected shoot growth in any of the cultivars. Wheat; Triticum aestivum ; cytokinin; zeatin riboside; benzyladenine; root inhibition     

Feeding: Models of Costs and Benefits in Energy Regulation

Models to predict feeding behavior at the level of consumptionand use of energy involve either details of internal (physiological)controls or economic principles of regulation based on optimal(evolutionary) foraging theory. These two approaches will ultimatelybe related, but the former requires more information for specificpredictions. The latter can provide predictions based on selectedcriteria for regulation. Meal sizes and feeding frequencies of hummingbirds are examinedrelative to two regulatory, criteria: maximizing rate of netenergy gain and maximizing efficiency (intakes/expenditures)through a "crop emptying" model that incorporates energy intakefrom food and energy expenditures for short-term (meal to meal)maintenance and longer-term (overnight) energy storage. Experimentalresults suggest that the feeding behavior of hummingbirds isdifferentially sensitive to short-term and daily uses of energy.Changes in overnight energy storage requirements result primarilyin changes in meal size, while changes in meal to meal maintenancerequirements result primarily in feeding frequency changes.The economic models predict these responses. The feeding behaviorof hummingbirds also appears to be sensitive to food quality,time spent flying to and from a food source, and costs associatedwith the weight of ingested food.     

Costs and Benefits of Opisthobranch Swimming and Neurobehavioral Mechanisms

After opisthobranch molluscs dislodge from the substrate duringonset of swimming, the ensuing flexion or undulatory motionsare usually not well oriented with respect to predators, preyor suitable substrate. Swimming motions are effective in launchinganimals off the substrate and elevating them into the watercolumn where they are primarily transported passively by ambientwaves and tidal currents. Both active swimming and passive transporton ambient currents may provide escape from predators, searchfor food and mates, and dispersal to new and potentially adaptivelocations. However, loss of contact with the substrate and launchinginto the water column may also bring a high cost in terms ofexposure to diverse risks. I illustrate several forms of opisthobranchswimming and describe their mechanisms and roles. In addition,adaptations of some opisthobranchs to reduce the risks of exposureto predators during swimming are suggested. These adaptationsinclude small size, transparency or inconspicuous color to reducepredation while swimming, and neurobehavioral mechanisms ofrheotaxis and geomagnetic sensitivity.     

Benefits and Costs of Dominance in the Angelfish Centropyge bicolor

Social groups are often structured by dominance hierarchies in which subordinates consistently defer to dominants. High‐ranking individuals benefit by gaining inequitable access to resources, and often achieve higher reproductive success; but may also suffer costs associated with maintaining dominance. We used a large‐scale field study to investigate the benefits and costs of dominance in the angelfish Centropyge bicolor, a sequential hermaphrodite. Each haremic group contains a single linear body size‐based hierarchy with the male being most dominant, followed by several females in descending size order. Compared to their subordinate females, dominant males clearly benefited from disproportionately high spawning frequencies, but bore costs in lower foraging rates and greater aggressive defence of their large territories. Within the female hierarchy, more dominant individuals benefited from higher spawning frequencies and larger home ranges, but displayed neither higher foraging rates nor spawn order priority. However, dominance in females was also linked to aggressiveness, particularly towards immediate subordinates, suggesting that females were using energetically costly aggression to maintain their high rank. We further showed by experimentally removing dominant females that the linear hierarchy was also a social queue, with subordinates growing to inherit higher rank with its attendant benefits and costs when dominants disappeared. We suggest that in C. bicolor, the primary benefit of high rank is increased reproductive success in terms of current spawning frequency and the prospect of inheriting the male position in the near future, which may be traded off against the cost of aggressively defending rank and territory.     

Costs and Benefits of Food Foraging for a Braconid Parasitoid

The costs and benefits of food foraging for the insect parasitoid, Phanerotoma franklini Gahan (Hymenoptera: Braconidae), were examined. Feeding benefited P. franklini by increasing longevity, but did not influence egg maturation. Costs of feeding are represented by the time required to locate and consume food. Field observations of starved wasps revealed that wasps spent approximately 25% of their time grazing on substances on the surface of cranberry foliage. However, our initial laboratory tests to determine the value of these substances were inconclusive. We also examined how grazing behavior integrated with host foraging by comparing the attack rate of fed and unfed wasps held under different host densities. While feeding status did not affect the mean attack rate of wasps, starvation enhanced the probability that a wasp will engage in movement over the host plant foliage. We conclude that feeding benefits P. franklini by increasing longevity, that travel time to food sources is likely to be low, and that the observed food-foraging behavior does not appear to influence host-foraging efficiency.     

Why Does the Frequency of Nest Parasitism by the Cuckoo Differ Considerably Between Two Populations of Warblers Living in the Same Habitat?

The rate of nest parasitism is a product of two interacting phenomena: host selection by cuckoos and defence by hosts. In our study area the rate of nest parasitism by cuckoos is significantly lower in the great reed warbler (GRW; Acrocephalus arundinaceus) than in the reed warbler (RW; A. scirpaceus), even though they breed in the same habitat and their reproductive biology is similar. We hypothesized that the difference in the proportion of parasitized nests may reflect a narrow selection of host by cuckoos (they prefer RW nests) or/and the relatively better alien egg discrimination in the GRW. In the egg discrimination experiment the GRW rejected the higher proportion of alien eggs than the RW. However, in both species the discriminative ability considerably varied in time, both within the day and within the breeding cycle. A logistic regression model suggests that the GRW would be a frequent host if only nest parasites could exploit the period of its lowest sensitivity to alien eggs. We conclude that the relatively low rate of nest parasitism in the GRW may reflect both its good discriminative ability and the low number of cuckoos that are specialized in dumping eggs to nests of this warbler. The adaptation of cuckoos to the particular host species may involve not only production of mimetic eggs, but also adjusting activity to temporal changes in sensitivity to alien eggs in the host.     

Female House Mice do not Differ in Their Exploratory Behaviour from Males

Dispersal is an important ecological trait affecting genetic variation and dynamics of populations. Hence, the exploratory behaviour prior to actual dispersal may be crucial for potentially dispersing individuals. In mammals, females are traditionally seen as the more philopatric sex and dispersal as male‐biased behaviour, and so behavioural strategies related to the exploration of novel resources should be differentially expressed in males and females. In addition, due to sexual selection exploratory strategies may be expected to vary according to females’ reproductive phase. We employed a standard open‐field test as an approximation of the first phase of dispersal, using adult house mice representing two subspecies, M. m. musculus and M. m. domesticus. We tested the prediction that exploration of neutral area varies in females during different phases of the oestrus cycle and is different between both sexes and subspecies. We expected to find higher exploration in males, as the more dispersing sex and less pronounced subspecies‐specific differences in females than in males. We found no significant effect of the oestrous phase on any of the parameters of the exploratory behaviour measured. Sexual dimorphism was found only in latency to enter the arena in M. m. domesticus where females hesitated longer to enter a new area than males. Significant subspecies‐specific differences were found in three of four tested exploration parameters, so we conclude that females of both subspecies follow similar strategies to those displayed by males. Musculus mice show shorter latency to enter a new area, but once inside, domesticus mice explore the arena significantly longer, with less frequent retreats to a shelter. Our results thus highlight that the role of female dispersal in interdemic gene flow should not be neglected.     

Strong Costs and Benefits of Winter Acclimatization in Drosophila melanogaster

Studies on thermal acclimation in insects are often performed on animals acclimated in the laboratory under conditions that are not ecologically relevant. Costs and benefits of acclimation responses under such conditions may not reflect costs and benefits in natural populations subjected to daily and seasonal temperature fluctuations. Here we estimated costs and benefits in thermal tolerance limits in relation to winter acclimatization of Drosophila melanogaster. We sampled flies from a natural habitat during winter in Denmark (field flies) and compared heat and cold tolerance of these to that of flies collected from the same natural population, but acclimated to 25 °C or 13 °C in the laboratory (laboratory flies). We further obtained thermal performance curves for egg-to-adult viability of field and laboratory (25 °C) flies, to estimate possible cross-generational effects of acclimation. We found much higher cold tolerance and a lowered heat tolerance in field flies compared to laboratory flies reared at 25 °C. Flies reared in the laboratory at 13 °C exhibited the same thermal cost-benefit relations as the winter acclimatized flies. We also found a cost of winter acclimatization in terms of decreased egg-to-adult viability at high temperatures of eggs laid by winter acclimatized flies. Based on our findings we suggest that winter acclimatization in nature can induce strong benefits in terms of increased cold tolerance. These benefits can be reproduced in the laboratory under ecologically relevant rearing and testing conditions, and should be incorporated in species distribution modelling. Winter acclimatization also leads to decreased heat tolerance. This may create a mismatch between acclimation responses and the thermal environment, e.g. if temperatures suddenly increase during spring, under current and expected more variable future climatic conditions.     

Benefits, Costs and Constraints of Anti-Parasitic Grooming in Adult and Juvenile Rodents

Grooming behaviour plays various roles in the health care, reproduction, and social life of an individual vertebrate. However, the reasons for the variability in time spent grooming amongst species, populations and individuals are not fully understood. We tested the hypothesis that the main role of grooming is ectoparasite removal and thus that time spent grooming by an animal reflects the costs of parasite infestation offset against the costs of grooming. The test was conducted on a rodent, Meriones crassus, that is parasitised by a flea, Xenopsylla conformis. We monitored behaviour of juvenile and adult rodents before and after flea infestation and quantified the probability of mortality of fleas with respect to the time spent grooming in adults compared with juvenile rodents. We predicted that: (1) increased costs of flea infestation (e.g. in parasitised as opposed to flea‐free rodents and in juveniles as opposed to adults) increases time spent grooming and (2) mortality probability per flea increases with increasing time spent grooming and is higher for fleas on juveniles than for fleas on adult rodents. We were interested to discover at the expense of which activity grooming is increased. Our findings established that the major role of grooming is in flea removal, as exposure to fleas evoked grooming activity in all rodents and grooming activity explained 57–70% of the variation in flea mortality. Furthermore, we showed that the rise in grooming activity was at the expense of resting. However, we found only partial support for the predicted increase in grooming time with increasing costs of flea infestation. Flea infestation did indeed increase the time spent grooming by rodents. Nevertheless, juvenile rodents who incur higher costs of flea infestation spent less time grooming than adults and sustained similar flea densities, suggesting that these hosts are constrained by some other factors, such as feeding time.     

Parental Responses to Changes in Costs and Benefits Along an Environmental Gradient

We evaluated the effects of dissolved oxygen on offspring survival, parental costs, and the pattern of parental care in Florida flagfish, Jordanella floridae (Cyprinodontidae). Specifically, we quantified (1) embryonic development and survival in the absence of parental care, (2) behavior of non-reproductive adults, and (3) behavior of parental males across a gradient in dissolved oxygen. Embryo developmental rates and survivorship increased with dissolved oxygen, with a relatively sharp increase in survival between medium and high oxygen treatments. Non-reproductive adults increased their frequency of aquatic surface respiration, reduced overall activity, and increased opercular beat rate as oxygen declined, suggesting increased costs of activity with reduced oxygen. Taking these cost measures together, costs appear to increase slowly as oxygen starts to decline and then increase sharply as conditions approach hypoxia. In contrast, parental effort increased gradually with dissolved oxygen. We conclude that the increase in care from low to medium oxygen primarily results from a sharp decline in physiological costs, whereas the continued increase in care from medium to high oxygen primarily results from an increase in offspring value. In addition, our results highlight that the benefits of fanning for offspring are not well understood and that they may increase with oxygen, contrary to what has been previously assumed.     

Estimating Costs and Benefits of CTL Escape Mutations in SIV/HIV Infection

Mutations that allow SIV/HIV to avoid the cytotoxic T lymphocyte (CTL) response are well documented. Recently, there have been a few attempts at estimating the costs of CTL escape mutations in terms of the reduction in viral fitness and the killing rate at which the CTL response specific to one viral epitope clears virus-infected cells. Using a mathematical model we show that estimation of both parameters depends critically on the underlying changes in the replication rate of the virus and the changes in the killing rate over time (which in previous studies were assumed to be constant). We provide a theoretical basis for estimation of these parameters using in vivo data. In particular, we show that 1) by assuming unlimited virus growth one can obtain a minimal estimate of the fitness cost of the escape mutation, and 2) by assuming no virus growth during the escape, one can obtain a minimal estimate of the average killing rate. We also discuss the conditions under which better estimates of the average killing rate can be obtained.