Nest Mates Research Articles

Social interactions in the central nest of Coptotermes formosanus juvenile colonies

Juvenile colonies of Coptotermes formosanus Shiraki were investigated to determine the social interactions among all individuals near the central nest of a colony. The behavioral repertoire of whole colonies of subterranean termites has yet to be identified because of their cryptic nests. Colonies were placed in planar arenas, and their behavioral repertoire and activities were recorded with video cameras. All castes and larval instars were determined and behavioral interactions were monitored and described, including feeding behaviors, grooming, nest maintenance, and inactivity. When two termites interacted, it was also determined which one was the donor or the recipient of the act. An ethogram was constructed by calculating relative frequency of each behavior for first instar larvae, second instar larvae, first instar workers, second instar workers or older, queen, king, soldiers and presoldiers. Larval instars, primary reproductives and soldiers were mostly passive during interactions. Workers performed most of the tasks; however, there was a difference of task divisions among worker instars. Young workers (W1) performed most of the grooming of individuals in the central nest, while older workers (W2+) provided nest maintenance and sanitation, by collecting fecal matter from most nest mates. In addition, older workers were mostly in charge of caring for the primary reproductives and the maintenance of the royal chamber. This study identified instar-specific activities and provides a first insight into caste and age polyethism in C. formosanus.

Colony contact contributes to the diversity of gut bacteria in bumblebees (Bombus terrestris).

Social bees, like honeybees and bumblebees, have a close contact with nest mates of different developmental stages and generations. This could enhance bacterial transfer between nest mates and offers opportunities for direct transfer of symbionts from one generation to the next, resulting in a stable host specific gut microbiota. Gut symbionts of honeybees and bumblebees have been suggested to contribute in digestion and protection against parasites and pathogens. Here we studied the impact of contact with the bumblebee colony on the colonization potential of the bacterial families (i.e., Neisseriaceae, Orbaceae, Lactobacillaceae and Bifidobacteriaceae) occurring in the gut of adult bumblebees (Bombus terrestris). Bacterial profiles of the gut microbiota of B. terrestris were determined based on the hypervariable V4 region of the 16S rRNA using paired-end Illumina sequencing. In our experiments, we created different groups in which we gradually reduced the contact with nest mates and hive material. We made 3 observations: (i) reducing the contact between the colony and the bumblebee during adult life resulted in a significant drop in the relative abundance of Lactobacillus bombicola and Lactobacillus bombi; (ii) Bifidobacteriaceae required contact with nest mates to colonize the gut of B. terrestris and a significant lower bacterial diversity was observed in bumblebees that were completely excluded from colony contact during the adult life; (iii) Snodgrassella and Gilliamella were able to colonize the gut of the adult bumblebee without any direct contact with nest mates in the adult life stage. These results indicate the impact of the colony life on the diversity of the characteristic bumblebee gut bacteria.

A social mechanism facilitates ant colony emigrations over different distances.

Behavioural responses enable animals to react rapidly to fluctuating environments. In eusocial organisms, such changes are often enacted at the group level, but may be organised in a decentralised fashion by the actions of individuals. However, the contributions of different group members are rarely homogeneous, and there is evidence to suggest that certain 'keystone' individuals are important in shaping collective responses. Accordingly, investigations of the dynamics and structuring of behavioural changes at both the group and individual level are crucial for evaluating the relative influence of different individuals. Here, we examined the composition of tandem running behaviour during colony emigrations in the ant species Temnothorax albipennis Tandem running is modulated in response to emigration distance, with more runs being conducted when a more distant nest site must be reached. We show that certain individuals are highly active in the tandem running process, attempting significantly more work in the task. Contrary to expectations, however, such individuals are in fact no more successful at conducting tandem runs than their less active nest mates. Instead, it seems that when more tandem runs are required, colonies rely on greater recruitment of workers into the process. The implications of our study are that in some cases, even when apparently 'key' individuals exist within a group, their relative contribution to task performance may be far from decisive.

Two pathogens change cuticular hydrocarbon profiles but neither elicit a social behavioural change in infected honey bees, Apis mellifera (Apidae: Hymenoptera)

AbstractSocial immunity is the cooperation of individual group members towards the control of disease transmission arising from social living. It has been identified as an important mechanism of natural disease control in honey bees, Apis mellifera Linnaeus, which can exhibit hygienic behaviours such as evicting pathogen‐infected or parasitised nest mates. Here, we examine if these bees exhibit a change in behaviour towards nest mates infected by the microsporidian pathogens Nosema apis and N. ceranae. We observed no significant change in the frequency of interactive and non‐interactive behaviours of bees towards Nosema‐infected nest mates, for both N. apis and N. ceranae. Thus, uninfected bees interacted and were exposed to pathogen‐infected bees equally often compared with uninfected bees. This lack of any behavioural modification suggests that bees are unable to recognise Nosema‐infected nest mates. These results were surprising given our analysis indicated that Nosema infection changes the hydrocarbon profiles of the bees, enabling the statistical discrimination of uninfected, N. apis and N. ceranae infected bees. The hydrocarbons we analysed were 16 straight‐chain alkanes ranging from heptadecane (C17H36) to tritriacontane (C33H68). Our results and those of others suggest that hygienic behaviour is currently unlikely to provide resistance towards Nosema pathogens in honey bees. The lack of social immunity was unexpected given the co‐evolution of one of the pathogens and honey bees. However, the modification of cuticular hydrocarbons by these pathogens provides a specific cue that may enable future selection and rearing of bees for Nosema‐related social immunity.

Extracting the Behaviorally Relevant Stimulus: Unique Neural Representation of Farnesol, a Component of the Recruitment Pheromone of Bombus terrestris.

To trigger innate behavior, sensory neural networks are pre-tuned to extract biologically relevant stimuli. Many male-female or insect-plant interactions depend on this phenomenon. Especially communication among individuals within social groups depends on innate behaviors. One example is the efficient recruitment of nest mates by successful bumblebee foragers. Returning foragers release a recruitment pheromone in the nest while they perform a ‘dance’ behavior to activate unemployed nest mates. A major component of this pheromone is the sesquiterpenoid farnesol. How farnesol is processed and perceived by the olfactory system, has not yet been identified. It is much likely that processing farnesol involves an innate mechanism for the extraction of relevant information to trigger a fast and reliable behavioral response. To test this hypothesis, we used population response analyses of 100 antennal lobe (AL) neurons recorded in alive bumblebee workers under repeated stimulation with four behaviorally different, but chemically related odorants (geraniol, citronellol, citronellal and farnesol). The analysis identified a unique neural representation of the recruitment pheromone component compared to the other odorants that are predominantly emitted by flowers. The farnesol induced population activity in the AL allowed a reliable separation of farnesol from all other chemically related odor stimuli we tested. We conclude that the farnesol induced population activity may reflect a predetermined representation within the AL-neural network allowing efficient and fast extraction of a behaviorally relevant stimulus. Furthermore, the results show that population response analyses of multiple single AL-units may provide a powerful tool to identify distinct representations of behaviorally relevant odors.

Performance of Altriset (TM) (Chlorantraniliprole) Termiticide Against Formosan Subterranean Termites, Coptotermes formosanus Shiraki, in Laboratory Feeding Cessation and Collateral Transfer Trials, and Field Applications

Chlorantraniliprole represents the first compound to be registered as a termiticide by the Environmental Protection Agency (EPA) in over a decade. This novel termiticide is currently registered as a 'reduced-risk pesticide' by the EPA. Laboratory and field trials were conducted to quantify mortality of Formosan subterranean termites (FST), Coptotermes formosanus Shiraki resulting from chlorantraniliprole treated soil, the degree to which the termites curtail feeding intensity post-exposure to chlorantraniliprole treated soil, collateral transfer of chlorantraniliprole among nest mates, and the effectiveness of chlorantraniliprole as a remedial treatment against structural infestations of HT. Termites which were exposed to chlorantraniliprole treated soil consumed significantly less paper than unexposed FST. The mean percent mortality of those termites exposed to chlorantraniliprole treated soil was significantly greater than that of unexposed FST. Depending on donor:recipient ratios, the mean mortality of recipients ranged from 14.65 - 90.00 % in the collateral transfer trials. There was a positive correlation between increased donor density and recipient mortality. Through 24 mo post-treatment, 27.3% of the structures which were treated in field trials were observed to have infestations of termites that required re-treatment; however, no FST were observed during the 30 and 36 month post-treatment inspections. Additionally, a novel scoring rubric was developed that will allow standardization of field study sites with respect to dissimilarity in site variables, and will allow for more consistent comparison of results across disparate field experiments. An explanation for the lack of successful remediation of many of the structures involved in the field trial is proposed and is based on our novel scoring system.

A siblicidal origin for avian brood parasitism?

We present a model for the evolution of host selection by avian brood parasites from the ecological context of siblicidal brood reduction tactics. Our analysis concentrates on the fitness costs and benefits that permit the evolution of brood parasitism as an adaptive strategy from a state of obligate parental care already featuring siblicide. Limited resources delivered by provisioning parents may incite siblicidal behaviour in offspring, directed towards nestmates regardless of kinship. The extent of siblicidal behaviour (in frequency of occurrence and number of nestmates killed) can extend to the eradication of all nestmates, as has been observed in some raptors and in seabirds. For parents of siblicidal offspring, laying each egg parasitically may maximize offspring survival by eliminating competition between related but siblicidal nest mates. To permit the evolution of conspecific (intraspecific) brood parasitism, costs of siblicide by the offspring of parasitic parents must exceed costs paid by the parasitic parents when losing related conspecifics (host offspring) in a host nest. To permit the evolution of obligate interspecific brood parasitism, costs to fitness from siblicidal offspring or nest reduction of related hosts must exceed costs of heterospecific parental care. Understanding the kin structure between parasites and hosts in conspecific parasitism, and measuring the costs paid by parasitic young due to mismatched incubation, provisioning, and social behaviours by heterospecific foster parents, should provide novel insights into the opportunities and constraints of the evolution of avian brood parasitism.

Ergonomic skew and reproductive queuing based on social and seasonal variation in foraging activity of eastern carpenter bees (Xylocopa virginica)

Reproductive division of labour in social carpenter bees differs from that in classically eusocial insects because reproductive output and ergonomic inputs are positively correlated—dominant females monopolize both foraging and reproduction. We quantified ergonomic skew in the facultatively social bee Xylocopa virginica (L., 1771) (eastern carpenter bee) based on detailed observations of foraging activity by individually marked females in 2009. Unusually for a univoltine bee, this species exhibits a spring foraging phase during which females feed pollen to other adults, probably as part of behavioural interactions to establish dominance hierarchies. During brood-provisioning, foraging in social nests was dominated by one female at a time, with replacement by a succession of foragers as dominants disappeared and were succeeded by a subordinate. The principal foragers (individuals that did the largest share of foraging in each colony) did 85%–100% of all pollen trips, so contributions to pollen-provisioning by female nest mates were highly uneven. Individual foraging rate was unaffected by group size and total colony foraging effort was a function of the number of foragers per group. Transient females that moved to new nests were as successful in achieving dominant forager status as females resident in their natal nests. This evidence indicates that colony social organisation is based on reproductive queues, whereby the first-ranked bee is the dominant forager and subordinates queue for opportunities to replace her.

Parent-Absent Begging in Barn Swallow Broods: Causes of Individual Variation and Effects on Sibling Interactions and Food Allocation

Altricial offspring solicit parental care using complex begging displays. Although such solicitations are mainly performed towards parents, nestlings of several birds often beg when parents are not at the nest. This parent-absent begging (PAB) has been interpreted as a mistake in correctly detecting parental arrival, but it may also reliably signal individual need to nest mates, potentially affecting intra-brood competition for food. Here, we focused on the proximate factors that may determine frequency and intensity of PAB, including brood size and sex ratio, as well as individual age, sex and body mass, in natural barn swallow (Hirundo rustica) broods, under conditions of normal and experimentally reduced food intake. We also investigated the relationship between PAB and begging intensity at parental arrival and food intake in the two different experimental conditions. The frequency of PAB was larger after food deprivation than before, indicating that PAB reliably reflects hunger level. In addition, nestlings increased their own begging intensity upon parental arrival after performing PAB. Concomitantly, siblings decreased begging effort, irrespective of sex or body mass, but this occurred only when nestlings were normally fed, suggesting that PAB diminishes scrambling for food by nest mates. Finally, such a reciprocal begging modulation resulted in a larger chance of obtaining food at the subsequent feeding event for nestlings performing PAB under normal food provisioning. Within-brood signalling in the absence of parents can therefore play an important role in determining competitive strategies among siblings and affecting parental decisions on food allocation in altricial broods.

Extreme excavation: fire ant style

Fans of The Lord of the Rings may disagree, but when it comes to exquisite excavation, the dwarves of Moria have nothing on the mighty fire ants of Georgia Tech. But Dan Goldman and Michael Goodisman aren't fascinated by the aesthetics of fire ant architecture alone. ‘I have an interest in animals interacting with complex materials’, explains Goldman, who has studied creatures such as sidewinder snakes and sandfish lizards moving through and across sand. With the ants on their doorstep, Goldman and Goodisman were intrigued to learn more about how the insects work together and the mechanical factors that affect ant nest construction in soils ranging from wet clay to coarse sand.However, producing consistent simulated soil conditions for the ants to excavate was not as simple as stirring soil into water – ‘Different people got different conditions’, Goldman recalls – until Nick Gravish came up with the idea of sieving mixtures of sand and water to create uniform distributions of water through the soil. Then, everything was ready for Daria Monaenkova to take 14.5 cm long plugs of the uniform soil samples – ranging from minute clay-like particles to ant head-sized grains of sand with a moisture content ranging from complete saturation to perfectly dry – drop mini-colonies consisting of 100 ants on the top and leave them to their excavations for 20 h. The challenge then was to visualise the nests without destroying them, so Monaenkova meticulously scanned the plugs with X-rays – taking 400 shots per nest – and laboriously reconstructed the 3D structures with Greggory Rodriguez and Rachel Kutner to see what the industrious insects had achieved.Analysing the structures, Monaenkova could see that no matter how large or small the grains of soil, the ants were able to excavate tunnels. However, the wetness of the soil dramatically affected their productivity. In completely dry soils, the ants couldn't dig at all, and Goldman says that they were only able to dig pitiful looking tunnels in slightly damp soils. But, when Monaenkova attempted to repeat the ants' efforts by driving a small steel rod into the relatively dry soils, they appreciated how impressive even these puny efforts were. ‘Daria couldn't do it’, says Goldman, adding that he suspects that the microengineers are building networks like Jenga puzzles to stabilise their structures. However, once the hydration reached an intermediate level, the ants were able to produce lengthy tunnels of a consistent diameter down through the soil. And, when the soil was completely saturated, the tiny engineers failed again: ‘It's like trying to build a sand castle with sloppy sand’, says Goldman. He suspects that the soils at intermediate levels of hydration yielded the most robust tunnels because the granules were bonded by strong capillary forces provided by minute droplets of water bridging the particles – although the stronger attachment did not impair the ants' excavations.Next, Monaenkova investigated the mechanics of ant excavation by enticing them to burrow against a glass cylinder wall while she filmed their Herculean efforts, revealing that the animals used two tactics. When the soil was coarse, they grasped a single grain and shuffled backward up the tunnel, dragging it with them. However, when the soil was fine and the ants could grasp multiple grains, they gathered a pellet of grains and marched upward. Goldman was most surprised by the ants' inventiveness, moulding bulky pellets like snowballs with their forelimbs, mandibles and even their antennae.Reflecting on the ants' engineering, Goldman says that he is impressed by their ability to work in a completely dark and confined environment while continually colliding with their nest mates. ‘It is just mind blowing how they can dig so well’, he says.

High begging intensity of great spotted cuckoo nestlings favours larger-size crow nest mates

In nests of birds parasitized by a larger non-evicting brood parasite, host chicks typically are at disadvantage in competing for food and often starve. However, when host chicks are larger, they may benefit from the presence of the parasite, which contributes to the net brood begging signal but cannot monopolize the food brought to the nest. Here, we show that, despite a higher begging intensity, great spotted cuckoos (Clamator glandarius) did not outcompete larger size carrion crow (Corvus corone corone) nestlings. Furthermore, cuckoos’ exaggerated begging allowed crow nest mates to decrease their begging intensity without negative consequences on food intake. Assuming an energetic cost to chicks of begging intensely, our results suggest that crow chicks sharing the nest with a cuckoo may obtain an advantage that should be weighed against the loss of indirect fitness due to parasitism.

Diet type modifies ingestion rates and trophallactic exchanges in leaf‐cutting ants

AbstractConventional control of leaf‐cutting ants is mainly carried out by application of solid insecticide baits. However, alternative approaches could increase the efficiency of control methods. Here, we investigated the hypothesis that liquid and semi‐solid baits are more readily ingested by leaf‐cutting ants and are therefore more toxic than solid baits. Furthermore, following increased ingestion rates, ants could perform higher frequencies of trophallactic exchanges with their nest mates, thus increasing dispersal rates within the colony. Each of three diets were offered to Acromyrmex subterraneus subterraneus (Forel) and Atta sexdens rubropilosa Forel (both Hymenoptera: Formicidae) for 1 h under laboratory conditions and subsequently crop volumes were quantified. The highest crop volumes for both species were seen when the diet was offered in liquid form, and the lowest crop volumes were observed after offering solid diets. Survival rates of the ants were monitored following addition of the neonicotinoid insecticide imidacloprid (IMI) to the three diets. The ingestion of liquid and semi‐solid diets + IMI by A. subterraneus resulted in 17 and 6% survival, respectively, whereas these diets caused 100% mortality of A. sexdens. Ingestion of solid diets with IMI resulted in 51% survival of A. subterraneus and 23% survival of Atta workers. Twenty‐three percent of A. subterraneus which had fed on liquid diet carried out trophallactic exchanges, whereas only 10 and 3% of ants carried out trophallaxis when fed on semi‐solid or solid diet, respectively. Lower trophallactic frequencies were observed for A. sexdens, with 13 and 3% of ants that had fed on liquid and semi‐solid diets performing trophallaxis, respectively. The low trophallactic exchange rates following ingestion of solid diets would reduce the dispersal of these compounds throughout the colony. Control strategies using solid baits should be re‐examined in the light of these findings, which indicate the importance of optimizing insecticide ingestion.

Threat detection: contextual recognition and response to parasites by ants

The ability of an organism to detect threats is fundamental to mounting a successful defense and this is particularly important when resisting parasites. Early detection of parasites allows for initiation of defense mechanisms, which are vital in mitigating the cost of infection and are likely to be especially important in social species, particularly those whose life history makes parasite pressure more significant. However, understanding the relative strength of behavioral responses in different species and situations is still limited. Here, we test the response of individual ants to fungal parasites in 3 different contexts, for 4 ant species with differing life histories. We found that ants from all 4 species were able to detect fungi on their food, environment, and nest mates and initiate avoidance or upregulate grooming behaviors accordingly to minimize the threat to themselves and the colony. Individuals avoided fungal-contaminated surfaces and increased grooming levels in response to fungal-contaminated nest mates. Ants from all species responded qualitatively in a similar way although the species differed quantitatively in some respects that may relate to life-history differences. The results show that ants of multiple species are capable of recognizing fungal threats in various contexts. The recognition of parasite threats may play an important role in enabling ant colonies to deal with the ever-present threat from disease.

Alternative models of familiarity and false claims concerning social recognition systems

Thrips represent an ideal biological system to investigate mechanisms of social recognition. In his commentary on our article (de Bruijn et al. 2014) introducing thrips for this purpose, Schausberger (2014) assumes a social recognition system in which individuals should memorize ‘distinct individual labels of the referents’. Clearly, this imposes increasing cognitive capabilities with increasing group size. He states that due to cognitive limitations, familiarity-based recognition is constrained by referent number and heterogeneity (label variability) during familiarization. We agree that under these assumptions, one should take care of group size and heterogeneity in experiments aiming to test this model of social recognition. However, there are alternative models. For example, ants groom, feed, or contact nest mates and thereby contaminate them with their own blend of cuticular hydrocarbons (Lenoir et al. 2001; Bos and d’Ettorre 2012). Ultimately, all nest mates harbour the same mix of hydrocarbons that is perceived as a single label. This is the model of the so-called Gestalt colony odour (Crozier and Dix 1979). Under this assumption, increasing group size does not pose a challenge to the cognitive capacities of group members. For the case of thrips, we do not know the cue or the cues they use to familiarize, or whether they originate from thrips individuals or from their environment. Hence, it is premature to theorize about which social recognition model applies to thrips. However, from a selectionist point of view, we expect the more simple (and less costly) social recognition system to evolve. In addition, we emphasize that Schausberger (2014) makes two false claims as to what we concluded from our experiments (de Bruijn et al. 2014). First, he rephrases our conclusion that ‘growing up together is a necessary but not sufficient condition for discrimination in thrips larvae’ into ‘thrips only familiarize with kin or kinship is needed for generating beneficial effects of familiarity under predation risk’. Then, he claims that this (rephrased) conclusion is invalid. However, we have never drawn this conclusion and instead found support for familiarization among thrips larvae in kin groups only. Second, Schausberger (2014) claims ‘familiarity is only established, or does only have an effect, in sibling but not non-siblings’ as being our conclusion. However, we recognized the difference in pre-experimental group size of siblings and non-siblings and separately analysed survival of familiar vs. unfamiliar thrips. Therefore, we carefully refrained from comparing sibling and non-sibling survival, a point that Schausberger (2014) acknowledges but subsequently ignores.

Cell position during larval development affects postdiapause development in Megachile rotundata (Hymenoptera: Megachilidae).

Megachile rotundata (F.) (Hymenoptera: Megachilidae) is the primary pollinator of alfalfa in the northwestern United States and western Canada and provides pollination services for onion, carrot, hybrid canola, various legumes, and other specialty crops. M. rotundata females are gregarious, nest in cavities either naturally occurring or in artificial nesting blocks, where they construct a linear series of brood cells. Because of the physical layout of the nest, the age of the larvae within the nest and the microenvironment the individual larvae experience will vary. These interacting factors along with other maternal inputs affect the resulting phenotypes of the nest mates. To further our understanding of in-nest physiology, gender and developmental rates were examined in relationship to cell position within the nest. Eighty-two percent of the females were located within the first three cells, those furthest from the nest entrance. For those individuals developing in cells located in the deepest half of the nest, the sex of the previous bee had a significant effect on the female decision of the gender of the following nest mate. Removing the prepupae from the nest and rearing them under identical conditions demonstrated that position within the nest during larval development had a significant effect on the postdiapause developmental rates, with males whose larval development occurred deeper in the nest developing more slowly than those toward the entrance. No positional effect on postdiapause developmental rates was noted for the females. The cell position effect on male postdiapause developmental rate demonstrates that postdiapause development is not a rigid physiological mechanism uniform in all individuals, but is a dynamic plastic process shaped by past environmental conditions.

Factors affecting vocalization in Tengmalm's owl (Aegolius funereus) fledglings during post-fledging dependence period: scramble competition or honest signalling of need?

Begging behaviour of nestlings has been intensively studied for several decades as a key component of parent-offspring conflict. There are essentially two main theories to account for intensity of food solicitation among offspring: that intensity of begging is related to some form of scramble competition between nest mates or that it offers honest signalling of need to parents. The vast majority of studies which have addressed begging behaviour have been based on observations of, and experiments on, nestlings and have not considered begging behaviour, during the post-fledging period. Begging vocalizations in this post-fledging phase of dependence have rarely been studied, despite the importance of vocalizations as a communication method between offspring and parents, particularly for nocturnal species. We radiotracked 39 fledglings of the Tengmalm’s owl (Aegolius funereus) in two years with different availability of prey: 2010 (n = 29 fledglings) and 2011 (n = 10 fledglings) and made 1320 nightly localizations in which we recorded presence or absence of begging calls. Within years, the most important measures related to the probability of vocalization were body condition at fledging, time of night, number of surviving siblings, age and weather conditions. Begging intensity increased with age in both years; however, in the year with low prey availability fledglings vocalized significantly more often. The main factor causing these differences between years was probably the different availability of prey, affecting breeding success, post-fledging behaviour, and thus also both short- and long-term needs of offspring. We believe that our results suggest honest signalling of their fledgling’s need.

Ants use directionless odour cues to recall odour-associated locations

Ants are key model organisms in the study of navigation and memory formation. Many ants learn food locations very quickly and with high accuracy. But can individual ants learn multiple separate food locations, associate them with a cue, and then correctly recall the food location and navigate towards it when later presented with that cue? In this experiment, we sequentially trained Lasius niger foragers to two scented feeders at either end of a T-maze. The next day, an odour cue corresponding to one of the food sources was presented to the ants in the air, on the substrate and via trophallaxis with nest mates. Trained foragers accurately navigated to the correct side of the T-maze (89 % correct decisions), but only after the first 10 min of testing. This demonstrates the ability of ants to perform associative recall, forming clear associates between odour cues and food locations and using these associations to navigate to food sources. We also found that trained ants in the first 10 min of testing showed no preference for the correct side (57 % correct decisions), which may be related to the motivational state of the ants tested. Ants with different motivational states (whether they are ‘scouting’ or ‘recruited’) made use of route memories in a completely different manner. This highlights the importance of taking account of motivational states when performing behavioural experiments.

Mate competition and resource competition are inter‐related in sexual selection

Sexual selection can be affected by the competition for limited breeding resources and/or the competition for limited mates. Although there is ample evidence for each type of competition by itself, little is known about their relative importance and interaction. To address these questions, we established 48 experimental breeding populations of the two-spotted goby (Gobiusculus flavescens), a substrate-breeding fish with paternal care. In three experimental treatments, males were limited in the access to either nest sites or mates or were provided with both nests and mates in excess. We quantified male competition behaviour (agonistic and courtship), the opportunity for selection and selection on male body size. Limited access to nests and mates produced similar opportunities for selection, but only limited access to mates increased male competitive behaviours and caused positive selection on male body size. Selection on body size in the mate-limited treatment was due both to larger males being more likely to take up nests and to larger males being more likely to mate once they had a nest. These findings demonstrate that resource and mate limitation can differ in their effects on sexual selection. The results also reveal that resource and mating competition can be highly inter-related and not always separated in time, implying that methods to disentangle the two processes must be chosen with care. Future research should consider experimental and analytical approaches similar to those of the present study in attempts to elucidate the interaction of resource and mating competition in animals.

A recoverable cost of brood parasitism during the nestling stage of the American robin (Turdus migratorius): implications for the evolution of egg rejection behaviors in a host of the brown-headed cowbird (Molothrus ater)

Hosts of brood parasitic birds face reduced reproductive success as a direct consequence of rearing parasitic young. The most commonly evolved host behavior to combat costly parasitism is the rejection of foreign eggs. Despite consistent patterns of reduced nesting success in broods parasitized by brown-headed cowbirds (Molothrus ater), most of its host species do not reject foreign eggs. Paradoxically, where it is present, egg rejection is more common among cowbird hosts with larger body sizes, yet cowbird chicks are less likely to outcompete larger host nest mates. This raises a fundamental question whether egg rejection, even in the minority of cowbird hosts, has specifically evolved in response to costly brood parasitism. Here we tested predictions associated with this hypothesis in an egg-rejecter host, the American robin (Turdus migratorius), by assessing whether experimental cowbird parasitism causes reduced nesting success. We cross-fostered cowbird and control, host chicks into robin nests, testing for experimental effects of chick species, brood size, and hatching asynchrony; unmanipulated nests served as additional controls. Rearing a foreign chick in the brood reduced the reproductive output of host robins, however, we detected no effect of parasitizing host nests with a cowbird versus robin chick. Cowbird chicks were significantly less likely to fledge than cross-fostered robin chick controls. These experiments reveal that parasitism itself can exert a cost on robin hosts during the nestling stage, representing a recoverable cost of cowbird parasitism that can be avoided by the host through rejecting parasite eggs prior to hatching. These results support the assumption that foreign egg rejection is an evolved host response to brood parasitism in this system, despite the poor survival rate of cowbird chicks in robin broods.

Fourier transform infrared photoacoustic spectroscopy as a potential tool in assessing the role of diet in cuticular chemical composition of Ectatomma brunneum.

The cuticular chemical composition plays a significant role in the recognition of nest mates in social insects, thus functioning as a chemical signature of the colony. The structure of cuticular chemicals is subject to interference from genetic and exogenous factors, including diet. In this study, various colonies of the Ectatomma brunneum ant were removed from their natural environment and housed in a laboratory to monitor the response of the cuticular chemical composition to dietary changes. Analyses were performed using gas chromatography and Fourier transform infrared photoacoustic spectroscopy, which has not been previously used for this type of analysis. The results indicate that this method is useful for analyzing biological and natural systems. We observed changes in the chemical signature with food traces in the first 30 days under feed control. Therefore, genetic information may not be the only criterion that can be used to describe the chemical signature of a species; environmental variations also influence recognition signals. Furthermore, these results reinforce the reliability of the Fourier transform infrared photoacoustic spectroscopy method.