Response to and transport of brood by workers of Tapinoma erraticum (Formicidae; Dolichoderinae) during nest disturbance

An attempt was made to describe the principle signals involved in the recognition of nymphs by Tapinoma workers. A behavioural measure, the way and extent to which workers transported different objects presented to them, was used to quantify this relationship. These objects were homo- or heterospecific nymphs, or different baits. Two types of test were generally used in such studies: retrieval — bringing back objects to the nest, and removal – transport of objects during displacement of the nest. The second type of test was used in this study. The results, in decreasing order of recognition were as follows. Tapinoma workers transport homospecific and Tetramorium nymphs at 100%. The smaller nymphs of Solenopsis impregnated with Tapinoma extract were transported at 77%. The nymphs of Solenopsis with their own odour were transported at 21%, paper impregnated. with Tapinoma extract at 12%, while ‘odourless’ Tapinoma nymphs and neutral paper were not transported at all. These results imply an intervention of both physical and chemical factors, the threshold significance of signals and their global implication depending on the test situation and its disturbing effect. They also depend on the nature of the different objects presented in combination; Tapinoma workers transport heterospecific brood much less readily in the presence of their own brood. The attractiveness of nymphs is not an all or none phenomenon. In a study of the adoption of homospecific nymphs from another nest, this gradation was apparent in the distribution of nymphs in the nest and their order of transport during removal tests; certain nymphs were left aside in the first 3 days of presentation, were amongst the last to be transported during removal, and then by the most active workers.The perception of the brood by the workers may thus occur at different levels: (1) Perception of a factor that may be vaguely defined as ‘transportable object’ in a removal test — with objects of type ‘nymph’ for example; (2) perception of the species; (3) perception of the colony. The worker ant during its life acquires a certain ‘knowledge’ of its own brood through familiarization, which expresses itself in terms of specific patterns of care for the brood, but this attention, although given preferentially to the brood, is not exclusive under stress.     

Polygyny in thief ants responds to competition and nest limitation but not food resources

Colonies of ants often house multiple queens, and variation in polygyny often tracks environmental conditions. Three hypotheses have been proposed to describe how environmental variation may account for the degree of polygyny: competition, food limitation and nest limitation. Here I evaluate these hypotheses with studies on litter-nesting thief ants (Solenopsis spp.) throughout a lowland tropical rain forest in Costa Rica. In one component, I measured how polygyny varied across a broad environmental gradient demonstrating substantial variation in resources and competition. In a second component, I manipulated the abundance of food, the spatial presentation of food and the availability of nesting space to assess the effects on queen number. The degree of polygyny increased with nest limitation and competition, but there was no indication that colonies produce queens to capitalize on food availability. The increase in queen number in response to the density of competitors suggests that an increase in queen number enhances exploitative abilities.     

Speed-versus-accuracy trade-offs during nest relocation in Argentine ants (Linepithema humile) and odorous house ants (Tapinoma sessile)

Animals are often forced to accommodate disturbance to their territories or nests. When nest relocation becomes necessary, it is important to efficiently evaluate alternative nest sites to choose the one most suitable under current conditions. However, if time is limiting, species may experience a speed-versus-accuracy trade-off when searching for a new home. We examined nest site selection under duress (in the form of flooding) in two species of ants: Linepithema humile and Tapinoma sessile. We predicted that if ants are able to assess and evacuate to the most suitable location, colonies should move to higher elevation, relative to their current nest site, in response to flooding. To test for a speed-versus-accuracy trade-off, we presented colonies with new nest chambers that were either higher, lower, or at the same height as their current nest and examined if their ability to efficiently choose a new site was influenced by the rate of flooding. When flooding rates were slow, both species favored the highest nest site and nearly always moved their entire nest to the same chamber. However, when the rate of flooding was doubled, colonies of T. sessile less often chose the highest nest site and were also more likely to split their nests between two of the available chambers. These results demonstrate a trade-off between speed and accuracy in nest site selection for odorous house ants, while L. humile retained their ability to adequately assess new nest sites under the conditions we presented. These patterns may arise from differences in exploratory behavior and activity between the two species. Despite having identical colony sizes, L. humile had approximately ten times more workers exploring the alternate nest sites 30 min into the experiment than did T. sessile.     

Army ants do not eat and run: Influence of food supply on emigration behaviour in Neivamyrmex nigrescens

Laboratory studies show that the amount and location of food strongly influence the frequency and direction of emigrations. For two overfed colonies, emigrations occurred on only 28% of the nomadic days. By contrast, underfed colonies emigrated on 62% of the nomadic days. In addition, overfeeding kept one colony from emigrating for seven consecutive days, as compared with a maximum of two consecutive days for the underfed colonies. Most emigrations took place in the direction of booty location. It was shown, however, that colonies can also recruit and emigrate to suitable nests, independent of the presence of food.     

Reproductive responses to variation in temperature and food supply by house mice: II. Lactation

Lactating HS/Ibg house mice housed at 21 degrees C and 5 degrees C were assigned to 3 feeding regimes: ad libitum, daily rations of 80% of ad libitum, or 60% of ad libitum beginning on the day that they bore litters. Significant interaction between temperature and food restriction was found for litter survivorship, pup survivorship, litter size, female body weight, and cumulative biomass production. The interaction was due to a magnification of the effects of food restriction at the colder temperature: i.e. mice fed ad libitum were similar at the two temperatures, mice fed the 80% ration differed, and mice fed the 60% ration differed to a greater extent. The dominant response to food restriction was cannibalism by females, which might be associated with the rate of loss in body weight by the female on the days preceding cannibalism of one or more pups. Incidents of cannibalism tended to involve a limited number of pups and to be repeated until a sustainable litter size was reached. In 3 of the food-restricted treatments, females weaned relatively large litters of relatively small pups, but in the most severe treatment (in the group fed the 60% ration at 5 degrees C), the females weaned small litters of large pups. The patterns of cannibalism and variable relative investment in individual pups reflect the aggressive breeding strategy of this classic colonizing species.     

Reproductive responses to variation in temperature and food supply by house mice. I. Mating and pregnancy

The effects of food restriction upon mating and pregnancy of female house mice were studied at a warm (21 degrees C) and a cold (5 degrees C) temperature to examine the hypothesis that the effects of temperature and food availability are not independent. Analyses of the data showed significant interaction between temperature and food availability for virtually all variables measured, supporting the initial hypothesis. Contingency analysis of mating, fertility, and litter survivorship showed that the interaction influenced not only the percentage of females successfully producing litters, but also the timing of abandonment of reproductive effort by those females that did not have surviving litters. The percentage of females who mated was reduced only in food-restricted females under cold conditions. Both low temperature and food restriction reduced the percentage of mated females that became pregnant. Food-restricted females under cold conditions who did become pregnant tended to kill their litters at birth. The net effect was an interaction between temperature and food restriction that resulted in females reducing or abandoning reproductive effort at progressively earlier stages of the reproductive cycle. The interaction between temperature and food restriction was further displayed in the growth curves of pregnant females, with the reduction of growth by food restriction being greater in the cold.     

Summer and fall ants have different physiological responses to food macronutrient content

Seasonally, long-lived animals exhibit changes in behavior and physiology in response to shifts in environmental conditions, including food abundance and nutritional quality. Ants are long-lived arthropods that, at the colony level, experience such seasonal shifts in their food resources. Previously we reported summer- and fall-collected ants practiced distinct food collection behavior and nutrient intake regulation strategies in response to variable food protein and carbohydrate content, despite being reared in the lab under identical environmental conditions and dietary regimes. Seasonally distinct responses were observed for both no-choice and choice dietary experiments. Using data from these same experiments, our objective here is to examine colony and individual-level physiological traits, colony mortality and growth, food processing, and worker lipid mass, and how these traits change in response to variable food protein–carbohydrate content. For both experiments we found that seasonality per se exerted strong effects on colony and individual level traits. Colonies collected in the summer maintained total worker mass despite high mortality. In contrast, colonies collected in the fall lived longer, and accumulated lipids, including when reared on protein-biased diets. Food macronutrient content had mainly transient effects on physiological responses. Extremes in food carbohydrate content however, elicited a compensatory response in summer worker ants, which processed more protein-biased foods and contained elevated lipid levels. Our study, combined with our previously published work, strongly suggests that underlying physiological phenotypes driving behaviors of summer and fall ants are likely fixed seasonally, and change circannually.     

Parental investment in nest defence by stonechats (Saxicola torquata)

Breeding stonechats (Saxicola torquata) made mixed sequences of two calls when a human intruder entered territories. ‘Whits’ are modulated notes with a small frequency range, and in laboratory tests caused nestlings to stop begging. ‘Chacks’ cover a wide range of frequencies, and in the field were combined with flights made so as to distract an intruder from the nest. On average male and female call-rates were similar, but varied greatly according to the intruder's distance from the nest, and at different stages of the nesting cycle. Rates increased rapidly after hatching, and this correlated most closely with the cumulative total of parents' visits to feed nestlings. This suggests that the level of defence may be adjusted to the value of the offspring to their parents. Call-rates declined about one week after fledging. A smaller peak by some pairs at the start of incubation was apparently related to probable poor condition after a previous breeding attempt, and after laying large clutches. Rates of Whits were higher at nests with larger broods, up to an asymptote, but rates of Chacks were independent of brood size. Birds suffering nest-predation showed lower call-rates before the event than equivalent successful birds, suggesting that the calls do reduce the risk of predation.     

Individual variation in nest size and nest site features of the Bornean orangutans (Pongo pygmaeus)

Nest construction is a daily habit of independent orangutans for sleeping or resting. Data on their nests have been used in various ecological studies (e.g., density estimation, ranging behavior, evolution of material culture) because they are the most observable field signs. We investigated nest size and nest site features of Bornean orangutans in the wild during 10 months' fieldwork at three sites in East Kalimantan, Indonesia: Kutai National Park, Birawa, and Meratus. To examine individual variation, we followed 31 individual orangutans and recorded the 92 nests they made for nest size (diameter) and nest site features (height of nest above ground, tree species used for the nest site, the diameter and height of the tree, whether the nest was new or reused, and nest location within the tree). Analyses taking age–sex classes of the focal individuals into consideration showed significant age–sex differences in nest size and location, but not in nest height or nest tree features (diameter, height of tree, and height of lowest branch). Mature orangutans (adult females, unflanged and flanged males) made larger nests than immatures (juveniles and adolescents). Flanged male orangutans with larger nests used stable locations for nesting sites and reused old nests more frequently than immatures. The overall proportion of nests in open (exposed) locations was higher than in closed (sheltered) locations. Flanged males and immatures frequently made open nests, whereas adult females with an infant preferred closed locations. The good correspondence between nest size and age–sex classes indicates that nest size variation may reflect body size and therefore age–sex variation in the population. Am. J. Primatol. 71:393–399, 2009. © 2009 Wiley‐Liss, Inc.     

Burrow sharing and nest transfer in the digger wasp Philanthus gibbosus (Fabricius)

Philanthus gibbosus is a solitary, ground-nesting wasp in which several individuals have been observed to occupy a single burrow. Evidence is presented which indicates that several emerging males and females often occupy the parental nest for several days, the males sometimes for life. The females, however, soon disperse to found new nests, although one may continue to occupy and expand the parental nest. It appears that the larger female often maintains possession of the nest, although the interactions have not been observed. On rare occasions two females may provision a single nest for a brief period. P. gibbosus may represent a unique stage in presociality in which temporary communal nesting occurs at certain phases of the nesting cycle.     

Colonial breeding reduces nest predation in the common gull (Larus canus)

It is often suggested that colonial breeding reduces nest predation for birds with a high defence capacity, but experimental comparison of predation at solitary and colonial nests is seldom feasible within a single species. We here report on such a test in the common gull (Larus canus). The rate of predation on experimental eggs was significantly lower near colonies than near solitary gull nests, and the eggs survived longer at the edge of a colony than farther away. Communal mobbing of nest predators is the likely reason. In both of two years, almost all nests of solitary gulls were destroyed by predators, while most clutches survived in colonies. Nest predation hence selects strongly for colonial breeding in the present population of common gulls.     

Tradeoffs between growth and reproduction in response to temporal variation in food supply

Allocating resources to growth or to reproduction is a fundamental tradeoff in evolutionary life history theory. In environments with unpredictable food resources, natural selection is expected to favor increased allocation to reproduction. Although effects of selection are realized only across generations, short-term changes in food predictability might influence intra-generational tradeoffs in resource allocation. We assessed the ability of fathead minnows, Pimephales promelas, to adjust allocation to growth and reproduction in response to predictable, unpredictable, and switched feeding schedules. Fish in the switched treatments were changed from unpredictable to predictable feeding schedules just after reaching sexual maturity. Egg production did not differ significantly among treatments despite the fact that females on the unpredictable and switched feeding schedules grew more slowly than those on the predictable schedule. Switched males were heavier and had proportionally larger testes than males in predictable and unpredictable treatments. Increased allocation to reproduction or growth by fish on unpredictable and switched feeding schedules was associated with changes in gut length relative to body mass. Both sexes showed a remarkable degree of phenotypic plasticity in response to resource availability and sex differences in allocation patterns were consistent with adaptive responses in the context of the fathead mating system.     

Control of nest water losses through building behavior in leaf-cutting ants (Acromyrmex heyeri)

Like many ants inhabiting temperate regions, leaf-cutting ant colonies of a number of Acromyrmex species build thatched nests that achieve more stable temperatures than those of the environment. Workers are expected to counteract short-term variations in nest microclimate by modifying the thatch structure, for instance by reducing thatch thickness or by permeating the thatch with openings so as to favor heat exchanges with the outside. Such thermoregulatory responses may compromise the control of nest humidity because of the concomitant water losses resulting from the escape of humid air to the environment. We asked whether water losses through the thatch trigger deposition of nest material as a regulatory response for humidity control. In a laboratory colony of A. heyeri, we defined four equidistant spots on the nest thatch through which losses of air with different humidities were experimentally simulated. The deposition of building material on the spot was recorded as indicative building response. Results showed that material deposition occurred significantly more frequently with higher humidity content of the air leaving the spot. Dry air leaving the nest hardly triggered material deposition. The observation of a continuous turnover of thatch material indicates that the building of a nest thatch is a permanent process, and that short-term responses for the control of nest climate, as the deposition of building material to suppress an outflow of humid air, are guided by specific cues such as the humidity content of the air stream.     

Rats (Rattus norvegicus) and pigeons (Columbia livia) are sensitive to the distance to food,but only rats request more food when distance increases

Three experiments investigated foraging by rats and pigeons. In Experiment 1, each response on a manipulandum delivered food to a cup, with the distance between the manipulandum and the cup varying across conditions. The number of responses made before traveling to collect and eat the food increased with distance for rats, but not for pigeons. In Experiment 2, two manipulanda were placed at different distances from a fixed food source; both pigeons and rats preferentially used the manipulandum closest to the food source. Experiment 3 was a systematic replication of Experiment 1 with pigeons. In different conditions, each peck on the left key increased the upcoming hopper duration by 0.5, 1.5 or 2.5 s. Completing a ratio requirement on the right key of 1, 4, 8, 16 or 32 pecks, depending on the condition, then produced the food hopper for a duration that depended on the number of prior left pecks. As the ratio requirement increased on the right key, pigeons responded more on the left key and earned more food. Overall, the results replicate previous research, underlining similarities and differences between these species. The results are discussed in terms of optimal foraging, reinforcer sensitivity and delay discounting.     

Emergence and dispersal relative to natal nest in the digger wasp Stizus continuus (Hymenoptera: Crabronidae)

The position of the emerging point has rarely been investigated as a factor possibly affecting the future nest settlement behaviour in Hymenoptera, in particular within nest aggregations. We studied the emergence and dispersion patterns of the digger wasp Stizus continuus. Individuals emerged daily in clumped patterns, possibly revealing a certain synchrony of emergence from the same nests, and protandry appeared both at seasonal and daily level. Differences between the number of females that nested relatively close or far from their emergence holes (EH) were either significant or not, depending on the year, and observed dispersal distances from the natal nests did not differ from those obtained by random simulations. By contrast, females nested close to the nearest conspecific nest. Size did not affect the dispersion patterns. EH are thus not important cues for nest establishment, and conspecific nests are probably the key cue for nest-founding females. In addition, males did not prefer to establish territories close to their natal nest.     

Defensive responses of gastropods to the predatory flatworms Freemania litoricola (Heath and McGregor) and notoplana acticola (Boone)

Three species of gastropods were tested in the laboraory and in the field for responses to contact with the polyclad flatworms Freemania litoricola (Heath and McGregor) and Notoplana acticola (Boone). The three limpets differed considerably in their responses to Freemania litoricola All specimens of Notoacmea scutum (Rathke) responded in some way to this flatworm, mostly by running. Fewer than half of the Collisella digitalis (Rathke) responded to Freemania litoricola, and these responded by mushrooming - elevating the shell several millimeters off the substratum. Collisella scabra (Gould) did not respond any differently to contact with Freemania litoricola than to contact with a control probe. Differences in the responses of these limpets to Freemania litoricola are discussed in relation to the characteristic intertidal distributions of this flatworm and the limpets. In contrast to Freemania litoricola, the polyclad Notoplana acticola typically did not elicit defensive responses. This difference is related to the diets of the two flatworms. Freemania litoricola was found to be a predator on limpets, whereas no evidence was found that Notoplana acticola eats limpets.