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Natural Aversive Learning in Tetramorium Ants Reveals Ability to Form a Generalizable Memory of Predators' Pit Traps
Abstract
Many species of ants fall prey to pit-digging larval antlions (Myrmeleon spp.), extremely sedentary predators that wait, nearly motionless at the bottom of their pit traps, for prey to stumble inside. Previous research, both in the field and laboratory, has demonstrated a remarkable ability of these ants to rescue trapped nestmates, thus sabotaging antlions' attempts to capture them. Here we show that pavement ants, Tetramorium sp. E, an invasive species and a major threat to biodiversity, possess yet another, more effective, antipredator strategy, namely the ability to learn to avoid antlion traps following a single successful escape from a pit. More importantly, we show that this learned antipredator behavior, an example of natural aversive learning in insects, is more complicated than a single cue-to-consequence form of associative learning. That is, pavement ants were able to generalize, after one experience, from the learned characteristics of the pit and its specific location, to other pits and other contexts that differed in many features. Such generalization, often described as a lack of precise stimulus control, nonetheless would be especially adaptive in nature, enabling ants to negotiate antlions' pit fields, which contain a hundred or more pits within a few centimetres of one another. Indeed, the ability to generalize in exactly this way almost certainly is responsible for the sudden, and heretofore inexplicable, behavioural modifications of ants in response to an invasion of antlions in the vicinity of an ant colony.
... In this study, we concentrate on how representatives of different task groups shape natural aversive learning in the context of repeated interactions with an enemy. Similar with Hollis et al. (2017) study, we use the term "natural aversive learning" meaning ants' behavior toward their natural enemies or/and predators, although agreeing with Hénaut et al. (2014) that even if a species demonstrates aversive learning in the laboratory, most often it is difficult to determine whether such a capacity is likely to occur in natural conditions (see also : Bernays, 1993). ...
... Ants' memory for an aversive event was tested shortly after their unpleasant experience. For example, Ectatomma tuberculatum appeared to learn how to break quickly through the spiders' web and kept this memory during 15 min after the first experience (Hénaut et al., 2014), Formica pratensis retained the memory of a single unpleasant collision with a hoverfly larva for 10-30 min after the event (Novgorodova, 2015), and pavement Tetramorium ants learned to avoid antlion traps following a single successful escape from a pit for 1 min after the encounter (Hollis et al., 2017). Long-term memory for an aversive event was demonstrated in the experiments of Dejean (1988) with Odontomachus troglodytes. ...
The adaptive benefits of individual specialization and how learning abilities correlate with task performance are still far from being well-understood. Red wood ants are characterized by their huge colonies and deep professional specialization. We hypothesized that red wood ants Formica aquilonia form aversive learning after having negative encounters with hoverfly larvae differently, depending on their task specialization. We tested this hypothesis, first, by examining whether hunters and aphid milkers learn differently to avoid the nuisance of contacts with syrphid larvae, and, second, by analyzing the difference between learning in “field” and laboratory-reared (naïve) foragers. During the first interaction with the syrphid larva in their lives the naïve foragers showed a significantly higher level of aggressiveness than the members of a natural colony. Naïve foragers applied the “mortal grip,” “prolonged bites,” and “nibbling” toward the enemy with a significantly higher frequency, whereas members of both “field” groups behaved more carefully and tried to avoid encounters with the larva. The aphid milkers, who had a negative experience of interaction with the larva, being “glued” with its viscous secretion, behaved much less aggressively in the follow-up experiments after 10 min and even 3 days, thus exhibiting the shaping of both short- and long-term memories. However, both “field” hunters and naïve foragers demonstrated no signs of aversive learning. These data provide some new insights into the relationship between task specialization and learning performance in ants. Given our previous results, we speculate that scouts and aphid milkers are the most cognitively gifted specialists in red wood ants, whereas hunters and guards are rather brave than smart.
... Cognitive abilities of ants are no less spectacular [110][111][112] and include, among others, cooperative transport of objects too large to be moved by a single individual [120][121][122], individual recognition of specific nestmates on the basis of chemical cues present on their body surface [123], tool use [124][125][126], ability to count steps to evaluate distances [127], rapid learning to avoid antlion traps following a single successful escape from a pit [128], and teaching of naive individuals by the more experienced ones [129,130]. ...
Ant rescue behaviour belongs to the most interesting subcategories of prosocial and altruistic behaviour encountered in the animal world. Several studies suggested that ants are able to identify what exactly restrains the movements of another individual and to direct their rescue behaviour precisely to that object. To shed more light on the question how precise is the identifi-cation of the source of restraint of another ant, we investigated rescue behaviour of workers of the red wood ant Formica polyctena using a new version of an artificial snare bioassay in which a nestmate victim was bearing on its body two wire loops, one placed on the petiole and acting as a snare, and an additional one on the leg. The tested ants did not direct preferentially their rescue behaviour to the snare. Moreover, the overall strategy adopted by the most active rescuers was not limited to precisely targeted rescue attempts directed to the snare, but consisted of attempts to find a solution to the victim’s problem through frequent trial-and-error switching between various subcategories of rescue behaviour. These findings highlight the importance of precise identifica-tion of cognitive processes and overall behavioural strategies for better understanding of causal factors underlying animal helping behaviour.
... This also suggests that the avoidance behaviour is not an innate response, as seen in naive tephritid fruit flies exposed to volatile cues of spiders and one ant species [36]. Evidence of ants learning to avoid predators comes from ant-antlions systems [37,38] and such trait of the ants could be adaptive for encountering novel predators in new environments and perhaps it contributes to the explanation of why this ant species is abundant in the neotropics [39]. Besides, rapid learning in E. ruidum occurs under multimodal stimuli during foraging [36] and it might occur also in the context of predation risk, which merits further work. ...
The ecology of fear refers to the non-fatal cost that predators and parasites impose on prey populations. These non-consumptive effects (NCEs) can influence animal–plant interactions, but evidence thereof comes mainly from vertebrate systems with less focus on invertebrates. Here, I investigated whether the foraging behaviour of the ant Ectatomma ruidum was influenced by its primary predator, the forest toad Rhinella alata. In field tests, the probability of seed removal by the ants was 25% for seeds placed with the forest toad compared to 32% for control seeds, suggesting that toads reduce ant foraging rates. A further experiment revealed that ants which had previously encountered the predator and its faeces were more likely (59%) than inexperienced ants (50%) to avoid the exit with the predator faeces. This outcome suggests that ants are capable of learning cues associated with predation risk, possibly leading to NCEs. This indicates that predators can exert NCEs on invertebrate prey with potential cascading effects on seed dispersal, extending results previously seen only in vertebrate seed dispersal systems.
... Studies addressing the role of social structure in nervous system trait evolution often propose that social complexity, generally measured by colony size, will be negatively correlated with individual worker behavioral complexity (Anderson and McShea, 2001;Gronenberg and Riveros, 2009;O'Donnell et al., 2015) and hypothesize that relative brain investment, particularly in brain regions associated with more complex behaviors such as multi-modal learning and memory, will decrease with increasing colony size (Riveros et al., 2012;O'Donnell et al., 2015;Kamhi et al., 2016). However, individual workers of social species often show behavioral and cognitive skills comparable to solitary relatives (Gruter et al., 2011;Pasquier and Grüter, 2016;Hollis et al., 2017;Yilmaz et al., 2017), and comparisons seeking to link colony size with changes in brain structure may be complicated by confounding variables such as habitat differences or phylogenetic distance (Kamhi et al., 2016;Godfrey and Gronenberg, 2019b). Furthermore, complex collective behaviors may emerge from expanded communication systems or require relatively small changes in neural circuitry (Lihoreau et al., 2012;Bouchebti and Arganda, 2020) without changes to individual behavioral complexity (Jeanson et al., 2012;Feinerman and Korman, 2017). ...
In social insects colony fitness is determined in part by individual worker phenotypes. Across ant species, colony size varies greatly and is thought to affect worker trait variation in both proximate and ultimate ways. Little is known about the relationship between colony size and worker trait evolution, but hypotheses addressing the role of social structure in brain evolution suggest workers of small-colony species may have larger brains or larger brain regions necessary for complex behaviors. In previous work on odorous ants (Formicidae: Dolichoderinae) we found no correlation between colony size and these brain properties, but found that relative antennal lobe size scaled negatively with colony size. Therefore, we now test whether sensory systems scale with colony size, with particular attention to olfactory components thought to be involved in nestmate recognition. Across three species of odorous ants, Forelius mccooki, Dorymyrmex insanus, and D. bicolor, which overlap in habitat and foraging ecology but vary in colony size, we compare olfactory sensory structures, comparing those thought to be involved in nestmate recognition. We use the visual system, a sensory modality not as important in social communication in ants, as a control comparison. We find that body size scaling largely explains differences in eye size, antennal length, antennal sensilla density, and total number of olfactory glomeruli across these species. However, sensilla basiconica and olfactory glomeruli in the T6 cluster of the antennal lobe, structures known to be involved in nestmate recognition, do not follow body size scaling observed for other structures. Instead, we find evidence from the closely related Dorymyrmex species that the larger colony species, D. bicolor, invests more in structures implicated in nestmate recognition. To test for functional consequences, we compare nestmate and non-nestmate interactions between these two species and find D. bicolor pairs of either type engage in more interactions than D. insaus pairs. Thus, we do not find evidence supporting a universal pattern of sensory system scaling associated with changes in colony size, but hypothesize that observed differences in the olfactory components in two closely related Dorymyrmex species are evidence of a link between colony size and sensory trait evolution.
... Naturally, the present results do not mean that sanddwelling ants are helpless in terms of antlion larva capture. Ants can minimize the risk of predation by avoiding antlion aggregation zones to some extent (Gotelli 1996;Morrison 2004;Hollis et al. 2017), which is their first "line of defense" against antlions. Additionally, earlier results obtained in rescue behavior investigations utilizing antlions (see, e.g., Miler 2016) are not invalidated by the present findings since rescue is a general behavioral category and major factors contributing to its occurrence (e.g., life expectancy) may very well be highly context independent. ...
The interaction of antlions and ants is postulated to be a predator-prey interaction in which the involved parties coevolve. Here, we investigated two issues of potential significance in terms of antlions and ants imposing selective pressures on one another. First, we determined whether trap-building antlions and sand-dwelling ants closely co-occurred in an area inhabited by both. In the field, we found that ants were the main potential prey items in artificial traps placed inside aggregation zones of antlions and that Formica cinerea workers comprised the majority of these ants. Second, we checked whether rescue behavior, a type of prosocial behavior displayed by F. cinerea workers and performed towards nestmates captured by antlions, reduced the hunting success of the latter. In the laboratory, we found that rescue attempts were very rarely successful. Overall, caution must be used when considering the coevolution of antlions and ants. Clearly, even though these two organisms can closely co-occur, the rescue behavior of ants seems to be unrelated to the predatory threat from antlions.
... At the same time, remembering profitable webs can be advantageous. Insects, and especially hymenopterans, are well known for their learning ability (Papaj and Lewis 1993;Avarguès-Weber et al. 2011;Giurfa 2015;Hollis et al. 2017); thus, we predict that Stenogastrinae likely remember previous web location after experiencing an encounter with the web. We hypothesize that wasps are able to learn about the position of a web after negative experience, avoiding the web in future trajectories. ...
Stealing prey items from other animals entails obvious benefits for the thief. However, this so-called kleptoparasitic behavior can also involve costs including injury or even death, especially when stealing from a potential predator. Here, we examined how kleptoparasitic hover wasps (Parischnogaster sp.) that steal prey items out of spider webs handle the risk of falling prey to their hosts. We tested the wasps’ ability to evade different webs under natural and experimental conditions and whether webs are perceived visually. Further, we tested whether wasps learn about web position and are able to avoid them in future trajectories as well as how quick wasps escape from webs once entangled. Additionally, we recorded the attack time for different spider species towards prey items placed into their webs, to estimate the risk of being attacked when entangled. Our results provide strong support for visual web perception by wasps facilitating the successful evasion of webs in flight trajectories, learning capability, and quick escape from webs once entangled. At the same time, the results, together with our observations in the field, suggest a specialization of kleptoparasitizing spider webs with overall lower risk of predation.
Significance statement:
Stealing prey from other predators often entails significant risk of injury and death. Yet, most research on such kleptoparasitism focused on the benefits to the kleptoparasite or the cost to the host, thereby overlooking an important component to explain the evolution and maintenance of kleptoparasitism. Here, we examine the potential costs for hover wasps when stealing prey from spider webs and test how wasps reduce the potential risks of this kleptoparasitic foraging behavior. While often described from casual observations, kleptoparasitism in hover wasps is so far unstudied. We show that kleptoparasitism from spider webs is associated with costs for hover wasps, but that visual detection of webs, avoidance learning, and rapid escape behavior mitigate those costs. Our study hints at hover wasps targeting certain host species where their mitigating strategies are most effective.
... At least for some species of lizards, this seems sufficient to acquire an aversion for predator chemical cues Webster et al., 2018; but see Gérard et al. 2016;Monks et al., 2019). Note that at present we do not know whether the chemical recognition of particular scents is passed on from one generation to another (which would probably require fast genetic adaptation or maternal effects) (Bourdeau et al., 2013), or whether each generation of Dalmatian wall lizards needs to learn which cues indicate danger (Griffin, 2004;Hollis et al., 2017). Previous research on other lacertid lizards suggests that chemical predator recognition is largely innate (Van Damme et al., 1995;Martín et al., 2015; see also Mori & Hasegawa, 1999;Downes & Adams 2001), but this research used long-established predator-prey models; whether naïve lizards can also recognize the cues of recently arrived predators has never been tested. ...
Newly introduced predators constitute a major threat to prey populations worldwide. Insular prey animals in particular often do not succeed in overcoming their naivety towards alien predators, making them specifically vulnerable. Why this is the case remains incompletely understood. Here, we investigate how the ability to detect and respond to predator chemical cues varies among populations of the Dalmatian wall lizard, Podarcis melisellensis. Lizards were sampled from five locations in southeastern Croatia (one mainland location and four islands) that varied in the composition of their predator community. We observed the lizards' behaviour in response to chemical cues of native saurophagous snakes (the Balkan whip snake, Hierophis gemonensis, and eastern Montpellier snake, Malpolon insignitus) and an introduced mammalian predator (the small Indian mongoose, Herpestes auropunctatus-a species held responsible for the loss of numerous insular reptile populations worldwide). Mainland lizards showed elevated tongue-flick rates (indicative of scent detection) as well as behaviours associated with distress in response to scents of both native and introduced predators. In sharp contrast, island lizards did not alter their behaviour when confronted with any of the predator cues. Alarmingly, even lizards from islands with native predators (both snakes and mammals) and from an island on which mongooses were introduced during the 1920s were non-responsive. This suggests that insular populations are chemosensorily deprived. As failure at the predator-detection level is often seen as the most damaging form of naivety, these results provide further insight into the mechanisms that render insular-living animals vulnerable to invasive species.
ADDITIONAL KEYWORDS: anti-predator response, biological invasions, chemical discrimination, insularity, prey naivety, small Indian mongoose.
... Interestingly, prey can generalize their acquired predator recognition to similar but novel species, and continuously update their recognition templates [62,63]. Animals also learn to avoid locations associated with predation: ants are able to form a generalized memory of their predators' pit traps after escaping a single time [64], and mice show risk assessment and escape behaviours when exploring an arena in which they previously encountered threats [19,65]. ...
Highlights
Escape behaviours are not only simple stimulus-reactions but are under cognitive control, allowing the study of processes such as decision-making and action selection in tractable organisms in ethological settings.
Successful escape relies on integrating multiple external and internal variables, such as for computing flight trajectories towards shelter, and implementing trade-offs by choosing between actions that satisfy competing motivations.
Some neural mechanisms of escape are innate and conserved across species, but are subject to control and modification by multiple systems, including the neocortex, which allow experience to be flexibly incorporated into escape behaviour.
New tools to quantify behaviour while recording neural activity enable analysis of ethologically-relevant behaviours in complex environments, and will advance our understanding of the neural basis of natural behaviours.
... To date, the majority of studies on rescue behaviour have been performed on sand-dwelling ants, which are known to be exposed to predation by antlion larvae and nest cave-ins, two agents that have likely contributed to the evolution of rescue behavioural patterns, making them especially prevalent in ants. Sand-dwelling ants can minimize the risk of predation by antlions by simply avoiding antlion aggregation zones and their pitfall traps (Gotelli, 1996;Morrison, 2004;Hollis et al., 2017), but even when a foraging ant stumbles into the trap, not all is lost if its nestmates come to rescue. Indeed, rushing into an antlion larva trap and acting to free a trapped nestmate has been observed in some species co-occurring with antlion larvae. ...
Some ants display rescue behaviour, which is performed by nearby nestmates and directed at individuals in danger. Here, using several ant species, we demonstrate that rescue behaviour expression matches predicted occurrences based on certain aspects of species' ecological niches. Rescue occurred in sand-dwelling ants exposed both to co-occurring antlion larvae, representing the threat of being captured by a predator, and to nest cave-ins, representing the threat of being trapped in a collapsed nest chamber. Rescue also occurred in forest groundcover ants exposed to certain entrapment situations. However, rescue never occurred in species associated with open plains, which nest in hardened soils and forage largely on herbaceous plants, or in ants living in close mutualistic relationships with their host plants. In addition, because we tested each species in two types of tests, antlion larva capture tests and artificial entrapment tests, we highlight the importance of accounting for test context in studying rescue behaviour expression.
Ant rescue behaviour belongs to the most interesting subcategories of prosocial and altruistic behaviour encountered in the animal world. Several studies suggested that ants are able to identify what exactly restrains the movements of another individual and to direct their rescue behaviour precisely to that object. To shed more light on the question of how precise the identification of the source of restraint of another ant is, we investigated rescue behaviour of red wood ant Formica polyctena workers, using a new version of an artificial snare bioassay in which a nestmate victim bore two wire loops on its body, one (acting as a snare) placed on its petiole and an additional one on its leg. The tested ants did not preferentially direct their rescue behaviour towards the snare. Moreover, the overall strategy adopted by the most active rescuers was not limited to precisely targeted rescue attempts directed towards the snare, but consisted of frequent switching between various subcategories of rescue behaviour. These findings highlight the importance of precise identification of cognitive processes and overall behavioural strategies for better understanding of causal factors underlying animal helping behaviour in light of new facts discovered by testing of various successive research hypotheses.
Efficiently avoiding predators is critical for animal survival. However, little is known about how the experience of predator attack affects behaviors in predator defense. Here, we caught mice by tail to simulate a predator attack. We found that the experienced mice accelerated the flight in response to the visual threaten cue. Single predator attack didn't induce anxiety but increased the activity of innate fear or learning related nucleus. The predator attack induced acceleration of flight was partly rescued when we used drug to block protein synthesis which is critical in the learning process. The experienced mice significantly reduced the focused exploration on the floor during the environment exploration, which might facilitate the discovery of predator. These results suggest that mice could learn from the experience of predator attack to optimize their behavioral pattern to detect the predator cue immediately and response intensely, and therefore increase the probability of survival.
Jednym z najważniejszych elementów społecznego trybu życia są zachowania prospołeczne, czyli działania, z których korzyści odnoszą inne osobniki. Do najbardziej interesujących podkategorii ryzykownych zachowań prospołecznych należą zachowania ratunkowe, czyli spieszenie z pomocą osobnikom, które znalazły się w niebezpiecznej sytuacji. W świecie zwierząt zachowania ratunkowe zostały po raz pierwszy opisane u mrówek legionistek z gatunku Eciton hamatum, a następnie badano je również u mrówek z wielu innych gatunków należących do podrodzin Formicinae, Myrmicinae, Ponerinae i Dolichoderinae. Badania te były prowadzone zarówno w terenie, jak i w warunkach laboratoryjnych i stosowano w nich szeroką gamę testów behawioralnych, podczas których potencjalne ratowniczki konfrontowano bądź z osobnikami o ograniczonej mobilności (unieruchomionymi w wyniku zasypania lub też uwięzionymi w sztucznym sidle), bądź też z mrówkami zaatakowanymi przez wrogów naturalnych, takich jak larwy mrówkolwa, pająki lub termity. W badaniach tych analizowano wpływ licznych czynników wpływających na gotowość mrówek do angażowania się w zachowania ratunkowe oraz na ujawniające się w tym kontekście wzorce behawioralne, w tym przede wszystkim tzw. precyzyjne zachowania ratunkowe stanowiące świadectwo nieoczekiwanie zaawansowanych możliwości poznawczych tych owadów. Do czynników tych należały wiek, specjalizacja behawioralna oraz oczekiwana dalsza długość trwania życia zarówno ofiar, jak i potencjalnych ratowniczek, a także przebyte doświadczenia, czynniki genetyczne oraz gatunek i specyfika jego ekologii. Sprawdzano też, czy ratowane są jedynie towarzyszki z własnej kolonii, czy również osobniki pochodzące z obcych kolonii własnego gatunku oraz z gatunków obcych. Podejmowano też próby identyfikacji sygnałów emitowanych przez ofiary w ramach tzw. wołania o pomoc. Zaobserwowano również, że niektóre mrówki otaczają opieką sanitarną towarzyszki zranione przez wrogów naturalnych lub też cierpiące wskutek infekcji i stwierdzono, że opieka taka może być korzystna zarówno dla osobników poszkodowanych, jak i dla ich zdrowych towarzyszek, gdyż uratowane osobniki mogą kontynuować pracę na rzecz kolonii, zaś kontakty z zakażonymi towarzyszkami mogą wywierać stymulujący wpływ na procesy odpornościowe zdrowych osobników i dzięki temu stanowić element profilaktyki przeciwdziałającej rozprzestrzenianiu się chorób zakaźnych. Niemniej jednak, skrócona oczekiwana dalsza długość trwania życia często idzie u mrówek w parze z tzw. wycofaniem społecznym, które może się wyrazić również w mniejszej gotowości do angażowania się w zachowania ratunkowe. Osobniki takie są również mniej chętnie ratowane przez towarzyszki. Zachowania ratunkowe opisywano i analizowano również u kręgowców: ptaków (dwa gatunki) i licznych ssaków (szczury, myszy, psy, mangusty, dziki, słonie, a także różne walenie i naczelne). Badania zachowań ratunkowych zwierząt rzucają istotne światło zarówno na ewolucję altruizmu i zachowań prospołecznych, jak i na zdolności poznawcze zwierząt i czynniki, które mogą je wspomagać lub osłabiać. Wyniki badań zachowań ratunkowych mrówek stanowią też świetną ilustrację tego, w jaki sposób badania porównawcze przyczyniają się do formułowania ogólnych zasad i prawidłowości ukazując pełniejszy obraz badanych zagadnień i pozwalając na wyciągnięcie wniosków o wyższym stopniu ogólności.
In a species of Mediterranean desert-dwelling ant, Cataglyphis piliscapa (formerly, C. cursor), some individuals, mostly foragers, engage in highly orchestrated behavior to free a trapped nestmate. Their behavior, which we have labeled rescue, is a heritable trait in this species, and it appears fully formed within a few days of an ant’s emergence as an adult. Not only is the rescue behavior by these ant specialists precisely targeted, but also it involves a complex, dynamic sequence of behavioral patterns. That is, each rescue operation is responsive both to the specific circumstances of the nestmate’s entrapment and to the way in which that particular rescue operation unfolds, relying on the rescuer’s short-term memory of its previous actions to increase efficiency and to decrease energy expenditure. Rescue appears in several other ant species as well, and, although the specific behavioral patterns and contexts vary across species, the outcome—namely, releasing a distressed nestmate—remains the same. Here, we describe research designed to address questions about the function, evolution, cause, and development of rescue behavior in C. piliscapa—a behavior ecological approach—drawing on research in other species, and by other researchers, both to highlight comparative similarities and differences and, importantly, to draw attention to still unanswered questions. In addition, by shedding light on the rescue behavior of ants, we also hope to engender increased attention to, and research on, this extraordinary form of helping behavior in multiple other taxa.
Rescue behaviour is observed when one individual provides help to another individual in danger. Most reports of rescue behaviour concern ants (Formicidae), in which workers rescue each other from various types of entrapment. Many of these entrapment situations can be simulated in the laboratory using an entrapment bioassay, in which ants confront a single endangered nest mate entrapped on a sandy arena by means of an artificial snare. Here, we compared numerous characteristics of rescue actions (contact between individuals, digging around the entrapped individual, pulling at its body parts, transport of the sand covering it and biting the snare entrapping it) in Formica cinerea ants. We performed entrapment tests in the field and in the laboratory, with the latter under varying conditions in terms of the number of ants potentially engaged in rescue actions and the arena substrate (marked or unmarked by ants’ pheromones). Rescue actions were more probable and pronounced in the field than in the laboratory, regardless of the type of test. Moreover, different test types in the laboratory yielded inconsistent results and showed noteworthy variability depending on the tested characteristic of rescue. Our results illustrate the specifics of ant rescue actions elicited in the natural setting, which is especially important considering the scarcity of field data. Furthermore, our results underline the challenges related to the comparison of results from different types of entrapment tests reported in the available literature. Additionally, our study shows how animal behaviour differs in differing experimental setups used to answer the same questions.
Antlion larvae and ants: Dimensions of predator-prey-relation in NorthEast-Germany (Euroleon nostras Fourcroy, Myrmeleontidae, Neuroptera) Six species of the genetic group Euroleon are widespread distributed form Korea to Spain. Reports about larvae of E. nostras of Northern Europe are scant; especially, it concerns reports about ecological conditions, prey profit in habitats, stipulation of biomass as well as survival strategies. Moreover, studies about Life history of larvae under intermitted access to prey will be under demand. This study deals with population, prey spectrum, prey diversity, pit design of antlions in habitats of southern Baltic Sea shores. It includes also abiotic characteristics as soil texture and water balance. Recent reports about evolution of antlion lacewings and simultaneous occurrence of Formicidae suggest existence of predator-prey relationships between them for around 100 million years. Earliest evidence appears in Baltic as well as Myanmar amber with ages of 50 and 100 million years, respectively. Populations were studied in sandy habitats (fine up to coarse sand). Sandy habitats allow for oxygen and also water exchange of larvae with surroundings. Dry sand comprises only 1 % of water. Therefore, antlions are dependent on rain and dew for stabilizing their fluid balance. On the other side, larvae dig pits for trapping of prey. It fails hugely when rain solidifies the sand design and living conditions for a population might become complicated. However, larvae are versatile in stabilizing water balance. Prey serves as prime source for fluid. Ants of species Formica, Porcellio (Isopoda), and Glomeris (Glomerida) comprise 76, 69 and 64 % of water, respectively. In contrast, water balance of antlion larvae is less stable it varies between 68 and 73 % of body mass. Ants, as prey, are not permanently available. Ants constitute around 60 to 80 % of prey in open-situated habitats. In forest-habitats, their portion shrinks to 5 %. Prey comes then chiefly from small animals of forest floor.-In summary, ambush predators live risky because they meet food unpredictably. Therefore, larvae must be equipped with low metabolic rates so that they survive for a long time without food. Let us have a quick glance to the ambush trap. The larva marks its site by a circular channel. Next, it crawls backwards in sand along the circular-spiral orbit. It pulls by aid of one front leg permanently the sand from inside out. The pit gets deeper and deeper when the larva moves along the spiral orbit. In fixing the open space and the depth of the pit it meets automatically the angle of repose of the sand. It has been found that larvae dig their pits in around 0.5 h. This is a very short time for constructing a pitfall trap in relation to the time at resting metabolic rate. This period of time does not depend on the larvae stage. The metabolism during this action exceeds the resting one by a factor of roughly nine (Example: L3, 22 mg; 5.3 µgC / h to 0.6 µgC / h). Therefore, the costs of the pit construction (volume, mass weight, energy) are of minor importance in relation to prey. The linear accession of pit traps diameter (benefit of prey catch) exponentially corresponds to ascent of costs. We collected data about transport of sand and time of design as well as related data by computer-aided data processing. The development cycle from ovi-positioning to pupa lasts for two years in NorthEast Germany. Interestingly, all three larvae stages exist in populations during certain periods, but with widely differing biomasses from 5 to 150 mg. This is chiefly caused by varying access to nourishment. * Meiner Frau Brigitte Meißner, geb. Schönermarck (15.07.1938-23.11.2019) gewidmet! Mitt. Dtsch. Ges. allg. angew. Ent. 22 Halle (Saale) 2020 52 We found in prey-poor habitats time restricted food access with waiting periods up to 24 days. It is interesting to note that single Formica may satisfy the resting metabolism over this very long period. Thus, difference in biomasses reflects prey-rich and prey-poor habitats. Antlions suck effectively their prey independently of their own mass. It has been observed, they gain from ants and larvae of Tenebrio 35 and 43 %, respectively. Lean larvae (30 mg) grow by 170 % of their mass whereas more heavy larvae (100 mg) bring it only to 40 % plus. This regime is important for their development towards pupa.
When an antlion captures a foraging ant, the victim’s nestmates may display rescue behaviour. This study tested the hypothesis that the expression of rescue behaviour depends on the life expectancy of the captured ant. This hypothesis predicts that the expression of rescue behaviour will be less frequent when the captured ant has a lower life expectancy than when it has a higher life expectancy because such a response would be adaptive at the colony level. Indeed, significant differences were found in the frequency of rescue behaviours in response to antlion victims with differing life expectancies. In agreement with prediction, victims with lower life expectancies were rescued less frequently, and those rescues had a longer latency and shorter duration. There was also a qualitative difference in the behaviour of rescuers to victims from the low and high life expectancy groups. Several explanations for these findings are proposed.
Learning abilities are exhibited by many animals, including insects. However, sedentary species are typically believed to have low capacities and requirements for learning. Despite this view, recent studies show that even such inconspicuous organisms as larval antlions, which employ an ambush predation strategy, are capable of learning, although their learning abilities are rather simple, i.e., limited to the association of vibrational cues with the arrival of prey. This study demonstrates, for the first time, that antlion larvae can use vibrational cues for complex modifications of their foraging strategies. Specifically, antlion larvae rapidly learn to differentiate between the vibrational cues associated with prey of different sizes, and they save resources by ignoring smaller prey in favour of larger, more energetically profitable prey. Moreover, antlion larvae can learn to associate vibrational cues with the loss of their prey, and they respond by burying their victims under the sand more often and more rapidly than do individuals with no opportunities to form such associations. These findings provide not only new insights into the cognitive abilities of animals but also support for the optimal foraging strategy concept, suggesting the importance of maximizing fitness output by balancing the costs and benefits of alternative foraging strategies.
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Cataglyphis
cursor worker ants are capable of highly sophisticated rescue behaviour in which individuals are able to identify what has trapped a nestmate and to direct their behaviour towards that obstacle. Nonetheless, rescue behaviour is constrained by workers’ subcaste: whereas foragers, the oldest workers, are able both to give and to receive the most help, the youngest workers, inactives, neither give nor receive any help whatsoever; nurses give and receive intermediate levels of aid, reflecting their intermediate age. Such differences in rescue behaviour across subcastes suggest that age and experience play a critical role. In this species, as in many others in which a sensitive period for nestmate recognition exists, newly enclosed ants, called callows, are adopted by ants belonging not only to different colonies but also to different species; foreign callows receive nearly the same special care provided to resident newborns. Because callows are younger than inactives, which are incapable of soliciting rescue, we wondered whether entrapped callows would receive such aid. In the present study, we artificially ensnared individual callows from their own colony (homocolonial), from a different colony (heterocolonial), and from a different species (heterospecific), and tested each one with groups of five potential C.
cursor rescuers, either all foragers or all nurses. Our results show that all three types of callows are able to elicit rescue behaviour from both foragers and nurses. Nonetheless, nurse rescuers are better able to discriminate between the three types of callow victims than are foragers.
Antlion larva, Myrmeleon formicarius, detects its victims while still a few centimetre away by sensing the vibrations they generate in the sand. The animal reacts to the approaching prey by opening its mandibles and/or by sand tossing. The larva is extremely sensitive to small disturbances of the substrate (the threshold amplitude lies at the frequency of 500 Hz below 50 nm, the threshold acceleration at the frequencies of 20 and 200 Hz below 0.1 ms-2). For tactile stimulation the thorax is the most sensitive part of the body.
Altruistic behavior, in which one individual provides aid to another at some cost to itself, is well documented. However, some species engage in a form of altruism, called rescue, that places the altruist in immediate danger. Here we investigate one such example, namely rescuing victims captured by predators. In a field experiment with two North American ant species, Tetramorium sp. E and Prenolepis imparis, individuals were held in artificial snares simulating capture. T. sp. E, but not P. imparis, exhibited digging, pulling, and snare biting, the latter precisely targeted to the object binding the victim. These results are the first to document precision rescue in a North American ant species; moreover, unlike rescue in other ants, T. sp. E rescues conspecifics from different colonies, mirroring their atypical social behavior, namely the lack of aggression between non-nestmate (heterocolonial) conspecifics. In a second, observational study designed to demonstrate rescue from an actual predator, T. sp. E victims were dropped into an antlion's pit and the behavior of a single rescuer was observed. Results showed that T. sp. E not only attempted to release the victim, but also risked attacking the predator, suggesting that precision rescue may play an important role in this species' antipredator behavior.
We report the results of field observations and experiments demonstrating that workers of Formica sanguinea Latr. and F. cinerea Mayr caught by a larva of an ant lion (Myrmeleon formicarius L.) can induce rescue behaviour in their nestmates. Typical rescue behaviour involves both the attempts to pull away the attacked ant by tugging at its limbs, and rapid, intense digging behaviour. In natural mixed colonies of F. sanguinea and F. fusca L., enslaved F. fusca workers display rescue behaviour when their heterospecific nestmate is caught by an ant lion larva. On the other hand, we did not observe nestmate rescue behaviour in monospecific F. fusca colonies. These data suggest that workers of F. sanguinea and F. cinerea caught by an ant lion emit some signals which summon their nestmates to arrive at their rescue. Workers of F. fusca either do not emit such signals, or their danger signals fail to elicit rescue behaviour in other ants. Exprcssion of rescue behaviour in the studied ant species is discussed in the context of their life strategies, of their position in the interspecific competitive hierarchy, and of our knowledge about nestmate rescue behaviour, and signals eliciting alarm and digging behaviour in ants.
Long-term behavioral changes related to learning and experience have been shown to be associated with structural remodeling in the brain. Leaf-cutting ants learn to avoid previously preferred plants after they have proved harmful for their symbiotic fungus, a process that involves long-term olfactory memory. We studied the dynamics of brain microarchitectural changes after long-term olfactory memory formation following avoidance learning in Acromyrmex ambiguus. After performing experiments to control for possible neuronal changes related to age and body size, we quantified synaptic complexes (microglomeruli, MG) in olfactory regions of the mushroom bodies (MB) at different times after learning. Long-term avoidance memory formation was associated with a transient change in MG densities. Two days after learning, MG density was higher than before learning. At days 4 and 15 after learning — when ants still showed plant avoidance — MG densities had decreased to the initial state. The structural reorganization of MG triggered by long-term avoidance memory formation clearly differed from changes promoted by pure exposure to and collection of novel plants with distinct odors. Sensory exposure by the simultaneous collection of several, instead of one, non-harmful plant species resulted in a decrease in MG densities in the olfactory lip. We hypothesize that while sensory exposure leads to MG pruning in the MB olfactory lip, the formation of long-term avoidance memory involves an initial growth of new MG followed by subsequent pruning.
Insects possess small brains but exhibit sophisticated behavioral performances. Recent works have reported the existence of unsuspected cognitive capabilities in various insect species, which go beyond the traditional studied framework of simple associative learning. In this study, I focus on capabilities such as attention, social learning, individual recognition, concept learning, and metacognition, and discuss their presence and mechanistic bases in insects. I analyze whether these behaviors can be explained on the basis of elemental associative learning or, on the contrary, require higher-order explanations. In doing this, I highlight experimental challenges and suggest future directions for investigating the neurobiology of higher-order learning in insects, with the goal of uncovering l architectures underlying cognitive processing. WIREs Cogn Sci 2015, 6:383-395. doi: 10.1002/wcs.1348 For further resources related to this article, please visit the WIREs website.
The author has declared no conflicts of interests for this article.
© 2015 John Wiley & Sons, Ltd.
A sand-dwelling Mediterranean ant, Cataglyphis cursor, recently was discovered to engage in two new forms of rescue behaviour, behavioural patterns that require would-be rescuers to recognize what, exactly, holds nestmates in place. That is, when sand digging and limb pulling, two well-known forms of rescue in ants, did not result in release of victims ensnared with nylon thread and partially buried beneath the sand, rescuers next began to transport sand away from the snare and to direct their behaviour to the snare in particular, biting and tugging at the snare itself. To determine whether these new forms of precisely directed rescue behaviour, as well as their exclusive delivery to nestmates, as in C. cursor, were characteristic of other ants occupying similar ecological niches, we conducted experiments with five sand-dwelling Mediterranean ant species: Cataglyphis floricola, Lasius grandis, Aphaenogaster senilis, Messor barbarus and Messor marocanus. Our experiments revealed the full range of rescue behaviour, including snare biting and sand transport, in two species, C. floricola and L. grandis. Both species directed rescue exclusively towards nestmates, treating other individuals, even conspecifics, with aggression, thus highlighting the ants' discriminative capacities. Differences in the performance of rescue behaviour between these and the remaining species mirror differences in their ecology, including the threat of predatory antlions. Finally, because this precisely directed and exclusively delivered rescue behaviour in ants resembles behaviour that has been labelled empathy in rats, our results demonstrate that what can appear to be complex, cognitively motivated behaviour might come about through much simpler mechanisms.
Ants use multiple sources of information to navigate, but do not integrate all this information into a unified representation of the world. Rather, the available information appears to serve three distinct main navigational systems: path integration, systematic search and the use of learnt information-mainly via vision. Here, we report on an additional behaviour that suggests a supplemental system in the ant's navigational toolkit: 'backtracking'. Homing ants, having almost reached their nest but, suddenly displaced to unfamiliar areas, did not show the characteristic undirected headings of systematic searches. Instead, these ants backtracked in the compass direction opposite to the path that they had just travelled. The ecological function of this behaviour is clear as we show it increases the chances of returning to familiar terrain. Importantly, the mechanistic implications of this behaviour stress an extra level of cognitive complexity in ant navigation. Our results imply: (i) the presence of a type of 'memory of the current trip' allowing lost ants to take into account the familiar view recently experienced, and (ii) direct sharing of information across different navigational systems. We propose a revised architecture of the ant's navigational toolkit illustrating how the different systems may interact to produce adaptive behaviours.
Cognitive abilities used by arthropods, particularly predators, when interacting in a natural context have been poorly studied. Two neotropical sympatric predators, the golden silk spider Nephila clavipes and the ectatommine ant Ectatomma tuberculatum, were observed in field conditions where their interactions occurred regularly due to the exploitation of the same patches of vegetation. Repeated presentations of E. tuberculatum workers ensnared in their web triggered a progressive decrease in the capture response of N. clavipes. All the spiders that stopped trying to catch the ant on the second and/or third trial were individuals that had been bitten during a previous trial. Behavioural tests in natural field conditions showed that after a single confrontation with ant biting, spiders were able to discriminate this kind of prey more quickly from a defenceless prey (fruit flies) and to selectively and completely suppress their catching response. This one-trial aversive learning was still effective after 24 h. Likewise, E. tuberculatum workers entangled once on a N. clavipes web and having succeeded in escaping, learned to escape more quickly, breaking through the web by preferentially cutting spiral threads (sticky traps) rather than radial threads (stronger structural unsticky components) or pursuing the cutting of radials but doing it more quickly. Both strategies, based on a one-trial learning capability, obviously minimize the number of physical encounters between the two powerful opponents and may enhance their fitness by diminishing the risk of potential injuries resulting from predatory interactions.
Insects possess miniature brains but exhibit a sophisticated behavioral repertoire. Recent studies have reported the existence of unsuspected cognitive capabilities in various insect species that go beyond the traditionally studied framework of simple associative learning. Here, I focus on capabilities such as attentional modulation and concept learning and discuss their mechanistic bases. I analyze whether these behaviors, which appear particularly complex, can be explained on the basis of elemental associative learning and specific neural circuitries or, by contrast, require an explanatory level that goes beyond simple associative links. In doing this, I highlight experimental challenges and suggest future directions for investigating the neurobiology of higher-order learning in insects, with the goal of uncovering the basic neural architectures underlying cognitive processing.
Division of labor, an adaptation in which individuals specialize in performing tasks necessary to the colony, such as nest defense and foraging, is believed key to eusocial insects' remarkable ecological success. Here we report, for the first time, a completely novel specialization in a eusocial insect, namely the ability of Cataglyphis cursor ants to rescue a trapped nestmate using precisely targeted behavior. Labeled "precision rescue", this behavior involves the ability of rescuers not only to detect what, exactly, holds the victim in place, but also to direct specific actions to this obstacle. Individual ants, sampled from each of C. cursor's three castes, namely foragers, nurses and inactives, were experimentally ensnared (the "victim") and exposed to a caste-specific group of potential "rescuers." The data reveal that foragers were able to administer, and obtain, the most help while members of the youngest, inactive caste not only failed to respond to victims, but also received virtually no help from potential rescuers, regardless of caste. Nurses performed intermediate levels of aid, mirroring their intermediate caste status. Our results demonstrate that division of labor, which controls foraging, defense and brood care in C. cursor, also regulates a newly discovered behavior in this species, namely a sophisticated form of rescue, a highly adaptive specialization that is finely tuned to a caste member's probability of becoming, or encountering, a victim in need of rescue.
Antlion larvae that construct conical pits to capture prey may strongly affect foraging of ants and other arthropods, yet are usually abundant only in sheltered microhabitats. Larval antlion (Myrmeleon crudelis Walker) densities increased in exposed areas in central Texas in late summer and early autumn of 1998, presumably because of extended dry conditions. I conducted a study to quantify larval antlion pit densities in sheltered and exposed areas over time, and to examine the effect of variation in pit density on the foraging activity of ants and other arthropods. Isolated rainfall events decreased pit densities in exposed areas, sometimes to zero, but pit densities returned to high levels as the soil dried out. Pitfall traps at sheltered sites caught significantly fewer ants and other arthropods inside antlion zones (i.e., areas of high antlion density) than in adjacent areas without antlions. At exposed sites, pitfall traps caught significantly fewer ants in antlion zones when pits were present (dry conditions) than when they were absent (wet conditions); there was no significant difference in foraging outside the antlion zones in wet compared with dry conditions. Significantly fewer ants were caught inside antlion zones at sheltered sites (that were permanent) compared with exposed sites (that were transient), although pit densities were similar at both types of sites. Attraction of ants to baits revealed similar patterns. Spatiotemporal variation in antlion pit densities and the associated predation risk to ants and other arthropods may result in behavioral modifications of foraging patterns, higher mortality rates, or both.
We experimentally determined whether the low density of antlion larvae found in ant-acacia clearings is due to high levels of ant predation or an inadequate substrate for pit-trap construction. Pit establishment was more affected by soil improvement than by the exclusion of ants, suggesting that soil condition is the main factor that affect antlions’density. The low density of this ant-predator in ant-acacia clearings may be considered as an indirect advantage of the ant's pruning behavior.RESUMENDeterminants experimentalmente si la baja densidad de larvas del “Ieón de las hormigas” en los claros de Acacia producidos por hormigas es consecuencia de los altos niveles de depredacion por hsormigas o de la condicion del suelo alrededor de las Acacias. El establecimiento de las trampas del “Ieón de las hormigas” estuvo más afectado por el mejoramiento del suelo que por la exclusión de las hormigas, sugiriendo que la condición del suelo es el factor más importante que afecta la densidad del “Ieón de las hormigas”. La baja densidad de este depredador de hormigas en los claros de Acacia puede ser considerada como una ventaja indirecta de la actividad “limpiadora” de las hormigas.
There is a large body of evidence indicating that predator behavior may strongly influence patterns and processes at the population and community level. Site selection is a major component of fitness in sit-and-wait predators, especially when relocation is rare. Although several review articles dealt with these issues in web-building spiders, this is the first attempt to summarize the effects of biotic and abiotic factors on site selection and relocation in another group of sit-and-wait predators, the pit-building antlions (Neuroptera: Myrmeleontidae). Our synthesis shows that prey abundance may have relatively little effect on pit relocation and that physical properties of the habitat or competition often override its effect. We suggest that owing to a variety of constraints such as physiological constraints or difficulties in assessing site quality, site selection and relocation are not necessarily optimal and thus food intake rate is not maximized. We call for a multi-factorial study on a single species in order to pinpoint the dominant factors and to assess to what extent they influence site selection and relocation. We conclude by proposing new research directions, such as studying whether pit relocation is an adaptive response, when controlling for possible phylogenetic effects.
Larvae of the antlion, Myrmeleon crudelis, build conical pitfall traps in sand that are asymmetric, with lower-sloped walls in the part of the pit where the antlion resides, and steeper walls in front of the antlion. The front walls also tend to be lined with a higher density of fine sand. Simulation of movement at the pit bottom showed that this asymmetry can result from movement by the antlion. If asymmetry reduces prey capture efficiency, antlions should shift their position in the pit, and thereby reduce the impact of their movement on any given wall. Alternatively, if asymmetry is a design feature, antlions can maintain this feature by remaining in the same position for extended periods of time. Observations support the later hypothesis. Sixty-one per cent of 41 antlions tested remained in the same orientation for the entire observation time (9–14 days), and 20% remained in the same orientation for at least 5 days, then maintained a different orientation for the remainder of the experiment. Ant escape behaviour was analysed in relation to the asymmetry of the pit walls. The initial escape direction was random, but if ants moved to another part of the pit after their initial escape attempt (66% of escapes), they tended to travel to a steeper wall. The opposite occurred when ants escaped from artificial pits containing no antlions. Thus by constructing an asymmetric pit, the antlion compensates for its inability to efficiently capture prey that escape to the front of the pit. The antlion can throw sand directly at prey that attempt to escape in the back of the pit; they can also reach over their backs to capture prey, and can walk after prey in this direction. None of these behaviours is available if prey try to escape forward in the pit. A change in pit design with antlion size is discussed in light of these results.
An antlion pit is lined with fine particles during construction. This feature appears to increase the effectiveness of the pit in prey capture. Pit structure is influenced by physical properties of sand and the building behaviour of the antlion. Two physical properties of sand govern pit structure: the angle of repose and Stoke's Law drag force. These two properties complement each other as follows: (a) Since larger particles have a lower angle of repose than smaller particles, fine sand grains tend to stay on the pit walls, whereas larger particles fall to the pit's centre. (b) Large particles have a lower drag to momentum ratio than do small particles. Thus, larger particles are more likely to be thrown out of the pit than are smaller particles. Several behavioural modifications were demonstrated that increase the number of fine particles on the pit walls while reducing construction costs for the antlion. (a) A trajectory angle of 45° is used when the antlion throws particles out of the pit. This angle will maximize the distance to which larger particles are thrown. A trajectory angle of 60° is used at the end of pit construction when the antlion is throwing fine particles on the sides of the pit. This angle reduces the number of these fine particles leaving the pit. (b) Antlions can alter the velocity with which they throw particles. When discarding prey carcasses and debris that have accumulated during prey capture, they use a velocity that is approximately 39% higher than the velocity used during pit construction. (c) By vibrating their forelegs, antlions appear to sift out the finer particles before each throw. This increases the percentage of larger particles discarded from the pit.
Unique in the insect world for their extremely sedentary predatory behavior, pit-dwelling larval antlions dig pits, and then sit at the bottom and wait, sometimes for months, for prey to fall inside. This sedentary predation strategy, combined with their seemingly innate ability to detect approaching prey, make antlions unlikely candidates for learning. That is, although scientists have demonstrated that many species of insects possess the capacity to learn, each of these species, which together represent multiple families from every major insect order, utilizes this ability as a means of navigating the environment, using learned cues to guide an active search for food and hosts, or to avoid noxious events. Nonetheless, we demonstrate not only that sedentary antlions can learn, but also, more importantly, that learning provides an important fitness benefit, namely decreasing the time to pupate, a benefit not yet demonstrated in any other species. Compared to a control group in which an environmental cue was presented randomly vis-à-vis daily prey arrival, antlions given the opportunity to associate the cue with prey were able to make more efficient use of prey and pupate significantly sooner, thus shortening their long, highly vulnerable larval stage. Whereas "median survival time," the point at which half of the animals in each group had pupated, was 46 days for antlions receiving the Learning treatment, that point never was reached in antlions receiving the Random treatment, even by the end of the experiment on Day 70. In addition, we demonstrate a novel manifestation of antlions' learned response to cues predicting prey arrival, behavior that does not match the typical "learning curve" but which is well-adapted to their sedentary predation strategy. Finally, we suggest that what has long appeared to be instinctive predatory behavior is likely to be highly modified and shaped by learning.
New research shows that honeybees can classify arrangements of two visual patterns according to their spatial configuration. Can bees learn relational concepts of 'above' and 'below'? And are the underlying psychological processes comparable in humans and other primates facing similar tasks?
The effect of increasing population density on the formation of pits, their size and spatial distribution, and on levels of mortality was examined in the antlion Myrmeleon acer Walker. Antlions were kept at densities ranging from 0.4 to 12.8 individuals per 100 cm(2). The distribution of pits was regular or uniform across all densities, but antlions constructed proportionally fewer and smaller pits as density increased. Mortality through cannibalism was very low and only occurred at densities greater than five individuals per 100 cm(2). Antlions in artificially crowded situations frequently relocated their pits and when more space became available, individuals became more dispersed with time. Redistribution of this species results from active avoidance of other antlions and sand throwing associated with pit construction and maintenance, rather than any attempt to optimise prey capture per se.
We review data from both ethology and psychology about generalization, that is how animals respond to sets of stimuli including familiar and novel stimuli. Our main conclusion is that patterns of generalization are largely independent of systematic group (evidence is available for insects, fish, amphibians, reptiles, birds and mammals, including humans), behavioural context (feeding, drinking, courting, etc.), sensory modality (light, sound, etc.) and of whether reaction to stimuli is learned or genetically inherited. These universalities suggest that generalization originates from general properties of nervous systems, and that evolutionary strategies to cope with novelty and variability in stimulation may be limited. Two major shapes of the generalization gradient can be identified, corresponding to two types of stimulus dimensions. When changes in stimulation involve a rearrangement of a constant amount of stimulation on the sense organs, the generalization gradient peaks close to familiar stimuli, and peak responding is not much higher than responding to familiar stimuli. Contrary to what is often claimed, such gradients are better described by Gaussian curves than by exponentials. When the stimulus dimension involves a variation in the intensity of stimulation, the gradient is often monotonic, and responding to some novel stimuli is considerably stronger than responding to familiar stimuli. Lastly, when several or many familiar stimuli are close to each other predictable biases in responding occur, along all studied dimensions. We do not find differences between biases referred to as peak shift and biases referred to as supernormal stimulation. We conclude by discussing theoretical issues.
Although helping behavior is ubiquitous throughout the animal kingdom, actual rescue activity is particularly rare. Nonetheless, here we report the first experimental evidence that ants, Cataglyphis cursor, use precisely directed rescue behavior to free entrapped victims; equally important, they carefully discriminate between individuals in distress, offering aid only to nestmates. Our experiments simulate a natural situation, which we often observed in the field when collecting Catagyphis ants, causing sand to collapse in the process. Using a novel experimental technique that binds victims experimentally, we observed the behavior of separate, randomly chosen groups of 5 C. cursor nestmates under one of six conditions. In five of these conditions, a test stimulus (the "victim") was ensnared with nylon thread and held partially beneath the sand. The test stimulus was either (1) an individual from the same colony; (2) an individual from a different colony of C cursor; (3) an ant from a different ant species; (4) a common prey item; or, (5) a motionless (chilled) nestmate. In the final condition, the test stimulus (6) consisted of the empty snare apparatus. Our results demonstrate that ants are able to recognize what, exactly, holds their relative in place and direct their behavior to that object, the snare, in particular. They begin by excavating sand, which exposes the nylon snare, transporting sand away from it, and then biting at the snare itself. Snare biting, a behavior never before reported in the literature, demonstrates that rescue behavior is far more sophisticated, exact and complexly organized than the simple forms of helping behavior already known, namely limb pulling and sand digging. That is, limb pulling and sand digging could be released directly by a chemical call for help and thus result from a very simple mechanism. However, it's difficult to see how this same releasing mechanism could guide rescuers to the precise location of the nylon thread, and enable them to target their bites to the thread itself.
Predators of pollinators can influence pollination services and plant fitness via both consumptive (reducing pollinator density) and non-consumptive (altering pollinator behaviour) effects. However, a better knowledge of the mechanisms underlying behaviourally mediated indirect effects of predators is necessary to properly understand their role in community dynamics. We used the tripartite relationship between bumblebees, predatory crab spiders and flowers to ask whether behaviourally mediated effects are localized to flowers harbouring predators, or whether bees extend their avoidance to entire plant species. In a tightly controlled laboratory environment, bumblebees (Bombus terrestris) were exposed to a random mixture of equally rewarding yellow and white artificial flowers, but foraging on yellow flowers was very risky: bees had a 25 per cent chance of receiving a simulated predation attempt by 'robotic' crab spiders. As bees learnt to avoid 'dangerous' flowers, their foraging preferences changed and they began to visit fewer yellow flowers than expected by chance. Bees avoided spider-free yellow flowers as well as dangerous yellow flowers when spiders were more difficult to detect (the colour of yellow spiders was indistinguishable from that of yellow flowers). Therefore, this interaction between bee learning and predator crypsis could lead flower species harbouring cryptic predators to suffer from reduced reproductive success.
Search is an important tool in an ant's navigational toolbox to relocate food sources and find the inconspicuous nest entrance. In habitats where landmark information is sparse, homing ants travel their entire home vector before searching systematically with ever increasing loops. Search strategies have not been previously investigated in ants that inhabit landmark-rich habitats where they typically establish stereotypical routes. Here we examine the search strategy in one such ant, Melophorus bagoti, by confining their foraging in one-dimensional channels to determine if their search pattern changes with experience, location of distant cues and altered distance on the homebound journey. Irrespective of conditions, we found ants exhibit a progressive search that drifted towards the fictive nest and beyond. Segments moving away from the start of the homeward journey were longer than segments heading back towards the start. The right tail distribution of segment lengths was well fitted by a power function, but slopes less than -3 on a log-log plot indicate that the process cannot be characterized as Lévy searches that have optimal slopes near -2. A double exponential function fits the distribution of segment lengths better, supporting another theoretically optimal search pattern, the composite Brownian walk.
A behavioural ecological approach to the relationship between pit-digging larval antlions and their common prey, ants, provides yet another example of how the specific ecological niche that species inhabit imposes selection pressures leading to unique behavioural adaptations. Antlions rely on multiple strategies to capture prey with a minimal expenditure of energy and extraordinary efficiency while ants employ several different strategies for avoiding capture, including rescue of trapped nestmates. Importantly, both ants and antlions rely heavily on their capacity for learning, a tool that sometimes is overlooked in predator-prey relationships, leading to the implicit assumption that behavioural adaptations are the result of fixed, hard-wired responses. Nonetheless, like hard-wired responses, learned behaviour, too, is uniquely adapted to the ecological niche, a reminder that the expression of associative learning is species-specific. Beyond the study of ants and antlions, per se, this particular predator-prey relationship reveals the important role that the capacity to learn plays in coevolutionary arms races.
Cannibalism, the process of killing and consuming conspecifics, can become enhanced by various environmental stresses. Organisms inhabiting Mediterranean habitats are better adapted for coping with competition—an adaptation that can manifest itself in increased cannibalism. Conversely, desert environments are characterized by long periods of food shortage, also selecting for cannibalism to overcome starvation. We tested for differences in the frequency of cannibalism between Mediterranean and desert populations of pit-building antlions. We also quantified the frequency of cannibalism within and between these populations. We could not detect a significant geographic variation in the frequency of cannibalism. We suggest that strong plastic responses to environmental stresses buffer against divergent selection, and thus no significant differentiation in cannibalism rate should occur. Cannibalism frequency was higher in mixed pairs comprised of individuals originating from different populations within and between climate regions, compared with that observed within populations. We suggest that this intraspecific discrimination ability is mediated by behavioral and/or chemical cues, associated with co-occurrence in a common environment, as well as by genetic relatedness.
Pit-building antlions capture their prey by digging funnel-shaped pits in loose sand and then laying in wait for prey to fall inside the trap. Behavioral experiments studying predator–prey interactions and measurements of vibrations propagated in sandy substrates revealed that antlions are extremely sensitive to substrate vibrations produced by prey crawling on the sand surface. Prey produce low-frequency sand-borne vibrations, and to locate a source of vibration, antlions rely on time differences of waveforms arriving at their receptors—tufts of hairs positioned on lateral parts of the mesothorax and metathorax. In this chapter, the role of physical properties of sand in substrate-borne vibration transmission is discussed.
The predatory behavior of a pit-making antlion, Myrmeleon mobilis, is characterized. Behavioral sequences among three prey types were similar, when compared via flow diagrams. A significant difference in behavioral frequency existed between hardbodied and soft-bodied prey types.
(1) The general feeding biology of Morter obscurus is described. (2) First instar larvae, because they use a different pit construction technique, have steeper-walled pits than later instars. Pit diameter and larval length are linearly related. (3) Capture success is determined mainly by the relative sizes of predator and prey. For a given relative size instar 1 larvae are more successful because of the steep-walled pits. Capture success drops to zero when ants can place some of their legs outside the pit. Third instar larvae were more successful than second instar larvae in pits of the same size. Capture success, particularly for large larvae, is 100% over much of the prey size range. (4) Successful attacks on ants with thick exoskeletons occurred almost exclusively via the gaster whereas mandible insertion for ants with thin exoskeletons frequently occurred elsewhere. (5) Differences in pit morphology and prey capture behaviour in Macroleon lynceus are documented and related to habitat differences. In Morter, pit morphology is crucial for prey capture, while strength is more important for the larger Macroleon. (6) Handling time was divided into time to capture (Tc), time to death (Td), and time to extract body contents (Te). Tc was constant for small prey but increased rapidly for larger prey. Td was constant for all sizes of predator and prey. Te increased with prey size and decreased with increasing predator size and temperature. Te seems to depend not only on the amount of extractable food but also on the shape of the victim. (7) Hunger has no effect on prey handling time or food extraction efficiency. However hungry larvae are more likely to move their pits. Ant-lions can capture prey falling into the pit when already feeding and so increase their food supply. (8) Growth rates of larvae feeding on different sized prey were measured. Large larvae grew more slowly than small ones when fed on the same sized prey because of higher maintenance costs. For a given sized predator, growth per unit weight of prey received declined with increasing prey size because of increased feeding costs. Each size of ant-lion had a prey size for which the costs per unit return were a minimum, this size changing abruptly from very small prey for the first two instars to large prey for the final instar. (9) The feeding biology of the three instars is compared and contrasted. First instar larvae are adapted to achieve a high capture success rate on a small prey size range because feeding costs are high and escapes therefore expensive. For large larvae, maintenance costs are more important and selection has favoured a large size range of catchable prey. While the behaviour of ant-lion larvae is consistent with an energy maximizer strategy it is concluded that the approach is of limited value in this instance.
The first 2 instars of Macroleon quinquemaculatus larvae construct steeper-walled pits than 3rd instar larvae. Capture success in the first two instars increased rapidly with pit size but in the third instar the relationship was weaker. A simple model assuming that pit size in Macroleon is determined by energy inputs and costs predicts that 1) there will be an optimum pit size for a given size of larva and that pit size will fall below this optimum because of increased costs (for example disturbance), reduced benefits (scarcity of food) or the time taken to recover from either of these; 2) there will be differences between instars in their response to changing benefits and costs because of differences in the importance of the pit to prey capture; and 3) pit construction activity will vary with both past and present energy inputs. Findings strongly support these predictions. Pit construction effort in Morter sp. was greater, and increased more rapidly with body size, than in Macroleon. Field data for Morter showed prey to be abundant and suggest that pit size is adjusted to achieve a constant energy supply per unit metabolic weight. -from Author
In C Oklahoma, two species of predaceous, pit-building ant lion larvae (Myrmeleon immaculatus and M. crudelis) coexist in a narrow, high-density (>50 animals/m2) zone at the base of sandstone cliffs, where they are sheltered from rain and afternoon sun. Athough larval movement is frequent and abundance within the zone varies seasonally, ant lions are rarely found >2 m from the cliff base. Rainfall limits ant lion distribution through an interaction with temperature. Within the ant lion zone, the soil remains dry and ant lion larvae bury themselves more rapidly in the sun than in the shade. Outside the ant lion zone, rainfall leads to the formation of a persistent soil crust. Larvae are unable to penetrate this crust, and they succumb to high temperatures in the sun. Because both species of ant lions are restricted to a narrow spatial zone, the probability of interspecific and intraspecific interactions is increased. The abundances of M. crudelis and M. immaculatus were negatively correlated in quadrats from the center of the ant lion zone. Across the ant lion zone, the relative abundance of the two species also differed significantly, although the differences were not consistent among sites. Because of overriding abiotic constraints, neither species can achieve an ideal free distribution with respect to food resources. High-density predator aggregations may also affect prey community structure. Arthropod abundance was low within the ant lion zone, perhaps because of direct predation by ant lions or predator avoidance behavior by prey. -from Author
This study examined the responses of ground-foraging ants to larval ant lions (Neuroptera: Myrmeleontidae). In central Oklahoma, these sit-and-wait arthropod predators are restricted by abiotic factors to sheltered cliff bases. A high-density ant lion zone forms an effective "minefield" of predation for local ant assemblages. The density of ant-nest entrances and the number of pitfall-trap captures of ant foragers were significantly lower in the ant lion zone than in the adjacent forest or grassland. Differences in ant abundance could not be attributed to differences in thermal microhabitat within and outside the ant lion zone. Over a 24-h period, ants foraged continuously at tuna-fish baits placed on the forest floor, but never utilized baits placed within the ant lion zone. Field behavioral tests with individual ant foragers confirmed that the risk of predation from ant lions was high for common ant species in the assemblage. Among species, predation risk was negatively correlated with worker body mass. Manipulative field experiments tested whether ants use biotic or abiotic cues to avoid ant lion aggregations. Ants foraged readily at baits on the forest floor and baits placed in the center of experimental sand patches, but they avoided baits placed in sand patches that contained ant lions. Ant foraging was also substantially lower in patches from which ant lions had been removed 3 h prior to the start of the experiment. Ant foraging was slightly reduced in patches with artificial ant lion pits that had never contained predators. These experiments suggest that ants use biotic cues associated with the presence or recent presence of predators. Previous studies have not implicated predation as an important factor structuring ant communities. This study suggests that predators can have important community-wide impacts on the distribution, abundance, and behavior of ground-foraging ants.
What factors permit the coexistence of competing species? In central Okla- homa, the predaceous ant lions Myrmeleon crudelis and M. immaculatus live in dense aggregations at the sheltered bases of cliff ledges. Three larval instars of each species act as predators and competitors of one another. In controlled field experiments, mortality of second and third instars increased with density, although intra- and interspecific effects were indistinguishable. The presence of third-instar larvae did not affect recruitment or survivorship of first-instar larvae. In all experiments, mortality was predictable on the basis of body mass and larval density, but not species identity. Increased food supply shortened development time and increased adult body mass but did not affect mortality. Larvae near the front of the ant lion aggregation grew faster due to greater food availability but suffered greater mortality in the pupal stage. Although food and space were limiting, neither species was excluded because (1) intra- and interspecific effects were similar; (2) third-instar larvae could not suppress the recruitment of first-instar larvae; and (3) recruitment was patchy in time and space. Oviposition behavior and interactions among adult ant lions may also contribute to larval coexistence.
Recent debate has questioned whether animal social learning truly deserves the label "social" [1]. Solitary animals can sometimes learn from conspecifics [2, 3], and social learning abilities often correlate with individual learning abilities [4-6], so there may be little reason to view the underlying learning processes as adaptively specialized. Here, we demonstrate how learning by observation, an ability common to primates, birds, rodents, and insects [7-9], may arise through a simple Pavlovian ability to integrate two learned associations. Bumblebees are known to learn how to recognize rewarding flower colors by watching conspecifics from behind a screen [9], and we found that previous associations between conspecifics and reward are critical to this process. Bees that have previously been rewarded for joining conspecifics copy color preferences, but bees that lack such experience do not, and those that associate conspecifics with bitter substances actively avoid those flower colors where others have been seen. Our findings place a seemingly complex social learning phenomenon within a simple associative framework that is common to social and solitary species alike.
Hungrige Silbermöwenkücken picken nach der Schnabelspitze des Altvogels. Diese Reaktion ist angeboren. Weiterbauend auf die Ergebnisse FR. GOETHES (1937) haben wir mittels Attrappenversuche die das Betteln auslösende Reizsituation so vollständig wie möglich zu vermitteln versucht. Für eine experimentelle Schema-Untersuchung war diese Reaktion ein ideales Objekt. Es hat sich aus den abgebildeten Attrappenversuchen ergeben, dass es der Schnabel ist, der die Schlüsselreize liefert, während der Kopf nach Form, Farbe und Grösse total irrelevant ist. Der Schnabel reizt durch: 1) Bewegung (Abb. 29); 2) Form; er muss länglich, nicht zu kurz im absolutem Sinne, und dünn sein (Abb. 15 und 17); 3) Niedrigkeit; je niedriger er gehalten wird, um so besser wirkt er (Abb. 22 und 24) ; 4) Nähe; je näher, umso stärker reizt er (Abb. 27); 5) Haltung; je stärker er nach unten zeigt, je besser wirkt er (Abb. 19); 6) Schnabelfleck; dieser wirkt durch rote Farbe und durch Kontrast mit der Schnabel-farbe (Abb. 2, 3, 4, 6) ; 7) Nahrung; etwas aus der Kontur herausspringendes (Abb. 34). Sämtliche Schlüsselreize 'enthalten relative Elemente. Von diesen Eigenschaften des Schnabels is nur der 6. ein wirklicher Auslöser in dem Sinne, dass er nicht nur Schlüsselreize für das angeborene Schema der Bettelreaktion liefert, sondern als Anpassung an diese Mitteilungsfunktion betrachtet werden muss. Durch Übertreibung mancher relativer Eigenschaften des Schnabels war es möglich, eine
Abstract European pit-building antlions (Euroleon nostras/ Geoffroy in Fourcroy/) detect their prey by sensing the vibrations that prey generate during locomotory activity. The behavioural reactions and some of the physical properties of substrate vibrations in sand are measured to observe signal transmission through the substrate. The frequency range of the signals of four arthropod species (Tenebrio molitor, Pyrrhocoris apterus, Formica sp. and Trachelipus rathkei) is 0.1–4.5 kHz and acceleration values are in the range 400 μm s−2 to 1.5 mm s−2. Substrate particle size and the frequency of prey signals both influence the propagation properties of vibratory signals. The damping coefficient at a frequency 300 Hz varies from 0.26 to 2.61 dB cm−1 and is inversely proportional to the size of the sand particle. The damping coefficient is positively correlated with the frequency of the pulses. Vibrations in finer sand are attenuated more strongly than in coarser sand and, consequently, an antlion detects its prey only at a short distance. The reaction distance is defined as the distance of the prey from the centre of the pit when the antlion begins tossing sand as a reaction to the presence of prey. The mean reaction distance is 3.3 cm in the finest sand (particle size ≤ 0.23 mm) and 12.3 cm in coarser sand (particle size 1–1.54 mm). The most convenient sands for prey detection are considered to be medium particle-sized sands.
Spatial modelling of species distributions has become an important tool in the study of biological invasions. Here, we examine the utility of combining distribution and ecological niche modelling for retrieving information on invasion processes, based on species occurrence data from native and introduced ranges. Specifically, we discuss questions, concerning (1) the global potential to spread to other ranges, (2) the potential to spread within established invasions, (3) the detectability of niche differences across ranges, and (4) the ability to infer invasion history through data from the introduced range. We apply this approach to two congeneric pavement ants, Tetramorium sp.E (formerly T. caespitum (Linnaeus 1758)) and T. tsushimae Emery 1925, both introduced to North America. We identify (1) the potential of both species to inhabit ranges worldwide, and (2) the potential of T. sp.E and T. tsushimae, to spread to 23 additional US states and to five provinces of Canada, and to 24 additional US states and to one province of Canada, respectively. We confirm that (3) niche modelling can be an effective tool to detect niche shifts, identifying an increased width of T. sp.E and a decreased width of T. tsushimae following introduction, with potential changes in niche position for both species. We make feasible that (4) combined modelling could become an auxiliary tool to reconstruct invasion history, hypothesizing admixture following multiple introductions in North America for T. sp.E, and a single introduction to North America from central Japan, for T. tsushimae. Combined modelling represents a rapid means to formulate testable explanatory hypotheses on invasion patterns and helps approach a standard in predictive invasion research.
We studied olfactory learning in two ant species, Camponotus mus from Argentina and Camponotus fellah from Israel. To this end, we established an experimental laboratory protocol in which individual ants were trained to associate odours with gustatory reinforcers. Ants were trained individually to forage in a Y-maze in which two odours had to be discriminated. One odour was positively reinforced with sucrose solution and the other was negatively reinforced with quinine solution. After a training session of 24 trials, ants of both species learned to differentiate the two odour pairs, the structurally dissimilar limonene and octanal, and the structurally similar heptanal and 2-heptanone. In nonreinforced tests, ants consistently chose the odour previously reinforced with sucrose solution and spent more time searching in the arm of the maze presenting this odour. Learning performances were more robust in the case of limonene versus heptanal. These results thus show for the first time that individual ants perceive and learn odours in controlled laboratory conditions. (c) 2006 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.
Foraging theory was first developed to predict the behaviour of widely-foraging animals that actively search for prey. Although the behaviour of sit-and-wait predators often follows predictions derived from foraging theory, the similarity between these two distinct groups of predators is not always obvious. In this review, we compare foraging activities of trap-building predators (mainly pit-building antlions and web-building spiders), a specific group of sit-and-wait predators that construct traps as a foraging device, with those of widely-foraging predators. We refer to modifications of the trap characteristics as analogous to changes in foraging intensity. Our review illustrates that the responses of trap-building and widely-foraging predators to different internal and external factors, such as hunger level, conspecific density and predation threat are quite similar, calling for additional studies of foraging theory using trap-building predators. In each chapter of this review, we summarize the response of trap-building predators to a different factor, while contrasting it with the equivalent response characterizing widely-foraging predators. We provide here evidence that the behaviour of trap-building predators is not stereotypic or fixed as was once commonly accepted, rather it can vary greatly, depending on the individual's internal state and its interactions with external environmental factors.
A recent study shows that desert ants use a precise behaviour, based on the internal cues of path integration, to facilitate the learning of visual landmark information. This raises fascinating questions about how insects encode familiar terrain.
Pit-building antlions, the larvae of a winged adult insect, capture food by digging funnel-shaped pits in sand and then lying in wait, buried at the vertex, for prey to fall inside. The sedentary nature of this sit-and-wait predatory behaviour and, especially, antlions' innate ability to detect prey arrival, do not fit the typical profile of insects that possess learning capabilities. However, we show, for the first time, that learning can play an important role in this unique form of predation. In three separate experiments, individual antlions received, once per training day, either a vibrational cue presented immediately before the arrival of food or that same cue presented independently of food arrival. Signalling of food not only produced a learned anticipatory behavioural response (Experiment 1), but also conferred a fitness advantage: Associative learning enabled antlions to dig better pits (Experiments 2 and 3), extract food more efficiently (Experiments 2 and 3), and, in turn, moult sooner (Experiment 3) than antlions not receiving the associative learning treatment.
Traditional ecological approaches to species evolution have frequently studied too few species, relatively small areas, and relatively short time spans. In The Coevolutionary Process, John N. Thompson advances a new conceptual approach to the evolution of species interactionsâthe geographic mosaic theory of coevolution. Thompson demonstrates how an integrated study of life histories, genetics, and the geographic structure of populations yields a broader understanding of coevolution, or the development of reciprocal adaptations and specializations in interdependent species. Using examples of species interactions from an enormous range of taxa, Thompson examines how and when extreme specialization evolves in interdependent species and how geographic differences in specialization, adaptation, and the outcomes of interactions shape coevolution. Through the geographic mosaic theory, Thompson bridges the gap between the study of specialization and coevolution in local communities and the study of broader patterns seen in comparisons of the phylogenies of interacting species.
Ants that forage in visually rich environments often develop idiosyncratic routes between their nest and a profitable foraging ground. Such route knowledge is underpinned by an ability to use visual landmarks for guidance and place recognition. Here we ask which portions of natural visual scenes are essential for visually guided navigation in the Australian desert ant Melophorus bagoti whose foragers navigate through a habitat containing grass tussocks, shrubs and trees. We captured M. bagoti foragers after they had returned to their nest from a feeder, but before they had entered their nest, and tested their ability to home accurately from a series of release locations. We used this simple release paradigm to investigate visually guided navigation by monitoring the accuracy of nestwards orientation when parts of the ants' visual field were obscured. Results show that the lower portion of the visual panorama is more important for visually guided homing than upper portions. Analysis of panoramic images captured from the release and nest locations support the hypothesis that the important visual information is provided by the panoramic contour, where terrestrial objects contrast against sky, rather than by a limited number of salient landmarks such as tall trees.
An adaptation in one lineage (e.g. predators) may change the selection pressure on another lineage (e.g. prey), giving rise to a counter-adaptation. If this occurs reciprocally, an unstable runaway escalation or 'arms race' may result. We discuss various factors which might give one side an advantage in an arms race. For example, a lineage under strong selection may out-evolve a weakly selected one (' the life-dinner principle'). We then classify arms races in two independent ways. They may be symmetric or asymmetric, and they may be interspecific or intraspecific. Our example of an asymmetric interspecific arms race is that between brood parasites and their hosts. The arms race concept may help to reduce the mystery of why cuckoo hosts are so good at detecting cuckoo eggs, but so bad at detecting cuckoo nestlings. The evolutionary contest between queen and worker ants over relative parental investment is a good example of an intraspecific asymmetric arms race. Such cases raise special problems because the participants share the same gene pool. Interspecific symmetric arms races are unlikely to be important, because competitors tend to diverge rather than escalate competitive adaptations. Intraspecific symmetric arms races, exemplified by adaptations for male-male competition, may underlie Cope's Rule and even the extinction of lineages. Finally we consider ways in which arms races can end. One lineage may drive the other to extinction; one may reach an optimum, thereby preventing the other from doing so; a particularly interesting possibility, exemplified by flower-bee coevolution, is that both sides may reach a mutual local optimum; lastly, arms races may have no stable and but may cycle continuously. We do not wish necessarily to suggest that all, or even most, evolutionary change results from arms races, but we do suggest that the arms race concept may help to resolve three long-standing questions in evolutionary theory.
This paper presents a general statistical methodology for the analysis of multivariate categorical data arising from observer reliability studies. The procedure essentially involves the construction of functions of the observed proportions which are directed at the extent to which the observers agree among themselves and the construction of test statistics for hypotheses involving these functions. Tests for interobserver bias are presented in terms of first-order marginal homogeneity and measures of interobserver agreement are developed as generalized kappa-type statistics. These procedures are illustrated with a clinical diagnosis example from the epidemiological literature.