A South East Asian ponerine ant of the genus Leptogenys (Hym., Form.) with army ant life habits

Summary The emigration and raiding behavior of the SE Asian ponerine ant Leptogenys sp. 1, which resembles L. mutabilis, were observed in the field (Ulu Gombak, Malaysia). The ants formed monogynous colonies that consisted of up to 52 100 workers. The bivouac sites of this species were found in leaf litter, rotten logs, ground cavities, etc., and were rarely modified by the ants. The colonies stayed in these temporary nests for several hours to 10 days; afterwards, they moved to a new nest site. The emigration distances ranged from 5–58 m. Since nest changing takes place at irregular intervals, and pupae and larvae are always present in the nest relocations of Leptogenys sp. 1, the emigration behavior is not linked to a synchronized brood development. Leptogenys sp. 1 is a nocturnal forager; in our study, up to 42 600 workers participated in each raid. The ants move forward on a broad front; behind the swarm a fan-shaped network of foraging columns converges to form a main trunk trail. A new system of foraging trails is developed in each raid. The workers search for their prey collectively; they attack and retrieve the booty together. The diet of Leptogenys sp. 1 consists mainly of arthropods. Army ant behavior is characterized by (1) formation of large monogynous colonies, (2) frequent emigrations, and (3) mass raids in which all foraging activities are carried out collectively. Since Leptogenys sp. 1 performs these typical army ant behavior patterns, this species represents the army ant ecotype. However, this species differs considerably from army ant species that have synchronized broods and huge colonies with dichthadiiform queens.Dedicated to Professor Dr. M. Lindauer on the occasion of his 70th birthday     

Behavioral ecology of the neotropical termite-hunting ant Pachycondyla (= Termitopone) marginata: colony founding,group-raiding and migratory patterns

This study provides the first detailed field account of colony founding, group-raiding and migratory habits in the neotropical termite-hunting ant rPachycondyla marginata, in a semi-deciduous forest in south-east Brazil. New colonies can originate by haplometrosis, pleometrosis, or colony fission. Incipient colonies with multiple foundresses persisted longer in the field, and most excavated nests contained more than one dealated female. A total of 202 group raids by P. marginata were registered, and in all cases the raided termite species was Neocapritermes opacus. Nearly 20% of the workers within a colony engage with raiding activity. Colonies of P. marginata hunt for termites approximately every 2–3 weeks, and group-raids may last for more than 24 h. Target termite nests are up to 38 m from the ant colony, and occasionally two nests are simultaneously raided by one ant colony. Raiding ants carry 1 or 2 paralysed prey, and nearly 1600 termites can be captured during a 9-h raid. Migration by P. marginata colonies lasted over 2 days and covered distances of 2-97 m (n = 48). Average residence time at a given location was 150 days. Three basic migratory patterns were noted: colony fission (only part of the colony moves), long-distance migrations, and short-distance migrations. Both raiding and migratory activities appeared to be strongly affected by seasonal factors. The group raiding and migratory patterns of P. marginata are compared with other ant taxa with similar habits. It is concluded that P. marginata presents a rudimentary form of the so-called army ant behavior, which is highly developed in the subfamilies Dorylinae and Ecitoninae. The extremely specialized diet of P. marginata and the associated high costs of migration are features likely to prevent it from evolving a full army ant life pattern.     

Nomadic behavior of army ants in a desert-grassland habitat

Summary Nomadic behavior of the army ant Neivamyrmex nigrescens was studied in a desert-grassland habitat. Six colonies were followed through eight nomadic phases (94 nomadic days) while direction and distance of emigrations, growth of larvae, number of adults and larvae per colony were determined.In all colonies, the nomadic phase began when newly eclosed adults and small larvae were present, and ended when the larvae were fully grown. Average emigration distance was positively related to number of larvae in the colony. These findings support Schneirla's theory that brood stimulation is a proximate cause of the nomadic phase.Failures to emigrate were equally likely at all points in the nomadic phase, and there was no systematic increase in emigration distance as the phase progressed. These findings do not support Schneirla's version of brood-stimulative theory.Number of adults per colony was positively related to the directionality of the nomadic phase; however, both the direction and distance of emigrations varied unpredictably from one nomadic day to the next, in marked contrast to predictions from optimal foraging theory.Schneirla's theory is useful in predicting phase differences in colony behavior, but it does not account for characteristics such as frequency, direction, or distance of emigrations within the nomadic phase. These aspects of nomadic behavior are more closely related to characteristics of the habitat such as prey density and availability of nest sites. Army ant nomadism in this habitat may depart from the optimum because of high prey density, small colony size, or lack of nesting sites.     

Effects of parasites on foraging and defense behavior of a termitophagous ant,Pheidole titanis Wheeler (Hymenoptera: Formicidae)

Summary Pheidole titanis Wheeler, an ant that occurs in desert and deciduous thorn forest in the southwestern United States and western Mexico, is a predator on termites. In the dry season well-coordinated raids against termite foraging parties occur early in the morning or late in the afternoon, whereas in the wet season most raids occur at night. This seasonal shift in the timing of raids is due to the increased activity of a fly (Diptera: Phoridae) that is a specialist parasitoid on P. titanis workers and soldiers. When parasitic flies discover P. titanis nest entrances or raiding columns, workers stop foraging and defend themselves against oviposition attacks. Flies are only active during the day and never interfere with foraging at night. However, P. titanis does not increase the frequency of raids at night and, as a result, colonies collect less food in the wet season compared to the dry season. Presence of parasitic flies also interferes with normal defense behavior of P. titanis against conspecific and heterospecific enemy ants. Dissections of P. titanis workers and soldiers suggest that the parasitism rate by flies is less than 2% and observations indicate that parasitic flies are much rarer than their host workers and soldiers. Nonetheless, these parasites exert a strong ecological impact on their host.     

Division of labor and slave raid initiation in slave-making ants

In social insect societies, division of labor, i.e., workers of a colony specializing in different tasks, is thought to improve colony performance. Workers of social parasitic slave-making ants focus on a single task, searching for and raiding host colonies to replenish their slave workforce. However, in the North American slavemaker Protomognathus americanus, some workers do not partake in raids but remain inside the colony. We analyzed raid participation, fertility, and cuticular hydrocarbon profiles of slavemaker workers and slaves to understand these behavioral differences and the regulation of division of labor in slavemaker colonies. Raid observations showed that some workers were repeatedly involved in raiding activities (exterior workers), whereas others stayed inside the nest (interior workers). Exterior workers were always infertile, while half of the interior workers were fertile. Analysis of cuticular hydrocarbons demonstrated differences between the groups. We also detected chemical differences between interior and exterior slaves, indicating an influence of the individuals’ tasks on their cuticular profiles. Task- and fertility-related profiles may allow selective nestmate recruiting. Division of labor should also adapt to varying conditions. Since slave raids are dangerous, they should only be initiated when the colony needs additional slaves. Exclusively fed by their slaves, slavemaker workers could determine this need via their nutritional status. In an experiment with various feeding regimes, colonies subjected to a lower food provisioning rate showed increased proportions of slavemaker workers searching for host colonies. Division of labor in slave-making ants, therefore, might be flexible and can change depending on the colonies’ needs.     

Predatory behavior and chemical communication in two Metapone species (Hymenoptera:Formicidae)

Summary. Colonies of two species of Metapone (M. madagascarica, M. new species.) were collected in Madagascar and established in laboratory nests. It could be demonstrated that both species are specialist predators of termites (Cryptotermes kirbyi). During hunting the ants sting the termites and thereby paralyze and preserve the prey alive. In this way prey can be stored in the ant nest for extended periods. During foraging and colony emigrations the ants lay chemical trails with poison gland secretions. Among the seven compounds identified in the venom only methyl pyrrole-2-carboxylate elicits trail following behavior in both Metapone species. Received 11 February 2002, accepted 23 February 2002.     

Effects of foundress number on brood raids and queen survival in the fire ant Solenopsis invicta

In several ant species, colonies are founded by small groups of queens (pleometrosis), which coexist until the first workers eclose, after which all but one queen is killed. It has been hypothesized that, by producing a larger cohort of workers, cooperating queens may increase colony success during brood raids, a form of competition in which brood and workers from losing nests are absorbed into winning colonies. To test whether this benefit is sufficient to favor pleometrosis, newly mated queens of the fire ant Solenopsis invicta were assembled in groups of one, two, three, or four, reared in the laboratory until the first workers eclosed, then planted in the field in replicated assemblages. The proportion of colonies engaging in brood raids increased with average foundress number per nest and with colony density but was unaffected by variance in foundress number among interacting colonies. Within mixed assemblages of single-queen and multiple-queen colonies, queen number had no effect on the likelihood of engaging in raids or the probability of nest survival through the brood raiding period. However, following nearly 30% of raids, queens moved to new nests and displaced the resident queens. When queen relocation and subsequent mortality were accounted for, it was found that the survival of queens from four-queen groups was substantially higher than that of solitary queens. By contrast, the survival of queens from two-queen colonies was no greater than that of solitary queens. These results show that the competitive advantages of multiple-queen colonies are sufficient to counterbalance the increased mortality of queens within groups only when the number of foundresses is greater than two and when colonies are founded at high density. When colonies lose brood raids, the workers appear to abandon their mothers to join surviving colonies. However, in laboratory experiments, queens attempting to enter foreign nests were significantly more likely to displace the resident queen if their own daughters were present within the invaded nest. Thus, workers may be able to bias the probability that their mother rejoins them and displaces competing queens.     

Thermal ecology of the neotropical army ant Eciton burchellii.

I explored the thermal ecology of Eciton burchellii, a New World army ant, in primary forest and forest fragments in the Atlantic lowlands of Costa Rica in 2002 and 2003. My primary objective was to determine whether high surface temperatures in pastures surrounding forest fragments posed a thermal barrier to ant colonies within those fragments; secondarily, I assessed whether thermal gradients within continuous moist forest were sufficient to elicit avoidance reactions from foraging colonies. E. burchellii colonies in forest fragments avoided entering open pasture in full sun (51.3 degrees C) on 100% of all edge interactions; however, edges were readily crossed where artificial shaded areas had previously been installed. Ant raids in primary forest avoided artificially established temperatures >43 degrees C but tolerated 45.5 degrees C in the presence of prey baits. Captive ants held at 43 degrees C survived 18.5 min; at temperatures of 51.3 degrees C survival time was only 2.8 min. Ants running on established foraging trails increased running velocity by 18% when substrate temperature was raised from 28.4 degrees to 38.0 degrees C, and they abandoned trails at temperatures >43 degrees C. The standard deviation (s) of temperatures on active raid trails in continuous forest was 2.13 degrees C, while nearby systematic sampling revealed a greater background standard deviation of 4.13 degrees C. E. burchellii colonies in this region appear to be living surprisingly near their upper limits of thermal tolerance. The heat of open pastures alone is sufficient to prevent their exiting forest fragments, or entering similarly hot areas within continuous forest. Shaded vegetative corridors are sufficient to permit mobility between isolated fragments, and their preservation should be encouraged. Despite views that tropical lowland moist forests have an essentially homogenous microclimate, army ants appear to avoid local hot spots on the forest floor, steering daily foraging trails to follow cooler routes than would be expected by chance. As deforestation remakes tropical landscapes worldwide, it is important to consider the thermal consequences of these actions and their effect on keystone organisms such as army ants. Changes in global climate patterns are likely to affect even evergreen tropical systems whose organisms may be sensitive to finer microclimatic variation than previously suspected.     

Energetics,reproductive suppression and obligate communal breeding in carnivores

Summary Leptogenys processionalis Jerdon forages on termites and other arthropods by raiding in branched trails. Growth and topology of these search trails were studied using Horton's (1945) technique orginally developed to analyze the branching pattern of river systems. Branching was always a bifurcating process and branches emerged symmetrically on either side of the main trail. Branching coefficients (R _b ) were similar to those of a few biological branching systems, such as lungs, that are considered to be non-random in their branching pattern. The R _b values indicated that the rate of branching and growth of trails remained constant within each foraging bout. The length of trails became shorter as they grew out and branched. The branching process was a function of the spatial separation of food patches in the terminal search field. Ants in the terminal search field send signals on encountering prey. The recruits cannot discriminate between these signals if they arise from two food patches situated <40 cm from each other, and hence converge on them in a single trail. However, discrimination is possible when food patches are >40 cm apart and hence recruits congregate on them separately in two trails, resulting in branching. Thus, the branching process is a result of independent decision by the ants conforming to certain simple rules and not a collective decision of the whole colony. We argue that mass recruiting ants selected to forage by branching pattern of trails because of its efficiency over other topologies (Stevens 1973) in minimizing the cost of travel, both from the nest to the food patches and between food patches. Further, the branch angles appear to be a trade-off to minimize travel cost and the resistance to the flow of ants comprising the column.Offprint requests to: T. Veena     

Balancing between mutualism and exploitation: the symbiotic interaction between Lasius ants and aphids

Nests of Lasius niger (L.) ants were given varied food regimens to test whether their behaviour towards an aphid partner, Aphis fabae (Scop.), changed with alternative food supplies. Honeydew collection and predation on aphids were measured by video monitoring the movement of ants between their nest and an aphid aggregation. Data collected from the aphid aggregations enabled comparisons between remaining aphid biomass and between the tending intensities of the ants. I tested how ant behaviour was influenced by their access to alternative prey and sugar. The results showed that ants accepted a honey solution as a substitute for the honeydew produced by aphids. Ants not only attended their aphid partners, but also preyed on them. The average predation rate increased eightfold when ants were offered the alternative of sugar, whereas alternative prey had no significant effect. In contrast, ant-tending intensity decreased with alternative sugar whereas alternative prey elicited no effect.     

Effects of habitat fragmentation and degradation on flocks of African ant-following birds.

Tropical rain forests are rapidly cleared, fragmented, and degraded in sub-Saharan Africa; however, little is known about the response of species and even of key ecological groups to these processes. One of the most intriguing (but often neglected) ecological phenomena in African rain forests is the interaction between swarm-raiding army ants and ant-following birds. Similar to their well-known Neotropical representatives, ant-following birds in Africa track the massive swarm raids of army ants and feed on arthropods flushed by the ants. In this study we analyzed the effect of habitat fragmentation and degradation of a mid-altitude Congo-Guinean rain forest in western Kenya on the structure of ant-following bird flocks. Significant numbers of swarm raids were located in all forest fragments and in both undegraded and degraded forest. Fifty-six different species of birds followed army ant raids, forming bird flocks of one to 15 species. We quantitatively differentiated the bird community into five species of specialized ant-followers and 51 species of opportunistic ant-followers. Species richness and size of bird flocks decreased with decreasing size of forest fragments and was higher in undegraded than in degraded habitat. This was caused by the decrease of the species richness and number of specialized ant-followers at swarms, while the group of opportunistic ant-followers was affected little by habitat fragmentation and degradation. The composition of bird flocks was more variable in small fragments and degraded forest, compared to undegraded habitat in large fragments. The effect of habitat fragmentation on flock structure was best explained by the strong decline of the abundance of specialized ant-followers in small forest fragments. To conserve the association of army ants and ant-following birds in its natural state, vast areas of unfragmented and undegraded tropical rain forest are necessary.     

Caste allocation in litter Pheidole: lessons from plant defense theory

The allocation to growth, defense and reproduction varies in social insects within a species' life cycle and between species. A life cycle model (Oster and Wilson 1978) generally failed to predict caste allocation in small litter-nesting colonies of Neotropical Pheidole. Two of its assumptions were often invalid: food was unlikely to be limiting in four of five populations, and sexual biomass production accelerated, not decelerated, with colony size in three of five populations. One of five Pheidole populations studied had higher caste ratios (soldiers /workers) in reproductive colonies as predicted, and in no species did caste functions conform to predictions. We also adapted three models from plant defense theory to study between-species patterns of caste allocation. Among 12 litter Pheidole the amount of sterile biomass devoted to soldiers varied from 18 to 62%. Queen size, growth rate, and soldier investment positively covaried. Only one model, the cost of replacement hypothesis (McKey 1979), correctly predicted that species with costly female alates invest more in defense. The two hypotheses linking apparency to defense may also be valid if fast-growing colonies are more likely to attract the attention of predators.     

The trophic link between squid and the emperor penguin <Emphasis Type="Italic">Aptenodytes forsteri</Emphasis> at Pointe Géologie,Antarctica

Cephalopod beaks retrieved from stomachs of dead emperor penguin chicks at Pointe Géologie, Terre Adélie, provide information on taxonomic and size composition of the penguin’s squid diet, on the trophic range of the squid species preyed upon and on the fractional trophic impact of the penguin on the whole food web. Emperor penguins prey upon four squid species (Psychroteuthis glacialis, Kondakovia longimana, Gonatus antarcticus, Alluroteuthis antarcticus) and do not take squid larger than 480 mm mantle length. Larger squid live either below the penguin’s diving range or are beyond its handling capacity. Nitrogen stable isotope ratios indicate that squids cover a range of about two trophic levels (2.5–8‰ δ¹⁵N). The impact of the emperor penguin, however, concentrates on the upper part of this range, about 68% of its squid prey being >6‰ δ¹⁵N. The principal components of the emperor’s diet, fish, krill and squid, differ distinctly in average trophic level. Consequently the trophic position of the emperor penguin changes accordingly with diet composition and may differ by almost one trophic level between different emperor penguin colonies.     

Discrimination between nestmate and non-nestmate kin by social wasps (Polistes fuscatus,Hymenoptera: Vespidae)

Summary The threespine stickleback,Gasterosteus aculeatus is a voracious cannibal of both its own eggs and those of conspecific neighbours. Females, but not males, can distinguish their progeny from those of other fish and attacked alien eggs more frequently. In experiments to examine nest raiding, females that initiated raids on nests resulting in cannibalism were the first females to spawn in the reconstructed nest. These results support the hypothesis that cannibalism by females may be adaptive in situations where intense female competition for male guardians occurs.     

Fight or flight? A geographic mosaic in host reaction and potency of a chemical weapon in the social parasite <Emphasis Type="Italic">Harpagoxenus sublaevis</Emphasis>

Ant social parasites use chemical warfare to facilitate host colony takeover, which is a critical but recurring step in their life cycle. Many slave-making ants use the secretion of the Dufour gland to manipulate host behaviour during parasitic nest foundation and slave raids. Harpagoxenus sublaevis applies this chemical weapon onto defending Leptothorax host workers, which elicits deadly fights amongst them. Host species are expected to evolve counter-adaptations against this behavioural manipulation and in this study we investigated the geographic structure of this co-evolving trait. We compared the effectiveness of the parasitic gland secretion from different H. sublaevis populations in host colonies from various sites and analysed the occurrence of local adaptation. The two host species L. muscorum and L. acervorum generally showed different responses to the parasites’ chemical weapon: L. acervorum attacked nestmates treated with Dufour gland secretion, while L. muscorum workers fled. Flight, instead of intraspecific fights, is an adaptive host reaction as it results in fewer host fatalities during raids. Beside interspecific host differences, we found a geographic mosaic of host resistance: parasites from a German population strongly manipulated the behaviour of both sympatric Leptothorax populations. Russian or Italian hosts instead did not react with intracolonial aggression, but fled when confronted with the gland secretion of their sympatric parasite. Not only variation in host resistance explains differences in the effectiveness of the parasitic gland secretion but also interpopulational differences in its chemical composition, which were revealed by gas chromatography and mass spectrometry.     

Polygyny in the Neotropical termite Nasutitermes corniger: life history consequences of queen mutualism

Summary ecological aspects of monogyny and polygyny in social insect colonies are important in comparing individual queen reproductive success. Inseminated, fecund, multiple foundresses are common in some groups of ants and eusocial wasps, but true polygyny in termites has not previously been studied. One third of Nasutitermes corniger (Isoptera: Termitidae) colonies sampled in areas of young second growth in Panama contained from 2–33 primary queens (not supplementary or neotenic reproductives). All queens in polygynous associations were fully pigmented, physogastric egg layers within a single royal cell. Multiple kings were found less frequently; true polyandry is apparently restricted to immature polygynous colonies.Data on queen weight and morphological features, and on colony composition, show that queens in polygynous nests are young and that a transition from polygyny to monogyny probably occurs after several years. The escalated growth rate of multiple queen colonies removes them from the vulnerable incipient colony size class more rapidly than colonies initiated by a single foundress, and gives them sufficient neuter support staff (workers and soldiers) to enable earlier production of fertile alates. Using a population model (Leslie matrix) I construct isoclines of equal population growth which show values of early age class probability of survival and reproductive output favoring monogyny or polygyny under individual selection. This model of queen mutualism accounts for the risk of a female in a polygynous group not succeeding as the final surviving queen.Multiple primary queens are considered rare in termites, but a review of the literature demonstrates that they may be more widespread than is currently recognized. Polygyny in termites has received scant attention but is of significance as an example of a further ecological and evolutionary convergence between the phylogenetically independent orders Isoptera and Hymenoptera.     

Foraging and spatiotemporal territories in the honey ant Myrmecocystus mimicus wheeler (Hymenoptera: Formicidae)

Summary The honey ant Myrmecocystus mimicus is a scavenger, forages extensively on termites, collects floral nectar, and tends homoptera. Individual foragers of M. mimicus usually disperse in all directions when leaving the nest, but there are also groups of foragers that tend to swarm out of the nest primarily in one direction. Such massive departues are usually at irregular intervals, which may last several hours. The results of field and laboratory experiments suggest that these swarms of foragers are organized by a group recruitment process, during which recruiting scout ants lay chemical orientation trails with hindgut contents and simultaneously stimulate nestmates with a motor display and secretions from the poison gland. Usually these columns travel considerable distances (4–48 m) away from the nest, frequently interfering with the foraging activity of conspecific neighboring colonies.To prevent a neighboring colony from access to temporal food sources or to defend spatiotemporal borders, opposing colonies engage in elaborate display tournaments. Although hundreds of ants are often involved during these tournaments almost no physical fights occur. Instead, individual ants confront each other in highly sterotyped aggressive displays, during which they walk on stilt legs while raising the gaster and head. Some of the ants even seem to inflate their gasters so that the tergites are raised and the whole gaster appears to be larger. In addition, ants involved in tournament activities are on average larger than foragers.The dynamics of the tournament interactions were observed in several colonies over several weeks-mapping each day the locations of the tournaments, the major directions of worker routes away from the nest, and recording the general foraging activities of the colonies. The results indicate that a kind of dominance order can occur among neighboring colonies. On the other hand, often no aggressive interactions among neighboring colonies can be observed, even though the colonies are actively foraging. In those cases the masses of foragers of each colony depart in one major direction that does not bring them into conflict with the masses of foragers of a neighboring colony. This stability, however, can be disturbed by offering a new rich food source to be exploited by two neighboring colonies. This invariably leads to tournament interactions.When a colony is considerably stronger than the other, i.e., with a much larger worker force, the tournaments end quickly and the weaker colony is raided. The foreign workers invade the nest, the queen of the resident colony is killed or dirven off, while the larvae, pupae, callow workers, and honey pot workers are carried or dragged to the nest of the raiders. From these and other observations we conclude that young M. mimicus queens are unlikely to succeed in founding a colony within approximately 3 m of a mature M. mimicus colony because they are discovered and killed, or driven off by workers of the resident colony. Within approximately 3–15 m queens are more likely to start colonies, but these incipient groups run a high risk of being raided and exterminated by the mature colony.Although populations of M. mimicus and M. depilis tend to replace each other, there are areas where both species overlap marginally. Foraging areas and foraging habitats of both species also overlap broadly, but we never observed tournament interactions between M. mimicus and M. depilis.The adaptive significance of the spatiotemporal territories in M. mimicus is discussed.     

The red and the black: habituation and the dear-enemy phenomenon in two desert Pheidole ants

Many species of territorial animals are more aggressive toward strangers than neighbors, a pattern of aggression referred to as the ’dear-enemy phenomenon.’ In many cases, the mechanism by which neighbors are discriminated from strangers and the function of neighbor-stranger discrimination remain controversial. We investigated the spatial patterns of inter-colony aggression within and between two Pheidole species of seed-harvesting ants in the Mojave Desert of California by quantifying aggression between colonies in standardized staged encounters. We also tested whether the level of fighting between workers of two colonies is affected by previous exposure to each other. We show that neighbors (i.e., colonies less that 2.6 m away) of either species are treated less aggressively than more distant colonies and that habituation may be a mechanism by which this discrimination is achieved. The variation in aggression among spatially distant colonies also suggests that additional genetic or environmental factors are involved in recognition. The function of the dear-enemy phenomenon in these ant species may be related to the greater risk to the resources of a colony presented by strange workers than workers from a neighboring colony. Received: 18 November 1999 / Received in revised form: 3 April 2000 / Accepted: 3 May 2000     

An indirect test of inbreeding depression in the termites Reticulitermes flavipes and Reticulitermes virginicus

We analyzed tandem-running pairs of the termites Reticulitermes flavipes and Reticulitermes virginicus utilizing 13 and 12 microsatellite loci, respectively. Newly formed pairs in both species were significantly related to one another, but this average relatedness was considerably higher in R. flavipes (0.130 vs 0.060). These average relatedness levels resulted from some tandem pairs forming between nestmate termites: more than one quarter of all R. flavipes pairs (26.1%) met this criterion, while this was the case for only about one of every 20 R. virginicus pairs (5.1%). The likelihood that termites paired with siblings was inversely related to the inferred dispersal ability of the two species. F _ST, measured over identical spatial scales, was significantly higher in R. flavipes (0.034) than in R. virginicus (0.008). A comparison in R. flavipes of the observed proportion of nestmate pairs observed during tandem running vs the proportion found in established colonies revealed a significant excess of close relatives when pairs were first formed. There are two possible causes of this discrepancy: inbreeding depression (ID) may eliminate inbred colonies early in development, or related pairs may part late in the tandem-running phase or after it is completed. The latter explanation of inbreeding avoidance implies either historical or contemporary ID, and these results therefore suggest that, either directly or indirectly, ID could be a more potent force in the evolution of termite mating systems than is generally appreciated. This work was funded by grants from the United States Department of Agriculture National Research Initiative Competitive Grants Program (nos. 00-35302-9377 and 2002-35302-12490).     

Feeding biology and ecological impact of an introduced nudibranch,Tritonia plebeia,New England,USA

The nudibranchTritonia plebeia (Johnston) was first observed in New England in 1983, on vertical rock walls at 7 m depth off Nahant, Massachusetts. This northern European species preys exclusively on the soft coralAlcyonium digitatum (Linneaus) in its natural habitat. At Nahant, it preyed primarily on the closely relatedAlcyonium siderium Verrill. Laboratory studies indicated that it could locate its prey by distance chemoreception and by visual orientation towards tall dark surfaces which could help it find the vertical walls, overhangs, and boulder sides where the soft corals occur. Field studies showed thatT. plebeia fed primarily on colony bases, causing extensive damage and whole colony mortality. The most important endemic predator onA. siderium, Coryphella verrucosa (Sars), preyed preferentially on hydroids, but would graze polyps off the top portions ofA. sederium colonies, causing little permanent damage to the colony, during the winter months when hydroids were scarce. AlthoughC. verrucosa occasionally behaved agonistically towardT. plebeia, there was no indication in laboratory or field studies that either nudibranch had an effect on the other's foraging through interference competition. Extensive predation byT. plebeia caused the disappearance ofA. siderium at two sites (Outer and Inner Shag Rocks) and a sharp reduction at a third site (Inner East Point). The higher mortalities at the Shag Rocks sites most likely occurred because of a simultaneous urchin (Strogylocentrotus droebachiensis) population expansion. As space among aggregates ofA. siderium opened up due toT. plebeia predation, urchins were able to forage on the vertical walls and scrape off remaining colonies. At a fourth site, Halfway Rock, whereT. plebeia were seldom present,A. siderium colonies also suffered high mortalities. This increae in mortality began nearly a year before urchin populations increased, and during a summer of abnormally high water temperatures at Halfway Rock. The high temperatures, followed by urchin predation on remaining colonies could account for the disappearance of allA. siderium colonies at this site.T. plebeia disappeared at all sites by summer 1986 andA. siderium populations have since stabilized, but community-level changes at all sites whereA. siderium were removed have persisted.