The Influence of Relatedness, Neighbourhood and Overall Distance on Colony Mate Recognition in a Polydomous Ant

The ‘dear enemy phenomenon’ predicts that territorial animals respond less aggressively towards more familiar neighbours than towards unfamiliar conspecifics if potential losses to strangers are more costly than potential losses to neighbours. Conversely, territorial animals should respond more aggressively to neighbours, if potential losses to them are more costly than potential losses to strangers. In social insects the question of how colony members distinguish neighbours from strangers, however, is intertwined with the more general question of how colony members discriminate themselves from non‐colony members; both genetic and spatial distance can correlate with levels of inter‐colonial aggression. In this paper I disentangle the role of experience, genetic and spatial distance on inter‐colonial aggression in a polydomous population of Iridomyrmex purpureus. In I. purpureus, aggression is related to the spatial distance between colonies irrespective of genetic similarity. Spatial distance affected aggression in two different ways. First, workers were more likely to exhibit aggression towards alien conspecifics of adjoining rather than non‐adjoining territories, suggesting the opposite of the dear enemy phenomenon. Second, workers were more often aggressive towards conspecifics of more distant colonies, implying that environmental cues play a role in the recognition system of I. purpureus.     

Nestmate discrimination in the queenless ponerine ant Diacamma sp. from Japan

We examined the nestmate discrimination ability of Diacamma sp., an ant that reproduces by colony budding. We also tested for a relationship between internest distance and hostility. Hostility toward non‐nestmates was significantly stronger than that toward nestmates, suggesting that Diacamma sp. discriminates between nestmates and non‐nestmates. There was no significant correlation between internest hostility and internest distance, which indicates the absence of a “dear enemy” phenomenon in this species.     

Performance and responses to competition in two congeneric annual species: does seed heteromorphism matter?

Variations in seed characteristics observed in heteromorphic species may affect various stages of their life cycles, e.g. seed dormancy, germination characteristics or even adult plant performance. Highly specialised seed morphs – described as colonisers and maintainers – exhibit a trade‐off between colonisation capacity and competitive traits. The performance of distinct seed morph progeny under competitive conditions, and especially in multi‐species arrangements, had previously not been given much attention. In this study, we compared performance and response to competition among distinct seed morph progenies in two congeneric, co‐occurring species: the invasive Bidens frondosa and the non‐invasive Bidens tripartita. We hypothesised that maintainer seed morphs of both species would perform better under increased plant densities and within inter‐morphic mixtures, while coloniser morphs would show stronger responses to increased densities and perform relatively poorly in inter‐morphic mixtures. We conducted a growth trial and a greenhouse experiment, which revealed that seed morph progeny differed significantly in plant height when grown without competition, while under competitive conditions such differences became less apparent. The observed pattern was more strongly pronounced in B. frondosa, which showed a general predominance in stature and biomass over its non‐invasive congener. Although seed morphs performed equally well under competitive conditions, increased plant height and more rapid germination can favour the maintainer seed morph on sites where vegetation is already present.     

Duet codes do not enhance neighbour recognition in two closely related species of duetting neotropical wrens

Numerous studies have shown that territorial animals exhibit less aggression in response to neighbours than to strangers, a phenomenon known as dear enemy effect. The influence of acoustic features, such as song type sharing and repertoire sizes, in neighbour recognition has been widely documented in male songbirds. However, few studies have focused on duetting species, and particularly on those where pairs have pair‐specific duet codes (consistent associations of their individual phrase types). Given that each pair in the population can have a unique repertoire of duet types, duet codes have been hypothesized to enhance discrimination. In this context, we tested for evidence of neighbour recognition and duet code discrimination in two closely related species of neotropical wrens, the riverside wren, Cantorchilus semibadius, and the canebrake wren, C. modestus zeledoni. Although both species have moderately large repertoires, riverside wrens have higher levels of phrase type and duet type sharing across the population. We compared the approach and vocal responses of focal pairs to three playback treatments: neighbours' correct duet type, neighbours' incorrect duet type and a strangers' duet type. We found that riverside wrens displayed a stronger response to the strangers' playback than to both neighbours' playbacks, whereas no differences among treatments were found in canebrake wrens. Given that both species exhibited similar levels of aggression during neighbour playbacks, regardless of whether the correct duet code was used, our findings suggest duet codes do not facilitate neighbour recognition. We conclude that the function of duet codes in these species might be more closely related to intra‐pair communication. Finally, we suggest that the level of dear enemy effect a species exhibits depends on ecological factors that influence the perceived level of threat of territory intruders.     

Phenological match drives pollen‐mediated gene flow in a temporally dimorphic tree

• Variation in flowering phenology is common in natural populations, and is expected to be, together with inter‐mate distance, an important driver of effective pollen dispersal. In populations composed of plants with temporally separated sexual phases (i.e. dichogamous or heterodichogamous populations), pollen‐mediated gene flow is assumed to reflect phenological overlap between complementary sexual phases. In this study, we conducted paternity analyses to test this hypothesis in the temporally dimorphic tree Acer opalus.
• We performed spatially explicit analyses based on categorical and fractional paternity assignment, and included tree size, pair‐wise genetic relatedness and morph type as additional predictors. Because differences between morphs in flowering phenology may also influence pollination distances, we modelled separate pollen dispersal kernels for the two morphs.
• Extended phenological overlap between male and female phases (mainly associated with inter‐morph crosses) resulted in higher siring success after accounting for the effects of genetic relatedness, morph type and tree size, while reduced phenological overlap (mainly associated with intra‐morph crosses) resulted in longer pollination distances achieved. Siring success also increased in larger trees.
• Mating patterns could not be predicted by phenology alone. However, as heterogeneity in flowering phenology was the single morph‐specific predictor of siring success, it is expected to be key in maintaining the temporal dimorphism in A. opalus, by promoting not only a prevalent pattern of inter‐morph mating, but also long‐distance pollination resulting from intra‐morph mating events.

     

Vocal Discrimination in Mate Guarding Male Australian Sea Lions: Familiarity Breeds Contempt

The vocal characteristics of a species can be immensely diverse, and can significantly impact animal social interactions. The social structure of a species may vary with geographical variation in call characteristics. The ability of pinnipeds (true seals, fur seals, sea lions and walrus) to distinguish between conspecifics may assist male reproductive strategies, particularly mate acquisition. We assessed the ability of mate guarding Australian sea lion (Neophoca cinerea) males to discriminate local from foreign males’ barks recorded from a geographically distant breeding colony. Bark characteristics were significantly different between colonies, with barks produced by males from the Lewis Island breeding colony higher pitched and longer in both duration and interval duration than barks produced by males on Kangaroo Island. Mate guarding males displayed inter‐colony discrimination of barks, with a significantly stronger response to barks from local males than to those of males from a colony approx. 180 km away. Local males’ barks were apparently considered a greater threat than barks from unfamiliar males. We propose that discrimination of acoustic characteristics may facilitate reproductive isolation in this species that may lead to an ethological–acoustic barrier between breeding colonies, and subsequent genetic isolation.     

Effects of prey aphid species on the abundance of a parasitoid and two predator species in aphid colonies attended by ants on citrus

This study focused on three species of enemies, the parasitoid wasp Lysiphlebus japonicus Ashmead (Hymenoptera: Aphidiidae), the ladybird Scymnus posticalis Sicard (Coleoptera: Coccinellidae) and the predatory gall midge Aphidoletes aphidimyza (Rondani) (Diptera: Cecidomyiidae), all of which are able to exploit aphids attended by ants. I experimentally evaluated the effects of prey aphid species on the abundance of each of the three enemy species in ant‐attended aphid colonies on citrus. The aphids compared were Aphis gossypii Glover versus Aphis spiraecola Patch in late spring, and Toxoptera citricidus (Kirkaldy) versus A. spiraecola in late summer (all, Hemiptera: Aphididae). Colonies of the three aphid species were attended by the ant Pristomyrmex punctatus Smith (Hymenoptera: Formicidae). The initial number of attending ants per individual aphid did not differ significantly between the colonies of the two aphid species compared in each season. Between A. gossypii and A. spiraecola, there was no significant difference in the number of mummies formed by the parasitoid or foraging larvae of each of the two predators per aphid colony. A significant difference was detected between T. citricidus and A. spiraecola for each of the three enemy species, with a far greater number of L. japonicus mummies in T. citricidus colonies and distinctly more larvae of each of the two predators in A. spiraecola colonies. Thus, the abundance of each of the three enemy species in ant‐attended aphid colonies was significantly influenced by the species of the prey aphids, with the three enemies showing different responses to the three aphid species.     

When are neighbours ‘dear enemies’ and when are they not? The responses of territorial male variegated pupfish, Cyprinodon variegatus, to neighbours, strangers and heterospecifics

Dear enemy recognition reduces the costs of territorial defence in some species, but not others, when a neighbour is more threatening to a resident's fitness than an intruder. I asked whether dear enemy effects were fixed in a particular species, or if the reduced aggression between a resident and neighbour was disrupted by the presence of potential mating opportunities. Observing variegated pupfish, Cyprinodon variegatus, in the field and in the laboratory, I examined the effects of a female's presence in a male's territory on residents' aggressive responses to conspecific neighbours and strangers as well as heterospecific opponents. Although reduced aggression consistent with dear enemy recognition was seen between conspecific neighbours in the absence of females, the presence of a female in a male's territory instigated comparably greater aggression between the neighbours. No reduction in aggression was seen between pupfish males and heterospecific opponents. These findings suggest that dear enemy recognition may be a flexible, rather than a fixed, feature of the relationship of neighbouring conspecific males. Despite the disruption in dear enemy recognition caused by a female, residents in the laboratory faced with neighbours spent more time associating with the female than residents faced with strangers. This allowed the residents to secure as many spawns as did males who had been faced with no competitor. Residents faced with any other type of opponent had reduced reproductive success, suggesting that the dear enemy relationship between residents and neighbours is more complex than simply a reduction in aggression. Copyright 2003 Published by Elsevier Science Ltd on behalf of The Association for the Study of Animal Behaviour.       

Bottom‐up effects of glucosinolate variation on aphid colony dynamics in wild cabbage populations

1. There is an ongoing debate about the relative importance of top‐down and bottom‐up regulation of herbivore dynamics in the wild. Secondary metabolites, produced by plants, have negative effects on survival and growth of some herbivore species, causing bottom‐up regulation of population dynamics. Herbivore natural enemies may use plant secondary metabolites as cues to find their prey, but their survival and reproduction can also be influenced by the upward cascade of secondary metabolites through the food web. Thus plant chemistry might also affect herbivore populations by mediating top‐down regulation. 2. We investigated the influence of heritable variation in aliphatic glucosinolates, a class of secondary metabolites produced by Brassica plants, on the relative importance of top‐down and bottom‐up regulation of Brevicoryne brassicae (mealy cabbage aphid) colonies in natural Brassica oleracea (wild cabbage) populations. We manipulated natural enemy pressure on plants differing in their glucosinolate profiles, and monitored aphid colony growth and disperser production. 3. Aphid colony sizes were significantly smaller on plants producing sinigrin, compared with plants producing alternative aliphatic glucosinolates. Aphid natural enemy numbers correlated with aphid colony size, but there was no additional effect of the plants' chemical phenotype on natural enemy abundance. Furthermore, experimental reduction of natural enemy pressure had no effect on aphid colony size or production of winged dispersers. 4. Our results provide evidence for glucosinolate‐mediated, bottom‐up regulation of mealy cabbage aphid colonies in natural populations, but we found no indication of top‐down regulation. We emphasise that more studies of these processes should focus on tritrophic interactions in the wild.     

Variation in ant aggression and kin discrimination ability within and between colonies

Significant variation in aggressiveness and kin discrimination ability occurs between different laboratory colonies of the ant Rhytidoponera confusa.Different colonies show consistently high (or low) levels of aggression toward nonnestmates over 4–19 weeks. Earlier studies excluded colony size and the natural presence or absence of the queen in colonies and differences in hunger as possible sources of variation. The present study excluded the number of larvae in colonies and the time of the light period of the light cycle when recognition tests were carried out. Highly significant variation occurs between the kin discrimination ability of individual workers in any particular colony. Approximately 28% of the workers in colonies of R. confusashowed very poor kin discrimination. Much of the colony's kin discrimination is carried out by a small number of highly aggressive workers.     

Ovarian self‐incompatibility in Narcissus papyraceus (Amaryllidaceae) is the result of a pre‐zygotic response

Ovarian self‐incompatibility, including pre‐ and post‐zygotic reactions, is a complex mechanism for which we still lack many details relating to its function and significance. The joint presence of ovarian self‐incompatibility with style polymorphism is a rare combination that is found in the genus Narcissus. Usually, style polymorphic species have heteromorphic (diallelic and linked to style length locus) incompatibility, which prevents fertilization between individuals of the same morph, thereby helping to maintain equal proportions of floral morphs in populations. However, when present, self‐incompatibility in Narcissus is not linked to style polymorphism and cross‐fertilization within each morph is possible. Hence, self‐incompatibility in Narcissus is of particular interest when attempting to unravel the nature of the rejection reaction and aiming to assess possible cryptic differences in the fertilization process in intra‐ and inter‐morph crosses, which might ultimately explain the wide variation of morph‐ratio in the field. We examined the breeding system of Narcissus papyraceus, a style‐dimorphic species that has biased morph ratios in most of its populations. We studied pollen‐tube growth in the pistil and ovule fate after experimentally controlled hand pollinations. The growth of pollen tubes in self‐ and intra‐ and inter‐morph crosses was similar up to the point of micropyle penetration in both morphs but, subsequently, a pre‐zygotic failure appeared to affect male and female gametophytes in selfed pistils. A high proportion of ovules from self‐pollinated flowers showed signs of collapse and self‐pollen tubes were blocked or behaved abnormally before entering the embryo sac. Self‐incompatibility was stronger in the long‐styled morph than in the short‐styled morph. We did not find any conclusive sign of differential functioning between intra‐ and inter‐morph cross‐pollinations in any morph. These results enable us to rule out the possible effects of pollen–pistil interactions in N. papyraceus as a cause of morph‐ratio biases and confirm the exceptional nature of the self‐incompatibility mechanism in this polymorphic species. © 2015 The Linnean Society of London, Botanical Journal of the Linnean Society, 2015, 177 , 629–643.     

Post‐pollination process in a partially self‐compatible distylous plant,Primula sieboldii (Primulaceae)

Pollen germination and pollen‐tube growth under natural conditions were observed in a population of a distylous species, Primula sieboldii, in which partial self‐compatibility has been demonstrated in some long‐styled genets. We observed post‐pollination processes microscopically in styles collected after self‐morph and inter‐morph hand pollination (with standardized pollen load on the stigmas) in four genets each from the following three ‘genet types’: self‐incompatible long‐styled (SI), partially self‐compatible long‐styled (SC) and self‐incompatible short‐styled morph genets. Irrespective of the genet type, pollen germination began within 24 h after pollination and tubes of pollen reached to the style base with 48–96 h after inter‐morph pollination. Although pollen tubes germinated after self‐pollination in the SC genets, the number of germinated pollen tubes was significantly lower than in the case of inter‐morph pollination. Few pollen tubes germinated after self‐pollination of the SI or short‐styled genets. In SC genets, the rate of pollen‐tube growth did not differ between self‐morph and inter‐morph pollination (～1.9 mm/day). Therefore, differences in self‐compatibility between SC and SI genets in P. sieboldii are likely to be attributable to differential pollen germination rates rather than to differential pollen‐tube growth rates.     

Neighbour recognition in two sister songbird species with a simple and complex repertoire – a playback study

The ability of individuals to recognize others based on vocalizations has been proven in many species of birds. However, we are still far from understanding important aspects of the discrimination process. For example, it is still not fully understood whether, and why, repertoire size hinders discrimination between individuals. Further, the strategies and vocal cues used for discrimination between individuals are largely unexplored. In this study, we tested the ability of chiffchaffs Phylloscopus collybita and willow warblers Phylloscopus trochilus, two closely related species with different repertoire sizes and song organization, to differentiate between their neighbours on the basis of a single song of a neighbouring male. We did playback experiments within the ‘dear enemy’ paradigm in which we tested resident males with a single song of a neighbour broadcast from the correct and opposite, incorrect territory border. Both species displayed a strong ability to discriminate between their neighbours representing further evidence that repertoire size per se has no negative impact on individual recognition in songbirds. Using a single song for playback allowed us to speculate about the nature of the possible cues used by males for recognition. Individual recognition in both species is most likely based on the modulation of syllables or on general voice characteristics. We suggest that specific changes in song organization, for example the tendency of individuals to insert a distinct phrase at the beginning of each song, may facilitate individual recognition and compensate for increased repertoire size in willow warblers.     

Low intraspecific aggression level in the polydomous and facultative polygynous ant Ectatomma tuberculatum

Nestmate recognition is a key feature of social insects, as it preserves colony integrity. However, discrimination of non‐nestmates and nestmate recognition mechanisms are highly variable according to species and social systems. Here, we investigated the intraspecific level of aggression in the facultative polygynous and polydomous ant, Ectatomma tuberculatum Olivier (Hymenoptera: Formicidae: Ectatomminae), in a population with a strong genetic structure. We found that the intraspecific level of aggression was generally low in this population of E. tuberculatum. However, the level of aggression was significantly correlated with the geographical distance, suggesting that both genetic and environmental cues could be involved in nestmate recognition and discrimination mechanisms. Moreover, polydomy was confirmed by the absence of aggression between workers from nests at a distance of 3 m, while the level of aggression was significantly higher between workers from nests separated by a distance of 10 or 1300 m. Field experiments showed that the low level of aggression between neighbouring colonies was associated with shared foraging areas, which could suggest that familiarization processes may occur in this species. We propose that the particular social organization of this species, with secondary polygyny, polydomy, and budding, may have favoured a high acceptance threshold, because of the low probability of interactions with unrelated conspecifics, the high cost of erroneously rejecting nestmates, and the low cost of accepting non‐nestmate workers. The resulting open recognition system can thus allow privileged relationships between neighbouring colonies and promote the ecological dominance of E. tuberculatum in the mosaic of arboreal ants.     

Seasonal Variation in Response to Neighbors and Strangers by a Territorial Songbird

Reduced aggression toward territorial neighbors, termed the ‘dear‐enemy’ effect, is thought to arise because territorial animals benefit by avoiding contests with neighbors with whom they have already established relationships. The dear‐enemy effect has been described in many taxa, but few studies have considered whether or not neighbors’ relationships are affected by changes in the social environment. In this study, I tested whether Carolina wrens, Thryothorus ludovicianus, behaviorally discriminate between neighbors and strangers in two different social environments: in spring when territories have been established for several months, and in fall when an influx of new birds claiming territories might de‐stabilize wren neighborhoods. Comparisons of responses of territorial males to playbacks of songs from neighbors and strangers showed that Carolina wrens show the dear‐enemy effect in spring, but not in fall in this design. The apparent lack of a differential response to neighbors and strangers in fall might be due to a reduction in aggression toward strangers. This study provides evidence that seasonal changes in the dear‐enemy effect coincide with seasonal changes in the social environment.     

Interactions between Males of the Lizard Liolaemus tenuis: Roles of Familiarity and Memory

For territorial organisms, recognition of familiar individuals can reduce the frequency and intensity of aggressive encounters (‘dear enemy’ phenomenon), stabilize social systems, and reduce the cost of territory maintenance. Here, we investigated the behavioural events displayed during contests between familiar and unfamiliar individuals in the lizard Liolaemus tenuis (Liolaemidae), a species in which males are territorial. The behaviours recorded were attack, warning, evasion, and submission, and the latencies to the first aggressive (attack or warning) behaviour. Additionally, we assessed the ability of individuals to remember a familiar conspecific after a period without social interaction. Individual males reduced and delayed aggressive behaviour directed towards socially familiar individuals compared with unfamiliar ones. These results suggest that males distinguished between familiar and unfamiliar conspecific males and are in agreement with the ‘dear enemy’ phenomenon. Other behaviours were similar in the contests between familiar and unfamiliar individuals. Recognition of familiar conspecifics was lost after 20 d without social interactions. This may be relevant for interactions with floater males or with neighbours that lose their territory and subsequently attempt to fight for their ex‐neighbour's territory.     

High herkogamy but low reciprocity characterizes isoplethic populations of Jasminum malabaricum,a species with stigma‐height dimorphism

• Studies of floral polymorphisms have focused on heterostyly, while stigma‐height dimorphism has received considerably less attention. Few studies have examined the reproductive biology of species with stigma‐height dimorphism to understand how factors influencing mate availability and pollen transfer are related to morph ratios in populations.
• Floral morphological traits, especially herkogamy and reciprocity, pollinator visitation, breeding system and spatiotemporal mate availability, are known to affect inter‐morph pollination and morph ratios in species with stigma‐height dimorphism. In this study, we investigated the presence of stigma‐height dimorphism and estimated morph ratios in four naturally occurring populations of Jasminum malabaricum. We quantified morph‐ and population‐specific differences in the abovementioned factors in these populations to understand the observed morph ratios.
• The positions of anthers and stigmas were characteristic of stigma‐height dimorphism, the first report of this polymorphism in the genus. All study populations were isoplethic, implying equal fitness of both morphs. Herkogamy was higher in the short‐styled morph, while reciprocity was higher between the long‐styled stigma and short‐styled anthers. Long‐ and short‐tongued pollinators were common floral visitors, and we observed no differences between morphs in spatiotemporal mate availability or pollinator visitation. Neither morph exhibited self‐ or heteromorphic incompatibility.
• The short‐styled stigma had lower reciprocity but likely receives sufficient inter‐morph pollen from long‐tongued pollinators, and also by avoiding self‐pollination due to higher herkogamy. These results highlight the importance of sufficient effective pollinators and floral morphological features, particularly herkogamy, in maintaining isoplethy in species with stigma‐height dimorphism.

     

Behavioural and molecular evidence for selective immigration and group regulation in the social huntsman spider,Delena cancerides

Movement among social groups interacts with the costs and benefits of group‐living in complex ways. Unlike most other social spiders, the social huntsman spider, Delena cancerides, appears to enter foreign colonies, discriminates kin from non‐kin, and has very limited dispersal options because their bark retreats are rare, making this species an interesting model organism with which to examine the role of inter‐colony movement on group‐living. We examined movement among field colonies of D. cancerides in three ways: (1) by tracking the dispersal and immigration of marked spiders into foreign colonies; (2) by recording resident spiders' behaviour toward introduced immigrants; and (3) by inferring intra‐colony relatedness and immigration patterns through allozyme electrophoresis. Of the marked spiders, only young juveniles moved into neighbouring colonies, whereas subadults and adults did not. Introduced juveniles were tolerated in foreign colonies, whereas introduced adult males and subadults were usually attacked by the resident adult female, unless she had similar sized subadult/adult offspring of her own. Allozyme profiles from unmanipulated field colonies showed that 47% of sampled colonies contained at least one immigrant and that average within colony relatedness was below 0.5. These data align with previous research on the costs and benefits of group‐living for D. cancerides, suggesting that spiders actively seek and regulate group membership based on interests of both the immigrant and the colony. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, ?? , ??–??.     

Species and Colony Components in the Recognition Odor of Young Social Wasps: Their Expression and Learning (Polistes biglumis and P. atrimandibularis; Hymenoptera: Vespidae)

In Polistes, nestmate recognition relies on the learning of recognition cues from the nest. When wasps recognize nestmates, they match the template learned with the odor of the encountered wasp. The social wasp Polistes biglumis use the homogeneous odor of their colony to recognize nestmates. When these colonies become host colonies of the social parasite P. atrimandibularis, colony odor is no longer homogeneous, as the parasite offspring have an odor that differs from that of their hosts. In trying to understand how the mechanism of nestmate recognition works in parasitized colonies and why parasite offspring are accepted by hosts, we tested the responses of resident Polistes biglumis wasps from parasitized and unparasitized colonies to newly emerged parasites and to nestmate and non-nestmate conspecifics. The experiments indicate that immediately upon eclosion both young parasites and young hosts lack a colony odor and that colony odor can be soon acquired from the accepting colony. In addition, while residents of nonparasitized colonies recognize only the odor of their species, resident hosts of parasitized colonies have learned a template that fits the odors of two species.