Sibling recognition in juvenile Arctic charr, Salvelinus alpinus (L.)

Juvenile Arctic charr, Salvelinus alpinus (L.), from two full sibling groups were studied concerning the possible existence of chemical cues with information about kinship. Each full sibling group was divided into two groups with the same number of specimens and placed in two separate aquaria. The division coincided with the start of exogenous feeding. Preference tests were performed about 7 and 10–13 months after the division. Due to the increasing size of experimental fish, two different sizes of apparatus were used. The first series of experiments was performed in a small Y-maze fluviarium and the second series in the large standard fluviarium. The momentary positions of one fish at a time in the test area were recorded by time-lapse photography with a 16-mm film camera and filtered flashlight (no transmittance <670 nm). The fish were given a choice between two water qualities; thus the following comparisons were made: (i) unconditioned water ν. water scented by siblings from the same aquarium; (ii) unconditioned water ν. unfamiliar non-siblings; (iii) siblings from the same aquarium ν. unfamiliar non-siblings; (iv) siblings from a separate aquarium ν. unfamiliar non-siblings; (v) siblings from the same aquarium ν. siblings from a separate aquarium. The test fishes preferred water scented by siblings over non-siblings, even though the siblings were taken from a separate aquarium. Nevertheless, they were attracted to water scented by unfamiliar non-siblings in preference to unconditioned water. No preference was shown between chemical cues from siblings taken from the same and a separate aquarium.     

Interplay between various aspects in social relationships of young rhesus monkeys: Dominance,agonistic help,and affiliation

Relationships between group-living primates depend strongly on their position in the group dominance hierarchy and on their relationships with other group members. The influence of various behaviours on social relationships of immature rhesus monkeys (Macaca mulatta) was investigated here. Dominance ranks were established and related to the degree of affiliation in a dyad. Older monkeys were mostly dominant to the younger ones, regardless of kinship. Subordinate monkeys left proximity of their dominant members more often than they were left by them both among siblings and non-siblings, but the effect of dominance rank on the amount of play initiation and grooming in a dyad differed between these two types of dyads. The amount of agonistic help two individuals provided for each other was low among immatures. Nevertheless, pairs of siblings gave help to each other in agonistic conflicts more often than non-siblings, and such help was more often reciprocated between siblings than between non-siblings. Help in agonistic conflicts was positively correlated with the amount of time monkeys spent playing, grooming, or in proximity. Adults tended to interfere less in conflicts of frequent sibling play partners or non-sibling grooming partners. No evidence was found for young monkeys to exchange reciprocally grooming for agonistic help. It is argued that the time monkeys spend interacting with each other in affiliative interactions increases their familiarity and thus promotes close relationships between them. On the whole, young monkeys' relationships, like those between adults, are influenced strongly by their kinship, and position in the dominance hierarchy.     

An investigation of sibling recognition in Rana cascadae tadpoles

Sibling recognition was studied experimentally in tadpoles of the Cascades frog, Rana cascadae. Sibships were divided into two groups at an early developmental stage. One group was reared with siblings and the second with a mixture of siblings and non-siblings. Whe given a choice of associating with a sibling or non-sibling group, individuals reared with siblings preferred siblings. One mixed-reared group spent more time associating with unfamiliar siblings than unfamiliar nonsiblings. Tadpoles of another mixed-reared group preferred to associate with pure siblings over a mixture of siblings and non-siblings with which they were reared. When the stimulus animals were taken exclusively from the mixed-rearing tank, two mixed-reared groups showed no sibling preferences. Our results suggest that early association with non-siblings does not affect sibling recognition in this species.     

Advantages of social foraging in crab spiders: Groups capture more and larger prey despite the absence of a web

Among group‐living spiders, subsocial representatives in the family of crab spiders (Thomisidae) are a special case, as they build protective communal leaf nests instead of extensive communal capture webs. It could thus be inferred that antipredator benefits (e.g., enhanced protection in larger nests) rather than foraging‐related advantages (e.g., capture of more and larger prey) promote sociality in this family. Nonetheless, subsocial crab spiders do share prey, and if this behaviour does not reflect mere food scramble but has a cooperative character, crab spiders may offer insights into the evolution of social foraging applicable to many other cooperative predators that hunt without traps. Here, we performed a comparative laboratory feeding experiment on three of the four subsocial crab spider species—Australomisidia ergandros, Australomisidia socialis and Xysticus bimaculatus—to determine if crab spiders derive advantages from foraging in groups. In particular, we tested artificially composed groups of five sibling spiderlings vs. single siblings in terms of prey capture success and prey size preference. Across species, groups had higher prey capture success (measured in terms of capture rates and capture latency) and were more likely to attack large, sharable prey—dynamics leading to reduced food competition among group members in favour of living and foraging in groups. Within groups, we further compared prey extraction efficiency among the three applied social foraging tactics: producing, scrounging and feeding alone. In A. ergandros, individuals were exceptionally efficient when using the non‐cooperative scrounger tactic, which entails feeding on the prey provided by others. Thus, our multispecies comparison confirms foraging advantages in maintaining a cooperative lifestyle for crab spiders, but also demonstrates the relevance of research into exploitation of cooperative foraging in this family.     

Kin recognition and cannibalism in a subsocial spider

Evolution of cooperation and group living in spiders from subsocial family groups may be constrained by their cannibalistic nature. A tendency to avoid cannibalizing kin may facilitate tolerance among spiders and implies the ability to identify relatives. We investigated whether the subsocial spider Stegodyphus lineatus discriminates kin by recording cannibalism among juveniles in experiments during which amount of food and size difference among spiders in groups were varied. We hypothesized that family groups should be less cannibalistic than groups of mixed‐parental origin. Further, we tested whether food‐stress would influence cannibalism rates differently in kin and nonkin groups and the effect of relatedness on cannibalism within groups of spiders of variable size compared with those of homogenous size. In groups of six spiders, more spiders were cannibalized in nonsib groups than in sib groups under low food conditions. A tendency for nonkin biased cannibalism in starved spider pairs supported that kin recognition in S. lineatus is expressed when food is limited. Size variance of individuals within well‐fed groups of siblings and unrelated spiders had no influence on cannibalism rates. Apparently, both hunger and high density are important promoters of cannibalism. In addition to inclusive fitness benefits, we suggest that an ability to avoid cannibalizing kin will favour the evolution of cooperation and group living in phylogenetically pre‐adapted solitary species.     

The ontogeny of kin recognition in tadpoles of the toadBufo melanostictus (Anura; Bufonidae)

The ontogeny of kin recognition and influence of social environment on the development of kin recognition behaviour was experimentally investigated in tadpoles of Bufo melanostictus that lived in aggregations and showed low larval dispersion. Embryos and tadpoles of the toad were reared as (i) kin only, (ii) with kin and non-kin (separated by a mesh screen), and (iii) in isolation. They were tested for the ability to discriminate between (i) familiar siblings and unfamiliar non-siblings, (ii) familiar siblings and familiar non-siblings and, (iii) unfamiliar siblings and unfamiliar non-siblings. All tadpoles were fed on boiled spinach before conducting trials. Preference of test tadpoles to associate near the end compartments whether empty or containing members of specific stimulus groups was assessed using a rectangular choice tank. When tested in tanks with empty end compartments, the test tadpoles showed random distribution and thus no bias for the apparatus or the procedure. In the presence of kin/non-kin in the end compartments a significantly greater number of test tadpoles spent the majority of the time near familiar or unfamiliar kin rather than near familiar or unfamiliar non-kin. Kin discrimination ability persisted throughout larval development. Familiarity with siblings is not required for discriminating kin from non-kin, and kin discrimination ability is not modified following exposure to non-kin. Also, involvement of dietary cues is unlikely to be the prime mechanism of kin recognition inB. melanostictus unlike in some other anurans.     

A specialized araneophagic predator's short‐term nutrient utilization depends on the macronutrient content of prey rather than on prey taxonomic affiliation

A specialist predator that has a specialized diet, prey‐specific prey‐capture behaviour and a preference for a particular type of prey may or may not be specialized metabolically. Previous studies have shown that jumping spiders of the genus Portia prey on other spiders using prey‐specific prey‐capture behaviour, prefer spiders as prey to insects and gain long‐term benefits in terms of higher survival and growth rates on spider diets than on insect diets. However, it is unclear whether there are substances uniquely present in spiders on which Portia depends, or, alternatively, spiders and insects all contain more or less the same nutrients but the relative amounts of these substances are such that Portia perform better on a spider diet. These questions are addressed by testing the hypothesis that prey specialization includes metabolic adaptations that allow Portia an enhanced nutrient extraction or nutrient utilization efficiency when feeding on spider prey compared with insect prey. Three groups of Portia quei Zabka are fed either their preferred spider prey or one of two types of flies (Drosophila melanogaster Meigen) that differ in nitrogen and lipid content. Portia quei shows a higher feeding rate of high‐protein flies than of high‐lipid flies and spiders but, after 5 days of feeding, there is no significant difference in growth between treatments, and the diets lead to significant changes in the macronutrient composition of P. quei as a result of variable extraction and utilization of the prey. The short‐term utilization of spider prey is similar to that of high‐lipid flies and both differ in several respects from the utilization of high‐protein flies. Thus, the short‐term nutrient utilization is better explained by prey macronutrient content than by whether the prey is a spider or not. The results suggest that spider prey may have a more optimal macronutrient composition for P. quei and that P. quei does not depend on spider‐specific substances.     

Kin recognition in Bufo scaber tadpoles: ontogenetic changes and mechanism

Ontogenetic changes in kin-recognition behavior, effect of social environment on kin-recognition ability, and use of visual and chemical cues in kin recognition have been studied in tadpoles of Bufo scaber after rearing them with kin, in mixed groups, or in isolation from Gosner stage 12 (gastrula). By use of a rectangular choice tank the tadpoles were tested for their ability to choose between (a) familiar siblings and unfamiliar non-siblings, (b) unfamiliar siblings and familiar non-siblings, and (c) unfamiliar siblings and unfamiliar non-siblings. When tested without any stimulus groups in the end compartments of the tank, random distribution was observed for the tadpoles and no bias for the apparatus or the procedure. In the presence of kin and non-kin in the end compartments, significantly more tadpoles spent most of their time near kin (familiar or unfamiliar) rather than near non-kin during early larval stages, up to stage 37. After stage 37 (characterized by the differentiation of toes), test tadpoles showed no preference to associate with kin, suggesting an ontogenetic shift in the kin-recognition ability in B. scaber. In experiments involving selective blockade of visual or chemical cues the test tadpoles preferentially associated near their kin on the basis of chemical rather than visual cues. These findings suggest that familiarity with siblings is not necessary for kin recognition and that kin-recognition ability is not modified after exposure to non-kin by mixed rearing. The findings for B. scaber indicate a self referent phenotype matching mechanism of kin recognition which is predominantly aided by chemical rather than visual cues.     

Effect of kinship on the allopreening among juvenile Bengalese finches

Kin-directed affiliative behavior is widespread in social animals and kin selection theory suggests that such behavior increases fitness of the performer and is thus adaptive. Allopreening in birds is an altruistic behavior as it involves cleaning body parts that cannot be cleaned by self-preening. In this study, we investigated the effects of genetic relatedness on allopreening behavior among juveniles of the Bengalese finch Lonchura striata domestica shortly after the cessation of parental care. Nestlings were cross-fostered in order to distinguish the effects of genetic relatedness (sharing genetic parents) from the effects of familiarity (sharing rearing environment). Preening bouts toward siblings were more frequent and of longer duration than toward non-siblings. The frequency and duration of physical contact within a preening bout did not differ between siblings and non-siblings. In addition, the frequency and duration of preening bouts did not differ between the juveniles that were reared by the same foster parents and between those that were not. Our results suggest that Bengalese finch juveniles recognized siblings and performed affiliative behavior based on genetic similarity rather than familiarity.     

Density-dependent growth and metamorphosis in the larval bronze frog<Emphasis Type="Italic">Rana temporalis</Emphasis> is influenced by genetic relatedness of the cohort

Effects of density and kinship on growth and metamorphosis in tadpoles ofRana temporalis were studied in a 2×4 factorial experiment. Fifteen egg masses were collected from streams in the Western Ghat region of south India. The tadpoles were raised as siblings or in groups of non-siblings at increasing density levels, viz. 15, 30, 60 and 120/5 l water. With an increase in density level from 15 to 120 tadpoles/5 l water, duration of the larval stage increased and fewer individuals metamorphosed irrespective of whether they belonged to sibling or non-sibling groups by day 100 when the experiments were terminated. The size of individuals at metamorphosis declined significantly with increase in the density of rearing. However, at higher densities (60 and 120 tadpoles/5 l water) sibling group tadpoles performed better compared to mixed groups and took significantly less time to metamorphose. Also, more individuals of sibling groups metamorphosed compared to non-sibling groups at a given density. Mixed rearing retarded growth rates, prolonged larval duration resulting in a wider spectrum of size classes, and lowered the number of individuals recruited to terrestrial life. The study shows that interference competition occurred more strongly in cohorts of mixed relatedness than in sibling groups.     

Intraspecific competition favors ant–plant protective mutualism

The dependency of the anti-herbivore defense on ant–plant protective mutualism often varies depending on abiotic and biotic conditions. Although intraspecific competition is a primary interaction between neighboring plants, its effects on ant–plant mutualisms have yet to be sufficiently elucidated. In order to determine the effects of intraspecific competition and competitor genotype on ant–plant mutualisms, I conducted competition and ant-removal experiments and examined their effects on damage to the leaves of Urena lobata var. tomentosa plants. I found that larger numbers of worker ants visited the plants growing with non-siblings than plants growing alone and that plants growing with non-siblings had a higher shoot to root ratio and secreted greater volumes of extrafloral nectar than plants growing alone and/or with siblings. Under the presence of both sibling and non-sibling competitors, I observed that when ants were removed from plants, those grown with conspecific neighbors were characterized by a higher percentage of damaged leaf area than plants harboring ants. The effect of ant exclusion on leaf damage was more pronounced in plants grown with non-siblings than those grown near siblings. However, when the plants were grown alone, I detected no significant difference in percentage leaf damage between the ant-excluded and ant-harboring plants. The results indicate that neighboring plants can exert strong effects on ant–plant protective mutualisms, thereby highlighting the need to take into consideration plant–plant interactions in studies on these mutualistic associations.     

Rana cascadae tadpoles aggregate with siblings: an experimental field study

Previous laboratory studies have shown that Rana cascadae larvae preferentially associated with siblings over non-siblings in choice tests. This study, conducted during three consecutive summers, tests the hypothesis that R. cascadae larvae aggregate nonrandomly with respect to sibship in natural ponds. Pairs of sibships were reared in separate tanks or together in the same tank in the laboratory. Each sibship within a pair was then stained with neutral red or methylene blue dye and released together in a natural pond. Over a period of several days, aggregations of tadpoles within test ponds were repeatedly captured, censused for sibship composition, and released. In control tests, two groups of tadpoles from the same sibship were dyed different colors and released together. In total, 25 different tests were conducted using tadpoles from 31 sibships and 456 aggregations were sampled. The distribution of color compositions of aggregations in control tests did not differ from an expected random distribution. Color compositions of aggregations in experimental tests differed from controls and from an expected random distribution. Aggregations in these tests tended to be dominated by one of the two colors (sibships). We conclude that R. cascadae tadpoles recognize and prefer to aggregate with siblings in natural field conditions. Circumstances of early rearing (i.e., whether tadpoles were reared with siblings or in mixed sibling/non-sibling groups) had no influence on preferences to associate with siblings, but there was an inverse correlation between group size and sibling association.     

Preference for feeding on honey solution and its effect on survival,development, and fecundity of Ebrechtella tricuspidata

Members of the spider families Thomisidae, Salticidae, Miturgidae, Anyphaenidae, and Corinnidae have been observed on floral and extrafloral nectaries of plants, where they are presumably feeding on nectar. Nectar feeding is a phenomenon that has long intrigued biologists. However, few studies have focused on the effect of nectar on biological characteristics of these spiders. The aim of this study was to determine whether crab spiders, Ebrechtella tricuspidata (Fabricius) (Araneae: Thomisidae), show an active preference for honey solution (a simulated nectar source) and to test the effect of honey solution on the survival and development time of spiderlings and the fecundity of adult E. tricuspidata. The results showed that the number of females feeding on the 10, 20, and 30% honey solution was significantly higher than those feeding on water alone, and there was no difference in the number of females feeding on the three concentrations of honey solution. Significantly more E. tricuspidata preferred feeding on the 20% honey solution, and they spent significantly more time feeding on 20% honey solution than on water, regardless of whether they were males or females, adults or spiderlings. Ingestion of honey solution significantly increased the survival and shortened the development time of E. tricuspidata. Female spiders that fed on honey solution had a shorter pre‐oviposition period and laid more eggs than those given only water. Our results suggest that nectar could be a high‐quality supplementary food to maintain normal growth and metabolism in spiderlings and adult female spiders in nature.     

An order-specific monoclonal antibody to Diptera reveals the impact of alternative prey on spider feeding behavior in a complex food web

Generalist predators have the capacity to restrict pest population growth, especially early in the season before densities increase. However, their polyphagous feeding habits sometimes translate into reduced pest consumption when they target alternative prey. An order-specific monoclonal antibody was developed to examine the strength of trophic connections between Diptera, a major category of non-pest prey, and linyphiid spiders in alfalfa. We report the development and characterization of a monoclonal antibody with order-level specificity to Diptera. This antibody elicited strong absorbance to 22 Diptera from 13 families, no false-positive reactivity to non-dipteran invertebrates, and antigen detection periods following prey consumption that were comparable between spiders. Over 900 field-collected females of the linyphiid spiders Erigone autumnalis and Bathyphantes pallidus were screened for Diptera antigen. Significantly more B. pallidus screened positive for Diptera (40%) compared to E. autumnalis (16%), indicating differential reliance on these prey. In parallel with the collection of spiders for gut-content analysis, prey availability was estimated at web sites. The two spiders exhibited different feeding responses to prey availability. Consumption of Diptera by B. pallidus was strongly correlated with Diptera abundance whilst the availability of other potential prey did not influence predation rates. Conversely, E. autumnalis did not prey upon Diptera in proportion to availability, but increased Collembola activity-density reduced dipteran consumption. Integration of molecular gut-content analysis with precise sampling of prey demonstrated how two closely related linyphiid spiders exhibit different feeding responses to the availability of prey under natural field conditions. Elucidating the feeding preferences of natural enemies is critical to effective incorporation of biological control by generalist predators in the management of agricultural pests.     

Kin recognition in a social spider

Social spiders accept immigrant spiders into their kin-based groups, suggesting that spiders cannot recognise kin and may lose inclusive fitness benefits. A field and two laboratory experiments on Diaea ergandros, a social crab spider, demonstrated that younger and older instar D. ergandros do discriminate siblings, but potential benefits were variable and not equally distributed. First, proportional survival was greater in large groups regardless of the within-group relatedness, so accepting immigrants increases probability of group survival (although relatedness was more important among smaller groups). Second, juvenile D. ergandros ate unrelated spiders instead of siblings when starved, so immigrants might represent a food reserve in times of food shortage. Third, subadult resident, sibling females cannibalised unrelated, immigrant females and their brothers instead of immigrant males when starved, suggesting that subadult female spiders may maximise outbreeding opportunities. These benefits provide selective pressure for groups to accept immigrants, but as benefits are realised differentially, conflict and cooperation will exist within spider groups similar to that shown in other group-living taxa.     

Kin recognition in Rana cascadae tadpoles: maternal and paternal effects

Cascades frog (Rana cascadae) tadpoles preferentially associate with full siblings over half sibling and half siblings over non-siblings when reared with siblings or as isolates. These tadpoles can use cues of maternal or paternal origin in distinguishing siblings from non-siblings, but maternal cues are preferred over paternal cues. This suggests that a hierarchy of cue importance may exist. Our results are consistent with both a phenotypic matching and a genetic recognition system of kin recognition. Thus, both learned and innate components may play a role in R. cascadae sibling recognition. Kin recognition may facilitate preferential treatment of kin, such as cooperation in food finding or in warning against predators, and therefore those individuals behaving altruistically in kin groups can increase their inclusive fitness.     

Risk Sensitivity and the Paradox of Colonial Web-Building in Spiders

Group foraging is rare in spiders, occurring only where preyavailability is high. If colonial web-building increases individualprey capture rates as shown, why does group foraging not occurmore often where prey are scarce? Risk sensitivity may explainthis paradox, as variance in prey capture is reduced in groups;risk-averse spiders should join groups only when prey exceeda threshold level. Field studies show that group foraging variesas predicted between species, between populations of a singlespecies, and between sites within a population. However, recentmodels suggest the necessity of examining variance within individualsover time rather than between individuals within populations.Additionally, mechanisms responsible for variance reductionin colonial webs may be less effective than previously assumed.New field data suggest that while prey variance over time maybe somewhat less for individual spiders in groups than for solitaries,the relationship between colonial web-building and variancein prey capture is far more complex than originally thought.The influence of risk sensitivity on reproductive success andthe evolution of colonial web-building is discussed.     

Factor of familiarity in sibling recognition in golden hamsters

Male hamsters, reared with their siblings and non-siblings, were tested for their exploratory behavior of conspecific in the 4th and 8th week after their birth. During the tests, a familiar sibling, an unfamiliar sibling, a familiar non-sibling and an unfamiliar non-siblings was presented in a choice box. Subjective distance among these testing animals was measured using the caseV of Thurston's paired-comparison test. The hamsters spent more time with the unfamiliar animals than with the familiar ones. Although biological relation (sibling or non-sibling) had a significant effect in the 4th-week test, only the familiarity determined the investigatory behavior in the 8th-week test. These results suggest sibling recognition based on learning in hamsters.     

Survival and growth in groups of a subsocial spider (Stegodyphus lineatus)

Summary In spiders, known as potentially cannibalistic, mutual tolerance is one important requirement for group life. Using the subsocial spiderStegodyphus lineatus which possibly resembles the ancestors of the social species, the effects of competition were investigated in the laboratory. When dispersal was prevented, spiderlings were capable of living in groups. The intensity of competition for food among spiders in groups was varied experimentally by varying group size or the relative size differences of individuals. Body mass and mortality were compared in the different experiments. Prey availability, the size of the spiders and initial body size differences among group members all influenced the survival probability and growth of the spiders. Spiders of equal size tolerated each other with a higher probability than spiders of different sizes. Feeding in groups was always disadvantagous even for the largest spiders.     

Growth, development, and survival of a generalist predator fed single- and mixed-species diets of different quality

It is often assumed that prey species consumed by generalist predators are largely, though not entirely, equivalent in terms of their value to the predators. In contrast to this expectation, laboratory feeding experiments uncovered distinctly varied developmental responses of a generalist predator, the wolf spider Schizocosa, to different experimental diets. Naive Schizocosa attacked and fed upon all the prey species offered; however, highly divergent patterns of survival, development, and growth of Schizocosa spiderlings reared on different single-prey diets revealed a wide spectrum of prey qualities. Spiderlings fed the collembolan Tomocerus bidentatus sustained the highest overall rates of survival, growth, and development. Fruit flies (Drosophila melanogaster) were intermediate-quality prey: spiders fed Drosophila initially exhibited rates of survival, growth, and development equal to those of spiders on a diet of T. bidentatus, but after about 3 months, rates declined markedly. Fungus gnats (Sciaridae; Bradysia sp.) and conspecfic spiderlings are low-quality prey for Schizocosa: a sole diet of either of these prey types resulted in positive but markedly submaximal rates of growth, retarded rates of development, and survival rates much lower than that supported by a diet of Drosophila. Worst were the collembolans Folsomia candida and Isotoma trispinata, and the aphid Aphis nerii: spiderlings fed solely one of these species did not grow and died without molting. A. nerii is classified as poor quality because survival was no better than that of starved controls. F. candida and I. trispinata were toxic: survival of Schizocosa hatchlings fed these collembolans was lower than that of starved controls. A mixed diet of T. bidentatus and fruit flies yielded positive synergistic effects with respect to growth, but development and rate of survival were similar to those of spiders on a sole diet of T. bidentatus. Including toxic prey did not produce a better diet, while inclusion of toxic prey with prey of higher quality created diets that were no better than the toxic prey alone. The results of these experiments suggest that prey species that are similar in morphology and behavior, and that are initially killed and consumed, may differ dramatically in their suitability as food for generalist arthropod predators. Received: 29 July 1998 / Accepted: 1 February 1999