Costs and benefits of maternal behaviour in the green lynx spider (Oxyopidae,Peucetia viridans)

I examined the adaptiveness of maternal behaviour in the green lynx spider Peucetia viridans (Hentz), by measuring the costs and benefits to the female of egg-sac tending. P. viridans guards her egg sac for 6–8 weeks until the young have emerged and dispersed. I removed females from egg sacs in the field either immediately after oviposition or after they had guarded the egg sacs for 2 weeks, and compared the fate of these sacs with that of control sacs which had females present throughout. Survival rates of egg sacs were significantly improved by the presence of a female. The major sources of mortality were ant predation and sac dislodgement, both of which were significantly reduced by a guarding female, and mantispid brood parasitism, which was not affected by the female. To measure the spiders' lifetime reproductive output, I allowed caged females to construct egg sacs. Half had their first egg sac removed shortly after oviposition, while half were allowed to guard. Significantly more non-guarding than guarding females produced second egg sacs. Thus for the green lynx spider, egg sac guarding decreases lifetime egg production, but increases offspring survival. Under north Florida conditions, the benefits of guarding outweight the costs, and the females have a higher lifetime reproductive success than if they did not guard.     

Age-related sequential web building in the colonial spider Metepeira incrassata (Araneidae): an adaptive spacing strategy

Colonial orb-weaving spiders provide insight into the proximate mechanisms by which social animals space themselves within a group. We examined mechanisms for the temporal patterns of web building that determine individual positions in Metepeira incrassata (Araneidae) colonies. The spiders display a characteristic age-related sequence of daily web building, with larger spiders completing their webs significantly earlier than smaller ones. We used data on behavioural interactions, web building, prey capture and predator attacks to evaluate four hypotheses. (1) Larger spiders are better competitors and pre-empt optimal spatial positions. (2) Smaller spiders reduce competition with larger individuals by building webs later. (3) Prey captured by different size classes is available at different times. (4) Differential predation risk determines web-building times. Large individuals dominated behavioural interactions. Disturbances by larger spiders during web construction significantly delayed the completion of smaller individuals' webs and precipitated movements to new web sites. One prediction of the first hypothesis, that spatial needs translate into earlier building, was confirmed by significantly earlier web building by mature females with egg sacs (which are unable to move their egg sacs) compared with same-sized females without eggs (which can change locations freely). Experiments to determine whether the presence of large spiders inhibited the web building of smaller individuals were equivocal. Prey availability and risk of predation are not factors affecting web-building patterns. Sequential web building appears to be a result of both larger spiders competing to pre-empt space from one another and smaller individuals attempting to reduce conflict during web construction. Sequential web building is a proximate mechanism that influences spacing among colonial orb-weaving spiders and helps shape the typical hierarchical size distribution of spiders within the colony. Similar spacing mechanisms may be seen in colonial birds and marine invertebrates. Copyright 2000 The Association for the Study of Animal Behaviour.     

The biology of Euryattus sp. indet., a web-building jumping spider (Araneae, Salticidae) from Queensland: utilization of silk, predatory behaviour and intraspecific interactions

The biology of an aberrant saltioid spider, Euryattus Thorell sp. indet., is described from observations in a Queensland rain forest and the laboratory. Pronounced morphological and behavioural changes occur during post-embryological development. Juveniles spin webs, but adult females make 'suspension nests' by suspending a curled-up leaf by heavy guylines from a rock ledge or vegetation. Adult males spin neither webs nor suspension nests. Females oviposit inside their suspension nests, but if denied access to leaves for suspension, they spin and oviposit in webs similar to those spun by juveniles. The flat, papery egg sacs of Euryattus are atypical for a salticid, being more like the egg sacs of many of the Gnaphosidae. Intraspecific display behaviour has characteristics in common with typical salticids, but also includes unique features. Male courtship includes vibratory displays performed on the surface of the suspended leaf. Mating occurs inside the curled-up leaf. Males co-habit with sub-adult females in suspension nests. Females take over suspension nests of other females and eat each other's eggs. Normal locomotion, intraspecific interactions, and predatory behaviour are characterized by frequent leaping. Euryattus routinely makes long and accurate leaps on to prey, including flying insects intercepted in mid-air and spiders and insects located in alien webs. The phylogenetic implications of the unusual characteristics of Euryattus are considered.     

Costs and Benefits of Maternal Care in a Subsocial Spider,Coelotes terrestris

The maternal social spider Coelotes terrestris demonstrates extended care towards its progeny: the mother guards its egg sac for 3–4 weeks, then stays with its young from the time of their emergence until their dispersal about 1 month later. The present investigation evaluates the adaptiveness of these maternal behaviours by comparing the fitness of females performing them with that of females separated from the egg sac or the spiderlings. By protecting their egg sacs from predation and parasites, and by pursuing this task while supplying the young with food, mothers enhance the survival rate and the development of many of their spiderlings. The costs linked with these activities, estimated by the ability to produce another clutch, appear variable according to the stage in the reproductive cycle. In such terms, the egg sac guarding appears to have a low cost in relation to the care given to the spiderlings.     

Egg sac damage and previous egg sac production influence truncated parental investment in the wolf spider,Pardosa milvina

Life history theory predicts that iteroparous animals adaptively partition reproductive effort between current and future reproduction. When rearing costs of current offspring exceed the potential benefits, parental care should be terminated and deferred toward future reproduction. We tested two related predictions that follow from life history theory: (a) parents should be sensitive to offspring viability and withhold parental care if offspring survival probability drops and future reproductive opportunities are likely, and (b) parents should be less sensitive to offspring survival probability when future reproduction is unlikely and maximize parental care late in life. The wolf spider, Pardosa milvina, demonstrates extensive parental care; however, they may also abandon or cannibalize their egg sacs. We tested the effects of egg sac damage and production of a previous egg sac on egg sac abandonment and cannibalism decisions. Among four egg sac groups (1st egg sac intact, 1st egg sac damaged, 2nd egg sac intact, 2nd egg sac damaged), we daily monitored egg sac abandonment and cannibalism and measured differences in egg sac searching, protection, and grooming among removed and damaged egg sacs (N = 116 with 1st egg sac and 88 with 2nd egg sac). Females with first egg sacs abandoned and cannibalized damaged egg sacs significantly more compared to unmanipulated egg sacs; however, females with second egg sacs were insensitive to egg sac damage. Females also spent significantly more time protecting second egg sacs compared to first egg sacs and groomed damaged egg sacs significantly more than undamaged. These results support the general predictions of life history theory that indicate that abandonment and cannibalism should decrease with diminished future reproductive potential and that parents should be less sensitive to indicators of offspring survival probability late in life.     

Experimental study of foundation and development ofAnelosimus eximius colonies in the tropical forest of French Guiana

Summary Possibilities for new colony foundation inAnelosimus eximius (Theridiidae) were tested with isolated females (both with and without egg sacs) and with groups of individuals (groups from 150 to 250 spiders). Experimental groups were deposited in three different habitats: within the forest, on the forest edge (where natural colonies develop most frequently) and outside the forest (low savannah or areas cleared of vegetation, but in which plant life had started to grow back between the path and the forest edge).Isolated adult females had very low founding success: less than 13 % settled and spun a web; the presence of an egg sac provided by investigators was not an influencing factor. Webs of isolated females had the same architectures as those of colonies with several hundreds of individuals. This web was a horizontal sheet linked to a thick vertical network of threads.All groups of 150 to 250 spiders established colonies in appropriate habitats. The colonies outside the forest, and more than 90 % of the colonies along the forest edges successfully developed during the one month observation period. Conversely, 35 % of the colonies in the forest disappeared either a few days after being placed there, or one or two weeks after. In the latter case, spiders apparently left their webs, and all silk structures were left intact. No dead spiders were found in the webs.Average web surface areas increased in all colony types with age, except for those placed in the forest. In these colonies, the number of individuals decreased, and there were fewer egg sacs than in the colonies placed outside the forest.Results are discussed with regard to natural colony distribution along open paths and to the dispersive characteristics of this spider species.     

Heterozygosity and fitness in a California population of the labyrinth spider Metepeira ventura (Araneae, Araneidae)

Abstract. The relationship between individual heterozygosity and characteristics likely to be associated with fitness was investigated in the labyrinth spider Metepeira ventura . Adult females and their egg sacs were collected at a coastal site in southern California, and three measures of bodily condition (carapace width, weight, residual index) and six measures of reproductive output (number of egg sacs, variation in egg number among sacs [coefficient of variation], total number of eggs, mean eggs/sac, mean eggs/sac divided by carapace width, mean eggs/sac divided by weight) were determined for each spider. The sample was polymorphic at three allozyme loci that were in Hardy–Weinberg equilibrium, and individual females were heterozygous at up to two of the three loci, forming three heterozygosity classes (0, 1, and 2). None of the bodily condition measures were significantly related to the number of heterozygous loci, while four of the reproductive output estimators (total number of eggs, mean eggs/sac, mean eggs/sac divided by carapace width, mean eggs/sac divided by weight) were significantly influenced by heterozygosity. In each significant case, values for class 2 females were less than those for class 0 and 1 females, whose values were usually more similar. Thus, while female bodily condition was comparable among classes, the most heterozygous females produced fewer total eggs and eggs per sac than their less heterozygous peers. The fact that females of M. ventura engage in a reproductive investment-number trade-off suggests that high-variability and low-variability females may be pursuing distinct reproductive strategies in the wild, with more heterozygous females being K -selected (smaller clutches, heavier eggs) and more homozygous females being r -selected (larger clutches, lighter eggs). Further investigation will be needed to assess more fully the fitness value of heterozygosity in M. ventura .     

Relationship between prey consumption and colony size in an orb spider

Summary I studied the relationship between prey consumption and colony size in the orb spiderPhiloponella semiplumosa. Observations of unmanipulated colonies showed that prey biomass per juvenile spider was positively correlated with colony size, indicating that prey consumption was highest in the largest colonies observed. In contrast, the relationship between prey biomass per adult female and colony size was curvilinear; prey consumption tended to be highest in intermediatesized colonies. Adult female cephalothorax width was positively correlated with colony size. Number of egg sacs per adult female tended to be highest in intermediate-sized colonies. Prey biomass per juvenile was lower in experimentally reduced colonies than in large control colonies. Aerial-arthropod abundance was not correlated with colony size, and experimental prey supplementation did not affect colony size. Thus, the relationship between prey consumption and colony size was influenced by coloniality directly, rather than by a correlation between prey abundance at a site and colony size.     

Reproductive state and care giving in Stegodyphus (Araneae: Eresidae) and the implications for the evolution of sociality

Cooperative brood care is a rare phenomenon in spiders and is restricted to a few social species, including three in the genus Stegodyphus. Brood care in Stegodyphus begins with regurgitation feeding followed by matriphagy: the young consume the body fluids of their mother causing her to die quickly. Whether such an extreme form of maternal care can become a communal task should depend on physiological or historical preconditions. I investigated whether femaleStegodyphus lineatus feed young or allow matriphagy according to their own reproductive state. Broods of young of two age classes (2 or 10 days after hatching) were isolated or fostered out to adult females that were unmated, had eggs or had young. Growth and survival of females and broods were followed over 21 days. The timing of matriphagy depended on the interaction between age of young and state of the foster mother. All broods that were fostered out to females with young grew and survived. Two-day-old young did not survive when isolated or fostered out to unmated females, but some survived and gained weight when placed with foster mothers that cared for egg sacs. Young of 10 days of age grew when fostered out to females with eggs but did not grow or lost weight when isolated or fostered out to unmated females. Survival among 10-day spiderlings was relatively high in all groups but differed significantly between treatments (young isolated or fostered out to unmated females or females with eggs) and control (left with the mother). The results show that these spiders will care for young from other females only when they are in the right developmental state. Such a constraint can have important consequences for the evolution of allomaternal care in social species: unless such a mechanism is overcome, nonreproductives cannot help in brood care. Copyright 2002 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved.     

Is Male Cohabitation Costly for Females of the Spider Stegodyphus lineatus (Eresidae)?

Reproductive interests of females and males can vary over a number of issues, including the number of matings and the occurrence and duration of mate guarding and cohabitation. The mating system of the spider Stegodyphus lineatus (Eresidae) is characterized by an exceptional sexual conflict where males induce females to remate by committing infanticide. Females experience high costs because of this male strategy, while males benefit. During the mating season, males tend to stay with females for several days. We examined whether this male strategy of cohabitation is also disadvantageous for females of S. lineatus. A field experiment revealed that male presence in a female's nest negatively affected her body condition, whereas cohabiting males gained weight because they fed on prey caught in webs of females. As a response, females did not renew their webs when males were present. Thus, females with a cohabiting male experienced the combined cost of prey loss and loss of time available for foraging. These costs are expected to increase with every additional cohabiting male. Mated females behaved more aggressively toward males than did virgin females. This behavior may be interpreted as an adaptive response to reduce mating costs.     

Within‐patch oviposition site shifts by spider mites in response to prior predation risks decrease predator patch exploitation

In egg‐laying animals with no post‐oviposition parental care, between‐ or within‐patch oviposition site selection can determine offspring survival. However, despite the accumulation of evidence supporting the substantial impact predators have on oviposition site selection, few studies have examined whether oviposition site shift within patches (“micro‐oviposition shift”) reduces predation risk to offspring. The benefits of prey micro‐oviposition shift are underestimated in environments where predators cannot disperse from prey patches. In this study, we examined micro‐oviposition shift by the herbivorous mite Tetranychus kanzawai in response to the predatory mite, Neoseiulus womersleyi, by testing its effects on predator patch exploitation in situations where predatory mites were free to disperse from prey patches. Adult T. kanzawai females construct three‐dimensional webs on leaf surfaces and usually lay eggs under the webs; however, females that have experienced predation risks, shift oviposition sites onto the webs even in the absence of current predation risks. We compared the predation of eggs on webs deposited by predator‐experienced females with those on leaf surfaces. Predatory mites left prey patches with more eggs unpredated when higher proportions of prey eggs were located on webs, and egg survival on webs was much higher than that on leaf surfaces. These results indicate that a micro‐oviposition shift by predator‐experienced T. kanzawai protects offspring from predation, suggesting adaptive learning and subsociality in this species. Conversely, fecundity and longevity of predator‐experienced T. kanzawai females were not reduced compared to those of predator‐naïve females; we could not detect any costs associated with the learned micro‐oviposition shift. Moreover, the previously experienced predation risks did not promote between‐patch dispersal of T. kanzawai females against subsequently encountered predators. Based on these results, the relationships of between‐patch oviposition site selection and micro‐oviposition shift are discussed.     

横纹金蛛多次产卵生物量分配初步研究

卵袋是雌蛛产卵、若蛛孵化等繁育后代的保护性场所.常见农林蜘蛛横纹金蛛(Argiopebruennichi)一般一生产卵3～6次,织制卵袋3～6个.本文对横纹金蛛的体重、卵袋生物量、卵粒数与卵粒重进行了测试研究.结果表明,随着产卵次数增加,产卵间隔时间更长,但雌蛛产卵后至下一次产卵前生物量的增量在减少,而对卵袋生物量的投...     

Spinning activity of the spider Trogloneta granulum (Araneae, Mysmenidae): web, cocoon, cocoon handling behaviour, draglines and attachment discs

The spider species Trogloneta granulum, which in the wild lives inside scree slopes, builds three-dimensional orb webs. During egg-laying and egg sac building, the females stay with their dorsa down at the central part of the web. In this process, the hub is used as a platform. The threads of the hub are not incorporated into the silk cover of the egg sac. The silk wall of the egg sac is very thin, with all the silken threads constituting it having a uniform ultrastructure. The silk wall of the egg sac and the spinnerets are permanently linked by a dragline. Draglines produced by T. granulum affect the direction of movements of the female carrying its cocoon. Egg sacs are handled using draglines. The low number of piriform glands leads to the formation of very simple attachment discs, which fix the individual threads to the substratum. Thread bundles are attached to the substratum by means of accumulated attachment discs.     

Colony size and individual fitness in the social spider Anelosimus eximius

ABSTRACT The effects of colony size on individual fitness and its components were investigated in artificially established and natural colonies of the social spider Anelosimus eximius (Araneae: Theridiidae). In the tropical rain forest understory at a site in eastern Ecuador, females in colonies containing between 23-107 females had india significantly higher lifetime reproductive success than females in smaller colonies. Among larger colonies, this trend apparently reversed. This overall fitness function was a result of the conflicting effects of colony size on different components of fitness. In particular, the probability of offspring survival to maturity increased with colony size while the probability of a female reproducing within the colonies decreased with colony size. Average clutch size increased with colony size when few or no wasp parasitoids were present in the egg sacs. With a high incidence of egg sac parasitoids, this effect disappeared because larger colonies were more likely to be infected. The product of the three fitness components measured-probability of female reproduction, average clutch size, and offspring survival-produced a function that is consistent with direct estimates of the average female lifetime reproductive success obtained by dividing the total number of offspring maturing in a colony by the number of females in the parental generation. Selection, therefore, should favor group living and itermediate colony sizes in this social spider.     

Cannibalism in a Zoophytophagous Omnivore is Mediated by Prey Availability and Plant Substrate

Cannibalism is a dietary option, the frequency of which, in most predator-prey systems, is inversely proportional to the abundance of primary prey. Under conditions of prey scarcity, in food webs involving plant-feeding omnivores, cannibals may choose to feed on either conspecifics or on the continuously-available but less nourishing plant substrate. We tested the effects of prey limitation and plant species on cannibalism in the omnivorous true bug, Dicyphus hesperus. Adult females preyed on first- and fourth-instar, and male conspecifics, and the rate of cannibalism increased under conditions of prey scarcity. Plant species affected cannibalism, with the highest cannibalism occurring on mullein, Verbascum thapsus and chrysanthemum, Chrysanthemum coronarium, and the lowest on tomato, Lycopersicon esculentum. Removal of leaf hairs from mullein reduced the rate of cannibalism. Host plant species affects the rates of cannibalism in D. hesperus and mechanisms other than the plant's value as food may contribute to this effect.     

Social behaviour of spitting spiders (Araneae: Scytodidae) from Singapore

The social organization of Scytodes sp., a spitting spider from Singapore, was investigated in the field and in the laboratory. The characteristics considered were colony structure, maternal care, prey capture, prey sharing, adults provisioning with prey and how feeding regime influences the level of tolerance expressed by juveniles that were living together. The characteristics of this species were compared with those of other Scytodes species that have been studied previously. Based on our findings, we conclude that in this species, social organization is 'periodic-social', with extended maternal care, this being a type of 'subsociality'. The females of Scytodes sp. wrapped their eggs in a silk egg sac and used their chelicerae to hold the eggs until they hatched. Spiderlings tended to remain in their mother's web until the fourth instar (i.e. after the third moult) but they were also highly aggressive and cannibalistic towards conspecifics after the third instar. Females carried prey to their spiderlings and either fed alongside the brood or left them to feed alone. Spiderlings also captured large prey cooperatively by spitting onto, biting and feeding on it together. The occurrence of cannibalism among her juveniles did not appear to be influenced by whether the adult female was present or not, nor did it appear to be influenced by prey abundance.     

Maternal Care and Infanticide by Males in Helvibis longicauda (Araneae: Theridiidae)

Maternal care in spiders varies from just the construction of a protective silken structure for the eggs and the selection of a safe site to place them, to a long period of association between the mother and spiderlings. Such extended care may involve the active protection from predators and parasitoids, food regurgitation, the production of trophic eggs and even matriphagy. In this study, we describe extended maternal care in Helvibis longicauda (Theridiidae) and evaluate the effectiveness of maternal protection against predators of eggs and spiderlings. We conducted experiments comparing the frequency of egg sac destruction and mortality of spiderlings in the presence and absence of mothers. We also observed the behaviour of the mother and spiderlings during prey capture events and interactions with possible predators. Helvibis longicauda females guard their egg sacs until the emergence of the young and guard the spiderlings for several instar stages, fighting possible predators, including conspecifics. We found that aggressive behaviour by females increased the survival of both eggs and spiderlings in our experiments. Intruder males were the main source of mortality in the absence of females. The benefits of maternal care for the young also include the acquisition of prey items that are captured, immobilized and pre‐digested by the mother. Effective maternal protection and the extended period of supplying food to juveniles probably contribute to the late dispersal of offspring in H. longicauda.     

Effect of cannibalism on predation,oviposition and longevity of the predacious mite,Agistemus exsertus Gonzalez (Acari: Stigmaeidae)

Cannibalism (intraspecific predation) on conspecific eggs was investigated in the predatory stigmaeid mite, Agistemus exsertus Gonzalez in the absence of eggs of Tetranychus urticae Koch (no-choice tests) and presence of three densities of prey eggs simultaneously (choice tests) in the laboratory. Data show that cannibalism occurs in immatures and adult females of the predator, which successfully developed and reproduced on conspecific eggs as an alternative prey in the absence of prey eggs. In no-choice tests, cannibalism rate on conspecific eggs by A. exsertus stages was significantly lower than the predation rate on T. urticae eggs. The predatory mite exhibited a marked decline in oviposition rate when preyed on conspecific eggs compared with feeding on prey eggs. The developmental duration and longevity of A. exsertus females were significantly longer 1.9 and 1.7 times, respectively, when fed on conspecific eggs than feeding on T. urticae eggs. The propensity of the predator towards cannibalism depends on the prey density, when T. urticae eggs and conspecific eggs are present simultaneously. Provision of increased densities of prey eggs significantly decreased cannibalism and predation by A. exsertus stages, which fed generally less on conspecific eggs than on T. urticae eggs in choice tests. The oviposition rate of the predator increased significantly, as the egg density of the prey increased. The developmental period and longevity of A. exsertus females showed significantly gradual shortness with increasing egg density of the prey.     

An arboreal spider protects its offspring by diving into the water of tank bromeliadsUne araignée arboricole utilise les réservoirs d’eau des broméliacées pour se protéger et protéger son cocon

Cupiennius salei (Ctenidae) individuals frequently live in association with tank bromeliads, including Aechmea bracteata, in Quintana Roo (Mexico). Whereas C. salei females without egg sacs hunt over their entire host plant, females carrying egg sacs settle above the A. bracteata reservoirs they have partially sealed with silk. There they avoid predators that use sight to detect their prey, as is known for many bird species. Furthermore, if a danger is more acute, these females dive with their egg sacs into the bromeliad reservoir. An experiment showed that this is not the case for males or females without egg sacs. In addition to the likely abundance of prey found therein, the potential of diving into the tank to protect offspring may explain the close association of this spider with bromeliads. These results show that, although arboreal, C. salei evolved a protective behavior using the water of tank bromeliads to protect offspring.     

Variation in life-history characteristics over a clinal gradient in three populations of a communal orb-weaving spider

Summary Adult size and fecundity, total reproductive biomass, egg size, and spiderling size and resistance to desiccation were compared in three populations of the communal orb-weaving spider,Metepeira spinipes, in Mexico. In a desert population and in one from a moist tropical forest adult size, fecundity, and total reproductive biomass were similar, but were markedly smaller than in a climatologically intermediate agricultural habitat. Egg size and protein content were greater in the desert and agricultural habitats than in the moist forest, but spiderling size increased from desert to agricultural to moist forest populations. Desert spiderlings survived significantly longer than moist forest spiderlings at all humidity treatments over a 10% to 100% range. An explanation for these results is proposed based on apparent differences in energy allocation and expenditure which arise from the distinct climate, colony structure, and prey and space availability in the three habitats.