Synchronized contractive movement of Amaurobius ferox spiderlings

During the post-matriphagy period, Amaurobius ferox spiderlings (Araneae, Amaurobiidae) show synchronous movement, contracting their bodies simultaneously. This paper describes this behavior for the first time and identifies influencing factors. The spiderlings’ contractions triggered by web vibration caused by intruders result in a strong pulsation of the whole web that a single individual would not be able to induce by itself. Repetition of the contractions was synchronized among individuals (n = 60 clutches). The movement appeared on the first day after matriphagy. The proportion of participants was maximum on the third day post-matriphagy, when on average 60.7% of the individuals were involved; thereafter the synchronicity progressively decreased. The spiderling groups performed contractions at the highest frequency on the fourth day post-matriphagy, and stopped contracting after the second molt. Experiments using mechanical stimuli produced by an electronic vibrator and a cricket’s movement showed that the vibrational intensity of the external stimuli was positively correlated with the number of contractions performed. Nestmate presence increased the number of contractions performed by individuals, and members of densely packed groups showed more contractions per individual than those in less dense groups. Contractions appeared only during the period when the mother was absent (after matriphagy, or when the mother was removed after the first molt of spiderlings and before matriphagy), and the young were not yet capable of capturing prey. Contractions may function as an antipredatory behavior.     

Adaptive advantages of matriphagy in the foliage spider, Chiracanthium japonicum (Araneae: Clubionidae)

Young of the Japanese foliage spider, Chiracanthium japonicum, show matriphagy, whereby they consume their own mothers before dispersal. By removing mothers in the laboratory, I examined the importance of this sacrificial habit for offspring survival and dispersal behavior. Spiderlings that cannibalized their mothers gained weight more than threefold and dispersed from their breeding nests after molting into the third instar. The third-instar spiderlings had relatively longer legs than the previous instars and appeared to be more adapted to a solitary hunting life style. On the other hand, most spiderlings separated from their mothers could not molt into the third instar and dispersed significantly earlier than those with matriphagy. Furthermore, the lack of matriphagy decreased the survival rate of predispersal spiderlings. These results showed that matriphagy of C. japonicum has a great advantage in allowing offspring to disperse at a more developed and active instar. Received: October 23, 2000 / Accepted: March 15, 2001     

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.     

Adaptive advantages of maternal care and matriphagy in a foliage spider,Chiracanthium japonicum (Araneae: Coubionidae)

I examined the function of maternal care in a foliage spider,Chiracanthium japonicum. Females of this species make breeding nests with rolled-up grass leaves and provide themselves to spiderlings as food at the end of maternal care. By removing mothers from their offspring at 2 different times, the effects of maternal care on egg and spiderling survival rates were estimated separately. Mother attendance greatly improved survival and development of eggs as well as spiderlings. Detailed observations on the fate of immatures in breeding nests with and without their mothers showed lower hatching and spiderling emergence rates when mothers were removed. Furthermore, spiderlings that fed on their mother’s body showed accelerated growth and quickly molted into the 3rd instar with the delay of dispersal. This suggests that matriphagy, or eating the mother, enables spiderlings of this species to disperse at a later instar. Therefore, I conclude that the maternal care of this spider consists of guarding offspring, supporting offspring development and feeding spiderlings.     

Social Facilitation of Synchronized Molting Behavior in the Spider Amaurobius ferox (Araneae, Amaurobiidae)

During the social period, molting behavior of the young spider, Amaurobius ferox, is highly synchronized within the clutch. Result of the experimental study suggests that social facilitation among group members increased the synchronization. The duration of the molting period of grouped spiderlings was significantly shorter than that of individually isolated spiderlings. Involving the particular maternal strategy in food supply, this phenomenon might have adaptive values in the maintenance of mutual tolerance among the siblings by decreasing the interindividual difference in development and in the avoidance of cannibalism on molting individuals. This probably will also serve to make the peaceful collective behaviors of the spiderlings in matriphagy and cooperative prey capture during their social period.     

Trophic egg laying in the spider, Amaurobius ferox: mother-offspring interactions and functional value

Offspring of the spider Amaurobius ferox (Araneae, Amaurobiidae) were provided with trophic eggs of their mother the day after their emergence from the egg sac. This precisely timed egg laying followed after a series of mother-offspring interactions involving specific behaviors. Experiments showed that the trophic egg laying of the mother (providing she is in the appropriate reproductive condition) necessitated not only their presence, but also the stimulating behavior of the spiderlings. By stimulating their mother the spiderlings actually inhibited the normal maturation of the second generation of maternal eggs and prompted the release. Comparing to the trophic egg-deprived clutches, the clutches provided with the trophic eggs developed with higher body mass, earlier moulting and matriphagy. More offspring survived at the matriphagy with the mother normally provisioning the first clutch with trophic eggs rather than with the mother that did not produced the trophic eggs for her first clutch but for her second clutch. By turning her potential second generation into food, the mother increases her reproductive success.     

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.     

Matriphagy in the hump earwig, Anechura harmandi (Dermaptera: Forficulidae), increases the survival rates of the offspring

Females of the hump earwig, Anechura harmandi, are completely consumed by their offspring at the end of their care (matriphagy). The effect of this matriphagy was assessed by manipulative experiments. Matriphagy led to a delay in the dispersal of the nymphs and an increase in their survival rate. The same results were obtained when mothers were removed and the nymphs were given sufficient food. Females separated from their offspring after larval hatching failed to produce a second clutch, and three-quarters of them did not develop their ovaries. These results suggest that the survival of nymphs and their stay in the nest are dependent on food availability and that A. harmandi females are strictly semelparous.     

Matriphagy in the Spider Amaurobius ferox (Araneidae,Amaurobiidae): an Example of Mother-Offspring Interactions

In the spider Amaurobius ferox, the mothers are systematically devoured by their young at a fairly constant interval. Observation of broods maintained under normal conditions showed the cannibalistic processes to be achieved within a few hours, in the course of which mothers and offspring appeared to exchange stimulation. In particular, the mothers exhibited ‘solicitation’ behaviours which appeared to activate and synchronize the young. An experiment was carried out to specify the respective role played by the two parties of the dyad in this case of matriphagy. The female's attitude towards the young (‘solicitation’, tolerance or predatory response) appeared to depend on her reproductive state. The attitude of the young towards the female (cannibalism, attraction, or flight) was shown to depend on their stage of development, but also on the female's attitude. These results support the hypothesis that, in A. ferox, matriphagy is regulated by mother-offspring interactions. Such a mechanism could ensure precise tuning of matriphagy in relation to the requirements of the young, and a certain amount of flexibility in reproduction.     

Functional Value of Matriphagy in the Spider Amaurobius ferox

The adaptive value of matriphagy, the consumption of the mother by her offspring, in the sub-social spider Amaurobius ferox (Araneae, Amaurobiidae) was experimentally evaluated in terms of the benefits to the offspring and the costs to the mother. Matriphagy resulted in a 2.5-fold weight gain in the offspring over their initial weight, advancement of their moulting time, and larger body mass at dispersal in comparison with clutches deprived of matriphagy, but otherwise well provisioned with prey. Matriphagous offspring were also more successful at capturing large prey items, had a more extended social period, and a higher survival rate at dispersal. Mothers separated from their broods just prior to matriphagy were able to produce second clutches, effectively producing 33% more viable offspring (compared with the first clutches). However, the estimated reproductive outputs of the alternative maternal strategies (being devoted to the first clutch vs. deserting the first and producing a second one) suggest that mothers of A. ferox that are cannibalized by their broods enjoy greater reproductive success than those that escape cannibalism and produce second clutches.     

Maternal inheritance in a subsocial spider: web for collective prey capturing of the young

Construction of a safe refuge is the first step toward the evolution of social organization in spiders. In the case of the subsocial spider Amaurobius Jerox (Araneae, Amaurobiidae), the young remain in the natal nest after consuming their mother's body (matriphagy). The benefit that the young could obtain from the maternal web was investigated in their collective prey capture. The results demonstrated the adaptive value of the maternal web. The prey capturing activity was more effective when the young were allowed to stay on the maternal web than when they used the web constructed by themselves. Maternal web may also provide a better transmission of information on prey state and clutch mates' activities, because more spiderlings were recruited to contact and hold the prey in a shorter period of time than when they were on a spiderling-constructed web. The young's inheritance of the maternal nest is probably one of the crucial ways in which the mother influences the post-maternal social period of the young.     

Physiological costs during the first maternal care in the wolf spider Pardosa saltans (Araneae,Lycosidae)

Many arachnids like other terrestrial arthropods, provide extensive maternal care. Few studies have quantified the underlying physiological costs of maternal care. We investigated how maternal care affects the free-moving wolf spider’s (Pardosa saltans) energy requirements. We described in detail their basic reproduction biology (i.e. carrying cocoon and young) and we evaluated the variation in the females’ energy reserves during maternal care. Our results show that mothers guard eggs until hatching and then guard their spiderlings for 27–30 more days. Laboratory observations indicated that spiderlings start leaving the maternal abdomen gradually 5–7 days after hatching. Females carry an egg sac (cocoon) that can weigh up to 77% of their post-reproduction weight and carry young that weigh 87–100% of their body mass. Females lost weight over time despite regular food intake, while carrying cocoon and young; but their weights increased gradually during the dispersal of young. The contributions of proteins, glucose and triglycerides to maintain females’ energy were calculated. Their energetic state varied during maternal care, in particular lipid levels declined, during the care of spiderlings when the females’ predatory behaviour was inhibited. Our results show that the maternal care provided by P. saltans females is particularly costly physiologically, during the 30 days following egg sac formation and development of spiderlings, even when food is available.     

Effects of Early Contact with Maternal Parent on Locomotor Activity and Exploratory Behavior in Spiderlings of Hogna carolinensis (Araneae: Lycosidae)

In this study we investigated the effect of rearing conditions (stimulus complexity) on the locomotor activity and exploratory behavior of spiderlings of Hogna carolinensis in a novel open field arena. Experimental groups consisted of spiderlings that were allowed to remain with their maternal parent for 1 day (group 1), 3 days (group 2), and 5 days (group 3) after emergence from their egg sacs, and those who had no contact (group 4) with a maternal parent. Spiderlings that had physical contact with their mothers for 3 and 5 days required significantly less time to enter the arena, to reach the central grid area of the arena, and for an initial return to the start box than spiderlings in groups 1 and 4. In addition, spiderlings in groups 2 and 3 exhibited a significantly greater number of grid crossings as compared to groups 1 and 4, and spent more time in the arena. This is the first demonstration that environmental complexity, in the form of a social factor such as physical contact with a maternal parent, can affect the subsequent behavior of spiderlings.     

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.     

千岛湖岛屿社鼠的扩散特征

2009年7月—11月,2010年3月—11月对千岛湖两个岛屿上的社鼠(Niviventer confucianus)种群进行标志重捕,通过分析扩散个体的性别、年龄及扩散距离等,探讨陆桥岛屿环境下社鼠的扩散特征。研究结果显示:岛屿环境下社鼠的扩散率为37.96%,不同季节社鼠的扩散率存在差异,社鼠倾向于在春季发生扩散,尤其是3月份,社鼠扩散个体数最多;对于整个捕获史而言,雌雄扩散个体数存在极显著的差异(x~2=12.542,df=1,P0.001),雄性个体更倾向于发生扩散;而在繁殖高峰期,当怀孕鼠存在时,雄性扩散数亦大于雌性,两者存在显著差异(x~2=4.504,df=1,P=0.034)。扩散个体体重的季节差异不显著;扩散与社鼠的年龄密切相关,社鼠更加倾向于在亚成年阶段发生扩散;另外,家群大小对社鼠扩散个体数量也有显著影响,家群越大,扩散个体越多;对扩散距离进行分析发现存在显著的性别差异(t=-9.229,df=50,P0.001),雌性个体的平均扩散距离为(282.97±16.14)m,显著大于雄性的(146.70±6.80)m,而扩散距离与年龄、体重、最大活动距离均无显著相关性。     

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.     

Maturing and Coordination of Web-Building Activity

Experiments are reported in which 114 Zygiella x-notata Cl.spiderlings were taken out of the cocoon before the time atwhich they normally left (2 weeks after the second molt); 67were placed on wooden frames and 47 on wire frames. Both groupsbuilt partial, irregular thread-patterns at first, and, as theygrew older, constructed more and more regular geometric orb-webs:the transition can be traced through several stages. The shapeof the web, particularly the presence of the free-sector, wasdependent on the frame; webs built in a circular wire framelacked the free-sector. It is assumed that the accomplishmentof full, regular orb webs is essentially based on the progressivehistological differentiation of the central nervous system inthe spiderlings during the developmental phase under observation;the wire frame could influence the shape of the web throughmaking construction of a retreat difficult.     

Life-history,bionomics and behaviour of the social spiderStegodyphus sarasinorum Karsch

Summary InStegodyphus sarasinorum Karsch the adult stage is attained after twelve instars. The secondary sexual characters become manifest in the twelfth instar. There is only one generation per year. Normally only one cocoon is made and taken care of by a fertilized female during her life-time.The various aspects of the bionomics and behaviour of this social spider, viz., the nest architecture, repair of webs, activity rhythm, food and feeding behaviour, population density at different stages, sex-ratio, sexual behaviour, maternal behaviour, dispersal and colony foundation, are discussed. Besides feeding her young ones during the second instar by regurgitation and by providing them with captured prey, the mother spider finally offers herself as a living food depot for her young ones which suck out her body fluids and she slowly dies.New colonies are formed after emigration over silken threads by either groups of spiderlings at various times in colonies during the fourth to ninth instars (sociotomy), or by individual fertilized females. In a second method of colony foundation, emigration of spiderlings of fourth to eighth instars takes place either by individuals or by small groups by means of silken threads produced and wafted in the wind (aerial navigation).

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Résumé ChezStegodyphus sarasinorum Karsh, l'état adulte est atteint après 12 stades. Les caractères sexuels secondaires deviennent visibles au douzième. Il y a seulement une génération par an. Normalement, durant sa vie, une femelle ne tisse et soigne qu'un seul cocon.On a analysé les différents aspects de la bionomie et du comportement de cette araignée sociale, c'est-à-dire l'architecture du nid, réparation de la toile, rythme d'activité, nourriture et comportement alimentaire, densité de population aux différents stades, sex-ratio, comportement sexuel, comportement maternel, dispersion et fondation de colonies. En plus du nourrissage de ses enfants au deuxième stade par régurgitation et apport de proies capturées, la mère s'offre finalement comme réserve vivante de nourriture pour ses enfants qui pompent la lymphe et elle meurt lentement.De nouvelles colonies apparaissent par migration sur fils de soie ou bien de jeunes du quatrième au neuvième stade à différents moments de la colonie, ou bien de femelles fécondées seules. Dans une deuxième méthode de fondation de colonie, la migration des jeunes du quatrième au huitième stade se fait seule ou en petits groupes par production de fils de soie et transport aérien.

     

Agonistic behaviour of female Tegenaria atrica in the presence of different aged spiderlings

The agonistic behaviour of adult female T. atrica increases with increasing age of spiderlings until 80 days post-emergence, then decreases. In all cases, cannibalism of spiderlings increases markedly after completion of their pre-dispersal period with a correlation between the switch of behaviour, from tolerance to cannibalism, and a modification of individual’s cuticular compounds. Experiments that compare spiderlings weight and mobility indicate that female agonistic behaviour are always low with spiderlings in pre-dispersal period, and high with spiderlings in post-dispersal period. Female reproductive state and the weight/mobility of spiderlings are not the only factors controlling the adult female’s agonistic behaviour towards spiderlings on her web, as tactochemical information plays an important role in modulating agonistic behaviour after close contact between female spiders and spiderlings. The agonistic behaviour of females appears to correspond with a change in the increase of polar compound levels (methylesters and fatty acids) and the decrease of apolar compound levels (hydrocarbons) in spiderlings of different ages.     

浅水湖泊浮水植物芡实收割对浮游植物群落的影响

浅水湖泊生态系统正遭受广泛而强烈的人为干扰,但是对收割水生植物干扰的研究甚少。于2019年8月对芡实过度生长的陈瑶湖进行通道式分区收割工程,分析了收割芡实（Euryale ferox）前后不同处理组浮游植物群落的变化。研究期间共鉴定出浮游植物6门47属72种,其中收割前63种,收割后71种。收割后浮游植物的细胞密度和生物量均高于收割前,分别增加了39.78%和5.09%。收割芡实导致陈瑶湖浮游植物群落为由蓝藻-绿藻-硅藻-隐藻群落转变为蓝藻-绿藻-硅藻群落。其中蓝藻细胞密度和生物量显著高于收割前（P<0.05）,归因于有害蓝藻（铜绿微囊藻Microcystis aeruginosa、水华束丝藻Aphanizomenon flos-aquae、小颤藻Oscillatoria tenuis、卷曲鱼腥藻Dolicospermum circinale、小席藻Phormidium tenu）的增加。收割还导致了硅藻群落由附生型向浮游型硅藻的转变,表现为尖针杆藻（Ulnaria acus）减少,而颗粒直链藻极狭变种（Aulacoseira granulata var.angustissima）、梅尼小环藻（Cyclotella meneghiniana）增加。在芡实收割过程中,未收割组和河道的浮游植物群落结构在时空分布上无显著性差异（P>0.05）,但收割组在收割后的不同阶段内差异较为明显,其细胞密度和生物量随着收割实验的结束逐渐降低。浮游植物与环境因子的相关性分析表明,水生植被覆盖度、总磷、总氮、溶解氧和叶绿素a浓度是影响浮游植物细胞密度和生物量变化的主要环境因子。综合陈瑶湖水质状态,本研究认为收割芡实并不能缓解浅水湖泊富营养化状况,研究结果为浅水湖泊水生植被的管理提供理论依据。