Natural history of the non-solitary sheetweaving spider Anelosimus jucundus (Araneae: Theridiidae)

Field observations were made on one Panamanian population of Anelosimus jucundus. Almost all webs were found in a relatively exposed area, on small shrubs and composites. This is in contrast to A. eximius , a colonial congeneric which in our study site built its large webs along moist, fern-covered banks. Web structure varied with different plant substrates; for example, only some of the webs incorporated a clearly defined lower sheet. Webs were built by penultimate instar females, and perhaps by adult females and males. In some cases, several adult females inhabited a web, but they remained under separate leaf canopies; during census observations co-operative efforts were not noted. Prey consisted mainly of winged insects. Juvenile sex ratio was about equal. The degree of sociality demonstrated by A. jucundus is discussed.     

Cooperation and Prey Capture Efficiency in a Social Spider,Anelosimus eximius (Araneae,Theridiidae)

We studied the efficiency of the hunt and the characteristics of cooperation during the prey capture in a social spider Anelosimus eximius. Two natural types of prey of roughly the same length (20 mm) were used: grasshoppers (Orthoptera) and moths (Lepidoptera); 128 tests were made on 14 colonies, the smallest with 20 and the largest with 1,700 individuals. Test times were 12.00 h, defined as an inactive period for the spiders and 18.00 h, defined as an active period. Overall capture rate of intercepted prey was 66%: it was higher in large colonies or at 18.00 h, when more spider alerts were triggered by the struggling prey. Characteristics of cooperation during capture did not vary with colony size. Capture rate was higher for grasshoppers than moths (73%-58%) in spite of similar number of alerts (76%-87%); so moths must have been more difficult to capture. For both prey types, large colonies capture more rapidly and so had advantages in terms of time gain. We showed that cooperation depended on prey type: more spiders mobilised to attack moths and attack was faster than on grasshoppers. This may be interpreted as an adaptive response of the group to the prey type.     

Prey Capture Behaviour in the Social Spider Anelosimus eximius (Araneae: Theridiidae): Responses to Prey Size and Type

Some species of web building spiders use different capture tactics for different prey types. The main factors influencing the attack behaviour are the ability of the insect to escape, the risks of injury to the spiders and prey size. This study evaluated the effects of size and prey type on prey capture behaviour of the social spider Anelosimus eximius as influenced by the number of spiders attracted by prey movements that did not bite until the immobilization (bystanders) and the number of spiders that contributed to prey immobilization (catchers). We carried out a two‐factor (prey size and type) experiment offering prey belonging to four orders: Diptera, Lepidoptera, Hymenoptera and Orthoptera, in a size gradient within each prey type. Both factors influenced the number of spiders recruited as bystanders, but only prey body size influenced the number of catchers in the subduing process. The possible advantages of the presence of bystanders around the interception site are discussed.     

Density-Dependent Natal Dispersal Patterns in a Leopard Population Recovering from Over-Harvest

Natal dispersal enables population connectivity, gene flow and metapopulation dynamics. In polygynous mammals, dispersal is typically male-biased. Classically, the ‘mate competition’, ‘resource competition’ and ‘resident fitness’ hypotheses predict density-dependent dispersal patterns, while the ‘inbreeding avoidance’ hypothesis posits density-independent dispersal. In a leopard (Panthera pardus) population recovering from over-harvest, we investigated the effect of sex, population density and prey biomass, on age of natal dispersal, distance dispersed, probability of emigration and dispersal success. Over an 11-year period, we tracked 35 subadult leopards using VHF and GPS telemetry. Subadult leopards initiated dispersal at 13.6 ± 0.4 months. Age at commencement of dispersal was positively density-dependent. Although males (11.0 ± 2.5 km) generally dispersed further than females (2.7 ± 0.4 km), some males exhibited opportunistic philopatry when the population was below capacity. All 13 females were philopatric, while 12 of 22 males emigrated. Male dispersal distance and emigration probability followed a quadratic relationship with population density, whereas female dispersal distance was inversely density-dependent. Eight of 12 known-fate females and 5 of 12 known-fate male leopards were successful in settling. Dispersal success did not vary with population density, prey biomass, and for males, neither between dispersal strategies (philopatry vs. emigration). Females formed matrilineal kin clusters, supporting the resident fitness hypothesis. Conversely, mate competition appeared the main driver for male leopard dispersal. We demonstrate that dispersal patterns changed over time, i.e. as the leopard population density increased. We conclude that conservation interventions that facilitated local demographic recovery in the study area also restored dispersal patterns disrupted by unsustainable harvesting, and that this indirectly improved connectivity among leopard populations over a larger landscape.     

Madagascar: an unexpected hotspot of social Anelosimus spider diversity (Araneae: Theridiidae)

Abstract. The spider genus Anelosimus Simon, 1891 (Theridiidae) currently contains over forty described species, found worldwide in tropical to warm temperate areas. American Anelosimus are all social, a rare trait among spiders, but social behaviour has not been reported for Anelosimus species elsewhere. Old World Anelosimus are poorly known, both behaviourally and taxonomically, and no Anelosimus species have yet been described from sub-Saharan Africa or Madagascar. Based on a preliminary phylogenetic analysis we predicted sociality in an undescribed Madagascar species because it grouped among social New World species. An expedition to Madagascar then found no less than five undescribed periodic-social (subsocial) Anelosimus species in Périnet reserve. A sixth species from the same locality is known from museum specimens and the Anelosimus diversity of Périnet is comparable with the most diverse single locality in the Americas. Subsocial species play a key role in understanding the evolution of permanent sociality (quasisociality). This increased pool of available subsocial study species demonstrates the utility of phylogenies as predictors of traits in species thus far unstudied. Here, A. andasibe sp.n. , A. may Agnarsson sp.n. , A. nazariani sp.n. , A. sallee sp.n. , A. salut sp.n. and A. vondrona sp.n. are described. Anelosimus locketi Roberts, 1977 from Aldabra Atoll is a junior synonym of A. decaryi ( Fage, 1930 ) comb.n. from Madagascar. Preliminary data on the behaviour of the new species are given, indicating a level of sociality similar to the American A.‘arizona’¹. The phylogenetic analysis supports the monophyly of the Madagascar group and places it as sister to a clade containing the eximius lineage from the Americas, and a pair of undescribed Tanzanian species.     

Task specialization in two social spiders,Stegodyphus sarasinorum (Eresidae) and Anelosimus eximius (Theridiidae)

Understanding the social organization of group‐living organisms is crucial for the comprehension of the underlying selective mechanisms involved in the evolution of cooperation. Division of labour and caste formation is restricted to eusocial organisms, but behavioural asymmetries and reproductive skew is common in other group‐living animals. Permanently, social spiders form highly related groups with reproductive skew and communal brood care. We investigated task differentiation in nonreproductive tasks in two permanently and independently derived social spider species asking the following questions: Do individual spiders vary consistently in their propensity to engage in prey attack? Are individual spiders' propensities to engage in web maintenance behaviour influenced by their previous engagement in prey attack? Interestingly, we found that both species showed some degree of task specialization, but in distinctly different ways: Stegodyphus sarasinorum showed behavioural asymmetries at the individual level, that is, individual spiders that had attacked prey once were more likely to attack prey again, independent of their body size or hunger level. In contrast, Anelosimus eximius showed no individual specialization, but showed differentiation according to instar, where adult and subadult females were more likely to engage in prey attack than were juveniles. We found no evidence for division of labour between prey attack and web maintenance. Different solutions to achieve task differentiation in prey attack for the two species studied here suggest an adaptive value of task specialization in foraging for social spiders.     

The Comb-footed spider genera Theridion, Achaearanea and Anelosimus of Israel (Araneae: Theridiidae)

Israeli thendiid spiders of the genera Theridion, Achaearanea and Anelosimus have been revised. A relative richness in species is presented providing thereby updated information on the little known Mediterranean spider fauna. All type and non-type material previously described from the Middle East, deposited in several European collections has been re-examined, along with species from adjacent regions considered pertinent to the study undertaken. Altogether 21 species are recognized. Systematic, ecologic and all available zoogeographic information on taxa treated are discussed along with recent, pertaining literature. The presence of seven species formerly reported from Israel has been confirmed and the occurrence of another four species unknown hitherto from this region, has been proved. Some of these have never been adequately described or illustrated.
Ten new species are described: Theridion ochreolus, T. agaricographus, T hierwhonticus, T. jordanensis, T. negebensis, T. gekkonicus, T. dafnensis, T. vallisalinarum, T. pustiliferus and Anelosimus giladensis. The male of Theridion melanostictum is described for the first time. Keys, illustrations of diagnostic characters and records of distribution are provided for each species, all readily applicable also in adjacent countries. These may provide clues for better understanding of zoogeographic patterns of the Palearctic fauna, including those of the Old World Desert belt extending south and east of the Mediterranean region.     

Revision and phylogenetic analysis of American ethicus and rupununi groups of Anelosimus (Araneae, Theridiidae)

Two species groups of the social spider genus Anelosimus are revised. The ethicus group contains six species found in South America, in an area ranging from the Guianas to southern Brazil and Argentina. Of these, A. rabus Levi, 1963, A. ethicus ( Keyserling, 1884 ), and A. nigrescens ( Keyserling, 1884 ) are redescribed, while A. nigrescens is removed from synonymy with A. ethicus . Three new species are described: A. misiones sp. nov., A. sumisolena sp. nov. and A. inhandava sp. nov. Anelosimus ethicus is reportedly either subsocial or solitary, while the behaviour of the other species in the group is unknown. The rupununi group contains two quasisocial species, A. rupununi Levi, 1956 and A. lorenzo Fowler & Levi, 1979, from the Caribbean and tropical South America. Both are redescribed here. A parsimony analysis of morphological characters provides support for the monophyly of both groups. In the phylogeny, subsociality optimizes to the base of Anelosimus , indicating that the common ancestor of the ethicus group was subsocial. Its members can thus be predicted to be subsocial, or secondarily solitary. Quasisociality arose de novo in the rupununi group, representing one of 6−7 independent origins in theridiids. Study of the biology of Anelosimus is important to advance our understanding of the evolution of sociality in spiders.     

Food Intake,Growth and Relatedness in the Subsocial Spider,Stegodyphus lineatus (Eresidae)

One of the presumed benefits of sociality in spiders is an improved foraging success although it has been shown that group feeding is less efficient than feeding alone. In spiders, communal feeding only occurs amongst kin. The effects of relatedness on the consequences of group feeding were investigated in the subsocial spider Stegodyphus lineatus. A significant difference between short-term intake rates and long-term growth rates was shown in a comparison between groups of siblings and groups of non-siblings. Groups of siblings extracted more out of a prey item in a given time and they had higher growth rates than groups of non-siblings.     

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.     

The phylogeny of the social Anelosimus spiders (Araneae: Theridiidae) inferred from six molecular loci and morphology

We use fragments of three nuclear genes (Histone 3, 18SrDNA, and 28SrDNA) and three mitochondrial genes (16SrDNA, ND1, and COI) totalling approximately 4.5kb, in addition to morphological data, to estimate the phylogenetic relationships among Anelosimus spiders, well known for their sociality. The analysis includes 67 individuals representing 23 of the 53 currently recognized Anelosimus species and all species groups previously recognized by morphological evidence. We analyse the data using Bayesian, maximum likelihood, and parsimony methods, considering the genes individually as well as combined (mitochondrial, nuclear, and both combined) in addition to a 'total evidence' analysis including morphology. Most of the data partitions are congruent in agreeing on several fundamental aspects of the phylogeny, and the combined molecular data yield a tree broadly similar to an existing morphological hypothesis. We argue that such congruence among data partitions is an important indicator of support that may go undetected by standard robustness estimators. Our results strongly support Anelosimus monophyly, and the monophyly of the recently revised American 'eximius lineage', although slightly altered by excluding A. pacificus. There was consistent support for the scattering of American Anelosimus species in three clades suggesting intercontinental dispersal. Several recently described species are reconstructed as monophyletic, supporting taxonomic decisions based on morphology and behaviour in this taxonomically difficult group. Corroborating previous results from morphology, the molecular data suggest that social species are scattered across the genus and thus that sociality has evolved multiple times, a significant finding for exploring the causes and consequences of social evolution in this group of organisms.     

Female body size, fecundity parameters and foundation of new colonies in Anelosimus jabaquara (Araneae, Theridiidae)

Summary. As in other social spider species, subadult Anelosimus jabaquara females found new colonies after solitary dispersal. Some individuals, however, usually remain and reproduce in their natal nests. To test the hypothesis that large females disperse more often than smaller ones, we compared the body size of A. jabaquara females that remained in their natal colonies with those that left to build solitary webs. We also compared clutch size, egg diameter, total egg volume and spiderling size in both conditions. Emigrating females were significantly larger and laid larger clutches. The smaller females that had not dispersed laid significantly larger eggs, although their total egg volume was lower. Spiderlings of solitary females were smaller and had a smaller range of size variation than those from colonies. We discuss the implications of these results in terms of costs and benefits of dispersion for spiders in different nutritional conditions.     

Delayed juvenile dispersal benefits both mother and offspring in the cooperative spider Anelosimus studiosus (Araneae: Theridiidae)

Anelosimus studiosus juveniles usually remain in their natalwebs with their mothers until maturity, forming temporary coloniesin which individuals cooperate in web maintenance and preycapture. In a semi-natural environment, we experimentally removedjuveniles from their natal webs at mid-development. In thecontrol group, the juveniles were immediately replaced in theirnatal webs; in the experimental removal group, the juvenileswere not replaced and a sample of them were allowed to buildindividual webs. Colonies and solitary juveniles were exposedto natural prey densities and censused regularly for numbersand stages of spiders, and for prey capture. On average, juvenilesin colonies survived longer, developed faster, and had more resources per individual than did solitary juveniles. However,some of the solitary juveniles obtained more resources thanindividual juveniles in colonies. Mothers in the control groupsurvived longer and produced second broods earlier than mothersin the experimental removal group. Within the control group,older and larger colonies captured more and larger prey. Larger colonies had a lower coefficient of variation in prey capturedper juvenile. Overall, delayed juvenile dispersal benefitsboth juveniles and mothers.     

Natal Dispersal and Philopatry in the Carnivorous Marsupial Phascogale tapoatafa (Dasyuridae)

The proximate and ultimate causes of dispersal in semelparous carnivorous marsupials (Phascogalinae) have previously been hypothesized to be maternal aggression and inbreeding avoidance, respectively. This study tests these hypotheses by exposing 26 litters of Phascogale tapoatafa to a diverse range of social and environmental conditions that potentially affect dispersal (e.g. supplemental feeding, post-weaning desertion by the mother, orphaning, and release of subadults into unoccupied habitat). The mean dispersal age was 162 ± 5.6 d, which is about 3 wk after weaning is complete. Juvenile dispersal was strongly male biased under all conditions, suggesting that extrinsic proximate causes do not adequately account for male emigration. Home range establishment by males was contingent on the presence of females. Half of the monitored daughters were philopatric, and others typically settled adjacent to the natal site, thus possibly enhancing their reproductive potential by occupying an area of known resource quality. Because philopatry increases the risk of incest, females may be selected to preferentially mate with unrelated males (immigrants), when they are available, to avoid inbreeding. If so, the presence of immigrant males would reduce the probability of locally born, related males reproducing at their natal site. Thus inbreeding avoidance by females may create local mate competition among males and select for male dispersal. Emigration also ensured that males avoided inbreeding, but, if they dispersed into unoccupied habitat, male P. tapoatafa often returned to the natal area. This 'boomerang strategy' of returning to mate with related females suggests that, in the absence of conspecifics along the dispersal path of a male, mate competition will be weak at the natal site and female mate choice will not preclude related males. Thus while inbreeding avoidance by either or both sexes is perhaps the most parsimonious explanation of male-biased emigration, dispersal patterns were apparently strongly influenced by additional factors, so that the ultimate causation of the dispersal regime may be more complex.     

Dispersal Patterns of some Phyteuma Species (Campanulaceae)

Abstract: In the genus Phyteurna spadix-shaped spikes or capitula are composed of xerochasic poricidal capsules, holding unspecialized seeds. Phyteurna betonicifoliurn VILL., Phyteuma hemisphaericum L, Phyteurna scheuchzeri ALL., and Phyteurna spica-turn L. were examined in wind tunnel experiments to determine the minimum wind speed necessary for seed release, and the relationship between wind speeds and dispersal distances. In a simplified practical simulation the dispersal strategies of these species were described with a leptokurtic curve. The short-distance seed dispersal of Phyteuma hernisphaericurn allows a limited enlargement of the occupied area, while the seeds of P. scheuchzeri are dispersed more remotely from the mother plant. P. spicaturn and P. betonicifoliurn mainly disperse closely around the mother plant but provide a certain percentage of seeds for colonization of more distant areas. It is demonstrated that the dispersal modes are determined by the characteristics of fruits, infructescences, and seeds. It is also shown that plants with similar morphological organization show different dispersal patterns, which must be interpreted as a fine-tuned adaptation to the habitat with all its biotic and abiotic factors.     

Regulation of the number of spiders participating in collective prey transport in the social spider Anelosimus eximius (Araneae, Theridiidae)

In an experimental study, mechanisms by which cooperative prey transport is achieved in social spiders were clarified. Factors that could influence the number of individuals that participate in prey transport (prey mass, length and vibration) were investigated. Results show that two factors are fundamental: the vibrations and the prey length. Prey mass did not seem to influence spiders' participation. Thus, the single fact that individuals respond locally to environmental stimuli (intensity of vibration, available site on the prey) explains how spiders cooperate and efficiently capture a wide range of prey types without complex communication systems.     

Philopatry and Dispersal Patterns in Tiger (Panthera tigris)

Background

Tiger populations are dwindling rapidly making it increasingly difficult to study their dispersal and mating behaviour in the wild, more so tiger being a secretive and solitary carnivore.

Methods

We used non-invasively obtained genetic data to establish the presence of 28 tigers, 22 females and 6 males, within the core area of Pench tiger reserve, Madhya Pradesh. This data was evaluated along with spatial autocorrelation and relatedness analyses to understand patterns of dispersal and philopatry in tigers within this well-managed and healthy tiger habitat in India.

Results

We established male-biased dispersal and female philopatry in tigers and reiterated this finding with multiple analyses. Females show positive correlation up to 7 kms (which corresponds to an area of approximately 160 km²) however this correlation is significantly positive only upto 4 kms, or 50 km² (r  = 0.129, p<0.0125). Males do not exhibit any significant correlation in any of the distance classes within the forest (upto 300 km²). We also show evidence of female dispersal upto 26 kms in this landscape.

Conclusions

Animal movements are important for fitness, reproductive success, genetic diversity and gene exchange among populations. In light of the current endangered status of tigers in the world, this study will help us understand tiger behavior and movement. Our findings also have important implications for better management of habitats and interconnecting corridors to save this charismatic species.