Holocnemus Pluchei Research Articles

Occurrence and duration of post-copulatory mate guarding in a spider with last sperm precedence

One male strategy to prevent female re-mating is post-copulatory mate guarding. In the pholcid spider Holocnemus pluchei last male's fertilization success is around 74% and females remain receptive after copulation. It is, thus, reasonable to suppose that males should engage in post-copulatory mate guarding. Chronologically, the present study focused on the following aspects: (1) to determine if male permanence near females corresponds to mate guarding. For this, a second male (intruder) was introduced. Time of permanence, distance and behaviour of residents did not change whether or not an intruder was present; (2) to investigate the duration of mate guarding and male distance to the female in a time series intervals after copulation. Males remained close to females during 14 h keeping a distance of less than 15 cm; (3) to evaluate whether guarding duration is influenced by female sexual receptivity. We found that 24 h after the first copulation, when the resident was placed again next to the female, he tried to re-mate; and (4) to examine differences in paternity in relation to whether or not the resident exerted guarding. P2 was higher when second males copulated again within the first 6 h compared to 24 h after the first copulation.

Spermatozoa and spermiogenesis of Holocnemus pluchei (Scopoli, 1763) (Pholcidae, Araneae)

Until now, the knowledge on pholcid spermatozoa is based on two species, Pholcus phalangioides and, incompletely, Holocnemus pluchei. To complete this knowledge and to reveal more potential phylogenetic characters, we have investigated sperm ultrastructure and spermiogenesis of H. pluchei. We found that the sperm cells of this species are clearly different from those of P. phalangioides with respect to: (1) the lack of specialization in the cylindrical acrosomal vacuole; (2) a nuclear canal which is located in the periphery and not in the center of the nucleus; (3) a more prominent postcentriolar elongation of the nucleus; (4) the presence of “inner microtubules” in the implantation fossa in early and mid-spermatids; (5) the absence of a helical band of nuclear material; (6) the proximal centriole which is not prolonged; (7) the types of secretion in the seminal fluid (only two types in H. pluchei). Similarities in the spermatozoa of both species concern: (1) a large implantation fossa which contains large amounts of glycogen in mature spermatozoa; (2) absence of a centriolar adjunct; (3) an axonemal basis located in the posterior part of the implantation fossa; (4) the formation of the so-called cleistospermia in the vas deferens. Our results strongly support systematic relationships within Pholcidae placing these two species in different subgroups.

Individual decisions and group dynamics: why pholcid spiders join and leave groups

To examine the role of individual variation in the dynamics of group formation, I conducted a mark–recapture study and a series of laboratory and field experiments with Holocnemus pluchei spiders (Araneae: Pholcidae). These spiders can either share webs or live alone, and individuals shift frequently between these strategies. Spiders' decisions were influenced by size and recent feeding success. In the laboratory, small hungry spiders introduced into a web that held a larger conspecific resident were more likely than small well-fed spiders to abandon the web and build their own web. This behaviour pattern gradually reversed as spiders grew: large hungry spiders were more likely than large well-fed spiders to stay in the shared web. When I introduced spiders into empty webs, they were more likely to stay compared with spiders tested with conspecifics. However, hunger level also influenced behaviour even when conspecifics were not present. Food-deprived spiders were more likely to abandon webs and build their own, consistent with the idea that spiders were following a win–stay/lose–shift strategy. In the field, spiders were more likely to stay in webs overnight when they were given supplemental food. In another experiment, spiders that were found building webs in cleared areas were smaller and thinner than average. Finally, I tested whether the size of the intruder or the resident affected whether spiders joined webs. Large intruders were more successful at remaining in webs than smaller intruders, although spiders of all sizes had some success in joining groups. Additional synthetic theoretical work is needed to integrate the complex processes underlying the formation and persistence of groups.

EFFECTS OF MATERNAL BODY SIZE ON CLUTCH SIZE AND EGG WEIGHT IN A PHOLCID SPIDER (HOLOCNEMUS PLUCHEI)

The pholcid spider Holocnemus pluchei (Scopoli 1763) competes for food with conspecifics, and spiders reared on high food levels are generally larger. In this study, we examined whether larger female body size (as estimated by tibia-patella length) translated into increased reproductive success in the form of increased clutch size, clutch weight, and average egg weight. Larger spiders had more eggs and thus heavier clutches, but there was no relationship between maternal size and average egg weight. We also looked for a tradeoff between average egg weight and egg number, and we found a weak relationship in which average egg weight was highest for intermediate-sized clutches. Larger female body size thus translates into increased reproductive success in terms of egg number and clutch weight, but not weight of individual eggs.

Ontogenetic Shifts in the Costs of Living in Groups: Focal Observations of a Pholcid Spider (Holocnemus pluchei)

Abstract Holocnemus pluchei spiders (Family Pholcidae) facultatively live in groups: sometimes they live alone and sometimes they share webs. In the field groups vary in size and composition and include spiders of all ages and either sex. Group membership is flexible and individuals move frequently among groups. To understand group formation and maintenance it is necessary to understand the costs of group membership. We used focal animal sampling to investigate the cost of group living for spiders of different ages across a range of group sizes. Both spider age and group size affected the costs incurred by group-living spiders. There was no variation among groups of different sizes in the percentage of time focal small or large spiders spent in costly behaviors (moving, web maintenance, bouncing or interactions with conspecifics), but medium-sized spiders spent more time engaged in costly behaviors with increasing group size. Medium and large spiders also had more interactions with greater numbers of diff...

Last-Male Sperm Priority in a Haplogyne Spider (Araneae: Pholcidae): Correlations between Female Morphology and Patterns of Sperm Usage

In species where the female mates more than once, sperm priority patterns have important implications for the mating behavior of both sexes. The shape of female sperm storage organs may play a role in determining priority patterns, although the extent of this effect has been controversial. Spiders provide an interesting test of this hypothesis because 2 phylogenetically distinct groups differ in the structure of sperm storage organs. In entelegyne spiders, the female sperm-storage organs have separate ducts for sperm entrance and exit. The male inseminates the female through the external fertilization duct. Sperm then travel through a “conduit” and are released from an internal fertilization duct to fertilize eggs. This arrangement has been hypothesized to lead to 1st-male priority. Six species in 3 entelegyne families have been shown to have 1st-male sperm priority with some mixing; 1 entelegyne species, however, shows last-male priority. Haplogyne females, in contrast, have a spermstorage area with only a single opening, which may be more likely to lead to last-male sperm priority because the last sperm to enter the storage area would be likely to be the 1st to leave. Few data are available for this group. We used a balanced sterile-male design to test the sperm priority pattern in females mated once with each of a pair of males of a haplogyne spider, Holocnemus pluchei Scopoli. Egg sacs from 72.5% of females were sired predominantly by 2nd males, 7.5% were predominantly sired by 1st males, and 20% showed mixed paternity ( n = 40); these frequencies differed significantly from random expectations. The average percentage of eggs fathered by the 2nd male, or P 2, was 74%. These data clearly differ from the predominantly 1st-male pattern generally found in entelegynes, thereby supporting the hypothesized relationship between female reproductive morphology and sperm use patterns. Mating behavior of spiders that exhibit 2nd-male priority should differ from that exhibiting 1st-male priority, and evidence from H. pluchei and other haplogynes supports this inference.

Copulatory Mechanism in Holocnemus pluchei and Pholcus opilionoides, With Notes on Male Cheliceral Apophyses and Stridulatory Organs in Pholcidae (Araneae)

AbstractHuber, B. A. 1994. Copulatory mechanism in Holocnemus pluchei and Pholcus opilionoides, with notes on male cheliceral apophyses and stridulatory organs in Pholcidae (Araneae).—Acta Zoologica (Stockholm) 76: 291–300.The pholcid spiders Holocnemus pluchei (Scopoli, 1763) and Pholcus opilionoides (Schrank, 1781) are investigated with respect to functional morphology of their genital organs using freeze‐fixation of spiders during copula in liquid nitrogen and subsequent preparation of histological serial sections of the copulatory organs in functional contact. Special attention is paid to the mode of male pedipalpal arrestation before copulation, which is achieved in two quite different ways: in Pholcus by contact of the lateral cheliceral apophysis with the pedipalpal trochanter‐apophysis, in Holocnemus by locking the pedipalpal trochanter between chelicera and pedipalpal coxa. The condition in Pholcus is considered to be apomorphic and to present a synapomorphy of about a dozen genera for which the name “Pholcus‐group” is proposed. The stridulatory apparatus of Holocnemus pluchei is described, its biological significance discussed and an overview of accounts on stridulation in Pholcidae given.

Anti‐predator defences of a web‐building spider, Holocnemus pluchei (Araneae, Pholcidae)

Anti‐predator defence behaviour of Holocnemus pluchei (Araneae, Pholcidae) was studied in the laboratory and the field. Bouncing, in which this web‐building spider moves its body rapidly up and down while keeping its legs on the silk, was the most frequent response to disturbance. Less often, H. pluchei left the web when disturbed. Experiments were carried out to determine the types of stimuli that elicited bouncing and leaving the web: tactile stimulation (striking the spider with a brush) and air movement (blowing on the spider) elicited bouncing and leaving the web, but there was no evidence that chemical stimuli from potential predators were important. Tactile stimulation elicited stronger responses than air movement. There were no evident differences in how H. pluchei responded to tactile stimulation in the laboratory and the field.

Predator‐prey interactions between web‐invading jumping spiders and a web‐building spider, Holocnemus pluchei (Araneae, Pholcidae)

Three species of web‐invading salticid spiders, with different predatory strategies, were tested with Holocnemus pluchei in the laboratory: Portia fimbriata and Portia labiata, which practise aggressive mimicry, and Euyattus sp., which leaps from outside on to spiders in webs but does not practise aggressive mimicry. Portia was shown to be more efficient than Euryattus at catching H. pluchei. Portia fimbriata from Queensland was more consistent at using aggressive mimicry than was Portia labiata and was also more efficient at catching H. pluchei. The web‐invaders that were more efficient at catching H. pluchei were also better able to avoid setting off bouncing, a special defence behaviour used by H. pluchei. An experiment, in which H. pluchei was artificially induced to bounce whenever the predator was near, provided additional evidence that bouncing is effective in defending H. pluchei against web‐invaders.

Costs and benefits of group living for pholcid spiderlings: losing food, saving silk

Holocnemus pluchei (Scopoli) spiderlings may either live alone or share webs with larger conspecifics. Three lines of evidence indicate that group-living spiderlings capture less food than do solitary spiderlings: (1) in field surveys, spiderlings in group webs were seen feeding less often than those living alone; (2) spiderlings in group webs had relatively smaller abdomens than did solitary individuals, indicating that recent foraging success had been poorer; and (3) when prey were introduced into group webs, the largest spider in the web that detected the prey won the prey approximately 77% of the time. In spite of this cost, spiderlings were found in groups more often than expected by chance. This observation may be explained by the high energy cost of constructing solitary webs, as demonstrated by (1) bomb calorimetry and (2) a web-removal experiment, which showed that spiders forced repeatedly to rebuild webs grew more slowly and were smaller than controls. The main benefit of group living is likely to be the reduction of the cost of web building when spiderlings take advantage of webs built by larger conspecifics.