- Nakata, K. (1992) "queenless" Diacamma., Insects and Nature 13-20 (in Japanese)
- Nakata, K. (1995) Age polyethism, idiosyncrasy and behavioural flexibility in the queenless ponerine ant, Diacamma sp. J. Ethol., 13, 117-127
- Nakata, K. (1996) Does behavioural flexibility compensate or constrain colony productivity?- relationship between age structure, labour allocation and production of workers in ant colony - J. Ins. Behav., 9, 557-569
- Nakata, K and Tsuji, K. (1996) The effect of colony size on the conflict over male-production between gamergate and dominant workers in the ponerine ant Diacamma sp.- Ethol., Ecol. & Evol., 8, 147-156
- Tsuji, K, Nakata, K. and Heinze, J. (1996) Lifespan and reproduction in a queenless ant. Naturwissenshaften, 83, 577-578
- Nakata, K. (1996) The difference in behavioural flexibility among task behaviours in a ponerine ant, Diacamma sp. Sociobiology, 27, 119-128
- Nakata, K. (1998) Absence of sex differential brood raising by workers in Diacamma sp. from Japan Behav. Ecol. Sociobiol., 43, 223-227
- Wakano, J., Nakata, K. & Yamamura, N. (1998) Dynamic model of optimal age polyethism in social insects under stable and fluctuating environments J. Theor. Biol., 193, 153-166
- Nakata, K., Tsuji, K., H嗟ldobler, B. & Taki, A. (1998) Sexual calling by workers using the metatibial glands in the ant, Diacamma sp. from Japan J. Ins. Behav., 11, 869-877
- Nakata, K. & Ushimaru, A. (1999) Feeding experience affects web relocation and investment in web threads in an orb-web spider, Cyclosa argenteoalba Anim. Behav., 57, 1251-1255
- Nakata, K. (2000) Stability in worker production and colony size in ant coloniesSociobiology, 35, 441-446
- Nakata, K. (2000) Foraging site selection, In: Miyashita, T. (ed): Biology of Spider, Tokyo Univ. Press, Tokyo, 159-180 (in Japanese)
- Nakajima, M., Nakata, K. and Murakami, O. (2000) Distribution and age structure of the Japanese pond turtle and reeves' pond turtle in a satoyama farm woodland area in Kyotanabe city, Kyoto prefecture, Bulletin of Kansai Organization for Nature Conservation, 22, 91-103 (in Japanese)
- Ushimaru, A. & Nakata, K. (2001) Evolution of flower allometry and its significance for pollination success in the deceptive orchid Pogonia japonica. Int. J. Plant Sci., 162
- Ushimaru, A. & Nakata, K. (2002) The evolution of flower allometry in selfing species. Evol. Ecol. Res., 4, 1217-1227
- Nakata, K. Ushimaru, A. & Watanabe, T. (2003) Using past experience in web relocation decisions enhances the foraging efficiency of the spider Cyclosa argenteoalba J. Ins. Behav., 16, 371-380.
- Nakata, K. & Ushimaru, A. (2004) Difference in web construction behavior at newly occupied web sites between two Cyclosa species Ethology, 110, 397-411
- Ushimaru, A., Kikuchi, S., Yonekura, R., Maruyama, A,. Yanagisawa, N., Kagami, M.,
Nakagawa, M., Kohmatsu, Y., Hatada, A., Kitamura, S., and Nakata, K. (2007) The influence of floral symmetry and pollination systems on flower size variation. Nordic Journal of Botany, 24:593-598
- Ushimaru, A., Watanabe, T., & Nakata, K. (2007) Colored floral organs influence pollinator behavior and pollen transfer in Commelina communis . Amer. J. Bot., 94, 249-258
- Nakata, K. (2007) Prey detection without successful capture affects spider's orb-web construction behaviour. Naturwissenshaften, 94:853-857
- Nakata, K. (2008) Spiders use airborne cues to respond to flying insect predators by building orb-web with fewer silk thread and larger silk decorations. Ethology, 114:677-685
- Mori, Y. & Nakata, K. (2008) Optimal foraging and information gathering: how should animals invest in repeated foraging bouts within the same patch? Evol. Ecol. Res.. 10:823-834
- Nakata, K. (2009) To be or not to be conspicuous: the effects of prey availability and predator risk on spider's web decoration building. Anim. Behav. 78:1255-1260
- Zschokke, S. & Nakata, K. (2010) Spider orientation and hub position in orb-webs. Naturwissenshaften 97:43-52
- Nakata, K. (2010) Attention focusing in a sit-and-wait forager: A spider controls its prey-detection ability in different web sectors by adjusting thread tension. Proc. R. Soc. B 277:29-33
- Nakata, K. & Zschokke, S. (2010) Upside-down spiders build upside-down orb webs - web asymmetry, spider orientation and running speed in Cyclosa. Proc. R. Soc. B 277:3019-3025
- Nakata, K. (2010) Does ontogenetic change in orb-web asymmetry reflect biogenetic law? Naturwissenshaften97:1029-1032
- Nakata, K. (2012) Plasticity in an extended phenotype and reversed up-down asymmetry of spider orb webs Anim. Behav. 83:821-826
- Nakata, K. & Ushimaru, A. (2013) The effect of predation risk on spider's decisions on web-site relocation Behaviour 150:103-114
- Nakata, K. (2013) Spatial learning affects thread tension control in orb-web spiders Biol.Lett. 9:
- Zschokke, S. & Nakata, K. (2015) Vertical asymmetries in orb webs. Biol. J. Linn. Soc. 116: 659-672
- Kondoh, M., Mougi, A., Ushimaru, A. & Nakata, K. (2015) Adaptive movement and food-chain dynamics: towards food-web theory without birth-death processes. Theor. Ecol.
- Takasuka K., Yasui T., Ishigami T., Nakata K., Matsumoto R., Ikeda K. & Maeto K. (2015) Host manipulation by an ichneumonid spider-ectoparasitoid that takes advantage of preprogrammed web-building behaviours for its cocoon protection. J. Exp. Biol. 218:2326-2332
- Nakata, K. & Shigemiya Y. (2015) Body-colour variation in an orb-web spider and its effect on predation success. Biol. J. Linn. Soc. 116:954-963
- Shigemiya Y. & Nakata, K. (2015) Method for rearing the orb-web spider Cyclosa argenteoalba. Acta Arachnol. 64:75-81
- Nakata, K. (2016) Female genital mutilation and monandry in an orb-web spider. Biol.Lett.
- Nakata, K. & Mori, Y. (2016) Cost of complex behaviour and its implications in antipredator defence in orb-web spiders. Anim. Behav.
Nakata, K. (2008) Spiders use airborne cues to respond to flying insect predators by building orb-web with fewer silk thread and larger silk decorations
- Nakata, K. (1995) Age polyethism, idiosyncrasy and behavioural flexibility in the queenless ponerine ant, Diacamma sp.
- Age-related behavioural change of individually marked and known-age workers of a colony of Diacamma sp. was observed through entire ant lives in the laboratory for more than a year. Although typical age polyethism was observed, activity of inside and outside tasks, life span, or time schedule of behavioural change varied considerably among workers. Idiosyncrasies in age-related behavioural change was detected among workers that eclosed on the same day. Cluster analyses revealed that individual patterns of behavioural change tended to be different when eclosion dates were far apart. This suggests that most workers change their behaviour flexibly. Thus, there is little effect of idiosyncrasy on colony response to changes in colony condition.
- Nakata, K. (1996) Does behavioural flexibility compensate or constrain colony productivity?- relationship between age structure, labour allocation and production of workers in ant colony -
- Temporal change in colonial labour allocation, age structure, eclosion of workers and number of brood of colonies of the ponerine ant, Diacamma sp. from Japan were surveyed more than a year.
Batch eclosion occurred in all colonies. Temporal fluctuation of broods indicated that the reason for batch eclosion lay in brood raising, not in cessation of egg supply. Labour allocation pattern at a given moment was connected to the subsequent productivity by multiple linear regression in a colony. Fluctuating eclosion patterns of other colonies were predicted from labour allocation patterns extrapolated from their age structure without considering behavioural flexibility. They fitted with observed patterns considerably. This suggests that behavioural flexibility does not fully compensate the deterioration in productivity caused by the fluctuation in age structure.
- Nakata, K and Tsuji, K. (1996) The effect of colony size on the conflict over male-production between gamergate and dominant workers in the ponerine ant Diacamma sp.-
- Colonies of the queenless ponerine Diacamma sp. have females with three types of functions with respect to reproductive status: a mated worker (gamergate), egg-laying unmated dominant workers, and non-reproductive unmated subordinate workers. In the laboratory, several dominant workers oviposited but most eggs were eaten by the gamergate. However, some eggs, which may have resulted in the production of males, were overlooked and escaped from oophagy by the gamergate.
The colony size of male-producing colonies was larger than that of non-male producing colonies. An increasing difficulty for the gamergate to find worker-laid eggs caused by large colony size appears to be responsible for this phenomenon.
- Nakata, K. (1996) The difference in behavioural flexibility among task behaviours in a ponerine ant, Diacamma sp.
- The temporal change in age structure among workers, the task demand, and the amounts of 6 task behaviors in a colony of the ponerine ant, Diacamma sp. were observed for a year. There are correlations between the number of larvae or cocoons and the amounts of larva caring or cocoon caring, respectively. This seemed to imply that the effect of age structure on the amounts of two behaviors were small because of behavioral flexibility. On the other hand, there are correlations between age structure and the amounts of foraging, social behavior and egg caring. Among these behaviors, behavioral flexibility seemed to stabilize the temporal variation only in egg caring. It is considered that productivity of the colony is mostly influenced by the behaviour which is affected by age structure, because discrepancy between task demand and the number of workers to do the task will occur.
- Nakata, K. (1998) Absence of sex differential brood raising by workers in Diacamma sp. from Japan
- To optimally allocate resources between workers, reproductive females and males, ant workers have to be able to identify the sex of larvae and raise them differently. The ability of workers to discriminate between the sexes in the brood was tested in colonies of queenless ponerine ants, Diacamma sp., from Japan. The ratio of male eggs in the egg pile was increased experimentally. This manipulation resulted in a corresponding increase in the ratio of adult males, suggesting that Diacamma workers do not raise the sexes differently.
- Nakata, K., Tsuji, K., H嗟ldobler, B. & Taki, A. (1998) Sexual calling by workers using the metatibial glands in the ant, Diacamma sp. from Japan
- Several species of the ant genus Diacamma reproduce through mated workers (gamergates). Such gamergates have no wings and therefore are unable of conducting nuptial flight. Instead they perform a sexual calling behavior by standing outside the nest and rubbing the tibiae of their hindleg over the surface of the arched gaster. In a series of exclusion experiments we demonstrate, that secretions from the metatibial gland are the most important component in making the virgin female attractive to the males.
- Nakata, K. & Ushimaru, A. (1999) Feeding experience affects web relocation and investment in web threads in an orb-web spider, Cyclosa argenteoalba
- Orb-web spiders often relocate their webs when they assess a web site as prey-poor. When a spider spins its web at a new site, it may not be able to accurately assess the prey availability at the site on the first day, due to stochastic variation in foraging success, but it is gradually able to make an assessment. Therefore, a spiderﾕs foraging behaviour may change according to how long it has been at its current web site. To test this possibility, a prey removal experiment was conducted using the spider Cyclosa argenteoalba to compare the response to prey deprivation of spiders that were on new sites with that of spiders that had been at a site for several days. Spiders in both groups had a higher relocation rate than the natural rate, but more spiders in the first group relocated their webs. Spiders seem to use previous experience of prey capture at a web site to decide whether to relocate their web. The spiders in the first group have a higher rate of web relocation because of their lack of previous experience of prey.
Observations of web structure revealed that the total thread length was longer on the second day at a new web site than on the first. Spiders are considered to minimise their investment in web threads until they are certain that the web site is prey-rich.
- Nakata, K. (2000) Stability in worker production and colony size in ant colonies
- I examined temporal variation in the number of workers produced daily in ponerine ant colonies of different sizes for one year. While there was no significant relationship between per capita productivity for 21 days and colony size, small colonies exhibited larger temporal variation in per capita productivity. It is thought that variation in the amount of nursing labour produces large temporal variation in the per capita productivity of a small colony, because workers work in parallel with each other.
- Nakata, K. Ushimaru, A. & Watanabe, T. (2003) Using past experience in web relocation decisions enhances the foraging efficiency of the spider Cyclosa argenteoalba
- The purpose of this study is to test whether the integration of past and present foraging experience in web relocation decision enhances foraging efficiency of the spider Cyclosa argenteoalba in its natural environment. We measured daily changes in the prey availability at several fixed sites in a natural environment and constructed a model environment based on these observational data. In the model environment, we simulated the behavior of spiders that foraged and relocated their webs according to several decision rules, which differed in terms of how a spider used its past experience. Results of the simulation revealed that the less past experience is discounted in making web relocation decisions, the more prey the spider is expected to capture. The expected number of web relocation decreased as spider kept past foraging experience longer. These results suggest that C. argenteoalba enhances foraging efficiency by using past foraging experience for long time for the decision of web relocation in its natural environment.
- Nakata, K. & Ushimaru, A. (2004) Difference in web construction behavior at newly occupied web sites between two Cyclosa species
- Animals make decisions based on subjective assessments of their environment. To determine their future foraging activities, animals probably assess food availability from past foraging experiences. Thus, foraging also functions as a way for animals to collect information, with the uncertainty of an assessment decreasing as foraging activity increases. This suggests that different needs for a correct assessment may affect the investment made in foraging activities. Orb-web spiders sometimes relocate their webs and relocation rate differs among species. After web relocation, several spider species have been reported to construct the first webs at newly occupied web sites using less silk than usual, possibly to avoid the risk of an overinvestment at sites where food availability has not been determined. Nevertheless, they may pay a cost, due to inadequate decision-making, if webs constructed with less silk convey less information and increase the uncertainty of an assessment. We expect that stronger site tenacity necessitates a greater requirement for correct assessment of web site and the degree to which spiders reduce the amount of web silk in the first web after web relocation is smaller in species that use the same site longer. To test this hypothesis, we examined web construction in two orb-web spiders, Cyclosa octotuberculata and C. argenteoalba. At the same time we found that these two species exhibit different web-site tenacity, as C. octotuberculata does not relocate its webs as frequently as does C. argenteoalba. After artificially induced web relocation, C. argenteoalba constructed webs that were initially smaller and contained only about 2/3 of the silk in control webs that were constructed at the original site. In contrast, C. octotuberculata did not exhibit such decreases in web size or in the amount of web silk used. This result is consistent with our hypothesis.
- Nakata, K. (2007) Prey detection without successful capture affects spider's orb-web construction behaviour
- Animals obtain information from past foraging experience to adjust their foraging activity according to their environment. The ability of spiders to obtain information from unsuccessful predation experiences was investigated by examining the effects on web building, a significant foraging investment, of prey detection without successful capture in the orb-web spider Cyclosa octotuberculata. Four treatments were employed: 1) successful capture and feeding: one syrphid fly was allowed to be captured and consumed by the spider on the web; 2) single prey-item detection: a syrphid fly was placed on the web to lure the spider, but was removed before capture; 3) five prey-item detection: above prey-item detection stimulus was given five times; and, 4) control: neither prey nor feeding on the web. While control spiders decreased the total thread length and capture area of their webs, prey-item detection spiders in both conditions increased them, indicating that the spider obtained information from unsuccessful predation experience to adjust their foraging investment. The fed spiders exhibited a significantly greater increase than the prey-detection-only spiders, suggesting that prey detection alone and prey detection with consumption had different informational effects. Total thread length did not differ between single and five prey-item detection spiders, but distance between two adjacent sticky spirals increased only in the former spiders, possibly because five times unsuccessful predations prevented spiders to reduce web stickiness. It suggests that the spider changed web morphology according to the number of prey detection.
Orb-web spiders are an important group of trap-building animals that feed upon an array of insect prey, and are themselves the prey of wasps and parasitoid flies. The purpose of this study was to examine whether spiders use airborne vibration cues to respond to these flying insect predators by changing their web-building behavior. While on its web waiting for prey, the orb-web spider Eriophora sagana was exposed to a vibrating tuning fork that emitted an airborne vibration signal when it was on its web waiting for prey. The signal mimicked the approach of flying insect predators, and its effect on the subsequent web-building was examined. No stimulus was provided during web-building. A significant treatment effect was observed with respect to the total thread length and area of the silk decoration (conspicuous white structure attached to the orb-webs of diurnal spiders) of their webs. While control spiders increased the total thread length in their second web, the stimulus group spiders did not, providing the first evidence that orb-web spiders use airborne vibration cues to assess the predation risk and change their foraging activity. It also indicates that spiders remember an encounter with a predator on their webs and use this information later to adjust their web building. My findings imply that spiders devote less effort to foraging (i.e., web building) in response to the presence of their predators, which is considered to reduce their foraging efficiency. In contrast, the stimulus group spiders increased the area of their silk decoration significantly more in their second webs than did the control spiders. This is considered an experimental support for the hypothesis that silk decorations have an anti-predator function.
Nakata, K. (2009) To be or not to be conspicuous: the effects of prey availability and predator risk on spider's web decoration building
Some spiders build conspicuous silk decorations, or stabilimenta, on their orb webs. The decorations are thought to function as visual signals, and there is evidence to support both prey attraction and predator defence hypotheses. This study was designed to test both hypotheses simultaneously in Cyclosa argenteoalba by examining whether spiders change web decorations according to perceived levels of prey availability and predation risk. Spiders built their webs with more thread when prey was experimentally supplied, but with less thread when exposed to the vibrating tuning fork that mimicked the wing beat of flying insect predators. The results indicate that spiders invest more in foraging activity in the presence of available prey, but invest less in response to perceived high levels of predation risk. Web decoration, on the other hand, was only affected by the perceived level of predation risk and not prey availability. Spiders built longer decorations when exposed to the tuning fork vibrations. The results indicate that silk decoration has a predator defence function, but not a prey attraction function in C. argenteoalba. They also suggest that orb web decoration by C. argenteoalba does not involve a trade-off between deterring predators and being avoided by prey.
Nakata, K. (in press) Attention focusing in a sit-and-wait forager: a spider controls its prey-detection ability in different web sectors by adjusting thread tension.
Focusing attention is a way for animals to search for and to obtain food efficiently. This study examines whether a sit-and-wait forager, the orb-web spider Cyclosa octotuberculata, focuses its attention on limited foraging areas. Video records of foraging activity revealed that the spiders detected prey trapped in the west and east sectors of their web less frequently than prey trapped in the north and south sectors. Comparison of photos of the web hub area with and without spiders present revealed that the spiders pulled radii towards the centre when waiting for prey. Radius pulling is stronger in the north and south web sectors than in the west and east sectors, possibly causing more tension in radii running vertically. Experimental manipulation indicated that the spiders responded to prey quicker when thread tension was increased. The results suggest that C. octotuberculata focus their attention on the web areas above and below the spider by adjusting the tension in web threads; and this causes higher prey detection rates in these areas.
Nakata, K. & Zschokke, S. (2010) Upside-down spiders build upside-down orb webs - web asymmetry, spider orientation and running speed in Cyclosa.
Almost all spiders building vertical orb webs face downwards when sitting on the hubs of their webs, and their webs exhibit an up-down size asymmetry, with the lower part of the capture area being larger than the upper. However, spiders of the genus Cyclosa, which all build vertical orb webs, exhibit inter- and intraspecific variation in orientation. In particular, Cyclosa ginnaga and C. argenteoalba always face upwards, and C. octotuberculata always face downwards, whereas some C. confusa face upwards and others face downwards or even sideways. These spiders provide a unique opportunity to examine why most spiders face downwards and have asymmetrical webs. We found that upward-facing spiders had upside-down webs with larger upper parts, downward-facing spiders had normal webs with larger lower parts and sideways-facing spiders had more symmetrical webs. Downward-facing C. confusa spiders were larger than upward- and sideways-facing individuals. We also found that during prey attacks, down- ward-facing spiders ran significantly faster downwards than upwards, which was not the case in upward- facing spiders. These results suggest that the spider’s orientation at the hub and web asymmetry enhance its foraging efficiency by minimizing the time to reach prey trapped in the web.
Nakata, K. (2010) Does ontogenetic change in orb-web asymmetry reflect biogenetic law?
Most orb web spiders face downward on the web hub, and their webs are vertically asymmetrical, that is, the lower part of the web is larger than the upper part and the ratio of the lower part to the whole web area increases as the spider grows. This phenomenon may reflect biogenetic law such that young animals exhibit a general ancestral trait whereas adults exhibit specific and derived traits. An alternative explanation is that vertical asymmetry may arise from the difference in time required by spiders to move up or down the web to capture prey. The present study tested these two hypotheses for Eriophora sagana. Subadults of this species build their webs with reverse asymmetry in that the upper part of the web area is larger than the lower part. In both subadults and adults, the upper proportion decreased with spider weight, and adult spiders built more symmetric webs. These results support the capture time difference hypothesis.
Nakata, K. (2012) Plasticity in an extended phenotype and reversed up-down asymmetry of spider orb webs
Orb webs built by spiders are an extended phenotype, and spiders can modify their morphology when rebuilding them. Internal and external environmental conditions can affect how spiders rebuild. Most spiders that build vertical orb webs wait for prey at the web hub and orient downwards. Moreover, their webs exhibit up-down size asymmetry; specifically, the area below the hub is larger than the area above it. However, some spiders reverse this asymmetry in their webs. To examine the relationship between phenotypic plasticity and web asymmetry reversal and whether spiders elongate their webs upwards in response to prey capture in the upper web, I manipulated prey capture location in two closely related spider species. Cyclosa octotuberculata build webs with typical asymmetry (larger area below the web hub). Cyclosa argenteoalba build webs with reversed asymmetry, a derived phenotype, and wait in a reversed orientation, facing upwards. I found that, when spiders fed in the lower part of the web, both species elongated their webs downwards and that C. argenteoalba webs lost their asymmetry and became symmetrical. In contrast, webs were not elongated in the upward direction when spiders of either species were fed in the upper part of the web. These results provided evidence that the up-down asymmetry of Cyclosa webs is a plastic trait regardless of whether spiders build webs with typical or reversed asymmetry. However, no significant upward elongation of webs indicates that there is no evidence of a relationship between plasticity in the extended phenotype and web asymmetry reversal.
Nakata, K. & Ushimaru, A. (2013) The effect of predation risk on spider's decisions on web-site relocation
Among the costs associated with animal-built structures, the cost of exposure to predators is important, because it affects the survival of builder animals. When predator risk increases, the builder may change the location of a structure or remain on the structure but modify its behaviour. The main purpose of this study was to examine whether builders leave their current structure locations and relocate to a new location upon predator attacks. To assess this, we used orb-web spiders that regularly renew their webs and occasionally relocates their web site upon web-rebuilding. Specifically, adult females of Cyclosa argenteoalba were exposed to the air-borne vibrations from a tuning fork. These vibrations simulate the vibrations from insect predators’ wings and trigger immediate anti-predator responses (jumping off the web to avoid attacks from predators and shaking webs). Spiders that received these simulated predator stimuli relocated more often on the day after treatment than did spiders that were not exposed to predator stimuli. This indicated that spiders estimated future predation risk from their predator-encounter experience and responded to perceived increase in predation risk at current site by abandoning their web site upon web-rebuilding. In addition, we examined whether the frequency of jumping behaviour and web relocation were correlated, but no significant relationship was detected. This result suggests that immediate anti-predator behaviour at the current site and the decision to relocate were independent of each other.
Nakata, K. (2013) Spatial learning affects thread tension control in orb-web spiders
Although it is well known that spatial learning can be important in the biology of predators that actively move around in search for food, comparatively little is known about ways in which spatial learning might function in the strategies of sit-and-wait predators. In this study, Cyclosa octotuberculata, an orb-web spider that uses its legs to contract radial threads of its web to increase thread tension, was trained to capture prey in limited web sectors. After training, spiders that had captured prey in horizontal web sectors applied more tension on radial threads connected to horizontal sectors than spiders that had captured prey in vertical sectors. This result suggests that the effect of experience on C. octotuberculata's behaviour is not expressed in the way the trained spider responds to prey-derived stimuli and is instead expressed in behaviour by which the spider anticipates the likely direction from which prey will arrive in the future. This illustrates that learning can be important even when the predator remains in one location during foraging bouts.
Nakata, K. & Shigemiya Y. (2015) Body-colour variation in an orb-web spider and its effect on predation success.
Animal body coloration serves several functions such as thermoregulation, camouflage, aposematism, and intraspecific communication. In some orb-web spiders, bright and conspicuous body colours are used to attract prey. On the other hand, there are other species whose body colour does not attract prey. Using a spider species showing individual body-colour variation, the present study aimed to determine whether or not the variation in body colour shows a correlation with predation rates. We studied the orb-web spider (Cyclosa argenteoalba) using both field observations and T-maze experiments, in which the prey were exposed to differently coloured spiders. Cyclosa argenteoalba has silver- and black-coloured areas on its dorsal abdomen, with the ratio of these two colours varying continuously among individuals. The bright and conspicuous silver area reflects ultraviolet light. Results of both field observations and colour choice experiments using Drosophila flies as prey showed that darker spiders have a greater chance of capturing prey than silver spiders. This indicates that body-colour variation affects predation success among individuals and that the bright silver colour does not function to attract prey in C. argenteoalba.
Nakata, K. (2016) Female genital mutilation and monandry in an orb-web spider.
Monandry, in which a female has only one mating partner during the repro- ductive period, is established when a female spontaneously refrains from re-mating, or when a partner male interferes with the attempts of a female to mate again. In the latter case, however, females often have countermeasures against males, which may explain why polyandry is ubiquitous. Here, I demon- strate that the genital appendage, or scape, of the female orb-web spider (Cyclosa argenteoalba) is injured after her first mating, possibly by her first male partner. This female genital mutilation (FGM) permanently precludes copulation, and females appear to have no countermeasures. FGM is con- sidered to confer a strong advantage to males in sexual conflicts over the number of female matings, and it may widely occur in spiders.
Nakata, K. & Mori, Y. (2016) Cost of complex behaviour and its implications in antipredator defence in orb-web spiders.
Complex behaviour may incur a cost. We assumed here that web-building behaviour for two species of orb-web spider, Cyclosa argenteoalba and Eriophora sagana, was more complex when their webs were asymmetric from top to bottom than when their webs were symmetric. The rationale for this assumption was that, while spiders have to adjust their spiral building behaviour in different web sectors to build asymmetric webs, they do not have to make these adjustments for symmetric webs. To estimate the costs involved in building more asymmetric webs, we measured the time taken for spiders to build orb-webs with various up-down size asymmetries and used this as a measure of the complexity of web-building behaviour. The results showed that the spiders required more time to lay the spiral threads as their webs became more asymmetric even when the length of spiral threads was the same, suggesting a time cost of processing complex information. Furthermore, we found that spiders built more symmetric webs when they perceived a risk of predation, perhaps to reduce the web-building time during which they are more vulnerable. This suggests that the cost of behavioural complexity may mediate the outcome of interspecific interactions and thus may be ecologically important.