Michio Imafuku

Sexual discrimination in the hermit crabPagurus geminus

Factors concerning sexual discrimination and related sensory receptors were investigated on the hermit crabPagurus geminus. In the breeding season, male crabs of this species were observed to hold receptive females but to reject males. By using this behavior, it was examined whether males on which some operation on the sensory receptors was performed could discriminate between presented male of female crabs. Test males could not discriminate sexes of the presented crabs only when antennules were removed bilaterally. On the other hand, intact test males reacted positively to an empty shell from which “female water” exuded after passing through the chamber containing females. Thus, the factor by which the hermit crab discriminates sexes was indicated to be a water-borne chemical and that the sensory receptor related to sex-discrimination appeared to exist on the antennules. Discussions are made with respect to predicted substances taking part in sexual discrimination of this hermit crab.

Territorial Behavior of a Green Hairstreak Chrysozephyrus smaragdinus (Lepidoptera: Lycaenidae): Site Tenacity and Wars of Attrition

Abstract Males of Chrysozephyrus smaragdinus were active from late morning to late afternoon, during which they showed territorial behavior, perhaps for mating. The territorial male stayed in a particular area and occasionally flew around it, referred to hereafter as the inspection area. When other male intruded into this area, the territorial male rushed to him. Then, they engaged in a circling flight regarded as a “war of attrition”. During this flight, the two males sometimes strayed far away from the territory. After the circling flight, the resident returned to his territory in almost all cases (98%). Despite such intrusions, many residents defended their territory for several successive days. This suggests strongly the “effect of prior residence”. We recorded the circling flights with a high-speed video camera, and confirmed that the male that ceased the circling flight first was the loser. This finding gave some validity to consider circling flight as wars of attrition. In a few cases, the territorial male mated with a female that came to the territory. These once mated males held the territory no longer, suggesting that mating experience should restrict the next mating opportunity in this species.

Wing Colors of Chrysozephyrus Butterflies (Lepidoptera;Lycaenidae): Ultraviolet Reflection by Males

Wing colors of the four species of Chrysozephyrus butterflies were analyzed by a spectrophotometer. As the dorsal wing surface of males showed a strong reflectance when the specimen was tilted, measurements were made by the tilting method. The dorsal wing surface of males which appears green to the human eye reflected UV (315–350 nm) as well as green light (530–550 nm). The reflectance rate of UV to visible green light varied among species with a higher rate for C. hisamatsusanus and C. ataxus, and a lower rate for C. smaragdinus and C. brillantinus. The peak wavelength and the peak height did not shift when the specimen was exposed to direct sunlight at least for 16 hr. Artificial removal of scales by scratching the wing surface decreased reflectance. Blue marks on the forewings of C. brillantinus, C. hisamatsusanus and C. ataxus females reflected UV to visible light of short wavelength, and orange marks on the dorsal surface of the forewing and the ventral surface of the hindwing of C. samaragdinus females showed a higher reflectance at longer wavelengths.

Activity Rhythm of Drosophila Kept in Complete Darkness for 1300 Generations

Locomotor activity rhythms of dark stock flies of Drosophila melanogaster kept in complete darkness for 700 to 1340 generations were examined. The stock was established by the late Prof. S. Mori in November 1954 to investigate long-term effects of darkness on organisms. The activity of flies was recorded under three types of light conditions: DD after LD12:12, and DD after exposure to a 3.5 h (P3) or 7.5 h (P7) light pulse. In all of these conditions, the experimental dark flies exhibited clear circadian rhythms similar to those of control light flies. We compare our results with those of various studies on troglobites.

BEHAVIOUR AND MORPHOLOGY OF PAGURID HERMIT CRABS (DECAPODA, ANOMURA) THAT LIVE IN TUSK SHELLS (MOLLUSCA, SCAPHOPODA)

Behaviour and morphology of the hermit crab, Pagurus imafukui, which occupies tusk shells in nature, were investigated. A positive correlation was found between the shield length of the crab and the width of the tusk shell. The uropods were nearly symmetrical, with an average asymmetry index of 0.04, such in contrast with a value of 0.28 for Pagurus filholi, that naturally occupies dextral shells. P. imafukui showed a weak preference for tusk shells over dextral shells. The crabs walked in a parallel pattern, while they adopted a cross pattern when forced to enter dextral shells or were in a shell-less condition. On the contrary, P. filholi individuals walked in a cross pattern when in a tusk shell as well as in a dextral shell. Behaviours of shell entering, copulation, and zoeal release as seen in P. imafukui, are similar to the conditions observed in other species. Nearly symmetrical uropods, preference for non-spiral shells, and the walking style comprising a parallel pattern, are thought to be specific to this hermit crab that lives in non-spiral dwellings. Verhalten und Morphologie des Einsiedlerkrebses Pagurus imafukui McLaughlin & Konishi, 1994 der Scaphopoden-Schalen bewohnt, wurden untersucht. Es wurde eine positive Korrelation zwischen Carapaxlange des Krebses und Breite der Scaphopoden-Schale gefunden. Die Uropoden sind fast symmetrisch. Der Medianwert des Asymmetrie-Indexes betragt 0,04 in deutlichem Gegensatz zu dem von 0,28 bei Pagurus filholi De Man, 1887, der rechtsgewundene Schalen bewohnt. P. imafukui zeigte eine schwache Bevorzugung von Scaphopoden-Schalen im Vergleich mit rechtsgewundenen Schalen. Die Gangart der Einsiedler ist parallel, aber uber Kreuz in schalenlosem Zustand oder in rechtsgewundener Schale. Von P. filholi wird sowohl in Scaphopoden-Schalen als auch in rechtsgewundenen Schalen nur letztere Gangart benutzt. Das Verhalten bei der Inbesitznahme der Schale, bei der Begattung und dem Entlassen der Zoeen gleicht dem bei anderen Arten. Fast symmetrische Uropoden, Bevorzugung ungewundener Schalen und die parallele Gangart werden als Besonderheiten dieser Einsiedler-Art betrachtet, die ungewundene Gehause bewohnt.

New shell acquisition in the hermit crab,Pagurus geminus

The process of how the hermit crab,Pagurus geminus, acquires a new shell was investigated in the natural habitat at Ezura in Shirahama, Wakayama Prefecture, during the non-breeding season, and the following results were obtained. Hermit crabs acquired new shells most frequently by shell exchange between 2 individuals and occasionally by attacking snails. Acquisition through location of empty shells was not found. At the snail attacking site or the site of shell exchange attempts, sometimes many other individuals appeared and, frequently, confusing or complex shell changes were observed. The importance of introduction of fresh shells to a hermit crab population and the possibility for a certain individual to acquire a shell introduced by others through shell exchange attempts are discussed.

Behavioral Batesian mimicry involving intraspecific polymorphism in the butterfly Papilio polytes.

Batesian mimics gain protection from predation by their similarity to distasteful models. In butterflies, it has been thought that distasteful species and Batesian mimics fly slowly and in a straight line, but few studies have demonstrated their behavioral similarity, and no studies have been conducted on behavioral mimicry Involving Batesian intraspecific polymorphism. Here, we compared the wing stroke among various butterflies: palatable non-mimetic Papilio xuthus, unpalatable Pachliopta aristolochiae, and palatable polymorphic Papilio polytes (cyrus form, non-mimetic females; polytes form, Batesian mimetic females) to clarify whether the wing stroke of unpalatable butterflies is different from that of palatable species, whether that of the non-mimetic females of Pap. polytes is different from the mimetic females, and whether that of the mimetic females resembles that of the model. We found that the minimum positional angle ( min) of Pach. aristolochiae and mimetic females of Pap. polytes was significantly larger than that of Pap. xuthus and non-mimetic females. We did not detect significant differences between that of Pach. aristolochiae and mimetic females of Pap. polytes. These results show that min differed between the mimicry group and palatable butterflies. In addition, the wingbeat frequency (WBF) of Pach. aristolochiae and mimetic females tended to differ from that of Pap. xuthus and non-mimetic females. This result suggests that there may be convergence of WBF in Batesian mimicry groups, as in the case of Müllerian mimicry groups, and serves as the first evidence of behavioral mimicry in Batesian intraspecific polymorphism.

Behavioural mimicry in flight path of Batesian intraspecific polymorphic butterfly Papilio polytes

Batesian mimics that show similar coloration to unpalatable models gain a fitness advantage of reduced predation. Beyond physical similarity, mimics often exhibit behaviour similar to their models, further enhancing their protection against predation by mimicking not only the models physical appearance but also activity. In butterflies, there is a strong correlation between palatability and flight velocity, but there is only weak correlation between palatability and flight path. Little is known about how Batesian mimics fly. Here, we explored the flight behaviour of four butterfly species/morphs: unpalatable model Pachliopta aristolochiae, mimetic and non-mimetic females of female-limited mimic Papilio polytes, and palatable control Papilio xuthus. We demonstrated that the directional change (DC) generated by wingbeats and the standard deviation of directional change (SDDC) of mimetic females and their models were smaller than those of non-mimetic females and palatable controls. Furthermore, we found no significant difference in flight velocity among all species/morphs. By showing that DC and SDDC of mimetic females resemble those of models, we provide the first evidence for the existence of behavioural mimicry in flight path by a Batesian mimic butterfly.

Wing colors based on arrangement of the multilayer structure of wing scales in lycaenid butterflies (Insecta: Lepidoptera)

Male wing colors and wing scale morphology were examined for three species of lycaenid butterflies: Chrysozephyrus ataxus, Favonius cognatus and F. jezoensis. Measurement of spectral reflectance on the wing surface with a spectrophotometer revealed species‐specific reflection spectra, with one or two peaks in the ultraviolet and/or green ranges. Observations of wing scales using an optical microscope revealed that light was reflected from the inter‐ridge regions, where transmission electron microscopy revealed a multilayer structure. Based on the multilayer dimensions obtained, three models were devised and compared to explain the measured reflectance spectrum. The results showed that the best fit is a model in which thicknesses of thin films of the multilayer system are not constant and air spaces between cuticle layers are more or less packed with cuticle spacers. This suggests that the specific wing colors of the species examined are produced by the species‐specific arrangement of the multilayer structure of wing scales.

Quality of shells occupied by the hermit crabPagurus geminus: How many hermit crabs are satisfied with their shells?

The rate of changing shells in the hermit crabPagurus geminus was investigated to determine how many hermit crabs are satisfied with their shells. Animal collected from the coast of Oya, Tanabe, Wakayama Prefecture, were presented with fresh gastropod shells newly made by removing the soft parts. Approximately 80% of the hermit crabs changed from their original shells acquired in the natural habitat into fresh shells experimentally given to them and, thus, were regarded as dissatisfied with the shells possessed in the natural habitat. This condition was thought to lead to the fact that hermit crabs occasionally attempted to exchange shells between 2 individuals and even to attack living snails in the natural habitat.