Social tolerance in Octopus laqueus—A maximum entropy model

Octopus laqueus is a small tropical octopus found in Okinawa, Japan and the greater Indo-Pacific. Octopus are often viewed as solitary animals but O. laqueus live in close proximity in the wild, and will potentially encounter one another on a regular basis, raising the possibility of social tolerance. Adopting shared den occupancy in aquaria as a potential measure of social tolerance in O. laqueus, we studied the animals’ preference for shared dens over solitude. We characterized dependence of sharing preference on sex, den availability and den occupancy density. We designed two simple social tolerance assays in aquaria with a total of 45 daily measurements: (i) Pots Equal, with equal numbers of octopuses and dens and (ii) Pots Limited, with a 3:1 ratio of octopuses to dens. We found that O. laqueus will socially tolerate other individuals by sharing tanks and dens and with typically no loss to cannibalism or escape. However, animals also exhibit significant levels of social repulsion, and individuals often chose a solitary den when given the option. The patterns of den occupancy are observed to be consistent with a maximum entropy model that balances seeking shelter against avoiding other animals. The model accurately captures and predicts the data and can be generalized to other organisms and their social interactions. Overall, in O. laqueus the preference for a den is stronger than the preference to be solitary. The animals are tolerant of others with a mixture of sizes in the tank and even in a den, a reported first for octopuses outside mating. The relaxed disposition and social tolerance of O. laqueus make it a promising species to work with in the lab to explore social and potentially other behaviors in octopuses

The 2006 November outburst of EG Aquarii: the SU UMa nature revealed

We report time-resolved CCD photometry of the cataclysmic variable EG Aquarii during the 2006 November outburst During the outburst, superhumps were unambiguously detected with a mean period of 0.078828(6) days, firstly classifying the object as an SU UMa-type dwarf nova. It also turned out that the outburst contained a precursor. At the end of the precursor, immature profiles of humps were observed. By a phase analysis of these humps, we interpreted the features as superhumps. This is the second example that the superhumps were shown during a precursor. Near the maximum stage of the outburst, we discovered an abrupt shift of the superhump period by ${\sim}$ 0.002 days. After the supermaximum, the superhump period decreased at the rate of $\dot{P}/P$=$-8.2{\times}10^{-5}$, which is typical for SU UMa-type dwarf novae. Although the outburst light curve was characteristic of SU UMa-type dwarf novae, long-term monitoring of the variable shows no outbursts over the past decade. We note on the basic properties of long period and inactive SU UMa-type dwarf novae.Comment: 9 pages, 7 figures, accepted for PAS

Survey of Period Variations of Superhumps in SU UMa-Type Dwarf Novae. II: The Second Year (2009-2010)

As an extension of the project in Kato et al. (2009, arXiv:0905.1757), we collected times of superhump maxima for 61 SU UMa-type dwarf novae mainly observed during the 2009-2010 season. The newly obtained data confirmed the basic findings reported in Kato et al. (2009): the presence of stages A-C, as well as the predominance of positive period derivatives during stage B in systems with superhump periods shorter than 0.07 d. There was a systematic difference in period derivatives for systems with superhump periods longer than 0.075 d between this study and Kato et al. (2009). We suggest that this difference is possibly caused by the relative lack of frequently outbursting SU UMa-type dwarf novae in this period regime in the present study. We recorded a strong beat phenomenon during the 2009 superoutburst of IY UMa. The close correlation between the beat period and superhump period suggests that the changing angular velocity of the apsidal motion of the elliptical disk is responsible for the variation of superhump periods. We also described three new WZ Sge-type objects with established early superhumps and one with likely early superhumps. We also suggest that two systems, VX For and EL UMa, are WZ Sge-type dwarf novae with multiple rebrightenings. The O-C variation in OT J213806.6+261957 suggests that the frequent absence of rebrightenings in very short-Porb objects can be a result of sustained superoutburst plateau at the epoch when usual SU UMa-type dwarf novae return to quiescence preceding a rebrightening. We also present a formulation for a variety of Bayesian extension to traditional period analyses.Comment: 63 pages, 77 figures, 1 appendix, Accepted for publication in PASJ, data correctio

Observations of schooling behaviour in the oval squid Sepioteuthis lessoniana in coastal waters of Okinawa Island

The schooling behaviour of the oval squid Sepioteuthis lessoniana was observed over 4 summers at 3 observation sites in the coastal waters of Okinawa Island, Ryukyu Archipelago, Japan. During this field study, 3 static appearances (belt, ball and sheet shape) and 2 transitional appearances (high and low density) were noted, recorded and described. In addition to formations, a member of S. lessoniana schools also displayed particular and repeated behavioural patterns such as vanguard and intimidating display. The 3 observation sites were tropical coral reefs near the coastline at a depth of 1 to 15 m on an average. All participating observers snorkelled and were equipped with various underwater digital video and photographic cameras. The schools observed consisted of 8 to over 100 members with a wide range of body sizes. Despite these biological and locational differences, both static and transitional appearances were consistently observed with equally consistent individual behavioural patterns. There have been studies on related species, Sepioteuthis sepioidea, at the San Blas Islands along the Caribbean coast of eastern Panama, and the same species, S. lessoniana, at a different geographical location, Casuarina Beach on Lizard Island, Australia. The findings of this study are consistent with those reported previously, with some notable differences

Nonfunctioning Juxtaglomerular Cell Tumor

The juxtaglomerular cell tumor (JGCT) is a rare renal tumor characterized by excessive renin secretion causing intractable hypertension and hypokalemia. However, asymptomatic nonfunctioning JGCT is extremely rare. Here, we report a case of nonfunctioning JGCT in a 31-year-old woman. The patient presented with a left renal tumor without hypertension or hypokalemia. Under a clinical diagnosis of renal cell carcinoma, radical nephrectomy was performed. The tumor was located in the middle portion adjacent to the renal pelvis, measuring 2 cm in size. Pathologically, the tumor was composed of cuboidal cells forming a solid arrangement, immunohistochemically positive for renin. Based on these findings, the tumor was diagnosed as JGCT. In cases with hyperreninism, preoperative diagnosis of JGCT is straightforward but difficult in nonfunctioning case. Generally, JGCT presents a benign biological behavior. Therefore, we should take nonfunctioning JGCT into the differential diagnoses for renal tumors, especially in younger patients to avoid excessive surgery