Biomechanical properties of fishing lines of the glowworm Arachnocampa luminosa (Diptera; Keroplatidae).

Animals use adhesive secretions in highly diverse ways, such as for settlement, egg anchorage, mating, active or passive defence, etc. One of the most interesting functions is the use of bioadhesives to capture prey, as the bonding has to be performed within milliseconds and often under unfavourable conditions. While much is understood about the adhesive and biomechanical properties of the threads of other hunters such as spiders, barely anything is documented about those of the New Zealand glowworm Arachnocampa luminosa. We analysed tensile properties of the fishing lines of the New Zealand glowworm Arachnocampa luminosa under natural and dry conditions and measured their adhesion energy to different surfaces. The capture system of A. luminosa is highly adapted to the prevailing conditions (13-15 °C, relative humidity of 98%) whereby the wet fishing lines only show a bonding ability at high relative humidity (>80%) with a mean adhesive energy from 20-45 N/m and a stronger adhesion to polar surfaces. Wet threads show a slightly higher breaking strain value than dried threads, whereas the tensile strength of wet threads was much lower. The analyses show that breaking stress and strain values in Arachnocampa luminosa were very low in comparison to related Arachnocampa species and spider silk threads but exhibit much higher adhesion energy values. While the mechanical differences between the threads of various Arachnocampa species might be consequence of the different sampling and handling of the threads prior to the tests, differences to spiders could be explained by habitat differences and differences in the material ultrastructure. Orb web spiders produce viscid silk consisting of ß-pleated sheets, whereas Arachnocampa has cross-ß-sheet crystallites within its silk. As a functional explanation, the low tear strength for A. luminosa comprises a safety mechanism and ensures the entire nest is not pulled down by prey which is too heavy.

Characterization of the Fishing Lines in Titiwai (=Arachnocampa luminosa Skuse, 1890) from New Zealand and Australia.

Animals use adhesive secretions in a plethora of ways, either for attachment, egg anchorage, mating or as either active or passive defence. The most interesting function, however, is the use of adhesive threads to capture prey, as the bonding must be performed within milliseconds and under unsuitable conditions (movement of prey, variable environmental conditions, unfavourable attack angle, etc.) to be nonetheless successful. In the following study a detailed characterization of the prey capture system of the world-renowned glowworm group Arachnocampa from the macroscopic to the ultrastructural level is performed. The data reveal that the adhesive droplets consist mostly of water and display hygroscopic properties at varying humidity levels. The droplet core of Arachnocampa luminosa includes a certain amount of the elements sodium, sulphur and potassium (beside carbon, oxygen and nitrogen), while a different element composition is found in the two related species A. richardsae and A. tasmaniensis. Evidence for lipids, carbohydrates and proteins was negative on the histochemical level, however X-ray photoelectron spectroscopy confirm the presence of peptides within the droplet content. Different to earlier assumptions, the present study indicates that rather than oxalic acid, urea or uric acid are present in the adhesive droplets, presumably originating from the gut. Comparing the capture system in Arachnocampa with those of orb-spiders, large differences appear not only regarding the silky threads, but also, in the composition, hygroscopic properties and size of the mucous droplets.

Geographic parthenogenesis and the common tea-tree stick insect of New Zealand.

Worldwide, parthenogenetic reproduction has evolved many times in the stick insects (Phasmatidae). Many parthenogenetic stick insects show the distribution pattern known as geographic parthenogenesis, in that they occupy habitats that are at higher altitude or latitude compared with their sexual relatives. Although it is often assumed that, in the short term, parthenogenetic populations will have a reproductive advantage over sexual populations; this is not necessarily the case. We present data on the distribution and evolutionary relationships of sexual and asexual populations of the New Zealand stick insect, Clitarchus hookeri. Males are common in the northern half of the species' range but rare or absent elsewhere, and we found that most C. hookeri from putative-parthenogenetic populations share a common ancestor. Female stick insects from bisexual populations of Clitarchus hookeri are capable of parthenogenetic reproduction, but those insects from putative-parthenogenetic populations produced few offspring via sexual reproduction when males were available. We found similar fertility (hatching success) in mated and virgin females. Mated females produce equal numbers of male and female offspring, with most hatching about 9-16 weeks after laying. In contrast, most eggs from unmated females took longer to hatch (21-23 weeks), and most offspring were female. It appears that all C. hookeri females are capable of parthenogenetic reproduction, and thus could benefit from the numerical advantage this yields. Nevertheless, our phylogeographic evidence shows that the majority of all-female populations over a wide geographic area originate from a single loss of sexual reproduction.

Sexual reconviction rates in the United Kingdom and actuarial risk estimates.

OBJECTIVE: Assessing the risk of further offending behavior by adult sexual perpetrators of children is highly relevant and important to professionals involved in child protection. Recent progress in assessing risk in sexual offenders has established the validity of actuarial measures, although there continues to be some debate about the application of these instruments. This paper summarizes the debate between clinical and actuarial approaches and reviews the "base rate" for United Kingdom sexual offense reconviction. METHOD: A review of the literature revealed 16 UK sexual reconviction studies, 8 using incarcerated samples (N=5,915) and 8 using non-incarcerated samples (N=1,274). UK estimates of sexual reconviction rates are compared with European and North American studies. RESULTS: The mean sexual reconviction rates for the incarcerated sample at 2 years (6.0%), 4 years (7.8%) and 6 years or more (19.5%) were higher than that of the comparative non-incarcerated sample at 2 years (5.7%), up to 4 years (5.9%), and 6 years or more (15.5%). The overall sexual reconviction rate for both samples combined was 5.8% at 2 years, and 17.5% at 6 years or more. CONCLUSIONS: The sexual reconviction rate for incarcerated sexual offenders is higher than that of non-incarcerated sexual offenders. The UK sexual reconviction rates were comparable with European and North American studies.

Treating sexual offenders with learning disabilities in the community: a critical review.

This study offers a critical review of a treatment group for sexual offenders with learning disabilities. The participants were diverted from criminal proceedings due to their level of cognitive functioning and attended a 7-month treatment program comprising of four main components: sex education, cognitive distortions, offending cycle, and relapse prevention. A number of psychometric assessments were administered immediately before and after intervention. Although no significant differences were found in attitudes toward sexual offending following treatment, the trend was for improvements in sex knowledge and honesty of sexual interest. Improvements in socialization skills (leisure time and interpersonal skills) were significant. No further incidents of sexual offending have been reported during a 12-month follow-up. A number of explanations for the nonsignificant improvement in attitudes are considered and recommendations for future treatment evaluation studies are made. The development of specific questionnaires and treatment programs for sexual offenders with learning disabilities is discussed.

Differences in personality and risk characteristics in sex, violent and general offenders.

BACKGROUND: Studies examining the characteristics of sex and violent offenders have found differences in personality and offence characteristics. However, none of these studies has examined differences in personality characteristics between violent, sex and general offenders using the Special Hospitals Assessment of Personality and Socialization (SHAPS). METHOD: Using a retrospective archival research design, data on 153 male offenders were divided into three groups, sexual (n = 85), violent (n = 46) and general offenders (n = 22). Of the sample 139 offenders had completed the SHAPS. The Sexual Violence Risk-20 (SVR-20) measure was used to categorize levels of risk. Reconviction data collected over a 10-year follow-up period were analysed using the receiver operating characteristic analysis. RESULTS: Violent offenders had significantly more chaotic lifestyles, displayed greater psychopathology than sex or general offenders, and were most likely to reoffend, with over a quarter committing further violent offences. The sexual offender group share more in common with the general offenders, in terms of personality characteristics and recidivism rates, than with the violent offenders. More of the violent offenders were categorized as at medium or high risk of recidivism than any other group. The SVR-20 significantly predicted any reconviction over five- and 10- year follow-up periods. DISCUSSION: The results from this study support the use of self-report inventories in assessing differences between offender groups. Such information may assist clinicians in prioritizing management and intervention strategies for those offenders, and in turn lower the risk of further offending.

Comparing sex offender risk assessment measures on a UK sample.

The purpose of this study on 139 sex offenders was to consider the application of six measures of risk: Static-99, SACJ-Min (Structured Anchored Clinical Judgment Scale-Minimum), RRASOR (Rapid Risk Assessment for Sexual Offence Recidivism), Risk Matrix 2000-Sexual/Violent, and SVR-20 (Sexual Violence Risk-20) and to compare risk assessments conducted by a Regional Secure Unit (RSU) and the Probation Service. Levels of risk for the RSU sample ranged from 1% to 42% low risk to 1% to 66% high risk compared with the Probation sample of 8% to 43% low risk to 4% to 70% high risk. Offenders with adult victims obtained significantly higher scores using the RM2000/S and SACJ-Min than did those with child victims who obtained significantly higher scores on the RRASOR. Sex offenders referred to a RSU scored significantly higher on RRASOR and RM2000/S than did sex offenders supervised by the Probation Service. Forensic practitioners may be better served if risk measures assess specific subcategories of sexual offenders.