Lennart Edsman

The aims of the present study were (1) to examine if feeding condition prior to mating influences male hormone levels and behavior, (2) to evaluate the effect of age on male hormone levels, (3) to examine a possible association between male social display activity and four steroid hormones (testosterone, dihydrotestosterone, estrogen, and corticosterone), and (4) to examine if female behavior influences male hormone levels. Thirty male and fifteen female mallards were used in this study. Observations were made on a mixed flock of mallards for 10 consecutive days in autumn. Five weeks before the observations, males were randomly assigned to a feeding regime with either an unlimited food supply (UL group) or a limited food supply (L group). Males in the UL group showed significantly greater social display activity compared to the L group males. Females never incited (courted) males from the L group. Dihydrotestosterone levels were significantly higher in males showing social display activity as compared to males not showing these behavior patterns. Testosterone levels were significantly higher in males incited by females compared to males not incited by females.

Recruitment is a vital factor in the assessment, management and population dynamics of decapods. Since the juvenile stages of crayfish often prefer heterogeneous habitats, sampling with quantitative and reproducible methods have so far been challenging. We evaluate a new quantitative sampling method for juvenile crayfish; the enclosure trap. A field test was carried out during two consecutive years on a population of signal crayfish, Pacifastacus leniusculus, in littoral areas of Swedish Lake Erken. The densities of 0+ crayfish varied substantially with year, sampling date and substrate type. As expected, juvenile crayfish densities decreased over time in both study years, indicating a high mortality rate during their first year of life. Juveniles preferred gravel and stone over soft and sand substrates. Mean growth rate varied from 0.15 to 0.22 mm day-1. We evaluate this method and present recommendations for how to design and optimize field studies using enclosure traps. We conclu...

ABSTRACT Invasive crayfish have attracted much attention by scientists and policy makers in Europe, partly due to their ability to transmit diseases to native crayfish species. In December 2012, 13 specimens of a new crayfish species were found in the River Märstaån in central Sweden. Mitochondrial DNA analyses identified them as Marmorkrebs Procambarus fallax f. virginalis. It is not known if Marmorkrebs can establish reproducing populations in Sweden, and knowledge of how different stressors negatively affect the eventual reproduction of Marmorkrebs is lacking. Since the parthenogenetic Marmorkrebs has potential to become an invasive species in Sweden and Scandinavia, it may pose a serious threat to native crayfish, fish and fisheries. Swedish authorities have produced an action plan with a national strategy in order to establish a system that manages the import, movement and release of alien species and genotypes. The River Märstaån leads to Lake Mälaren, without barriers, which enhances the risk that the crayfish will also invade the lake. Due to the potential threat of further spread, it is imperative to make an action plan with a risk assessment targeted specifically towards the Marmorkrebs in River Märstaån.

The introduction of non-native crayfish in aquatic ecosystems is very common due to human activities (e.g. aquaculture, recreational and commercial fisheries). The signal crayfish, Pacifastacus leniusculus (Dana, 1852), is one of the most widespread invasive species in Europe. Although several important ecological and economic impacts of this species have been reported, its European population genetic characterisation has never been undertaken using nuclear markers. Thus, the aim of this study was to develop and characterise new microsatellite markers for signal crayfish that can be useful in future studies in its invaded range, since only five are available so far. In total, 93 individuals from four geographically distinct European populations (Portugal, Great Britain, Finland and Sweden) were scored for the new markers and for those previously described, with the Bayesian analysis revealing a clear distinction among populations. These markers are suitable for future studies of the...

Noble crayfish Astacus astacus is threatened in Europe due to invasive crayfish carrying the crayfish plague agent Aphanomyces astaci. Norway is among the last countries in which the introduction of non-indigenous crayfish has been limited through strict legislation practices. However, North American signal crayfish Pacifastacus leniusculus were recently discovered in a water-course that has been repeatedly hit by the plague. We mapped the distribution and relative density (catch per unit effort) of signal crayfish within this lake, and performed agent-specific real-time PCR to estimate the prevalence of A. astaci in the population. The resulting length frequencies and relative density estimates clearly demonstrate a well-established signal crayfish population, in which 86.4% of the analysed individuals were confirmed carriers. The success of detection was significantly higher (84.1%) in the crayfish tailfan (i.e. uropods) than in the soft abdominal cuticle (38.4%), which is commonly used in prevalence studies. We therefore propose tailfan (uropods and telson) as the preferred tissue for studying A. astaci prevalence in signal crayfish populations. The likelihood of detecting an A. astaci-positive signal crayfish increased significantly with increasing crayfish length. Further, large female crayfish expressed significantly higher PCR-forming units values than large males. In surveys primarily exploring the presence of A. astaci-positive individuals in a population, large females should be selected for molecular analyses. Our study demonstrates that a potent crayfish plague infection reservoir, evidently originating from the illegal human introduction of signal crayfish, has permanently been established in Norway.

1. In ecological studies on freshwater crayfish, determination of basic population parameters is often complicated by the lack of a suitable age estimation method. 2. Previously, lipofuscin age pigment in the olfactory lobe cell masses (OLCM) of short-lived tropical crayfish has ...