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Mate choice is often assumed to be a prerogative of females because of their putatively larger reproductive investment than males. However, recent evidence suggests that spermatogenesis is far from being limitless and that males show a high selectivity towards their mates, thus maximizing their reproductive success. We investigated mutual mate choice in the crayfish Procambarus clarkii through two experiments. The first experiment explored the effects of body size, chelar size and chelar symmetry and social status of a potential partner. In the second experiment, we asked whether this species can discriminate between partners of the same body size but with different mating status. We used a binary choice test paradigm, in which two ‘targets’ with opposing characteristics were simultaneously presented to a test animal, the ‘chooser’. The results showed that P. clarkii males are more selective than expected. Similar to the other sex, they were significantly attracted by targets with large body sizes, but not by individuals with larger and symmetric chelae or with a dominant status. An inter-sexual difference was found in the second experiment, in which only males seemed to select virgin potential mates. The several adaptive explanations for these preferences, still under debate, are finally discussed. [ABSTRACT FROM AUTHOR]

Since the nineteenth century, the mud snail Potamopyrgus antipodarum (Gray 1843), native to New Zealand, has been introduced into several European countries, Italy included. As a first step to contain its spread and establishment, it seems necessary to understand the characteristics of the environment that are more favourable for this species' invasion. To this aim, we analysed a number of physico-chemical and biotic parameters of four streams, two invaded and two not yet invaded, in the National Park of the Foreste Casentinesi, Monte Falterona, Campigna (Central Italy), where the species was first recorded in 2008. The two categories of streams, invaded and non-invaded, differ in only three of the 20 analysed characteristics of the habitat; that is, availability of crevices, width stream, and maximum water depth. This suggests that, despite P. antipodarum's documented tolerance to pollution, the high-quality waters of the park are highly susceptible to its invasion, if its vectors and pathways are not identified and adequately monitored. Most of the environmental parameters analysed in the studied streams were shown to be similar to those reported in the literature as preferred/tolerated by the species. Our findings pinpoint the vulnerability of nature reserves to species invasions, and call for more effective preventative measures. [ABSTRACT FROM AUTHOR]

The red swamp crayfish Procambarus clarkii is an invasive alien species spreading worldwide. The sterile male release technique (SMRT) is among the methods used to contrast the growth of P. clarkii populations within invaded areas. In this study males underwent X-ray sterilisation with a dose of 40 Gy and their immunocompetence was analysed in comparison to untreated animals to ascertain whether radiation can affect welfare parameters other than reproductive organs. The present research investigated the immune function in P. clarkii males in term of (1) morphological haemocyte characterisation by transmission electron microscopy to identify the main phagocyting haemocyte after in vivo artificial non-self challenge with latex beads; (2) total and differential haemocyte counts; and (3) basal and total phenoloxidase activities as components of the humoral defence. Three types of circulating haemocytes were characterised via transmission electron microscopy: hyaline, semigranular and granular haemocytes. The ultrastructural features of haemocyte granules allowed the characterisation of a fourth type of haemocyte, the medium granule haemocyte. In vivo artificial non-self-challenge with latex beads identified the semigranular haemocytes as primarily involved in phagocyting activity. Circulating haemocytes of males irradiated with a dose of 40 Gy, after 20 days, showed a significantly lower diameter in the granules of hyaline and semigranular haemocytes, but no other evident ultrastructural alterations in comparison with un-irradiated animals were found. Irradiated males showed a significant decrease of about 80% of circulating haemocytes and an increase in frequency of semigranular and granular haemocytes. No significant differences in basal and total phenoloxidase activity were recorded and this could, in part, explain the good survival level of irradiated males despite the drastic decline of the haemocyte number. This study represents the basis to appraise whether SMRT affects important functions, such as those of the immune system, in addition to altering the gonad tissue. [ABSTRACT FROM AUTHOR]

In 2007, the invasive crayfishProcambarus clarkii(Girard 1852) was identified for the first time in the “Parc Naturel Régional de la Brenne” (Indre department, Centre region, France). Ten infestation sites were found in the park, with 62 fishponds colonised. To better understand how the fishponds could be affected, and changes in invaded ponds, we followed crayfish burrowing activity in recently drained fishponds in two areas. Weekly investigations of burrowing activity by analysing their density, occupation and location with respect to the banks, and micro-habitat features were carried out for 2 months in spring. Burrow densities of 1.16 and 1.05 burrows m–2were found at Le Terrier Blanc and Coudreau 3 respectively.Procambarus clarkiisought humid soil in a dry pond and preferred burrowing on silt substrates. While no statistical differences were found between sites, some differences were observed among weeks independently of the sites. The mean mouth diameter of burrows in the two sites was 5.7 cm (SD = 2.17,n = 214; min. value: 1.2 cm; max. value: 14 cm). Notwithstanding the situation in the last weeks of the study (when most chimneys were built), there was a certain turnover between open and plugged burrows, and in occupancy. Given the scale and duration of the study and the number of fishponds surveyed, this study successfully quantified the dynamics of burrowing in these ponds and conclusions provide a useful basis for future studies and give suggestions of how other colonised fishponds may be affected. [ABSTRACT FROM PUBLISHER]