Gianluca Fea

Female freshwater crayfish adjust egg and clutch size in relation to multiple male traits

Females may invest more in reproduction if they acquire mates of high phenotypic quality, because offspring sired by preferred partners may be fitter than offspring sired by non-preferred ones. In this study, we tested the differential maternal allocation hypothesis in the freshwater crayfish, Austropotamobius italicus, by means of a pairing experiment aimed at evaluating the effects of specific male traits (body size, chelae size and chelae asymmetry) on female primary reproductive effort. Our results showed that females laid larger but fewer eggs for relatively small-sized, large-clawed males, and smaller but more numerous eggs for relatively large-sized, small-clawed males. Chelae asymmetry had no effects on female reproductive investment. While the ultimate consequences of this pattern of female allocation remain unclear, females were nevertheless able to adjust their primary reproductive effort in relation to mate characteristics in a species where inter-male competition and sexual coercion may mask or obscure their sexual preferences. In addition, our results suggest that female allocation may differentially affect male characters, thus promoting a trade-off between the expression of different male traits.

Movement behaviour and shelter choice of the native crayfish Austropotamobius pallipes complex: survey on a population in a semi-natural pond in Northern Italy

This is a study of movements and artificial shelters use by a 3-year established population of Austropotamobius pallipes complex, in a lentic environment in the Parco Lombardo della Valle del Ticino (NW Italy). Home-checking and mark-recapture methods were used to investigate movements of 178 crayfish and shelter use by 389 crayfish in summer and in autumn. Most crayfish (97.2%) moved but the movement was highly variable. The greater part of the distances moved was less than 10 m day−1. Multi-hole bricks with one opening have been mostly selected, and the lower level was preferentially occupied; frequently a single crayfish per brick was found. The animals size affected the majority of the analysed variables: mean daily distance, area fidelity, level of shelter; on the other hand no case was significant for sex. The results highlight that this species is fairly mobile and could colonize waterbodies with similar features even rather rapidly. Mobility does not appear to affect the endangered status of this species.

Complexity of biogeographic pattern in the endangered crayfish Austropotamobius italicus in northern Italy: molecular insights of conservation concern

The protection of freshwater biodiversity has become a priority task for conservation practices, as freshwater ecosystems host high levels of cryptic diversity, while also record similarly high rates of extinction. The Italian white-clawed crayfish Austropotamobius italicus is an endemic freshwater crustacean, threatened by several anthropogenic impacts such as habitat fragmentation, pollution, invasion of exotics, and climate change. Previous phylogenetic studies conducted in Italy pointed out a complex phylogeographic framework for the species, with four different subspecies currently recognized. Conservation efforts, particularly when involving restocking and reintroduction, require a detailed knowledge of their population genetics. In this study we describe the genetic structure of A. italicus populations in northern Italy (Lombardy Alpine foothills and northern Apennines) by using the informative mitochondrial marker cytochrome c oxidase subunit I, in order to assess their current evolutionary diversity and past phylogeographic history from a conservation perspective. Our results contribute to the mapping of the contact area among A. i. carsicus and A. i. carinthiacus in the Orobie Larian Prealps. More interestingly, we highlight the existence of two deeply differentiated evolutionary lineages within A. i. carsicus, showing alternative phylogeographic patterns and past demographic trends. We propose to consider these two clades as distinct molecular operational taxonomic units for the conservation of this endangered crayfish.

Quantitative Habitat Models for the Conservation of the Endangered European Crayfish Austropotamobius pallipes Complex (Astacoidea: Astacidae)

Crayfish are the largest mobile freshwater invertebrates and are keystone species in European aquatic ecosystems particularly in small streams and rivers. The white-clawed crayfish Austropotamobius pallipes (a species complex) is currently classified by the IUCN Red List as an endangered species (EN), because its populations have decreased significantly over the last decades in a number of European countries including Italy, due mainly to habitat modifications and the introduction and spread of alien species. Data on the ecological requirements of A. pallipes are needed to quantify the effects of habitat alteration, to simulate restoration scenarios, and to implement effective conservation measures for this species. We describe here a new methodology for modelling the habitat requirements for this endangered crayfish using the mesohabitat scale approach based on data from crayfish living in small streams draining the Italian foothills of the Alps (Lombardy region) and in streams in the mountainous areas of the Gran Sasso and Monti della Laga National Park (Abruzzo region). Data from seven morphologically different streams were used to train and validate the habitat models. The Random Forests algorithm was used to identify the best and most parsimonious habitat model, and to define the lowest number of variables to be surveyed in the future. The best habitat models were applied to each stream and used to classify each mesohabitat into suitability categories. Habitat flow-rating curves were developed to analyze spatio-temporal variation of habitat availability, and habitat time series analysis were used to define detailed management schemes for environmental river management. Flow releases and water temperature regimes were assessed for individual water diversions in order (1) to represent how physical habitat changes through time, and (2) to identify stress conditions for A. pallipes created by the persistent limitation of habitat availability. Results indicated that the kind of substrate in the stream bed (such as the proportion of fine-grained substrates), the water depth (whether shallow or deep), and the available cover (such as the presence of boulders, woody debris, and undercut banks) were all significant factors governing the occurrence of crayfish. The habitat models performed well in both calibration and validation phases (with accuracy ranging from 71 to 79 % in training and from 69 to 73 % in validation) and can be considered to be a valuable tool to predict the distribution of A. pallipes over a wide range of stream types. An example of how to establish environmental standards for small streams is presented. The proposed habitat model provides a useful tool that can be applied even when other commonly used methodologies are unsuitable. As such, this habitat model can be used to develop regional rules for the conservation of the endangered crayfish A. pallipes complex and for defining more site-specific management criteria.

Ultrastructural and molecular characterization of Vairimorpha austropotamobii sp. nov. (Microsporidia: Burenellidae) and Thelohania contejeani (Microsporidia: Thelohaniidae), two parasites of the white-clawed crayfish, Austropotamobius pallipes complex (Decapoda: Astacidae)

The microsporidiosis of the endangered white-clawed crayfish Austropotamobius pallipes complex has generally been attributed to only one species, Thelohania contejeani, the agent of porcelain disease. Species identification was mostly assessed by macroscopic examination or microscopic evaluation of muscle samples rather than by molecular or ultrastructural analyses. A survey conducted on A. pallipes complex populations in Northern Italy highlighted the presence of two different microsporidia causing similar muscular lesions, T. contejeani and an undescribed octosporoblastic species Vairimorpha austropotamobii sp. nov. Mature spores and earlier developmental stages of V. austropotamobii sp. nov. were found within striated muscle cells of the thorax, abdomen, and appendages of the crayfish. Only octosporoblastic sporogony within sporophorous vesicles (SPVs) was observed. Diplokaryotic sporonts separated into two uninucleate daughter cells, which gave rise to a rosette-shaped plasmodium, and eight uninucleate spores were produced within the persistent SPV. Ultrastructural features of stages in the octosporoblastic sequence were similar to those described for Vairimorpha necatrix, the type species. Mature spores were pyriform in shape and an average of 3.9 × 2.2 µm in size. The polar filament was coiled 11-14 times, lateral to the posterior vacuole. The small subunit ribosomal RNA gene (SSU rRNA) and the large subunit RNA polymerase II gene (RPB1) of V. austropotamobii sp. nov. were sequenced and compared with other microsporidia. The highest sequence identity of SSU rRNA (99%) and RPB1 (74%) genes was with the amphipod parasite Nosema granulosis and subsequently with V. cheracis, which infects the Australian yabby Cherax destructor. In our work we discuss about the reasons for placing this new species in the genus Vairimorpha. In addition, we provide for T. contejeani a RPB1 gene sequence, supplemental sequences of SSU rRNA gene and ultrastructural details of its sporogony in the host A. pallipes complex.