Stone Crayfish Austropotamobius Torrentium Research Articles

Climate change threatens unique genetic diversity within the Balkan biodiversity hotspot – The case of the endangered stone crayfish

The stone crayfish Austropotamobius torrentium is globally endangered due to anthropogenic pressure on its habitats, climate change and the invasive crayfish species, particularly the signal crayfish Pacifastacus leniusculus . Aiming to guide A. torrentium conservation within the hotspot of its genetic diversity in the western Balkan Peninsula, we combined population genetics and species distribution models (SDMs) to reveal the impact of climate change and the invasive P. leniusculus on A. torrentium diversity. Population genetic analyses based on newly developed microsatellites revealed moderate within-population genetic diversity and high differentiation among populations, reflecting isolated populations with limited gene flow. Alongside strong genetic structuring, we discovered high level of inbreeding coefficient indicating homozygote excess within the majority of populations. The SDMs results predicted substantial reductions of suitable habitats for A. torrentium by 2070; 80 % of its currently suitable habitat is predicted to be lost under high‐warming climate change scenario. Obtained results indicated that 44 % of populations with high and/or unique genetic diversity, including three highly divergent and geographically restricted evolutionary lineages, are located in the areas predicted to become unsuitable in the future, highlighting their vulnerability to extinction. Further, SDMs revealed considerable decrease of future habitat suitability for P. leniusculus , suggesting that climate change represents greater threat to A. torrentium . Our study highlights the importance of conserving remnant A. torrentium populations, among other, through assisted migration and population mixing that could help populations overcome the risks of inbreeding and maladaptation, and thus enabling A. torrentium to withstand the ongoing climate change. • Native freshwater crayfish decline is a global conservation concern. • The first study of Austropotamobius torrentium genetic diversity in its hotspot (Balkan Peninsula). • Climate change poses a higher risk to A. torrentium than invasive crayfish species. • Transboundary conservation actions needed for species long-term preservation. • . Conservation strategies should include assisted migration and population reinforcement.

Morphometric characteristics and condition indices of stone crayfish Austropotamobius torrentium (Shrank, 1803) from the Mlinska River

Regarded as a protected species on the IUCN list of endangered species, and classified as data deficient species, the stone crayfish (Austropotamobius torrentium) is one of the five European species from the Astacidae family that lives in freshwater ecosystems across Bosnia and Herzegovina. The aim of this study was to investigate the variability of selected morphometric characteristics of male and female crayfish of the A. torrentium species from the upper reaches of the Mlinska River. The crayfish were sampled in June 2021 when 62 individuals (22 males and 40 females) were caught. They were analyzed fresh in the field and in the laboratory. The treatment included the measurement of 12 morphometric features: total body length (TBL), weight (W), claw length (CLL), claw width (CLW), carapace length (CPL), carapace width (CPW), rostrum length (ROL), rostrum width (ROW), abdominal length and width (ABL, ABW) and telson length and width (TEL, TEW). The mean body length ± SD was 79.05 ± 7.35 in males and 60.54 ± 10.03 mm in females. The mean recorded body weight ± SD was 17.51 ± 8.3 g in males and 7.02 ± 4.41 g in females. Using the linear regression method, a positive correlation was found between body length and weight (♂ R2=0.7644; ♀ R2=0.8222), body weight and claws length (♂ R2=0.876; ♀ R2=0.9661), as well as carapace width and body length (♂ R2=0.7216; ♀ R2=0.8411). Using the T-test, a statistically significant difference of the analyzed morphometric parameters was found between the sexes, which is explained by the pronounced sexual dimorphism of stone crayfish. The calculated values for Condition factor and the Crayfish constant indicate that the males are of better fitness, which is in line with the results of previous research in Europe. Data presented in this paper can serve as a basis for further research of A. torrentium in this area.

Detection of the Endangered Stone Crayfish Austropotamobius torrentium (Schrank, 1803) and Its Congeneric A. pallipes in Its Last Italian Biotope by eDNA Analysis

The stone crayfish, Austropotamobius torrentium, is a European freshwater crayfish. Although this species is relatively widespread throughout the continent, it is undergoing significant declines throughout its range. However, as the decline rates have not been quantified in detail, this species is classified as data deficient by the IUCN Red List of Threatened Species. The present study describes the development and validation of two species-specific assays based on hydrolysis probe chemistry for the detection of A. torrentium and A. pallipes environmental DNA (eDNA) in water samples collected in the Julian Alps of Italy (Friuli Venezia Giulia). The eDNA-based method was applied to 14 sites within the Danubian Slizza basin, known to be inhabited by A. torrentium, but with insufficient information on their distribution. In addition, one station in the Tagliamento River basin was sampled to test the performance of the A. pallipes probe. The presence of A. torrentium is confirmed at 6 out of 15 sites. At four of these sites, A. torrentium is detected for the first time. In contrast, the presence of A. torrentium was not detected at two sites already known to harbour the species. Finally, the presence of A. pallipes was confirmed in the station belonging to the Tagliamento basin. The methodology described, which allows the distinction between the two species, paves the way for the parallel detection of the stone crayfish and the white-clawed crayfish (A. pallipes) through eDNA analysis.

How well does NATURA 2000 protect threatened stone crayfish in Croatia?

The stone crayfish Austropotamobius torrentium (Schrank, 1803) is a threatened native European freshwater crayfish species for which Natura 2000 network represents the most important conservation effort at the European level. In Croatia, there are altogether 25 Natura 2000 sites defined specifically for this species. In the present study, we aimed to assess the effectiveness of Natura 2000 sites in preserving stone crayfish diversity through gap analysis, a GIS-based approach that overlays species distribution data on a map of designated Natura 2000 sites. Our results showed that the existing Natura 2000 network in Croatia encompasses most of the areas with a high diversity of A. torrentium; currently designated sites harbour 73.3% of recorded A. torrentium populations. Future conservation planning efforts, and possible expansion of Natura 2000, should be focused on newly discovered A. torrentium populations that present divergent evolutionary lineages.

Conservation genetics of the vulnerable stone crayfish using DNA barcoding and microsatellites

The stone crayfish Austropotamobius torrentium is a native European freshwater species with significant population declines caused by anthropogenic pressure onto its habitats, climate change and spreading of non-native invasive crayfish and their pathogens. Large-scale DNA barcoding based on sequencing a short fragment of the mitochondrial cytochrome c oxidase subunit I (COI) gene revealed this species represents a highly divergent taxon whose evolutionary heritage is preserved in genetically divergent mtDNA phylogroups, with majority of them having restricted distribution ranges. Guarding in mind vanishing populations trends and potential loss of genetic diversity, effective conservation planning and monitoring are needed for ensuring the persistence and long-term survival of this endangered species. Since genetic data are often critical for defining populations for conservation and management purposes, along with DNA barcoding, we employed microsatellites to examine samples of more than 400 individuals from 17 populations across its entire distribution range in Croatia, known as the stone crayfish diversity hot spot. Microsatellite analyses revealed high level of genetic diversity and differentiation among studied populations that grouped according to their geographical position and mtDNA phylogroup. Almost all sampled populations represent a distinct genetic cluster, showing high level of differentiation and reflecting long periods of isolation. Results of genetic characterisation enabled selection of suitable donor populations for future restocking and reintroduction programs. Combination of DNA barcoding and microsatellites provided good insight into genetic diversity and population structure as well as enabled sound conservation programs for this threatened species in Croatia.

Only one can remain? Environmental and spatial factors influencing habitat partitioning among invasive and native crayfishes in the Pannonian Ecoregion (Hungary)

Biological invasions have increasingly threatened indigenous species, influence metacommunity organisation and consequently, global biodiversity. World-wide expansion of non-indigenous crayfish (NICS) is associated with dramatic changes in species poor indigenous crayfish (ICS) assemblages challenging conservation planning. We analysed long-term changes of crayfish occurrences from the pre-invasion state, through the first appearance of NICS, to their intensive spread in Hungarian waters. Further, we analysed present-day crayfish metacommunity patterns for co-occurrences and influence of spatial and environmental factors. Historic data revealed a marked pre-invasion decline in indigenous noble crayfish Astacus astacus and stone crayfish Austropotamobius torrentium populations, but not in the narrow-clawed crayfish Pontastacus leptodactylus. Historic data provided no direct evidence for the impact of NICS on ICS, rather it supported that NICS often entered areas where ICS had been extinct or were not present at all. Crayfish species extremely rarely co-occurred which could indicate their strong competition and be related to utilization of empty sites by NICS. Crayfish metacommunities were predominantly spatially structured indicating the primary influence of ongoing invasion. Crayfish species also exhibited different environmental preferences mainly along the altitude and temperature gradients. We conclude that the invasion is still in the expanding phase and without an effective conservational program the future of ICS is doubtful in Hungary. Conservation policy should focus on the preservation and reintroduction of the stone and noble crayfishes in highland refugees. Expansion of NICS should be prevented in refugee areas by utilizing possibilities provided by natural and artificial barriers, and education and strict ban should be simultaneously applied to prevent further illegal releases by aquarists.

Telemetry of co-occurring noble crayfish (Astacus astacus) and stone crayfish (Austropotamobius torrentium): diel changes in movement and local activity

Telemetry of co-occurring noble crayfish (Astacus astacus) and stone crayfish (Austropotamobius torrentium): diel changes in movement and local activity

The occurrence of branchiobdellidans on stone crayfish (Austropotamobius torrentium) in the Czech Republic

The stone crayfish Austropotamobius torrentium (Schrank, 1803) is one of only two native crayfish species in the Czech Republic. Epibiotic branchiobdellidans present on this crayfish species have not been studied before in the Czech Republic. Here we evaluate the occurrence, and basic population characteristics of branchiobdellidans inhabiting A. torrentium in 12 small streams in the Czech Republic. Three Branchiobdella species were found: Branchiobdella parasita , and B. pentadonta dominated. B. hexadonta was found only exceptionally, as we did not focus on species inhabiting the gill chamber. The overall abundance varied between 0.3 and 17 individuals per crayfish. The mean length of B. parasita was 3.58 (1.1–7.1) mm, of B. pentadonta 2.00 (0.9–4.9) mm, and of B. hexadonta 1.73 (1.4–2.2) mm.

Morphological evidence for hidden diversity in the threatened stone crayfish Austropotamobius torrentium (Schrank, 1803) (Decapoda: Astacoidea: Astacidae) in Croatia

The stone crayfish Austropotamobius torrentium (Schrank, 1803) is a native European species distributed in central and southeastern Europe. Recent molecular phylogenetic research has shown that at least seven distinct monophyletic phylogroups exist within A. torrentium, with the highest genetic diversity found within the northern-central Dinaric (NCD) region in Croatia. Genetic divergence for some of these phylogroups was sufficiently large to suggest that they might actually represent cryptic species. Our research studied the morphometric and meristic characteristics of stone crayfish populations in the Žumberak-Samoborsko gorje Nature Park (Croatia) situated in the genetically diverse NCD region. The aim was to test whether there are some morphological features that clearly separate stone crayfish belonging to the three previously identified phylogroups into distinct groups based on morphology. We analysed morphological data of stone crayfish belonging to three distinct populations inhabiting small streams within the Žumberak-Samoborsko gorje Nature Park. Analyses showed that there are significant differences in some of the recorded morphometric and meristic characteristics between the studied populations for both males and females. Multivariate discriminant analyses of the measured morphological features revealed the characteristics that clearly separate populations in a similar way as molecular methods. For males these were the characteristics describing claws, carapace, and rostrum, and for females those describing carapace, rostrum, and total length. Percentage of correctly classified crayfish per population was high (91-100%) for both sexes. Even though separation of the stone crayfish populations, based on morphologic and genetic analyses, is similar, there was no significant correlation between them. Therefore, analyses of additional samples and application of different genetic markers are needed to elucidate the relationships among different populations of the stone crayfish.

Mitochondrial DNA provides evidence of a double origin for the stone crayfish Austropotamobius torrentium in the Elbe basin

• Native status of stone crayfish in the Elbe basin has been challenged in the past. • We studied genetic variation of representative populations from this region. • Haplotype variation of the mitochondrial COI gene confirms species’ double origin. • Stone crayfish probably colonised the Elbe basin from the Danube basin naturally. • One population in eastern Bohemia was introduced by men, probably from Slovenia. The stone crayfish Austropotamobius torrentium is the smallest native European crayfish, restricted to central and southeast Europe. Northeast boundary of its range is located within the Elbe basin but considerable uncertainties existed regarding its status in this area. Until recently, known stone crayfish populations in the Elbe basin were very scattered and human translocations have been implicated in such distribution pattern. Discoveries of additional populations in the Czech Republic and Saxony (east Germany) nevertheless suggest that the species may have been more widespread there. We provide data on genetic variation (based on 181 sequences of the mitochondrial COI gene) of 20 representative populations from the Elbe basin (both from the Czech Republic and Saxony). We tested whether the haplotype variation is consistent with a scenario of natural dispersal or whether long-range transport has been involved. All analysed individuals from the easternmost, geographically isolated Czech stone crayfish population carried a haplotype previously recorded only in Slovenia and its vicinity; it is therefore likely that such population has been introduced by humans. In contrast, all remaining studied populations were dominated by a haplotype widespread in adjacent regions of species’ distribution in Germany, and additional haplotypes differing by point mutations were occasionally detected. This is consistent with a scenario of a postglacial colonization from Bavaria (southeast Germany). Our study provides evidence for a double origin of stone crayfish populations in the upper Elbe basin, with both natural and anthropogenic factors likely affecting the present diversity and distribution of this species.

Morphometry of the stone crayfish (Austropotamobius torrentium) in the Czech Republic: allometry and sexual dimorphism

The stone crayfish Austropotamobius torrentium (Schrank, 1803) is a native crayfish species in the Czech Republic. Biometric analysis of this crayfish species in the Czech Republic has not been performed up to now. The aim of this paper is to provide these data. The maximum observed body length was 94.8 mm in females and 103.6 mm in males. As the main characters of sexual dimorphism were observed, males had the carapace and chelae relatively longer in relation to the total body length and the carapace length respectively, while females showed longer rostro-cervical part of the carapace and wider abdomen. The chelae width/length ratio was larger in females; the chelae width/length ratios and abdomen width differed between sexes in both adults and juveniles. Most of observed body parts grow allometrically. The positive allometry was found in the following length relations: the carapace length in males only, carapace width, and abdomen width (all related to the carapace length) in females, and chelae width/length ratio in females. Negative allometric growth was recorded in the length of the rostro-cervical part of the carapace, chelae width, and chelae height in males.

Frequency of new marble-colored morph in wild population of Austropotamobius torrentium (Decapoda: Astacidae)

In contrast with the usual coloration of stone crayfish (Austropotamobius torrentium), we newly discovered a rare marble morph in a brook in the Czech Republic (Central Europe). During mark-recapture sessions, we captured by hand 1,103 individuals over the 3 years 2008–2010 from which only 5 were marble-colored. This color morph’s frequency of occurrence was thus less than 1% within the estimated subadult and adult stone crayfish population. Although many biological papers and determination keys regarding crayfish are based upon analysis of exoskeletal coloration, recent studies have asserted that this characteristic provides unreliable guidance when determining species inasmuch as it easily results in errors because many crayfish species exhibit an extensive variety of color morphs.

Aphanomyces astaci in wild crayfish populations in Slovenia: first report of persistent infection in a stone crayfish Austropotamobius torrentium population

All 5 crayfish species inhabiting Slovenian freshwaters, of which 3 are indigenous crayfish species (ICS: Astacus astacus, Austropotamobius pallipes, and A. torrentium) and 2 are non-indigenous (NICS: Pacifastacus leniusculus and Cherax quadricarinatus), were inspected for the presence of Aphanomyces astaci, the causative agent of crayfish plague. Wild crayfish populations showing no clinical signs of infection were inspected using A. astaci-specific real-time PCR. In addition, a conventional PCR assay was employed and confirmative sequencing was performed. Out of 88 analyzed crayfish, 15/27 (55.6%) specimens of A. torrentium from Borovnišcˇ%%KERN_ERR%%ica Brook and 4/35 (11.4%) of P. leniusculus from the Mura River tested positive, showing low to moderate levels of infection (agent levels A1-A4 and A1-A3, respectively). Results revealed the presence of A. astaci not only in the resistant NICS but also in ICS, since the infected population of A. torrentium presumably had no contact with the NICS carrier and appeared to sustain A. astaci infection in the 2 sampling years. Although the A. astaci genotype has not yet been identified, a connection between the latent infection in ICS and a Group A strain of A. astaci, co-evolving with A. torrentium since its first introduction to Slovenia, is suggested as the most plausible conclusion. This is the first reported population of the genus Austropotamobius with persistent infection, in addition to the already known populations of the genus Astacus. Findings of the presumed co-evolution of A. astaci and ICS hosts open new perspectives, necessitating additional studies on the presence of A. astaci genotypes in the persistently infected ICS populations.

Comparative ultrastructure of the spermatozoa of three crayfish species: Austropotamobius torrentium, Pacifastacus leniusculus, and Astacus astacus (Decapoda: Astacidae)

This study reports about the spermatozoal ultrastructure of three species of astacid crayfish, i.e., the stone crayfish Austropotamobius torrentium, signal crayfish Pacifastacus leniusculus, and noble crayfish Astacus astacus. The acrosome is a cup shaped and electron-dense structure at the anterior of the spermatozoon and comprises three layers of differing electron densities filled with parallel filaments that extend from the base to the apical zone. The acrosome was significantly longer in A. astacus than in P. leniusculus and the shortest acrosome belongs to A. torrentium. The width of the acrosome was significantly narrower in A. torrentium than in P. leniusculus and the widest acrosome belongs to A. astacus. The L:W ratio was significantly greater in A. torrentium than in P. leniusculus and the lowest ratio belongs to A. astacus. Radial arms are visible on each side of the acrosome or nucleus in sagittal view and wrap around the spermatozoon. Each radial arm comprises a parallel bundle of microtubules arranged along the long axis within a sheath. The nucleus, with decondensed material, is located in the posterior of the cell. All parts of the spermatozoon are tightly enclosed within an extracellular capsule. Despite a well-conserved general structure and similarity of pattern among these spermatozoa, differences in the dimensions of the acrosome within the studied species may be useful to help distinguish the different crayfish species.

Current limitations of the stone crayfish distribution in Romania: Implications for its conservation status

The stone crayfish Austropotamobius torrentium is one of three indigenous crayfish species in Romania. Extensive research to assess the conservation status of this highly protected species is overdue in this country. Presently, the populations are concentrated in two distinct regions, the southwest and northwest of the country. Most populations were found living in habitats with little anthropic impact. Using logistic and negative binomial regression models, we determined the ecological preferences of the species. The most favourable conditions suggest an equilibrium between the availability of dissolved oxygen, moderate river velocity, and low concentration of organic pollutants. Due to these ecological requirements, the species is generally restricted to sub-montane areas (around 500 m a.s.l.) leading to a high degree of population fragmentation. The spectrum of limitations is completed by invasive species and the crayfish plague agent Aphanomyces astaci. Contact with non-indigenous Orconectes limosus and the crayfish plague is a real threat, especially to the populations inhabiting the order I tributaries of the Danube, in southwestern Romania. We recommend that the Romanian stone crayfish A. torrentium be taken into consideration as an “endangered species”.

Associations between stream habitat characteristics and native and alien crayfish occurrence

Human mediated introductions of non-indigenous crayfish species (NICS) are responsible for their rapid colonisation of European freshwaters. The introduction of North American crayfish is furthermore linked to the spread of crayfish plague and the decline of indigenous crayfish species (ICS). As the management of ICS and NICS have become necessary, a detailed knowledge on their distribution and ecological requirements is needed. We studied the current range of native noble crayfish Astacus astacus and stone crayfish Austropotamobius torrentium, as well as alien signal crayfish Pacifastacus leniusculus in Carinthia (Austria) and evaluated environmental and physical habitat features in streams with and without crayfish. Meanwhile, the loss of many ICS populations was recorded and alien P. leniusculus was found to be widespread in this region. Most of the habitat features of streams having crayfish differed significantly from sites lacking crayfish for at least one investigated native or alien species. Furthermore, multivariate and regression analyses showed specific differences in the habitat use of the investigated crayfish. Our results showed that the presence of alien P. leniusculus was associated with larger and smoother sloped lowland rivers, while the occurrence of the two native species was confined to smaller streams either at higher altitudes and with distinct physical habitat conditions (A. torrentium) or with moderate water temperatures (A. astacus). This study helps to identify potential refuge areas for the endangered native species and to predict the further spread of the most common non-native crayfish species in European streams.

The distribution of stone crayfish Austropotamobius torrentium (Schrank, 1803) (Crustacea: Decapoda: Astacidae) in the south-west Romanian mountain and sub-mountain area

The distribution of stone crayfish Austropotamobius torrentium (Schrank, 1803) (Crustacea: Decapoda: Astacidae) in the south-west Romanian mountain and sub-mountain area Data is presented in relation to the geographical distribution of the endangered crayfish species Austropotamobius torrentium. One hundred and seventy-four sampling stations situated along the streams of 15 geographical units from the South-West of Romania (Anina Mountains, Almăj, Dognecea, Godeanu, Locva, Ţarcu, Retezat, Semenic, Mehedinţi, Vâlcan, Parâng, Şureanu, Poiana Ruscă, Lipova Hills and Mehedinţi Plateau) have been investigated. A distribution map was compiled. The data from older publications were collated. The actual habitat of this species occupies a large area of South-West Romania in the mountain and sub-mountain area, being absent in the Poiana Ruscă Mts, Lipova and Dognecea Hills.

Status of Freshwater Crayfish Distribution in Thrace Region of Turkey

This review focuses on the present distribution of two crayfish species: narrow-clawed crayfish Astacus leptodactylus Eschscholtz and stone crayfish Austropotamobius torrentium (Schrank, 1803) in Thrace region of Turkey. The only known native (indigenous) freshwater crayfish species of Turkey is A. leptodactylus. It is found at more sites than A. torrentium. On the other hand, A. torrentium is only found in Thrace region of Turkey. The first population of A. torrentium was observed in Velika River in 1995. In 2006, the second population of A. torrentium was found in Madara Brook in the region, but the abundance of A. torrentium in Madara Brook was very low in comparison to Velika River. Moreover, further studies carried out in some water resources near the population of A. torrentium, such as De[vgrave]irmen Brook, Poyralı Brook, and Hasköy Brook confirmed that no other populations of this species are present in the region at present. Therefore, it can be concluded that A. torrentium is only present in the northwest of Marmara river basin (Istaranca Mountain Part) and A. leptodactylus is widely distributed throughout the places located to the south of Marmara river basin, and Istaranca Mountain might be a border line that separates A. leptodactylus and A. torrentium populations. Moreover, except the presence of these two species, no other crayfish species are found in the Thrace region of Turkey at present.

Microhabitat preferences of the stone crayfishAustropotamobius torrentium(Schrank, 1803)

The stone crayfish Austropotamobius torrentium (Schrank, 1803) is a species that usually prefers small and medium-sized streams. It is mainly dependent on coarse grained substrata, which it uses as shelter, but has also been observed on clay in which it creates burrows, similarly to other species of crayfish. In this study, the microhabitat preferences of the stone crayfish in day-time were evaluated. In 2008 (June–November) we collected data on stone crayfish abundances in 1263 patches, recording their position in streams (in five categories: 1. current, 2. lee, 3. shoreline, 4. backwater, 5. rapids), dominant substratum (in seven categories: 1. mud, 2. sand, 3. fine gravel, 4. gravel, 5. pebbles, 6. stones, 7. boulders) in eight streams in the West Bohemia region. This data was evaluated using an index of microhabitat electivity (calculated as the difference between the expected (calculated from all the samples) and actual frequency of occurrence in habitats within a given environmental parameter) and multivariate analysis (redundancy detrended analysis). Substratum type was the major determinant of microhabitat preference for all size classes ( 90 mm). There was a generalised avoidance of fine-grained substrata and a preference for coarser ones, which was more evident in larger size groups. The substrata character explained 8.7% of the variability in distribution. The parameter “depth” explained 1% of the overall crayfish variability distribution. Nevertheless, an avoidance of greater depths by small stone crayfish individuals was found, as well as an avoidance of shallows by the largest size categories. No major preference was noted for different stream positions (which explained only 0.7% of the microhabitat use variability), but crayfish avoided rapids with higher water velocities.

Recent distribution, population densities and ecological requirements of the stone crayfish (Austropotamobius torrentium) in the Czech Republic

The stone crayfish Austropotamobius torrentium (Schrank) is one of five species of crayfish inhabiting waters in the Czech Republic, usually occupying small and medium-sized streams. The stone crayfish is protected by national and European laws. At present, stone crayfish are known to occur in 41 streams in the Czech Republic. For each of these streams, we measured the population density, sex ratio and age structure of the stone crayfish populations. The average population density varied between 0.3–4.72 spms·m−2 , with a maximum estimated population density at some sites reaching 8.6 spms·m−2 . The sex ratio was evaluated only in abundant populations (> 0.5 spms·m−2 and it did not significantly vary from the expected rate of 0.5 (0.3–0.72).