Crab Pachygrapsus Marmoratus Research Articles

Assessment of connectivity patterns of the marbled crab Pachygrapsus marmoratus in the Adriatic and Ionian seas through combination of genetic data and Lagrangian simulations

Seascape connectivity studies, informing the level of exchange of individuals between populations, can provide extremely valuable data for marine population biology and conservation strategy definition. Here we used a multidisciplinary approach to investigate the connectivity of the marbled crab (Pachygrapsus marmoratus), a high dispersal species, in the Adriatic and Ionian basins. A combination of genetic analyses (based on 15 microsatellites screened in 314 specimens), Lagrangian simulations (obtained with a biophysical model of larval dispersal) and individual-based forward-time simulations (incorporating species-specific fecundity and a wide range of population sizes) disclosed the realized and potential connectivity among eight different locations, including existing or planned Marine Protected Areas (MPAs). Overall, data indicated a general genetic homogeneity, after removing a single outlier locus potentially under directional selection. Lagrangian simulations showed that direct connections potentially exist between several sites, but most sites did not exchange larvae. Forward-time simulations indicated that a few generations of drift would produce detectable genetic differentiation in case of complete isolation as well as when considering the direct connections predicted by Lagrangian simulations.Overall, our results suggest that the observed genetic homogeneity reflects a high level of realized connectivity among sites, which might result from a regional metapopulation dynamics, rather than from direct exchange among populations of the existing or planned MPAs. Thus, in the Adriatic and Ionian basins, connectivity might be critically dependent on unsampled, unprotected, populations, even in species with very high dispersal potential like the marbled crab. Our study pointed out the pitfalls of using wide-dispersing species with broad habitat availability when assessing genetic connectivity among MPAs or areas deserving protection and prompts for the careful consideration of appropriate dispersing features, habitat suitability, reproductive timing and duration in the selection of informative species.

Food and feeding habits of Pachygrapsus marmoratus (Grapsidae) crab in the southern Mediterranean Sea (Eastern Libya)

The present study aimed to establish spatiotemporal food and feeding habits of the crab Pachygrapsus marmoratus inhabiting the rocky shores of the southern Mediterranean Sea coast, exemplified by Al-Haniyah, Al-Hamamah, and Susah sites in eastern Libya, and relate them to crab morphometric traits, and abundance of food organisms in the habitat. A total of 425 crabs collected during 2019 were used in the study. The minimum and maxim carapace length (CL), and total weight (TW) were: 8.5-35.1mm, and 0.4-31.0g in order, the means were 26.79mm and 12.37g. P. marmoratus is an omnivore facultative feeder, i.e. feeds on what is available in its habitat. Stomach fullness was established and discussed in terms of season, site, crab sex and growth, and availability of food in the habitat. The abundance of food in the stomach by taxa vary according to the site, and crab sex and size, but the overall trend was cnidaria and algae > crustacea > mollusca > seaweed, by season it was fall > spring > winter > summer. Cnidaria and mollusca were more abundant in stomachs of P. marmoratus of Al-Haniyah, Crustacea in Al-Hamamah, and mollusca and crustacea in Susah crab’s stomachs.

Cholinesterase characterization and effects of the environmental contaminants chlorpyrifos and carbofuran on two species of marine crabs, Carcinus maenas and Pachygrapsus marmoratus.

Among the most frequent targets for toxic effects of modern pesticides, namely organophosphates and carbamates, one may find cholinesterases (ChEs). ChEs exist in a wide variety of animals and have been used actively to discriminate among the environmental effects of different pollutant groups, including the aforementioned pesticides. This study had three purposes, namely (i) identifying the ChE forms present in tissues (eyes and walking legs muscle) of two crab species, Carcinus maenas and Pachygrapsus marmoratus; to (ii) determine the in vitro toxicological effects, and (iii) compare the sensitivity of such enzymatic forms towards commonly used anti-ChE pesticides, namely the organophosphate chlorpyrifos and the carbamate carbofuran. Our results showed that there was not a clear preference for any of the tested substrates in any of the tissues from both species. Furthermore, the ChE activity was almost completely suppressed following incubation with eserine and with the specific inhibitor BW284C51 in all tissues from both species. In vitro exposure to chlorpyrifos promoted a significant decrease in ChE activity in both species. Furthermore, the ChE activity was completely suppressed following incubation with carbofuran and chlorpyrifos. These results suggest that the major ChE forms present in tissues of both crab species show intermediate structural properties and activity patterns, halfway between classic acetylcholinesterase and pseudocholinesterases. However, the sensitivity of the found forms towards ChE inhibitors was established, and the responsiveness of such forms towards common anti-ChE chemicals was established. Both tested species seem to be promising test organisms to be used in marine and coastal scenarios of putative contaminations by anti-ChE chemicals, considering the here reported patterns of response.

Investigation of mechanisms underlying chaotic genetic patchiness in the intertidal marbled crab Pachygrapsus marmoratus (Brachyura: Grapsidae) across the Ligurian Sea

BackgroundStudies on marine community dynamics and population structures are limited by the lack of exhaustive knowledge on the larval dispersal component of connectivity. Genetic data represents a powerful tool in understanding such processes in the marine realm. When dealing with dispersion and connectivity in marine ecosystems, many evidences show patterns of genetic structure that cannot be explained by any clear geographic trend and may show temporal instability. This scenario is usually referred to as chaotic genetic patchiness, whose driving mechanisms are recognized to be selection, temporal shifts in local population dynamics, sweepstakes reproductive success and collective dispersal.In this study we focused on the marbled crab Pachygrapsus marmoratus that inhabits the rocky shores of the Mediterranean Sea, Black Sea and East Atlantic Ocean, and disperses through planktonic larvae for about 1 month. P. marmoratus exhibits unexpectedly low connectivity levels at local scale, although well-defined phylogeographic patterns across the species’ distribution range were described. This has been explained as an effect of subtle geographic barriers or due to sweepstake reproductive success. In order to verify a chaotic genetic patchiness scenario, and to explore mechanisms underlying it, we planned our investigation within the Ligurian Sea, an isolated basin of the western Mediterranean Sea, and we genotyped 321 individuals at 11 microsatellite loci.ResultsWe recorded genetic heterogeneity among our Ligurian Sea samples with the occurrence of genetic clusters not matching the original populations and a slight inter-population divergence, with the geographically most distant populations being the genetically most similar ones. Moreover, individuals from each site were assigned to all the genetic clusters. We also recorded evidences of self-recruitment and a higher than expected within-site kinship.ConclusionsOverall, our results suggest that the chaotic genetic patchiness we found in P. marmoratus Ligurian Sea populations is the result of a combination of differences in reproductive success, en masse larval dispersion and local larval retention. This study defines P. marmoratus as an example of marine spawner whose genetic pool is not homogenous at population level, but rather split in a chaotic mosaic of slightly differentiated genetic patches derived from complex and dynamic ecological processes.

Locomotory behaviour of the intertidal marble crab (Pachygrapsus marmoratus) supports the underwater spring-loaded inverted pendulum as a fundamental model for punting in animals

In aquatic pedestrian locomotion the dynamics of terrestrial and aquatic environments are coupled. Here we study terrestrial running and aquatic punting locomotion of the marine-living crab Pachygrapsus marmoratus. We detected both active and passive phases of running and punting through the observation of crab locomotory behaviour in standardized settings and by three-dimensional kinematic analysis of its dynamic gaits using high-speed video cameras. Variations in different stride parameters were studied and compared. The comparison was done based on the dimensionless parameter the Froude number (Fr) to account for the effect of buoyancy and size variability among the crabs. The underwater spring-loaded inverted pendulum (USLIP) model better fitted the dynamics of aquatic punting. USLIP takes account of the damping effect of the aquatic environment, a variable not considered by the spring-loaded inverted pendulum (SLIP) model in reduced gravity. Our results highlight the underlying principles of aquatic terrestrial locomotion by comparing it with terrestrial locomotion. Comparing punting with running, we show and increased stride period, decreased duty cycle and orientation of the carapace more inclined with the horizontal plane, indicating the significance of fluid forces on the dynamics due to the aquatic environment. Moreover, we discovered periodicity in punting locomotion of crabs and two different gaits, namely, long-flight punting and short-flight punting, distinguished by both footfall patterns and kinematic parameters. The generic fundamental model which belongs to all animals performing both terrestrial and aquatic legged locomotion has implications for control strategies, evolution and translation to robotic artefacts.

Population Structure and Relative Growth of the Marbled Crab (Pachygrapsus marmoratus) in the Aegean Sea (Turkey)

Although crab Pachygrapsus marmoratus, is one of the common species in the intertidal zones of the Aegean coasts of Turkey, its’ population structure has not been investigated to date. This study aimed to provide information on population characteristics of Pachygrapsus marmoratus, including the sex ratio, size distribution, spawning period, relative growth and catch per unit effort (CPUE). The samples were collected by hand monthly between January 2018 and December 2018, from the rocky shores of Izmir, Turkey. The results indicated that males were dominant except for the months of July, August and September. The CW (carapace width) of female and male crabs ranged from 5.5 to 36.0 mm and 5.5 to 40.0 mm, respectively. The berried (egg-carrying) females were found in May, June and July and their CW varied from 13.0 to 27.0 mm. Only 0.8% of the P. marmoratus population was shown to be infected with the parasite Sacculina sp. The CPUE of P. marmoratus significantly changed monthly and there was a significant correlation between the CPUE and seawater temperature. Concerning the relative growth, the carapace width-cheliped length relationship in males and carapace width-abdomen width relationship in females showed positive allometry. Males were significantly heavier in comparison to females of the same size. Future survey designs would need to investigate whether spatial differences in the population characteristics and size at maturity occur in the Aegean coasts of Turkey.

De novo transcriptome assembly for Pachygrapsus marmoratus, an intertidal brachyuran crab.

The marble crab Pachygrapsus marmoratus inhabits the rocky shores of the Mediterranean Sea, Black Sea and East Atlantic Ocean. As other intertidal species, it is considered a model species to study the effects of environmental stressors on natural populations. In this study, we performed Illumina next-generation sequencing on eleven P. marmoratus specimens with the aims to (i) reconstruct their whole transcriptome, (ii) perform a functional annotation of the assembled transcriptome and (iii) develop gene-based markers for future genetic and genomic studies on this as well as other brachyuran species. We obtained a transcriptome assembly constituted by 56,308 unigenes and covering about 60.3 Mbp. We detected 43,915 Simple Sequence Repeats (SSRs) and 192,631 high-quality Single Nucleotide Polymorphisms (SNPs). Due to the scarcity of genomic resources in decapods, and crabs in particular, our results constitute a valuable resource for future studies on brachyuran crabs. The present data also represent a sound resource to investigate biological responses to pollution in intertidal and marine populations.

Effects of copper on larvae of the marbled crab Pachygrapsus marmoratus (Decapoda, Grapsidae): Toxicity test and biochemical marker responses

The importance of trace elements in ecotoxicological investigations is a well-known issue when monitoring polluted areas such as commercial harbors. Copper represents one of the most common metal contaminants, often detected in these areas as it is widely employed in various fields and has many sources of inflow in the marine environment. Pachygrapsus marmoratus is a widespread intertidal crab species that has been extensively studied in ecology, ethology and population genetics. Ecotoxicological studies have also been performed, exclusively on the adult stage. In the present study we investigated the mortality and biochemical (oxidative stress and neurotoxicity) responses of P. marmoratus larvae exposure to environmental relevant concentration of copper. Results showed dose-dependent responses in terms of larval mortality, with a calculated LC50 value of 0.5 mg/L of Cu2+. The LC50 concentration was used as the starting point for subsequent biochemical response evaluation. Results also demonstrated dose-dependent activation of antioxidant systems assuming a compensatory antioxidant activity to prevent higher cellular damage when larvae were exposed to the highest concentrations of copper. Moreover, a significant enhancement of neurotransmitter activities was observed, assuming a possible direct interaction of copper with the enzymes or an increase of free copper ion aliquot into the cells.

CORRELATION PROFILES OF THE ACCUMULATED METALS IN SEAWATER, SEDIMENT AND Pachygrapsus marmoratus (Fabricius) TISSUES IN BLACK SEA (ORDU, TURKEY)

This study was performed in order to investigate the interactions of accumulation patterns of some metals (Al, As, Cd, Cr, Cu, Fe, Mn, Ni, Pb and Zn) in exoskeleton, gill, hepatopancreas and muscle tissues of the marbled crab Pachygrapsus marmoratus (Fabricius) sampled from near streams and domestic discharge points along the coastal region of Black Sea along Ordu in Turkey as well as patterns in sediment and seawater samples of the crab sampling sites. The study area covering a coastal stretch of 28 km along Black Sea lies between the latitudes 41°03'46.42"-41°07'42.35"N and longitudes 37°28'45.63"-37°41'15.29"E. The metal contents of the samples were analysed by the inductively coupled plasma - optical emission spectrometry (ICP-OES) technique. The results showed that the accumulation orders of the metals, in a descending order, were Fe>Al>Mn>Zn>Cr>Pb>Cu>As>Ni>Cd in the sediment, Fe>Mn>Cr>As>Cd in the water, and Al>Fe>Cu>Mn>Zn in crab tissues when evaluated together. In the crab samples, the amount of the accumulation of all metals was ordered as gills>exoskeleton>hepatopancreas>muscle. Al and Fe were the predominant metals in the sediment and crab tissues but Al was not detected in the seawater samples. A correlation test was performed to reveal the interaction of accumulation in the sediment, water and crab tissues. Metal-metal interactions and their co-accumulation was detected by correlation test. These interactions which exist in the crab tissues but not in the seawater and sediment were the main point of this study. Gills and exoskeleton displayed the greatest number of significant correlations between metal–metal interactions. Also, metal concentrations were found to be higher in the gills and exoskeleton. Strong correlations between Mn-Al (r=0.954, correlation p<0.001), in the exoskeleton, Al-Fe (r=0.849, correlation p<0.001), Mn-Zn (r=0.854, correlation p<0.001) in the gills, Al-Zn (r=0.882 correlation p<0.001) in the hepatopancreas were determined. Moderate correlations between Zn-Cu were found in the hepatopancreas. These metal-metal interactions may have been a result of metallothionein activity. No significant relations were found between metal levels in sediment samples and crap tissues (p>0.05). The results also showed that metals present in the seawater and sediment did not directly transform to tissue accumulation. This result showed that metal amounts in the tissues of the P. marmoratus did not reflect environmental contaminations and that sediment accumulated higher amounts of metals than seawater and tissues.

Comparative population biology and reproduction of two sympatric crabs (Grapsidae) on Azores cobble beaches

ABSTRACTPopulation biology of the intertidal crabs Pachygrapsus marmoratus Fabricius, 1787 and P. maurus (Lucas 1846) was investigated at cobble beaches with different levels of wave exposure. Surveys were taken monthly over 1.5 years at three intertidal levels. The growth rate of both species was similar, although P. marmoratus reached larger sizes. This species was more abundant on the mid-littoral zone of sheltered beaches, whereas P. maurus was more abundant on more exposed ones. The sex ratio was male biased in both species, particularly for the smaller and larger size classes. Both species showed an extended reproductive season, coinciding with the rising temperatures of spring and summer, with ovigerous females being found from June to September for P. marmoratus and from May to August for P. maurus. The present study indicates that both could develop adaptive strategies allowing them to coexist in the Azores littoral. The greater size of P. marmoratus seems to be an advantage on the competition for refuges with P. maurus, which results in its higher abundance and general dominance in the higher shore levels and in less exposed shores. However, P. maurus seems to be more fitted to live in the higher hydrodynamic habitats.

Unravelling population genetic structure with mitochondrial DNA in a notional panmictic coastal crab species: sample size makes the difference.

BackgroundThe extent of genetic structure of a species is determined by the amount of current gene flow and the impact of historical and demographic factors. Most marine invertebrates have planktonic larvae and consequently wide potential dispersal, so that genetic uniformity should be common. However, phylogeographic investigations reveal that panmixia is rare in the marine realm. Phylogeographic patterns commonly coincide with geographic transitions acting as barriers to gene flow. In the Mediterranean Sea and adjoining areas, the best known barriers are the Atlantic-Mediterranean transition, the Siculo-Tunisian Strait and the boundary between Aegean and Black seas. Here, we perform the so far broadest phylogeographic analysis of the crab Pachygrapsus marmoratus, common across the north-eastern Atlantic Ocean, Mediterranean and Black seas. Previous studies revealed no or weak genetic structuring at meso-geographic scale based on mtDNA, while genetic heterogeneity at local scale was recorded with microsatellites, even if without clear geographic patterns. Continuing the search for phylogeographic signal, we here enlarge the mtDNA dataset including 51 populations and covering most of the species’ distribution range.ResultsThis enlarged dataset provides new evidence of three genetically separable groups, corresponding to the Portuguese Atlantic Ocean, Mediterranean Sea plus Canary Islands, and Black Sea. Surprisingly, hierarchical AMOVA and Principal Coordinates Analysis agree that our Canary Islands population is closer to western Mediterranean populations than to mainland Portugal and Azores populations. Within the Mediterranean Sea, we record genetic homogeneity, suggesting that population connectivity is unaffected by the transition between the western and eastern Mediterranean. The Mediterranean metapopulation seems to have experienced a relatively recent expansion around 100,000 years ago.ConclusionsOur results suggest that the phylogeographic pattern of P. marmoratus is shaped by the geological history of Mediterranean and adjacent seas, restricted current gene flow among different marginal seas, and incomplete lineage sorting. However, they also caution from exclusively testing well-known biogeographic barriers, thereby neglecting other possible phylogeographic patterns. Mostly, this study provides evidence that a geographically exhaustive dataset is necessary to detect shallow phylogeographic structure within widespread marine species with larval dispersal, questioning all studies where species have been categorized as panmictic based on numerically and geographically limited datasets.Electronic supplementary materialThe online version of this article (doi:10.1186/s12862-016-0720-2) contains supplementary material, which is available to authorized users.

Phylogeography of the marbled crab Pachygrapsus marmoratus (Decapoda, Grapsidae) along part of the African Mediterranean coast reveals genetic homogeneity across the Siculo-Tunisian Strait versus heterogeneity across the Gibraltar Strait

ABSTRACTWe investigate the influence of previously postulated biogeographic barriers in the Mediterranean Sea on the population genetic structure of a highly dispersive and continuously distributed coastal species. In particular, we examine nuclear and mitochondrial genetic variation in the marbled crab, Pachygrapsus marmoratus, across part of the African Mediterranean coast in order to assess the influence of the Siculo-Tunisian Strait on its population genetic structure. Four polymorphic microsatellite loci were genotyped for 110 individuals, collected from eight locations covering parts of the Algerian, Tunisian and Libyan coasts. In addition, mtDNA corresponding to the Cox1 gene was sequenced for 80 samples. The corresponding results show contrasting patterns of genetic differentiation. While mtDNA results revealed a homogeneous haplotype composition in our study area, microsatellite data depicted genetic differentiation among populations, but not associated with any geographic barrier. This pattern, already recorded for this species from different geographic regions, may hint at the involvement of a complex series of abiotic and biotic factors in determining genetic structure. Demographic history reconstruction, inferred from mtDNA data, supports demographic and spatial expansion for the North African metapopulation dating back to the Mid-Pleistocene and following an historical bottleneck. Comparison of these African mitochondrial sequences with new sequences from a Turkish population and previously published sequences revealed a weak but significant separation of Atlantic and Mediterranean populations across the Gibraltar Strait, which was not recorded in previous studies of this grapsid species.

The trade-off between heat tolerance and metabolic cost drives the bimodal life strategy at the air-water interface.

The principle of oxygen and capacity limitation of thermal tolerance in ectotherms suggests that the long-term upper limits of an organism's thermal niche are equivalent to the upper limits of the organism's functional capacity for oxygen provision to tissues. Air-breathing ectotherms show wider thermal tolerances, since they can take advantage of the higher availability of oxygen in air than in water. Bimodal species move from aquatic to aerial media and switch between habitats in response to environmental variations such as cyclical or anomalous temperature fluctuations. Here we tested the prediction that bimodal species cope better with thermal stress than truly aquatic species using the crab Pachygrapsus marmoratus as a model species. When in water, oxygen consumption rates of P. marmoratus acutely rise during warming. Beyond a temperature threshold of 23 °C the crab's aerobic metabolism in air remains lower than in water. In parallel, the haemolymph oxygen partial pressure of submerged animals progressive decreases during warming, while it remains low but constant during emersion. Our results demonstrate the ability of a bimodal breathing ectotherm to extend its thermal tolerance during air-breathing, suggesting that there are temperature-related physiological benefits during the evolution of the bimodal life style.

Biological traits suggest a niche overlap between two grapsid crabs sharing the rocky intertidal of the eastern Mediterranean

The current study investigated basic biological features for two co-occurring shore crabs Pachygrapsus marmoratus and P. transversus in the eastern Mediterranean Sea. Differences in population structure, reproductive periods and settlement patterns were studied along the coast of Lebanon. Sizes of sampled individuals ranged from 4 to 37 mm carapace width (CW) for P. marmoratus and from 3.5 to 24 mm CW for P. transversus. Males were larger than females in both species, each of them exhibiting different size frequency distributions. Both male and female proportions were similar for P. marmoratus while males dominated the population of P. transversus. Fecundity and egg sizes were higher in P. marmoratus and fecundity was directly related to body size for the two crabs. Size structures differed between studied locations showing size restrictions for specific size-classes. Females from both species remained ovigerous for about 5 months, with P. transversus (May–August) started 1 month after P. marmoratus. Larger sized females displayed higher fecundities. The recruitment of juveniles lasted 5 months for both P. marmoratus (December–May) and P. transversus (November–April). Our results showed that niche partitioning occurred between the two species, where P. marmoratus starts incubating earlier than P. transversus while young of the year of the latter settle earlier on the reefs, taking advantage of convenient seawater temperatures and thus minimizing competition. This study shed some light on the populations of grapsid crabs living in the eastern Mediterranean and provided baseline information on the biology and ecology of the two congeneric shore crabs and their interactions.

Partitioning of food resources at the intertidal zones between the marble rocky crab, Pachygrapsus maromratus (Grapsidae) and warty crab, Eriphia verrucosa (Eriphiidae) along the Mediterranean Sea coasts, Alexandria, Egypt

The food habits of the warty crab, Eriphia verrucosa and the marbled rocky crab Pachygrapsus marmoratus are examined during this study using the frequency occurrence (% F) and point assessment (% P) methods. The overall annual stomach contents exhibited that E. verrucosa tends to be carnivore; whereas P. marmoratus is herbivorous. The two species consume a wide variety of benthic organisms comprised benthic animals as well as macro and micro algae. The stomach contents of E. verrucosa contained 57.40 % of animal origins, 23.26 % from algae and 19.34% of bottom sediments. In P. marmoratus, the stomach contents comprised 53.85 %, 27.30 % and 18.85 % of the benthic animals, benthic algae and bottom sediments, respectively. The benthic animals in the stomachs of the two species belong to different phyla, dominated by Mollusca representing 24.95 % in E. verrucosa and 21.68 % in P. marmoratus, followed by Crustacea, which have 14.04 % and 11.68 % in the two species, respectively. Results have also shown remarkable seasonal fluctuations in the diet composition and stomach fullness (feeding intensity) of the two species. The highest ratios of algae was 32.58 % and 27.32 % recorded during winter in P. marmoratus and E. verrucosa, respectively, declined sharply to the minimum values (21.49% and 19.12 %) during autumn, associated with the lowest values of sediments during winter. Animal ratios reached the maximum (60.11 % and 63.42%) in autumn and winter, but declined to the minimum (46.36% and 53.26 %) during summer in P. marmoratus and E. verrucosa, respectively. These results indicated that, both of E. verrucosa and P. marmoratus had succeeded in sharing their food resources and escape or decrease competition between them by changing types of food items either temporally or spatially according available foods.

Patterns of genetic and morphometric diversity in the marbled crab (Pachygrapsus marmoratus, Brachyura, Grapsidae) populations across the Tunisian coast

The present study reports on population structure analysis of the marbled crab Pachygrapsus marmoratus (Fabricius, 1787) from the Tunisian coast, an appropriate location to study biogeographical processes because of the presence of a well-known discontinuous biogeographic area (the Siculo-Tunisian Strait). Patterns of morphological and genetic variation of this highly dispersive and continuously distributed decapod species were assessed among its geographically close populations which cover almost the entire Tunisian coastline. A total of 386 specimens from nine sites were collected and examined for morphometric variability at 14 morphometric traits. The results of multivariate analyses of linear morphometric traits showed the existence of sexual dimorphism in this species by PERMANOVA (Permutational multivariate analysis of variance). In addition, both CDA (Canonical discriminant analysis) and NPMANOVA (Non parametric MANOVA test) analyses revealed statistically significant differences among the studied locations for both sexes. Overall, the outcome of CDA analysis showed that over 87% of individuals could be assigned correctly to three regional groups in both sexes (North, Center and South). Specifically, SIMPER (Similarity Percentages) analysis showed that carapace length, carapace width and merus length were major contributors to the morphometric separation between populations. The pattern of phenotypic variation suggested by morphometric analyses was found to be highly discordant with that suggested by the analysis of a mitochondrial marker (cytochrome oxidase I, COI). Indeed, the results inferred from restriction fragment analysis of the COI in 180 crabs, suggested high genetic homogeneity. Very low levels of haplotype diversity (h) were found in almost all the studied populations, associated with non significant genetic distances for nearly all population comparisons. Explanations to these morphometric and mtDNA patterns as well as the discrepancy between them are discussed.

Physiological adaptation to Mediterranean habitats of the native crab <em>Pachygrapsus marmoratus</em> and the invasive <em>Percnon gibbesi</em> (Crustacea: Decapoda)

Markers of oxidative stress in the hepatopancreas and carotenoid and vitamin E content in the carapace of the invasive crab Percnon gibbesi and the native crab Pachygrapsus marmoratus were compared as indicators of their physiological condition and environmental adaptation. Crabs similar in size were collected from coastal waters of Portals Vells (Mallorca Island, Spain; 39°28’18.79”N, 2°28’19.63”E) at < 1 m depth. Vitamin E levels were significantly higher in P. marmoratus than in P. gibbesi, whereas all carotenoid concentrations, except astaxanthin, were significantly higher in P. gibbesi. Catalase, glutathione peroxidase and glutathione reductase activities were significantly greater in P. marmoratus. Malondialdehyde concentration, a marker of lipid peroxidation, was higher in the hepatopancreas of P. gibbesi. The differences in carotenoid and vitamin E contents and in the antioxidant enzyme activities are a reflection of the different physiological activity of the two species and may suggest that P. gibbesi is not a potential competitor for the native crab P. marmoratus.

Synergy of environmental variables alters the thermal window and heat shock response: An experimental test with the crab Pachygrapsus marmoratus

The intertidal zone is an extremely variable habitat, imposing stressful conditions on its inhabiting communities. Tolerance towards extremes of temperature, salinity and pH are crucial in these habitats. Despite the vast literature on stress tolerance, few studies have focused on the synergistic effects of several variables on thermal tolerance and HSP70 (heat shock protein 70 kDa) levels. In this work, the crabs were exposed to three experimental conditions 1) thermal ramp at standard pH (8) and saline conditions (35‰) (named T), 2) thermal ramp at standard pH (8) and hyposaline conditions (15‰) (named T plus HypoS), and 3) thermal ramp at lower pH (7) and standard saline conditions (35‰) (named T plus A). Two physiological parameters (Critical Thermal Maximum – CTMax, and osmolality) and a stress biomarker (HSP70) were chosen for this analysis. These parameters were measured in all of the aforementioned conditions. CTMax for each set of conditions was reached by exposing the organisms to a rate of temperature increase of 1 °C h−1 until loss of equilibrium. Haemolymph samples were taken every 2 °C to quantify HSP70 and osmolality. Results showed that CTMax did not differ between crabs solely exposed to T stress and crabs exposed to T plus HypoS stress. However, HSP70 production was impaired in T plus HypoS stress. When crabs were exposed to T plus A stress, they showed a significantly higher CTMax, suggesting that short-term exposure to acidified conditions may alter the thermal window of this species. Nevertheless, in T plus A conditions HSP70 production was impaired as well. Regarding osmolality it decreased according to temperature increase in all tested stress conditions. This study showed that the heat stress response is altered by the synergistic effect of variables. Physiological end-points (i.e. CTMax) may vary and the expression of stress proteins such as HSP70 may be impaired.

Pattern of genetic isolation in the crab Pachygrapsus marmoratus within the Tuscan Archipelago (Mediterranean Sea)

The genetic connectivity level of the benthic crab Pachygrapsus marmoratus was assessed within the Tuscan Archipelago, an area between the Ligurian and Tyrrhenian Seas, Italy. The archipelago comprises 7 islands lying inside the largest marine protected area of the Medi terranean Sea. We genotyped a total of approximately 230 individuals from 8 populations (4 protected and 4 unprotected) at 8 microsatellites. Overall, our results showed a clear partitioning of genetic variation within this area; all populations were separated from one another, except the 2 southernmost islands. This genetic subdivision could be due to a ‘sweepstakes reproductive effect’ (i.e. only a small proportion of the available gene pool successfully contributes to the replenishment of each population). Furthermore, the lack of a pattern of isolation by distance, coupled with a low percentage of individuals assigned to their own populations, indicates that retention of larvae near the parent population is unlikely to be the main cause of the recorded genetic structure. However, we also found evidence of past demographic events in all populations, which may have played a pivotal role in shaping the recorded pattern of intraspecific differen tiation. Finally, we did not detect any difference in the level of genetic variation between populations that were protected (i.e. experiencing less human pressure) and those that were unprotected. This suggests that, from a genetic point of view, the effects of protection have not yet been demonstrated.

Thermal tolerance of the crab Pachygrapsus marmoratus: intraspecific differences at a physiological (CTMax) and molecular level (Hsp70)

Temperature is one of the most important variables influencing organisms, especially in the intertidal zone. This work aimed to test physiological and molecular intraspecific differences in thermal tolerance of the crab Pachygrapsus marmoratus (Fabricius, 1787). The comparisons made focused on sex, size, and habitat (estuary and coast) differences. The physiological parameter was upper thermal limit, tested via the critical thermal maximum (CTMax) and the molecular parameter was total heat shock protein 70 (Hsp70 and Hsp70 plus Hsc70) production, quantified via an enzyme-linked imunosorbent assay. Results showed that CTMax values and Hsp70 production are higher in females probably due to different microhabitat use and potentially due to different hormonal regulation in males and females. Among females, non-reproducing ones showed a higher CTMax value, but no differences were found in Hsp70, even though reproducing females showed higher variability in Hsp70 amounts. As reproduction takes up a lot of energy, its allocation for other activities, including stress responses, is lower. Juveniles also showed higher CTMax and Hsp70 expression because they occur in greater shore heights and ageing leads to alterations in protein synthesis. Comparing estuarine and coastal crabs, no differences were found in CTMax but coastal crabs produce more Hsp70 than estuarine crabs because they occur in drier and hotter areas than estuarine ones, which occur in moister environments. This work shows the importance of addressing intraspecific differences in the stress response at different organizational levels. This study shows that these differences are key factors in stress research, climate research, and environmental monitoring.