John Campbell McNamara

Neotropical regions near the equator are recognized as speciation “hot spots” reflecting their abundant biodiversity. In western South America, the coasts of Panama, Colombia, Ecuador, the Galápagos Archipelago, and northern Peru form the Tropical Eastern Pacific biome. This area has the greatest heterogeneity of sympatric fiddler crab species of any portion of the planet. Since the coastal fauna has not been assessed for almost 50 years, we studied fiddler crab species diversity in Ecuador and on the Galápagos Archipelago. Preserved collecting records for various species were examined at the U.S. National Museum of Natural History, Washington, DC, the American Museum of Natural History, New York, and the Naturalis Biodiversity Center, Leiden, the Netherlands. During a field study, 51 locations were collected resulting in over 870 preserved specimens (120 lots) along the 2237‐km (1390 mi) coast of Ecuador and on three Galápagos Islands. A neighbor‐joining tree was constructed using the Kimura 2‐parameter model with a partial DNA sequence of the cytochrome oxidase‐subunit 1 gene (COI) for a barcoding study. Twenty‐five taxa were collected during the surveys, while two more were noted from the literature and museum collections. Five published species are new to Ecuador. The species assemblage was divided among four genera: Uca, Leptuca, Minuca, and Petruca. Morphological definitions and photographic images are given for 27 species. COI sequences were obtained for 27 operational taxonomic units from Ecuador, with three morphologically indistinguishable cryptic or pseudocryptic taxa also revealed. Based on species distributions, it appears that the area between Cabo San Lorenzo and Punta Santa Elena serves as a weak barrier separating some “northern” from “southern” taxa. Since coastal Ecuador is undergoing rapid economic development, the construction of maricultural facilities and the deforestation of mangroves promote wholesale habitat destruction. As habitat diversity is reduced, it is expected that there will be, in general, a local decline in fiddler crab species diversity with some taxa becoming rare or extinct.

We redescribe a species of fiddler crab, Minuca panema (Coelho, 1972), from the Atlantic coast of South America. It is closely related to M. mordax (Smith, 1870), and until now, the taxon has been considered to be synonymous with another closely related species Minuca burgersi (Holthuis, 1967). However, we found that two clades of M. burgersi sensu lato were restricted to the Caribbean Basin. This distribution differs from than that of M. panema , which occurs primarily along the eastern coast of South America, ranging from the island of Trinidad to Praia da Arma & ccedil;& atilde;o, Santa Catarina, Brazil. Based on our field studies, the geographical boundary between M. burgersi sensu stricto and M. panema is the Tobago Basin, north of Trinidad. Since the two species diverged only 3 to 4 million years ago, as dated from the phylogeny of the genus Minuca Bott 1954, there are few reliable morphological features that can be used to distinguish them clearly. In live crabs, there is a striking difference in coloration between the cherryred South American M. panema and the rusty -red Caribbean M. burgersi sensu lato. In males, the pattern of tubercles on the inner surface of the major cheliped varies between the two species. In females, the vulva is slightly larger in M. burgersi sensu stricto. Ocean tides and currents together with siltation owing to freshwater outflow from the Amazon and Orinoco rivers most likely have driven the divergence of these species. In the Caribbean, small tidal amplitudes have minimized long-distance gene flow in M. burgersi sensu stricto from isolated insular lagoons. In contrast, large tidal amplitudes and exposed habitats on riverbanks along the eastern Atlantic coast of South America have enabled long-distance dispersal in M. panema . DNA analysis reveals that haplotypes of cytochrome c oxidase subunit 1 are not shared between the species. Since natural selection and/or genetic drift have yet to produce extensive morphological divergences between M. panema and M. burgersi sensu stricto, we speculate that changes in the genes regulating mitochondrial DNA functions have led to speciation at the molecular level. According to the mitonuclear compatibility concept, we propose that mitochondrial DNA may be at the forefront of speciation events and that co -evolved mitonuclear interactions are responsible for some of the earliest genetic incompatibilities arising among isolated populations.

Osmoregulatory findings on crabs from high Neotropical latitudes are entirely lacking. Seeking to identify the consequences of evolution at low temperature, we examined hyperosmotic/hypo-osmotic and ionic regulation and gill ion transporter gene expression in two sub-Antarctic Eubrachyura from the Beagle Channel, Tierra del Fuego. Despite sharing the same osmotic niche, Acanthocyclus albatrossis tolerates a wider salinity range (2–65‰ S) than Halicarcinus planatus (5–60‰ S); their respective lower and upper critical salinities are 4‰ and 12‰ S, and 63‰ and 50‰ S. Acanthocyclus albatrossis is a weak hyperosmotic regulator, while H. planatus hyperosmoconforms; isosmotic points are 1380 and ∼1340 mOsm kg−1 H2O, respectively. Both crabs hyper/hypo-regulate [Cl−] well with iso-chloride points at 452 and 316 mmol l−1 Cl−, respectively. [Na+] is hyper-regulated at all salinities. mRNA expression of gill Na+/K+-ATPase is salinity sensitive in A. albatrossis, increasing ∼1.9-fold at 5‰ compared with 30‰ S, decreasing at 40–60‰ S. Expression in H. planatus is very low salinity sensitive, increasing ∼4.7-fold over 30‰ S, but decreasing at 50‰ S. V-ATPase expression decreases in A. albatrossis at low and high salinities as in H. planatus. Na+/K+/2Cl− symporter expression in A. albatrossis increases 2.6-fold at 5‰ S, but decreases at 60‰ S versus 30‰ S. Chloride uptake may be mediated by increased Na+/K+/2Cl− expression but Cl− secretion is independent of symporter expression. These unrelated eubrachyurans exhibit similar systemic osmoregulatory characteristics and are better adapted to dilute media; however, the expression of genes underlying ion uptake and secretion shows marked interspecific divergence. Cold clime crabs may limit osmoregulatory energy expenditure by hyper/hypo-regulating hemolymph [Cl−] alone, apportioning resources for other energy-demanding processes.

Weakly osmoregulating crustaceans use intracellular free amino acids (FAA) to attenuate cell volume changes consequent to alterations in hemolymph osmolality. Whether semiterrestrial, strong hyper/hypo‐osmoregulators exhibit this ability is unknown. We investigate FAA mobilization in muscle tissue of 10 fiddler crabs from the genera Minuca, Leptuca, and Uca distributed along the Atlantic coast of South America. Crabs were subjected to severe hypo‐ or hyper‐osmotic challenge at their lower or upper critical salinity limits for 5 days; reference crabs were held in isosmotic media. Hemolymph osmolality was measured, chela muscle FAA were identified and quantified, and percent contribution to intracellular osmolality (%FAA) was calculated. At isosmoticity, total FAA were nominally twofold higher in Minuca species (≈116 mmol/kg wet mass) compared to Uca (≈60 mmol/kg wet mass). Glycine, alanine, arginine, and taurine constituted >80% of the total FAA pool. On hyperosmotic challenge, hemolymph osmolalities ranged from 843 to 1282 mOsm/kg H₂O. FAA increased, although %FAA remained unaltered. Hypo‐osmoregulating crabs thus can mobilize FAA, likely owing to a lesser ability to secrete salt near their upper critical limits. On hypo‐osmotic challenge, osmolalities were regulated more tightly, between 475 and 736 mOsm/kg H₂O. Total FAA and %FAA showed little change, probably due to the crabs' strong hyper‐osmotic extracellular regulatory ability, FAA consequently playing a diminished role in isosmotic intracellular regulation (IIR). Total FAA responses to hyper/hypo‐osmotic challenge are thus asymmetrical. The lack of phylogenetic signal in FAA mobilization suggests that closely related fiddler crabs do not share similar strategies of IIR.

To evaluate the crustacean gill (Na ⁺ , K ⁺ )-ATPase as a molecular marker for toxic contamination by heavy metals of estuarine and coastal environments, we provide a comprehensive analysis of the effects of Co ²⁺ in vitro on modulation of the K ⁺ -phosphatase activity of a gill (Na ⁺ , K ⁺ )-ATPase from the blue crab Callinectes danae . Using p -nitrophenyl phosphate as a substrate, Co ²⁺ can act as both stimulator and inhibitor of K ⁺ -phosphatase activity. Without Mg ²⁺ , Co ²⁺ stimulates K ⁺ -phosphatase activity similarly but with a ≈4.5-fold greater affinity than with Mg ²⁺ . With Mg ²⁺ , K ⁺ -phosphatase activity is almost completely inhibited by Co ²⁺ . Substitution of Mg ²⁺ by Co ²⁺ slightly increases enzyme affinity for K ⁺ and NH ₄ ⁺ . Independently of Mg ²⁺ , ouabain inhibition is unaffected by Co ²⁺ . Mg ²⁺ displaces bound Co ²⁺ from the Mg ²⁺ -binding site in a concentration dependent mechanism. However, at saturating Mg ²⁺ concentrations, Co ²⁺ does not displace Mg ²⁺ from its binding site even at elevated concentrations. Saturation by Co ²⁺ of the Mg ²⁺ binding site does not affect p NPP recognition by the enzyme. Given that the interactions between heavy metal ions and enzymes are particularly complex, their toxic effects at the molecular level are poorly understood. Our findings elucidate partly the mechanism of action of Co ²⁺ on a crustacean gill (Na ⁺ , K ⁺ )-ATPase. Highlights: Without Mg ²⁺ , cobalt ions stimulate the gill (Na ⁺ , K ⁺ )-ATPase Co ²⁺ has a 4.5-fold greater affinity for the gill (Na ⁺ , K ⁺ )-ATPase than does Mg ²⁺ Mg ²⁺ displaces Co ²⁺ from the Mg ²⁺ -binding site in a concentration dependent manner Ouabain inhibition with Co ²⁺ or Mg ²⁺ is identical Saturation by Co ²⁺ of Mg ²⁺ -binding sites does not affect substrate recognition Graphical Graphical abstract (synopsis): Using a crab gill (Na ⁺ , K ⁺ )-ATPase, we demonstrate that Co ²⁺ inhibits K ⁺ -phosphatase activity with Mg ²⁺ , which is stimulated without Mg ²⁺ . Mg ²⁺ displaces Co ²⁺ from the Mg ²⁺ -binding site but Co ²⁺ cannot displace Mg ²⁺ . Ouabain inhibition is unaffected by Co ²⁺ , independently of Mg ²⁺ . The molecular mechanism of Co ²⁺ toxicity is partly elucidated.

Weakly osmoregulating crustaceans use intracellular free amino acids (FAA) to attenuate cell volume changes consequent to alterations in hemolymph osmolality. Whether semi-terrestrial, strong hyper/hypo-osmoregulators exhibit this ability is not known. We investigate FAA mobilization in muscle tissue of ten fiddler crabs from the genera Minuca, Leptuca and Uca distributed along the Atlantic coast of South America. Crabs were subjected to severe hypo- or hyper-osmotic challenge at their upper or lower critical salinity limits for five days; control crabs were held in isosmotic media. Hemolymph osmolality was measured, chela muscle FAA were identified and quantified, and percent contribution to intracellular osmolality (%FAA) was calculated. At isosmoticity, total FAA were nominally 2-fold higher in Minuca species (≈116 mmol/kg wet mass) than in Uca (≈60 mmol/kg wet mass). Glycine, alanine, arginine and taurine constituted >80% of total FAA. On hyper-osmotic challenge, hemolymph osmolalities ranged from 843 to 1,282 mOsm/kg H ₂ O. FAA increased, although %FAA remained unaltered. Hypo-osmoregulating crabs thus can mobilize FAA, likely owing to a lesser ability to secrete salt near their upper critical limits. On hypo-osmotic challenge, osmolalities were more tightly regulated, between 475 and 736 mOsm/kg H ₂ O. Total FAA and %FAA showed little change, probably due to the crabs’ strong hyper-osmotic extracellular regulation, FAA consequently playing a diminished role in isosmotic intracellular regulation. Total FAA responses to hyper/hypo-osmotic challenge are thus asymmetrical. There was no effect of crab genus on total FAA or on %FAA at isosmoticity or on either osmotic challenge, reinforced by the absence of phylogenetic signal.

Early marine invertebrates like the Branchiopoda began their sojourn into dilute media some 500 million years ago in the Middle Cambrian. Others like the Mollusca, Annelida, and many crustacean taxa have followed, accompanying major marine transgressions and regressions, shifting landmasses, orogenies, and glaciations. In adapting to these events and new habitats, such invertebrates acquired novel physiological abilities that attenuate the ion loss and water gain that constitute severe challenges to life in dilute media. Among these taxon-specific adaptations, selected from the subcellular to organismal levels of organization, and constituting a feasible evolutionary blueprint for invading freshwater, are reduced body permeability and surface (S) to volume (V) ratios, lowered osmotic concentrations, increased osmotic gradients, increased surface areas of interface epithelia, relocation of membrane proteins in ion-transporting cells, and augmented transport enzyme abundance, activity, and affinity. We examine these adaptations in taxa that have penetrated into freshwater, revealing diversified modifications, a consequence of distinct body plans, morpho-physiological resources, and occupation routes. Contingent on life history and reproductive strategy, numerous patterns of osmotic regulation have emerged, including intracellular isosmotic regulation in weak hyper-regulators and well-developed anisosmotic extracellular regulation in strong hyper-regulators, likely reflecting inertial adaptations to early life in an estuarine environment. In this review, we address osmoregulation in those freshwater invertebrate lineages that have successfully invaded this biotope. Our analyses show that across 66 freshwater invertebrate species from six phyla/classes that have transmuted into freshwater from the sea, hemolymph osmolalities decrease logarithmically with increasing S:V ratios. The arthropods have the highest osmolalities, from 300 to 650 mOsmoles/kg H₂O in the Decapoda with 220–320 mOsmoles/kg H₂O in the Insecta; osmolalities in the Annelida range from 150 to 200 mOsmoles/kg H₂O, and the Mollusca showing the lowest osmolalities at 40–120 mOsmoles/kg H₂O. Overall, osmolalities reach a cut-off at ∼200 mOsmoles/kg H₂O, independently of increasing S:V ratio. The ability of species with small S:V ratios to maintain large osmotic gradients is mirrored in their putatively higher Na⁺/K⁺-ATPase activities that drive ion uptake processes. Selection pressures on these morpho-physiological characteristics have led to differential osmoregulatory abilities, rendering possible the conquest of freshwater while retaining some tolerance of the ancestral medium.

Seeking to identify consequences of evolution at low temperature, we examine hyper/hypo-osmotic and ionic regulation and gill ion transporter gene expression in two sub-Antarctic Eubrachyura from the Beagle Channel, Tierra del Fuego. Despite sharing the same osmotic niche, Acanthocyclus albatrossis tolerates a wider salinity range (2-65 ‰S) than Halicarcinus planatus (5-60 ‰S); respective lower and upper critical salinities are 4 and 12 ‰S, and 63 and 50 ‰S. Acanthocyclus albatrossis is a weak hyperosmotic regulator, while H. planatus hyper-osmoconforms; isosmotic points are 1,380 and ≈1,340 mOsm kg ⁻¹ H ₂ O. Both crabs hyper/hypo-regulate [Cl ⁻ ] well with iso-chloride points at 452 and 316 mmol L ⁻¹ Cl ⁻ , respectively. [Na ⁺ ] is hyper-regulated at all salinities. mRNA expression of gill Na ⁺ /K ⁺ -ATPase is salinity-sensitive in A. albatrossis , increasing ≈1.9-fold at 5 ‰S compared to 30 ‰S, decreasing at 40 to 60 ‰S. Expression in H. planatus is very low salinity-sensitive, increasing ≈4.7-fold over 30 ‰S, but decreasing at 50 ‰S. V(H ⁺ )-ATPase expression decreases in A. albatrossis at low and high salinities as in H. planatus . Na ⁺ -K ⁺ -2Cl ⁻ symporter expression in A. albatrossis increases 2.6-fold at 5 ‰S, but decreases at 60 ‰S compared to 30 ‰S. Chloride uptake may be mediated by increased Na ⁺ -K ⁺ -2Cl ⁻ expression but Cl ⁻ secretion is independent of symporter expression. These unrelated eubrachyurans exhibit similar systemic osmoregulatory characteristics and are better adapted to dilute media; however, the gene expressions underlying ion uptake and secretion show marked interspecific divergences. Cold clime crabs may have limited energy expenditure by regulating hemolymph [Cl ⁻ ] alone, apportioning resources for other metabolic processes. Summary statement: Sub-Antarctic crabs may skimp on osmoregulatory capabilities to apportion energy for metabolic processes. They regulate chloride but not sodium or osmolality. Transporter gene expressions diverge markedly. Adaptive, differential ion regulation may characterize cold clime crabs.

Early marine invertebrates like the Branchiopoda began their sojourn into dilute media some 500 million years ago in the Middle Cambrian. Others like the Mollusca, Annelida and many crustacean taxa have followed, accompanying major marine transgressions and regressions, shifting landmasses, orogenies and glaciations. In adapting to these events and new habitats such invertebrates acquired novel physiological abilities that attenuate the ion loss and water gain that constitute severe challenges to life in dilute media. Among these taxon-specific adaptations, selected from the subcellular to organismal levels of organization, are reduced body permeability and surface (S) to volume (V) ratios, lowered osmotic gradients, increased surface areas of interface epithelia, relocation of membrane proteins in ion-transporting cells and augmented transport enzyme abundance, activity and affinity. We examine adaptations in taxa that have penetrated into fresh water, revealing diversified modifications, a consequence of distinct body plans, morpho-physiological resources and occupation routes. Contingent on life history and reproductive strategy, numerous patterns of osmotic regulation have emerged, including intracellular isosmotic regulation in weak hyper-regulators and well-developed anisosmotic extracellular regulation in strong hyper-regulators, likely reflecting inertial adaptations to early life in an estuarine environment. Our analyses show that across sixty-four freshwater invertebrate species from six phyla/classes, hemolymph osmolalities decrease logarithmically with increasing S: V ratios. The arthropods have the highest osmolalities, from 300 to 650 mOsmoles/kg H ₂ O in the Decapoda with 220 to 320 mOsmoles/kg H ₂ O in the Insecta; osmolalities in the Annelida range from 150 to 200 mOsmoles/kg H ₂ O, the Mollusca showing the lowest osmolalities at 40 to 120 mOsmoles/kg H ₂ O. Overall, osmolalities reach a cut-off at ≈200 mOsmoles/kg H ₂ O, independently of increasing S: V ratio. The ability of species with small S: V ratios to maintain large osmotic gradients is mirrored in their putatively higher Na ⁺ /K ⁺ -ATPase activities that drive ion uptake processes. Selection pressures on these morpho-physiological characteristics have led to differential osmoregulatory abilities, rendering possible the conquest of fresh water while retaining some tolerance of the ancestral medium.