Temperature-related heart rate in water and air and a comparison to other temperature-related measures of performance in the fiddler crab Leptuca pugilator (Bosc 1802).

Performance in poikilotherms is known to be sensitive to temperature, often with a low-sloping increase with temperature to a peak, and a steep decline with increasing temperature past the peak. We complemented past measures of performance by measuring heartbeat rates of the fiddler crab Leptuca pugilator in water and in air as a function of a range of temperatures previously shown to affect other measures of performance. In water over a range of 20-50 °C, heartbeat increased steadily to a peak at 40 °C and then steeply declined to near zero at 50 °C. In air, heartbeat also increased, but to a peak at 35 °C and then with a gentler decline than was found in water. Part of this different response may be due to evaporative water loss, which reduced body temperature in air, and therefore thermal stress, relative to body temperature when crabs were immersed in water. Increased availability of oxygen from air, according to the oxygen and capacity-limited thermal tolerance hypothesis, likely increased aerobic scope past the thermal peak, relative to within water, where oxygen delivery at higher temperatures may have been curtailed. We compared the heart rate performance relations to two previous measures of performance - endurance on a treadmill and sprint speed, both done in air. The peak performance temperature increased in the order: treadmill endurance time, sprint speed, heart rate in air, and heart rate in water, which demonstrates that different performance measures give different perspectives on the relation of thermal tolerance and fitness to temperature. Endurance may therefore be the limiting upper thermal stress factor in male fiddler crabs, when on hot sand flats. Temperature preference, found to be for temperatures <30 °C in air, could be a bet-hedging evolutionary strategy to avoid aerobic scope affecting endurance.

Genetic differentiation and reduced genetic diversity at the northern range edge of two species with different dispersal modes.

Theory predicts that genetic variation should be reduced at range margins, but empirical support is equivocal. Here, we used genotyping-by-sequencing technology to investigate genetic variation in central and marginal populations of two species in the marine gastropod genus Crepidula. These two species have different development and dispersal types and might therefore show different spatial patterns of genetic variation. Both allelic richness and the proportion of private alleles were highest in the most central populations of both species, and lower at the margin. The species with low dispersal, Crepidula convexa, showed high degrees of structure throughout the range that conform to the pattern found in previous studies using other molecular markers. The northernmost populations of the high-dispersing species, Crepidula fornicata, are distinct from more central populations, although this species has been previously observed to have little genetic structure over much of its range. Although genetic diversity was significantly lower at the range margin, the absolute reduction in diversity observed with these genomewide markers was slight, and it is not yet known whether there are functional consequences for the marginal populations.

Sexual selection and the physiological consequences of habitat choice by a fiddler crab.

In mid-Atlantic salt marshes, reproductively active male sand fiddler crabs, Uca pugilator, use a single greatly enlarged major claw as both a weapon to defend specialized breeding burrows from other males and an ornament to attract females for mating. During the summer breeding season, females strongly prefer to mate with males controlling burrows in open areas high on the shore. Food availability decreases while temperature and desiccation stress increase with increasing shore height, suggesting that the timing and location of fiddler crab mating activity may result in a potential trade-off between reproductive success and physiological condition for male crabs. We compared thermal preferences in laboratory choice experiments to body temperatures of models and living crabs in the field and found that from the perspective of a fiddler crab, the thermal environment of the mating area is quite harsh relative to other marsh microhabitats. High temperatures significantly constrained fiddler crab activity on the marsh surface, a disadvantage heightened by strongly reduced food availability in the breeding area. Nevertheless, when the chance of successfully acquiring a mate was high, males accepted a higher body temperature (and concomitantly higher metabolic and water loss rates) than when the chances of mating were low. Likewise, experimentally lowering costs by adding food and reducing thermal stress in situ increased fiddler crab waving display levels significantly. Our data suggest that fiddler crabs can mitigate potential life history trade-offs by tuning their behavior in response to the magnitude of both energetic and non-energetic costs and benefits.

Quantitative genetics approaches to study evolutionary processes in ecotoxicology; a perspective from research on the evolution of resistance.

Quantitative genetic approaches are often used to study evolutionary processes in ecotoxicology. This paper focuses on the evolution of resistance to environmental contaminants-an important evolutionary process in ecotoxicology. Three approaches are commonly employed to study the evolution of resistance: (1) Assessing whether a contaminant-exposed population has an increased resistance relative to a control population, using either spatial or temporal comparisons. (2) Estimating a population's heritability of resistance. (3) Investigating responses in a laboratory selection experiment. All three approaches provide valuable information on the potential for contaminants to affect a population's evolutionary trajectory via natural selection. However, all three approaches have inherent limitations, including difficulty in separating the various genetic and environmental variance components, responses being dependent on specific population and testing conditions, and inability to fully capture natural conditions in the laboratory. In order to maximize insights into the long-term consequences of adaptation, it is important to not just look at resistance itself, but also at the fitness consequences and at correlated responses in characteristics other than resistance. The rapid development of molecular genetics has yielded alternatives to the "black box" approach of quantitative genetics, but the presence of different limitations and strengths in the two fields means that they should be viewed as complementary rather than exchangeable. Quantitative genetics is benefiting from the incorporation of molecular tools and remains an important field for studying evolutionary toxicology.

Temporal and geographic trends in mercury concentrations in muscle tissue in five species of Hudson River, USA, fish.

We analyzed a New York (USA) state database of mercury concentrations in muscle tissue for five species of fish (striped bass, yellow perch, largemouth bass, smallmouth bass, and carp) over a range of locations in the Hudson River (USA) between 1970 and 2004. We used regression models to discern temporal and geographic change in the fish while controlling for a positive correlation between mercury concentration and body mass. Mercury concentrations significantly increased in fish from New York Harbor waters to the mid-Hudson River. Striped bass and yellow perch showed a shallower increase in mercury concentration with river mile than did carp, largemouth bass, and smallmouth bass. Mercury concentrations declined over the 34-year period. These results imply that a geographically restricted source of mercury may be spread throughout the watershed by toxin-laden dispersing species. The increase of mercury toward the north may relate to a point source in the mid-Hudson River, or it may indicate mercury released from the Adirondack watershed. The decline of mercury over three decades corresponds to a reduction of various inputs in the region. The temporal and geographic pattern of mercury in sediments corresponds to the geographic trend of mercury in fish.

Declining metal levels at Foundry Cove (Hudson River, New York): response to localized dredging of contaminated sediments.

This study examines the effectiveness of remediating a well-recognized case of heavy metal pollution at Foundry Cove (FC), Hudson River, New York. This tidal freshwater marsh was polluted with battery-factory wastes (1953-1979) and dredged in 1994-1995. Eight years after remediation, dissolved and particulate metals (Cd, Co, Cu, Pb, Ni, and Ag) were found to be lower than levels in the lower Hudson near New York City. Levels of metals (Co, Ni, Cd) on suspended particles were comparatively high. Concentrations of surface sediment Cd throughout the marsh system remain high, but have decreased both in the dredged and undredged areas: Cd was 2.4-230mg/kg dw of sediment in 2005 vs. 109-1500mg/kg in the same area in 1983. The rate of tidal export of Cd from FC has decreased by >300-fold, suggesting that dredging successfully stemmed a major source of Cd to the Hudson River.

The effect of density upon deposit-feeding populations: Movement, feeding and floating of Hydrobia ventrosa Montagu (Gastropoda: Prosobranchia).

Crawling rate, feeding rate and floating frequency were measured for laboratory populations of the deposit-feeding snail Hydrobia ventrosa at densities of 0.3-16 snails cm-2. Both movement and feeding were depressed with increasing density. However, floating increased with increasing density. Crowding effects are thus important in deposit-feeding populations and must be considered along with resource-renewal in considerations of population control. Floating may be an adaptation to escape crowded conditions.

The availability of microorganisms attached to sediment particles as food for Hydrobia ventrosa Montagu (Gastropoda: Prosobranchia).

The deposit-feeding prosobranch Hydrobia ventrosa Montagu feeds most rapidly upon sediment particles that pass through a 10 µm sieve. Ingestion rate decreases with particles 80-125 µm, then increases with larger particles, which are fed upon by scraping fine material from their surfaces. Hydrobia is capable of digesting diatoms and bacteria from sediment particles, but with generally lower efficiencies than reported when fed pure cultures. Digestion of microorganisms appears to be constrained by ability of the snail to detach cells from sediment particles; only those cells detached from sediment seem to be available for digestion. In contrast, the amphipod Corophium volutator is capable of utilizing most of the diatoms not digested by Hydrobia. For a given sediment, a constant number of microorganisms appear to be safe from digestion by H. ventrosa, and bacteria and microalgae over this amount constitutes the available food.

Experimental tests of sex allocation theory with two species of simultaneously hermaphroditic acorn barnacles.

Sex allocation theory for simultaneous hermaphrodites predicts increases in relative allocation to male-specific function as competition for fertilizations increases. Theoretical models developed specifically for competing acorn barnacles predict that the proportional allocation to male function increases toward an asymptote of 50% as the number of competitors for fertilizations increases. Experimental manipulations were used to investigate how mate competition affected both relative and absolute allocation to the sex functions for two species of acorn barnacle: Semibalanus balanoides and Balanus glandula. The ratio of male to female allocation did not increase with the number of competitors for either species. However, both species showed increased allocation to male function (estimated as total mass of sex-specific tissues) with increased crowding. Allocation to female function seemed to be limited by other factors and did not vary with mating group size as predicted. Allocation to male and female function were both positively related to body size, but a trade-off between male and female function, a key assumption of prior models, was not observed.

Loss of evolutionary resistance by the oligochaete Limnodrilus hoffmeisteri to a toxic substance--cost or gene flow?

The oligochaete Limnodrilus hoffmeisteri at Foundry Cove (FC), New York evolved genetic resistance to cadmium (Cd) and lost resistance after contaminated sediments were removed by dredging. Selection (on survival time in dissolved Cd) was used to generate tolerance to evaluate fitness cost, the commonplace expectation for evolutionary reversal. The hypothesis that gene flow from neighboring populations could "swamp" resistance was addressed by 16S rDNA sequences. In disagreement with the cost hypothesis, selected-Cd tolerant worms and controls showed no difference in total fecundity or growth rate in environments. Highly-Cd-tolerant worms of the FC-selected population grew rapidly at different temperatures and showed no growth impairment in the presence of Cd, indicating metabolically efficient resistance. Genetic structure at FC was consistent with invasion of genotypes from an adjacent population in the time since dredging. Applying selection to lines from FC and a reference site, demonstrated a more rapid increase in Cd tolerance in FC-origin lines, indicating standing allelic variation for resistance at FC (despite phenotypic erosion). The selection experiment supports the view that resistance is simply controlled--probably by one allele of large effect. Whether such rapid "readaptation" could occur naturally is an important question for understanding broad effects of pollutants.

Superfund dredging restoration results in widespread regional reduction in cadmium in blue crabs.

A nickel-cadmium battery factory released about 53 tons of mostly cadmium and nickel hydroxide suspended solid waste between 1953 and 1979 into Foundry Cove, which is tidally connected to the Hudson River estuary. A major Superfund dredging cleanup in 1994-1995 removed most of the cadmium from the sediment from within Foundry Cove. Here, we demonstrate that the cleanup reduced cadmium tissue concentrations (hepatopancreas and leg muscle) in an important fishery species, the blue crab Callinectes sapidus near Foundry Cove, but also across a broad reach of the Hudson River. Before the cleanup, cadmium concentrations in crabs were 4-5 times higher on average than after the cleanup and geographic variation in crab cadmium concentration along the Hudson River estuary was strongly reduced after the cleanup. The factor of reduction in crab tissue concentrations was far less than the factor of reduction of export of cadmium from Foundry Cove into the Hudson or the factor of reduction of cadmium sediment concentrations within the cove following the cleanup. This unique study demonstrates the efficacy of a major dredging cleanup and quantifies the spatial and temporal impact of the cleanup. It demonstrates that cleanup of a point source can have dramatic effects over large spatial scales.

THE LATITUDINAL COMPENSATION HYPOTHESIS: GROWTH DATA AND A MODEL OF LATITUDINAL GROWTH DIFFERENTIATION BASED UPON ENERGY BUDGETS. I. INTERSPECIFIC COMPARISON OF OPHRYOTROCHA (POLYCHAETA: DORVILLEIDAE).

A northern (North Carolina) sibling species of Ophryotrocha grew more rapidly than a southern sibling species (Florida); this presumed advantage, however, diminished to zero as temperature increased from 15 to 30°C. Survival of the northern sibling species was low at 30°C. The differential response probably had a genetic basis since both species had been reared for 2-3 generations under the same conditions. The effect lasted in laboratory populations reared for a year in the laboratory at 25°C (ca. 10 generations). My results are consistent with a graphical model that suggests an evolutionary shift of metabolism-temperature curves and feeding efficiency curves for the two sibling species. These shifts predict a changing advantage of growth of one species relative to the other as temperature increases.

THE LATITUDINAL COMPENSATION HYPOTHESIS: GROWTH DATA AND A MODEL OF LATITUDINAL GROWTH DIFFERENTIATION BASED UPON ENERGY BUDGETS. II. INTRASPECIFIC COMPARISONS BETWEEN SUBSPECIES OF OPHRYOTROCHA PUERILIS (POLYCHAETA: DORVILLEIDAE).

Individuals of two subspecies of Ophryotrocha puerilis (Polychaeta; Dorvilleidae) were collected from differing thermal regimes, and cultures were maintained for over a year. Despite common rearing, the two subspecies show substantial differences in somatic growth rate. At 15°C, the warm-water subspecies grew more slowly, while at 20°C growth for the two subspecies was not significantly different. At 24°C, the warm-water subspecies grew more rapidly and suffered substantially less mortality than the northern subspecies. These results conform to a model predicting genetic differentiation of metabolic efficiency, leading to differences in growth efficiency among populations adapting to thermally differentiated habitats. The problems faced by the cold-water subspecies at 24°C conforms to expectations based upon natural habitat temperatures.

Rapid loss of genetically based resistance to metals after the cleanup of a Superfund site.

Over the period 1953-1979, a battery factory on the Hudson River in New York released approximately 53 tons of cadmium (Cd) and nickel hydride wastes into Foundry Cove. The most common aquatic benthic species, the oligochaete Limnodrilus hoffmeisteri, rapidly evolved resistance to Cd. The capacity for detoxification and internal storage of Cd resulted in a strong potential for trophic transfer of Cd through the aquatic food web. As a result of United States Superfund legislation, a major remediation effort in 1994-1995 removed the majority of the Cd, thereby removing the selective force for resistance. The cleanup of this cove resulted in the maintenance of resistant forms but then there ensued a rapid loss of resistance in approximately 9-18 generations, showing the potential for ecological restoration to rapidly reduce the potential for trophic transfer of Cd through the ecosystem. This study demonstrates a genetic approach to the study of ecological restoration and connects a genetic indicator of restoration to transfer of toxic metals through ecosystems.