Carl L. Thurman

EVAPORATIVE WATER LOSS, CORPORAL TEMPERATURE AND THE DISTRIBUTION OF SYMPATRIC FIDDLER CRABS (UCA) FROM SOUTH TEXAS

Desiccation and thermal stress are among the primary factors limiting terrestriality in crustaceans. Water loss was estimated as weight change in five sympatric species of Uca from south Texas for periods up to 7 hr in dry air. Simultaneously, corporal temperature was measured with a thermocouple placed under the carapace. To estimate integumental permeability to water, 115 mm2 portions of dorsal carapace were glued to U-shaped tubes containing a crab Ringers solution. These were exposed to dry air and water permeability was estimated from weight change. In whole-animal studies, most rapid weight loss occurred in the first 5 min of exposure to dry air as the body temperature fell below ambient (25 degrees C) in all species. The three most terrestrial species exhibited significant survival over more aquatic congeners after prolonged desiccation. The greatest rate of water loss was observed in Uca subcylindrica which lost 22.9+/-3.0% body weight. Uca panacea and Uca spinicarpa lost 14.1+/-1.6% and 18.5+/-1.8%, respectively. Based on blood osmolarity changes, Uca longisignalis and Uca rapax were more resistant to water loss than Uca subcylindrica under these conditions. Water loss from sections of the dorsal carapace were highest in Uca spinicarpa (10.4 mg/hr/cm2) and Uca longisignalis (8.9 mg/ hr/cm2). Uca subcylindrica and Uca panacea were intermediate (4.5 and 4.2 mg/hr/cm2) while Uca rapax expressed the lowest value (2.9 mg/hr/cm2). These observations support the notion that water loss can effectively lower body temperature in fiddler crabs. However, an inverse relationship between terrestriality and integumental permeability was not evident in these sympatric congeners. Ultimately a balance between physiological and behavioral mechanisms must be achieved for adaptation to the semi-arid habitats in south Texas.

Unravelling the Ecological Significance of Endogenous Rhythms in Intertidal Crabs

Organisms living along the shore are exposed to complex sets of environmental oscillations. In addition to solar (24.0 h) and lunar (24.8 h) cycles, local tides may reoccur on a 12.4 h schedule. Beyond daily routines, biweekly, monthly and annual rhythms may each have a significant impact on an animals activity. For some time, it has been established firmly that intertidal crabs possess several internal biological clocks with distinctly different periods and properties. However, the versatility of these clocks has not been obvious. Crabs living in the littoral zone must adjust their internal chrono-meters to be synchronous with the specific temporal structure of the immediate habitat. Fine adjustments in their clocks will depend upon on a particular tide province and the location of their niche in the intertidal zone. Over a wide geographic range, the location of an intertidal habitat for one species may be in as many as four tidal provinces. Based on wave form and harmonic components, tide provinces are characterized as either a) semidiurnal, b) mixed, mainly semidiurnal, c) mixed mainly diurnal, or d) diurnal. Likewise, the primary frequency associated with an intertidal niche in each tide province may be augmented by diel (24 h) and semilunar (14 day) periods. In addition, supralittoral habitats may be influenced by monthly (28 day) and seasonal rhythms. Since some species live in several tidal provinces and different positions in the littoral zone, locomotor and larval release rhythms of intertidal crabs must naturally be adjusted to the timetable of the local habitat. Flexibility in ambulatory and egg hatching rhythms of crabs are discussed from this environmental perspective. The nature and location of the underlying circadian and tidal oscillators tracking these environmental rhythms are reviewed.

Osmoregulation by six species of fiddler crabs (Uca) from the Mississippi delta area in the northern Gulf of Mexico

Abstract Six species of fiddler crabs (Ocypodidae: Uca ) were collected for osmoregulation studies from 25 locations near the delta of the Mississippi River in the northern Gulf of Mexico. Three of the species are classified as members of the Celuca subgenus, Uca spinicarpa , Uca panacea and Uca pugilator , while the remaining three are in the Minuca subgenus, Uca minax , Uca longisignalis and Uca rapax . In the field, U. minax , U. spinicarpa and, occasionally, U. longisignalis are found in freshwater habitats (FW; 0–299 mosM). Two Minuca species, U. longisignalis and U. rapax , are typically collected in brackish water habitats (BW; 300–629 mosM). On the other hand, U. panacea and U. pugilator are most abundant in eurysaline habitats (EH; >630 mosM). In the laboratory, populations of each species were challenged with media ranging from 30 to 3450 mosM (1–110‰). The FW species, U. spinicarpa and U. minax , did not tolerate osmotic concentrations >2100 mosM. The EH species, U. panacea and U. pugilator , however, tolerate concentrations >2800 mosM. The BW species, U. longisignalis and U. rapax , succumb to osmolalities between 2100 and 2800 mosM. Each species keeps its hemolymph concentration fairly constant in 30–1400 mosM solutions. The [ISO], isosmotic medium concentration (in mosM), is calculated for each taxon: U. minax , 659; U. spinicarpa , 682; U. longisignalis , 693; U. rapax , 769; U. pugilator , 816; and U. panacea , 822. In media with >1600 mosM, each species expresses different osmoregulating capabilities. The FW species, U. spinicarpa and U. minax , cannot control hemolymph osmolality above 1500 mosM while the BW-EH species, U. panacea , U. pugilator and U. rapax , regulate hemolymph values in media up to 2300 mosM. Within the FW/BW species U. longisignalis , the ability to osmoregulate corresponds with site of collection. Specimens from FW populations do not regulate as well as those from BW if challenged with hypertonic media. If adapted to a 1800 mosM in the laboratory, survivorship for U. longisignalis shifts to the right and the [ISO] increases to 832 mosM. This suggests that this species adapts to acute hypertonic conditions by tolerating elevated internal osmolality. Generally, these observations extend our knowledge about the physiological capabilities of fiddler crabs from different salinity populations across the northern Gulf of Mexico.

Ecophenotypic physiology: osmoregulation by fiddler crabs (Uca spp.) from the northern Caribbean in relation to ecological distribution

Nine species of Uca were collected across the northern Caribbean from 50 locations ranging in habitat osmolality from 18 to 2760 mmol kg−1 (mosmol). The osmoregulating ability of each species was assessed in solutions ranging from 30 to 3550 mosmol. Survivorship, lower and upper median lethal concentration and haemolymph isosmotic concentration ([ISO]) were estimated for each. A lower lethal concentration could not be calculated for some due to survival in low osmolality. By subgenus, average [ISO] for four species from the subgenus Minuca ranged from 587 to 768 mosmol and three species from the subgenus Leptuca from 805 to 881 mosmol. For species from the subgenus Boboruca and the subgenus Uca the [ISO] was 805 and 930 mosmol, respectively. These values reflect the habitat preference of each species in a subgenus. This study broadens our understanding of ecological physiology in Caribbean Uca and demonstrates intra- and inter-specific differences among tropical fiddler crabs.

Locomotor Activity of the Fiddler Crab, Uca subcylindrica (Stimpson), under Artificial Illumination

Specimens of the fiddler crab Uca subcylindrica (Stimpson) were captured in south Texas (USA) for locomotor rhythm studies. Actographic data were analyzed using Tau™ sofware. Under constant illumination (LL) and darkness (DD), the semiterrestrial crabs express a circadian rhythm of locomotion. When exposed to illumination/darkness cycles (LD12:12 or LD14:10), their bouts of activity are entrained to the photoperiod. In LD, activity is generally bimodal with an initial burst about 0.5 h after illumination. A second burst of activity begins 1 to 2 h before the end of illumination. When transferred from LD to LL, a locomotor rhythm with an average period of 24.6 ± 1.0 h (n = 19) is expressed in 89 percent of the crabs. On the other hand, when placed in DD after LD (n = 8), the crabs are either arrythmic or weakly rhythmic (period = 23.8 ± 0.2 h; n = 2). If the onset of illumination is advanced by 6 h, a period of less than 24.0 h is detected in the actogram. If the onset of illumination is delayed by 6 h, a locomotor rhythm with a period greater than 24.0 h appears. The locomotor behavior of this species of fiddler crab, Uca subcylindrica, is not related to the tidal rhythmicities seen in other members of the genus Uca. Rather, it has strong circadian components.

Phylogenetic patterns and the adaptive evolution of osmoregulation in fiddler crabs (Brachyura, Uca)

Salinity is the primary driver of osmoregulatory evolution in decapods, and may have influenced their diversification into different osmotic niches. In semi-terrestrial crabs, hyper-osmoregulatory ability favors sojourns into burrows and dilute media, and provides a safeguard against hemolymph dilution; hypo-osmoregulatory ability underlies emersion capability and a life more removed from water sources. However, most comparative studies have neglected the roles of the phylogenetic and environmental components of inter-specific physiological variation, hindering evaluation of phylogenetic patterns and the adaptive nature of osmoregulatory evolution. Semi-terrestrial fiddler crabs (Uca) inhabit fresh to hyper-saline waters, with species from the Americas occupying higher intertidal habitats than Indo-west Pacific species mainly found in the low intertidal zone. Here, we characterize numerous osmoregulatory traits in all ten fiddler crabs found along the Atlantic coast of Brazil, and we employ phylogenetic comparative methods using 24 species to test for: (i) similarities of osmoregulatory ability among closely related species; (ii) salinity as a driver of osmoregulatory evolution; (iii) correlation between salt uptake and secretion; and (iv) adaptive peaks in osmoregulatory ability in the high intertidal American lineages. Our findings reveal that osmoregulation in Uca exhibits strong phylogenetic patterns in salt uptake traits. Salinity does not correlate with hyper/hypo-regulatory abilities, but drives hemolymph osmolality at ambient salinities. Osmoregulatory traits have evolved towards three adaptive peaks, revealing a significant contribution of hyper/hypo-regulatory ability in the American clades. Thus, during the evolutionary history of fiddler crabs, salinity has driven some of the osmoregulatory transformations that underpin habitat diversification, although others are apparently constrained phylogenetically.

Constraints on geographic variation in fiddler crabs (Ocypodidae: Uca) from the western Atlantic.

A key question in evolutionary biology is how intraspecific variation biases the evolution of a population and its divergence from other populations. Such constraints potentially limit the extent to which populations respond to selection, but may endure long enough to have macroevolutionary consequences. Previous studies have focused on the association between covariation patterns and divergence among isolated populations. Few have focused on geographic variation among semi‐connected populations, however, even though this may be indicative of early selective pressures that could lead to long‐term divergence and speciation. Here, we test whether covariation in the shape of the carapace of fiddler crabs (genus Uca Leach, 1814) is important for structuring geographic variation. We find that morphological divergence among populations is associated with evolvability in the direction of divergence in only a few species. The shape of the ancestral covariation matrix in these species differs from other species in having notably more variation concentrated along fewer directions (i.e. higher eccentricity). For most species, there is some evidence that covariation has constrained the range of directions into which populations have diverged but not the degree of divergence. These results suggest that even though fiddler crab populations have diverged morphologically in directions predicted by covariation, constraints on the extent to which divergence has occurred may only be manifested in species where variation patterns are eccentric enough to limit populations’ ability to respond effectively in many directions.

Effect of a Sport Food Bar on Lipolysis and Fat Oxidation During Prolonged Exercise

The purpose of this study was to investigate a manufacturers claim that the Access Fat Conversion Activity Bar increases lipolysis and fat oxidation during prolonged exercise. Eight subjects completed two identical 120‐min bouts (58% of VO2Peak) after consuming either an Access bar or nothing. No significant difference between the two trials or trials x time were observed for the respiratory exchange ratio (RER) or plasma glycerol concentration (P > 0.05). Overall, the RER group mean value averaged 0.82 ±0.02 and 0.83 ±0.03 for the control and Access bar trials, respectively. The average group mean plasma glycerol concentration for the control and Access bar trials was 0.32 ±0.18 and 0.26 ± 0.07 mmol‐P1. Further, there were no differences between trials or trials x time for perceived exertion, blood glucose and lactate concentration. The Access bar was concluded not to influence lipolysis or fat oxidation during moderate intensity exercise.