Publication Search Results

ID: 155497
Type: article
Authors: Bashevkin, Samuel M.; Christy, John H.; Morgan, Steven G.
Keywords: STRI

ID: 155485
Type: article
Authors: Pardo, Juan C. F.; Stefanelli-Silva, Gabriel; Christy, John H.; Costa, Tânia
Keywords: STRI

ID: 155491
Type: article
Authors: Schaefer, Jessica L. B.; Christy, John H.; Marko, Peter B.
Keywords: STRI
Abstract: Abstract. Pair-living is a common social system found across animal taxa, and the relationship between pair-living and reproduction varies greatly among specie

ID: 152691
Type: article
Authors: Bashevkin, Samuel M.; Christy, John H.; Morgan, Steven G.
Keywords: STRI
Abstract: Morphological defenses of plankton can include armor, spines, and coloration. Spines defend from gape-limited fish predators while pigmentation increases visibility to fishes but defends from ultraviolet radiation (UVR). Planktonic crab larvae (zoeae) exhibit inter- and intra-specific variability in the lengths of defensive spines, extent of pigmentation, and body size. The determinants of this variability and the relationships among these traits are largely unknown. Larvae may employ generalized defenses against the dual threats of UVR and predation or specialized defenses against their primary threat, with an unknown role of allometric or phylogenetic constraints. Generalization would result in longer spines compensating for the increased predation risk imposed by darker pigments, while specialization would lead to more investment in either defense from predation (long spines) or UVR (dark pigments), at the expense of the other trait. We examined 1) the relationship between spine lengths and pigmentation, 2) the scaling of spine lengths with body size, and 3) phylogenetic constraint in spine lengths, pigmentation, and body size, among and within 21 species of laboratory-hatched and 23 species of field-collected crab larvae from Panama and California. We found a negative relationship between spine length and pigmentation among species from laboratory and field. Within species, we found a marginally significant negative relationship among field-collected larvae. Spine lengths showed positive allometric scaling with carapace length while spine and carapace lengths, but not pigmentation, had significant phylogenetic signals. The negative relationship we observed between pigmentation and spine length supports our defense specialization hypothesis. Positive allometric scaling of spine lengths means larger larvae are better defended from predators, which may indicate that larvae face greater predation risk as they grow larger. Phylogenetic constraint may have arisen because related species encounter similar predation threats. Conversely, phylogenetic constraint in the evolution of spine lengths may induce convergent behaviors resulting in related species facing similar predation threats. Our results improve understanding of the evolution of the larval morphology of crabs, morphological defenses in the plankton, and evolutionary responses of morphology to multiple spatially-segregated selective forces.

ID: 151807
Type: article
Authors: Bashevkin, Samuel M.; Christy, John H.; Morgan, Steven G.
Keywords: STRI
Abstract: Plankton live under the countervailing selective pressures of predation and ultraviolet radiation (UVR). In lakes, zooplankton are transparent reducing visibility to predatory fishes but are pigmented in the absence of fishes, hypothetically reducing UVR damage. In the sea, planktivorous fishes are widespread, so plankton typically are transparent and ascend to productive surface waters at night to forage and descend during the day to reduce visibility to predators. However, larvae of some species face the unique constraint of traveling in surface currents in the daytime during migrations between adult and larval habitats. We would expect these larvae to be transparent since companion studies demonstrated increased predation risk of pigmented larvae under strong sunlight. Paradoxically, larvae range from being darkly to lightly pigmented. We hypothesize that some larvae are more heavily pigmented to reduce UVR damage, while other species travelling in subsurface currents with low UVR might be more transparent. Linking larval morphology to depth-dependent selective pressures would add a key element to help improve predictions of larval vertical distributions, which are important for simulating larval transport trajectories. We quantitatively tested the hypothesis that selection may have favored photoprotective pigmentation for larvae in the predominantly transparent plankton community while testing the differential effects of UVA and UVB radiation. We measured larval pigmentation of 12 species of crabs and exposed them to visible light only, visible + UVA, or visible + UVA + UVB in the tropics. Controlling for phylogeny, more pigmented species survived UVR better than less pigmented species, especially on sunnier days, though intraspecific comparisons for four species were equivocal. Most species died even from UVA exposure, which has long been regarded as relatively harmless despite penetrating deeper underwater than UVB. Thus, we demonstrate with a phylogenetically controlled analysis that crab larvae are pigmented in the predominantly transparent planktonic community to protect from UVR, improving our understanding of the selective forces acting on animal coloration and the factors determining planktonic distributions, survival, and dispersal. This linkage of morphology with susceptibility will be important for developing mechanistic models of environmental stress responses to better predict larval dispersal in current and future climates. This article is protected by copyright. All rights reserved.

ID: 148524
Type: article
Authors: Heatwole, Siobhan J.; Christy, John H.; Backwell, Patricia R. Y.
Keywords: STRI
Abstract: Courtship is costly for males when it increases their energy expenditure and predation risk. There are several ways in which males might be able to mitigate these costs, or compensate for them by elevating the benefits of courtship. First, they could selectively court more profitable females. Second, they could adjust the amount of risk they take against their residual reproductive value. Third, they could sometimes use cheaper signals to deceive females. In the fiddler crab Leptuca terpsichores (Crane, 1941), males risk losing their burrow to another crab and falling prey to a bird when they leave their burrow to intercept a mate-searching female and lead her back to the burrow for mating. Some males build sand hoods at their burrow entrances, which are landmarks that attract females and allow males to relocate their burrows quickly with little error. Here, we show that (1) males took greater risks when courting larger females by travelling farther away from their burrows; (2) the distance a male moved from his burrow did not depend on his size (hence, age); and (3) males with sand hoods did not travel farther away from their burrows than males without hoods, and they were not more likely to reach females. Taking greater risks when courting larger (more fecund) females appears to be a key means through which male fiddler crabs can achieve a more favourable balance between the costs and benefits of courtship.Significance statementCourtship and mate choice can be costly for males. Males may improve the balance between courtship costs and benefits by modifying their risk-taking during courtship according to the perceived value of the female, or their expectations of future reproduction. Male fiddler crabs move away from their burrows to court females, which is risky because they may lose the burrow or be attacked by predators. We used the distance a male travels from his burrow as an index for the level of risk he is willing to take. We explored the effects of female size, male age, and the presence of a sand hood at the burrow entrance on distance travelled during courtship. Males took greater risks to court larger females, but did not adjust risk-taking according to their age (expected future reproduction) or whether their burrow had a sand hood.

ID: 143597
Type: article
Authors: Luque, Javier; Christy, John H.; Hendy, Austin J. W.; Rosenberg, Michael S.; Portell, Roger W.; Kerr, Kecia A.; Palmer, A. R.
Keywords: STRI
Abstract: Concentrations of fully articulated crabs are rare in the fossil record, especially for terrestrial and semi-terrestrial taxa, which tend to be represented by scarce, fragmentary and poorly preserved fossils due to preservational biases. A newly discovered fossiliferous locality at Bahia Bique, west of Panama City, Panama, yielded a collection of supratidal, intertidal and shallow subtidal invertebrates and vertebrates of mid-Holocene age. Notable discoveries include the first fossils of the sally lightfoot crab Grapsus, the first for the land crab Cardisoma in the Eastern Pacific and, remarkably, the most complete and abundant collection of fossil fiddler crabs, Uca, yet discovered. The abundance and exceptional preservation of fossil male, female, juvenile and adult individuals of Uca aff. ornata in eroded burrow infills suggest that rapid entombment and early diagenesis were crucial for their preservation. The habitat preference of extant U. ornata for soft muds of open intertidal mudflats indicates that part of Bahía Bique must have been a large estuarine mudflat with close proximity to freshwater influx, in contrast to the present-day gravel field where the fossils are found as ex situ boulders, cobbles and gravel-sized clasts eroded from rocks of the poorly known Pacific Muck. We examine the systematic relationships of fossil fiddler crabs from Bahía Bique via synthetic and cladistic approaches, and conclude that they were from an extinct population of the extant Uca ornata. The fidelity of living–death assemblages between the Bique faunule and extant faunas of the tropical Eastern Pacific confirm the Quaternary age of the assemblage, and stimulate a detailed discussion of the preservation and palaeoecology of terrestrial and semi-terrestrial crabs in tropical assemblages.

ID: 139664
Type: article
Authors: Christy, John H.; Ribeiro, Pablo D; Iribarne, Oscar O; Nuñez, Jesús D
Keywords: STRI

ID: 139862
Type: article
Authors: deVries, Maya S.; Stock, Brian C.; Christy, John H.; Goldsmith, Gregory R.; Dawson, Todd E.
Keywords: fellow; STRI

ID: 139540
Type: article
Authors: Lim, Shirley S. L.; Yong, Adeline Y. P.; Christy, John H.
Keywords: STRI
Abstract: There are conflicting reports as to whether Ocypode gaudichaudii individuals switch from carnivory as juveniles to deposit-feeding primarily on diatoms as adults, or whether they expand diet range and become omnivorous with maturity. At the onset of deposit-feeding, crabs develop specialized claws with truncated ends that they use to shovel sediment during foraging. Eighty-eight crabs were collected from Culebra Island (Republic of Panama) to study how the diet of this crab shifts with changes in claw shape, mouthpart proportions, and setation, as well as gastric mill width. Forty-four crabs had identifiable material in their foreguts: 30 had animal material, 12 had diatoms, and two had a mix of both. There were no differences between the gastric mill, mandibles, and the proximal endites of the first maxillipeds of predators and deposit-feeders, but extra rows of plumose setae were present on the second maxilliped of deposit-feeding crabs with carapace length (CL) >10.6 mm. All individuals with CL <12.3 mm and non-truncated claws ate animals, but those with larger CL and truncated claws had animal, diatom, or mixed diets; hence, claw truncation does not restrict the crab's diet to diatoms but, instead, broadens the diet to include both animals and diatoms. Perhaps this is a strategy to balance the economics of foraging on animals and diatoms on medium to low-energy beaches that lack the larger invertebrates that adults of other species of ghost crabs eat. More generally, our study shows that specialized feeding structures need not imply a narrow or specialist diet.

ID: 140460
Type: article
Authors: Perez, Daniela M.; Christy, John H.; Backwell, Patricia R. Y.
Keywords: STRI

ID: 138194
Type: article
Authors: How, Martin J; Christy, John H.; Temple, Shelby E; Hemmi, Jan M; Marshall, N. Justin; Roberts, Nicholas W
Keywords: STRI
Abstract: Summary We are constantly surprised by the ability of relatively simple animals to perform precise visually guided movements within complex visual scenes, often using eyes with limited resolution. Exceptional examples include the capture of airborne prey by dragonflies 1], the learning flights of bees and wasps 2], and the tracking of conspecifics by crabs on intertidal mudflats 3–5]. Most studies have focused on how animals do this using sensitivity to intensity or color. However, it is increasingly evident that a third ability, polarization vision, may contribute to such tasks. In many insects, polarization-sensitive photoreceptors are confined within an area of the eye known as the dorsal rim 6], which detects the polarized sky pattern specifically for navigation 7]. However, some animals, including fiddler crabs, are sensitive to the polarization of light across the majority of their image-forming eyes 8, 9], potentially allowing them to use polarization information to increase perceived contrast for general visual tasks 10–13]. Investigations into the use of polarization image-parsing by animals have largely been confined to laboratory settings under artificial lighting 10, 13–18]. This approach can occasionally mislead if the lighting conditions are different from natural 19]. This study presents the first behavioral evidence from the natural context for a function of polarization image parsing. Using experimental manipulations in wild populations of the fiddler crab Uca stenodactylus, we provide evidence that these animals use their polarization vision to enhance contrast in their visual environment, thereby increasing their ability to detect and respond to objects on the mudflat surface.

ID: 133458
Type: article
Authors: Kim, Tae Won; Christy, John H.
Keywords: STRI

ID: 137664
Type: article
Authors: Shih, Hsi-Te; Ng, Peter K. L.; Christy, John H.
Keywords: STRI

ID: 120880
Type: article
Authors: How, Martin J.; Christy, John H.; Roberts, Nicholas W.; Marshall, N. Justin
Keywords: STRI
Abstract: The polarisation of light is used by many species of cephalopods and crustaceans to discriminate objects or to communicate. Most visual systems with this ability, such as that of the fiddler crab, include receptors with photopigments that are oriented horizontally and vertically relative to the outside world. Photoreceptors in such an orthogonal array are maximally sensitive to polarised light with the same fixed e-vector orientation. Using opponent neural connections, this two-channel system may produce a single value of polarisation contrast and, consequently, it may suffer from null points of discrimination. Stomatopod crustaceans use a different system for polarisation vision, comprising at least four types of polarisation-sensitive photoreceptor arranged at 0°, 45°, 90° and 135° relative to each other, in conjunction with extensive rotational eye movements. This anatomical arrangement should not suffer from equivalent null points of discrimination. To test whether these two systems were vulnerable to null points, we presented the fiddler crab Uca heteropleura and the stomatopod Haptosquilla trispinosa with polarised looming stimuli on a modified LCD monitor. The fiddler crab was less sensitive to differences in the degree of polarised light when the e-vector was at -45°, than when the e-vector was horizontal. In comparison, stomatopods showed no difference in sensitivity between the two stimulus types. The results suggest that fiddler crabs suffer from a null point of sensitivity, while stomatopods do not.

ID: 121054
Type: article
Authors: Kerr, Kecia A.; Christy, John H.; Joly-Lopez, Zo; Luque, Javier; Collin, Rachel; Guichard, Frédéric
Keywords: STRI

ID: 114326
Type: article
Authors: Dennenmoser, Stefan; Christy, John H.
Keywords: STRI
Abstract: Male fiddler crabs, genus Uca, have one greatly enlarged claw with which they court females and threaten and fight other males. Longer claws are more effective signals but are thought to be less effective weapons because the relative closing force at the tip of the claw decreases with claw length. We studied claw morphology and fighting in Uca terpsichores and Uca beebei and found a mechanism that may resolve opposing selection for signaling and fighting ability. When males fought they delivered gripping forces not at the tips but at the tubercles on the inner margins of their claws' fingers. As claws grow, these tubercles remain relatively close to the apex of the gape. Consequently, the mechanical advantage that governs the forces that can be delivered at these tubercles decreases only slightly with increasing claw length allowing the claw to be an effective signal and a powerful weapon. Animal weapons are exceptionally diverse in form and detail of armature and the causes of this diversity are poorly understood. We suggest that the designs of weapons may often reflect compensatory patterns of growth and placement of armature that enhances the weapon's overall utility for multiple uses in competition for mates.

ID: 114560
Type: article
Authors: Lombardo, Roberto C.; Christy, John H.; Cipriani, Roberto
Keywords: STRI

ID: 115486
Type: article
Authors: Matsumasa, Masatoshi; Murai, Minoru; Christy, John H.
Keywords: STRI
Abstract: Empirical studies of the reliability of sexual signals are needed to test the prediction that females should prefer males in good condition. We examined whether an attractive sexual signal used by male fiddler crabs, Uca beebei, reliably indicates male condition by measuring male blood glucose and lactate levels in the field. The signal is a mud structure, a ‘pillar’, that attracts females for mating. Blood lactate levels (a measure of energy expenditure) of pillar builders (P males) immediately after they built their pillars did not differ from those of nonbuilders (NP males), suggesting that the cost of building a pillar is small. However, P male lactate levels were significantly higher than those of NP males late in the activity cycle after P males had invested more in vigorous courtship using claw ‘waving’. Whereas P males maintained their glucose levels (a measure of energy availability as the major fuel for ATP production) at around 30 mg/dl throughout their daily activity period, NP males showed significantly lower levels in the middle of the period. These results confirm that pillars reliably signal a male’s condition, as measured by his ability to maintain a blood glucose level necessary for costly courtship, even though the construction of a pillar has minimal energetic cost.

ID: 116552
Type: article
Authors: Swanson, Brook O.; George, Matthew N.; Anderson, Stuart P.; Christy, John H.
Keywords: STRI