Author Institution: Chesapeake Biological Laboratory, Solomons, Maryland 26088 and Institute of Marine Sciences, University of North Carolina, Morehead City, N. C. 28557Male and female xanthid mud crabs, Rhithropanopeus harrisii, when subjected both to paired and to simultaneous-combination color tests, exhibited nearly identical preference patterns for black, yellow, green, red, blue, and ultraviolet colors (listed in order of choice), although some individual variation occurred. Further investigations into the statistically significant reactions to blue and ultraviolet colors by both sexes is warranted

Gerberg, Gary

Schwartz, Frank J.

The Ohio Journal of Science

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COLOR PREFERENCES OF THE XANTHID MUD CRABRHITHROPANOPEUS HARRISIPGARY GERBERG AND FRANK J. SCHWARTZChesapeake Biological Laboratory, Solomons, Maryland 86088 andInstitute of Marine Sciences, University of North Carolina, Morehead City, N. C. 28557ABSTRACTMale and female xanthid mud crabs, Rhithropanopeus harrisii, when subjected both topaired and to simultaneous-combination color tests, exhibited nearly identical preferencepatterns for black, yellow, green, red, blue, and ultraviolet colors (listed in order of choice),although some individual variation occurred. Further investigations into the statisticallysignificant reactions to blue and ultraviolet colors by both sexes is warranted.Although decapods are known to possess color discrimination, few have beensubjected to color-preference tests (Waterman, 1961). Little is known regardingcolor preferences of the xanthid crab, Rhithropanopeus harrisii (Gould), whichabounds in Chesapeake Bay (Ryan, 1956) and in the brackish waters of thePatuxent River adjacent to Solomons, Maryland. Experiments were performedto see if this crab could discern between colors, whether there were color preferences,and whether they were sex specific.TEST ANIMALS AND EXPERIMENTAL PROCEDURESDuring the period 13 to 17 July 1962, five male and five female Rhithropanopeusharrisii were tested to determine if they exhibited color preferences when sub-jected to seven colored lights (hereafter called colors): black (darkness), white,red, yellow, green, blue, and ultraviolet. Between 4 and 17 September 1962,additional specimens (3cf o71, 3 9 9 ) were subjected to tests where all seven colorconditions were presented simultaneously to corroborate the original color-combina-tion test results.Crabs 10.1-15.3 mm in carapace width were collected from trays of oysterslocated at the end of the 250 m Chesapeake Biological Laboratory pier whichextends into the Patuxent River. Prior to testing, all specimens were kept aliveseparately in plastic ice cube trays in running water of the same temperature andsalinity (8-18°/°°) as that pumped from the Patuxent River. Food, except duringtest periods, consisted of bits of oysters or soft-shell clams. ; .Test chamber for the July experiments consisted of an oblong 56.8-liter aquar-ium with glass sides and slate bottom, darkened on all sides to prevent entry ofoutside light. A cardboard placed vertically across the center of the aquariumextended to within 61 mm of the bottom, to divide it into two smaller and nearlyequal chambers. No substrate was employed. A constant flow of unfilteredPatuxent River water was maintained by plastic tubes entering the aquariumalong either end of the divider. Siphons, one at each end of the aquarium, main-tained a 61-mm water depth. This water-circulation pattern seemed least likelyto cause the crabs to learn to prefer one segment of the aquarium over that ofanother. Each test chamber was covered by a removable light source in the formof a 30.5-cm-square, 27.9-cm-high pyramidal cardboard enclosure containing a100-watt incandescent bulb. Light from this source passed through a 19-cmcircular hole at the base of the enclosure containing the light and through one ofseveral color niters. Color filters were made from colored cellophane often severallayers thick. Light intensity for all niters was standardized to that level passingthrough the blue filter.ijVlanuscript received August 3, 1968.THE OHIO JOURNAL OF SCIENCE 70(2): 115, March, 1970.116 GARY GERBERT AND FRANK J. SCHWARTZ Vol. 70July experiments consisted of placing one each of the five male or five femalecrabs into the small color-overlap zone, produced at the base of the cardboarddivider in the oblong aquarium by any two color-test combinations. Twenty-onecombinations (i.e. black with yellow) of the seven original colors were conducted,each tested 10 times, for a total of 1,050 tests per sex (5 crabs) (Table 1). Eachtest was of a five-minute duration. Pre-experiment trial observations noted thatcrab "selection" of one color or another occurred in less than one minute. Thecolor in which the crab was found was considered the "chosen" color. At all times,TABLE 1Two color preference and avoidance reactions exhibited by male and female mud crabs tested summer,1962. Lower half of table indicates preference, upper half avoidance, 50 tests for each colorcombinationColorBlackWhiteRedYellowGreenBlueUltravioletSexMFMFMFMFMFMFMFBlack484643353128314042394644White2424272312191620223742ColorRed71526231925201936304245Yellow192227383125341732283843Green191031343031163335243739Blue81130281420182215262637Ultra-violet461388512713112413TotalAvoidance5968175177150143119127132129189156226250Total PreferenceGrand TotalMF2412324731251232481501573071811733541681713391111442557450124105010502100to eliminate a learning factor, test-color pairs were selected randomly and altered(i.e. red could occur in one end of the aquarium during combination tests 1, 4, 7,8, 9 and in the other during tests 2, 3, 5, 6, and 10) between ends of the tanks tofurther eliminate preference to some pecularity in one end of the test aquarium.Specimens were likewise tested randomly. The 2,100 tests were conducted be-tween 0900 and 2300 hr, with the preponderance being between 0900 and 1700hr. (0900, 100 tests; 1000, 190; 1100, 260; 1200, 220; 1300, 180; 1400, 210; 1500,210; 1600, 170; 1700, 120; 1800, 70; 1900, 70; 2000, 100; 2100, 110; 2200, 80;2300, 10).A circular 22.9-cm glass tank 30.5 cm high was darkened throughout withblack paint and served as a test chamber for the second series (September) of colorobservations. A 10-cm water depth was maintained by a circulating water systementering down the center of the tank and passing up through a plastic disk whichhad been drilled with 3-mm holes, situated 6.1 cm off the bottom. Water wassiphoned off from near the center of the tank. A conical overhead enclosure wasdivided by cardboard dividers into six pie-shaped chambers. Each pie-shapedNo. 2 COLOR PREFERENCES OF XANTHID MUD CRABS 117wedge contained a color identical in composition to the July experiments (ultra-violet being excluded because of bulb size).Round-tank tests consisted of introducing the specimen at the center of thetank, at a point where all of the colors overlapped and observing the crab's posi-tion, relative to a color, after five minutes. The top, which contained the colors,was rotated randomly after each test to reduce chamber-cue bias. Thus, whitemay have been over position 1 during test 1, but over position 5 during test 2, etc.Chi-square analyses were performed to see if the patterns of color choices be-tween sexes were different and if some colors were selected more than others.Water temperatures and salinities were recorded throughout both test periodsand ranged between 25.3-26.7°C and 12.9-13.6°/oo for July and 24.5-25.8°C and15.3-16.0/oo for September.RESULTSAquarium tests.—Male and female Rhithropanopeus harrisii exhibited nearlyidentical color preferences (Table 1), which were, in order of preference: black,yellow, green, red, blue, white, and ultraviolet. Slight variations were attribut-able to specific individuals who, no matter what color combination was presented,moved either to the right or left.As expected, a highly significant positive reaction to black (Table 1) wasexpressed by both males (241 of 300 tests) and females (232 of 300) (Table 2).TABLE 2Chi-Square Analyses of Positive reactions within and between Male and Female Mud Crabs toIndividual Colors and to all Colors, 1962ColorBlackWhiteRedYellowGreenBlueUltravioletTotalMaleX2110.410.330.0112.814.3220.2877.01225.17Within SexesSignificance FemaleX** 89.659.720.657.055.88** 0.48** 13.33** 126.76Significance********BetweenSexes0.170.020.160.190.034.274.659.491d.f.11111117lNot significant P~0.2 .Unexpectedly, yellow was second choice by both males and females. Howevermales, when subjected to a yellow and green choice combination between 0900-1200 hr and 1500-1700 hr, moved toward the yellow more often than toward thegreen color, whereas at other times of the day, yellow and green were split choices.Females during the same hours exhibited just the reverse reaction to a choicebetween yellow and green. While it is known that coastal waters generally havetheir maximum transparency in the yellow-green portion of the spectrum (Hill,1962), it was not known whether, locally, yellow or green were the wave lengthsthat filtered down to the crabs, during the 1000-1700-hr portion of any sunnysummer day, to influence their behavior. Red was chosen more often than blue,a reverse of what one would have expected for these shallow-water-inhabitingcrabs, where blue colors characteristic of the deeper water layers should havefiltered down through the water column to them rather than the red. Why bluewas chosen less often by males (Table 1) than by females needs additional experi-118 GARY GERBERG AND FRANK J. SCHWARTZ Vol. 70mentational investigation. White (a mixture of all colors) was, contrary to ex-pectations, sixth in color preference, despite the fact that Rhithropanopeus harrisiimay be observed moving actively about in its natural environment during day-light hours. Males and females both exhibited a highly significant avoidance ofultraviolet light.Round-tank tests.—Round-tank tests corroborated the results achieved by thetwo-color-aquarium choice tests. The same sequence of color preference—black,yellow, green, red, blue, white, and ultraviolet—was noted for each sex. Malesand females also exhibited their peculiar yellow-green reverse phases in thesetests, as they had done in the earlier ones.ACKNOWLEDGMENTSThanks are due to Drs. William E. Ricker, Fisheries Research Board of Canada,Nainaimo; J. Muncy, Colorado State University, Fort Collins; and V. Schultz,Washington State University, Pullman, Washington, for valuable comments onthe statistical approaches to this problem; to Dr. R. V. Miller, Tropical AtlanticLaboratory, M. D. G. Cargo, Chesapeake Biological Laboratory, and to Dr.A. F. Chestnut, University of North Carolina Institute of Marine Sciences, for areview of the manuscript and discussion regarding the results and their implica-tions; and Mr. A. W. Kendall for laboratory assistance.LITERATURE CITEDHill, M. N. (ed). 1962. The Sea. Interscience Publ. N. Y. Vol. 1. XV+864.Ryan, E. P. 1956. Observations on the life histories and the distribution of the Xanthidae(mud crabs) of Chesapeake Bay. Amer. Midi. Nat. 56(1): 138-162.Waterman, T. H. (ed.). 1961. The physiology of Crustacea. Academic Press. N. Y. Vol. II.xiv+681.

Color Preferences of the Xanthid Mud Crab Rhithropanopeus Harrisii

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Color Preferences of the Xanthid Mud Crab Rhithropanopeus Harrisii

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