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ANIMAL BEHAVIOUR, 26, 1

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Krebs, J . R . 1977 . The significance of song repertoires :the Beau Geste hypothesis . Anim. Behav., 25,475-478 .

Lemaire, F. 1975. Le chant de la Rousserolle Verderole(Acrocephalus palustris) : Fidelit6 des imitationset relations avec les esp6ces imitees et avec lescongen6res. Le Gerfault ., 65, 3-28 .

Morton, E . S . 1976. Vocal mimicry in the Thick-billedEuphonia . Wilson Bull., 88, 485-487 .

Robinson, F. N . 1975 . Vocal mimicry and the evolutionof bird song. Emu, 75, 23-27.

Thorpe, W. H . 1964. Mimicry, vocal. In : A New Diction-ary of Birds (Ed. by A . L. Thomson). London :Nelson.

Wickler, W . 1968 . Mimikry. Munchen : Kindler .

(Received 17 August 1977 ; revised 9 September 1977 ;MS. number : s-18)

Fishes as Experimental Subjects for Studies of VertebrateColour Vision

Fishes can serve as convenient experimental subjects forcomparative experiments on vertebrate colour vision.Existing data indicate striking parallels between spectralresponses of fishes and other vertebrates . Inter-classcomparisons suggest several possibly fruitful lines ofresearch as follows .

There is extensive evidence that fishes have trichromaticcolour vision (Kawamoto & Takeda 1951 ; McCleary& Bernstein 1959 ; Muntz & Cronly-Dillon 1966 ;Yager 1967; Niwa & Tamura 1969; Marc & Sperling1976), based on cone pigments with absorption maximaat 453 to 455 nm, 530 to 535 nm and 620 to 625 nm(Yager 1967 ; Marc & Sperling 1976) . Human vision isalso trichromatic on the basis of visual pigments .

Bornstein et al . (1976) have inferred from optomotorfixation-time (as a measure of stimulus novelty) thathuman infants categorize the visual spectrum into fourhue categories (blue, 430 to 480 nm ; green, 510 to 560nm; yellow, 570 to 600 nm; red, 620 to 640 nm), withthese perceptual 'plateaus' separated by transitionalboundaries . Bornstein et al. (1976) cite similar hue-categorization phenomena in bees and pigeons, and infera biological basis independent of language . Similarexperiments do not seem to have been conducted as yetwith fishes.

Goldfish show (psychometric function) spectralsensitivity maxima at 450 nm, 535 to 554 nm, and 625to 653 nm, whereas similarly measured human fovealspectral sensitivity functions show peaks or plateausat 484 nm (blue), 550 to 560 nm (green), and 625 to 653nm (red) (Yager 1967). Discrimination of saturation ingoldfish is most sensitive at the ends of the spectrum,and from 510 to 535 nm ; minima at 490 to 500 nm andat about 600 nm (Yager 1967) correspond to Bornsteinet al .'s (1976) human blue-green and yellow-red transi-tions, respectively. Two of Yager's (1967, Fig. 6) threegoldfish showed some evidence of a minimum corres-ponding to the narrower human green-yellow transition(Bornstein et al . 1976) at about 560 to 570 nm. Hailman(1967) has pointed out that use of a frequency scale(THz) rather than a wavelength scale (nm) results in animproved correspondence between spectral discrimina-tion (jnd or 'just-noticeable-difference') and hue-namingcurves, principally by shifting the shallow 'green' peak

of poor discrimination to shorter wavelengths, and alsoby making the discrimination values at the extremes ofthe spectrum more similar .

It is puzzling that there should be four major per-ceptual hue categories (Bornstein et al . 1976), but onlythree cone pigments (the 'yellow' perceptual categoryapparently does not correspond to any specific pigment),a discrepancy as yet unexplained. J. P. Hailman (personalcommunication) points out that categorical tests tendto have outcomes dictated by how the test is set up ;indeed, older literature tended to recognize as many asseven categories (violet, indigo, blue, green, yellow,orange and red) . On a priori grounds, one would expectthe truly fundamental hue categories to correspond tothe three cone pigments .

Hailman & Jaeger (1974) have shown that amphibiansexhibit a 'blue-mode' spectral response (preference forblue) at ambient light intensities below the range preferredby the species, whereas a 'U-shaped' spectral response(preference for the ends of the spectrum) appears atintensities exceeding the species-specific preferendum('OAI'). At intermediate (non-aversive) intensities withinthe preferred range, a unimodal 'unclassified' spectralpreference (often for green or yellow) occurs . There isevidence of similar responses in teleost fishes . A bluepreference has been reported in the photopositive speciesBox salpa (Bauer 1910) and goldfish Carassius auratus(Muntz & Cronly-Dillon 1966), whereas the photo-negative Anguilla japonica (Kawamoto & Kobayashi1952) showed a U-shaped spectral response (Kawamoto& Takeda 1951) . Spheroides niphobles exhibited anunclassified response (unimodal yellow preference)(Kawamoto & Takeda 1951) at about its preferred lightintensityof 55 lux (Kawamoto & Nagata 1952). The blue-gill Lepomis macrochirus shows a blue-mode preferenceat intensities below 10 lux, and unclassified preferencesfor yellow or green at 50 to 125 lux (Ostrowski &Reynolds, unpub . data presented at 1976 SoutheasternDiv. Animal Behavior Society Meeting) . The intensitynecessary to evoke a U-shaped response has yet to bedetermined .

The above considerations, along with Hailman &Jaeger's (1974, p. 792) conclusion that 'the origins ofboth the blue-mode and U-shaped spectral responseslie in the remote ancestors of the anurans', andParvatheswararao's (1975) proposed phylogenetic schemeoutlining the inferred evolutionary relationships ofvisual pigments among the lower vertebrates, point theway toward further investigations of colour perceptionand responses among classes which promise to unravelmore fully the mysteries of the evolution of vertebratevisual systems .

WILLIAM W. REYNOLDS, ANTHONY C . OSTROWSKI& MARTHA E. CASTERLIN

Department of Biology,The Pennsylvania State University,Wilkes-Barre, Pennsylvania 18708.

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mogen der Fische. Pjliigers Arch. ges . Physiol .,133,7-26 .

Bornstein, M. H., Kessen, W . & Weiskopf, S . 1976.The categories of hue in infancy . Science, N. Y.,191, 201-202.

Hailman, J. P . 1967 . Spectral discrimination : an impor-tant correction. J. Opt . Soc . Amer., 57, 281-282.

Hailman, J . P. & Jaeger, R. G. 1974. Phototacticresponses to spectrally dominant stimuli and useof colour vision by adult anuran amphibians : acomparative survey. Anim . Behav., 22, 757-795 .

Kawamoto, N . Y. & Kobayashi, H. 1952 . Influence ofvarious light conditions on the gathering rates offish . Rept. Faculty Fish . Prefectural Univ. Mie, 1,139-150 .

Kawamoto, N . Y. & Nagata, S . 1952. On the relationbetween light gradient and fish behavior . Rept.Faculty Fish . Prefectural Univ. Mie, 1, 151-173 .

Kawamoto, N. Y. & Takeda, M . 1951 . The influenceof wave lengths of light on the behaviour of youngmarine fish . Rept. Faculty Fish. PrefecturalUniv. Mie, 1, 41-53 .

Marc, R. E. & Sperling, H . G. 1976 . Color receptoridentities of goldfish cones . Science, N. Y., 191,487-489 .

McCleary, R.A. & Bernstein, J. J. 1959. A uniquemethod for control of brightness cues in study ofcolor vision in fish . Physiol. Zool., 32, 284-292.

Muntz, W. R . A. & Cronly-Dillon, J . R. 1966. Colour dis-crimination in goldfish . Anim. Behav ., 14,351-355 .

Niwa, H. & Tamura, T . 1969. Investigations of fishvision by means of S-potential . Spectral sensitivityand colour vision . Can . Rev . Biol ., 28, 79-88 .

Parvatheswararao, V . 1975. Distribution of visualpigments in the teleostei-a comment . Mar .Biol., 33, 67-70 .

Yager, D . 1967. Behavioral measures and theoreticalanalysis of spectral sensitivity and spectralsaturation in the goldfish, Carassius auratus .Vision Res ., 7, 707-727 .

(Received 24 March 1977 ; revised 23 May 1977 ;2nd revision 7 June 1977 ; MS . number: As-14)

Aggressive Courtship as a Means of Avoiding CuckoldryZahavi (1977) recently addressed the often neglectedquestion of why social relationships among animalsare initiated by behaviour patterns that have an aggressivecharacter . Although there may be many instances inwhich the aggression exists only in the eye of the humanobserver, we are inclined to accept Zahavi's assumptionthat such behaviour is often demonstrably aversive to therecipient but has compensatory advantages for theperformer . Actually, in some contexts, initial episodes ofaggression may benefit the performer, recipient, or both .The purpose of our response is to suggest other benefitsof aggression when it occurs upon the initiation of asocial relationship, and we shall confine our attentionto the aggressive courtship of male birds .

Most explanations of aggressive courtship emphasizeits role in mate selection . As a test for the quality offemale mates, Trivers (1972) suggested that it may `actas a sieve, admitting only those females whose highmotivation correlates with early egg laying and highreproductive potential' (p . 172) . Zahavi's suggestion thatmale aggression tests the bonding inclinations of thefemale is similar to Trivers's view, but we are not con-vinced that either the reproductive potential or thebonding inclinations of a female can be expected toremain unchanged by the test. In short, a blow to thenose is unlikely to leave the affections of the recipientuntarnished. Male aggression may also aid the femalein selecting a mate. Possibly, it could inform a female ofthe dominance status of a male (Trivers 1972) or, in thecase of extended breeding relationships, it could providea gauge of a male's capacity to protect the nest and young .

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In each of the instances described above the aggressivecourtship of males has been viewed as a basis for mateacquisition . However, it is possible that this aggressionprovides benefits that are independent of any role in mateselection, affecting the chosen female in order to improveher quality as a mate. Aggressive courtship may servethe important function of avoiding cuckoldry. In arecent study (Erickson & Zenone 1976) we found thatnot only are male ring doves (Streptopelia risoria)aggressive toward females when they first meet, they arefar more aggressive when these females have recentlyassociated with other males . Barash (1976) has observedsimilar behaviour in male mountain bluebirds (Sialiacurroides) . In our report we interpreted the high aggres-sion as an attempt to drive away those females thatmight already have been inseminated by other males, atactic for avoiding cuckoldry . But as both Barash (1976)and Maynard-Smith (1977) point out, the value of such astrategy in terms of protecting male parental investmentmay depend upon the availability of other, uninseminatedfemales as alternative mates . Male aggression may bemore effective if it protects the male's genetic paternityshort of driving the female away. One effect might be todelay female ovulation beyond the effective lifetime ofany sperm cells she might be carrying in her reproductivetract . For example, Riddle & Behre (1921) estimated,and we have confirmed, that female ring doves can besuccessfully fertilized for about 6 days after insemination .

In a recent study Hutchison & Lovari (1976) showedthat when female ring doves are paired with malesexhibiting highly aggressive courtship, they requireabout 8 days to lay their first egg . (Ovulation and fertili-zation can be assumed to have occurred about 40 hbefore oviposition .) On the other hand, females pairedwith males that were much less aggressive required only5 . 25 days to lay their first egg . Therefore, one can pre-sume that if the females had been carrying sperm from aprevious mating when the males first encountered them,there was a higher probability that the more aggressivemales would be the genetic fathers of the young produced .It must be emphasized that the males need not delayovulation beyond the lifetime of any sperm the femalemay be bearing; he need only postpone ovulation to thepoint where his own sperm cells can compete successfullywith the aging sperm in her reproductive tract . Manyyears ago Warren & Kilpatrick (1929) demonstrated thatsperm stored in the reproductive tract of female domesticfowl (Gallus gallus) could successfully fertilize eggs forseveral weeks after insemination, yet these sperm cellscould not compete successfully with fresh sperm from asecond male for more than a few days . Finally, it shouldalso be noted that if male aggression is stressful to thefemale, it may not only delay ovulation, but it may alsoproduce temporary hormonal changes creating an ecologi-cally inhospitable climate for sperm within the repro-ductive tract.

In conclusion, we agree with Zahavi that aggressivecourtship may benefit the performer by screening partnersfor extended relationships, but we feel that in the contextof male-female relationships, the male's aggression mayalso protect him from the possibility of cuckoldry .

Some of these thoughts grew out of our correspondencewith R . L. Trivers, and we are grateful for his interestand encouragement.

CARL J. ERICKSON & PATRICIA G. ZENONE

Department of Psychology,Duke University,Durham, North Carolina 27706 .