Ultraviolet reflectance patterns of the guppy (Poecilia reticulata) andtwo morphs of its predator, the convict cichlid (Archocentrus nigrofasciatus)

Kevin S. Hollick, Biological Sciences Department, York College of Pennsylvania

Introduction Many fish species can see into portions of the ultraviolet and exhibit patterning that reflects UV light. The ability to see into the UV portion of the spectrum requires eye pigments that have a max in the ultraviolet region. These UV visual cone pigments are found in many fish. UV vision may be beneficial to fishes for various reasons including sexual selection, navigation, feeding, communication, and preventing UV overexposure (1). The two species of fish used in this study were the guppy (Poecilia reticulata) and the convict cichlid (Archocentrus nigrofasciatus). P. reticulata has a maximum cone sensitivity at 389nm and is able to see into the near UV (2). UV reflectance patterns of guppies are used in mate selection. Males with higher levels of UV reflectance are more attractive to females (3). This study will be used to confirm previous studies on guppy UV reflectance. A. nigrofasciatus is a natural predator of P. reticulata. The convict cichlid has two distinct morphs, the zebra (striped) form and the pink (near-albino) form (4). Convicts cannot see into the UV (5). Mate selection is based on size, called size-assortative pairing. Males pick larger females up to their own size (6). This study is important because there has been no UV reflectance research on convict cichlids in the literature to date. If convict cichlids do, in fact, reflect highly in ultraviolet, the next step would be to determine if this UV reflectance serves a particular purpose. Studies are now showing that some African cichlid species can see into the UV (7). An appearance of UV reflectance patterns in the convict cichlid may indicate that it might have been able to visualize UV earlier in its evolution and lost the ability at some point.

Hypotheses This study will entail two separate comparisons. (1) The UV reflectance patterns of guppies and the striped morph of convict cichlid will be compared. It is hypothesized that guppies will have a significantly higher area of UV reflectance relative to their size than do convicts. (2) The UV reflectance patterns of the two convict cichlid morphs will be compared. It is hypothesized that the UV reflectance of the pink morph will be significantly less than the zebra morph.

Materials and Methods•Guppies were bred from laboratory stock (initially purchased from retailer).•Cichlids were purchased from a local retailer.•Fish were selected at random.•Only males of each species were used.•Fish species were kept in separate glass tanks with corner filters.•Water temperature was kept @ about 23C.•Standard fluorescent aquarium lights were used on a 14 hour day/10 hour night cycle. •Fish were fed daily with TetraMin® flake food.•MS-222 (tricaine methanesulfonate) was used as the anesthetic.•Fish were transferred individually from the original tank to the MS-222 tank.•The fish were placed on a Petri dish with a ruler for scale.•A model UVSL-58 Mineralight lamp @ 366nm was used as the UV light source.

•Three pictures were taken of each fish:•A color, visible light photo using an Olympus Camedia C-2500L digital SLR camera.•A B&W, visible light photo using a Nikon EM, 35mm f/2.5 lens, and TMax 400 film.•A B&W, UV light photo using a Nikon EM, UV transmitting modified 35mm f/2.5 lens, B+W 403 filter, Tiffen Hot filter, and TMax 400 film.

•Fish were then placed in a fresh water recovery tank.•The photos were analyzed for area of UV reflectance and total body area (in cm2) using ScionImage 4.0.2b software (Scion Corporation, Maryland, USA).

Results Ultraviolet reflectance patterns of the guppy were found chiefly on the head region, tail, and dorsal fin (Fig. 1). Some reflectance was also found on the main body. The mean area of UV reflectance of the guppy was 1.03±0.09cm2. The mean total body area was 3.01±0.19cm2 (Fig. 2). The mean AUV:AT ratio was 0.38 ±0.08. (Fig. 3). UV patterns on the zebra convict typically followed the visible light striped patterns. The mean area of UV reflectance of the zebra convict was 4.11±0.37cm2. The mean total body area was 9.05±1.18cm2 (Fig. 2). The mean AUV:AT ratio was 0.50±0.14 (Fig. 3). UV patterns of the pink convict, if any, generally appeared as a small line across the dorsal side. The mean area of UV reflectance of the pink convict was 1.55±0.24cm2. The mean total body area was 11.46±0.51cm2 (Fig. 2). The mean AUV:AT ratio was 0.13±0.02 (Fig. 3). A one way ANOVA test followed by a Bonferroni's Multiple Comparison test showed that there was no significant difference (p>0.05) between the AUV:AT ratios of the guppy and the zebra convict cichlid. There was a significant difference (p<0.01) in the AUV:AT ratios of the two convict cichlid morphs.

Figure 1.

Figure 1. Generalized illustrations of ultraviolet reflectance (UV reflectance shown by a dark black area) and actual photographs of color-visible, black and white-visible, and black and white-UV light, respectively.

Figure 2. Mean ultraviolet reflectance area and total body area of P. reticulata and the two morphs of A. nigrofasciatus. Error bars represent one standard error of the mean.

Figure 3. A comparison of the mean AUV:AT ratios of P. reticulata and the two morphs of A. nigrofasciatus from a one way ANOVA test (p<0.05). The sample size (n) was 23 for theguppy and 12 for both cichlid morphs. A “ns” designates that there is no significant difference in the means of the guppy vs. the zebra cichlid (p>0.05) from a Bonferroni's Multiple Comparison test. An asterisk (*) designates that there is a significant difference in the means of the zebra morph vs. the pink morph (p<0.01). Error bars represent onestandard error of the mean.

Conclusion• The data do not support the first hypothesis.

• There is no significant difference between the AUV:AT ratios of guppies and zebra convict cichlids.

• The data do support the second hypothesis.• Zebra convict cichlids do have a significantly higher AUV:AT ratio than do pink

convict cichlids. The mean UV reflectance of the guppies in the current study was 38% of the totalbody area. This is larger than previous studies. Kodric-Brown and Johnson (3) found that only 4-24% of the area of the male guppies they used to be UV reflective. White et al. (8) found their male guppies to range in UV reflectance from 6.4-10.1%. This discrepancy may be due to the strain of guppies used or a difference in what eachscientist considered as actual UV reflectance. The ultraviolet photographs appear as grayscale gradients, not only black and white. It is possible that certain dark areas would be counted as part of the UV reflectance area by one scientist and not the other. Surprisingly, zebra convict cichlids do have a considerable amount of UVreflectance even though they are not able visualize it. It also apparent that this UV reflectance has been reduced along with visible light reflection patterns by selective breeding in the pink morph. This raises several questions:

• Does the cichlid UV reflectance alter visibility by potential prey (guppies) and affect predator/prey interactions?

• Does the UV reflection serve a purpose to the convict and if so, what is that purpose? • Was there some point in the evolution of the zebra cichlid when it could visualize UV?

Literature Cited(1) Losey, G.S., Cronin, T.W., Goldsmith, T.H., Hyde, D., Marshall, N.J., and McFarland, W.N. 1999. The UV visual world of fishes: a review. Journal of Fish Biology 54:921-943.(2) Archer, S.N. and Lythgoe, J.N. 1990. The visual pigment basis for cone polymorphism in the guppy, Poecilia reticulata. Vision Research 30:225-233. (3) Kodric-Brown, A. and Johnson, S.C. 2002. Ultraviolet reflectance patterns of male guppies enhance their attractiveness to females. Animal Behaviour 63:391-396.(4) Mills, D. 2000. The Encyclopedia of Aquarium Fish. Barron’s, Hauppauge NY.(5) Douglas, R.H. and McGuigan, C.M. 1989. The spectral transmission of freshwater teleost ocular media –an interspecific comparison and a guide to potential ultraviolet sensitivity. Vision Research 29:871-879.(6) Beeching, S.C. and Hopp, A.B. 1999. Male mate preference and size-assortative pairing in the convict cichlid. Journal of Fish Biology 55:1001-1008.(7) Carleton, K.L., Ha´rosi, F.I. and Kocher, T.D. 2000. Visual pigments of African cichlid fishes: evidence for ultraviolet vision from microspectrophotometry and DNA sequences. Vision Research 40:879-890.(8) White, E.M., Partridge, J.C., Stuart, C.C. 2003. Ultraviolet dermal reflexion and mate choice in the guppy, Poecilia reticulata. Animal Behaviour 65:693-700.

Acknowledgements: I would like to thank: Bradley Rehnberg, PhD, Karl Kleiner, PhD, Jeffrey Thompson, PhD, Bjørn Rørslett, Lori Reever, Margaret Hollick, Getty’s Pet Shop, That Fish Place, The Camera Shop of York, and B&H Photo-Video.