Effects of male colouration on female choice in Siamese fighting fish (Beta splendens) sexual selection
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Bettas, or Siamese fighting fish (Betta splendens) live in fresh waters of Southeast Asia in stagnant lakes, slow moving streams and rice paddies (Rainboth 1996). Bettas have been bred in captivity for increased fin length, greater color, and increased aggression (Allen and Nicoletto 1997). They are readily available, low maintenance, and display highly stereotypical aggression and courtship displays, making them a good subject for behavioral studies (Allen and Nicoletto 1997).
In sexual selection, male coloration has been shown to influence female mate choice in a wide range of animals including birds (Ballentine and Hill 2003), primates (Waitt et al. 2003), and fish (Seehausen and van Alphen 1998). In this experiment, I sought to determine whether male coloration also plays a role in female mate choice in bettas; that is, do female bettas have a preference for males of a certain color over others? I predicted that female bettas would prefer one of the male color types tested (green, blue, and red) over the others. As a possible explanation for this prediction, I hypothesized that females would preferentially chose a certain color of male because it has been shown in other fish species that male coloration can be an important indicator to females of species identity (Seehausen and van Alphen 1998) and male quality (Pilastro et al. 2004), and similar factors may cause female bettas to select for a particular color of male. A corresponding null hypothesis is that female choice is not influenced by male coloration.
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Methods
Ten males (two red, four blue, and four green) were kept in individual clear plastic tanks and visually isolated from one another and from females – also kept in individual, clear plastic tanks – prior to the experiment. To determine whether the females had a preference for males of a certain color we placed a pair of males on either side of a female’s tank, allowing them to see and react to each other, and observed for one minute to determine which male the female chose, or which male “won.” A male was said to have won if the female spent more than half of the minute on the side of her tank closest to that male. We repeated this for all possible pairings of males (45) with a new female selected for each pairing in order to avoid any bias a particular female might have for or against a particular male from biasing all the results for that male.
Next, the number of expected wins for each color of male was calculated by taking the number of males of a color, dividing by the total number of males, and multiplying the resulting proportion by the total number of trials: 2 red/10 = .2; .2*45 = 9 expected wins for red males. 4 green/10 = .4; .4*45 = 18 expected wins for green males. 4 blue/10 = .4; .4*45 = 18 expected wins for blue males. The actual number of wins for blue, green, and red males was summed and compared to the number of expected wins; I graphed the number of wins for each color as a percentage of the expected wins for each color in order to demonstrate possible trends. I performed a Chi Square test to determine if the observed trends in the data were significant.
Results
Table 1: Female choice of males by color
OBSERVED EXPECTED Observed as percentage of expected
RED 7 9 77.8
GREEN 22 18 122
BLUE 16 18 88.9
(n=45)
The results for observed wins, expected wins, and observed wins as a percentage of expected wins are summarized in table 1, above. Green males were chosen most, 22 wins, or 122% of expected wins, followed by blue males with 16 wins, or 88.9% of expected wins. Red males were chosen the least with 7 wins, or 77.8% of the wins they were expected to achieve.
Although it appeared that green males were chosen the most often, the Chi Square p value for the data was equal to 0.45942548, indicating a non-significant result.
Discussion
Females did choose the green males slightly more often and the red males least often, but no significant preference for any of the three colors of males was shown. This result fails to support my hypothesis that females would prefer a certain color of males as a form of sexual selection. While evidence of male coloration as a component of female mate choice has been observed in some fish species (Pilastro et al. 2004, Seehausen and van Alphen 1998) it as also been found to be unimportant in female mate choice in other fish species (Pyron 1995). Similar to Pyron’s (1995) findings on orangethroat darters (Etheostoma spectabile), Betta spelendens may be one species where male coloration is not an important part of female mate choice. Other factors may be involved, such as male dominance status (Doutrelant and McGregor 2000), the size of males (Jaroensutasinee and Jaroensutasinee 2001), or male fin length (Allen and Nicoletto 1997). A potential reason why male coloration might not be important for female betta mate choice is that, in domestic bettas at least, the coloration of males has been artificially selected for by humans and not by females of the species over evolutionary time. Alternatively, if female bettas do use male color as a selection criterion, they may be looking at the brightness of the color as an indicator of male quality, as with female guppies (Pilastro et al. 2004) rather than simply the color (green, blue, or red) itself.
This experiment was performed on a relatively “simple” species (bettas) which is far less social and intelligent than many other animals, such as birds and mammals. Yet the results are far from being clear-cut or conclusive, and seem to agree with some similar studies while contradicting others. If anything, these results demonstrate the overall complexity and challenge of studying animal behavior, and especially of applying generalizations across species.
Literature Cited
Allen JM, Nicoletto PF. 1997. Response of Betta splendens to computer animations of males with fins of different length. Copeia 1997(1), 195-199.
Ballentine B, Hill GE. 2003. Female mate choice in relation to structural plumage coloration in Blue Grosbeaks. Condor 105 (3), 593-598.
Doutrelant C, McGregor PK. 2000. Eavesdropping and mate choice in female fighting fish. Behaviour 137, 1655-1669.
Jaroensutasinee M, Jaroensutasinee K. 2001. Sexual size dimorphism and male contest in wild Siamese fighting fish. Journal of Fish Biology 59(6), 1614-1621.
Pilastro A, Simonato M, Bisazza A, Evans JP. 2004. Cryptic female preference for colorful males in guppies. Evolution 58 (3), 665-669.
Pyron M. 1995. Mating patterns and a test for female mate choice in Etheostoma spectabile (Pisces, Percidae). Behavioral Ecology and Sociobiology 36 (6), 407-412.
Rainboth WJ. 1996. Species summary: Betta splendens. Fishbase (online). Accessed November 13, 2006 at http://filaman.ifm-geomar.de/Summary/SpeciesSummary.php?id=4768
Seehausen O, van Alphen JJM. 1998. The effect of male coloration on female mate choice in closely related Lake Victoria cichlids (Haplochromis nyererei complex). Behavioral Ecology and Sociobiology 42(1), 1-8.
Waitt C, Little AC, Wolfensohn S, Honess P, Brown AP, Buchanan-Smith HM, Perrett DI. 2003. Evidence from rhesus macaques suggests that male coloration plays a role in female mate choice. Proceedings of the Royal Society of London Series B -- Biological Sciences 270, S144-S146 Suppl. 2.
