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. 2019 Aug 8:16:34.
doi: 10.1186/s12983-019-0333-x. eCollection 2019.

Artificial selection for male winners in the Siamese fighting fish Betta splendens correlates with high female aggression

A Ramos  1 , D Gonçalves  1
Affiliations

Artificial selection for male winners in the Siamese fighting fish Betta splendens correlates with high female aggression

A Ramos et al. Front Zool. .

Abstract

In Southeast Asia, males of the Siamese fighting fish Betta splendens have been selected across centuries for paired-staged fights. During the selection process, matched for size males fight in a small tank until the contest is resolved. Breeders discard losing batches and reproduce winner batches with the aim of increasing fight performance. We assessed the results of this long-term selection process by comparing under standard laboratory conditions male and female aggressive behaviour of one strain selected for staged fights ("fighters") and one strain of wild-types. The aggressive response of adult fish was tested against their mirror image or a size-matched conspecific. Fighter males were more aggressive than wild-type males for all measured behaviours. Differences were not only quantitative but the pattern of fight display was also divergent. Fighter males had an overall higher swimming activity, performing frequent fast strikes in the direction of the intruder and displaying from a distance. Wild-type males were less active and exhibited aggressive displays mostly in close proximity to the stimuli. Females of the fighter strain, which are not used for fights, were also more aggressive than wild-type females. Aggressive behaviours were correlated across male and female fighter siblings, suggesting common genetic and physiological mechanisms to male and female aggression in this species. The study further shows that results were largely independent of the stimulus type, with the mirror test inducing similar and less variable responses than the live conspecific presentation. These results suggest that selection for male winners co-selected for high-frequency and metabolic demanding aggressive display in males and also enhanced female aggression, opening a wide range of testable hypothesis about the ultimate and proximate mechanisms of male and female aggression in B. splendens.

Keywords: Aggression; Artificial selection; Domestication; Mirror test; Sexual conflict.

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Conflict of interest statement

Competing interestsThe authors declare that they have no competing interests.

Figures

Fig. 1
Fig. 1
A wild-type (top) and fighter (bottom) male B. splendens of the strains used in the experiments
Fig. 2
Fig. 2
Aggression score and activity behaviours quantified for wild-type and fighter males (left) and females (right). For the aggression score only the mirror and conspecific treatments are included as fish did not display these behaviours during glass (control) trials. Numbers in columns indicate N. Means ± S.E. are shown
Fig. 3
Fig. 3
Representative 2D side-view tracks of a wild-type (a) and fighter (b) male during mirror trials. Tracks from the fish with a total distance travelled closest to the strain average were used
Fig. 4
Fig. 4
Behavioural correlation networks for each of the aggression-eliciting groups. The diameter of circles represents the frequency of the behaviour, total distance travelled or time spent close to stimuli (normalized between 0 and 1). FD – frequency of frontal display; LD – frequency of lateral display; Ch – frequency of charge; CS – frequency of caudal swing; Ap – frequency of approach; AB – frequency of air breathing; TD – total distance travelled; TC – time spent close to stimuli. Distinct (≠) and similar (=) correlation network patterns among groups are indicated. Lines within groups represent Pearson’s correlation coefficients (r), with line thicknesses proportional to r value and positive / negative correlations indicated by line colour (green / yellow, respectively). Asterisks indicate significant correlations after adjustment for multiple comparisons: *P < 0.05; **P < 0.01 and ***P < 0.001
Fig. 5
Fig. 5
Aggression scores for 10 pairs of male and female fighter siblings from different families. Spearman correlation coefficient: rs = 0.73, N = 10, P = 0.021
Fig. 6
Fig. 6
Example of tanks used for staged pair-fights in fighting rings across Southeast Asia
See this image and copyright information in PMC

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