Agonistic interactions with asymmetric body size in two adult‐age groups of the annual killifish Millerichthys robustus (Miller & Hubbs, 1974)

Abstract

In this study, the author evaluated two adult age groups of the Mexican rivulus Millerichthys robustus with body size asymmetries to determine the strategies used by an annual killifish during agonistic interactions of different ontogenetic stages. To achieve this goal, the author first characterized the ethogram of agonistic interactions of M. robustus composed of seven behavioural units in males and five behavioural units in females. The author then analysed agonistic interaction strategies used by males and females with body size asymmetries in two groups of different adult ages that represent different ontogenetic stages: (a) just after sexual maturity was reached, at 5 weeks of age, and (b) near natural death, at 24 weeks of age. The agonistic behaviour patterns of M. robustus were compatible with the logic of mutual assessment. Large males had an advantage during their interactions in both age groups, winning all of the encounters. Nonetheless, there was more aggression in 5‐week‐old fish encounters. In addition, small 24‐week‐old fish were more aggressive than small 5‐week‐old fish. These changing strategies may be because of the cost–benefits required during a fight at each ontogenetic stage. In the female encounters, size did not predict winners, as both small and large fish won a similar number of encounters, and some contests remained unresolved regardless of age group. There was a tendency for small females of any age to risk more than males in fights to maintain reproductive fitness.

Aggressiveness overcomes body‐size effects in contests between native and invasive cichlid fishes

“…In the invasive convict cichlid, the number of behavioral displays between individuals of different sizes was previously shown to remain constant (Leiser et al., 2004). Previous studies have emphasized the role of size in determining the dominant contender (Domínguez‐Castanedo, 2021; Reddon et al., 2019), but our study demonstrates that the native mojarra wins contests against the invasive convict cichlid despite the size disadvantage. Cooperative territorial defense behavior has been observed in the convict cichlid when it encounters the Mexican mojarra in the Balsas basin, suggesting that they can dominate Mexican mojarras by the coalition (Molina et al., 2021).…”

Protogynous functional hermaphroditism in the North American annual killifish, Millerichthys robustus

“…This happens when large males win agonistic encounters over the best territories and can monopolize food resources, habitat patches with lower mortality, reproductive resources and access to females 39 . In this context, it has been documented that the larger males of M. robustus always win male-male agonistic interactions with asymmetric body size, regardless of their age 40 . Although there is no information on potential male territoriality in M. robustus , dominant male annual killifish have superior access to females 30 , 41 and are actively preferred by females 42 .…”

“…Female M. robustus are highly aggressive to each other and body size does not play a role in predicting the winner. When males are not present, similarly-sized female avoid overt mutual aggression 40 , apparently to reduce the risk of injuries. In contrast, we commonly observed aggression between similarly sized females in this study.…”

“…Each observation lasted 20 min. We recorded the expression of 8 behaviours (Table 1 ) which were defined from previously published ethograms for courtship, reproduction and agonistic encounters of M. robustus 40 , 59 . They were composed of aggressive and courtship displays characteristic of female and male behaviour.…”

Behavioral Interactions between a Native and an Invasive Fish Species in a Thermally Heterogeneous Experimental Chamber

“…β.temp j ∼ Normal µ β.temp , σ 2 β.temp ; β.move j ∼ Normal µ β.move , σ 2 β.move (5) We additionally fit a model that evaluated whether inter-trial variation in intercepts and slopes could be explained by variation in the body length of C. eos between trials, because agonistic inter-specific interactions depend frequently on the body lengths of fish [46][47][48]. Specifically, we fitted linear models on intercepts (α.temp j and α.move j ) and slopes (β.temp j and β.move j ), where µ j is the mean-standardized body length of C. eos (total length in mm) used in trial j:…”