Close encounters of the three morphs: does color affect aggression in a polymorphic lizard?

Abstract

Color polymorphism is genetically controlled and the process generating and maintaining morphs can affect speciation and/or extinction rates. Competition and aggression among morphs can contribute to polymorphism maintenance and color badges are useful signals in intraspecific communication, because they convey information about alternative strategies and avoid unnecessary conflicts. This could lead to an uneven spatial distribution of morphs in a population, because the local frequency of each morph establishes the intensity of the competition in that neighborhood, and then the fitness of each male. We used a polymorphic lizard, Podarcis muralis, to assess if aggression varies among morphs under two contrasting hypotheses: a heteromorphic vs. a homomorphic aggression. We used laboratory mirror tests after lizard color manipulation and we verified the results consistency with the analysis of the spatial distribution of morphs in a wild population. Both the experiments confirmed that aggression is morph-specific and notably homomorphic. The adoption of behavioral alternative strategies that minimize risks and costs of unwanted conflicts could facilitate the stable coexistence of the phenotypes and reduce the resource competition. A bias in aggression to like-coloured males would advantage rarer morph, which would suffer less harassment by common morphs and obtain a fitness advantage. This process would be negatively-frequency-dependent and would stabilize polymorphism in the populations, possibly leading to sympatric speciation.

Morph-specific seasonal variation of aggressive behaviour in a polymorphic lizard species

“…Sacchi et al (2009) did not find any correlations between the aggressive strategy and individual's morph; instead, Abalos et al (2016) found a lower fighting ability in red males, but this could be due to the size of black patches. Finally, Scali et al (2020) demonstrated that P. muralis shows a greater aggressive response if the contender belongs to its own morph. The results of our experiments clearly show that aggression is modulated over time by morphs, and it is important to consider the time window when carrying out this type of behavioural experiment because it would provide different seasonal results based on the morph.…”

“…with two alternative strategies), depending on the costs they are willing to sustain during aggressive interactions with conspecific males. Male Common wall lizards can recognise individuals belonging to their morph (Pérez i de Lanuza et al, 2018) and they show higher aggression towards individuals belonging to their same morph (Scali et al, 2020). They also show greater aggressiveness in a familiar context (i.e.…”

“…their territory) with a high subjective resource value than in unfamiliar context (Sacchi et al, 2009;Sacchi et al, 2020 unpublished data). Having said that, our experimental setting reflect the most stimulating context, regard with Resource-Holding-Potential and morph-specific aggressive pattern (Sacchi et al, 2009;Scali et al, 2020;Sacchi et al, 2020 unpublished data), which allows to consider the obtained results as the maximum possible aggressive response in a given period. These results agree with the morph-specific seasonal pattern in plasma T levels found in Sacchi et al (2017b) and support our initial hypothesis which envisaged the existence of a more aggressive strategy (played by yellow males) as opposed to a more conservative one (played by white males).…”

“…To measure the aggressive response, we used a mirror test to mimick an intrusion of a stranger in the individual's territory (the cage). This method allows removing the size and motivation effects by showing to the tested individual an image with the same behaviour, size, and motivation (Sacchi et al, 2009;Scali et al, 2019Scali et al, , 2020. After acclimation, lizards were tested in their own cage after removing the water bowl.…”

Rare morph Lake Malawi mbuna cichlids benefit from reduced aggression from con- and hetero-specifics

“…In many taxa, species-recognition cues have diverged through reproductive or antagonistic character displacement to reduce hybridisation or unnecessary exertion and risk of injury among heterospecifics which are not in direct competition for mates or resources (Seehausen & Schluter 2004;Grether et al 2009). Rare colour morphs can benefit from lack of recognition by receiving less mating-related harassment (Takahashi et al 2010) or less intrasexual aggression from conspecifics (Dijkstra et al 2008;Lehtonen 2014;Pérez i de Lanuza G et al 2017;Scali et al 2020). In aggressive species, negative frequency-dependent antagonism, generated through either evolution of an own-morph bias (Dijkstra et al 2008;Lehtonen 2014;Scali et al 2020) or by a dynamic common morph bias based on experience (Bolnick et al 2016), can prevent an increase in the frequency of rare morphs as they would only benefit from increased fitness (due to reduced aggression) while they are rare (Seehausen & Schluter 2004;Dijstra et al 2007;Bolnick et al 2016).…”