Morph-specific assortative mating in common wall lizard females

Abstract

Color polymorphism often is associated with alternative reproductive strategies and may reflect different adaptive optima that coexist within populations. The equilibrium among morph frequencies is maintained by the occurrence of opposite selective pressures (disruptive vs. stabilizing), which promote polymorphism while preserving gene flow. Sexual selection may contribute on both sides, particularly when morphs do not mate randomly. Reptiles offer a good model, notably lizards. Nevertheless, previous studies on mate choice in polymorphic lizards have generated contrasting results, with some studies suggesting that female morphs might tune their preference depending on environmental/social conditions such as crowding. We experimentally manipulated the number of individuals a female common wall lizard Podarcis muralis perceives around her, to test if females of different morphs (white or yellow) tune their choice for white and yellow males in order to maximize the probability that hatchlings follow the strategy best adapted to the population density. Results showed that crowding experienced by females did not affect mate choice, arguing against a flexible choice strategy by females. However, white females significantly associated with white males, whereas yellow females did not significantly associate with yellow males. Thus, sexual selection could contribute to the maintenance of color polymorphism in this species by a mix of assortative and non-assortative mating strategies, which could maintain the equilibrium between gene divergence and gene flow among morphs.

Morph-specific protein patterns in the femoral gland secretions of a colour polymorphic lizard

“…In a CP system, assessing the morph identity of a potential rival or mate without (or before) seeing it (i.e., before the visual modality can be activated) may give a great advantage in decision-making and allows better tuning intraspecific interaction 12,39 . Indeed, non-random mating has been recognized as a key mechanism contributing to CP maintenance 9 , and it has been reported also for the common wall lizard 42,45 , where both male-male competition 109,110,134 and female flexible choice 45,135 seem to be at work. Combined with female preference for chemical rather than visual stimuli 135 , the occurrence of a dual modality (visual and chemical) of morph-specific signals gains even more importance.…”

“…A potential environmental role in CP expression has been recently documented, suggesting that both natural and sexual selection may be involved in CP expression 107,108 . Nonetheless, the signal function of the ventral colouration is strongly supported by the morph assortative pairing 42,45,46 , by the morph-specific male-male interactions 109,110 , and by the lizard ability to discriminate colour morph 18 . Further, previous studies have already highlighted the occurrence of a chemical segregation of morphs 41 .…”

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

“…The Common wall lizard (Podarcis muralis) is a medium-sized diurnal lizard (50-70 mm adult snout-vent length, SVL) that shows three main colour morph in both sexes, white, yellow, and red, on throat and belly (Sacchi et al, 2007b). The colourations develop from the second year of life (Cheylan, 1988) and the role of CP in social communication was widely studied in the last decades (Sacchi et al, 2009(Sacchi et al, , 2015(Sacchi et al, , 2017a(Sacchi et al, , 2017bScali et al, 2013;Pellitteri-Rosa et al, 2014;Abalos et al, 2016;Pérez i de Lanuza, Carretero & Font, 2017;Mangiacotti et al, 2019aMangiacotti et al, , 2019b. A morph-specific pattern in the immune response has been demonstrated (Sacchi et al, 2007a) and the same occured in plasma T levels throughout the breeding season (Sacchi et al, 2017b).…”

Convergence and divergence in lizard colour polymorphisms

“…Conversely, negative frequency‐dependent selection can promote disassortative mating because rarer morphs have more mating opportunities and thus higher fitness (Jamie & Meier, 2020). A combination of assortative and disassortative mating strategies could contribute to maintenance of colour polymorphism in Podarcis muralis (Sacchi et al ., 2018). Females of different morphs appear to show both assortative and disassortative association preferences in captivity (Sacchi et al ., 2015; Sacchi et al ., 2018), although it is unclear the extent to which these preferences determine pairings in the wild.…”