Abstract
Phenotypic plasticity in heterogeneous environments can provide tight environment-phenotype matching. However, the prerequisite is a reliable environmental cue(s) that enables organisms to use current environmental information to induce the development of a phenotype with high fitness in a forthcoming environment. Here, we quantify predictability in the timing of precipitation and temperature change to examine how this is associated with seasonal polyphenism in tropical Mycalesina butterflies. Seasonal precipitation in the tropics typically results in distinct selective environments, the wet and dry seasons, and changes in temperature can be a major environmental cue. We sampled communities of Mycalesina butterflies from two seasonal locations and one aseasonal location. Quantifying environmental predictability using wavelet analysis and Colwell's indices confirmed a strong periodicity of precipitation over a 12-month period at both seasonal locations compared to the aseasonal one. However, temperature seasonality and periodicity differed between the two seasonal locations. We further show that: (a) most females from both seasonal locations synchronize their reproduction with the seasons by breeding in the wet season but arresting reproduction in the dry season. In contrast, all species breed throughout the year in the aseasonal location and (b) species from the seasonal locations, but not those from the aseasonal location, exhibited polyphenism in wing pattern traits (eyespot size). We conclude that seasonal precipitation and its predictability are primary factors shaping the evolution of polyphenism in Mycalesina butterflies, and populations or species secondarily evolve local adaptations for cue use that depend on the local variation in the environment.
Highlights
Phenotypic plasticity is the capacity of a genotype to produce different phenotypes in different environments
Seasonal polyphenism, which is an extreme case of phenotypic plasticity (Nijhout, 1999; Shapiro, 1976), can provide a tight environment-phenotype matching by expressing distinct developmental pathways, and distinct alternative forms in different seasons, depending on the cues experienced during a critical period of juvenile development (Beldade et al, 2011; Nijhout, 1999, 2003; Smith-Gill, 1983)
It was synchronized with temperature, which was leading precipitation by at least a month. Such a seasonal trend was absent in Genting and here both variables were highly out of phase. Such a characteristic pattern of temperature rising before the rainfall and dropping towards the end of the wet season, at least in East Africa (e.g. Zomba), is suggested to signal the forthcoming wet-and dry season, respectively, and acts as a reliable cue (Brakefield & Reitsma, 1991; Kooi & Brakefield, 1999; Windig et al, 1994)
Summary
Phenotypic plasticity is the capacity of a genotype to produce different phenotypes in different environments. Seasonal precipitation in the tropics results in distinct environments (i.e. wet- and dry seasons), which impose contrasting selection pressures across seasons and is the major driver of morphological and life-history evolution in Mycalesina butterflies (Brakefield & Reitsma, 1991, Roskam & Brakefield 1999, Brakefield et al, 2007). Such marked seasonal fluctuation in temperature could, be used as a cue to predict the forthcoming season (Brakefield & Reitsma, 1991; Windig et al, 1994) This field observation is corroborated by common garden experiments, which show that rearing larvae at 25°C results in the WSF The occurrence of distinct seasonal forms at Sanguem and Genting will indicate either that species have evolved a new polyphenic threshold for temperature or that they use cues other than temperature
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