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Female-limited polymorphism occurs in different animal taxa but is particularly abundant among species of damselflies (Insecta: Odonata), most likely as a consequence of selection to avoid excessive male harassment. Recent work on the damselfly Nehalennia irene indicated that within year spatial variation in female morph frequencies was limited in nearby populations (i.e. intra-regional scale), but large at a continental scale. As anticipated, some of the observed variation in morph frequency was correlated with variation in the estimated degree of male harassment towards female morphs, measured by male density and operational sex ratio. Here, we extended earlier work by quantifying variation in morph frequency over two to three years, allowing us to elucidate how morph frequencies vary temporally at both intra-regional and continental scales (data for 8 populations over three years and for 33 populations over two years, respectively). Annual variation in morph frequencies was relatively high at the intra-regional scale, but was never large enough to obscure the underlying spatial pattern at the continental scale. At both geographic scales, male density and operational sex ratio were highly variable between years. The estimated degree of male harassment correlated with variation in morph frequency within some regions, but not all. Together, the observed natural variation in female morph frequencies may be partly explained by variation in male harassment, but it appears that a complete understanding will require considering the role of other environmental factors. [ABSTRACT FROM AUTHOR]

Sex-limited colour polymorphism occurs in several animal taxa and is usually explained in the context of sexual selection. Specifically, for polymorphism restricted to the female sex, multiple phenotypes may have evolved in response to male harassment. Such male harassment is generally considered to entail differential costs to female morphs, which may ultimately result in fitness differences. However, contrary to this prediction, most previous studies do not support that female morphs (andromorphs and heteromorphs) differ in measures of quality and (or) fitness components. In this study, we evaluate quality and fitness differences between mated female morphs of the damselfly Enallagma cyathigerum. We suggest that many earlier studies may have failed to observe morph differences in quality or fitness because selection by male harassment was weak. Here, we selected a study population for which our expectation was that levels of per female capita male harassment were high. Nevertheless, also in this population mated female morphs did not differ in body size or condition (body mass/body length). However, mated female morphs did differ in levels of developmental instability: heteromorphs consistently showed a higher level of fluctuating asymmetry than andromorphs. Also, mated female morphs differed in fecundity: andromorphs had a lower clutch size than heteromorphs. In addition, larger females contained more eggs, but the slope of this relationship was steeper in heteromorphs. In conclusion, mated female morphs of the damselfly E. cyathigerum at our study site clearly differed in one quality estimate (developmental instability) and in our measure of fitness (fecundity). [ABSTRACT FROM AUTHOR]

Sex-limited polymorphism is widely distributed among animal taxa, but has only rarely been studied from a macro-evolutionary perspective. We investigate the evolution of female-limited polymorphism by mapping presence or absence of multiple discrete morphs on published phylogenetic trees for North American representatives of two damselfly genera. The results indicate that female polymorphy represents the ancestral condition based on the species included with subsequent loss and monomorphy representing the evolutionary end-point in most cases. According to one phylogeny, character optimization suggests that expression of the polymorphism may be lost (to a state of monomorphy) and gained again (back to polymorphy). Earlier work indicated that changes from polymorphy to monomorphy might be coupled with evolution of the mating system from polyandry to monandry. The results presented here, however, do not convincingly support such view. [ABSTRACT FROM AUTHOR]