Frequency-dependent variation in mimetic fidelity in an intraspecific mimicry system

Abstract

Contemporary theory predicts that the degree of mimetic similarity of mimics towards their model should increase as the mimic/model ratio increases. Thus, when the mimic/model ratio is high, then the mimic has to resemble the model very closely to still gain protection from the signal receiver. To date, empirical evidence of this effect is limited to a single example where mimicry occurs between species. Here, for the first time, we test whether mimetic fidelity varies with mimic/model ratios in an intraspecific mimicry system, in which signal receivers are the same species as the mimics and models. To this end, we studied a polymorphic damselfly with a single male phenotype and two female morphs, in which one morph resembles the male phenotype while the other does not. Phenotypic similarity of males to both female morphs was quantified using morphometric data for multiple populations with varying mimic/model ratios repeated over a 3 year period. Our results demonstrate that male-like females were overall closer in size to males than the other female morph. Furthermore, the extent of morphological similarity between male-like females and males, measured as Mahalanobis distances, was frequency-dependent in the direction predicted. Hence, this study provides direct quantitative support for the prediction that the mimetic similarity of mimics to their models increases as the mimic/model ratio increases. We suggest that the phenomenon may be widespread in a range of mimicry systems.

Negative frequency-dependent selection or alternative reproductive tactics: maintenance of female polymorphism in natural populations

“…Furthermore, we observed increasing egg mass and decreasing egg number towards Northern latitudes. It has been suggested before that body size may increase with latitude due to temperature related physical constraints of growth and development (Bergmann’s rule, reviewed by [62]), a general pattern which is also confirmed in damselflies [45,50]. Taken together, investment in heavier eggs may depend on several ecological variables, including abiotic conditions [78] and degree of the competitive environment [73], but will most likely come at the expense of producing numerous eggs.…”

“…Female morphs are easily classified into andromorphs or gynomorphs based on their body coloration. Thus, while andromorph females resemble the conspecific male’s body blue coloration and melanin pattern [47,48], gynomorph females have distinctive yellowish lateral thorax sides and a less conspicuous abdominal melanin pattern; for colour figures see [49], for pictures see [50]. The species has one generation per year, with reproduction occurring between early June and mid-August.…”

“…Next, a digital picture was taken (Nikon D70/Tamron macro lens 90 mm 1:2.8) of the right hind wing. Using ImageJ 1.38x [57], wing length was measured from the second antenodal cross vein to the stigma; see [50] for more details. Residuals of body mass were calculated by regressing body mass against wing length and were used as a measure for relative body mass (RBM).…”

The Sicker Sex: Understanding Male Biases in Parasitic Infection, Resource Allocation and Fitness

“…One example is the case of damselflies with female polymorphism in which the male-mimicking morph shows a higher parasite burden compared to other female morphs. This is presumably [57] due to resource-allocation cost of becoming a good male mimic [58], [59]. In fact, one of our study species, E. novahispaniae , has two polymorphic females.…”

Ecological and Evolutionary Processes Drive the Origin and Maintenance of Imperfect Mimicry

“…While some researchers doubt the adequacy of human perception of mimetic fidelity, recent comparative analyses of various measures of mimetic fidelity have found that subjective human rankings [5], [18] are comparable to rankings based on multivariate analyses of morphological features [5], [19] and avian response rankings [20], [21] indicating that human rankings can be an effective measure of mimetic fidelity.…”