Reinforcement of pre-zygotic isolation and karyotype evolution in Agrodiaetus butterflies

Abstract

The reinforcement model of evolution argues that natural selection enhances pre-zygotic isolation between divergent populations or species by selecting against unfit hybrids or costly interspecific matings. Reinforcement is distinguished from other models that consider the formation of reproductive isolation to be a by-product of divergent evolution. Although theory has shown that reinforcement is a possible mechanism that can lead to speciation, empirical evidence has been sufficiently scarce to raise doubts about the importance of reinforcement in nature. Agrodiaetus butterflies (Lepidoptera: Lycaenidae) exhibit unusual variability in chromosome number. Whereas their genitalia and other morphological characteristics are largely uniform, different species vary considerably in male wing colour, and provide a model system to study the role of reinforcement in speciation. Using comparative phylogenetic methods, we show that the sympatric distribution of 15 relatively young sister taxa of Agrodiaetus strongly correlates with differences in male wing colour, and that this pattern is most likely the result of reinforcement. We find little evidence supporting sympatric speciation: rather, in Agrodiaetus, karyotypic changes accumulate gradually in allopatry, prompting reinforcement when karyotypically divergent races come into contact.

Beauty in the eye of the beholder: the two blue opsins of lycaenid butterflies and the opsin gene-driven evolution of sexually dimorphic eyes

“…We speculate that the expression of the LWRh transcript has been suppressed in males due to strong selection for male-male and conspecific mate recognition (Fig.·6). Visual signals appear to play a major role in the interspecific social interactions of lycaenid butterflies, as evidenced by behavioral observations and the unparalleled diversity of wing colors among sympatric species (Lukhtanov et al, 2005). We suggest that the molecular evolution of the 500·nm visual pigment and the novel ommatidial subtypes have likely enhanced color vision in the short wavelength part of the spectrum and have provided a mechanism for the rapid evolution of wing color in the largest of lycaenid subfamilies (Polyommatinae+Theclinae+ Lycaeninae) (Johnson and Coates, 1999).…”

The Phylogenetic Pattern of Speciation and Wing Pattern Change in Neotropical Ithomia Butterflies (Lepidoptera: Nymphalidae)

“…In most cases, pattern classes are easily distinguished and unambiguous but are nonetheless based on subjective human judgment. Previous studies have used a similar approach (Beccaloni 1997;Lukhtanov et al 2005), the validity of which is supported by the fact that bird predators are unable to distinguish species that humans perceive to be mimetic (Turner 1977) and that birds perceive similarity between species in a similar manner to humans (Dittrich et al 1993). A classification of wing patterns, termed the mimicry classification, was devised based on mimicry pattern variation throughout the Ithomiinae, including previously published studies of mimicry within ithomiine populations (Beccaloni 1997;Haber 1978).…”

“…Mimetic butterflies have been used both in the identification of putative forest refugia (Brown 1979) where vicariant speciation might have occurred, as well as in studies of ecological speciation (Jiggins et al 2004a). Butterfly wing patterns are obvious phenotypic traits that show rapid evolution and play a role in reproductive isolation (Vane-Wright 1978;Jiggins et al 2001;Lukhtanov et al 2005), being used in sexual signaling and mate choice (Stride 1957(Stride , 1958Brower 1959;Lederhouse and Scriber 1996;Deering and Scriber 2002;Fordyce et al 2002), as well as in predator defence. A number of butterflies in Neotropical forests are unpalatable to predators and bear warning color patterns, and sympatric species tend to converge in pattern through mimicry to facilitate predator recognition (Mü ller 1879).…”

Speciation: Reinforced butterfly speciation

“…This study improves on data sets such as that of Coyne and Orr because it includes phylogenetic information rather than simply genetic distances between taxa, ensuring that data points are phylogenetically independent. It also presents a novel line of evidence not observed in previous data sets, namely that the more divergent sympatric taxa are actually less likely to differ in colour pattern (Lukhtanov et al, 2005). This provides strong evidence for divergence being directly due to interactions between closely related species in sympatry.…”

“…In other butterflies, particular wing patterns are known to be associated with ecological variables such as host plant use (Willmott and Mallet, 2004). The authors argue that 'ecological divergence in allopatry does not lead to a change in colouration' (Lukhtanov et al, 2005; supplementary material), but this argument is unconvincing without detailed studies of how allopatric and sympatric species differ ecologically. Ecological character displacement can only occur in sympatry, and might drive sympatric species to diverge along different ecological dimensions as compared to allopatric species.…”