What can hybrid zone tell us about speciation? The case of Heliconius erato and H. himera (Lepidoptera: Nymplalidae)

The Galton Laboratory, Department of Biology, University College London, NW1 2HE, London
Biological Journal of the Linnean Society (Impact Factor: 2.26). 11/1996; 59(3). DOI: 10.1111/j.1095-8312.1996.tb01464.x


To understand speciation we need to study the genetics and ecology of intermediate cases where interspecific hybridization still occurs. Two closely related species of Heliconius butterflies meet this criterion: Heliconius himera is endemic to dry forest and thorn scrub in southern Ecuador and northern Peru, while its sister species, H. erato, is ubiquitous in wet forest throughout south and central America. In three known zones of contact, the two species remain distinct, while hybrids are found at low frequency. Collections in southern Ecuador show that the contact zone is about 5 km wide, half the width of the narrowest clines between colour pattern races of H. erato. The narrowness of this cline argues that very strong selection (s ≈ 1) is maintaining the parapatric distributions of these two species. The zone is closely related with a habitat transition from wet to dry forest, which suggests that the narrow zone of parapatry is maintained primarily by ecological adaptation. Selection on colour pattern loci, assortative mating and hybrid inviability may also be important. The genetics of hybrids between the two species shows that the major gene control of pattern elements is similar to that found in previous studies of H. erato races, and some of the loci are homologous. This suggests that similar genetic processes are involved in the morphological divergence of species and races. Evidence from related Heliconius supports a hypothesis that ecological adaptation is the driving force for speciation in the group.

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    • "o , for example , have distinctive colour - pattern phenotypes , but belong to the same species . In con - trast , the geographic replacement of H . erato found in south eastern Ecuador , H . himera , is considered a dis - tinct species because , where the two species co - occur , hybrids are rare ( but still account for ~10% of individ - uals ) ( Jiggins et al . , 1996 ) . In other words , the Geno - typic Cluster Definition implies that where they co - occur , ' species ' are characterized by a bimodal dis - tribution of traits , even if gene flow persists . By emphasizing the importance of multilocus genotypes , the Genotypic Cluster Definition is a useful tool for investigating gene flow and the ma"

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    • "Some previous studies of H. erato have concluded that hybrid zones associate with ecological adaptation leading to parapatric speciation to distinct habitats (Jiggins et al. 1996; Arias et al. 2008; Blum 2008). However, wing pattern differences do not necessarily constitute adaptations to the local environment. "
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    ABSTRACT: Multilocus clines between Müllerian mimetic races of Heliconius butterflies provide a classic example of the maintenance of hybrid zones and their importance in speciation. Concordant hybrid zones in the mimics Heliconius erato and H. melpomene in northern Peru were carefully documented in the 1980s, and this prior work now permits a historical analysis of the movement or stasis of the zones. Previous work predicted that these zones might be moving towards the Andes due to selective asymmetry. Extensive deforestation and climate change might also be expected to affect the positions and widths of the hybrid zones. We show that the positions and shapes of these hybrid zones have instead remained remarkably stable between 1985 and 2012. The stability of this interaction strongly implicates continued selection, rather than neutral mixing following secondary contact. The stability of cline widths and strong linkage disequilibria (gametic correlation coefficients Rmax = 0.35–0.56 among unlinked loci) over 25 years suggest that mimetic selection pressures on each colour pattern locus have remained approximately constant (s ≈ 0.13–0.40 per locus in both species). Exceptionally high levels of precipitation at the edge of the easternmost Andes may act as a population density trough for butterflies, trapping the hybrid zones at the foot of the mountains, and preventing movement. As such, our results do not support one prediction of the Pleistocene Refugium theory: that the ranges of divergent species or subspecies should be centred on regions characterized by maxima of rainfall, with hybrid zones falling in more arid regions between them.
    Evolution 10/2014; 68(12). DOI:10.1111/evo.12539 · 4.61 Impact Factor
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    • "Reproductive barriers contributing to speciation can occur at prezygotic and postzygotic levels (Mayr 1963; Dobzhansky 1970). Prezygotic isolation may occur by factors such as ecological differences (Jiggins et al. 1996), seasonal or temporal mating differences (Monteiro et al. 2012), gametic incompatibilities (Howard and Waring 1991), and assortative mating as observed between the subspecies Mus musculus musculus and M. m. domesticus (Smadja et al. 2004; Bímová et al. 2005; Vošlajerová Bímová et al. 2011). Alternatively, mechanisms including hybrid inviability (Allen et al. 1993; Zechner et al. 1996) and the generation of infertile hybrids (Forejt and Ivanyi 1974; Forejt 1996) may occur at the postzygotic level. "
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    ABSTRACT: Reproductive barriers exist between the house mouse subspecies, Mus musculus musculus and M. m. domesticus, members of the Mus musculus species complex, primarily as a result of hybrid male infertility, and a hybrid zone exists where their ranges intersect in Europe. Using single nucleotide polymorphisms (SNPs) diagnostic for the two taxa, the extent of introgression across the genome was previously compared in these hybrid populations. Sixty-nine of 1316 autosomal SNPs exhibited reduced introgression in two hybrid zone transects suggesting maladaptive interactions among certain loci. One of these markers is within a region on chromosome 11 that, in other studies, has been associated with hybrid male sterility of these subspecies. We assessed sequence variation in a 20 Mb region on chromosome 11 flanking this marker, and observed its inclusion within a roughly 150 kb stretch of DNA showing elevated sequence differentiation between the two subspecies. Four genes are associated with this genomic subregion, with two entirely encompassed. One of the two genes, the uncharacterized 1700093K21Rik gene, displays distinguishing features consistent with a potential role in reproductive isolation between these subspecies. Along with its expression specifically within spermatogenic cells, we present various sequence analyses that demonstrate a high rate of molecular evolution of this gene, as well as identify a subspecies amino acid variant resulting in a structural difference. Taken together, the data suggest a role for this gene in reproductive isolation.
    Mammalian Genome 02/2014; 25(5-6). DOI:10.1007/s00335-014-9506-2 · 3.07 Impact Factor
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