THE PHYLOGENETIC PATTERN OF SPECIATION AND WING PATTERN CHANGE IN NEOTROPICALITHOMIABUTTERFLIES (LEPIDOPTERA: NYMPHALIDAE)

Abstract

Abstract. Species level phylogenetic hypotheses can be used to explore patterns of divergence and speciation. In the tropics, speciation is commonly attributed to either vicariance, perhaps within climate-induced forest refugia, or ecological speciation caused by niche adaptation. Mimetic butterflies have been used to identify forest refugia as well as in studies of ecological speciation, so they are ideal for discriminating between these two models. The genus Ithomia contains 24 species of warningly colored mimetic butterflies found in South and Central America, and here we use a phylogenetic hypothesis based on seven genes for 23 species to investigate speciation in this group. The history of wing color pattern evolution in the genus was reconstructed using both parsimony and likelihood. The ancestral pattern for the group was almost certainly a transparent butterfly, and there is strong evidence for convergent evolution due to mimicry. A punctuationist model of pattern evolution was a significantly better fit to the data than a gradualist model, demonstrating that pattern changes above the species level were associated with cladogenesis and supporting a model of ecological speciation driven by mimicry adaptation. However, there was only one case of sister species unambiguously differing in pattern, suggesting that some recent speciation events have occurred without pattern shifts. The pattern of geographic overlap between clades over time shows that closely related species are mostly sympatric or, in one case, parapatric. This is consistent with modes of speciation with ongoing gene flow, although rapid range changes following allopatric speciation could give a similar pattern. Patterns of lineage accumulation through time differed significantly from that expected at random, and show that most of the extant species were present by the beginning of the Pleistocene at the latest. Hence Pleistocene refugia are unlikely to have played a major role in Ithomia diversification.

Recent Speciation in Three Closely Related Sympatric Specialists: Inferences Using Multi-Locus Sequence, Post-Mating Isolation and Endosymbiont Data

“…Species level phylogenetic analysis allows insights into recent evolutionary history, especially patterns of divergence and speciation [52]. However, resolving phylogenies among closely related species can be extremely difficult when there is incongruence among gene trees [53], [54].…”

Secondary Sympatry Caused by Range Expansion Informs on the Dynamics of Microendemism in a Biodiversity Hotspot

“…For pairs of terminal species, the degree of sympatry was calculated as the number of quadrats in which two species co-occur, divided by the number of quadrats occupied by the species with the smallest range [56], [57], [58], [59]. For deeper nodes in the tree we followed an alternative methodology using independent contrasts between pairs of taxa, which does not bring to artefactual increase of degree of sympatry through time [60], [61], [62], by acknowledging that unlike a phenotypic trait, distribution is an extrinsic feature of species that should not be interpreted only by mapping on a tree [63]. Average pairwise overlaps were calculated for each node.…”

North Andean origin and diversification of the largest ithomiine butterfly genus

“…In Ithomiini, experimental evidence for the role of colour pattern as a mating cue is absent due to the difficulty of maintaining and rearing Ithomiini in captivity, but observation suggests that this may be the case70. Moreover, shifts in colour patterns have been shown to be statistically associated with cladogenesis in phylogenies3671, consistent with a role of colour pattern in reproductive isolation. Shifts in colour pattern may therefore have contributed to Andean diversification in the genus Pteronymia .…”

“…Commonly known as the clearwing butterflies because of the transparent wings in many species, they are well-known because of their involvement in Müllerian mimicry rings, whereby co-occurring unpalatable species converge in wing colour pattern amongst themselves, other Lepidoptera and some other insects34. Their diversity and broad distribution makes them a relevant study system to investigate patterns of spatial and temporal diversification in the Neotropics and they have previously been the focus of a number of diversification studies463536. Most ithomiine clades have been found to show a peak of species richness in the Andes37, but the biogeographic histories that have led to this pattern are surprisingly diverse.…”