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Aim The aim was to determine processes driving the latitudinal diversity gradient (LDG) in New World swallowtail butterfly diversity. We tested three mechanisms commonly invoked to explain the LDG: ecological opportunity, evolutionary rates and biogeographical history. Location New World and Eurasia. Time period Oligocene–Present. Major taxa studied New World swallowtail butterfly clade (Papilio: Agehana, Alexanoria, Chilasa, Heraclides and Pterourus). Methods We integrated data from the most complete current phylogeny of this clade with geographical distributions of each species inferred from ecological niche models (ENMs). We tested for correlation between breadth of available abiotic ecological niche space, latitude and differential rates of diversification between tropical and non-tropical lineages. The clade's history of climatic and geographical occupancy was also reconstructed using both continuous ancestral character reconstructions and biogeographical history inferred under a dispersal–extinction–cladogenesis model. We considered both latitudinal and climatic definitions of tropicality in our reconstructions. Results There was no strong support for ecological opportunity or macroevolutionary processes as latitudinal diversity gradient drivers. Instead, we recovered discordant patterns in phylogenetic reconstructions of latitudinal geographical range and suitable abiotic climate conditions. Heraclides are likely to have originated and diversified in climatically and latitudinally tropical environments before some lineages dispersed to temperate habitats. The Alexanoria + Chilasa + Pterourus clade is likely to have originated in climatically and latitudinally temperate habitat before dispersing and diversifying; some lineages are likely to have dispersed into the latitudinal tropics via highland temperate-analogue environments. Main conclusions The LDG in New World swallowtails results from complex interactions between ecological niche evolution and biogeographical history; both out-of-the-tropics and into-the-tropics processes have contributed to the LDG. Our results present an example where temperate zones appear to be a source, instead of a sink, for biodiversity. Our results emphasize the need to consider biogeographical history not only from the perspective of shifts in geographical space, but also in terms of constraints enforced by ecological niche conservatism.

1. In the study of the evolution of insect–host plant interactions, important information is provided by host ranking correspondences among female preference, offspring preference, and offspring performance. Here, we contrast such patterns in two polyphagous sister species in the butterfly family Nymphalidae, the Nearctic Polygonia faunus, and the Palearctic P. c-album. 2. These two species have similar host ranges, but according to the literature P. faunus does not use the ancestral host plant clade – the ‘urticalean rosids’. Comparisons of the species can thus test the effects of a change in insect–plant associations over a long time scale. Cage experiments confirmed that P. faunus females avoid laying eggs on Urtica dioica (the preferred host of P. c-album), instead preferring Salix, Betula, and Ribes. 3. However, newly hatched larvae of both species readily accept and grow well on U. dioica, supporting the general theory that evolutionary changes in host range are initiated through shifts in female host preferences, whereas larvae are more conservative and also can retain the capacity to perform well on ancestral hosts over long time spans. 4. Similar rankings of host plants among female preference, offspring preference, and offspring performance were observed in P. c-album but not in P. faunus. This is probably a result of vestiges of larval adaptations to the lost ancestral host taxon in the latter species. 5. Female and larval preferences seem to be largely free to evolve independently, and consequently larval preferences warrant more attention.

One hundred and fifty years after Alfred Wallace studied the geographical variation and species diversity of butterflies in the Indomalayan-Australasian Archipelago, the processes responsible for their biogeographical pattern remain equivocal. We analysed the macroevolutionary mechanisms accounting for the temporal and geographical diversification of the charismatic birdwing butterflies (Papilionidae), a major focus of Wallace’s pioneering work. Bayesian phylogenetics and dating analyses of the birdwings were conducted using mitochondrial and nuclear genes. The combination of maximum likelihood analyses to estimate biogeographical history and diversification rates reveals that diversity-dependence processes drove the radiation of birdwings and that speciation was often associated with founder-events colonizing new islands, especially in Wallacea. Palaeo-environment diversification models also suggest that high extinction rates occurred during periods of elevated sea level and global warming. We demonstrated a pattern of spatio-temporal habitat dynamics that continuously created or erased habitats suitable for birdwing biodiversity. Since birdwings were extinction-prone during the Miocene (warmer temperatures and elevated sea levels), the cooling period after the mid-Miocene climatic optimum fostered birdwing diversification due to the release of extinction. This also suggests that current global changes may represent a serious conservation threat to this flagship group.