Gourbiere, S., & Mallet, J. (2005). Has adaptive dynamics contributed to the understanding of adaptive and sympatric speciation? Journal of Evolutionary Biology , 18, 1201-1204. REPRINT
Mallet, J. (2005). Hybridization as an invasion of the genome. Trends in Ecology and Evolution , 20, 229-237.Abstract

Hybridization between species is commonplace in plants, but is often seen as unnatural and unusual in animals. Here, I survey studies of natural interspecific hybridization in plants and a variety of animals. At least 25% of plant species and 10% of animal species, mostly the youngest species, are involved in hybridization and potential introgression with other species. Species in nature are often incompletely isolated for millions of years after their formation. Therefore, much evolution of eventual reproductive isolation can occur while nascent species are in gene-flow contact, in sympatry or parapatry, long after divergence begins. Although the relative importance of geographic isolation and gene flow in the origin of species is still unknown, many key processes involved in speciation, such as 'reinforcement' of post-mating isolation by the evolution of assortative mating, will have ample opportunity to occur in the presence of continuing gene flow. Today, DNA sequence data and other molecular methods are beginning to show that limited invasions of the genome are widespread, with potentially important consequences in evolutionary biology, speciation, biodiversity, and conservation.

Whinnett, A., Willmott, K. R., Brower, A. V. Z., Simpson, F., Lamas, G., & Mallet, J. (2005). Mitochondrial DNA provides an insight into the mechanisms driving diversification in the ithomiine butterfly Hyposcada anchiala (Lepidoptera: Nymphalidae, Ithomiinae). European Journal of Entomology , 102, 633-639.Abstract

Geographic subspecies of several ithomiine butterflies on the lower east Andean slopes display a black and orange“melanic tiger” aposematic wing pattern that occurs from Colombia to Bolivia, while geographically adjacent lowland subspeciestypically bear a coloured, “tiger” pattern. However, it is not clear whether subspecies with similar wing patterns in different regionshave arisen through independent events of convergent adaptation, possibly through parapatric differentiation, or result from allopatricdifferentiation, as proposed by the refuge hypothesis. Here, we examine geographic patterns of divergence in the widespreadand common ithomiine butterfly Hyposcada anchiala. We present phylogenetic hypotheses for 5 subspecies of H. anchiala, basedon 1567 bp mitochondrial DNA. All topologies indicated that a single switch in mimetic pattern best explained the wing patterningof the H. anchiala studied here. This finding suggests that the subspecies of H. anchiala studied here result from at least two stagesof differentiation, and is consistent with a single colonisation into a novel altitudinal zone coincident with a wing pattern switch, followedby subsequent divergence within, rather than across altitudinal zones. The subspecies divergences indicated diversificationswere consistent with the Pleistocene. Furthermore, the lowland subspecies were more recently derived than the montane taxa, in contrastto predictions of the “Andean species pump” hypothesis.

Drès, M., & Mallet, J. (2005). Molecular and behavioural evidence for gene flow between host races of the larch budmoth Zeiraphera diniana (Lepidoptera: Tortricidae). Proceedings of the Royal Society B , Submitted.Abstract

Larch and pine associated populations of Zeiraphera diniana (Lepidoptera: Tortricidae) differin a number of heritable traits, but pheromone-mediated cross-attraction occurs betweenthem in the wild. Using a quartet mate choice design (one male and one female of each typeper cage) we estimate that, following cross-attraction by pheromones, the subsequentprobability of hybridization is approximately 28%. We also examined molecular data, andwere unable to distinguish between the races on the basis of 695bp of mitochondrial COI,tRNA-leucine, and COII gene sequence. Both results support earlier field studies suggestingthat larch- and pine-feeding populations are host races that hybridize at an appreciable levelin the wild. The shared mitochondrial haplotypes we observed are also consistent withongoing and successful gene flow between the two host races.

Whinnett, A., Brower, A. V. Z., Lee, M. - M., Willmott, K. R., & Mallet, J. (2005). Phylogenetic utility of Tektin, a novel region for inferring systematic relationships among Lepidoptera. Annals of the Entomological Society of America , 98, 873-886.Abstract

Rapidly evolving nuclear coding sequences are highly desirable for phylogeneticstudies of closely related species. Here, we investigated an 807-bp region, homologous to the testisspeciÞcTektin gene from Bombyx mori (L.), in 34 nymphalid butterßy taxa in the subfamiliesIthomiinae, Danainae, and Heliconiinae. Within Ithomiinae, relationships inferred from Tektin sequencedata were remarkably similar to those in trees based on combined morphological andecological data. Partitioned Bremer analysis, with mitochondrial cytochrome oxidase I and II, andnuclear wingless and elongation factor 1- sequences, revealed Tektin to have the greatest utility forinferring relationships at the genus, tribe, and subfamily levels across the studied taxa.Wethink Tektinwill provide a useful source of molecular characters for inference of relationships among otherbutterßies, and perhaps among other insect taxa.

Mallet, J., Isaac, N., & Mace, G. (2005). Response to Harris and Froufe, and Knapp : Taxonomic inflation. Trends in Ecology and Evolution , 20, 8-9. REPRINT
Mallet, J. (2005). Speciation in the 21st Century. Review of "Speciation", by Jerry A. Coyne & H. Allen Orr. Heredity , 95, 105-109. REPRINT
Whinnett, A., Zimmermann, M., Willmott, K. R., Herrera, N., Mallarino, R., Simpson, F., Joron, M., et al. (2005). Strikingly variable divergence times inferred across an Amazonian butterfly 'suture zone'. Proceedings of the Royal Society B , 272, 2525-2533.Abstract

'Suture zones' are areas where hybrid and contact zones of multiple taxa are clustered. Such zones have been regarded as strong evidence for allopatric divergence by proponents of the Pleistocene forest refugia theory, a vicariance hypothesis frequently used to explain diversification in the Amazon basin. A central prediction of the refugia and other vicariance theories is that the taxa should have a common history so that divergence times should be coincident among taxa. A suture zone for Ithomiinae butterflies near Tarapoto, NE Peru, was therefore studied to examine divergence times of taxa in contact across the zone. We sequenced 1619bp of the mitochondrial COI/COII region in 172 individuals of 31 species from across the suture zone. Inferred divergence times differed remarkably, with divergence between some pairs of widespread species (each of which may have two or more subspecies interacting in the zone, as in the genus Melinaea) being considerably less than that between hybridizing subspecies in other genera (for instance in Oleria). Our data therefore strongly refute a simple hypothesis of simultaneous vicariance and suggest that ongoing parapatric or other modes of differentiation in continuous forest may be important in driving diversification in Amazonia.