Taxonomy of coccids (Hemiptera: Coccidae: Coccus L.) associated with Crematogaster ants (Hymenoptera: Formicidae) in the stems of Macaranga plants (Euphorbiaceae) in Southeast Asia.

The Southeast Asian soft scale insects (Hemiptera: Coccomorpha: Coccidae) associated with ants of the Crematogaster borneensis-group (Hymenoptera: Formicidae) and living in the hollow stems of Macaranga plants (Euphorbiaceae) are revised taxonomically. Ten species of the genus Coccus L. are recognised: seven were described previously and three new species are described herein. The species are: Coccus caviramicolus Morrison, C. circularis Morrison, C. heckrothi Gullan Kondo sp. n., C. lambirensis Gullan Kondo sp. n., C. macarangicolus Takahashi, C. macarangae Morrison, C. penangensis Morrison, C. pseudotumuliferus Gullan Kondo sp. n., C. secretus Morrison and C. tumuliferus Morrison. All of these species are described or redescribed and newly illustrated based on the adult females, and a key to distinguish the species is provided. We designate a lectotype for C. macarangicolus. The first-instar nymphs of all species are morphologically extremely similar and therefore only the first-instar nymph of C. macarangae is described and illustrated. Seven of these species currently are known only from Macaranga, but C. macarangae, C. secretus and perhaps C. pseudotumuliferus have been recorded from the hollow stems of several other ant-plants and a few non-myrmecophytes. The Coccus species from Macaranga are closely related to C. hesperidum L., the type species of the genus, and therefore are retained in the genus Coccus even though the adult females exhibit a few morphological differences from C. hesperidum. The species of Coccus from Macaranga appear to be parthenogenetic because no male nymphs or adults have been found, despite extensive collecting.

Comparative population genetics of mimetic Heliconius butterflies in an endangered habitat; Brazil's Atlantic Forest.

BACKGROUND: Brazil's Atlantic Forest is a biodiversity hotspot endangered by severe habitat degradation and fragmentation. Habitat fragmentation is expected to reduce dispersal among habitat patches resulting in increased genetic differentiation among populations. Here we examined genetic diversity and differentiation among populations of two Heliconius butterfly species in the northern portion of Brazil's Atlantic Forest to estimate the potential impact of habitat fragmentation on population connectivity in butterflies with home-range behavior. RESULTS: We generated microsatellite, AFLP and mtDNA sequence data for 136 Heliconius erato specimens from eight collecting locations and 146 H. melpomene specimens from seven locations. Population genetic analyses of the data revealed high levels of genetic diversity in H. erato relative to H. melpomene, widespread genetic differentiation among populations of both species, and no evidence for isolation-by-distance. CONCLUSIONS: These results are consistent with the hypothesis that the extensive habitat fragmentation along Brazil's Atlantic Forest has reduced dispersal of Heliconius butterflies among neighboring habitat patches. The results also lend support to the observation that fine-scale population genetic structure may be common in Heliconius. If such population structure also exists independent of human activity, and has been common over the evolutionary history of Heliconius butterflies, it may have contributed to the evolution of wing pattern diversity in the genus.

Dissecting comimetic radiations in Heliconius reveals divergent histories of convergent butterflies.

Mimicry among Heliconius butterflies provides a classic example of coevolution but unresolved relationships among mimetic subspecies have prevented examination of codiversification between species. We present amplified fragment length polymorphism and mtDNA datasets for the major comimetic races of Heliconius erato and H. melpomene. The AFLP data reveal unprecedented resolution, clustering samples by geography and race in both species. Our results show that, although H. erato and H. melpomene co-occur, mimic each other, and exhibit parallel shifts in color pattern, they experienced very different modes of diversification and geographic histories. Our results suggest that H. erato originated on the western side of South America whereas H. melpomene originated in the east. H. erato underwent rapid diversification and expansion with continued gene-flow following diversification, resulting in widely dispersed sister taxa. In contrast, H. melpomene underwent a slower pace of diversification with lower levels of gene flow, producing a stepwise directional expansion from west to east. Our results also suggest that each of the three main wing pattern phenotypes originated and/or was lost multiple times in each species. The rayed pattern is likely to be the ancestral phenotype in H. erato whereas postman or red patch is likely to be ancestral in H. melpomene. Finally, H. cydno and H. himera are monophyletic entities clearly nested within H. melpomene and H. erato, rather than being their respective sister species. Estimates of mtDNA divergence suggest a minimum age of 2.8 and 2.1 My for H. erato and H. melpomene, respectively, placing their origins in the late Pliocene.

An ancient tripartite symbiosis of plants, ants and scale insects.

In the Asian tropics, a conspicuous radiation of Macaranga plants is inhabited by obligately associated Crematogaster ants tending Coccus (Coccidae) scale insects, forming a tripartite symbiosis. Recent phylogenetic studies have shown that the plants and the ants have been codiversifying over the past 16-20 million years (Myr). The prevalence of coccoids in ant-plant mutualisms suggest that they play an important role in the evolution of ant-plant symbioses. To determine whether the scale insects were involved in the evolutionary origin of the mutualism between Macaranga and Crematogaster, we constructed a cytochrome oxidase I (COI) gene phylogeny of the scale insects collected from myrmecophytic Macaranga and estimated their time of origin based on a COI molecular clock. The minimum age of the associated Coccus was estimated to be half that of the ants, at 7-9Myr, suggesting that they were latecomers in the evolutionary history of the symbiosis. Crematogaster mitochondrial DNA (mtDNA) lineages did not exhibit specificity towards Coccus mtDNA lineages, and the latter was not found to be specific towards Macaranga taxa, suggesting that patterns of associations in the scale insects are dictated by opportunity rather than by specialized adaptations to host plant traits.

Codiversification in an ant-plant mutualism: stem texture and the evolution of host use in Crematogaster (Formicidae: Myrmicinae) inhabitants of Macaranga (Euphorbiaceae).

We investigate the evolution of host association in a cryptic complex of mutualistic Crematogaster (Decacrema) ants that inhabits and defends Macaranga trees in Southeast Asia. Previous phylogenetic studies based on limited samplings of Decacrema present conflicting reconstructions of the evolutionary history of the association, inferring both cospeciation and the predominance of host shifts. We use cytochrome oxidase I (COI) to reconstruct phylogenetic relationships in a comprehensive sampling of the Decacrema inhabitants of Macaranga. Using a published Macaranga phylogeny, we test whether the ants and plants have cospeciated. The COI phylogeny reveals 10 well-supported lineages and an absence of cospeciation. Host shifts, however, have been constrained by stem traits that are themselves correlated with Macaranga phylogeny. Earlier lineages of Decacrema exclusively inhabit waxy stems, a basal state in the Pachystemon clade within Macaranga, whereas younger species of Pachystemon, characterized by nonwaxy stems, are inhabited only by younger lineages of Decacrema. Despite the absence of cospeciation, the correlated succession of stem texture in both phylogenies suggests that Decacrema and Pachystemon have diversified in association, or codiversified. Subsequent to the colonization of the Pachystemon clade, Decacrema expanded onto a second clade within Macaranga, inducing the development of myrmecophytism in the Pruinosae group. Confinement to the aseasonal wet climate zone of western Malesia suggests myrmecophytic Macaranga are no older than the wet forest community in Southeast Asia, estimated to be about 20 million years old (early Miocene). Our calculation of COI divergence rates from several published arthropod studies that relied on tenable calibrations indicates a generally conserved rate of approximately 1.5% per million years. Applying this rate to a rate-smoothed Bayesian chronogram of the ants, the Decacrema from Macaranga are inferred to be at least 12 million years old (mid-Miocene). However, using the extremes of rate variation in COI produces an age as recent as 6 million years. Our inferred timeline based on 1.5% per million years concurs with independent biogeographical events in the region reconstructed from palynological data, thus suggesting that the evolutionary histories of Decacrema and their Pachystemon hosts have been contemporaneous since the mid-Miocene. The evolution of myrmecophytism enabled Macaranga to radiate into enemy-free space, while the ants' diversification has been shaped by stem traits, host specialization, and geographic factors. We discuss the possibility that the ancient and exclusive association between Decacrema and Macaranga was facilitated by an impoverished diversity of myrmecophytes and phytoecious (obligately plant inhabiting) ants in the region.