Phylogenetics and evolution of the eastern Asian-eastern North American disjunct aphid tribe, Hormaphidini (Hemiptera: Aphididae)

A test of morphological hypotheses for tribal and subtribal relationships of Aphidinae (Insecta: Hemiptera: Aphididae) using DNA sequences

Aphidinae is the most diverse major lineage of aphids (Aphididae). Aphidinae currently dominate the temperate, northern-hemisphere fauna, but only since the late Tertiary, and few species are native to the southern hemisphere. The success of Aphidinae may be linked to the evolution of an unusual life cycle, host alternation. The classification and phylogeny of Aphidinae have been controversial; schemes based on morphology have been confounded by widespread homoplasy. Here we present the first phylogenetic study of higher-level Aphidinae relationships based on molecular data (elongation factor-1alpha, leucine tRNA, and cytochrome oxidase II sequences). Analyses supported the monophyly of Aphidini and its subtribes, Aphidina and Ropalosiphina, but revealed novel relationships concerning Pterocommatini and Macrosiphini, with the former nested within the latter tribe as the sister to Cavariella. Several relationships within Pterocommatini + Macrosiphini corresponded better with host-plant affiliations than with aphid classification. Overall, relationships found here challenge several traditional views of Aphidinae evolution: they suggest more than one origin of host alternation in the family, and they question the assumption that Aphidinae originated in the northern hemisphere.

Speciation by host-switching in pinyon Cinara (Insecta: Hemiptera: Aphididae)

Parasite-host cospeciation has received much attention as an important mechanism in the diversification of phytophagous insects. However, studies have shown that for certain taxa, it is not host fidelity but host-switching that plays the critical role in speciation. Cinara are aphids (Insecta: Hemiptera: Aphididae: Lachninae) that feed exclusively on the woody parts of conifers of the Cupressaceae and Pinaceae. They are unusual aphids because most Pinaceae play host to several species of Cinara. The aphids show relatively strong host fidelity, and as a consequence historically have been treated based on the taxonomy of their hosts. The historical paradigm of aphid evolution implies that Cinara species have radiated to different parts of the same host species and/or speciated with their host. Using mitochondrial cytochrome oxidase 1 and nuclear elongation factor 1-alpha DNA sequences, we performed molecular phylogenetic analysis of Cinara species, concentrating on those associated with pinyon pines in the southwestern USA. We determined that switching hosts has played a key role in the speciation of the genus, reflected in the polyphyly of pinyon-feeding Cinara. Furthermore, species sharing a common feeding site on different hosts were more closely related to each other than to those sharing the same host but at different feeding sites, suggesting that feeding site fidelity plays a more important role in speciation than does host fidelity in general. This study also elucidated the primary taxonomy of various species: it suggested that Cinara rustica Hottes is a junior synonym of C. edulis (Wilson) and that C. wahtolca Hottes represents two species on the two different pinyon pine species, Pinus edulis Englem. and P. monophylla Torr. & Frem.

Recent Intron Gain in Elongation Factor-1α of Colletid Bees (Hymenoptera: Colletidae)

We discovered the presence of a unique spliceosomal intron in the F1 copy of elongation factor-1alpha (EF-1alpha) restricted to the bee family Colletidae (Hymenoptera: Apoidae). The intron ranges in size from 101 to 1044 bp and shows no positional sliding. Our data also demonstrate the complete absence of this intron from exemplars representing all other bee families, as well as from close hymenopteran relatives. A review of the literature finds that this intron is likewise absent from all other arthropods for which data are available. This provides unambiguous evidence for a relatively recent intron insertion event in the colletid common ancestor and, at least in this specific instance, lends support to the introns-late hypothesis. The comparative distribution of this novel intron also supports the monophyly of Colletidae and the exclusion of the Stenotritidae from this family, providing an example of the potential of some introns to act as robust markers of shared descent.