Reviews

Maternally transmitted bacteria have been important players in the evolution of insects and other arthropods, affecting their nutrition, defense, development, and reproduction. Wolbachia are the best studied among these and typically the most prevalent. While several other bacteria have independently evolved a heritable lifestyle, less is known about their host ranges. Moreover, most groups of insects have not had their heritable microflora systematically surveyed across a broad range of their taxonomic diversity. To help remedy these shortcomings we used diagnostic PCR to screen for five groups of heritable symbionts-Arsenophonus spp., Cardinium hertigii, Hamiltonella defensa, Spiroplasma spp., and Wolbachia spp.-across the ants and lepidopterans (focusing, in the latter case, on two butterfly families-the Lycaenidae and Nymphalidae). We did not detect Cardinium or Hamiltonella in any host. Wolbachia were the most widespread, while Spiroplasma (ants and lepidopterans) and Arsenophonus (ants only) were present at low levels. Co-infections with different Wolbachia strains appeared especially common in ants and less so in lepidopterans. While no additional facultative heritable symbionts were found among ants using universal bacterial primers, microbes related to heritable enteric bacteria were detected in several hosts. In summary, our findings show that Wolbachia are the dominant heritable symbionts of ants and at least some lepidopterans. However, a systematic review of symbiont frequencies across host taxa revealed that this is not always the case across other arthropods. Furthermore, comparisons of symbiont frequencies revealed that the prevalence of Wolbachia and other heritable symbionts varies substantially across lower-level arthropod taxa. We discuss the correlates, potential causes, and implications of these patterns, providing hypotheses on host attributes that may shape the distributions of these influential bacteria.

We review recent work at the interface of economic game theory and evolutionary biology that provides new insights into the evolution of partner choice, host sanctions, partner fidelity feedback and public goods. (1) The theory of games with asymmetrical information shows that the right incentives allow hosts to screen-out parasites and screen-in mutualists, explaining successful partner choice in the absence of signalling. Applications range from ant-plants to microbiomes. (2) Contract theory distinguishes two longstanding but weakly differentiated explanations of host response to defectors: host sanctions and partner fidelity feedback. Host traits that selectively punish misbehaving symbionts are parsimoniously interpreted as pre-adaptations. Yucca-moth and legume-rhizobia mutualisms are argued to be examples of partner fidelity feedback. (3) The theory of public goods shows that cooperation in multi-player interactions can evolve in the absence of assortment, in one-shot social dilemmas among non-kin. Applications include alarm calls in vertebrates and exoenzymes in microbes.

The estimated 6000 species of Lycaenidae account for about one third of all Papilionoidea. The majority of lycaenids have associations with ants that can be facultative or obligate and range from mutualism to parasitism. Lycaenid larvae and pupae employ complex chemical and acoustical signals to manipulate ants. Cost/benefit analyses have demonstrated multiple trade-offs involved in myrmecophily. Both demographic and phylogenetic evidence indicate that ant association has shaped the evolution of obligately associated groups. Parasitism typically arises from mutualism with ants, arid entomophagous species are disproportionately common in the Lycaenidae compared with other Lepidoptera. Obligate associations are more common in the Southern Hemisphere, in part because highly ant-associated lineages make up a larger proportion of the fauna in these, regions. Further research on phylogeny and natural history, particularly of the Neotropical fauna, will be necessary to understand the rote ant association has played in the evolution of the Lycaenidae.

Moths and butterflies whose larvae do not feed on plants represent a decided minority slice of lepidopteran diversity, yet offer insights into the ecology and evolution of feeding habits. This paper summarizes the life histories of the known predatory and parasitic lepidopteran taxa, focusing in detail on current researchin the butterfly family Lycaenidae, a group disprotionately rich in aphytophagous feeders and myrmecophilous habits.

Larvae and pupae of the Australian lycaenid butterfly, Jalmenus evagoras Donovan (Lepidoptera; Lycaenidae), are protected from parasites and predators by attendant ants. In return, the juveniles of J.evagoras secrete to the ants a solution containing substantial amounts of sugars and amino acids. Larvae of J.evagoras were reared from hatching until adult eclosion either with or without ants. Experiments were performed to examine whether fifth (final) instar larvae attempt to compensate for the nutrient loss to ants, by consuming more food, digesting food more efficiently, or extending development time. The presence or absence of ants had no effect on the feeding rate, efficiency of digestion or development time of fifth instar larvae. Larvae with ants converted a smaller proportion of ingested food into biomass, and consequently grew less than their counterparts without ants. Thus fifth instar larvae of J.evagoras do not appear to compensate for the nutrient loss to ants. Possible reasons for the failure to compensate are discussed.

Many organisms make a living from seratching each other's backs. and many survive at the expense of othcrs. Once a complex interaction has arisen between two organisms. what elfect can such a relationship have on their subsequcnt cvolution·! This pllpcr will consider thc evolutionary conscquences of ussocintions UIllOlIg Iycllcnid buttcrflics, their host plants, unts. purusitoids. lind prcdators. Thc Lycacllidac llfC cspecially intcrc.'1ting from an ccologicul and evolutionary pcrspcctivc because they exhibit dramatic variety in their life histories. The larvae of many species associate with ants, and these relationships can be parasitic. commensal, or mutualistic. larvae cun be carnivorous or hcrbivorous: and some species interact with many species of ants, whereas others are species-specific. It is partly because of this complexity and diversity that the lycaenidae have not been studied as intensively as other buUerny families, and I will discuss at least three problems that have hampered our understanding of their ecology and evolution. In particular. more must be learned about the nature of the exocrine secretions of lycaenid larvae, and whether they function to reward. appease, and/or deceive their associated ants. The association between lycaenids and ants has had several important evolutionary consequences, and I will show how these relate to the question of why there are so many species of Iycaenid buuernies. Finally. I will discuss an unresolved pattern in the biogeography oflycaenid buuernies: association with ants in general, and species-specific interactions in particular, are far more common among Iycaenids found in Ethiopian, Oriental. and Australasian regions than among those from the Holarctic.