Assessment of the diversity and species specificity of the mutualistic association between Epicephala moths and Glochidion trees

Abstract

The obligate mutualisms between flowering plants and their seed-parasitic pollinators constitute fascinating examples of interspecific mutualisms, which are often characterized by high levels of species diversity and reciprocal species specificity. The diversification in these mutualisms has been thought to occur through simultaneous speciation of the partners, mediated by tight reciprocal adaptation; however, recent studies cast doubt over this general view. In this study, we examine the diversity and species specificity of Epicephala moths (Gracillariidae) that pollinate Glochidion trees (Phyllanthaceae), using analysis of mitochondrial and nuclear gene sequences. Phylogenetic analysis of Epicephala moths associated with five Glochidion species in Japan and Taiwan reveal six genetically isolated species that are also distinguishable by male genital morphology: (i) two species specific to single host species (G. acuminatum and G. zeylanicum, respectively); (ii) two species that coexist on G. lanceolatum; and (iii) two species that share two, closely-related parapatric hosts (G. obovatum and G. rubrum). Statistical analysis shows that the two species associated with G. lanceolatum are not sister species, indicating the colonization of novel Glochidion host in at least one lineage. Behavioural observations suggest that all six species possess the actively-pollinating habit, thus none of the studied species has become a nonmutualistic 'cheater' that exploits the benefit resulting from pollination by other species. Our results parallel recent findings in ecologically similar associations, namely the fig-fig wasp and yucca-yucca moth mutualisms, and contribute to a more general understanding of the factors that determine ecological and evolutionary outcomes in these mutualisms.

Repeated colonization of remote islands by specialized mutualists

“…Adult Epicephala were recognized by the two-lobed valvae of the male genitalia, sclerotized ovipositor and forewing pattern. Female Epicephala were examined for pollen-bearing hairs on the proboscis [16]. 18.00 and 1.00 h. All flower visitors were observed and photographed while on flowers, captured, preserved dry in glassine envelopes and examined for pollen.…”

Allopatric distribution and diversification without niche shift in a bryophyte-feeding basal moth lineage (Lepidoptera: Micropterigidae)

“…We sequenced fragments of the mitochondrial cytochrome oxidase subunit I (COI) and nuclear 18S rRNA and elongation factor 1-alpha (EF-1a) genes. Laboratory protocols, as well as the PCR primers used, are detailed in Kawakita et al [32] and Kawakita & Kato [33].…”

Mutualism favours higher host specificity than does antagonism in plant–herbivore interaction

“…Sampling was conducted within precisely the same geographical range as that used to assess pollinator specificity in our previous study (Kawakita & Kato 2006); this enabled a direct comparison of host specialization among herbivores using the same sets of Glochidion species. Diphtheroptila and Caloptilia were collected by sampling the leaves containing the larvae and were reared to adults in the laboratory.…”

“…PCR amplification and direct sequencing of the COI, EF-1a, ArgK and 18S rRNA genes were conducted using the primers and protocols detailed in Kawakita et al (2004) and Kawakita & Kato (2006. Heterozygous sites in EF-1a and ArgK were identified as double peaks of similar height in the chromatograms of both forward and reverse strands and accordingly coded using degenerate bases.…”

“…Among them are plants of the genus Glochidion, which is the largest radiation and comprises more than 300 species distributed throughout the Asian -Australian tropics (Govaerts et al 2000). Previous detailed assessment of pollinator specificity in the Japanese species of Glochidion has found that, although some Epicephala species are associated with two closely related Glochidion hosts in different parts of their ranges, each Epicephala species is specialized to only one of the several co-occurring hosts in all populations studied, thus showing very strict local host specificity (Kawakita & Kato 2006). …”