Synchronous speciation of hosts and herbivorous insects predicts a congruent topology of host and insect phylogenies and similar evolutionary ages of host and insect taxa. To test these predictions for the specialized herbivorous fly genus Urophora (Diptera: Tephritidae), we used three different approaches. (i) We generated a phylogenetic tree of 11 European Urophora species from allozyme data and constructed a phylogeny of their hosts from published sources. Superimposing the Urophora tree on the host-plant tree we found no evidence for general congruence. (ii) We correlated genetic distances (Nei distances) of the host plants vs. the genetic distances of associated Urophora species. Overall, the relationship was not positive. Nevertheless, for some pairs of Urophora species and host plants genetic distances were in the same order of magnitude. (iii) We collected allozyme data for pairs of thistle taxa and pairs of herbivores on thistles together with independent time estimates. With these data we calibrated a molecular clock. There was a non-linear relationship between phylogenetic age and genetic distance, rendering the dating of deep events in thistle–insect evolution difficult. Nevertheless the derived molecular clock showed that the split of insect taxa lagged behind the split of hosts. © 2005 The Linnean Society of London, Biological Journal of the Linnean Society, 2005, 84, 775–783.

Flies on thistles: support for synchronous speciation?

Rich and diversified assemblages of larval stage phytophagous insects exploit the flower heads of the thistle tribe Cardueae. As these insects form communities within a shared resource unit with well-defined spatial boundaries, they offer a good opportunity to study the guild organization of communities of endophytic insects. We used random combinations of members of phytophagous taxa, which radiated on hosts of the subtribes Centaureinae and Carduinae, as species pools for null models to determine whether and to what extent the composition of the guilds in Cardueae flower heads follows predictable assembly rules. We tested two hypotheses and found that in both cases the null model can be rejected. Assembly rule 1: species assemblages in flower heads follow the rule of intra-generic isolation (i.e. each guild member belongs to a different genus) significantly more often than random combinations of Cardueae insects. We show that, where violations of this rule occur, they are almost exclusively due to the occurrence of a combination of those congeners of the genera Urophora, Larinus and Cerajocera, whose larval activities differ to some extent temporally and/or spatially. Assembly rule 2: the composition of guilds tends to develop towards a maximum of intra-guild differentiation – the three complementary trophic types (e.g. gall and callus feeders, receptacle and ovary chewers, omnivores and intra-guild predators) co-occur in guilds significantly more often than in random combinations. Our results show that the organization of phytophagous guilds in Cardueae flower heads is mainly a result of invasions due to host shifts. We suggest that in addition to larval competition for space and food, constraints such as the availability of enemy-free space and/or ‘free rendezvous arenas’ have shaped the structure of the guilds investigated.

/pdf/the-organization-of-phytophagous-guilds-in-cardueae-flower-gesw8c4jpg.pdf

The organization of phytophagous guilds in Cardueae flower heads: conclusions from null models

Symphagy, as used in this chapter, is the collective sharing of flower heads of a single host-plant species of Asteraceae by more than one species from one or more genera of nonfrugivorous fruit flies (Diptera: Tephritidae) (Goeden 1987, 1989, 1992, 1993, 1994). The manner in which this symphagy is achieved, e.g., whether by spatial or temporal partitionings of the resource that a host-species’ flower heads collectively represent (Zwolfer 1987, 1988; Zwolfer and Arnold-Rinehart 1993), is beyond the scope of this chapter and best examined at the individual tephritid and host plant species level (cf. Zwolfer 1965, 1982, 1987, 1988, 1990; Goeden and Ricker 1986, 1987; Headrick and Goeden 1990; Goeden and Headrick 1991, 1992; Goeden et al. 1994). This chapter describes and analyzes 14 years of data on symphagy among 15 genera of florivorous Tephritidae and 12 tribes of Asteraceae in southern California. This is the first comprehensive analysis of symphagy by a multigeneric grouping of geographically defined, nonfrugivorous, Nearctic fruit flies, and was inspired in part by Helmut Zwolfer’s comprehensive, long-term field and laboratory studies of the biology, ecology, and evolution of Tephritidae, and other Palearctic insect associates of asteraceous thistles and knapweeds (Zwolfer 1965, 1982, 1988, 1990). I dedicate this analysis of original data as a token of my admiration, respect, and friendship for Helmut on the occasion of his recent retirement from the Faculty of the University of Bayreuth.

Symphagy Among Florivorous Fruit Flies (Diptera: Tephritidae) in Southern California

Data are presented on allozyme variation between 15 populations of the stenophagous capitulum weevil, Larinus cynarae, and three populations of its congener, L. latus, that had been collected throughout the northern mediterranean range of these species. A phenetic analysis of these data revealed no direct relationship between genetic variation and host-plant association within L. cynarae, but there was a strong geographical structuring of allozyme patterns. Most of the genetic variation was due to differences between geographical regions and variation within these was small. Wright's FST values showed that Italian and Greek populations of L. cynarae were most distinct from L. latus, with southern Iberian, northern Spanish and French populations increasingly less so. This pattern was associated with a cline in the frequencies of certain alleles along this geographical arc from France to Greece. A phenogram of Nei's genetic distances indicated the close genetic relationship between the two species of Larinus and separated the populations of L. cynarae into three allopatric groups. These groups have different host-plant spectra — dominated by Cynara cardunculus in Italy and Greece, Cynara humilis/Onopordum in southern Iberia and Onopordum spp. in France/Northern Spain — and can be considered to be host biotypes of L. cynarae. L. latus, which occurs in Greece and further east is also an Onopordum specialist. An analysis of the phylogeny of this group of Larinus indicates a primary separation into eastern (L. latus) and western (L. cynarae) taxa, with further branching of the L. cynarae lineage into the putative host-biotypes. An hypothesis for the evolution of these taxa is given, based on the evolutionary history of host-plant taxa and geographical constraints.

Micro‐evolution in the weevil genus Larinus: the formation of host biotypes and speciation

13 – Adjustment of Gene Flow at the Population, Species, and Ecosystem Level: Thistles and Their Herbivores

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13 – Adjustment of Gene Flow at the Population, Species, and Ecosystem Level: Thistles and Their Herbivores