Spatial turnover in host-plant availability drives host-associated divergence in a South African leafhopper (Cephalelus uncinatus)

Abstract

BackgroundThe evolution of reproductive isolation between herbivorous insect populations is often initiated by shifts to novel host-plants, a process that underlies some of the best examples of ecological speciation. However, it is not well understood why host-shifts occur. Arguably the most common hypothesis is that host-shifts occur in response to competition, while a less frequently invoked hypothesis is that herbivores adapt locally to geographic differences in potential host-plant communities. Here we investigate whether geographic variation in host-plant availability is likely to have driven host-shifts in restio leafhoppers. We studied local adaptation of a camouflaged restio leafhopper species, Cephalelus uncinatus, to host-plants in the Restionaceae (restios); a family of plants with exceptional diversity in the anomalously species-rich Cape Floristic Region (CFR). To determine whether C. uncinatus experiences heterogeneous host communities across its range, we first quantified the degree of geographic overlap between C. uncinatus and each of its associated host-plant species. Then we quantified trait divergence (host preference, body size and colour) for three pairs of C. uncinatus populations found on different host-plant species differing in their degree of spatial overlap. Spectral reflectance was modelled in bird visual space to investigate whether body colour divergence in C. uncinatus corresponds to leaf sheath colour differences between restio species as perceived by potential predators.ResultsWe demonstrate that C. uncinatus is forced to use different restio species in different regions because of turnover in available host species across its range. Comparisons between geographically separated populations were consistent with local adaptation: restio leafhoppers had preferences for local host-plants over alternative host-plants and matched local plants better in terms of size and colour.ConclusionsSpatial turnover in host-plant availability has likely facilitated host-shifts in C. uncinatus. Spatial turnover in host-plant availability may be an important driver of insect diversification in the CFR and globally.Electronic supplementary materialThe online version of this article (doi:10.1186/s12862-017-0916-0) contains supplementary material, which is available to authorized users.

Interactions among predators and plant specificity protect herbivores from top predators

“…This seems likely since one of the main hypothesis explaining the specialization of herbivorous insects to plants is predator avoidance, with plant specialists notably benefiting from greater crypsis or chemical defense (EFS; Bernays andGraham 1988, Singer et al 2014). For example, in the region (Cape Floristic Region), the Cephalelini (Cicadellidae; Hemiptera) present morphological traits to mimic sheaths of the reed-like Restionaceae (Augustyn et al 2013(Augustyn et al , 2017 on which they feed and to which they are often specific at the species level (Augustyn et al 2013, Kemp et al 2017. In our study, one Cephalelini morpho-species in particular was identified as one of the most plant-specialized herbivores (Cephalelini.sp4; Appendix S4: Fig.…”

“…For example, in the region (Cape Floristic Region), the Cephalelini (Cicadellidae; Hemiptera) present morphological traits to mimic sheaths of the reed‐like Restionaceae (Augustyn et al. , ) on which they feed and to which they are often specific at the species level (Augustyn et al. , Kemp et al.…”

“…The evolution of their particular morphology in association with their host plants likely provides protection against visual predators such as birds (Augustyn et al. ). However, such visual crypsis would not offer protection from spiders, as most of the spider species in our study were web‐builders or nocturnal wanderers, therefore not relying on visual cues to hunt their prey.…”

High spatial turnover in springtails of the Cape Floristic Region

“…A strong relationship was also found between plant phylogenetic diversity and detritivore insect richness within the Fynbos at the 20 m sampling scale in a previous investigation (Procheş et al, ), bearing out the independent, but likely similar, influence of environmental drivers on plants and on detritivorous arthropods. Understanding just what these mechanistic drivers are will require the kinds of coupled ecological and phylogenetic work that has provided so much insight into the mechanisms underlying plant diversity in the region (Cowling et al, ; Dupont et al, ; Linder, ; Linder & Verboom, ; Rundel et al, ), including explicit tests of Kemp et al () hypotheses and other drivers such as interspecific interactions (Augustyn, Anderson, Merwe, & Ellis, ). Initial evidence suggests that some springtail genera, such as Seira , may have undergone significant radiations in the CFR (Janion, Bedos, Bengtsson, et al, ; Liu, ), which points to the importance of eco‐evolutionary processes, as is the case in the plants.…”

Is there a host-associated molecular and morphological differentiation between sympatrically occurring individuals of the invasive leaf miner Cameraria ohridella?

“…Nevertheless, the fitness of leaf miners in a new host is initially suboptimal compared to the original ancestral host, probably as a result of differences in the chemistry of a new host (Thompson 1988;Péré et al 2010;Augustyn et al 2017). Aesculus glabra and Ae.…”