Genetic differentiation associated with host plants and geography among six widespread species of South American Blepharoneura fruit flies (Tephritidae)

Why are there not more herbivorous insect species?

Insect species richness is estimated to exceed three million species, of which roughly half is herbivorous. Despite the vast number of species and varied life histories, the proportion of herbivorous species among plant-consuming organisms is lower than it could be due to constraints that impose limits to their diversification. These include ecological factors, such as vague interspecific competition; anatomical and physiological limits, such as neural limits and inability of handling a wide range of plant allelochemicals; phylogenetic constraints, like niche conservatism; and most importantly, a low level of concerted genetic variation necessary to a phyletic conversion. It is suggested that diversification ultimately depends on what we call the intrinsic trend of diversification of the insect genome. In support of the above, we survey the major types of host-specificity, the mechanisms and constraints of host specialization, possible pathways of speciation, and hypotheses concerning insect diversification.

Genetic Variation in Anastrepha obliqua (Diptera: Tephritidae) in a Highly Diverse Tropical Environment in the Mexican State of Veracruz

There has been considerable interest in understanding biological, ecological, historical, and evolutionary processes that contribute to the diversification of species and populations among tephritid fruit flies. Only a limited number of studies have examined the genetic diversity and population biology of species belonging to the genus Anastrepha considering fine-scale differentiations associated to locality as well as hosts over an entire fruiting season. To expand our understanding of population structure and genetic diversity in one of the critical Anastrepha fruit flies populations in a highly diverse tropical environment we analyzed Anastrepha obliqua (Macquart) (Diptera: Tephritidae) in the Mexican state of Veracruz from five host fruit species and 52 geographic collections using sequence data from mtDNA and microsatellite markers from nuclear DNA. Indeed, we examined the population structure of this pest in a micro-geographic region and report on relationships and historical processes for individuals collected within a small portion of the geographic range of its distribution. Analyses of 1055 bp mtDNA sequences from CO1and ND1genes across 400 individuals detected 34 haplotypes. Haplotype and nucleotide diversity was low, with 53% of the individuals exhibiting a single haplotype (OBV1). Host association and fine-scale differentiation at 17 microsatellite markers across 719 individuals from 32 of the 52 geographic collections reveal fragmented A. obliqua populations. These findings have important implications for the implementation of the Sterile Insect Technique (SIT) and other pest management programs used to control this pestiferous fruit fly.

Anatomy of a Neotropical insect radiation

Background

Much evolutionary theory predicts that diversity arises via both adaptive radiation (diversification driven by selection against niche-overlap within communities) and divergence of geographically isolated populations. We focus on tropical fruit flies (Blepharoneura, Tephritidae) that reveal unexpected patterns of niche-overlap within local communities. Throughout the Neotropics, multiple sympatric non-interbreeding populations often share the same highly specialized patterns of host use (e.g., flies are specialists on flowers of a single gender of a single species of host plants). Lineage through time (LTT) plots can help distinguish patterns of diversification consistent with ecologically limited adaptive radiation from those predicted by ecologically neutral theories. Here, we use a time-calibrated phylogeny of Blepharoneura to test the hypothesis that patterns of Blepharoneura diversification are consistent with an “ecologically neutral” model of diversification that predicts that diversification is primarily a function of time and space.

Results

The Blepharoneura phylogeny showed more cladogenic divergence associated with geography than with shifts in host-use. Shifts in host-use were associated with ~ 20% of recent splits (< 3 Ma), but > 60% of older splits (> 3 Ma). In the overall tree, gamma statistic and maximum likelihood model fitting showed no evidence of diversification rate changes though there was a weak signature of slowing diversification rate in one of the component clades.

Conclusions

Overall patterns of Blepharoneura diversity are inconsistent with a traditional explanation of adaptive radiation involving decreases in diversification rates associated with niche-overlap. Sister lineages usually use the same host-species and host-parts, and multiple non-interbreeding sympatric populations regularly co-occur on the same hosts. We suggest that most lineage origins (phylogenetic splits) occur in allopatry, usually without shifts in host-use, and that subsequent dispersal results in assembly of communities composed of multiple sympatric non-interbreeding populations of flies that share the same hosts.

Electronic supplementary material

The online version of this article (10.1186/s12862-018-1146-9) contains supplementary material, which is available to authorized users.