Population structure of Spodoptera frugiperda maize and rice host forms in South America: are they host strains?

Abstract

Determining which factors contribute to the formation and maintenance of genetic divergence to evaluate their relative importance as a cause of biological differentiation is among the major challenges in evolutionary biology. In Spodoptera frugiperda (Smith) (Lepidoptera: Noctuidae) two host strains have been recognized in the 1980s: the corn‐strain prefers maize, sorghum, and cotton, whereas the rice‐strain prefers rice and wild grasses. However, it is not clear to what extent these so‐called ‘strains’, which have also been called ‘host races’ or even ‘sibling species’, are really associated with host plants. Due to the indeterminate evolutionary status, we will use the term ‘host forms’ (sensu Funk). Here, we characterized populations collected from maize, rice, and wild grasses from three countries in South America. Using two mitochondrial cytochrome oxidase I (mtCOI) markers and 10 polymorphisms in the triose phosphate isomerase (Tpi) gene, we found various patterns of host association. Two hundred twenty‐seven nuclear amplified fragment length polymorphisms (AFLPs) markers revealed significant genetic differentiation among populations, which was generally correlated to the host from which the larvae were collected. Using a multivariate discriminant analysis and a Bayesian clustering approach, we found that individuals could be grouped into 2–5 genetically distinct clusters, depending on the method. Together, our results indicate that although host‐associated differentiation is present in this species, it does not account for all observable genetic variation and other factors must be maintaining genetic differentiation between these forms. Therefore, the term ‘host strains’ should be abandoned and ‘host forms’ should be used instead for S. frugiperda.

Genotyping‐by‐sequencing approach indicates geographic distance as the main factor affecting genetic structure and gene flow in Brazilian populations of Grapholita molesta (Lepidoptera, Tortricidae)

“…; Juarez et al. ), and for the tortricid moth Cydia pomonella (L.), based on divergent biological responses and oviposition behavior adaptations related to larval host plants (Phillips and Barnes ; Barnes ).…”

A Z-linked sterility locus causes sexual abstinence in hybrid females and facilitates speciation inSpodoptera frugiperda

“…However, the association between strain and host plant is not absolute (Juárez et al. , ). The two strains differ in their sex pheromone blend (Groot et al.…”

Using intron sequence comparisons in the triose‐phosphate isomerase gene to study the divergence of the fall armyworm host strains

“…Demonstration of sympatric speciation is difficult and to date there are few unambiguous examples of it occurring (Coyne, ; Mallet et al ., ). The fall armyworm, Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae), has been implicated as being in the early stages of divergence into two species and appears to be doing so under largely sympatric conditions (Prowell, ; Dres & Mallet, ; Prowell et al ., ; Juárez et al ., ; Dumas et al ., ). The diverging subpopulations were initially characterized on the basis of genetic differences observed between larvae collected in the field from corn and rice plant hosts, and were designated ‘corn strain’ and ‘rice strain’ based on initial observations (Pashley et al ., ; Pashley, ).…”