Abstract
Successful geographic range expansion by parasites and parasitoids may also require host range expansion. Thus, the evolutionary advantages of host specialization may trade off against the ability to exploit new host species encountered in new geographic regions. Here, we use molecular techniques and confirmed host records to examine biogeography, population divergence, and host flexibility of the parasitoid fly, Ormia ochracea (Bigot). Gravid females of this fly find their cricket hosts acoustically by eavesdropping on male cricket calling songs; these songs vary greatly among the known host species of crickets. Using both nuclear and mitochondrial genetic markers, we (a) describe the geographical distribution and subdivision of genetic variation in O. ochracea from across the continental United States, the Mexican states of Sonora and Oaxaca, and populations introduced to Hawaii; (b) demonstrate that the distribution of genetic variation among fly populations is consistent with a single widespread species with regional host specialization, rather than locally differentiated cryptic species; (c) identify the more‐probable source populations for the flies introduced to the Hawaiian islands; (d) examine genetic variation and substructure within Hawaii; (e) show that among‐population geographic, genetic, and host song distances are all correlated; and (f) discuss specialization and lability in host‐finding behavior in light of the diversity of cricket songs serving as host cues in different geographically separate populations.
Highlights
Evolutionary specialization is often viewed as a double-edged sword: specialization may facilitate efficient exploitation of favored resources, but may inhibit exploitation of novel resources
Some species are sufficiently host specific to be used for classical biological control of pests (Parkman et al, 1996, Vargas et al, 2007), others routinely utilize a broad range of hosts (Stireman, 2005, Tschorsnig, 2017, Arnaud, 1978), and in other aCC-BY-NC-ND 4.0 International license
Longitude explained the primary axis of variation among the mainland populations, with a clear east-west gradient evident in both the discriminant function analysis of principal components (DAPC) and mtDNA haplotype network (Fig. 1), as well as in the pairwise Fst and Nei’s distances (Table 4)
Summary
Evolutionary specialization is often viewed as a double-edged sword: specialization may facilitate efficient exploitation of favored resources, but may inhibit exploitation of novel resources. For specialist species to expand their geographic range, they must readily encounter suitable resources, exhibit phenotypic plasticity enabling adoption of novel resources, and/or show rapid evolutionary adaptation. Parasitoid insects, especially Ichneumonid and Braconid wasps (Hymenoptera) and Tachinid flies (Diptera), are especially illuminating for studies of host specialization, ranging from extreme generalists to extreme specialists (Quicke, 2014, Stireman et al., 2006). Some species are sufficiently host specific to be used for classical biological control of pests (Parkman et al, 1996, Vargas et al, 2007), others routinely utilize a broad range of hosts (Stireman, 2005, Tschorsnig, 2017, Arnaud, 1978), and in other cases, presumed generalists are later revealed to be complexes of cryptic specialists (Smith et al, 2008)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
