Evidence for spatial clines and mixed geographic modes of speciation for North American cherry‐infesting Rhagoletis (Diptera: Tephritidae) flies

SAINT JEAN, GILBERT; HOOD, GLEN R.; GLOVER, MARY M.; GOUGHNOUR, ROBERT; FEDER, JEFFREY L.; EGAN, SCOTT P.; SCHULER, HANNES; SMITH, JAMES J.; RULL, JUAN; DOELLMAN, MEREDITH M.; POWELL, THOMAS H. Q.; BRUZZESE, DANIEL J.; YEE, WEE L.; ALUJA, MARTIN

Ecology and Evolution

wiley

Lugar: Chicago; Año: 2020

2045-7758

An important criterion for understanding speciation is the geographic context ofpopulation divergence. Three major modes of allopatric, parapatric, and sympatricspeciation define the extent of spatial overlap and gene flow between divergingpopulations. However, mixed modes of speciation are also possible, whereby populations experience periods of allopatry, parapatry, and/or sympatry at different timesas they diverge. Here, we report clinal patterns of variation for 21 nuclear-encodedmicrosatellites and a wing spot phenotype for cherry-infesting Rhagoletis (Diptera:Tephritidae) across North America consistent with these flies having initially divergedin parapatry followed by a period of allopatric differentiation in the early Holocene.However, mitochondrial DNA (mtDNA) displays a different pattern; cherry flies at theends of the clines in the eastern USA and Pacific Northwest share identical haplotypes, while centrally located populations in the southwestern USA and Mexico possess a different haplotype. We hypothesize that the mitochondrial difference couldbe due to lineage sorting but more likely reflects a selective sweep of a favorablemtDNA variant or the spread of an endosymbiont. The estimated divergence time formtDNA suggests possible past allopatry, secondary contact, and subsequent isolationbetween USA and Mexican fly populations initiated before the Wisconsin glaciation.Thus, the current genetics of cherry flies may involve different mixed modes of divergence occurring in different portions of the fly´s range. We discuss the need foradditional DNA sequencing and quantification of prezygotic and postzygotic reproductive isolation to verify the multiple mixed-mode hypothesis for cherry flies anddraw parallels from other systems to assess the generality that speciation may commonly involve complex biogeographies of varying combinations of allopatric, parapatric, and sympatric divergence.