Figure 2.

Geographic variation in host fruiting phenology and fly eclosion time along a latitudinal transect of 18 different Rhagoletis pomonella populations analyzed at 13 sites from Grant, MI, United States, to the highlands of Chiapas, Mexico (MX) (Data are from Dambroski & Feder, 2007; Hood et al., 2015; Lyons‐Sobaski & Berlocher, 2009; Xie et al., 2007; see Figure 1 for a map of the 13 sampled sites and Supporting Information Table S2 for population designations and additional information. Sites with the same number but different letters represent flies sampled from different hosts at the site). (a) Host fruiting time, as indicated by the collecting date of fly populations at sites, plotted against latitude; (b) mean time to eclosion measured as the average number of days following postwinter warming of fly populations determined from controlled laboratory rearing studies plotted against latitude; and (c) mean eclosion time of fly populations plotted against host fruiting time at sites. Grant, MI (site 1), and Urbana, IL (site 4), represent the approximate northernmost and southernmost ends, respectively, where apple (green circles) and Crataegus mollis (red triangles) host races geographically overlap in the Midwestern United States. Note that flies from site 5 infest C. mollis v. texana in Texas which is also depicted with a red triangle, while other hawthorn‐infesting fly populations are shown in black triangles. Geographic and host‐related differentiation in host fruiting time and fly eclosion in the Midwestern United States is subsumed within a larger pattern of variation across North America. There is a general trend for both host fruit to ripen and flies to eclose later in the year with decreasing latitude, as evidenced by significant negative correlations (r values are given considering the hawthorn data alone = r, and for all hosts including apples = r all). The relationship is complicated, however, by R. pomonella attacking different hawthorn species moving southward from the Midwest (see Supporting Information Table S2) that fruit at varying times during the season (Lyons‐Sobaski & Berlocher, 2009; Rull et al., 2006; Xie et al., 2007), as well as altitudinal effects in Mexico