Altitudinal clines for cyanogenesis in introduced populations of white clover near Vancouver, Canada

Abstract

Frequencies of cyanogenic and acyanogenic plants were determined in 15 populations of white clover, Trifolium repens, representing altitudinal comparisons at five localities in southwestern British Columbia, Canada and one in northwestern Washington State, U.S.A. The percentage of cyanogenic plants averaged 538 per cent in low elevation (<100 m) populations, 25•7 per cent in mid elevation (500-650 m) populations, and 11 •6 per cent in high elevation (1000-1500 m) populations. At all of the localities except Grouse Mountain, North Vancouver, B.C., the frequency of cyanogenic plants was lowest in high elevation populations. The altitudinal ratio-dine for cyanogenesis parallels dines found in the Swiss Alps and Wales, where white clover is a native species. White clover is introduced in North America, and the dine in southwestern British Columbia must have been established in less than a century, and in some populations less than 15 years. This pattern is consistent with the hypothesis of strong selective pressure for alternative phenotypes by temperature and/or predation by slugs and snails.

Searching for the bull’s eye: agents and targets of selection vary among geographically disparate cyanogenesis clines in white clover (Trifolium repens L.)

“…The cyanogenesis system is similar to these other study systems in that there must be intense selection acting within these populations; after all, multiple parallel clines have evolved in regions where white clover was introduced only within the last 500 years (Daday, 1958;Ganders, 1990;Kooyers and Olsen, 2012). Parallel cyanogenesis clines in white clover provide a unique perspective on adaptive divergence; we observe broadly parallel phenotypic patterns despite the fact that there are apparent differences among regions in both the agents of selection and their genetic targets.…”

“…For instance, in the central United States, where white clover is abundant, the range of aridity index is 10 times less than that observed in New Zealand. An additional explanation for the lack of previous documentation is that in most previously documented clines, aridity is closely correlated with MWT (for example, Daday, 1954a,b;Ganders, 1990;Majumdar et al, 2004). As MWT is more closely associated with herbivore pressure than aridity (see above), the latter variable would have been more easily overlooked in studies focusing on the role of cyanogenesis as a chemical defense.…”

“…Previous studies have reported higher frequencies of cyanogenic plants in warmer areas, and latitudinal and altitudinal cyanogenesis clines have been extensively documented in both the native and introduced species range (Daday, 1954a(Daday, ,b, 1958de Araujo, 1976;Till-Bottraud et al, 1988;Ganders, 1990;Majumdar et al, 2004). Here, we have investigated clinal variation in a sampling of introduced North American and New Zealand populations.…”

“…These clines were initially documented as a latitudinal cline across white clover's native range in Eurasia and an altitudinal cline in the Swiss Alps (Daday, 1954a, b). Over the last 60 years, similar clines have been documented elsewhere in the native range of the species (for example, see de Araujo, 1976;Till-Bottraud et al, 1988;Majumdar et al, 2004), as well as in non-native populations worldwide, where white clover has been introduced as a temperate forage crop and lawn plant (for example, Daday, 1958;Ganders, 1990;Kooyers and Olsen, 2012). In a recent study, we have documented an adaptive latitudinal cyanogenesis cline in introduced populations across the central United States, where the AcLi cyanotype frequency increases from B11% in Wisconsin to B86% in southern Louisiana (Kooyers and Olsen, 2012).…”

Evidence on the Molecular Basis of the Ac/ac Adaptive Cyanogenesis Polymorphism in White Clover (Trifolium repens L.)

“…EU370164-EU370205. 1 genesis, with frequencies of cyanogenic plants closely correlated with minimum winter temperatures in both the native and the introduced range (e.g., Daday 1954aDaday ,b, 1958De Araujo 1976;Till-Bottraud et al 1988;Ganders 1990;Majumdar et al 2004). Comparisons of cyanogenic and acyanogenic plants have revealed trade-offs between cyanogenesis and several fitnessrelated traits, including flowering rate (Daday 1965;Foulds and Grime 1972;Dirzo and Harper 1982b;Kakes 1989), drought tolerance (Foulds and Grime 1972), and resistance to rust (Dirzo and Harper 1982b).…”