Early History of Willow Leaf Beetle Project

  1. JS initially hypothesized that, as beetles increased in elevation, biotic factors such as predation and parasitism would give way to abiotic factors such as temperature in controlling the beetles' populations (Smiley 1986). One aspect of the beetles' natural history was particularly interesting in this regard. The larvae of the beetles secreted large amounts of a pungeantly aromatic white liquid, which would probably be active in repelling predators. A literature review revealed that, in European species of Chrysomela, this liquid was derived from salicylate precursor chemicals in the willow food (Pasteels et al 1983).
  2. JS assembled a team of students from UC Irvine and, in 1982, began an in-depth study of the biology of these organisms. The first season's results revealed marked differences in the timing of spring emergence of the beetles, with late spring emergence from under late melting snow packs. They also revealed that beetle growth rates were not affected by removal of secretion, as predicted by Pasteels' et. al. theories of the sequestration process. In 1983 and 1984 the study was expanded to specifically address aspects of the elevation gradient. A survey of salicylate chemistry revealed strong changes with increasing elevation, as well as improved survival on plants with greater amounts of salicylates (Smiley et al 1985). Studies also revealed two Chrysomela-specific hunting predators, Symmorphus cristatus, a eumenid hole-nesting wasp (Hymenoptera: Vespidae) and Parasyrphus melanderi, a hover fly whose larvae feed on Chrysomela eggs and larvae (Diptera:Syrphidae). In addition, in 1984 and 85, lower-elevation willow beetle populations were compared with upper populations, including transplant experiments. The results indicated differences in survival and growth rate between elevations, as well as providing evidence for local adaptation (Smiley and Rank 1986).
  3. In 1985 NR began in depth studies of egg-laying and food plant choice behavior in C. aeneicollis, and discovered a marked preference for plants rich in salicylates. He generally did not record higher survivorship on those plants, however. He speculated that the specialist hunting predators were keying in on the salicylate rich plants, nullifying any advantage for the beetles of feeding on those plants. (Rank 1992, 1994) He verified this prediction for syrphid fly females, who preferentially oviposit on salicylate-rich plants (Rank and Smiley 1994). In 1988, NR began what has since become a long-term study of the population genetic structure of the willow beetles. Analyzing beetles from numerous populations in the eastern Sierra Nevada, he found ample evidence of differentiation at all scales: between-drainage, between-elevation (site), and down to between plant within site. The pattern of differentation suggested gene flow between populations, as well as evidence for selection for particular genotypes at particular elevations (Rank 1992).
  4. In 1987 the numbers of willow beetles began to decline, corresponding with a widespread drought in California, which lasted until 1993. In the summer of 1994 the populations began to rebound, in some areas spreading out from the highest elevation sites which may have served as refugia. By 1995 populations were healthy, and remained so until 2003 and 2004, when some populations began to decline. The patterns of beetle abundance roughly correspond with annual precipitation, mainly in the form of winter snow.
  5. In 1996, NR resampled the newly expanded beetle populations to look for genetic change. The subsequest analysis, done in collaboration with ED (Rank and Dahlhoff, 2003), showed strong evidence for directional selection at the PGI locus, possibly based on cooler temperatures and interactions with heat shock proteins (HSP's). This began a productive collaboration, involving many students from both institutions, specifically into the evolution of thermal tolerance in willow beetles and more broadly, into the behavior, ecology and evolution of the beetles (Dahlhoff and Rank, 2000, Neargarter et al 2003, McMillan et al 2005).
  6. In 1997 JS began intensive observations on Symmorphus hole nesting wasps in Big Pine Creek. He verified that Symmorphus only take 3rd instar C. aeneicollis larvae, and observed many interactions between wasps, nest holes, and beetle prey (Sears et al 2001). The possibility that Symmorphus could nearly or completely extirpate local populations of C. aeneicollis was confirmed. Observations along the Big Pine Creek gradient have also confirmed that the wasps are colonizing upper elevation sites for the first time since the study started. (Nakatani 2004). This corresponds to a more complex upward shift in beetle populations.

1981 John and Nancy Smiley, Dick MacMillen visit BPC

1982 John brings UCI student team to falls site. Team includes Charles Wisdom, Jeff Ihara, Joe Evans, Kim Miller, George Shakaraschwili, Mike Kingston

1983 2nd year of student team

1984 Jonathon Horn, Wendy Goldstein, Dave Bershauer

1985 last row