PGI Genotype1-1 1-4 4-4

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Affiliations(1) Dept. of Biology, Santa Clara Univ.; (2) Dept. of Biology, Sonoma State Univ., (3)Univ. of California White Mountain Research Station

Elizabeth Dahlhoff (1), Nathan Rank (2), John Smiley (3)

GENETICS, PHYSIOLOGY AND ECOLOGY OF SUBALPINE BEETLE POPULATIONS: RESPONSES TO CLIMATE CHANGE

Beginning in 1981, we have studied changing populations of the leaf beetle Chrysomela aeneicollis, feeding on willow shrubs (Salix spp.) at 2375-3550m above sea level in the Eastern Sierra Nevada mountains, California. During 25 years of observation we have observed range expansion and contraction during at least two wet-dry cycles, along with other changes. In 1988 we began sampling beetles at sites in three drainages (Rock Creek, Bishop Creek and Big Pine Creek) which revealed genetic variation across temperature gradients and elevations. In 1998 we began continuous monitoring of Salix habitat temperatures and snowmelt dates in these same drainages. These long term data sets, along with numerous other studies of the beetles’ predators, ecology, behavior, physiology and genetics, have revealed a complex and unusually complete picture of changing insect populations in high mountain environments.

Findings

•Drainage-dependent air temperature differences, superimposed on a complex altitudinal gradient.

•Summer air temperatures lethal to beetles, with corresponding differences in mortality.

•Expansion and contraction of beetle populations during wet/dry cycles

•Beetle populations shifted upwards in elevation in BPC, the warmest drainage, during recent warm dry years, but that this altitudinal shift did not occur in RC or BC.

•Beetle abundance is lower in RC, the coolest drainage, than BC or BPC.

•Populations of the specialist hunting wasp Symmorphus cristatus, one of the beetles’ principal predators, have shifted upwards in elevation. We have also measured temperature-related foraging success for this wasp.

Day of Year150 160 170 180 190 200 210

Mea

n m

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um T

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Mean Maximum Temperature (°C)

20 22 24 26 28-1.2

-0.8

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0.8(a) Old Adults to Larvae (b) Larvae to New Adults

r = -0.88

P = 0.01r = 0.80

P = 0.03

SiteRV: 2883 m SL: 3005 m PL: 3170 m SC: 3194 m

PGI-1

alle

le fr

eque

ncy

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ance

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Elevation, meters2600 2800 3000 3200 3400

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Elevation Gradient and Climate Change

Air Temperatures and Snow Pack

Genetics, Physiology and Evolution

Big Pine Creek1981-present

Bishop Creek1988-present

Rock Creek1988-present

beetle abundance peaks at 3200m in BP and 3000m in BC and RC.

wet dry wet dry wet?

beetle elevation range expands during wet periods and contracts during dry periods.

has there been an upward expansion since 2000?

Study site drainages (arrow points north)

Air temperature, oC13 14 15 16 17 18 19 20 21

log

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Year1998 1999 2000 2001 2002 2003 2004

log

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Predation

S. cristatus hunting success (reduced hunting time) depends on prey abundance and air temperatures. Since 2000, wasp has colonized sites above 3100m (upper edge of green zone) in BPC.

Plans for 2006-2015

Using the University of California White Mountain Research Station (WMRS) as a base of operations, we plan to continue and expand these studies for at least 10 more years, funding permitting:

•Monitor air temperatures and humidity along four elevation gradients (add North Lake-Piute Pass drainage) and relate them to fluctuations in abundance of C. aeneicollis and two specialist predators S. cristatus and P. melanderi.

•Quantify variation in physiological response to temperature in C. aeneicollis and its predators.

•Survey changes in frequency of phosphoglucose isomerase (PGI) in a drainage where PGI is polymorphic.

•Quantify effects of climate on S. cristatus ecology and behavior.

•Make weather and insect abundance data available on the WMRS web site www.wmrs.edu

This work provides a unique opportunity to integrate studies of the mechanisms underlying population change with comprehensive data on climate, for native insect species in physically challenging environments. These graphs show how PGI frequencies evolve (selection

coefficient) as a function of temperature, and how selection is reversed in the later stages

Elevation color bands:4000-4250m light gray3750-4000m light blue3500-3750m blue3250-3500m blue-green3000-3250m green2750-3000m yellow-green2500-2750m tan2250-2500m light tan2000-2250m yellow

North Palisade Peak

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2000 2001 2002 2003 2004 2005

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ly M

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survival of beetle larvae improves if predators are excluded

wasp: Symmorphus cristatus(Hymenoptera: Vespidae)

Fly: Parasyrphus melanderi(Diptera: Syrphidae)

beetle: Chrysomela aeneicollisColeoptera: Chrysomelidae

Rock Creek was the coolest drainage, and Big Pine Creek the warmest. The coolest drainages often had the longest-lasting snowpack.

Willow foliage air temperature: After factoring out elevational differences using ANCOVA, mean daily minima increased through the summer. In all 3 drainages, June was the most likely month to experience sub-zero temperatures.

Frequency of phosphoglucose isomerase (PGI) allele 1 declines with elevation in Bishop Creek, yet increased at all sites between 1988 and 1996.

PGI-1 allele is associated with increased expression of heat shock proteins (HSP70), which protect against cold temperatures. PGI-4 confers increased tolerance to high temperatures (CTmax critical thermal maximum)

Some examples of our work…Some examples of our work….

yellow dots = Salix foliage air temperature loggersorange dots = loggers planned for 2006