Coevolution of the Checkerspot butterfly - Euphydryas chalcedona

8/18/2019 Coevolution of the Checkerspot butterfly - Euphydryas chalcedona

1/8

Oecologia (Berl) (1982) 52:216-223

ecologia

9 Springer-V erlag 1982

Coev olu t ion of the Ch eckerspo t u t ter f ly E uph ydryas chalcedona

and i t s Larval Food P lant

D ip lacus aur an t iacus

L a r v a l R e s p o n s e to P r o te i n a n d L e a f R e s i n

D. E . L i n c o l n * , T . S . Ne wt o n , P . R . Eh r l i c h a n d K . S . W i l l i a m s

Department of Biological Sciences, Stanford University, Stanford, California, 94305 USA

S u m m a r y . P r e d i a p a u s e l a r v a e o f t h e c h e c k e r s p o t b u t t e r f l y Eu

phydryas chalcedona we r e r a i s e d f r o m h a t c h u n t i l e n t r a n c e i n t o

d i a p a u s e o n a r t i f i c i a l d i e ts . Th e p r o p o r t i o n s o f p r o t e i n a n d h o s t

p l a n t l e a f r e si n d i f f e r e d a m o n g t h e d i e ts . La r v a l s i ze , g r o wt h

r a t e s a n d m o r t a l i t y we r e m o n i t o r e d a n d o v e r a l l r a t e s a n d e f fi c ie n -

c ie s o f f o o d u s e we r e c o m p u t e d .

La r v a l s u r v i v o r s h i p , g r o wt h r a t e s a n d s i z e o f l a r v a e a t i d a -

p a u s e we r e s i g n i f ic a n t l y e n h a n c e d b y i n c r e a s in g d i e t a r y p r o t e i n

c o n t e n t , p a r t i c u l a r l y o v e r t h e r a n g e f o u n d i n l e a v e s o f t h e h o s t

p l a n t . I n c o n t r a s t , a n i n c r e a s i n g d i e t a r y c o n t e n t o f Diplacus au

rantiacus

l ea f r e s in s ign i f i can t ly dep resse d l a rva l su rv iv io r sh ip ,

g r o wt h r a t e s a n d s i z e o f l a r v a e a t d i a p a u s e . A s i m p l e d o s e -

d e p e n d e n t i n t e r a c t i o n wa s o b s e r v e d b e t we e n t h e e f fe c ts o f d i e t a r y

l e a f r e s in a n d p r o t e i n o n l a r v a l s u c c e ss . D i e t a r y c o n t e n t o f l e a f

r e s i n a n d p r o t e i n s i g n i f ic a n t l y i n f l u en c e d s o m e m e a s u r e s o f f o o d

u t i l i z a t i o n e f f ic i e n cy ( ECI a n d E CD ) , b u t n o t o t h e r s ( AD a n d

N U E ) .

Th e n e g a t i v e i n t e r a c t i o n b e t we e n t h e e f f e c t s o f d i e t a r y l e a f

r e s in a n d p r o t e i n c o n t e n t s u g g e s t s th e l e a f r e si n p h e n o l i c c o m -

p o u n d s r e d u c e t h e a v a i l a b i l i t y o f p r o t e i n t o t h e l a r v a e . Th e

resu l t s fo r e f f i c iency ind ices o f l a rva l food use a re po ten t i a l ly

in con f l i c t wi th th i s in t e rp re ta t ion .

Th e i n f lu e n c e o f h o s t p l a n t l e a f r es i n a n d p r o t e i n o n l a r v a l

s u c c e s s , c o u p l e d w i t h t h e r e l a t i o n b e t we e n p h o t o s y n t h e s i s a n d

l e a f n i t r o g e n c o n t e n t , a r e c o n s i s t e n t w i t h t h e h y p o t h e s i s t h a t

p r o d u c t i v i t y c a n b e e n h a n c e d b y h e r b i v o r e d e t e r r e n c e r e s u l ti n g

f r o m l e a f r e s in p r o d u c t i o n .

ntroduction

Co n s u m p t i o n o f l e a v e s b y i n s e c t s is c l o s e ly r e la t e d t o t wo p r i n c i -

p a l l e a f c h a r a c te r i s t i c s : t h e i r n u t r i ti o n a l v a l u e a s f o o d a n d t h e

p r e s e n c e o f s e c o n d a r y c h e m i c a l s (Eh r l i c h a n d Ra v e n 1 96 5 ;

F r a e n k e l 1 9 69 ; W h i t t a k e r a n d F e e n y 1 9 7 1; Be c k a n d Re e s e

1 97 6 ). A f u l l u n d e r s t a n d i n g o f p l a n t h e r b i v o r e i n t e r a c t i o n s c a n

o n l y e m e r g e , h o we v e r , f r o m a q u a n t i t a t i v e c o n s i d e r a t i o n o f t h e

i m p l i c a t i o n s o f t h e s e q u a l i t ie s f o r t h e p l a n t a s we l l a s t h e h e r b i -

vo re .

Th e p h o t o s y n t h e t i c r a t e o f le a v e s h a s b e e n c o r r e l a t e d w i t h

lea f n i t rog en con te n t (M oon ey , e t a l . (1978) . T h i s i s pa r t ly be -

c a u s e c a r b o n f i x a t i o n b y r i b u l o s e - l , 5 - d i p h o s p h a t e c a r b o x y l a s e

i s c o m m o n l y t h e r a t e l i m i t i n g s t e p i n p h o t o s y n t h e s i s a n d t h i s

e n z y m e c o n s t i t u t e s a la r g e p r o p o r t i o n o f t h e l e a f p r o t e i n ( B j o r k -

* Present address : Department of Biology, University of South Caro-

l ina , Columbia, South C arol ina 29208 US A

man 1973) . On the o the r hand , s ince n i t rogen i s an e s sen t i a l

n u t r i e n t f o r a l l o r g a n i s m s , i n s e c t g r o wt h a n d f e e d i n g h a s , n o t

s u r p r i s in g l y , a l s o b e e n r e p e a t e d l y s h o wn t o b e r e l a t e d t o l e a f

n i t r o g e n c o n t e n t ( S o o Ho o a n d F r a e n k e l 1 9 6 6 ; Va n Em d e n

1966; Fox and M cCa u ley 1977 ; Sc r ibe r and Fe eny 1979). Hence ,

a c h a n g e i n g r o w t h o r s u r v i v o r s h i p o f a l e a f h e r b i v o r e i n r e s p o n s e

t o c h a n g e d n u t r i t i o n a l q u a l i t y ( n i t r o g e n c o n t e n t ) w i l l d i r e c t l y

a f f e c t p l a n t p r o d u c t i v i t y . F o r e x a m p l e , lo w l e a f p r o t e i n c o n t e n t

m a y r e s u l t i n r e d u c e d h e r b i v o r e g r o wt h a n d s u r v i v o r s h i p a n d

l e ss h e r b iv o r e d a m a g e t h a n h i g h l e a f p r o t e i n , b u t w i l l a l s o r e s u l t

i n r e d u c e d p l a n t p r o d u c t i v i t y .

Th e p r e s e n c e o f l e a f s e c o n d a r y c h e m i c a l s c a n s i g n i f i c a n t l y

a l t e r t h e p a t t e r n s o f p l a n t - h e r b i v o r e r e l a ti o n s a r i s i n g f r o m n u t r i -

t i o n a l q u a l i ty . Le a f s e c o n d a r y c h e m i c a l s m a y a c t a s f e e d i n g s ti m -

u l a n t s f o r l e p i d o t e r a n l a r v a e ( F r a e n k e l 1 9 5 9 ; Da v i d a n d Ga r -

d i n e r 1 96 6; Be c k a n d S c h o o n h o v e n 1 9 7 9 ), b u t m o r e c o m m o n l y

a p p e a r t o f u n c t i o n a s f e e d i n g d e t e r r e n t s , t o x i n s o r s u b s t a n c e s

wh i c h r e d u c e t h e a v a i l a b i l i t y o f n u t r i e n t s ( F e e n y 1 97 6 ; R h o a d e s

a n d Ca t e s 1 9 7 6 ) . Th e q u a n t i t a t i v e a l l o c a t i o n o f p l a n t r e s o u r c e s

s u c h a s c a r b o n , n i t r o g e n o r e n e r g y , t o c h e m i c a l de f e n se s p r e s u m -

ab ly evo lves in r e sponse to a ba lanc e be tween cos t s and bene f i t s .

Th e b e n e f i ts a r e t h e p r o d u c t i v i t y o f u n e a t e n l e a v e s. Th e c o s t s

a re the va lue o f the r e sou rce i f u sed in o th e r func t ions , such

a s le a f , r o o t o r s t e m g r o wt h o r r e p r o d u c t i o n . Le a f n i t r o g e n

c o n t e n t , b e c a u s e o f i t s i m p o r t a n c e t o b o t h h e r b i v o r e a n d p l a n t ,

m a y p l a y a k e y r o l e i n th e p r o c e s s e s c o n t r o l l in g c a r b o n a l l o c a t i o n

t o s e c o n d a r y c h e m i c a l s .

Th e p l a n t - h e r b i v o r e s y s t e m we h a v e c h o s e n f o r i n t e n si v e

s t u d y i s t h e Ch a l c e d o n c h e c k e r s p o t b u t t e r f l y , Euphydryas chalce

dona

D o u b l e d a y a n d H e w i t s o n ( L e p i d o p t e r a : N y m p h a l i d a e ) ,

a n d o n e o f i ts p r i n c i p a l h o s t p l a n t s , Diplacus aurantiacus (Cur t i s )

Jeps . (Sc rophu la r i aceae ) . In the l a rva l s t ages , E. chalcedona is

a n o l i g o p h a g o u s l e a f f e e d e r a n d a p p e a r s t o b e t h e o n l y s i g n i f i ca n t

l e a f h e r b i v o r e o n

D. aurantiacus. Diplacus aurantiacus

i s a pa r -

t i a l ly d r o u g h t - d e c i d u o u s c h a p a r r a l s u b - s h r u b wh i c h p r o d u c e s

la rge quan t i t i e s o f an ex te rna l phen o l i c l ea f re s in (Linc o ln 1980) ,

g i v i n g r i se t o i t s c o m m o n n a m e , s t i c k y m o n k e y f l o w e r .

Th e l e a f r e s in o f

D. aurantiacus

i s c o m p o s e d o f m o n o m e r s

c o n t a i n i n g a f l a v o n o i d n u c l e u s w i t h s e v e r a l p h e n o l i c g r o u p s ( L i n -

c o l n 1 9 8 0 ) . P h e n o l i c c o m p o u n d s s u c h a s t h e s e b i n d t o p r o t e i n s ,

t h e p r i n c i p a l l e a f n i t r o g e n s o u r c e , a n d m a y r e d u c e t h e a v a i l a b i l i t y

o f t h e n u t r i e n t s t o h e r b i v o r e s ( Go l d s t e i n a n d S wa i n t 9 6 5 ; F e e n y

1969 , 1970 ; Rh oade s 1975 ; Fo x and M cCa u ley 1977); Because

o f t h i s b i n d i n g , t h e g r o wt h a n d f e e d i n g r e s p o n s e s o f t h e h e r b i v o r e

m a y b e r e l a t ed n o t t o o n e o r t h e o t h e r , b u t t o a c o m b i n a t i o n

o f l e a f n i tr o g e n a n d r e s in c o n t e n t s .

Th e i m m e d i a t e o b j e c t i v e s o f t h e p r e s e n t s t u d y we r e t o t e s t

0029-8549/82/0052/0216/$01.60


2/8


3/8

218

remaining water were brought to a boil and added to the blender.

After mixing and cooling to 40 ~ C, the ascorbic acid and tetracyc-

line hydrochloride were mixed in and the still liquid diet was

immediately poured into molds and refrigerated at 6~ C.

Gravid females of E. chalcedona were captured at Jasper

Ridge Biological Preserve, Stanford University, in a population

where D. aurantiacus is the principal larval host plant (Brown

and Ehrlich 1981). Twelve females oviposited on Serophularia

californica, an alternate host plant, in a greenhouse and the

egg masses were collected. Larval hatch was synchronized among

masses by controlli ng incubati on temperature. Freshly hatched

larvae from each egg mass were distributed equally among all

treatments to control for genetic variance. One hundred larvae

were used for each treatment. They were divided into five repli-

cates o f twenty larvae each. The larvae were reared in an incuba-

tor on a 16 h, 25~ day and 8 h, 1 5~ night cycle. Relative

humidity was not controlled. Light was provided by Grolux

fluorescent lamps. The total weight of larvae and the number

surviving were determined for each replicate at approximately

weekly intervals. At the same time, frass for each treatment

was collected, dried and weighed. Fresh diet, about 1 cm 3, was

added if the food had dried or at least every other day. Uneaten

diet was also collected, dried and weighed. Feeding was ad lib

turn, and the larvae allowed to develop until they entered dia-

pause during the fourth instar. The length of time to enter dia-

pause in each replicate was determined by monitoring the

number of larvae in each instar at two-day intervals and noting

the time (Dso) when 50 of the larvae were in diapause. Under

the treatment conditions, larvae entering diapause crawled to

the upper parts of the feeding chamber (a 9 cm petri dish),

spun a small attachment web and remained motionless. Reduced

frass production was also observed at this time. No cannibalism

was observed on living larvae, al though freshly dead larvae were

occasionally eaten in treatments with high resin or low nitrogen

contents.

Mean larvae weight for each replicate was calculated by divid-

ing the total larval weight for the replicate by the number of

surviving larvae. The tr eatment values for larval weight and

mortality are based on the mean and variance among replicates.

Larval weight at diapause was, however, measured on all individ-

uals for the treatment. The dry weight/fresh weight proportion

(0.234) for larvae was determined on diapausing larvae and did

not differ significantly among treatments.

All statistics were computed using release 79.4B of Statistical

Analysis System Institute, Inc. at the University of South Caro-

lina Computer Services. The statistics for percent mortality in

Fig. 2 were calculated using an arcsin square root transforma-

tion.

The overall relative growth rate (RGR) for each treatment

was calculated as a time-weighted average of each s ampling peri-

od relative growth rates, te rmina ting when 50 of the larvae

had entered diapause (Ds0). The relative growth rate for each

sampling period was calculated by the following formula using

the treatment meal larval fresh weight values at the beginning

and end of the period.

Relative growth rate (RGR)

fresh weight growth per larva for period (mg)

m e a n larval fresh weight throughout period (mg)

x days in period (d)

The total dry weight of diet eaten for each treatment was

calculated from a nitrogen budget equation:

E

(G x nitrogen conc entra tion in larvae)

+ (F • nitrogen concentr ation in frass)

nitrogen concentration in diet

E = dry weight of diet eaten (rag)

G = dry weight of larval growth (mg)

F = dry weight of frass produced (mg).

This method of calculation will underestimate the amount

eaten by the proportion of nitrogen lost from the system, for

example as volatile nitrogen compounds. Losses should be

small in comparison to the amount retained in growth or

produced in frass (Morrow and Fox 1980).

All dry weights of frass and larvae were made on material

dried at 70-80~ for at least 24h. Nitrogen conten t was

determined with a Technicon Auto Analyzer II System using

Technicon Industrial Method No. t46171A for total Kjeldahl

nitrogen and a block digestor. The digestion procedure of

Isaac and Johnson (1976) was modified by no t gri nding the

samples and increasing the digestion t ime to 1 h at 200 ~ C, 1 h

increasing from 200~ to 400 ~ C, and 1 h at 400 ~ C.

Efficiencies of food util izat ion were ca lculated by the fol-

lowing equations (Waldbauer 1968):

E - F

Approximate Digestibility (AD) = x 100 .

E

Efficiency of Conversion of Ingested food (ECI)

G

=- -x 100 .

E

Efficiency of Convers ion of Digested food (ECD)

G

=- -x 100 .

E - F

The nitrogen utilization efficiency (NUE) was calculated

a s

NUE

G x nitrogen concentra tion in larvae at diapause x 100

E x nitrogen concentration in diet

The overall relative consumption rate (RCR) was calculat-

ed fi-om the following formula:

RCR

E

so

0 . 2 34 x m e a n l a r v a l f r e sh w e i g h t d u r i n g p e r i o d m g )

Period= 1 X number of larvae at end of period

x days in period (d)

where E is the amount eaten for the treatment from the nitrogen

balance equation above, the divisor is a summation among all

periods terminating when 50 of the larvae have entered dia-

pause and 0.234 is the dry weight/fresh weight proportion for

the larvae.

The overall relative elimination rate (RER) was calculated

in a manner analogous to the RCR, but with F (the total amoimt

of frass produced for the treatment) substituted for E.

Results

Dietary Ef fects on Larval Growth and Development Time

The effects of dietary nit rogen and leaf resin levels on the relative

growth rate (RGR) of the larvae is shown in Fig. 1. Higher


4/8

219

1 2 0 -

' ' ~ I O 0 -

I f : r , .

o ' , 8 0 _

E

r ' r 6 0 -

( . 9

or

4 0 -

/

~ 5 0 /

/ /,~---4 150

,~ , / a ~

/ e . . .

......... .

g

1 1 I

I 0 2 0 3 ~ 3 4 0

N con ten~ (rag g-I)

Fig

1. Effect of dietary nitrogen and resin content on the relative

growth rate (RGR) of prediapause

Euphydryas chalcedona

larvae9

Values for dietary resin content (mg g- 1 dry weight of diet) are given

on the f igure. Value on control diet is circled. Multiple regression

analysis showed significant effects for resin content (F=60.43, P<

0.001) and for nitrogen content (F=40.43, P< 0.001)

%

E

v

~ 1 0

(o

4

~ 5

o

C 21

"B

6 o - I

20-t

4

I

e . . . . . . . . . . .

, .............. 3 0 0

~ o 2 0 0

. . . . . . -, , 15 0

N content (rag g-t) N conten t (rag g-I)

Fig. 2. A Effect of dietary nitrogen and resin content on fresh weight

of Euphydryas chalcedona larvae at diapause. Values for resin content

(nag g- 1 dry weight of diet) are given on the figure. Value on control

diet is circled. Vertical bars indicate 95% confidence intervals. Multiple

regression analysis showed significant effects for resin content (F=

202.11, P


5/8


6/8

221

or resin content was observed for the AD or NUE indices (mea-

sures of the gross digestib ility of the diets).

i scuss ion

The effects of varying protein and

D . a u r a n t i a c u s

leaf resin con-

tent in the food of E . cha leedona larvae are clear: increased

protein stimulates and increased resin inhibits all measured

growth, development and survival characteristics of

E . cha lce -

d o n a larvae. Numerous studies have shown that an increased

protein content in the food of lepidopteran latwae allows more

rapid growth (see for example, Soo Hoo and Fraenkel 1966;

Fox and McCauley 1977; Scriber and Feeny 1979; Scriber and

Slansky 1981). Consideration of the nutritional value of dietary

proteins, or their constituent amino acids, coupled with mortality

and fecundity responses of insects to these has led to the sugges-

tion that the growth of individuals, and perhaps the populati on

size, of many insects is limited by the available nitrogen content

of their food (Mattson 1980). Thus, if only herbivore responses

to nitrogen content are considered, it could be hypothesized

that selective pressures would favor plants with low leaf nitrogen

content over plants with high leaf nitrogen content.

The results of this study provide evidence that the growth

of individuals, their fitness, and the population size of E . cha lce -

d o n a when feeding on D. auran t iacus may be limited by the

protein content of its food, particularly in the presence of the

phenolic leaf resin. In addition to survivorship, the growth of

the larvae was stimulated over the range of nitrogen contents

which commonly occur in D. auran t iacus (10-25 mg g-1 leaf

dry weight). Because larval size may inf luence survivorship dur-

ing diapause and eventual reproduction by adults; the dietary

nitrogen content could also influence fitness and population size

in E . c h a l c e d o n a beyond prediapause larval mortality. Also, di-

etary protein concentration can offset the deleterious effects of

D i p l a c u s

leaf resin and thus increase both survivorship and

growth. Several other lines of evidence also suggest that the

population size of

E . cha lcedona

at Jasper Ridge is determined

by the quality ofD. auran t iacus as food for the larvae, particular-

ly the prediapause larvae. There is a ten-fold decrease in the

peak larval population size between prediapause and postdia-

pause populations (Mooney, et al. 1980), suggesting that cont rol

of the population size occurs early in the life cycle as it does

in the closely related E u p h y d r y a s e d i t h a at the same site (Ehrlich

et al. 1975; Singer and Ehrlich 1980). The mortality of predia-

pause larvae observed in the present study (Fig. 3) is consistent

with these field obseawations. The rates of larval parasitism are

low (< 5 ), as they are in E . ed i tha and the imago of E . cha lee -

d o n a has been found to be unpalat able to bird predators (Bowers,

1981). These suggest that the population size of E cha lcedona

is not primarily controlled by predation or parasitism. Lastly,

the increase in development time to reach diapause induced by

the leaf resin could cause high mortality because the prediapause

larvae are tightly constrained at the end of the plant growth

season by a rapidly deteriorating food supply due to leaf senes-

cence of D. auran t iacus (Mooney et al. 1980, 1981).

While D i p l a c u s leaf resin is detrimental to the herbivorous

larve, production of the resin benefits the shrub. Indeed, its

value to the plant is a direct function of its effect on food

consumption by E . eha lcedona . The relative values of particular

leaf resin contents can only be determined, however, by also

considering the nitrogen cont ent of the leaf, because of the inter-

action of resin and protein on larval growth a nd mortality, and

because of the relation between leaf protein content and photo-

synthesis. Gul mon and Chu (1981) have shown that the maxi-

Table 5. Predicted percent benefit accruing to plants with different

leaf nitrogen and resin contents. Values are calculated from the multi-

ple regression of prediapause larval survivorship on dietary content

of nitrogen and leaf resin. See text for explanation

Dietary nitrogen

content (mg g-1)

Dietary Resin Content (mg g-l )

0 50 100 i50 200 250 300

10 46 58 70 83 95 107 119

20 31 43 55 67 79 91 103

30 15 28 40 52 64 76 88

40 0 i2 24 36 48 60 72

mum photosynthetic rate, i.e. light-saturated rate, of D. auran t ia -

cus

is directly proportional to the leaf nitrogen content. Thus,

the cost of reduced photosynthesis from a low nitrogen content

may counterbalance the benefits of reduced herbivory from the

low nitrogen content.

One method for assessing the relative herbivore-deterring

benefits which would accrue to plants or leaves with different

combinations of leaf nitrogen and resin contents is to use the

present result as a scaling factor. The decrease in larval survivor-

ship (benefit to the plant) can be calculated from a multiple

regression of survivorship on dietary nitrogen and resin content,

using the maximal survivorship on the diet with no host plant

resin and highest nitrogen content (40 mg g-l) as equivalent

to zero benefit. These relative benefits, using a regression equa-

tion calculated from the data presented in Fig. 3 [ survivor-

ship=38.8-0.245 (resin content)+l.57 (nitrogen content)], are

presented in Table 5.

These data show, for the range of nitrogen and resin concen-

trations considered, resin production can produce greater herbi-

vore-deterring benefits than can low nitrogen content (Table 5).

A comparison of the benefit data for differing nitrogen contents

with a similar analysis of Gulmon and Chu's data for photosyn-

thetic cost of low nitrogen content, shows that the slope of

the cost function for photosyntheiss is approximately twice as

great as the benefit function for herbivore deterrence. The reduc-

tion in photosynthesis between 40 mg N g-1 and 10 mg N g-1

would be 91 compared to a benefit of 46 (Table 5) over

the same range of nitrogen contents. Thus, although considera-

tion of the effects of nitrogen content on the herbivore would

appear to suggest that selective pressures may favor plants with

low leaf nitrogen content, consideration of plant photosynthesis

as welI as herbivore mortaility indicates that plants with high

leaf nitrogen content would be favored over plants with low

leaf nitrogen content . These results do indicate~ however, that

if high leaf nitrogen content does not contribute substantial bene-

fit to the pl ant then costs from increased herbivory would prevail.

Production of the leaf resin by D. auran t iacus can have greater

herbivore-deterring benefits than reduced nitrogen cont ent

(Table 5). For equivalen t effect on the herbivore, p roduc tion

of even 300 mg resin g-1 leaf appears less costly to the p lant

than the reduced photosynthetic rate resulting from low nitrogen

content. Under certain conditions, however, the costs of produc-

tion of the resin could outweigh benefits. In Table 5 the survivor-

ship is reduced over 100 at the lowest nitrogen and highest

resin concentr ations. The mortal ity beyond 100 to which this

corresponds is obviously not possible and the effect of resin

production beyond this level would only impose a cost on the

plant without commensurate benefit. To more fulty assess the

costs and benefits of carbon allocation to leaf resin production,

it would be necessary to include the biosynthetic cost of the


7/8

222

r e s in , a c t u a l h e r b i v o r y l e v e l i n t h e f i e l d a n d t o t a l l e a f p r o d u c t i v i t y

i n t h e a n a l y s i s .

T h e a m o u n t o f f o o d c o n s u m e d b y a c o h o r t o f la r v a e w o u l d

r e f le c t n o t o n l y t h e n u m b e r s o f I a r v a e , b u t a l s o t h e i r s iz e a n d

r e l a ti v e c o n s u m p t i o n r a te s . I n g e n e r a l , h i g h d i e t a r y n i t r o g e n l e v -

e l s l e a d s t o h i g h g r o w t h r a t e s ( F i g . 1 ) a n d s u r v i v o r s h i p ( F i g . 3 )

a n d , p r e s u m a b l y , g r e a t e r h e r b i v o r y a s d i s c u s s e d a b o v e . W i t h

r e g a r d t o c o n s u m p t i o n r a t e s , h o w e v e r , t h e o p p o s i t e r e s u l t w a s

o b s e r v e d ( T a b l e s 3 , 4 ). L o w n i t r o g e n c o n t e n t l e a d s to s i g n i f i c a n t l y

i n c r e a s e d la r v a l c o n s u m p t i o n r a t e s c o m p a r e d t o h i g h n i t r o g e n

d i e ts . I t h a s b e e n h y p o t h e s i z e d t h a t s o m e l e p i d o p t e r a n l a r v a e

a d j u s t t h e i r fe e d i n g r a t e t o c o m p e n s a t e f o r v a r i a t i o n s i n d i e t a r y

n i t r o g e n c o n t e n t ( S l a n k s y a n d F e e n y 1 97 7) . F o r E. chalcedona,

t h e r e s u lt s s h o w t h a t c o m p e n s a t o r y f e e d i n g d o e s o c c u r b u t d o e s

n o t a l l e v i a t e t h e s t re s s o f l o w d i e t a r y n i t r o g e n c o n c e n t r a t i o n s

w h i c h o c c u r i n t h e f o o d p l a n t

D. aurantiacus.

A t a h i g h e r r a n g e

o f p r o t e i n c o n c e n t r a t i o n s ( > 25 m g g 1 ) a d a p t i v e c o m p e n s a t i o n

i n f e e d i n g ra t e m a y b e m o r e e f fe c t iv e . T h e l e a f r e si n h a d n o

d i r e c t e f f e c t o n c o n s u m p t i o n r a t e b u t h a s a v e r y l a r g e i n h i b i t o r y

e f f e c t o n t o t a l c o n s u m p t i o n t h r o u g h i t s e f f e ct s o n t h e o t h e r

f a c t o r s, l a r v a l s iz e , g r o w t h r a t e a n d s u r v i v o r s h i p . T h u s , n o t o n l y

d o e s l o w l e a f n i t r o g e n c o n t e n t l e a d t o g r e a t e r c o s t s i n p h o t o s y n -

t h e s i s t h a n b e n e f i t s f r o m h e r b i v o r e m o r t a l i t y , b u t i t a l s o l e a d s

t o h i g h c o n s u m p t i o n r a t es b y t h o s e l a r v a e w h i c h s u r v iv e . T h e

h a l v i n g o f l a rv a l s u r v i v o r s h i p ( T a b l e 5 , c o l u m n 2 ) w o u l d b e o f f s et

b y a n a p p r o x i m a t e d o u b l i n g o f c o n s u m p t i o n r a t e s ( T a b l e 3 , c o l -

u m n 4 ) .

T h e o f f s e t ti n g e f fe c t s o f d ie t a r y c o n t e n t s o f h o s t p l a n t r e s in

a n d p r o t e i n o n l a r v a l s u c c e ss s u g g e s t s o m e f o r m o f i n t e ra c t i o n

b e t w e e n t h e t w o c o n s t i t u e n t s . S t a t is t i c ia l a n a l y si s i n d i c a t e n o

s i g n i f i c a n t m u l t i p l i c a t i v e i n t e r a c t i o n ( s e e l e g e n d s f o r F i g s . 2 a n d

3 ), b u t d o i n d i c a t e a s i g n i f i c a n t a d d i t i v e i n t e r a c t i o n . B e c a u s e

t h e g e n e r a l l in e a r m o d e l u s e d f o r t h e a n a l y s i s i s a n a d d i t i v e

m o d e l , t h e s i g n i f i c a n t e f fe c t s o f d i e t a r y r e s i n a n d n i t r o g e n a r e ,

b y d e f i n i t i o n , i n d i c a t i v e o f a s i g n i f ic a n t a d d i t i v e i n t e r a c t i o n . I n -

s p e c t i o n o f th e d a t a s h o w s t h a t t h e i n t e r a c t i o n i s n e g a t i v e ; t h a t

i s, th e e f f ec t s d u e t o o n e d i e t a r y f a c t o r a r e c o u n t e r b a l a n c e d

b y e f f e c t s f r o m t h e o t h e r .

T h i s i n t e r a c t i o n b e t w e e n n i t r o g e n a n d l e a f r e s in l e v e ls o n

l a r v a l s u c c e s s s u g g e s t s t h a t t h e l e a f r e s i n m a y e x e r t i t s e f fe c t s ,

a t l e a s t to s o m e e x t e n t , b y l o w e r i n g t h e a v a i l a b i li t y o f p r o t e i n

t o t h e l a r v ae . T h e p h e n o l i c l e a f r e si n o f D. aurantiacus i s c o m -

p o s e d o f m o n o m e r i c f l a v o n o i d s ( L i n c o l n 1 9 80 ). R h o a d e s ( 19 7 7)

h a s s h o w n f o r m o n o m e r i c p h e n o l s i n Larrea, w h i c h a r e s i m i l a r

t o t h o s e i n Diplacus, a n d F e e n y ( 1 9 6 9 , 1 97 0 ) h a s s h o w n f o r

p o l y p h e n o l s , t h a t t h e s e a l l e lo c h e m i c s c a n b i n d w i t h d i e t a r y p r o -

t e in s a n d c a r b o h y d r a t e s a n d l o w e r t h e a v a i l a b il i t y o f t h e n u -

t r ie n t s t o i n s e c t h e rb i v o r e s . A s i m i l a r m o d e o f a c t i o n f o r D .

aurantiacus l e a f re s i n i s s u g g e s t e d b y t h e o f f s e t t i n g e f f e c t s o f

r e s in a n d p r o t e i n o n t h e g r o w t h e f f ic i e n c y o f f o o d u t i l iz a t i o n

( E C I ) , a s w e l l a s o n s u r v i v o r s h i p a n d l a r v a l g r o w t h .

T h e d i re c t m e a s u re s o f f o o d d i g es t ib i li ty ( A D a n d N U E )

w e r e n o t a f f e c t e d b y d i e t a r y r e s i n c o n t e n t ( T a b l e s 3 , 4) . A l t h o u g h

t h e s e m e a s u r e s w o u l d a p p e a r t o d i s c o u n t d i g e s t i b i l i t y r e d u c t i o n

o f p r o te i n a v a i l a b i l i t y a s a m o d e o f a c t i o n f o r t h e l e a f r e s in ,

o t h e r i n t e r p r e t a t i o n s a r e p o s s i b l e i f r e s p o n s e s b y t h e i n s e c t t o

d e t o x i f y t h e a ll e l o c h e m i c a l s a r e c o n s i d e r e d . O n e w a y t o c o n -

s i d e r s u c h e f fe c t s i s b y t h e e x a m i n a t i o n o f t h e E C D . T h e E C D ,

w h i c h i s n o t s u p p o s e d t o b e i n f l u e n c e d b y d i g e s t i b il i ty ( W a l d -

b a u e r 1 9 6 8 ) , w a s i n f l u e n c e d b y d i e t a r y r e s i n c o n c e n t r a t i o n a s

w e l l a s b y n i t r o g e n c o n t e n t . T h e E C D i s a m e a s u r e o f l a rv a l

g r o w t h p e r a m o u n t o f f o o d d i g e s t e d , b u t is al s o a m e a s u r e

o f t h e p a r t i ti o n i n g o f d i g e s t e d fo o d b e t w e e n g r o w t h a n d m e t a b o -

l i s m . I f e n e r g y is e x p e n d e d d u r i n g d i g e s t i o n , t h i s p a r t i t i o n i n g

c o u l d b e a l te r e d a n d r e s u l t i n t h e l o w e r E C D s o b s e r v e d f o r

i n c r e a s i n g r e s in c o n c e n t r a t i o n s . O n e w a y i n w h i c h l e p i d o p t e r a n

l a r v a e m a y a v o i d t h e e ff e c ts o f p h e n o l i c c o m p o u n d s c o m p l e x i n g

w i t h p r o t e in s i s b y m a i n t e n a n c e o f a h i g h m i d g u t p H ( B e r e n b a u m

1 9 8 0 ) I n d u c t i o n o f a h ig h l a r v a l g u t p H f r o m f e e d i n g o n D .

aurantiacus

h a s b e e n o b s e r v e d i n

E. chalcedona

( K . W i l l i a m s ,

u n p u b l i s h e d d a t a ) . I f t h is p r o c e s s c a u s e s i n c r e a s e d m e t a b o l i c

a c t iv i t y , i t c o u l d a c c o u n t f o r t h e l a c k o f a n e f f e c t o f th e l e a f

r e s in o n t h e d i g e s ti b i li t y i n d i ce s ( A D a n d N U E ) .

Acknowledgements. We thank M .D. Bowers , S . Gu lm on , H . M ooney ,

P . L inco ln and S . Wo od in f o r u se fu l d iscuss ions and comm ent s . T ech-

nical assistance was provided by C. Chu and B. Li l ley. This research

was suppor t ed by NSF Gr an t DE B78 02067 .

e f e r en c e s

Beck SD, R eese JC ( 1976 ) I nsec t - p l an t i n t e r ac t i ons : nu t r i t i on and

metabo l i sm. Rec A dv Ph y tochem 10 : 41 - 92

Ber enbaum M ( 1980) Adap t ive s ign if icance o f midgu t pH in l a rva l

L ep idop te r a . Am er N a tu r a l i s t 115 : 138-146

Bjo r kman O ( 1973) Compar a t ive s tud i es on pho tosyn thes i s i n h igher

p l an t s . I n : AC Giese ( ed ) Pho tophys io logy Vo l I I I . Aca demic P r ess

N e w Y o r k p p 1 -6 3

Bower s M D ( 1981) Unpa la t ab i l i t y a s a de f ense s t r a tegy o f wes t e rn

checker spo t bu t t e rf l i e s (EuphydryasScudder , Nympha l idae ) . E vo lu -

tion 35 : 367-375

Br own I L , E hr l i ch PR ( 1980) Popu la t i on b io logy o f t he checker spo t

but ter f ly , Euphydryas chaleedona I . s t r uc tu r e o f t he Jasper Ridge

Colo ny. Oec ologia (Ber l) 47 : 239-251

Dav id W AL , Gar d ine r B OC ( 1966) Mu sta r d o i l g lucos ides as f eed ing

s t imu lan t s f o r Pier brassicae larvae in a semi-synthet ic diet . Ent

E xp & App l 9 :247- 255

E hr l i ch PR, Ra ven PH ( 1965) Bu t t e r f li e s and p l an t s : a s t udy in co -

evolut ion . Evo lut ion 18 : 586-608

E hr l i ch PR, Whi t e RR, S inger MC, McKechn ie SW, Gi lbe r t L E ( 1975)

Che ckersp ot but ter f l ies: a histor ical perspective. Science 188:

221-228

Feeny PP ( 1969) I nh ib i to r y e f fec t o f oak l ea f t ann ins on the hydr o lys i s

of proteins by trypsin. Phyto chem ist ry 8:2119-2126

Feeny PP ( 1970) Seasona l changes i n oak l ea f t ann ins and nu t r i en t s

as a cause o f sp r ing f eed ing by win t e r mo th ca t e r p il l a rs . E co logy

51:565-581

Feeny PP ( 1976) P l an t appar ency and chem ica l de fense. Rec Ad v

Phyf ichem 10 : l 40

Fox L R, M acau ley BJ ( 1977) Insec t g r az ing on Eucalyptus in response

to va r i a t i on i n l ea f t ann ins and n i t r ogen . Oec o log ia ( Berl )

29 : 145-162

E r aenke l G ( 1959) T he r a i son d ' e t r e o f secondar y p l an t subst ances.

Science 129:146 170

Fr aenke l G ( 1969) E va lua t ion o f ou r t hough t s on secondar y p l an t

substances. Science 129:146-170

Golds t e in JL , Swain T ( 1965) T he inh ib i t ion o f enzymes by t ann ins .

Phytochemist ry 4: 185-192

Gulm on SL , Chu CC ( 1981) T he e f f ec ts o f l i gh t and n i t r ogen on

pho tosyn thes i s , l ea f char ac t e ri s t ic s , and d r y m at t e r a l l oca t ion in

the chapar r a l sh r ub ,

Diplacus aurantiaeus.

Oecologia (BerI )

49 : 207-212

I saac RA, Johnso n W C ( 1976) De te r m ina t ion o f t o t a l n i t rogen in

p l an t t is sue, u s ing a b lock d iges to r . J Assoc i a t i on o f O f f i c ia l Ana ly t -

i ca l Chemis t s 59 :98 - 100

L inco ln DE ( 1980) L eaf res in f l avono ids o f Diplacus aurantiacus. Bio-

chem ical Systematics and Eco logy 8:397 -400

Ma t t son W J ( 1980) Her b ivo r y i n r e l a t i on t o p l an t n i t r ogen con ten t .

Ann Rev Ecol Syst 11:119-161

Mo oney HA , Fer r a r P J , S l ay t e r RO ( 1978) Pho tosyn the t i c capac i ty

and ca r bon a l l oca t ion pa t t e r ns i n d ive rse g r owth f o r ms o f

Eucalyp-

tus. Oec ologia (Ber l ) 36:103-111

Mo oney HA , E hr l i ch PR, L inco ln DE , W i l li ams KS ( 1980) E nv i r on -

men ta l con t r o l s on t he seasona l i t y o f a d r ough t - dec iduous sh rub ,


8/8

223

Diplacus aurantiacus a n d i t s p re d a t o r , t h e c h e c k e rsp o t b u t t e r f l y ,

Euphydryas chalcedona.

O e c o l o g i a (B e r l ) 4 5 : 1 4 3 -1 4 6

M o o n e y H A , W i l l i a m s K S , L i n c o l n D E , E h r l i c h P R ( 1 9 8 1 ) T e m p o r a l

a n d sp a t i a l v a r i a b i l i t y i n t h e i n t e ra c t i o n b e t w e e n t h e c h e c k e rsp o t

b u t t e r f l y ,

Euphydryas chatcedona

a n d i t s p r i a c i p a t fo o d so u rc e , t h e

c a l i fo rn i a n sh ru b ,

Diplacus aurantiacus.

O e c o l o g i a (B e r l ) 5 0 :

195-198

R h o a d e s D F (19 7 7) In t e g ra t e d a n t i h e rb i v o re , a n t i d e s i c c a n t a n d u l t r a -

v i o l e t s c re e n in g p ro p e r t i e s o f c re o so t e b u sh re s in . B i o c h e m i c a l Sy s te -

ma t i c s a n d Ec o l o g y 5 : 2 8 1 -2 9 0

R h o a d e s D F, C o t e s R G (1 9 7 6 ) To w a rd a g e n e ra l t h e o ry o f p l a n t

a n t i h e rb i v o re c h e mi s t ry . R e c A d v Ph y t o c h e m I0 : 1 6 8 2 1 3

Sc h o o n h o v e n LM (1 9 7 3) P l a n t r e c o g n i t i o n b y l e p i d o p t e ro u s l a rv a e .

S y r u p R E n t o m o l S o c L o n d o n 6 : 8 7 - 9 9

Sc r i b e r JM , Fe e n y P (1 97 9 ) G ro w t h o f h e rb i v o ro u s c a t e rp i l l a r s in

re l a t i o n t o fe e d i n g sp e c i a l i z a t i o n a n d t o g ro w t h fo rm o f t h e i r fo o d

p l a n t s . Ec o l o g y 6 0 : 8 2 8 5 0

Sc r i b e r JM , S l a n sk y F (1 9 81 ) Th e n u t r i t i o n a l e c o lo g y o f i mma t u re

i n se c t s . A n n R e v En t o mo l 2 6 : 1 8 3 -2 1 1

Si n g e r M C , Eh r l i c h PR ( i 9 7 9) Po p u l a t i o n d y n a m i c s o f t h e c h e c k e rsp o t

b u t t e r f l y Euphydryas editha. F o r t s c h r Z o o l 2 5 : 5 3 - 6 0

Sl a n sk y F (1 9 7 7 ) S t a b i l i z a t i o n o f t h e ra t e o f n i t ro g e n a c c u mu l a t i o n

b y l a rv a e o f t h e c a b b a g e b u t t e r f l y o n w i l d a n d c u l t i v a t e d fo o d

p l a n t s , E c o l M o n o g r 4 7 : 2 0 9 -2 2 8

So o H o o D F, Fra e n k e l G (1 9 6 6 ) Th e c o n su mp t i o n , d i g e s t i o n , a n d

u t i l i z a ti o n o f fo o d p l a n t s b y a p o t y p h a g o u s i n se c t ,

Prodenia eridania

(C ra me r ) . J In se c t Ph y s i o l 1 2 : 7 1 1 -7 3 0

V a n Em d e n H F (1 96 6 ) S t u d i es o n t h e re l a t i o n s o f i n se c t a n d h o s t

p l a n t I I I . a c o mp a r i so n o f t h e re p ro d u c t i o n o f

Breviocoryne brassi

cae

a n d

Myzus persicae

( H e m i p t e r a : A p h i d a e ) o n b r u s s e l s p r o u t

p l a n t s su p p l i e d w i t h d i f fe re n t r a t e s o f n i t ro g e n a n d p o t a s s i u m.

E n t E x p & A p p l 9 : 4 4 4 - 4 6 0

W a l d b a u e r G P ( 19 68 ) T h e c o n s u m p t i o n a n d u t i li z a ti o n o f f o o d b y

i n se ct s . A d v In se c t Ph y s i o l 5 : 2 2 9 -2 8 8

Wh i t t a k e r R H , Fe e n y PP (1 9 7 1 ) A l l e l o c h e mi c s : c h e mi c a l i n t e ra c t i o n s

between species . Science 171:757-770

Received Apri l 9 , 1981

Documents

Coevolution of the Checkerspot butterfly - Euphydryas chalcedona