Biological Journal of the I.mnean Society (1985), 24: 329-335. With 2 figures
Comparison of two independent scoring
techniques for spot variation in Maniola jur Una
(L.) and the consequences of some differences
PAUL M. BRAKEFIELD
of Biological Sciences, (W.S.L.), Perry Road, University of Exeter, Exeter
KX4 40J'
AND
W. H. DOWDESWELL
Mwnl of Education, University of Bath, Bath BA2 7 AY
•\«rplc<i /„> /luli/nalH'ti Di.imhn I'M!
w
mdcpcndcntly by P. M. Br.,k«-l.,-M and W . H " " " C „„ , spots overall than
m m b i n a l i o n S p u r s , / , - was RWMUred by f '•".•;_ sp..l-IV(-(|i'i<-nc-\ distributions. There l' M B. ( J V = 554). This rooked in some marked d, 1, m . - ™J^ sn,,,,d h, both Of us
I nth« MHW» threshold oflf>O«-i*< a >(.>V''.r! ,' \VI,,'n thed«U of P.M. B. arc transformed
below wlm h mcisi siiois were only scored by 1 snot-freauencies is found.
'
and below wlm h mcisi siiois were only
b| «ChKfim all spots 'bclow ... csh,,,d a close
R e l a t i v e d,l!c,en,es between samples lend I» 1»' conse(|nemes of the d , l l e , c , , , c s ,„ sconng teclnn<|..o a.r
K E Y W O R D S ,\ 1ORDS ,\ 1aa»,,,l« ,«,!,««»,,,« ,«,!,«« -"""K
ns,,,cn,v .pot-«« llncshold „ansfonncd q n a n U i a m , , h a , a
oinson spotfrequency distribution
-introduction
Material and mclhods
Results . . . . Hiscnssion . . . . Ai knowledgemenH R e l c i e i K es CONTENTS 329 330 330 334 334 334 INTRODUCTION
•>•> ... • ... s ... "..
J«rtwo. cxliil.h v.iri.ili,m in ill«'• - '952). TÛ variadon h», by Ford, 1975; Dowdcswell, 329 "024 4066/85/040329 + 07 $03.00/0 30 years (see
-
330 P. M. BRAKEFIELD AND W. H. DOWDESWELL
between populations throughout the species's range have been identified with reference to the spot-frequency distribution within them and to the mean number of spots or spot-average. The spots are found at each of five (rarely six) defined positions on the hindwing at which they may be present or absent. Only a limited number of the possible spot-combinations occur. McWhirter & Creed (1971) devised a costality index describing the proportion of spots which are positioned costally as a measure of the spot-placing variation within populations. At each position on the hindwing the spots vary in size in a quantitative manner (Brakefield, 1984). The work on M.jurtina has been concerned with a number of problems in ecological genciics, including the evolution of adaptations to differing environments (e.g. Ford, 1975).
Until the early 1970s, the investigation was carried out almost exclusively by a group of workers based at the University of Oxford and led by E. B. Ford and W. H. Dowdeswell. Other workers have become actively, but largely independently, involved during the lasl decade (see e.g. Brockie, 1972; Fra/cr & Willcox, 1975; Tudor & Parkin, 1979; Brakefield, 1984). Comparisons of some of the samples obtained by these workers with those described earlier by the group based at Oxford (e.g. Dowdeswell & McWhirter, 1967) suggest that changes in spot variation have occurred within some geographical /.ones or populations (see Brakefield, 1984). Observations of this kind underline the importance of ensuring the consistency of the scoring techniques employed. We therefore report here the results of a test which show that whilst there can be a (lose correspondence between different scorers there may also be i m p o r t a n t differences which must be taken into account when comparisons are made. Failure to do this could lead to misleading conclusions.
MATERIALS AND METHODS
Samples of female M.jurtina from eight populations in England were scored for spot-variation on the left hindwings by P. M. Brakefield (P.M.B.). The sample si/.e ranged from 29 to 51 with a mean of 37.25 and a total of 298. The w i d t h of each spot along the wing internervules was measured using a binocular microscope fitted with a micrometer (1 unit «0.054 m m ) . Each b u t t e r f l y was stored in a numbered envelope. They were subsequently scored independent!) by W. H. Dowdeswell (W.H.D.). He recorded the n u m b e r and position of the spots according to the t e c h n i q u e used by each member of E. B. Ford's group.
RESULTS
SPOT VARIATION IN MAXIOLA No of spots ( P M B ) 10 15 45 50 61 70 47 46 41 38 39 17 22 15 10 28 331 i i i e K 100 80 60 40 20 ' ' 3 4 _i 1 i i 5 6 7 8 9 10 II 12 13 14 15 16
Spot-size (PM B ) (micrometer units)
Fim.ro ,. The „l.u,„„s,„p between the si«- of spois ,n d* „ M - a x u r e d hv P. M. H,,,krii,-l,l »d .!„• pro,«,,,,,,, of the qxtt ico
w,,e scored as t h e same s p o t - n u m b e r (and spo.-placing
•pol was scored In P.M.B in 105 (35.2%) specimen, and an
spots in (lic o t h e r 19.
Tl,, nature of the difference u. scoring technique can
""»'^ °f ""' '—»" -"''• IV'-MA «;! jj7;
r e l a t i o n s h i p hctvvccn these d a t a and those ol W.H H' w H D
smallest spots of * to i or 5 micrometer u n i t s are . -om > o • ^ Qf
represenl only a small number (in the ease „I ! s » V h v i n,r s/T l u- faci
black vvinir seal« a t t h e del.ned positions lor spots on \ ^ \
thai such spots are no, recorded by W.H.D. corresponds v h ^
description of scoring bv Dowdeswell & Ford ( I« wh,d, s. . 1 a ; a P was rinded as absent if it could no, be **frjg£^£^ of larger m i g h t have occurred a n y u h e r e on the u i n g . t - • Ij f ^ These spots as measured bv P.M.». were also not scored 'i l m t olls'(Table 1).
a ( T ( ) ( m ( for mu(
.
h ()|.
|hr (|]tl(.
mi(T m t l l (. spot-frequenc, dumbuu< K i ^
The range in spo.-si/r lor which the probability ol a ^^^ ))v
s u b s t a n t i a l is r a t h e r narrow (Fig. 1). Tims only . , ' • ' k.(1 onl by
W.H.n. were below 7 u n i t s in si/e and only 5 0 C
,,,,„,. ,. ( ; o m p a n s ( ) n ( ) f s p o,l l T qnency CUStributions «or th \lnniolnjurlL scored nulependen.ly bv each
t i t | ' \ 1 |!R \ M | H | |) \ \ | ) U I) I M >V\ 1)1,SU I I I
e\< h i d i n g spots below fi si/.e u n i t s (here is ,i e lose < e n re-spotidene e in the spot-l t e &spot-lt; | u e - i i e v distribution! w i t h n o d i f f e r e n c e s I x - spot-l u e e n those spot-l o r t h e i n d i v i d u a spot-l s,impies Fig. 2H & C . F u t t h e t m o t e , ( h e r e is ,1 s i g n i f i c a n t Spe;irm.m r.ink c o r r e l a t i o n b e t w e e n the spot-averages for the t v \ o seiies of s p o t - f r c t p i e n c v d i s t r i b u t i o n s (r, = 0.92'), / ' < 0.05 and see Fig. 2'. The heterogenem l>etv\een t h e f i r s t l o u t s a m p l e s a n d t h e l,ist loin f o r U ' . H . D . ' s d a t a i s also e v i d e n t i n these t r a n s f o r m e d d a t a (%2 = I.').')'). ^ d . C , / > < ( ) . 0 1 ) . Disc.i SSION I he r e s u l t s of t i n s a n a l y s i s show t h a t to c o m p a r e - om d a t a tot s p o t - n u m b e r a n d s p o t - p l a c i n g it is necessary to t r a n s f o r m those of P . M . H . u s i n g m e a s u r e m e n t s of spol-si/e. U o v \ e v e t . t h e m i l l a n s f o t med d a t a of P . M . H . r e l l e i I t h e r e l a t i v e d i f l e r e n c e s b e t w e e n p o p n l , l i i o n s e v i d e n t f r o m a n a l y s i s o f W . H . D . ' s d a t a KC l ig. 2). Tfiiis. t h e groupings of the f i r s t lorn and last lout samples a r e a g a i n heterogeneous / ' 10.10. 1 d.i., / ' < ( ) . ( ) " ) a s a t e t h e e i g h t i n d i v i d u a l - a m p l e s (^ = 51.62, 28 d . f . , /'< 0 0 |
I he basK d i f f e r e n c e b e t w e e n t h e scoring t e c h n i q u e s e m p l o y e d b\ us is t h a t w h i l s t t h e - ( o n i p l e l e c o n t i n u o u s d i s t i i b n l i o n of spot-si/e is r e f l e c t e d by the tec I m i c p i e of P . M . B . . a lot m of threshold is used I n V\ 11 I ) SIK h t h a t t h e - lower t a i l of the d i s t r i b u t i o n represents a w i d e r t ä t i g e of p h e n o t v pes.
I he- p o s s i b i l i t y o f some- \ a t i a b i l i t y b e t w e e n scorers v \ a s t a k e n i n t o a c c o u n t w h e n t h e - si o r i n g Ire I m i l pie e m p l o y e d l i \ I , I? Foul a n d \\ I I . D o w d e s w e l l w a s developed see- D o w d e s w e l l \- F o r d . I ' t ' i . ' ' F i n i s , t h e y use a lot m of c o n s e n s u s scoring w h e r e i f t h e r e is d o u b t a b o u t t h e - s p o t t i n g o f a n \ specimen a t le.ist t w o w o r k e r s are a v a i l a b l e to give an opinion. Flic- eflee I of t h i s is to r e d u c e v a r i a t i o n s i n i n t e i pi e t a l i o n o f t h e - t v p e a n a l y s e d i n t h e present s t u i K
O u t r e s u l t s i l l u s t r a t e t h a t f o r ( p r a i i t i t a l i v e c h a r a c t e r s of ( l i e - I v p e s t u d i e d m
\! jiirlina it is necessary to s t a n d a t d i / e t h e - scoring l e c ' l u m p i e s e m p l o v e d l>\
d i l l e r e n l workers p a r t i c u l a r l y w h e n t h e absolute- si/c- of t h e c l i . n a i l e r is not m e a s u r e d a n d w h e r e l l i e - r e m a v b e some- i p i e s t i o n ,is to w h a t l o i i s l i t u t e s e x p r e - s s i o i i o f ( h e i h a t a c l r t A t i v d i f l e r e n e e s l ) c l \ \ e - e t i t h e - te-c h m e p i c - s m u s t b e l a k e - t i i n t o a c c o u n t w h e n t h e - d a t a arc- interpreted, I I t h e - piesen! d a t a sets h a d bei-n obtained independend) and w i t h o u t c o - o p e - t a l i o n H w o u l d h.ivc- been c o t i c l u d e - e l t h a t i h c v r e - p r e s e n t e d samples f r o m d i l l e i e n l groups o f | ) o p i i l a l i o n s a l t h o u g h ones e x h i b i t i n g s i m i l a r ' p a t t e r n s o f r e l a t i v e - d i U c - r e n c e s . l hese-obse-iv a l l o n s a r e - also r c - l e - v a n t to t h e - n u m e r o u s s t u d i e s of v a r i a t i o n m spot p a t t e r n s in other spec ic-s of I .epiclopter a H t a k e f i e l d . 1W1
\< K \ o \ \ l i I H , I A l l \ i s
\\ i a r e most g r a t e - f i l l to Pmfe-ssor F. B. Imd lor Ins c o m m e n t s on the-m a n n s c i i p t . I ' h c - s t u d y the-m a l e - r i a l w a s o b t a i n e d w l u i s t P M . I ? w a s snppor t e - e l b y a g r a n t No. d R l 1'tO'l to I ) i \ F R . \ F i c n a n f r o m t h e - N a i m a l F n v i t o n m e - n t K e - s e a r e h ( ioiine i l
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