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Psyche 8:59-62, 1897.

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A NEW HYPOTHESIS
OF SEASONAL-DIMORPHISM IN
LEPIDOPTERA. - TI.
BY ALFRED GOLDSBOROUGH MAYER. CAMBRIDGE, MASS. (2) New Hypothesis of Seasonal-
Dimorphism.
I know of only one experiment upon
the effect of excessive heat upon Lepi-
tloptera, and that was performed upon
the pupae of Vanessa anti@, by
Fischer ('95) who, it will be lernem-
bered, subjected them, when fresh, for
3 hours and then daily for 2-3 hours to
a temperature of 40'-4zo C. keeping
them at all other times at $5'-3S0 C.
The butterflies which issued resembled
those which would hiive resulted from
exposure to cold of oO-io C.
It has occurred to me that in this
remarkable fact we may have a clue to
at least a partial explanation of the
action of cold upon seasonally-dimor-
phic Lepidoptcra. It is well known
from the researches of Dutsocliet, Ross- bach, and Plateau that if organisms be
subjected to gradually increasing heat
the metabolic processes as evinced by
increased excretion in protoplasm, and
more rapid rate of development, become
more and more active ; until suddenly
all movements cease and heat rigor sets
in. This is not death howeverfor if the
organism be now cooled down, recovery
takes place, and the life processes return with normal vigor.
According to Pla-
teau* the temperature of heat rigor in
various insects varies between 38O-43O
C. It is highly probable then that the
high temperature of 4.0'-4.2' C. pro-
duced heat rigcw in the pupae, am1
therefore the metabolic processes were
checked, exactly as they would have
been by the benumbing influence of
cold. If this be true it becomes proh-
able that the peculiar color-aberrations caused by cold are only an expression
of the decreased metabolism in the
pupae. It will be that
heat of 3s0 C. produces an aberration in V. a'rttiofa 'which is just the reverse of that caused by cold. In this case the
peculiar coloration could be explained as one of the results of the increased ineta- holism in the pupae.
Now it may well be that it is an advan-
tage to a pupa which is destined to with- stand the winters cold to inherit a
tendency toward a low metabolism, for
resistance to the cold would naturally
require the possession of low metabolic
processes ; hence those pupae which
already possessed low metabolism would'
'Plateau, '72 ; Bulletin d lYAcademie royale des sciences de Belgique, xxxiv, pp. 315-317.
Pu&e 8 059-62 (pre.1903). hfp //psyche cntclub o@S-0359 htd



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60 PLY rc1'3E. [May ,897.
be in better condition to withstand the
effects of the cold. Natural selection
would then operate to weed out all
pupae having high metabolic processes,
for they would be more likely to freeze ; whereas those individuals in which the
metabolism was low would be pre-
served. Also this inherited tendency
in the overwintering pupae .to possess
low metabolic activity might become so
strongly fixed that it would be found
difficult to alter it by the mere subjection of the pupae to a high temperature,
such as 32'-3s0 C. Moreover it would
doubtless be of advantage to the insects if they had the power to resist the in-
fluence of such warmth, for there are
often hot periods of weather in the
autumn through which the over-win-
tering pupae must pass; but their
development must not be hastened
thereby, for if the butterflies emerged
they or their progeny would probably
perish of the cold.
Professor Weismann's former (1875,
'82) idea that in the seasonally-diinor- phic butterflies of the temperate zone
the phylogenetically older form issues
from the wintered chrysalids, and repre- sents the form winch existed during the
glacial epoch, is to my mind improb-
able. His hypothesis may be true as
far as the European Vanessa levana-
i)rorsa is concerned, because, as is well known, the butterflies of Europe are
more closely related to those of Siberia, than to those of Africa or India. (See
Bath ('~5)).* The cause of this lies
Bath, W. H. 1893; Entomologist Vol. 38, p. 347 in the well known fact that there has
been, according to Gcikie, no land con-
nection between Europe and Africa
since the close of the glacial epoch.
Moreover the deserts of Sahara, and
Arabia, and the snow clad peaks of the
Himalayas form an insuperable barrier
beyond which tropical forms could not
pass to enter the northern regions. In
America, however, the case is very dif-
ferent, for almost 50% of all the known
species of Lepidoptera of the world come from South Americ:i,* and there can be
but little doubt that the ancestors of most of the North American butterflies came
from South America. The ancestors
of the North American fornis have
gradually crept in from South America
after the glacial epoch, and as their
range extended further and further
north, they were obliged to become
adapted to the cold, or perish. This
adaptation would mean the acquisition
OF a low metabolism in the ova--win-
teriq pupae. In this connection it is
interesting to notice that Merrifield ('93) has shown that in England those pupae
of Pyrameis atalmta which form in
the autumn all perish of the cold. This
insect usually hibernates as an imago,
and is not seasonally-dimorphic. In-
deed, the seasonally-dimorphic butter-
flies, of the temperate zone, according
to Sciidder (Butterflies of New En"
land, 1889, p. 1384) probably all winter



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over as pupae. Dr. Scudder has also
observed, that in a few cases of seasonal- dimorphism we find differences between
the earlier and later appearing members
of the spring brood, the later members
showing an approach toward the sum-
mer form.
It is highly probable that the vast
majority of Lepidoptera which existed
ill North America before the glacial
epoch, simply retreated southward upon
the approach of the ice. For to have
them remain we are obliged to assume
that not only they, but theirfood plants, also, became acclimated to the cold.
Many of those which did remain, and
succeeded in defying the cold would
probably for the most part become so
thoroughly acclimated to it that they
would finally $refer a cold climate,
and when the ice retreated they would
probably follow it northward leaving
a few representatives stranded, as it
were, upon the tops of the highest
mountains ; as has been shown by Grote
and, also, ~cudder ('89 p. 588) to
have been thecase with Oeneis semidea
of Mount Washington.
In the case of Papilio e x , which
was experimented upon by Edwards,
I have reason to believe that it could
not have existed in North America dur-
ing the ice period. For its nearest allies are all in Mexico, and South America,
none of them being found in the colder
parts of North America. Moreover its
food plant, the papaw (Asimina triloha,
Dunal.) belongs to the characteristically tropical family Anonaceae, and cannot
live in a cold climate. This leads me
to suggest that walshii or telemonides
are not primitive forms as would be the
case were Weismanu's 1875 hypothesis
true. I also predict that if the ovel-
wintering pupae of Papilio @ax be
subjected to a constant heat of from
30'-3s0 C. they will be transformed into the summer foi m marcellus.
Conclusions: In lepidoptera of the
temperate regions it is an advantage for the summer pupae to possess high meta-
bolic processes, for under these circum- stances their development is rapid. On
the other hand it is an advantage for the overwintering pupae to posses low meta-
bolic process, for under these circum-
stances they would be the better able to withstand the influence of warm pel iods of weather in the autumn; for if the
butterflies emerged at this time they or their progeny would probably perish of
the cold. Moreover in order that the
pupae may withstand the influence of
the winter's cold it is essential that they possess a low metabolism. Natural selec- tion would then operate to cause all
summer pupae to inherit a high meta-
bolism, while all overwintering pupae
would be forced to inherit a low meta-
bolism. Pupae which possess a ccmstitu-
tional tendency toward high metabolism
give rise to the summer form of imago,
while those pupae which possess a con-
stitutional tendency toward low meta-
bolism
give rise to the overwintered
form of butterfly. The summer and
winter forms of imago are only expres-
sions of this difference in constitution of the summer and winter pupae.
It is well known through the re-




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62 PSYCHE. [May 1897.
searches of Barker," F5randes.t Butler, ]: and others that tropical butterflies
exhibit seasonal dimorphisn~. It has
occurred to me that this maypossibly be
due to the direct influence of the vary- ing humidity upon the pupae.
Pupae
reared in a dry atmosphere may give
rise to the dry season form, while those reared in a humid atmosphere may give
rise to the wet season form. I am
assured by Mr. E. A. C. Olive of Cook-
town, Queensland, Australia that the
development of pupae in that region is
mole rapid in the wet season llian in
the dry.
I freely admit that Weismann's
"adaptive" seasonal-dimorphism may
exist, but I believe that the explanation gi~en in this paper is more probable.
I hope that some of the many able
entomologists who are carrying out re-
searches upon seasonal-dimorphism will
test its tiuth or falsity by experiment. Literature Recording Temperature Experi- ments upon Lepidoplwa.
Dorfmeister, G. '64. -Mittheil. des naturwis- sen. Vereins fur Steierinark, Heft 11. p. 99, Plate.
*Barker, C. W.: Notes on Seasonal-Dimorphism of Rhopalocera in Natal, Trails. Ent, Soc. Lund. iSgs, pp. 413-428.
t Brandes, G.; Der Saison-Diinorpliismus bei einheimi- schen und exotisclien Schmetterli~tgen, Zeit. Naturw. Leipig, 66. Bd., pp. 277~1,00, Fig. T. 2. 1894. Butler, A. G.; Notes on Seasonal-Dimorphism in Cer- titin African Butterflies. Traiis. Ent. Soc. Lond. I%, pp. 519-522,
Dorfmeister, G. '79. -Mittheil. des naturwis. sen Vereins fur Steiermark, Jahrgang
1879. p. 3. Plate.
Edwards, W. H. '68. - " The Butterflies of North America," Philadelphia, and Bo8-
ton, 1868.
Edwards, W. H. '75. -The Canadian ento-
n~ologist, Vol. vii, p. 228.
Edwards, W. 11. '77. -The Canadian
entomologist, Vol. viii, p. 203.
Edwards, W. H. 'So.-Psyche, Vol. 3, No.
69, P. 3-
Edwards, W. H. '81. -Psyche, Vol. 3, No. 82: p. 174.
Edwards, W. El. '84. -The Canadian Ento- mologist, Vol. xvi, p. 232.
Fischer, E.'Qs.-Transmutation der Scbmet- terlingc infolge Ten~peratirunderungen,
Berlin, 1895.
Meri-ifield, F. \io, '91, '92, '93, '94, -Trans. ent. soc. London, 1890, p. 131 ; 1891, p. 15.5; 189% p. 33; 1893, P. 55; 1894, p.
425-
Merrifield, F. '96. -Proc. ent. soc. Lond. ii, 1896.
Reichenau, W. van, '82. -Kostnos, Vol. 12, 182, p. 46.
Standfi.1~6, M. '96. - Handbuch ilcr palark- tischer gross-Sclimetterlinge, Jena, 1896, p. 236.
Stange, G. 86. - Stettiner entomolog. Zeit- ung, 1886, p. 279.
Weismann, A. '75. - Studien znr Desendenz- Theorie, I. Leipzig, 1875.
Weismann, A. 82. Studies in the Theory of descent. Translated by Raphael Meldola.
London. 1882.
Weismann! A. '95. - Zoologische Jahr-
bticher, Syst. Abth. Bd. 8, p. 611. See
also translation of the same by W. E.
Nicholson, The Entomologist, Vol. xxix,
1896, PP. 29, 74, 103, 153, 173, 202; 240.



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