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Letter 5474

Bates, H. W. to Darwin, C. R.

29 Mar 1867

    Summary Add

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    Working on sexual differences in collection of horned beetles and will send CD results.

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    Answers CD's questions [sent on behalf of Miss Tollet of Betley Hall, Staffs.] on mimicry – how it helps prevent extinction, the modifications occurring with a change of habitat until mimicry occurred.

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    Also gives some cases of sexual differences.

Transcription

Royal Geographical Society | 15, Whitehall Place, S.W.

March 29 1867

My Dear Mr Darwin

I was interrupted in the examination of horned-beetles required to answer your last question by the arrival of a large addition to my collection of them from Paris. The development of horns & excrescences & the sexual differences in this respect are so wonderfully diversified that I think of tabulating the species & furnishing you with results, if I think they are worth your having. Meantime I will try to answer your other questions.

First, the poser of the Lady Darwinian. It is a very fair question & ought to be answered. There are no doubt great gaps in the gradation of forms, as now existing, between the ordinary white Pierid Leptalis & its highly specialised congeners which mimic Heliconidæ. But we must not exaggerate the width of these gaps, nor think that all the existing links are represented on the plates to my Linnæan paper. There are a good many species in collections bridging over the differences between the extreme forms in the genus. Some of these do not wear the livery of any Heliconids, although the wings are elongated like them, departing in this character from the Pierid type. They are forest insects, fly slowly & are rare; how they escape extermination I cannot say. This much however may be said that the undersurface of their wings is coloured & marked something like a dead leaf & this would probably stand them in some stead, as their wings are closed in repose, & they fly very little. (These species are Leptalis Licinia, Psamathe, Kollari Nemesis &c). Amongst the Leptalids mimicking Heliconids there is a very considerable diversity of coloration, for the various species are adapted to almost all the extreme forms of Heliconidæ. I have shown also in my paper that one Leptalis mimics not a Heliconid but a member of a totally different group, which nevertheless has a general resemblance in form & colours to the Heliconidæ.

Now let us put all these facts together. We see that the weak, struggling Leptalids manage to escape extermination by various disguises; some perhaps more effective than others, for I ought to have mentioned that one Leptalis, at least, is an abundant insect (L. Eumelia, a perfect imitation of a very common Ithomia, I. Eurimedia). There can be no difficulty, therefore, in understanding how at all previous periods in the history of the group, the species of Leptalis have found some means of escaping extinction, even though the forms had not reached the extreme divergence from the family type which they have now attained. It must be remembered that the Leptalids are inhabitants of humid forests where none, or scarcely any, of their Family allies live. The proper places for Pieridæ are open sunny grass lands; the Leptalidæ therefore, in intruding into the forest, encountered unusual difficulties & it became a necessity that they should become greatly modified if they were to maintain their ground at all. First their wings became elongated— this I believe was totally independent of adaptation to the long winged Heliconids—it may be connected with relaxation of muscular development—for many forest genera of butterflies are long-winged. Being long-winged & sporting into various colours—not at first the gayer colours of Heliconids—accidental resemblances of their varieties to some other object, no matter what, saved them from extinction. This continued for countless generations & in various parts of the great Tropical forest until the astonishing mimicry of Heliconidæ was brought about.

Another question you asked was whether any female Vanessa or Machaon group of Papilio existed differing in colours from its partner & from the usual gay colouring of its genus.—

I believe none is known. If you extended the search to the next allied genus (to Vanessa) Junonia, I could give you a string of cases of sexual disparity in colour. There are all grades of disparity among the species of Junonia (1) Male & female alike.— (2) male & female same colours but male brighter (3) male & female different in colours but a certain resemblance betraying their relationship (4) male & female so different that no one would judge them to belong to one & the same species.

Yours sincerely | H W Bates

I know of no case of male monkeys fighting together.

    Footnotes Add

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    f1 5474.f1
    The letter to Bates to which this is a reply has not been found. Bates had recently been investigating the colour of male and female butterflies, and the horns and sexual differences of lamellicorn beetles, to reply to earlier questions of CD's regarding sexual selection (see letter from H. W. Bates, 11 March 1867). For Bates's published descriptions of his collection of lamellicorn beetles, see Bates 1886--90.
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    f2 5474.f2
    In the missing letter, CD had sent a question from Georgina Tollet (see letter to H. W. Bates, 30 March [1867] and n. 3).
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    f3 5474.f3
    Tollet evidently asked about the extreme difference between the white Leptalis nehemia with shorter and broader wings, and the colourful Leptalis species with elongated wings. One of the plates in Bates's paper on the Amazonian Heliconidae, published in the Transactions of the Linnean Society of London (Bates 1861), showed the white L. nehemia as well as several more colourful Leptalis species and five Heliconidae. Leptalis nehemia is now Pseudopieris nehemia (Lamas 2004). Most species in the genus Leptalis in the family Pieridae are now in the genera Dismorphia or Enantia (for a recent checklist of the genera of the family Pieridae, see Braby 2005). See also letter from H. W. Bates, 11 march 1867 and n.5.
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    f4 5474.f4
    Bates refers to what are now known as Enantia melite melite, E. lina psamathe, and Lieinix nemesis. Leptalis kollari is a synonym of E. lina psamathe (Lamas 2004).
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    f5 5474.f5
    Bates noted the variability in colour among Leptalis species in Bates 1861, pp. 504--6, and also referred to a Leptalis imitating a Stalachtis species; Stalachtis is a genus of the family Riodinidae (see Bates 1861, p. 504).
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    f6 5474.f6
    In Bates 1861, p. 539, Bates described Ithomia eurimedia (now Aeria eurimedia), and mentioned that Leptalis melia (now Dismorphia melia) was often found with it.
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    f7 5474.f7
    Bates discussed how a mimetic species may develop through natural selection in Bates 1861, pp. 511--15. However, in considering the first stage of a Leptalis species coming to mimic Heliconidae species, he also wrote: `In what way our Leptalis originally acquired the general form and colours of Ithomiæ I must leave undiscussed' (ibid., p. 513).
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    f8 5474.f8
    Bates refers to the genus Vanessa and to related forms of Papilio machaon (swallowtails).
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    f9 5474.f9
    CD mentioned some of these differences in Junonia in Descent 1: 389. His draft for this discussion is in DAR 81: 183.
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    f10 5474.f10
    CD was interested in what he called the `law of battle', when males fought over females, and the related secondary sexual characteristics; on the `law of battle' in mammals, see Descent 2: 251--68. He mentioned the fighting of some male primates, but not monkeys, in ibid., pp. 324--5.
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