But I stumbled on this in the paper Polymodal emergence of the tiger swallowtail, Papilio glaucus (Lepidoptera: Papilionidae): source of a false second generation in central New York State ROBERT H. HAGEN and ROBERT C. LEDERHOUSE* 1985:
early recognition of polymodal emergence in Eurytides rnarcellus was due solely to phenological differences in the adults associated with emergence time (Edwards, 1897). Our results suggest that polymodal emergence within a season may be masked by its resemblance to a truly bivoltine life cycle.
Looking for this paper I stumbled on POLYMORPHIC TERMINATION OF DIPAUSE in' CECROPIA: GENETIC AND GEOGRAPHICAL ASPECTS G. P. WALDBAUER AND J. G. STERNBURG 1973. This paper demonstrates that (at least in part of Illinois in 1970s) cecropia were split into two distinct groups which had different emergence periods. One group did not beget the other; the first group's offspring would emerge when the parents did, and the second group likewise. In other words, the early group would always emerge early, never later- so it's not like one generation emerging at two periods, it's two separate generations emerging at two separate times.
Further, the above reference states: It has long been known that the emergence of the zebra swallowtail (Eurytides mar cell us) from overwintering pupae is bimodal, and that in this case the dimorphism involves color and form as well as physiology (Scudder, 1889,pages 1273- 1278).
It may have been known, or as put in another publication "we've known" a long time that the "spring form" and "summer form" of marcellus are not two generations of progeny from the same group, but in fact are separate groups that have different morphology, however NOBODY EVER TOLD ME.
That cecropia exhibits bimodal emergence is amazing to me. I wonder if the spring and summer forms of luna are bimodal emergence.
Anyone have any more insights into this thing that's been kept secret from me?
it's been known for ages that these aren't really "broods", sensu stricto. Just a bi- or poly-modal emergence pattern? Guess I need to read the really old literature. It's awful being ignorant!
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In many Leptocircini most offspring of the summer generation go into diapause and only a few emerge in late summer. The offspring of those then add to the spring generation of the following year. The many spring specimens are mostly not the offspring of the third generation.
Kind of reminds me of different magicicada broods.
Neominois ridingsii is kind of like this with the late summer wyomingo entity vs early-mid summer every else.
Euphilotes enoptes/battoides and Apodemia mormo are also this way in some places with diverse Eriogonum hosts but most experts seem to consider the host/brood time differences to be separate species nowadays.
with Group I and some of which emerge with Group II." A subsequent publication on the subject by the same authors strips out inferences that the groups are isolated. So it appears that cecropia in Illinois is/was demonstrating polymodal emergence but there is no correlation between the time of the larval stage and the emergence group.
Further, in reading various (which is few) studies on polymodal emergence it wasn't clear, but is now, that the term "polymodal emergence" is just that and nothing more; it means that there are more than one emergence/ flight periods, with no further inference of where those groups come from or their relationship.
Case in point, as Adam cited (I cannot find a published reference on this) Eurytides marcellus has three flight periods so exhibits polymodal emergence, but which period is not determined by the previous generation, i.e., Spring form larvae do not necessarily always emerge the following spring.
MikeH answered my next question, citing magicicada. This species is an excellent example of polymodal emergence of a single species in which the various emergences rarely meet. Group A begets Group A, and Group B begets group B, only.
Question then: what would be the term or phrase for the polymodal emergence of a species where the offspring of each group turns into same group following eclosion? That is, for example, spring form always yields spring form, summer form always yields summer form.
Well, I think it's a grammatical issue in part.eurytides wrote: ↑Fri Oct 07, 2022 5:31 pm In the situation where group A begets A and group B begets B, I personally don’t consider that polymodal. Any one group has a single emergence peak! It would be more accurate to say there are in fact 2 populations, and if the temporal isolation is sustained, these may eventually evolve into 2 separate species (perhaps because of different host plant usage at different times of the year or other environmental factors over many generations).
If a species has bimodal eclosion, it indicates that there are two emergences; it does not dictate one larger than the other, nor does it indicate the source generation.
Gramatically speaking, Group A always yielding (for example) "spring form" and Group B yielding "summer form" would still be bimodal eclosion because they are the same species. If one is talking about a particular population Group A, which has a single emergence then Group A does not exhibit bimodal distribution in emergence- but the discussion has to be limited to that group. As was mentioned, as a species magicicada has polymodal emergence, even though those groups/ emergences are geographically distributed.
Temporal and topographical isolation of a species has led to separation into different species, as is the case of appalachiensis. One could argue it was never a split since it's a hybrid but the papers discuss appalachiensis splitting from glaucus. If we follow that some group within the glaucus species became isolated (hybridized or otherwise) at some point it was still glaucus so was bimodal; once it split (not once it was named) each became a unimodal again.
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