Moved here from a discussion started July 17, 2009 so as to have all M. corona related material in one location.

7/17/09  Marlo: There has recently been a long discussion on Conch-L regarding variations in M. corona, should they be named, and reasons why they vary. I thought it might be a good idea to preserve that conversation.

7/12/09 Leslie A. Crnkovic asked:

"Can anyone ID the difference between Melongena corona from Tampa vs Keys?"

Harry Lee responded:

"The Keys form is usually smaller, more slender, and less ornate than the shells typical of Tampa Bay.

However, a small percentage of the Keys snails break with the herd mentality of eating small clams, e.g., Anomalocardia cuneimeris (Conrad, 1846) [+ A. auberiana (d�Orbigny, 1853)] and Polymesoda maritima (d'Orbigny, 1853), and resort to cannibalism. The result is significantly larger animal which morphometrically approaches the Tampa Bay form.

I am of the opinion that Crown Conchs all belong to one gene pool and they "are what they eat."

Phil Poland concurred:

"I agree with Harry 100%. I spent a few years slogging through M. c. habitat in an attempt to understand them and reached that conclusion. Recent genetic work seems to agree."

"I'd like to add that the food associated with the smallest of M. c. forms is usually Batillaria minima. The tiniest (about 20 mm) adult M. c. I'd ever found were at Matheson Beach in Miami. The B. minima they were feeding on were exceptionally tiny, for what reason I haven't a clue. Could the tiny aperture of the B. minima be limiting the size of the M. corona that feed primarily on them?

C. lutosum is a similar species fed upon by the small M. c. in the Keys."

Harry Lee noted:

"It appears that the molecular genetics data (click here to read paper) do not support the popular (e.g., Abbott, 1974) taxonomy, but there is restricted gene flow among certain populations, as one might expect from a species living in backwaters and producing young which crawl away upon hatching. However, as demonstrated at JAXSHELL Presentation of Florida Melongena corona, similar conchological morphs appear in a haphazard zoogeographic pattern."

"Main conclusions [of the molecular genetics] ... study supports the designation of only four extant species within the genus: M. corona, M. patula, M. melongena and M. bispinosa. The subspecies M. corona corona, M. c. johnstonei and M. c. altispira, and the species M. sprucecreekensis and M. bicolor, should all be considered to be M. corona. Surprisingly, even with very low larval and adult vagility, no population subdivisions were noted in our genetic analyses."

Peter Krull wrote:

"I am fascinated with M. corona myself and feel there is more to the genetics than just diet. there is a great old book called "Collecting Seashells" by Kathleen Yerger Johnstone. Chapter 18, beginning on page 114, has a remarkable account of the genus that I would urge anyone interested in Melongenas to read. Actually, the entire book is great conchological reading."

7/13/09 Peter Krull commented about the molecular study:

"I'm good with having just one species of M. corona, and even no subspiecies. However, I guess I'm a "splitter". I like the idea of having named "forms" for M. corona. After all, there are a number of local or even widespread geographically distinct varieties and there is some value in giving them names that everyone recognizes."

7/14/09 Phil Poland replied:

"The problem, Pete, is that there are no clearly definable lines between, for example, an M. c. altispira and an M. c. bicolor, or between an M. c. johnstonei and an M. c. sprucecreekensis. The material used in Clench & Turner (Johnsonia) was limited. It was like looking at a jigsaw puzzle with only 15% of the pieces in place. As one slogs up estuaries and looks at new habitats and localities, the seemingly unique "subspecies" are found to be just points in a number of different clines. Polymesoda-feeders of Florida Bay (aspinosa), Batillaria-feeders of the Atlantic side of the Keys, estuarine Crassostrea-feeders, cannibals, even open Gulf Macrocallista-feeders have been found.

I never came up with plausible theories for the varying degrees of spinosity, for the color variations ("blonde," banded, even pastels), or for the elongate morphs. It may well be that local genetics plays a part."

Peter commented:

"Phil, your response itself points out the need for form names. You used the names in your reply and without those names you would have had no easy way to talk about each of those. Theories as to why there are differences can go on forever but having names to call them makes all that easier. And there are geographic ranges for many of those forms. M.c. altispira was probably a mistake but the others all have recognizeable characteristics."

Phil replied:

"I was using some familiar names that really don't work in strictly geographic terms (subspecies). An example would be the M. c.. of Sebastian Inlet. On the oyster bars in the Indian River, well inside the Inlet, large shells (100 - 150 mm), not very different from the ones on the bars of Spruce Creek, lived a mile or two from a little grass-filled bay in the 1960s and early 1970s. There were huge numbers of beautiful Neritina virginea. Bob Lipe will remember my taking him there. The M. corona were rather small (40 mm) and very much like the M. c. altispira of Clench & Turner. The bay was lost when a small creek feeding it was lost to a new park road. It's now a beach near the A1A bridge within Sebastian State park. Intermediate morphs were found in the mangrove-rimmed backwaters nearby. I don't remember what they were feeding on. In Key Largo, on the Bay side, nearly spineless and typically unbanded M. c. were, and probably still are, common in the shallow and often seasonal runs within the mangrove - 40 -50 mm. A few miles away on the Atlantic shore are the 25 mm "bicolor." Equidistant from these two groups, near the Biscayne National Park headquarters at Homestead, are M. c. with significant shoulder spines (and often basal ones) and dark banding, 30 - 40 mm, that compare well with the altispira of Titusville.

There are many other examples of M. c. morphs that compare well with multiple named "subspecies" but live in quite close proximity. There are undoubtedly genetic differences between isolated populations but most of the variability seen is almost certainly habitat, mainly food. I don't argue that there aren't genetic differences, but to defend the traditional names on the basis of geography just isn't accurate."

7/15/09 Mike Gray responding to Phil agreed:

"I think you are right, and I think too many conchologists spend too much time trying to come up with new species/subspecies names for the tall, skinny, glabrous, big-nosed specimen living in West Boca vs. the short, plump, hirsute, small nosed specimen living in Boynton Beach. We're not really separate species, just dive buddies. The taxonomists' desire for all memmbers of a species to be identical is simply unnatural.

For a while, I observed a large colony (3,000 - 5,000+?) of S. alatus on the outside of the main reef here in Palm Beach county. They were there for the better part of a year, then were gone. The four specimens I took, all the same time and within a 20' circle, are noteworthy because of their variance in shape and especially color; one purple, one dark brown, one tan, one blond.

A convention of subspecies? I doubt it. Food variations? Only if they had personal preferances (which O. vulgaris definitely does, btw). I am convinced it is just blonde vs brunette vs redhead vs bald."

Peter:

"Mike; you and Phil both make very good points. And you can't argue with DNA analyses that indicate one species and no subspecies. However, to give "form"(not subspecies) names to local or even widespread repeating variations makes a lot of sense to me. It would be nearly impossible to study, collect or even discuss Liguus, for instance, if they weren't given form (or variety?) names. You would spend all your time describing which variation you were talking about without names for them."

Phil:

"Varietal or form names are sometimes helpful when a species or subspecies is especially polymorphic, the Florida tree snail Liguus fasciatus being an example. It's not hard to notice scores of distinct and repeating combinations of color characteristics within a single subspecies, L. f. testudineus. Intergrades don't overwhelm the process. Melongena corona isn't so tidy. Would you have a varietal name for the big Crassostrea-eaters and another for the small Batillaria-eaters?

In terms of distribution (suggesting subspeciation), it may be tempting to think of the M.c. from southeast Florida as a separate subspecies based on the many records of small tidepool morphs, but a visit to San Pedro Bay near Islamorada will surprise you with 50+ mm snails with very un-bicolor characteristics.

I just can't pin down distinct and consistent varieties. The only candidate for a second subspecies, based on possible isolation, that I can think of, is the johnstonei of Alabama and the Florida panhandle, and that may be because I haven't spent enough time in the Big Bend finding intergrades and other morphs. The genetic work didn't show much evidence of divergence and I'll go with that."

John K. Tucker asked:

"...for all those interested in attributing variation in shell morphology in M. corona to some ecotypic magic. I would ask that you please demonstrate this experimentally. If M. sprucecreekensis does not have oysters to eat, I think it starves rather than growing up to be an M. c. altispira."

7/16/09 Phil replied:

" 'Ecotypic magic?' I'm sure there is plenty of genetic variation within the complex. My point is that there is clearly a response to habitat/prey that is very dramatic in terms of appearance. It would be interesting to give johnstonei eggs a shot at the Keys tidepools and the Florida Bay Polymesoda. Likely the egg-bearing adults would have a high if not 100% mortality but I suspect that surviving hatchlings would develop into much smaller and adapted adults. A higher success rate might result from a less extreme change of venue to start with. We can't do the experiments, unfortunately.

Another example of dichotomous morphs in the same area was found on Honeymoon Island in Pinellas County. Again, a small bay with marine grasses and algae provided the local M.c. with an abundance of small prey. The adult M.c. were rather uniformly small. A few hundred meters away, just outside of the bay, on oyster bars, were much larger snails.

What's the intensity over genetics vs. prey? I'm just sharing observations."

Peter then asked:

"Phil; Are you suggesting that, in most cases, Melongena colonies with only small prey available remain small as adults whereas when larger food is available the colony is, on average, larger individuals?"

Phil answered:

"I'm not being absolutist here. I've seen many examples like those mentioned this last week. It was noted long before I arrived on the scene that the M. corona found near or on oyster bars were the largest, reaching 200 mm. The Matheson Beach colony that was found feeding on dwarf Batillaria led me to suspect that the tiny apertures of the prey limited the size of the predator's proboscis and thus the entire animal. It's just a theory arising from my encounter with these tiny (20 mm) predators and prey. I can't prove anything. The shells were given away long ago. Interested parties should just get out of the office and take a look. I'm happy to give suggestions as to where they might look."