Hi Alexandra - I would be cautious about eliminating the possibilities of a cryptic species complex without genetic data. Are the populations from the same depth?

Yes. They are from the same depth. Both populations live in the lower intertidal and are found associated with the same sea anemone in the Mediterranean and in the Bay of Biscay. The species is an ectoparasite of a sea anemone. A colleague of mine suggests that maybe a ecophenotypic plasticity may account for the differences. Alternatively, I'm considering that maybe also genetic differences may account for the diversity but these may not be so wide as to consider them two different species. At the Bay of Biscay the species is at the northernmost border of its distribution range, and at the border maybe the populations may be in the middle of a parapatric speciation process. The first hypothesis - ecophenotypic plasticity - can be checked experimentally. For the second, I would need a colleague that are happy to collaborate with me and sequence specimens from these populations and maybe from others in the middle of the distribution range.

Hi Alexandra, There are many instances of genetic differentiation of populations moving from east to west in the Mediterranean and into the Atlantic - some examples Mol Ecol 19: 557, Mol Ecol 16: 1377, Mar Biol 147: 153, Mar Biol 148: 853, J. Hered 90: 591 and many more..... We may be able to sequence a few beasts for you for an initial look-see - we'd need them in ethanol (a piece of tissue) or some DNA.

Hi Alexandra,

Besides to assess genetic data, (or maybe after that, once you have the results); have you thought about doing some translocation experiments? t would be helpful to conclude on phenotypic plasticity instead of just discard/accept genetic differences and not necessarily must be more work.

Hi Nahuel, I thought of doing some laboratory experiments by growing specimens from the Mediterranean under conditions similar to that of the itnertidal of the Bay of Biscay (T, subrate, salinity, presence of other sea anemone...). But transplantations experiments I think are also an excelent approach. Logistically, maybe less feasible. I will see what we can do.

Hi Alex, great! Well, the species here in the Bay of Biscay lives in very low density and it takes a while to collect them. We spent almost a few months just to get little more than 10. In the Mediterranean I know from a place where they are relative abundant. How many would you need? 5 individuals per locality? Thanks also for the references. As to the beasts, as soon as I get them, I will let you know and ask you for your postal address. I will send you samples of living tissue - the foot - carefully processed and preserved in 96% (?) or 100% (?) ethanol.

Hi Alexandra,

5 per population should be good. Drop me a line by email when you're ready ([email protected]). My gastropod student will be very interested (he works on vent molluscs). Best wishes

Alex

Hi Alexandra, I agree with Alex that it is difficult to eliminate the possibility of cryptic species without some basic genetic data. If radulae are so different it may indicate a different species : there are examples of cryptic species where differences occur in radulae, like in Crepidula species (Collin 2000, Veliz et al. 2003). In these examples however, development may differ between the cryptic species (planktonic vs direct development). Are you sure development is the same in the two populations ?

In the opposite there are examples where radulae differ within a single species (Simison & Lindberg 1999, Reid & Mak 1999).

To check in your own case I would go in the sense of Alex, and do some molecular analyses.

Collin (2000) Can. J. Zool. 78: 1500–1514

Veliz et al. (2003) Marine Biology 143(1):131-142

Simison & Lindberg (1999) J. Mollus. Stud. 65 (1): 99-109

Reid & Mak (1999) J. Mollus. Stud. 65 (3): 355-370

Hi Thierry, I do agree that it is not so easy to discard the possibility of the existence of cryptic species, but in my case I have the feeling that it is the same species for the following reason. First, both populations occupy the same niche (feed on the same sea anemone and are found in the same depth range), and have the same type of larval development (planktotrophic larval development). At least, I have seen in both populations individuals with a multispiral protoconch although I still need to examine the protoconch better with SEM to see if both populations have a sinusigera lip (in that of SE Spain I detected a sinusigera; in the population from here I haven't found a quite good perserved protoconch to check whether there is or not a sinusigera). Second, there is an amazing plasticity of radula types within the same population in the SE Iberian Peninsula (at least 6 different radula models can be distinguished). In the Northern population the radula type is not so plastic, and one character of the radula - which is variable in the SE population of Spain - is invariable (presence of central tooth). The single two different radula types present in the Northern Population are also present in the SE Spain population.

So my hypothesis is that both belong to the same species but slight differences among the population in the frequency of certain genes coding for a functional trait may account for the difference in the radula or ecological factors may "induce" the development of differences in the radula. But, I do agree in the fact that - considering that the possibility of a cryptic species complex may exists - the first step is to compare genetically the populations. :-) In this way, we can find out both, whether it is a cryptic species complex or not and also, in the case it is the same species, whether there are important genetic differences among both geographically separated populations. :-)

PD: And thanks for the references. By the way, Thiery, I see we work both in invasive Calyptraeids. :-) Do you have in Roscof also Crepipatella dilatata?

"I wonder if there are more cases of marine invertebrate species with planktotrophic development where important anatomical features vary geographically"

please let me know if You (really) find out this detail

Here is some work on fish from different latitudes showing genetic differences in vertebral number, a morphological character. Silversides fish have planktonic larvae like most fishes, and the increase in vertebral number from low to high latitudes is very common (so called Jordan's Rule).

Did this help?

Hi Hannes, I think it helps quite a lot! :-) At least, it gives an example of anatomical difference among geographicallly separated populations within a species with planctonic larval dispersal. :-)

Dear Alexandra

Interesting observation indeed. As far as I understand, there could be two major possibilities of what you have observed:

1. Those are cryptic species.

2. Radular tooth morphology has a relation with the dietary specialization of a species. Now there is a possibility that the geographically distant populations of the subject species have developed slightly different feeding preferences and so have developed different radular structures as well (through natural selection).

Now, you may look into the following:

a. Food & feeding biology (strategies/ preferences/ etc.) of your subject species.

b. If a population at a site carries only a characteristic type of radula, or the population is composed of mixed individuals.

c. How far the planktonic stages of the subject species is getting dispersed.

Hope this will be of some help. Let us know your findings.

Best

Dola

See the attachment

Hello Dola,

I've considered both possibilities, but as I don't see at the moment anatomical differences among the individuals of both populations and as type of development is in both population planctotrophic, I regard the possibility of the existence of a cryptic species complex as the least plausible hypothesis. Nevertheles, it should be tested also to definitively discard this possibility. As to the dietary preferences, I've found the individuals of both populations close to the same host species, a common sea annemone. But In North Spain, I also found once one of the individuals below the pedal disc on a different sea anemone. So, maybe in the population from here the individuals can feed on at least two different sea anemone depending on the local conditions and their radula pattern has been selected for the special conditions in North Spain. In the population of Southeast Spain, however, there is a great intraspecific variability in the radula; maybe there the individuals can switch even more easily to different sea anemones. In the laboratory they can do, but I don't know what happens there in the field. There is still a third possiblity and this is of an inducible change in the radula; that is, the same individual may in its ontogeny change the form of its radula depending on the prey, T, etc. to which it is exposed. To the last, thanks for the reference.

Answers here seem to consider most of the plausible explanations. Surely you have either (i) genetically different individuals/populations, whether judged to be the same species or not, or (ii) inducible changes in radula morphology triggered at some time(s) in ontogeny or even later life. Could you do rearing experiments with newly-settled juveniles? (tricky, first catch your juveniles, and then spend a long time rearing them ...). Or even prey choice experiments with snails from different populations? Seems to me that avenues like this could be as valuable as molecular approaches, though they would surely be useful also.

I will try to expose my specimens from South Spain and from North Spain to different preys. That's feasible, but rearing newly settled juveniles are extremely difficult, since the species has a planktotrophic development and live in low denisties. I will try first with any animal that I may collect. In an adult I found a radula in which the central tooth and lateral tooth seemed to be splitting. So, maybe some or all individuals are able at any time to respond to changes in the ecological conditions. Maybe this capacity is determined also genetically and varies among individuals. Who knows. the first step is to go to Souht Spain, collect some beasts and bring the to Oviedo, North Spain, where I'm working. :-) I always think that experiments and field studies clear up quite a lot problems, and are useful. Putting altogether - field work, experiments, and genetics will lead to a nice work! :-)

Yes, the synergy between lab and field is good. Many years ago Etter (I think) showed that Nucella lapillus early juveniles would switch morph (exposed or sheltered) in development, but in one direction the switch was irreversible, while in the other direction it could be reversed. There has been lots of stuff on plasticity since then, of course ...

Alexandra, when you found consistent morphological differences in two populations I would not consider them possible cryptic species anymore, the difference suggests that we are indeed dealing with two distinct species. Of course you should rule out ontogenetic and allometric shifts or gender dimorphism, and a molecular analysis and hybridization experiments might support your hypothesis of a new species.

Planktotrophic larva does not necessarily imply that populations are genetically connected, sea currents might strongly influence the relationships between related marine taxa with less mobile adults.

The three East Pacific species of the land crab genus Johngarthia are another case of marine invertebrate species with planktotrophic development where important anatomical features vary geographically. See my profile for some papers.

Hy Robert, we have rouled out already ontogentic changes and sexual dimorphism, in the population of South Spain; a few characters that we checked were not related to sex neither to size. We need a bit more females from the northen population to see whether in this there are or not sexual dimorphism. We could rule out however ontogenetic changes at least within the size range that we considered and with the small sample that we had. I consider two hypothesis as explanation for the differences that we see, either ecophentypic plasticity, or that the populations are genetically different, though pertaining to the same species. I suspect that both population have low connectivity in spite of the planktotrophic larval development. A third possibility, is again, the possibility of the existence of a cryptic species complex, of course.

Hello Luis, I will have a look. thanks for the references.

Robert, I will also have a look to your profile.

Hi all!

I have found this topic just now and very sorry for the "later" comment.

As I understand only couple populations were studied. In this case difference in radula morphology may not to be a result of geograohical isolation but may also marks interpopulation variety and may occurs sympatrically.

It is neccessary to know - what kind of differences were found: teeth number, shape or number of cusps, different general plan of radula :-)?

Regards,

Ivan