Well I've been searching for an invertebrate species in the Mediterranean sea. The Specie is familiar to the local seamen. However they say that the same specie but appear to be larger exist in the Red Sea. (The suez canal seperates the two seas)
Could it be possible they are the same specie or should I confirm via their DNA markers?
You certainly need to see if there are differences other than mere size, including DNA markers if possible. I do not know about marine animals, but certainly land snails can vary greatly in size within a species, depending on location. Sometimes, a lot of this difference is environmentally induced rather than just genetic. Size alone is not a good indicator of being different species
I think you should do the confirmation with DNA markers. I have seen some marine species with different sizes apparently within the same species, but even if you use a taxonomic key, which may be highly recomended depending on your objectives, you can't be completely sure unless you perform a molecular test.
Also, depending on how much time these groups have been separated, and if there exist gene flow between them or not, they may be experiencing speciation that would eventually lead to the appareance of subspecies or even two different species.
But if there is a known phenomenon specific for this specie and easy to test would it be sufficient to validate that I have done my experiment on such specie
In answering your question, it might be worth thinking about what you mean by species. For example, you could show that the large and small individuals come from different mtDNA lineages (satisfying a phylogenetic species concept), but may freely exchange genes (thus not qualifying as biological species). Under a differential fitness or morphological clustering species concept, one might also refer to them as species.
I live in the North Atlantic coast of the Iberian Península (Spain) and we have some species of marine invertebrates that its distribution range is the Mediterranean Sea and the Atlantic coasts of Europe and Africa. Many of them show differences in sizes, but also in color and shape, but they are the same species.
Chiton tuberculatus is a common specie of polyplacophoran in the Caribbean. The population in the Bahamas (northern Caribbean) doubles the average size of central and southern Caribbean populations. Samples of these giants chitons from Bahamas and the small C. tuberculatus from Puerto Rico do not show genetic differences (COI). My hypothesis is that a greater range in tides favors the survival of individuals with more volume (avoid drying).
Since you are dealing with geographically and (most likely) reproductively separated populations, you must first make sure that these population satisfy the general (especially, genetic) requirements for cospecificity.
If the species in question is not a recent immigrant into the Mediterranean (through the Suez Canal and/or as a passenger in ship ballast tanks), then the Mediterranean population has been separated from the Red Sea population for a geologically significant time (since the end of the Miocene if memory serves right). Even if the Mediterranean population is cospecific with the Red Sea one, it is quite likely that there are significant genetic differences that may partly explain the different sizes.
Other than this, it is common to see different adult sizes among cospecific populations that live in different environments. Strombid gastropods are a good example, since they have determinate shell growth and therefore you can immediately tell if you are looking at an adult, subadult or juvenile. Common species of Strombus in the tropical Indo-Pacific vary in adult shell length by 2-3 times between litoral tidal flats and shallow subtidal backreefs only a few tens of meters away.
About fish found on the east and west coasts of India I can comment something . Due to less pressure of exploitation on the east coast of India especially on the West Bengal and Ordisa as coasts the size of many of the marine species are larger as compared to that on the West Coast of India we get It is mainly due to the fact that the fish have an unique way of growth in the sense they continue to grow even at old age at a small rate. For this reason If the fish is not caught , as is the case on the east coast where the fishing pressure is less , it reaches bigger size.
S?k Chakraborty , CIFE MUMBAI , INDIA
Hallo Saif,
the first question is what you want top study. Is it genetics your main focus? There are many marine invertebrates species in which different populations achieve different sizes. For example in marine snails there is a pattern in which the same species tends to be larger towards the poles. Deep can also affect. Moreover, in the centre of the distribution, where the species is in optimum conditions the can be also bigger. So, depending on your hypotesis, you can go for the genetics if it is mandatory to your work. If its is not your intention to do a taxonomical comparison between sites you can focus on the population of your interest and base on previous reports on the study area to identify the species. If you can let us know the aim of your study I think we can give you a better answer. Best regards.
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