population genetics

[New Publication] Species or ecotype? The curious case of the Key silverside Menidia conchorum

What constitutes a species …

…in the true sense has kept biologist’s head scratching for quite some time, and matters have only gotten more complex since the thunderous advent of genetic methods. Yet the distinction between a species and – say – an ecotype of a species is more than just academic quibble.

In the case of the key silverside, Menidia conchorum, a species that is only found in the hypersaline ponds on the Florida Keys, it’s quite literally an existential question. So far, the protocols and steps of protection apply only in cases of threatened species, which is perhaps something that ought to change.

O’Leary et al. went down to the Florida Keys and sampled the silversides in order to compare them morphologically and genetically to the ‘parent’ species, the tidewater silverside Menidia peninsulae. Their findings show that key silversides are distinct, but not quite their own species yet. In addition, the study revealed the large amount of inbreeding and genetic drift that is happening in each of these small hypersaline ponds.

The paper concludes that although ‘only’ an ecotype, the key silverside is threatened by loss of habitat and therefore still needs our protection!

O'Leary et al. BMS2016
Depiction of morphometric landmarks (upper left) and distinguishing shapes (lower left) between tidewater and key silverside (M. peninsula & M. conchorum). Key silversides are an ecotype that can only be found in hypersaline ponds on the Florida Keys (right: lead and co-authors seining).

O’Leary, S.J., Martinez, C.M., Baumann, H., Abercrombie, D.L., Poulakis, G.R., Murray, C.H., Feldheim, K.A., Chapman, D.D. (2016)
Population genetics and geometric morphometrics of the Key silverside, Menidia conchorum, a marine fish in a highly fragmented inland habitat.
Bulletin of Marine Science 92:33-50