Genetic differentiation of deep-sea hydrothermal vent alvinellid populations (Annelida: Polychaeta) along the East Pacific Rise

Abstract

The alvinellid polychaetes, which live in the hottest part of the deep-sea hydrothermal environment, have a nested island-like distribution and locally are subjected to extinctions. They are sedentary and exhibit a peculiar reproductive behaviour and a development which may result in little or no planktonic stage (i.e. larval dispersal). The genetic variation within and among populations of the three main species (A/vine/la pompejana, A/vine/la caudata and Para/vinella grasslei) inhabiting vents along the East Pacific Rise was examined at a hierarchy of spatial scales using allozyme electrophoresis. The genetic diversity of P. grasslei is high (H0 = 0.24), about twice that of both the Alvinella species (H0 = 0.10). The three species show a strong tendency towards a heterozygote deficiency which systematically occurs at the same loci in nearly all the populations. These structures are particularly obvious in the genus Alvinella and might be explained by differential allozyme fitness. Populations display considerable genetic differentiation at the microgeographical scale, which could be explained by repeated founder effects in populations, but it varies from species to species according to their possible ability to be transported by crabs from vent to vent. However, the genetic variation among populations separated by at least 1000 km is of the same magnitude as that found within the 13°N/EPR segment. These results demonstrate that each species maintains its genetic identity along the oceanic rifts despite the evidence for founder effects.To explain this phenomenon, we hypothesize that in such a harsh environment, genetic drift in alvinellid populations could be balanced by a uniform selective pressure stemming from the vent chemistry.Keywords: allozymes, Alvinellidae, FST, genetic variation, hydrothermal vents. IntroductionGenetic variation in subdivided populations at equilibrium results from a balance between gene flow, natural selection and genetic drift. In sessile marine invertebrates, numerous studies have reported a correspondence between the ability of larvae to disperse and the amount of genetic differentiation between populations. It is generally admitted that a long larval planktonic phase favours extensive gene flow resulting in little differentiation among populations over large geographical distances, whereas a short *Correspondence dispersal period or direct development are the main grounds for significant differences between marine populations (Avise, 1994). Nevertheless, whatever the dispersal strategy adopted by organisms, local genetic differentiation in populations may also be a result of selection and/or some form of drift derived from bottleneck effects.Fauna inhabiting deep-sea hydrothermal vents represent ideal biological material with which to study the relative contributions of these influences. These endemic organisms experience natural radioactivity (Cherry et a!., 1992) (Tunnicliffe, 1991). As a consequence, this island-like arrangement of vents along the ridge axes results in a pecul...

Thermal selection of PGM allozymes in newly founded populations of the thermotolerant vent polychaeteAlvinella pompejana

“…Unlike other key enzyme loci from the glycolytic and Krebs pathways investigated so far in A. pompejana ( Jollivet et al 1995a) (which could be subject to temperature selection), such as glucose phosphate isomerase (Gpi), the Pgm-1 locus (coding for phosphoglucomutase (PGM)) is polymorphic and consists of two major allozymes, Pgm90 and Pgm100, and two rare ones, Pgm78 and Pgm112. A previous study ( Jollivet et al 1995b) suggested that allozyme 90 might be more thermostable than allozyme 100.…”

Cryptic species ofArchinome(Annelida: Amphinomida) from vents and seeps

“…111 species) of the named hydrothermal vent animal species [2]. The East Pacific Rise (EPR) has among the best-studied vent annelids [23][24][25][26][27][28][29][30] and the incorporation of molecular data has shed light on cryptic diversity found along this system [12,14,21,31,32]. The giant vestimentiferan tubeworm, Riftia pachyptila, is a dominant feature of hydrothermal vent sites along the EPR and was shown to be genetically homogeneous across a broad range (278 N-328 S), with a genetic break identified at the Easter microplate (approx.…”

Variation in genetic traits of the lugworm Arenicola marina:temperature related expression of mitochondrial allozymes?

“…The picture for other polychaetes is not as uniform as in the abovementioned bivalves; but, similar to the lugworms, the genetic diversity of other polychaetes seems to be lower in general. In Hediste limnicola, H. diversicolor and H. japonica heterozygosity ranged from 0.01 to 0.02 (Fong & Garthwaite 1994), in Neanthes succinea from 0.02 to 0.04 (Abblati & Maltagliati 1992), and in 3 alvinellide polychaetes (Alvinella pompejana, A. caudata and Paralvinella grasslei) from 0.10 to 0.24 (Jollivet et al 1995). Seven Nephtys species from different European locations proved even to be monomorphic in all 6 isoenzyme systems investigated (Schmidt & Westheide 1994).…”