Biosynthesis of thyroglobulin in an adult lamprey, Lampetra planeri (Bloch)]

Thyroglobuline (Tg) biosynthesis has been studied in an adult fresh water lamprey Lampetra planeri (Bloch), by injection in coelomic cavity or by in vitro incorporation in follicles of branchial region of various radioactive labels: 125I-, 3H-leucine, 3H-mannose, 3H-galactose, N-acetyl mannosamine and 3H-N-acetylglucosamine. Labelling by all theses substances, present in Tg of mammals, proceeds efficiently in two hours. It has been demonstrated that the cyclostome studied synthetizes a 18 S iodinated glycoprotein analogous to Tg of higher vertebrates by its molecular size. It contains all the same hexose and N-acetyl derivatives of these in its sugar moiety and the same iodinated aminoacids. Purified 18 S Tg of the lamprey has been prepared; it is very poor in iodine (127I) and has a very low T3 and T4 content.     

Population genetics of a cyclostome species pair, river lamprey (Lampetra fluviatilis L.) and brook lamprey (Lampetra planeri Bloch)

Horizontal agarose gel electrophoresis of 24 allozyme loci in four species of Central European lampreys (321 Lampetra planeri , 83 L. fluviatilis , 11 Eudontomyzon mariae and nine Petromyzon marinus ) was used to study the 'paired species' L. fluviatilis and L. planeri . The genetic differentiation of the anadromous river lamprey ( L. fluviatilis ) from the stationary brook lamprey ( L. planeri ) was within the range of ingroup differentiation of the latter, but L. fluviatilis exhibited much greater population cohesion over a more extended geographic range: G _ST = 0.0537 versus G _ST = 0.3398, N _em = 4.402 versus N _em = 0.4856, mean genetic among-stock distances D = 0.0047 versus D = 0.0257. L. planeri populations coexisting geographically with L. fluviatilis in the Rhine and Elbe river systems were genetically more cohesive than L. planeri stocks from the Danubian basin where L. fluviatilis is absent. Danubian L. planeri populations exhibit a lower degree of heterozygosity than brook lampreys from the Rhine river system, but comprise deeper genetic lineages ( G _ST = 0.4629 versus G _ST = 0.2434), despite being sampled from a much more restricted area. Isolation-by-distance is observed for L. planeri from the Danubian but not from the Atlantic drainage basins. Transspecific gene flow between L. planeri from Atlantic drainage basins and the long-distant migrating L. fluviatilis is inferred, raising doubt on the validity of two separate biospecies. E. mariae and P. marinus are clearly differentiated from Lampetra spp. at several allozyme loci.     

Ultrastructure of the presumed ion-transporting cells in the gills of ammocoete lampreys,Lampetra fluviatilis (L.) and Lampetra planeri (Bloch)

Summary Mitochondria-rich cells were located in the interplatelet area of gill filaments from ammocoete Lampetra fluviatilis and L. planeri. The ultrastructure of this cell type differs from typical teleost chloride cells by the absence of a tubular, smooth endoplasmic reticulum (SER). This difference is discussed in relation to the presumed functions of the cell and to the evolutionary histories of lampreys and teleosts. It is concluded that the mitochondria-rich cell is responsible for the active uptake of ions by the ammocoete gill.     

Phylogeography of the European brook lamprey (Lampetra planeri) and the European river lamprey (Lampetra fluviatilis) species pair based on mitochondrial data

The European river lamprey Lampetra fluviatilis and the European brook lamprey Lampetra planeri (Block 1784) are classified as a paired species, characterized by notably different life histories but morphological similarities. Previous work has further shown limited genetic differentiation between these two species at the mitochondrial DNA level. Here, we expand on this previous work, which focused on lamprey species from the Iberian Peninsula in the south and mainland Europe in the north, by sequencing three mitochondrial marker regions of Lampetra individuals from five river systems in Ireland and five in southern Italy. Our results corroborate the previously identified pattern of genetic diversity for the species pair. We also show significant genetic differentiation between Irish and mainland European lamprey populations, suggesting another ichthyogeographic district distinct from those previously defined. Finally, our results stress the importance of southern Italian L. planeri populations, which maintain several private alleles and notable genetic diversity.     

Habitat selection of larval brook lampreys (Lampetra planeri,Bloch) in a South Swedish stream

Summary The burrowing larvae of the brook lamprey Lampetra planeri (Bloch) were shown by discriminant analysis to inhabit stream sites having certain qualities. Although a few larvae occurred in far-from-optimal habitats, most larvae selected those with low current velocity, low water depth, a low number of particles in the 0.5–1 mm range, and with low chlorophyll content. Other factors normally positively attributed to larval lamprey distribution such as organic content, shade, and presence of algae did not improve the discriminant model. The last factor even showed a negative correlation. Stream bed stability was considered to be of great importance although it was not possible to estimate quantitatively.     

Evolutionary history of lamprey paired species Lampetra fluviatilis (L.) and Lampetra planeri (Bloch) as inferred from mitochondrial DNA variation

A remarkable trend in the evolution of lampreys is the occurrence in most genera of 'paired species', in which the parasitic anadromous lampreys are believed to have given rise to nonparasitic freshwater resident populations. The present work examines the phylogeography of the European paired species Lampetra fluviatilis and Lampetra planeri, in an attempt to elucidate species pair evolutionary history. We studied sequence variation in cytochrome b and ATPase 6, 8 mitochondrial genes in 63 individuals from 21 localities of the paired species throughout their distribution range. Results from the phylogenetic and nested clade analyses were largely consistent, suggesting the existence of three major evolutionary lineages: lineage I and possibly lineage II are widespread throughout Europe, while the most ancestral lineage III is apparently restricted to the Iberian Peninsula. The high genetic diversity observed in the Iberian Peninsula is probably the result of refugial persistence and subsequent accumulation of variation over several ice ages, whereas the low levels of genetic diversity observed in central and northern Europe should reflect a rapid postglacial colonization. Results suggest that L. planeri originated within at least two distinct evolutionary lineages, rejecting the single origin hypothesis. The observed lack of taxa monophyly within lineage I may be the result of ongoing gene flow if the two taxa are alternate life-history forms of a single species. However, structure within lineage I is also consistent with the hypothesis of divergence of taxa after postglacial dispersion (around 2000 generations ago) with incomplete lineage sorting. Further testing of the alternative hypotheses is warranted.     

Isolation and characterization of eight microsatellite loci in the brook lamprey Lampetra planeri (Petromyzontiformes) using 454 sequence data

Eight polymorphic microsatellite loci were developed for the brook lamprey Lampetra planeri through 454 sequencing and their usefulness was tested in 45 individuals of both L. planeri and the river lamprey Lampetra fluviatilis. The number of alleles per loci ranged between two and five; the Italian and Irish populations had a mean expected heterozygosity of 0·388 and 0·424 and a mean observed heterozygosity of 0·418 and 0·411, respectively.     

Enzyme variation in the brook lamprey,Lampetra planeri (Bloch), a member of the vertebrate group Agnatha

A natural population of the brook lamprey, Lampetra planeri, was assayed for electrophoretically detectable variation at 30 enzyme loci. The mean heterozygosity per locus of this primitive vertebrate, a member of the Agnatha, was found to be 0.076 ± 0.031, a value similar to those recorded for other vertebrates. The high chromosome numbers recorded for this and related species have been attributed to polyploidy, but our studies do not indicate the existence of large numbers of duplicated loci. Indeed, several enzymes that are encoded by duplicate loci in other vertebrate species appear to be encoded by single loci in the lamprey. It is suggested that studies on the biology and taxonomy of lampreys will benefit greatly from an electrophoretic approach.     

Gill Morphometrics of the Lampreys Lampetra fluviatilis (L.) and Lampetra planeri (Bloch)

Morphometric measurements have been made on various gill components of different stages in the life cycle of the anadromous parasitic lamprey, Lampetra fluviatilis, and its nonparasitic derivative Lampetra planeri. The total gill area, expressed in terms of body weight, of both larval (1462–2717 mm² g^–1) and adult (1402–2337 mm² g^–1) L. fluviatilis are greater than those previously recorded in the rather meagre literature on lamprey gill measurements and are comparable with those found in the most active teleosts. The gills of the two Lampetra species are apparently identical in the larval stages and those of metamorphosing and adult L. planeri are similar to those of metamorphosing L. fluviatilis. Although the pharyngeal arrangement of lampreys differs greatly from that of teleosts, there are many features of the gills indicative of convergence between the two groups. Thus, in a given stage in the life cycle of lampreys, the secondary lamellae on either side of the filaments also alternate, become more widely spaced as the filament length increases and increase in area as the body weight becomes greater. Furthermore, the fractional cumulative increase in secondary lamellae area along a line following the presumed direction of water flow is also represented by a sigmoid curve. While at metamorphosis the pharynx becomes considerably modified to accommodate the change from a unidirectional to a tidal respiratory water flow, the total gill areas of the ammocoete are similar to those of metamorphosing stages which have attained adult characteristics. However, there are clearly differences in some of the components that influence and contribute towards the total gill area. Thus, in terms of body weight, the number and total length of the filaments and the total number of secondary lamellae, together with the number of secondary lamellae found on a given distance of filament, are greater in late metamorphosing stages, while the reverse is true for the average bilateral area of the secondary lamellae which is considerably greater in ammocoetes.     

Biosynthesis of thyroglobulin in the endostyle of larva (ammocoetes) of a fresh water lamprey, Lampetra planeri B1]

The biosynthesis of thyroglobulin (Tg) in larva of a fresh-water lamprey, Lampetra planeri B1. has been established. This glycoprotein presents the same characters as in thyroid follicles of adult lampreys, as shown by its 18-19 S sedimentation coefficient and by the incorporation (in vivo and in vitro experiments of 4, 12, 72 h) of 125I, 3H-leucine and 3H-galactose. 3-8 S fractions and a 12 S monomer are the precursors of the 18-19 S protein. Total I % of Tg is very low (0.002 %) ; about 5 % of 125I are present in thyroid hormones (T3 and T4) in the 125I-labeled protein. The biosynthesis of 18-19 S Tg proceeds in larvs before the morphological differentiation of thyroid cells and follicles after metamorphosis. However, the biosynthesis of this protein is much slower in the endostyle of larvs, in which a primitive mechanism of storage is poorly efficient, compared to the accumulation of Tg in the colloid of the follicles of adults.     

The spawning migration of the brook lamprey, Lampetra planeri Bloch, in a South Swedish stream

The spawning migration of brook lampreys ( Lampetra planeri , Bloch) was investigated in a South Swedish lake and stream system for two consecutive years. The nightly variations were analysed by a multiple regression technique. In one of the seasons, characterized by frequent rain storms, water level was the most important factor explaining 60% of the observed variation in migration. In the following year, when the migration period was unusually dry, temperature and on-shore winds at the mouth of the stream were the most influential environmental variables explaining 50% of the observed changes in behaviour. When data were combined for the two years only temperature showed a significant influence. The critical temperature for the onset of migration was estimated to be 7.5°C. Size distributions and sex ratios of the migrating lampreys, which are semelparous, indicated that the age distribution was complex and that females were older than males. Migration was essentially nocturnal, but late in the season day migration was also observed. A marking experiment resulted in few recaptures probably because of high predation and/or orientation difficulties.     

Purine nucleoside phosphorylase variation in the brook lamprey,Lampetra planeri (Bloch) (Petromyzone,Agnatha): Evidence for a trimeric enzyme structure

Genetic evidence for a trimeric structure for purine nucleoside phosphorylase in the brook lamprey is presented. This enzyme is encoded by a single locus with two alleles segregating at frequencies of 0.98 and 0.02 in a Welsh population. It is suggested that this enzyme is likely to be a trimer in all classes of vertebrates.B. J. McAndrew and G. P. Wallis were supported by NERC Research Studentships.