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.     

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.     

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.     

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.     

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.     

Histochemical and spectrophotometric demonstration of hydroxysteroid dehydrogenase activity in the presumed steroid producing cells of the brook lamprey (Lampetra planeri Bloch) during metamorphosis

Pronephric, opisthonephric, ovarian, and testicular tissue rich in presumed steroid producing cells taken from the brook lamprey during metamorphosis was investigated by histochemical and spectrophotometric methods. Histochemical results seemed to provide evidence for hydroxysteroid dehydrogenase activity using pregnenolone as substrate. Spectrophotometric evidence for hydroxysteroid dehydrogenase activity was obtained from presumed adrenocortical tissue, ovarian and testicular homogenates using pregnenolone, dehydroepiandrosterone, androsterone, and 3 beta, 17 beta-dihydroxy-5 alpha-androstane as substrates.     

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.     

Ciliated Receptors in the Pharyngeal Terminal Buds of Larval Lampetra planeri (Bloch) (Cyclostomata)

Terminal buds on the gill arches of larval Lampetra planeri have been investigated by scanning and transmission electron microscopy. Each terminal bud is composed of two types of elongated cells, which extend from an apical depression to the basal lamina; one type bears a pair of cilia and the other, microvilli. In addition there are peripheral and basal cells. Nerve-fibre profiles are lacking within the terminal bud epithelium and contacts between nerves and ciliated cells are established through holes in the basal lamina. The presence of ciliated receptor cells with such a mode of innervation presents a distinct contrast to the morphology of the taste buds of gnathostome vertebrates.     

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.     

Ultrastructural features of the synaptic complex of the vestibular nuclei of Lampetra planeri (Bloch)

Summary The vestibular fibres of ammocoetes of Lampetra planeri form a peculiar type of synaptic contact with the large nerve cells of the vestibular nuclei. In fact, a large expansion of the fibre is enveloped by the nerve cell cytoplasm, which makes a sort of spoon or actual channel by sealing its own plasma membrane with adhesion plaques around the fibre.In the whole area of juxtapposition between the fibre and the cell membranes, three different types of specialized contacts occur: desmosomoid junctions, which are the most numerous; zones having the characteristics of chemically active synapses on account of the presence of vesicles clustered on the presynaptic side; gap-junctions, where electrical transmission might occur. A puzzling feature is the presence of an enormous number of presynaptic vesicles located in the central part of the axoplasm of the fibre expansion.Supported in part by a grant to the Centre of Neuroembryology from the National Research Council.We wish to thank Prof. Aldo Rossi for supplying the perfusion technique and Mr. Dino Scorsini for his skilful technical assistance.