Strong genome-wide divergence between sympatric European river and brook lampreys

Abstract

Lampreys, together with hagfishes, are the only extant representatives of jawless vertebrates and thus of prime interest for the study of vertebrate evolution [1]. Most lamprey genera occur in two forms with divergent life histories: a parasitic, anadromous and a non-parasitic, freshwater resident form [2-8]. The taxonomic status of such 'paired species' is disputed, however. While indistinguishable at larval stages, but clearly distinct as adults, they cannot be differentiated with available genetic data [6,7], which has fuelled speculations that the two forms may in fact represent products of phenotypic plasticity within a single species. Here, we use restriction site-associated DNA sequencing (RADseq) to examine the genetic population structure of sympatric European river (Lampetra fluviatilis L., 1758) and brook (Lampetra planeri Bloch, 1784) lampreys. We find strong genetic differentiation and identify numerous fixed and diagnostic single nucleotide polymorphisms (SNPs) between the two species, 12 of which can be unequivocally assigned to specific genes.

Low reproductive isolation and highly variable levels of gene flow reveal limited progress towards speciation between European river and brook lampreys

“…Accordingly, Mateus et al . () found a strong differentiation ( F ST = 0.37) in a population pair sampled in the same river system in Portugal. These pairs may be a step further along the divergence continuum, which suggests that disruptive selection and other isolating factors may act in these systems.…”

“…However, Mateus et al . () found a strong genome‐wide divergence between L. fluviatilis and L. planeri sampled in a single river and concluded on the taxonomic validity of the two species. In addition, the different size of adults of both species has been hypothesized to induce size‐assortative mating leading to reproductive isolation (Beamish & Neville, ).…”

Variations in the presence of chloride cells in the gills of lampreys (Petromyzontiformes) and their evolutionary implications

“…It should be recognised, however, that these two species are genetically distinct, with some nuclear genes showing interspecific fixed allelic differences that are related to adaptations to an anadromous life v . freshwater residency (Mateus et al ., ).…”

The Central Nervous System of Jawless Vertebrates: Encephalization in Lampreys and Hagfishes

“…These changes in absolute body size may produce variation in the level of encephalization via dwarfism (phylogenetic reduction in absolute body size that were not accompanied by a reduction in absolute brain size), or they may have the opposite effect, i.e., gigantism [Striedter, 2005]. In many cases, however, despite these phenotypic differences, null genetic differentiation has been found between paired species of lampreys [reviewed in Docker, 2009, but see Mateus et al, 2013]. In such cases, these paired species have been interpreted as polymorphic populations of the same species [Kucheryavyi et al, 2007;Nazarov et al, 2011;Hume et al, 2013b], representing individual epigenetic realizations [Makhrov and Popov, 2015].…”

“…1 ). This has led various authors to discuss an ongoing process of sympatric speciation in lampreys resulting from size-assortative mating [e.g., Hardisty and Potter, 1971a;Beamish and Neville, 1992;Hume et al, 2013a;Mateus et al, 2013Mateus et al, , 2016Bracken et al, 2015;Rougemont et al, 2015]. In this case, it could be hypothesized that the differences in relative brain size between the parasitic and nonparasitic pairs, where nonparasitic species have, on average, a relatively larger brain than parasitic species ( Fig.…”