Movements of adult fish in a hybrid zone revealed by microsatellite genetic analysis and capture‐recapture data

Abstract

Summary Barbus barbus and Barbus meridionalis (Cyprinidae) form a hybrid zone in the Lergue river (southern France). We attempted to characterise the pattern of adult dispersal with the aim of understanding the evolutionary interactions maintaining this hybrid zone. In a previous capture/recapture study, movements between localities at a distance of 2.5 km or more appeared extremely rare. We therefore decided to investigate adult movement using a different method, based on genetic markers. As this hybrid zone has produced allele frequency clines, massive population movements would produce temporal variations in genetic composition at a given locality. In order to determine the relationship between gene frequency and position, we surveyed four diagnostic or semidiagnostic microsatellite loci over the hybrid zone and estimated the cline produced by introgression. Then, we focused on a single locality at the centre of the hybrid zone and established its introgression index over 11 periods during two years. The introgression index varied between periods producing significant Fst. A synthetic hybrid index, based on principal component analysis of the logit frequencies, was used for regression analyses and appeared significantly correlated with the river flow. This may be explained by displacement of adult fishes in response to flow increase. Using the information from the cline, we estimate that the most important gene frequency changes among dates, if created exclusively by population movement, correspond to a distance of 1500 m. Additionally, we performed recaptures on a finer geographic scale than previously, around the central locality. No recaptured fishes were observed at 1875 m or more downstream, and at 875 m or more upstream, from the central locality. A high proportion of recaptured fishes (20% and 12%) was found in the nearest points (312 m downstream and 437 m upstream, respectively). Thus, we established that (i) individual movements appear limited to a few hundred metres and (ii) individuals in a location tend to move in the same direction at the same time, probably in response to the same environmental factor.

Phylogenetic relationships among Spanish Barbus species (Pisces, Cyprinidae) shown by RAPD markers

“…Studies based on morphology, osteology, ecology and, to a lesser extent, on genetics, have all made contributions to the present understanding of the Barbus genus Granado-Lorencio, 1988, 1997;CollaresPereira and Madeira, 1990;Torralva et al, 1997;Aparicio and Sostoa, 1998;Chenuil et al, 1998Chenuil et al, , 2000Tsigenopoulos et al, 1999, Callejas andOchando, 2000;Tsigenopoulos and Berrebi, 2000). However, basic questions on its evolutionary differentiation remain unsolved (see Tsigenopoulos and Berrebi, 2000 and references therein).…”

Autosomal differences between males and females in hybrid zones: a first report from Barbus barbus and Barbus meridionalis (Cyprinidae)

“…There is evidence for both exogenous selection (B. barbus is unable to live in typical B. meridionalis habitats and a capture-marked-recapture study demonstrated marked differences in survival between upstream and downstream sites (Crespin et al, 2002); and endogenous selection (eg more than 50% of experimental F1 hybrids are unviable or sterile; Philippart and Berrebi, 1990;Crespin, 1996). Clines along the hybrid zone were detected using diagnostic allozymic (Crespin and Berrebi, 1994; nine locations) and microsatellite loci (Chenuil et al, 2000; five locations). The introgression index was calculated as the percentage of alleles diagnostic of B. meridionalis in a given population (100% for a pure B. meridionalis population, 0% for a pure B. barbus).…”

“…The upstream station, Cartel, had an allozymic introgression index (defined above, see also below) of about 60% in 1992 (Crespin and Berrebi, 1994) and an average microsatellite introgression index of about 40% in 1993-1995 (Chenuil et al, 2000), whereas the downstream location, Saint-Fréchoux, had a 40% introgression index with allozymes in 1992 and around 20% with microsatellites in 1993-1995. For each station, samples were taken in spring (the spawning season) and in winter, and were analysed with either allozymes or microsatellite loci (Table 1).…”

“…Samples were named according to their location and, within each location, were ranked by decreasing sizes, for example, Fréchoux1, Fréchoux2, etc. Samples from the different seasons taken at a particular location may not be comparable because (i) concerted population movements have previously been inferred from significant temporal variations in introgression (Chenuil et al, 2000) and (ii) migrations for reproduction are suspected in this hybrid zone (unpublished field and microsatellite data from spawning individuals) and were proven for B. barbus in other rivers (Hunt and Jones, 1974;Baras and Cherry, 1990;Lucas and Batley, 1996). Therefore, despite small female sample sizes, we were unable to analyse larger samples by pooling different dates for each location.…”

“…All loci had alleles diagnostic of one or both pure species; some loci were diagnostic loci sensu stricto. Locus B62 has two alleles, one of them being absent from B. barbus pure populations; locus B59 has 17 alleles, of which three and 12 are respectively diagnostic of B. barbus and B. meridionalis, whereas one allele is too rare to display a clinal pattern and another allele has its maximum frequency (12%) in a station of the hybrid zone (SaintFréchoux); locus B79 has six alleles, respectively one and five alleles diagnostic of B. meridionalis and B. barbus; and locus B37 has one diagnostic allele for each species (Chenuil et al, 1997(Chenuil et al, , 2000. Introgression indices are calculated as the frequency of diagnostic meridionalis alleles (ie alleles absent from pure B. barbus populations) divided by the sum of the frequency of all alleles diagnostic of either B. meridionalis or B. barbus, so that even for loci B62 and B59 introgression indices theoretically range from 1 to 0.…”