Natacha Mesquita

Phylogeography of the cyprinid Squalius aradensis and implications for conservation of the endemic freshwater fauna of southern Portugal

The Iberian cyprinid fauna, characterized by the presence of numerous endemic species, has suffered from significant habitat degradation. The critically endangered Squalius aradensis is restricted to small drainages of southern Portugal, habitats that typically exhibit a characteristic Mediterranean‐type heterogeneous hydrological system throughout the year, including alternation of flooding events during winter and complete drought in large river sections during summer. To assess the effect of historical and recent processes on genetic diversity in S. aradensis we examined within‐ and among‐population variability in cytochrome b and six polymorphic microsatellite loci. Estimates of genetic diversity in time and space through the combined use of traditional Φ‐/F‐statistics, phylogenetic trees, ordination methods and nested clade analysis indicated significant and congruent structuring among populations. Data suggest that the Arade drainage represent the evolutionary centre of the species, with subsequent allopatric fragmentation across drainages. Factors other than isolation by distance strongly affected the within‐drainage genetic differentiation observed in these Mediterranean‐type drainages, including recent population expansion from a bottleneck event and restricted gene flow imposed by a long‐term barrier (brackish water area). Significant correlation was found between S. aradensis allelic diversity and upstream drainage area. The relevance of findings for conservation issues is discussed in relation to local intermittent hydrological conditions, the highly restricted distribution and the critically endangered status of the species.

River basin-related genetic structuring in an endangered fish species, Chondrostoma lusitanicum, based on mtDNA sequencing and RFLP analysis.

Chondrostoma lusitanicum is a Portuguese endemic cyprinid with a restricted distribution and reduced numbers in some basins, justifying its status as a threatened species. We examined genetic population structure using samples from throughout its geographical range in Portugal, using sequencing of b cytochrome and restriction fragment length polymorphism analysis of the NADH subunits 5 and 6. There was reduced within-population genetic variability but considerable among-population differentiation, particularly marked between both the Mira and Arade basins in the extreme south and other populations. These results confirm phylogeographic relationships suggested by previous fragmentary allozyme studies for C. lusitanicum, and are in accordance with allozyme and mitochondrial DNA on phylogeography of coexisting cyprinid species of the genus Leuciscus. The levels of genetic divergence revealed by sequence and RFLP data showed strongly concordant patterns: geographical genetic structuring, with the definition of three distinct groups, was observed. The high values of nucleotide divergence and pairwise sequence divergence of the Mira and Arade groups, when compared with all other samples, support a distinct taxonomic status probably at the species level. Results are also discussed in relation to conservation of this highly fragmented species, in terms of Evolutionary Significant Units and Management Units.

Spatial variation in fish assemblages across small Mediterranean drainages: effects of habitat and landscape context

Much debate about assemblage organization in stream fish may stem from analysing the effects of both local and large-scale processes on assemblage attributes over whole geographic regions. This study addresses this issue, by examining the contribution of local habitat attributes and landscape context to fish assemblage variation across small Mediterranean drainages in southern Portugal. Fish abundance and species composition was estimated in 28 sites, across 10 drainages, in both a dry year (1999) and a wet year (2001), and related to two sets of variables reflecting habitat and landscape characteristics. Fish showed responses to both sets of variables with variance partitioning indicating that landscape context had important effects on species richness whereas habitat attributes were the primary determinants of local fish abundance. In general, high species richness was associated with larger drainage area and higher rainfall variability, whereas variation in species abundances mostly reflected the influence of width, depth, conductivity, current velocity, substrate size and emergent vegetation. The relative contributions of both landscape context and habitat attributes to species richness and abundance were generally lower in 1999 than in 2001, with much less diversified species–habitat relationships being found in the former dry year. These results point to the dynamic nature of assemblage organization, emphasizing the importance of innovative, multi-scale approaches in advancing our knowledge of fish assemblage structure in Mediterranean streams.

European Lampreys: New Insights on Postglacial Colonization, Gene Flow and Speciation

Ice ages are known to be the most dominant palaeoclimatic feature occurring on Earth, producing severe climatic oscillations and consequently shaping the distribution and the population structure of several species. Lampreys constitute excellent models to study the colonization of freshwater systems, as they commonly appear in pairs of closely related species of anadromous versus freshwater resident adults, thus having the ability to colonize new habitats, through the anadromous species, and establish freshwater resident derivates. We used 10 microsatellite loci to investigate the spatial structure, patterns of gene flow and migration routes of Lampetra populations in Europe. We sampled 11 populations including the migratory L. fluviatilis and four resident species, L. planeri, L. alavariensis, L. auremensis and L. lusitanica, the last three endemic to the Iberian Peninsula. In this southern glacial refugium almost all sampled populations represent a distinct genetic cluster, showing high levels of allopatric differentiation, reflecting long periods of isolation. As result of their more recent common ancestor, populations from northern Europe are less divergent among them, they are represented by fewer genetic clusters, and there is evidence of strong recent gene flow among populations. These previously glaciated areas from northern Europe may have been colonized from lampreys expanding out of the Iberian refugia. The pair L. fluviatilis/L. planeri is apparently at different stages of speciation in different locations, showing evidences of high reproductive isolation in the southern refugium, and low differentiation in the north.