Fernando Cánovas

Adaptive Traits Are Maintained on Steep Selective Gradients despite Gene Flow and Hybridization in the Intertidal Zone

Gene flow among hybridizing species with incomplete reproductive barriers blurs species boundaries, while selection under heterogeneous local ecological conditions or along strong gradients may counteract this tendency. Congeneric, externally-fertilizing fucoid brown algae occur as distinct morphotypes along intertidal exposure gradients despite gene flow. Combining analyses of genetic and phenotypic traits, we investigate the potential for physiological resilience to emersion stressors to act as an isolating mechanism in the face of gene flow. Along vertical exposure gradients in the intertidal zone of Northern Portugal and Northwest France, the mid-low shore species Fucus vesiculosus, the upper shore species Fucus spiralis, and an intermediate distinctive morphotype of F. spiralis var. platycarpus were morphologically characterized. Two diagnostic microsatellite loci recovered 3 genetic clusters consistent with prior morphological assignment. Phylogenetic analysis based on single nucleotide polymorphisms in 14 protein coding regions unambiguously resolved 3 clades; sympatric F. vesiculosus, F. spiralis, and the allopatric (in southern Iberia) population of F. spiralis var. platycarpus. In contrast, the sympatric F. spiralis var. platycarpus (from Northern Portugal) was distributed across the 3 clades, strongly suggesting hybridization/introgression with both other entities. Common garden experiments showed that physiological resilience following exposure to desiccation/heat stress differed significantly between the 3 sympatric genetic taxa; consistent with their respective vertical distribution on steep environmental clines in exposure time. Phylogenetic analyses indicate that F. spiralis var. platycarpus is a distinct entity in allopatry, but that extensive gene flow occurs with both higher and lower shore species in sympatry. Experimental results suggest that strong selection on physiological traits across steep intertidal exposure gradients acts to maintain the 3 distinct genetic and morphological taxa within their preferred vertical distribution ranges. On the strength of distributional, genetic, physiological and morphological differences, we propose elevation of F. spiralis var. platycarpus from variety to species level, as F. guiryi.

Driving south: a multi-gene phylogeny of the brown algal family Fucaceae reveals relationships and recent drivers of a marine radiation.

BackgroundUnderstanding the processes driving speciation in marine ecosystems remained a challenge until recently, due to the unclear nature of dispersal boundaries. However, recent evidence for marine adaptive radiations and ecological speciation, as well as previously undetected patterns of cryptic speciation is overturning this view. Here, we use multi-gene phylogenetics to infer the family-level evolutionary history of Fucaceae (intertidal brown algae of the northern Pacific and Atlantic) in order to investigate recent and unique patterns of radiative speciation in the genus Fucus in the Atlantic, in contrast with the mainly monospecific extant genera.ResultsWe developed a set of markers from 13 protein coding genes based on polymorphic cDNA from EST libraries, which provided novel resolution allowing estimation of ancestral character states and a detailed reconstruction of the recent radiative history. Phylogenetic reconstructions yielded similar topologies and revealed four independent trans-Arctic colonization events by Fucaceae lineages, two of which also involved transitions from hermaphroditism to dioecy associated with Atlantic invasions. More recently, reversion of dioecious ancestral lineages towards hermaphroditism has occurred in the genus Fucus, particularly coinciding with colonization of more extreme habitats. Novel lineages in the genus Fucus were also revealed in association with southern habitats. These most recent speciation events occurred during the Pleistocene glaciations and coincided with a shift towards selfing mating systems, generally southward shifts in distribution, and invasion of novel habitats.ConclusionsDiversification of the family occurred in the Late-Mid Miocene, with at least four independent trans-Artic lineage crossings coincident with two reproductive mode transitions. The genus Fucus arose in the Pliocene but radiated within a relatively short time frame about 2.5 million years ago. Current species distributions of Fucus suggest that climatic factors promoted differentiation between the two major clades, while the recent and rapid species radiation in the temperate clade during Pleistocene glacial cycles coincided with several potential speciation drivers.

Metatranscriptomes reveal functional variation in diatom communities from the Antarctic Peninsula.

Functional genomics of diatom-dominated communities from the Antarctic Peninsula was studied using comparative metatranscriptomics. Samples obtained from diatom-rich communities in the Bransfield Strait, the western Weddell Sea and sea ice in the Bellingshausen Sea/Wilkins Ice Shelf yielded more than 500K pyrosequencing reads that were combined to produce a global metatranscriptome assembly. Multi-gene phylogenies recovered three distinct communities, and diatom-assigned contigs further indicated little read-sharing between communities, validating an assembly-based annotation and analysis approach. Although functional analysis recovered a core of abundant shared annotations that were expressed across the three diatom communities, over 40% of annotations (but accounting for <10% of sequences) were community-specific. The two pelagic communities differed in their expression of N-metabolism and acquisition genes, which was almost absent in post-bloom conditions in the Weddell Sea community, while enrichment of transporters for ammonia and urea in Bransfield Strait diatoms suggests a physiological stance towards acquisition of reduced N-sources. The depletion of carbohydrate and energy metabolism pathways in sea ice relative to pelagic communities, together with increased light energy dissipation (via LHCSR proteins), photorespiration, and NO3− uptake and utilization all pointed to irradiance stress and/or inorganic carbon limitation within sea ice. Ice-binding proteins and cold-shock transcription factors were also enriched in sea ice diatoms. Surprisingly, the abundance of gene transcripts for the translational machinery tracked decreasing environmental temperature across only a 4 °C range, possibly reflecting constraints on translational efficiency and protein production in cold environments.

Microsatellite variability reveals beekeeping influences on Iberian honeybee populations

The genetic structure of the Iberian honey bee (Apis mellifera iberiensis) was studied by analysing 10 microsatellite loci in 362 workers representative of nine Spanish provinces. Heterozygosity values of Iberian honeybee populations are intermediate between African and west European ones whereas allelic diversity is remarkably high at several loci. There is no definite geographic structure of Iberian honeybee populations. At a peninsular scale, the expected clinal pattern observed with mitochondrial data has been probably lost due to the extensive practice of mobile beekeeping and increased colony trade-off. Due to these practices, it is expected that the genetic homogenisation will increase during the next years. Though this might have positive effects on honey production, putative ecotypes existing in Iberia would be prone to disappear.

DNA barcodes, cryptic diversity and phylogeography of a W Mediterranean assemblage of thermosbaenacean crustaceans

We assess the occurrence of crypticism and analyse the phylogeography of a thermosbaenacean crustacean, the monodellid Tethysbaena scabra, endemic to the Balearic Islands (W Mediterranean). This species occurs only in mixohaline waters of coastal wells and caves adjacent to the seashore. We have used the mitochondrial DNA barcode region to assess its genetic population structure throughout the anchialine environment of the islands. Maximum likelihood phylogenetic analyses showed that the Balearic Tethysbaena and those from the NW Italian Peninsula form a monophyletic assemblage subdivided into several lineages. Cytochrome c oxidase subunit 1 (cox1) p‐distances among the more divergent Mallorcan lineages are remarkably high and on par with those established between the formally described species T. scabra from Menorca and T. argentarii from Italy. This result and the application of the generalised mixed Yule coalescence model (GMYC) suggest that at least some of the Mallorcan lineages represent cryptic species. A clear‐cut phylogeographic pattern is displayed by this anchialine assemblage: six of its seven lineages appear in allopatry, with the exception of a Mallorcan lineage limited to a single cave nested within the geographic range of another lineage. All lineages show a distribution reduced to a single cave or to short portions of coast not exceeding 60 km in length. Our coalescence estimations suggest an early Tortonian (10.7 Ma) origin for the Balearic + Italy Tethysbaena clade, an age that is largely prior to the onset of the eustatic oscillations associated with the Quaternary glaciations. Only the diversification that took place within some of the Mallorcan lineages could be coeval with the broad glacio‐eustatic oscillations of the Quaternary.

Development and characterization of 35 single nucleotide polymorphism markers for the brown alga Fucus vesiculosus

We characterized 35 single nucleotide polymorphism (SNP) markers for the brown alga Fucus vesiculosus. Based on existing Fucus Expressed Sequence Tag libraries for heat and desiccation-stressed tissue, SNPs were developed and confirmed by re-sequencing cDNA from a diverse panel of individuals. SNP loci were genotyped using the SEQUENOM® single base extension iPLEXTM system for multiplex assays on the MassARRAY® platform, which uses matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) to discriminate allele-specific products. The SNP markers showed a wide range of variability among 16 populations from the south-west of the UK, northern Portugal and Morocco. The analysis of the information provided by these markers will be useful for studying population structure, historical demography and phylogeography of F. vesiculosus. They can also be used for the identification of genes and/or linked genomic regions potentially subject to selection in response to abiotic stressors like temperature extremes and desiccation intensity that vary across habitats and geographical range.

Isolation and characterization of microsatellite loci for the cavehopper Palmorchestia hypogaea (Amphipoda: Talitridae)

Eight polymorphic microsatellite loci for the subterraneous microphtalmous Palmorchestia hypogaea (Amphipoda: Talitridae) were isolated from a genomic library enriched for AG, AC and AAC repetitive elements. The number of alleles ranged from 2 to 8 per locus with the observed heterozygosity ranging from 0.00 to 0.94 in the two studied populations. These variable markers will be useful in evaluating gene flow and population structure within the subterranean populations and should provide valuable information about the importance of dispersal through the underground in the dynamic of cave biotas.

Analysis of a contact area between two distinct evolutionary honeybee units: an ecological perspective

Determining the relationships between environmental variables and genetic diversity is critical to understand the processes that drive evolution in species-contact areas. We employed a combination of modeling approaches and multivariate statistical analyses to analyze mtDNA diversity in a hybrid zone between two evolutionary lineages of honeybees in order to interpret the microevolutionary processes that led to the observed spatial pattern of diversity. The model located the west European honeybee lineage mainly across temperate areas characterized by mild winters and high water availability throughout the year, whereas the African lineage was mainly associated with warmer and drier areas. Selection could be playing an important role in shaping the life history evolution, particularly affecting the mitochondria, and also resulting in hitchhiking effects on particular regions of the mitochondrial genome.

New records of sea cucumbers inhabiting Mar Menor coastal lagoon (SE Spain)

Two sea cucumber species, Holothuria impatiens and Oestergrenia digitata, were reported officially on Mar Menor coastal lagoon (SE Spain). Seven specimens of the first species were identified, using traditional taxonomy and genetic barcoding, in Los Narejos (Mar Menor). However, only one belonging to O. digitata species was found in Los Urrutias (Mar Menor). These findings could support the ‘mediterranisation’ process of the lagoon favoured by the enlargement of the El Estacio inlet in 1972. In the last several years, there has been a decrease in salinity, a smoothing of the most extreme temperatures and many anthropogenic actions which have produced modifications in Mar Menor, affecting the seagrass and seaweed coverage and causing an increase of organic matter in sediments. These modifications, together with the current patterns, are favouring the colonisation of Mar Menor by Mediterranean species.