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  • Population genetics of Zostera noltii along the west Iberian coast: Consequences of small population size, habitat discontinuity and near-shore currents
    Publication . Diekmann, O. E.; Coyer, J. A.; Ferreira, J.; Olsen, J. L.; Stam, W. T.; Pearson, G. A.; Serrão, Ester
    The effects of oceanographic patterns on marine genetic biodiversity along the SW Iberian Peninsula are poorly understood. We addressed the question of whether gene flow in this region depends solely on geographic distance between isolated patches of suitable habitat or if there are superimposed effects correlated with other factors such as current patterns. Zostera noltii, the dwarf eelgrass, is the keystone habitat-structuring seagrass species on intertidal mudflats along the Iberian west coast. We used 9 microsatellite loci to analyze population genetic diversity and differentiation for all existing 8 populations from NW Spain (Ria de Vigo) to SW Spain (Puerto Real, Cadiz). Populations are highly genetically differentiated as shown by high significant FST,Wright’s fixation index, (0.08 to 0.26) values. A neighbor-joining tree based on Reynold’s distances computed from allele frequencies revealed a split between northern and southern populations (bootstrap support of 84%). This pattern of differentiation can be explained by (1) ocean surface current patterns present during Z. noltii’s reproductive season which cause a dispersal barrier between the northern and southern populations of this region, (2) habitat isolation, due to large geographic distances between suitable habitats, preventing frequent gene flow, and (3) small effective population sizes, causing high drift and thus faster differentiation rates.
  • Temperature effects on the microscopic haploid stage development of laminaria ochroleuca and sacchoriza polyschides, kelps with contrasting life histories
    Publication . Pereira, T. R.; Engelen, Aschwin; Pearson, G. A.; Serrão, Ester; Destombe, C.; Valero, Myriam
    Kelp forests are one of the most diverse and productive ecosystems worldwide. Global climate change and human exploitation threaten the stability of many of these ecosystems.
  • Broad scale agreement between intertidal habitats and adaptive traits on a basis of contrasting population genetic structure
    Publication . I Zardi, Gerardo; Nicastro, Katy R; Ferreira Costa, J.; Serrão, Ester; Pearson, G. A.
    Understanding the extent to which neutral processes and adaptive divergence shape the spatial structure of natural populations is a major goal in evolutionary biology and is especially important for the identification of significant levels of biodiversity. Our results identified replicated habitat-specific (adaptive) phenotypic divergence in the brown macroalga Fucus vesiculosus that is independent of population (neutral) genetic structure. F. vesiculosus inhabits contiguous and contrasting marine to estuarine intertidal habitats. Combining analyses of genetic and phenotypic traits of populations living under differential selective regimes (estuaries and open coast), we investigated levels of neutral genetic differentiation and adaptive physiological responses to emersion stress. In southwest England (SW UK) and northern Iberia (N. Iberia), populations living in estuaries and marine coastal habitats were genetically characterized at six microsatellite loci. In N. Iberia, two clades with limited admixture were recovered, each including one open coast site and the adjacent estuarine location. In contrast, SW UK samples clustered according to habitat and formed three distinct groups of genotypes; one including the two open coast locations and the other two representing each of the estuarine sites. Temperature loggers revealed distinct emersion regimes that characterized each habitat type independently of the region, while water and air temperature profiles showed site-specific trends. Despite acclimation under usual conditions, trait means of emersion stress resilience showed a strong phenotypic divergence between habitats, consistent with environmental clines in exposure time observed in the different habitats. We demonstrate that neutral genetic clusters do not reflect locally adapted population units. Our results identified replicated habitat-specific (adaptive) phenotypic divergence that is independent of population (neutral) genetic structure in F. vesiculosus. The significance of such findings extends beyond the theoretical evolutionary and ecological interest of discovering parallel adaptive responses to the broader implications for conservation of intraspecific biodiversity.
  • Polar marine biology science in Portugal and Spain: Recent advances and future perspectives
    Publication . Xavier, J.; Barbosa, Ana B.; Agustí, S.; Alonso-Sáez, L.; Alvito, P.; Ameneiro, J.; Ávila, C.; Baeta, A.; Canário, J.; Carmona, R.; Catry, P.; Ceia, F.; Clark, M. S.; Cristobo, F. J.; Cruz, B.; Duarte, C. M.; Figuerola, B.; Gili, J.-M.; Gonçalves, A. R.; Gordillo, F. J. L.; Granadeiro, J. P.; Guerreiro, M.; Isla, Enrique; Jiménez, C.; López-González, P. J.; Lourenço, S.; Marques, J. C.; Moreira, E.; Mota, A. M.; Nogueira, M.; Núñez-Pons, L.; Orejas, C.; Paiva, V. H.; Palanques, A.; Pearson, G. A.; Pedrós-Alió, C.; Peña Cantero, T. L.; Power, Deborah; Ramos, J. A.; Rossi, S.; Serrão, Ester
    Polar marine ecosystems have global ecological and economic importance because of their unique biodiversity and their major role in climate processes and commercial fisheries, among others. Portugal and Spain have been highly active in a wide range of disciplines in marine biology of the Antarctic and the Arctic. The main aim of this paper is to provide a synopsis of some of the results and initiatives undertaken by Portuguese and Spanish polar teams within the field of marine sciences, particularly on benthic and pelagic biodiversity (species diversity and abundance, including microbial, molecular, physiological and chemical mechanisms in polar organisms), conservation and ecology of top predators (particularly penguins, albatrosses and seals), and pollutants and evolution of marine organisms associated with major issues such as climate change, ocean acidification and UV radiation effects. Both countries have focused their polar research more in the Antarctic than in the Arctic. Portugal and Spain should encourage research groups to continue increasing their collaborations with other countries and develop multi-disciplinary research projects, as well as to maintain highly activememberships within major organizations, such as the Scientific Committee for Antarctic Research (SCAR), the International Arctic Science Council (IASC) and the Association of Polar Early Career Scientists (APECS), and in international research projects.
  • Blue- and green-light signals for gamete release in the brown alga, Silvetia compressa
    Publication . Pearson, G. A.; Serrão, Ester; Dring, M.; Schmid, R.
    The intertidal brown alga Silvetia compressa releases gametes from receptacles (the reproductive tissue) rapidly upon a dark transfer (following a photosynthesisdependent period in the light, termed potentiation). In this study, the wavelength-dependence of this process was investigated. During the potentiation period in white light (WL), gametes are not released. However, gametes were released during potentiation in blue light (BL), or in low red light/blue light (RL/BL) ratios, but not in RL alone, high RL/BL ratios, or in broadband blue-green light (BGL) (presence of BL, but absence of RL). RL was as effective as WL for potentiation, i.e., both lead to gamete release following transfer to darkness. Rates of linear photosynthetic electron transport were similar in RL and BL. Gamete release in BL was inhibited by equal amounts of additional narrow-waveband light between the green and red regions of the spectrum, with light-induced gamete release restricted between <491 nm and 509 nm. Very little light-induced gamete release occurred between 530 nm and 650 nm. It is proposed that a BL-responsive photoreceptor is responsible for light-induced gamete release. Transfer of WL-potentiated receptacles to GL near 530 nm resulted in significant de-potentiation and reduced gamete release during a subsequent dark transfer. This effect was not seen at 509 nm or 560 nm and revealed the presence of a second photoreceptor system repressing or counteracting potentiation in the light. We propose that the restriction of gamete release to periods when irradiance is blue-shifted may constitute a depth-sensing mechanism for this intertidal alga, allowing controlled release of gametes at high tide and/or less turbid periods, thus minimizing gamete dilution, and promoting fertilization success.
  • Love thy neighbour: group properties of gaping behaviour in mussel aggregations
    Publication . Nicastro, Katy R; I Zardi, Gerardo; McQuaid, C. D.; Pearson, G. A.; Serrão, Ester
    By associating closely with others to form a group, an animal can benefit from a number of advantages including reduced risk of predation, amelioration of environmental conditions, and increased reproductive success, but at the price of reduced resources. Although made up of individual members, an aggregation often displays novel effects that do not manifest at the level of the individual organism. Here we show that very simple behaviour in intertidal mussels shows new effects in dense aggregations but not in isolated individuals. Perna perna and Mytilus galloprovincialis are gaping (periodic valve movement during emersion) and non-gaping mussels respectively. P. perna gaping behaviour had no effect on body temperatures of isolated individuals, while it led to increased humidity and decreased temperatures in dense groups (beds). Gaping resulted in cooler body temperatures for P. perna than M. galloprovincialis when in aggregations, while solitary individuals exhibited the highest temperatures. Gradients of increasing body temperature were detected from the center to edges of beds, but M. galloprovincialis at the edge had the same temperature as isolated individuals. Furthermore, a field study showed that during periods of severe heat stress, mortality rates of mussels within beds of the gaping P. perna were lower than those of isolated individuals or within beds of M. galloprovincialis, highlighting the determinant role of gaping on fitness and group functioning. We demonstrate that new effects of very simple individual behaviour lead to amelioration of abiotic conditions at the aggregation level and that these effects increase mussel resistance to thermal stress.
  • Driving south: a multi-gene phylogeny of the brown algal family Fucaceae reveals relationships and recent drivers of a marine radiation
    Publication . Cánovas, Fernando G.; Mota, Catarina; Serrão, Ester; Pearson, G. A.
    Understanding 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. Results We 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. Conclusions Diversification 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.
  • Shift happens: trailing edge contraction associated with recent warming trends threatens a distinct genetic lineage in the marine macroalga Fucus vesiculosus
    Publication . Nicastro, Katy R; I Zardi, Gerardo; Teixeira, Sara; Neiva, J.; Serrão, Ester; Pearson, G. A.
    Significant effects of recent global climate change have already been observed in a variety of ecosystems, with evidence for shifts in species ranges, but rarely have such consequences been related to the changes in the species genetic pool. The stretch of Atlantic coast between North Africa and North Iberia is ideal for studying the relationship between species distribution and climate change as it includes the distributional limits of a considerable number of both cold- and warm-water species. We compared temporal changes in distribution of the canopy-forming alga Fucus vesiculosus with historical sea surface temperature (SST) patterns to draw links between range shifts and contemporary climate change. Moreover, we genetically characterized with microsatellite markers previously sampled extinct and extant populations in order to estimate resulting cryptic genetic erosion. Results Over the past 30 years, a geographic contraction of the southern range edge of this species has occurred, with a northward latitudinal shift of approximately 1,250 km. Additionally, a more restricted distributional decline was recorded in the Bay of Biscay. Coastal SST warming data over the last three decades revealed a significant increase in temperature along most of the studied coastline, averaging 0.214°C/decade. Importantly, the analysis of existing and extinct population samples clearly distinguished two genetically different groups, a northern and a southern clade. Because of the range contraction, the southern group is currently represented by very few extant populations. This southern edge range shift is thus causing the loss of a distinct component of the species genetic background. Conclusions We reveal a climate-correlated diversity loss below the species level, a process that could render the species more vulnerable to future environmental changes and affect its evolutionary potential. This is a remarkable case of genetic uniqueness of a vanishing cryptic genetic clade (southern clade).
  • Drifting fronds and drifting alleles: range dynamics, local dispersal and habitat isolation shape the population structure of the estuarine seaweed Fucus ceranoides
    Publication . Neiva, J.; Pearson, G. A.; Valero, Myriam; Serrão, Ester
    Aim: The seaweed Fucus ceranoides is restricted to spatially discrete estuarine habitats and lacks planktonic dispersal phases; it is therefore expected to exhibit strong population differentiation. Its cold-temperate affinities and mtDNA variation imply that the northern part of the species’ range, where F. ceranoides is now ubiquitous, was recently colonized after the onset of the last deglaciation, potentially resulting in areas with greater genetic homogeneity. Here we examine the population structure of F. ceranoides to test these predictions, emphasizing the contrasting genetic signatures of limited dispersal in refugial versus recently colonized regions. Location: North-eastern Atlantic estuaries from Portugal to Norway. Methods: A total of 504 individuals from 21 estuarine sites spanning the entire range of F. ceranoides were sampled and genotyped for nine microsatellite loci. Population structure was inferred from several genotypic and allele-frequency analyses. Geographical patterns of genetic diversity were used to reconstruct the historical biogeography of the species. Results: Genetic diversity and regional population differentiation showed a consistent decline with increasing latitude. Southernmost populations harboured most of the endemic variation, whereas the northern populations (> 55 N) were almost fixed for the same alleles across loci. In southern and central regions of its distribution, F. ceranoides showed striking population subdivision, with many of the sampled estuaries corresponding to coherent genetic units that were easily discriminated from one another with standard clustering methods. Main conclusions: The geographical pattern of genetic diversity supports the long-term refugial status of Iberia and a post-glacial range expansion of F. ceranoides into previously glaciated latitudes. Despite the species’ capacity to colonize newly available habitats, the genetic structure of F. ceranoides outside the recently (re)colonized range reveals that gene flow between populations is extremely low. This study provides a remarkable example of how infrequent and spatially limited dispersal can have contrasting effects at the scales of metapopulation (connectivity) versus range dynamics (habitat tracking), and of how dispersal restrictions can result in either genetic divergence or homogeneity depending on the maturity and demographic conditions of the populations.
  • Molecular characterization of the "Cottonii" form of fucus in the North-Eastern Pacific versus the Atlantic
    Publication . Serrão, Ester; Vliet, M. S.; Hansen, G. I.; Maggs, C. A.; Pearson, G. A.
    Along the west coast of North America, three species of Fucus are reported to occur: F. gardneri Silva, F. spiralis Linnaeus, and the controversial F. cottonii Wynne & Magne. Our study investigates the identity of F. cottonii in this area and compares it with isolates from the NortheasternAtlantic. The thalli from both areas vegetatively resemble one another, lacking midribs, and they occur in similar salt marsh habitats.