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Glacial History of the North Atlantic Marine Snail, Littorina saxatilis, Inferred from Distribution of Mitochondrial DNA Lineages  [PDF]
Marina Panova,April M. H. Blakeslee,A. Whitman Miller,Tuuli M?kinen,Gregory M. Ruiz,Kerstin Johannesson,Carl André
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0017511
Abstract: The North Atlantic intertidal gastropod, Littorina saxatilis (Olivi, 1792), exhibits extreme morphological variation between and within geographic regions and has become a model for studies of local adaptation; yet a comprehensive analysis of the species' phylogeography is lacking. Here, we examine phylogeographic patterns of the species' populations in the North Atlantic and one remote Mediterranean population using sequence variation in a fragment of the mitochondrial cytochrome b gene (607 bp). We found that, as opposed to many other rocky intertidal species, L. saxatilis has likely had a long and continuous history in the Northwest Atlantic, including survival during the last glacial maximum (LGM), possibly in two refugia. In the Northeast Atlantic, several areas likely harboured refugial populations that recolonized different parts of this region after glacial retreat, resulting in strong population structure. However, the outlying monomorphic Venetian population is likely a recent anthropogenic introduction from northern Europe and not a remnant of an earlier wider distribution in the Mediterranean Sea. Overall, our detailed phylogeography of L. saxatilis adds an important piece to the understanding of Pleistocene history in North Atlantic marine biota as well as being the first study to describe the species' evolutionary history in its natural range. The latter contribution is noteworthy because the snail has recently become an important model species for understanding evolutionary processes of speciation; thus our work provides integral information for such endeavours.
Insights into the role of differential gene expression on the ecological adaptation of the snail Littorina saxatilis
Mónica Martínez-Fernández, Louis Bernatchez, Emilio Rolán-Alvarez, Humberto Quesada
BMC Evolutionary Biology , 2010, DOI: 10.1186/1471-2148-10-356
Abstract: Among the 99 transcripts shared between ecotypes, 12.12% showed significant differential expression. At least 4% of these transcripts still displayed significant differences after correction for multiple tests, highlighting that gene expression can differ considerably between subpopulations adapted to alternative habitats in the face of gene flow. One of the transcripts identified was Cytochrome c Oxidase subunit I (COI). In addition, 6 possible reference genes were validated to normalize and confirm this result using qPCR. α-Tubulin and histone H3.3 showed the more stable expression levels, being therefore chosen as the best option for normalization. The qPCR analysis confirmed a higher COI expression in SU individuals.At least 4% of the transcriptome studied is being differentially expressed between ecotypes living in alternative habitats, even when gene flow is still substantial between ecotypes. We could identify a candidate transcript of such ecotype differentiation: Cytochrome c Oxidase Subunit I (COI), a mitochondrial gene involved in energy metabolism. Quantitative PCR was used to confirm the differences found in COI and its over-expression in the SU ecotype. Interestingly, COI is involved in the oxidative phosphorylation, suggesting an enhanced mitochondrial gene expression (or increased number of mitochondria) to improve energy supply in the ecotype subjected to the strongest wave action.Unravelling processes that underlie population divergence is a crucial step towards elucidating the origin and maintenance of biodiversity [1], and towards understanding the genetic basis of speciation, which is one of the most fundamental goals in evolutionary genetics [2]. However, there is still much to be learned about how divergent populations adapt to different environments under the effect of natural selection, which ultimately may evolve into biological species [3]. The new "omics" technologies, despite being very young, can contribute to this since they have taken
Population differences in susceptibility to stress in Littorina saxatilis from metal contaminated and uncontaminated sites in the Isle of Man
DAKA Erema Ransome,
DAKA
,Erema,Ransome

环境科学学报(英文版) , 2006,
Abstract: The population of the intertidal gastropod Littorina saxatilis from Laxey estuary in the Isle of Man is exposed to mine-related contamination of Zn (and is tolerant to Zn and Pb) compared to those of Castletown, Derbyhaven, Peel and Ramsey.Toleranc
Habitat Choice and Speciation  [PDF]
Sophie E. Webster,Juan Galindo,John W. Grahame,Roger K. Butlin
International Journal of Ecology , 2012, DOI: 10.1155/2012/154686
Abstract: The role of habitat choice in reproductive isolation and ecological speciation has often been overlooked, despite acknowledgement of its ability to facilitate local adaptation. It can form part of the speciation process through various evolutionary mechanisms, yet where habitat choice has been included in models of ecological speciation little thought has been given to these underlying mechanisms. Here, we propose and describe three independent criteria underlying ten different evolutionary scenarios in which habitat choice may promote or maintain local adaptation. The scenarios are the result of all possible combinations of the independent criteria, providing a conceptual framework in which to discuss examples which illustrate each scenario. These examples show that the different roles of habitat choice in ecological speciation have rarely been effectively distinguished. Making such distinctions is an important challenge for the future, allowing better experimental design, stronger inferences and more meaningful comparisons among systems. We show some of the practical difficulties involved by reviewing the current evidence for the role of habitat choice in local adaptation and reproductive isolation in the intertidal gastropod Littorina saxatilis, a model system for the study of ecological speciation, assessing whether any of the proposed scenarios can be reliably distinguished, given current research.
Habitat Choice and Speciation  [PDF]
Sophie E. Webster,Juan Galindo,John W. Grahame,Roger K. Butlin
International Journal of Ecology , 2012, DOI: 10.1155/2012/154686
Abstract: The role of habitat choice in reproductive isolation and ecological speciation has often been overlooked, despite acknowledgement of its ability to facilitate local adaptation. It can form part of the speciation process through various evolutionary mechanisms, yet where habitat choice has been included in models of ecological speciation little thought has been given to these underlying mechanisms. Here, we propose and describe three independent criteria underlying ten different evolutionary scenarios in which habitat choice may promote or maintain local adaptation. The scenarios are the result of all possible combinations of the independent criteria, providing a conceptual framework in which to discuss examples which illustrate each scenario. These examples show that the different roles of habitat choice in ecological speciation have rarely been effectively distinguished. Making such distinctions is an important challenge for the future, allowing better experimental design, stronger inferences and more meaningful comparisons among systems. We show some of the practical difficulties involved by reviewing the current evidence for the role of habitat choice in local adaptation and reproductive isolation in the intertidal gastropod Littorina saxatilis, a model system for the study of ecological speciation, assessing whether any of the proposed scenarios can be reliably distinguished, given current research. 1. Introduction The role of divergent natural selection in speciation has been widely studied in recent years [1]. There is now broad acceptance that selection of this type can lead to the evolution of reproductive isolation, even in the face of gene flow [2]. Nevertheless, significant controversy remains. Is “ecological speciation” really distinct from other modes of speciation [3]? Why does reproductive isolation remain incomplete in some cases but not in others [4]? Do chromosomal re-arrangements [5] or divergence hitchhiking [6] help to overcome the antagonism between selection and recombination? What is the role of the so-called “magic traits” [7]? “Habitat isolation” is one part of the ecological barrier to gene exchange between species that includes effects due to local adaptation, competition, and choice [8]. In this paper, we will focus our attention on habitat choice, discussing the nature of its role in ecological speciation and the potential contribution towards reproductive isolation of various forms of habitat choice. We define habitat choice as any behaviour that causes an individual to spend more time in one habitat type than another
Can sexual selection and disassortative mating contribute to the maintenance of a shell color polymorphism in an intertidal marine snail?  [cached]
E. ROLáN-ALVAREZ, M.SAURA, A. P. DIZ, M. J. RIVAS, M. ALVAREZ, B. Cortés, A. de COO, D. ESTéVEZ, L. IGLESIAS
Current Zoology , 2012,
Abstract: Littorina fabalis is an intertidal snail commonly living on the brown algae Fucus vesiculosus and showing frequent shell-color polymorphisms in the wild. The evolutionary mechanism underlying this polymorphism is currently unknown. Shell color variation was studied in mated and non-mated specimens of this species from different microareas in one locality from NW Spain, in order to estimate sexual selection and assortative mating that may (still) be operating in this population. The analyses across microareas allowed us to investigate frequency-dependent selection and assortative mating components, mechanisms that could maintain the polymorphism. The presence of shell scars caused by crab attacks, an environmental variable not related with sexual selection or assortative mating, was used as experimental control. This study provides new evidence of significant disassortative mating and some degree of sexual selection against some shell colors, supporting the results found 21 years ago in a similar study, i.e. in the same species and locality. The similarity of these estimates during the studied period suggests that this experimental approach is consistent and valid to be extended to other populations and organisms. In addition, sexual selection and assortative mating estimates did not change across microareas differing in shell color frequencies, suggesting than the polymorphism can not be maintained by a frequency-dependent (sexual selection-based) mechanism. Our main hypothesis is that negative assortative mating could contribute to the maintenance of the polymorphism, perhaps by males showing distinct female color preferences when searching for mates [Current Zoology 58 (3): 460–471, 2012].
Radiating on Oceanic Islands: Patterns and Processes of Speciation in the Land Snail Genus Theba (Risso 1826)  [PDF]
Carola Greve, France Gimnich, Rainer Hutterer, Bernhard Misof, Martin Haase
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0034339
Abstract: Island radiations have played a major role in shaping our current understanding of allopatric, sympatric and parapatric speciation. However, the fact that species divergence correlates with island size emphasizes the importance of geographic isolation (allopatry) in speciation. Based on molecular and morphological data, we investigated the diversification of the land snail genus Theba on the two Canary Islands of Lanzarote and Fuerteventura. Due to the geological history of both islands, this study system provides ideal conditions to investigate the interplay of biogeography, dispersal ability and differentiation in generating species diversity. Our analyses demonstrated extensive cryptic diversification of Theba on these islands, probably driven mainly by non-adaptive allopatric differentiation and secondary gene flow. In a few cases, we observed a complete absence of gene flow among sympatrically distributed forms suggesting an advanced stage of speciation. On the Jandía peninsula genome scans suggested genotype-environment associations and potentially adaptive diversification of two closely related Theba species to different ecological environments. We found support for the idea that genetic differentiation was enhanced by divergent selection in different environments. The diversification of Theba on both islands is therefore best explained by a mixture of non-adaptive and adaptive speciation, promoted by ecological and geomorphological factors.
Stable Suppression of Lactate Dehydrogenase Activity during Anoxia in the Foot Muscle of Littorina littorea and the Potential Role of Acetylation as a Novel Posttranslational Regulatory Mechanism  [PDF]
Ali Shahriari,Neal J. Dawson,Ryan A. V. Bell,Kenneth B. Storey
Enzyme Research , 2013, DOI: 10.1155/2013/461374
Abstract: The intertidal marine snail, Littorina littorea, has evolved to withstand extended bouts of oxygen deprivation brought about by changing tides or other potentially harmful environmental conditions. Survival is dependent on a strong suppression of its metabolic rate and a drastic reorganization of its cellular biochemistry in order to maintain energy balance under fixed fuel reserves. Lactate dehydrogenase (LDH) is a crucial enzyme of anaerobic metabolism as it is typically responsible for the regeneration of NAD+, which allows for the continued functioning of glycolysis in the absence of oxygen. This study compared the kinetic and structural characteristics of the D-lactate specific LDH (E.C. 1.1.1.28) from foot muscle of aerobic control versus 24?h anoxia-exposed L. littorea. Anoxic LDH displayed a near 50% decrease in (pyruvate-reducing direction) as compared to control LDH. These kinetic differences suggest that there may be a stable modification and regulation of LDH during anoxia, and indeed, subsequent dot-blot analyses identified anoxic LDH as being significantly less acetylated than the corresponding control enzyme. Therefore, acetylation may be the regulatory mechanism that is responsible for the suppression of LDH activity during anoxia, which could allow for the production of alternative glycolytic end products that in turn would increase the ATP yield under fixed fuel reserves. 1. Introduction Lactate dehydrogenase catalyzes the reversible conversion of pyruvate to lactate, with the concomitant oxidation of NADH to NAD+. Under anaerobic conditions, LDH becomes an important enzyme due to its ability to regenerate NAD+ and allows for continued carbon flow through the glycolytic pathway to support anaerobic ATP synthesis [1]. This process can be especially important in those organisms that are exposed to hypoxic or anoxic conditions for extended periods of time and require energy balance to be maintained solely through the functioning of glycolysis. Littorina littorea are marine molluscs that are native to the intertidal zones of the Atlantic coast of Europe (from Scandinavia to Spain) and have been introduced to the east coast of North America as well as several other locations around the world. Changing tides frequently expose these gill-breathing snails to prolonged oxygen deprivation at low tide [2]. Moreover, environmental conditions, such as high salinity, predation, or water pollutants can cause the snails to shut their shell openings, which over an extended period of time can also generate an anoxic exposure [3, 4]. In order to survive
The evolution of reproductive isolation in a simultaneous hermaphrodite, the freshwater snail Physa
Robert T Dillon, Amy R Wethington, Charles Lydeard
BMC Evolutionary Biology , 2011, DOI: 10.1186/1471-2148-11-144
Abstract: Here we report the results of no-choice mating experiments yielding no evidence of hybridization between gyrina and any of four other populations (pomilia, carolinae, Philadelphia acuta, or Charleston acuta), nor between pomilia and carolinae. Crosses between pomilia and both acuta populations yielded sterile F1 progeny with reduced viability, while crosses between carolinae and both acuta populations yielded sterile F1 hybrids of normal viability. A set of mate-choice tests also revealed significant sexual isolation between gyrina and all four of our other Physa populations, between pomilia and carolinae, and between pomilia and Charleston acuta, but not between pomilia and the acuta population from Philadelphia, nor between carolinae and either acuta population. These observations are consistent with the origin of hybrid sterility prior to hybrid inviability, and a hypothesis that speciation between pomilia and acuta may have been reinforced by selection for prezygotic reproductive isolation in sympatry.We propose a two-factor model for the evolution of postzygotic reproductive incompatibility in this set of five Physa populations consistent with the Dobzhansky-Muller model of speciation, and a second two-factor model for the evolution of sexual incompatibility. Under these models, species trees may be said to correspond with gene trees in American populations of the freshwater snail, Physa.Although the evolution of reproductive isolation has been a focus of intense interest since the birth of the Modern Synthesis, its quantification is often not a trivial exercise. Among animal taxa, most research effort has focused on Drosophila [1,2], birds [3,4], amphibians [5,6], and fish [7,8]. In gastropod mollusks, the mechanisms of reproductive isolation have been elucidated only in the marine prosobranch snail Littorina [9,10], opisthobranch sea slugs [11], certain terrestrial (stylommatophoran) pulmonates [12,13], and in the freshwater (basommatophoran) pulmonates that
Glucose-6-phosphate dehydrogenase regulation in the hepatopancreas of the anoxia-tolerant marine mollusc, Littorina littorea  [PDF]
Judeh L. Lama,Ryan A.V. Bell,Kenneth B. Storey
PeerJ , 2013, DOI: 10.7717/peerj.21
Abstract: Glucose-6-phosphate dehydrogenase (G6PDH) gates flux through the pentose phosphate pathway and is key to cellular antioxidant defense due to its role in producing NADPH. Good antioxidant defenses are crucial for anoxia-tolerant organisms that experience wide variations in oxygen availability. The marine mollusc, Littorina littorea, is an intertidal snail that experiences daily bouts of anoxia/hypoxia with the tide cycle and shows multiple metabolic and enzymatic adaptations that support anaerobiosis. This study investigated the kinetic, physical and regulatory properties of G6PDH from hepatopancreas of L. littorea to determine if the enzyme is differentially regulated in response to anoxia, thereby providing altered pentose phosphate pathway functionality under oxygen stress conditions. Several kinetic properties of G6PDH differed significantly between aerobic and 24 h anoxic conditions; compared with the aerobic state, anoxic G6PDH (assayed at pH 8) showed a 38% decrease in Km G6P and enhanced inhibition by urea, whereas in pH 6 assays Km NADP and maximal activity changed significantly between the two states. The mechanism underlying anoxia-responsive changes in enzyme properties proved to be a change in the phosphorylation state of G6PDH. This was documented with immunoblotting using an anti-phosphoserine antibody, in vitro incubations that stimulated endogenous protein kinases versus protein phosphatases and significantly changed Km G6P, and phosphorylation of the enzyme with 32P-ATP. All these data indicated that the aerobic and anoxic forms of G6PDH were the high and low phosphate forms, respectively, and that phosphorylation state was modulated in response to selected endogenous protein kinases (PKA or PKG) and protein phosphatases (PP1 or PP2C). Anoxia-induced changes in the phosphorylation state of G6PDH may facilitate sustained or increased production of NADPH to enhance antioxidant defense during long term anaerobiosis and/or during the transition back to aerobic conditions when the reintroduction of oxygen causes a rapid increase in oxidative stress.
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