Emilio Rolán-Alvarez

University of Vigo | UVIGO · Department of Biochemistry, Genetics and Immunology

How colour polymorphisms are maintained in natural populations constitutes a key subject of study for evolutionary ecologists. One of the mechanisms that has been put forward to explain this phenomenon is negative frequency-dependent selection, which can be caused by different mechanisms. Among these mechanisms is mate choice, or the selection as a...

Speciation typically occurs in a time frame too long to be observed directly. This issue can be over-come by studying pairs of populations at different points in the speciation continuum, ideally within clades so that patterns are not confounded by differences among taxa. Such comparisons are possible in the marine snail Littorina saxatilis because...

The evolution and maintenance of color clines is a classic topic of research in evolutionary ecology. However, studies analyzing the temporal dynamics of such clines are much less frequent, due to the difficulty of obtaining reliable data about past color distributions along environmental gradients. In this paper, we describe a case of decades-long...

Uno de los atributos más característicos de al ciencia es el cambio: al menos una parte de las teorías e hipótesis aceptadas por la comunidad científica en un momento determinado son modificadas a medida que la investigación avanza y se acumulan nuevas evidencias. En este sentido, la biología evolutiva no es una excepción. Durante la última década,...

Thermal performance curves (TPCs) provide a powerful framework to assess the evolution of thermal sensitivity in populations exposed to divergent selection regimes across latitude. However, there is a lack of consensus regarding the extent to which physiological adjustments that compensate for latitudinal temperature variation (metabolic cold adapt...

Marine gastropods are characterized by an incredible variation in shell color. In this review, we aim to introduce researchers to previous studies of shell color polymorphism in this group of animals, trying to provide an overview of the topic and highlighting some potential avenues for future research. For this, we tackle the different aspects of...

In the last years, the interest in evolutionary divergence at small spatial scales has increased and so did the study of speciation caused by ecologically based divergent natural selection. The evolutionary interplay between gene flow and local adaptation can lead to low-dispersal locally adapted specialists. When this occurs, the evolutionary inte...

In the last years the interest on evolutionary divergence at small spatial scales has increased and so did the study of speciation caused by ecologically-based divergent natural selection. The evolutionary interplay between gene flow and local adaptation can lead to low-dispersal locally adapted specialists. When this occurs the evolutionary interp...

Colour polymorphism is a widespread phenomenon in natural populations of several species. In particular, it is especially common on marine gastropod species from the genus Littorina. Recently, it has been argued that intrapopulation shell colour polymorphism in Littorina fabalis could be caused by negative frequency-dependent sexual selection via a...

Thermal stress is a potentially important selective agent in intertidal marine habitats, but the role that thermal tolerance might play in local adaptation across shore height has been underexplored. Northwest Spain is home to two morphologically distinct ecotypes of the periwinkle Littorina saxatilis, separated by shore height and subject to subst...

Proteomic analysis was carried out on the Crab (upper-shore) and Wave (lower-shore) ecotypes of Littorina saxatilis from a hybrid zone at Silleiro Cape, Spain. Proteome profiles of individual snails were obtained. Protein expression in F1 hybrid snails bred in the laboratory and snails with intermediate shell phenotypes collected from the mid-shore...

Size-assortative mating and sexual selection on size are common across species. Since both may be a result of mate choice, mate choice based on size should also be a widespread process. This behaviour is, however, rarely studied directly and thus the biological causes that determine size-based mate choice are poorly understood. To address this, we...

The presence of shell bands is common in gastropods. Both the marine snails Littorina fabalis and Lttorina saxatilis are polymorphic for this trait. Such polymorphism would be expected to be lost by the action of genetic drift or directional selection, but it appears to be widespread at relatively constant frequencies. This suggests it is maintaine...

Colour polymorphism is a widespread phenomenon in natural populations of several species. In particular, it is especially common on marine gastropod species from the genus Littorina . Recently, it has been argued that intrapopulation shell colour polymorphism in Littorina fabalis could be caused by negative frequency-dependent sexual selection via...

Natural color polymorphisms are widespread across animal species and usually have a simple genetic basis. This makes them an ideal system to study the evolutionary mechanisms responsible for maintaining biodiversity. In some populations of the intertidal snail Littorina fabalis, variation in shell color has remained stable for years, but the mechan...

The theory of evolution is one of the greatest scientific achievements in the intellectual history of humankind, yet it is still contentious within certain social groups. Despite being as robust and evidence-based as any other notable scientific theory, some people show a strong reluctance to accept it. In this study, we used the Measure of Accepta...

Two sympatric ecotypes (‘crab’ and ‘wave’) of Littorina saxatilis are adapted to different microhabitats. It has been claimed, based on the comparison of proteomic differentiation across ontogeny, that the wave ecotype may have evolved by paedomorphosis from an ancestor more similar to the crab ecotype. Here, we test the paedomorphosis hypothesis a...

The intertidal snail Littorina saxatilis is well known for its remarkable variety of locally adapted populations. A unique L. saxatilis habitat is represented by the sheltered rocky environment found in the natural coastal lagoon of the Cíes Islands (NW Spain). The present-day characteristics of this habitat are relatively recent (~ 70–150 years),...

Traditionally it has been suggested that sexual selection can cause sexual size dimorphism (SSD). However, a recent review in gastropods shows that SSD itself can also cause sexual selection (Ng et al., 2019. Animal Behaviour, 148, 53–62). This may be the case if mate choice exists, with males preferring to mate with females similar in body size bu...

Wolbachia is an intracellular endosymbiont that can produce a range of effects on host fitness, but the temporal dynamics of Wolbachia strains have rarely been experimentally evaluated. We compare interannual strain frequencies along a geographical region for understanding the forces that shape Wolbachia strain frequency in natural populations of i...

The rough periwinkle Littorina saxatilis is characterised for showing shell phenotypic variation associated to environmental clines and this is found in parallel across shores. In order to disentangle the additive genetic effects and the environmental factors involved in this variation, we analysed natural populations subjected to a gradient in wav...

Sexual size dimorphism is widespread among dioecious species, but its underlying driving forces are often complex. A review of sexual size dimorphism in marine gastropods revealed two common patterns: first, sexual size dimorphism, with females being larger than males, and, second, females being larger than males in mating pairs. Both patterns sugg...

Mate choice is a key life history trait and has been widely examined across animal taxa, yet the spatial scale at which animals exercise this choice has rarely been examined. Here we propose a novel method to estimate the spatial scale of mate choice in situ based on a recently developed experimental approach to evaluate, in an unbiased fashion, as...

Abstract Natural selection often produces parallel phenotypic changes in response to a similar adaptive challenge. However, the extent to which parallel gene expression differences and genomic divergence underlie parallel phenotypic traits and whether they are decoupled or not remains largely unexplored. We performed a population genomic study of p...

Periwinkles of the family Littorinidae (Children, 1834) are common members of seashore littoral communities worldwide. Although the family is composed of more than 200 species belonging to 18 genera, chromosome numbers have been described in only eleven of them. A molecular cytogenetic analysis of nine periwinkle species, the rough periwinkles Litt...

Mating preference can evolve as a side effect of ecological adaptation and simultaneously contribute to speciation in certain scenarios. However, theoretical predictions have been difficult to test experimentally because there has not been any simple way to relate empirical and theoretical parameters. Recently, it has been shown that the r coeffici...

Mating preference can be a driver of sexual selection and assortative mating and is, therefore, a key element in evolutionary dynamics. Positive mating preference by similarity is the tendency for the choosy individual to select a mate which possesses a similar variant of a trait. Such preference can be modelled using Gaussian-like mathematical fun...

Rocky intertidal organisms are commonly exposed to environmental gradients, promoting adaptations to these conditions. Emersion time varies along the intertidal range and in the supralittoral zone is frequently larger than a single tidal cycle, even lasting for weeks. The planktonic-dispersing gastropod Melarhaphe neritoides is a common species of...

The intertidal snail Littorina saxatilis has repeatedly evolved two parallel ecotypes assumed to be wave adapted and predatory shore crab adapted, but the magnitude and targets of predator‐driven selection are unknown. In Spain, a small, wave ecotype with a large aperture from the lower shore and a large, thick‐shelled crab ecotype from the upper s...

The marine snail Littorina saxatilis exhibits extreme morphological variation between and within geographical regions and represents an excellent model for assessing local adaptation. Previous studies support the hypothesis of parallel evolution in sympatry of two morphologically different ecotypes (named as RB and SU) that co-inhabit different hab...

Relationships between Galician and North Atlantic L. saxatilis snails. (a) Statistical parsimony network for North Atlantic populations of L. saxatilis. Data include Galician and 32 additional populations (from western, central and eastern North Atlantic) using a much smaller mtDNA fragment. Grey indicates L. arcana; black indicates L. compressa. H...

Summary of the mtDNA diversity in Galician L. saxatilis. Estimates of mtDNA nucleotide variation for each ecotype and locality of Galician L. saxatilis (PDF)

Assortative mating in the wild is commonly estimated by correlating between traits in mating pairs (e.g. the size of males and females). Unfortunately, such an approach may suffer from considerable sampling bias when the distribution of different expressions of a trait in the wild is nonrandom (e.g. when segregation of different size classes of ind...

We present a detailed review of 269 published studies using Littorina species in the field of evolutionary ecology during the last 18 years. We first identify the reasons for the special place of the genus Littorina in the field: its horizontal and vertical distribution along the steep environmental gradients that comprise the intertidal zone, its...

The mode in which sexual organisms choose mates is a key evolutionary process, as it can have a profound impact on fitness and speciation. One way to study mate choice in the wild is by measuring trait correlation between mates. Positive assortative mating is inferred when individuals of a mating pair display traits that are more similar than those...

We present a detailed review of 269 published studies using Littorina species in the eld of evolutionary ecology during the last 18 years. We rst identify the reasons for the special place of the genus Littorina in the eld: its horizontal and vertical distribution along the steep environmental gradients that comprise the intertidal zone, its within...

Simulating the evolution of reproductive isolation under sympatric speciation scenarios is a complex process that requires modelling several phases, including evolution of phenotypes, demography, migration, fitness components and mating preference. The last has been shown to be a key parameter in several simulation studies, allowing the incorporati...

In small organisms where gene expression analyses are accomplished on whole specimens rather than individual tissues, the differences observed in gene expression levels between groups of samples are assumed to be caused by regulatory differences in gene expression within tissues. An alternative explanation is the lack of homogeneity distribution of...

Unravelling the form of selection acting on hybrids of ecotypes undergoing ecological speciation is essential to understand the mechanisms behind the evolution of reproductive isolation in the face of gene flow. Shell phenotype is known to be affected by natural selection and is involved in the fitness of the marine snail Littorina saxatilis. Here,...

Haplotype networks derived from mtDNA and nuclear sequence data.

Logistic regressions for model validation.

Primers and annealing temperatures.

Summary statistics for all datasets, as used in the ABC analyses.

Parameter estimates from the ABC models.

Posterior quantile analyses used in model checking.

Parallel evolution of similar phenotypes provides strong evidence for the operation of natural selection. Where these phenotypes contribute to reproductive isolation, they further support a role for divergent, habitat-associated selection in speciation. However, the observation of pairs of divergent ecotypes currently occupying contrasting habitats...

Unravelling the form of selection acting on hybrids of ecotypes undergoing ecological speciation is essential to understand the mechanisms behind the evolution of reproductive isolation in the face of gene flow. Shell phenotype is known to be affected by natural selection and is involved in the fitness of the marine snail Littorina saxatilis. Here,...

The role of post-zygotic isolation in nonallopatric ecological speciation is still mostly unknown and information on the nature and strength of these barriers in well-known speciation models is essential for a deeper understanding of such processes. The Galician ecotypes of the marine snail Littorina saxatilis represent one of the best studied case...

Hybrid zones of ecologically divergent populations are ideal systems to study the interaction between natural selection and gene flow during the initial stages of speciation. Here, we perform an amplified fragment length polymorphism (AFLP) genome scan in parallel hybrid zones between divergent ecotypes of the marine snail Littorina saxatilis, whic...

The intertidal zone represents an interesting model system to study adaptation because several ecological factors change abruptly across this area, causing strong divergent selective pressures on a scale of meters. On the Galician shore (NW Spain), 3 species (Littorina saxatilis, Nucella lapillus and Melarhaphe neritoides) show similar adaptation t...

The exposed and sheltered ecotypes of the marine snail Littorina saxatilis from European rocky shores are considered a key model system to study adaptation and ecological speciation. Previous studies showed that two ecotypes (RB and SU) of this species in NW Spain have adapted differently to different shore levels and microhabitats. In order to und...

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 lo...

In the marine gastropod Littorina saxatilis differences in relative shell apertural form between two ecotypes from NW Spain have been associated with an environmental cline related to the degree of wave exposure. Such differences have been claimed to have a strong genetic basis, with little influence of phenotypic plasticity. However, dietary chang...

The study of the proteome (proteomics), which includes the dynamics of protein expression, regulation, interactions and its function, has played a less prominent role in evolutionary and ecological investigations in comparison with the study of the genome and transcriptome. There are, however, a number of arguments suggesting that this situation sh...

Two sympatric and divergent adaptive ecotypes of Littorina saxatilis (RB and SU) are known to hybridize showing partial premating isolation in the wild. Previous studies have revealed that morphological intermediate forms (presumably hybrids) present fitness (viability, sexual selection and fecundity) similar to that from pure ecotypes at the mid-s...

Intertidal species inhabiting Galician rocky shores are exposed to a strong vertical gradient in environmental and ecological conditions. Such a gradient is determined by a combination of wave action (impacting the low shore in particular) as well as heat, osmotic stress and predation (impacting the high shore in particular). In this area, 2 conver...

In the past 40 years, there has been increasing acceptance that variation in levels of gene expression represents a major source of evolutionary novelty. Gene expression divergence is therefore likely to be involved in the emergence of incipient species, namely, in a context of adaptive radiation. In this study, a genome-wide expression profiling a...

We carried out a simulation study to compare the efficiency of three alternative programs (DFDIST, DETSELD and BAYESCAN) to detect loci under directional selection from genome-wide scans using dominant markers. We also evaluated the efficiency of correcting for multiple testing those methods that use a classical probability approach. Under a wide r...

Distinct ecotypes of the snail Littorina saxatilis, each linked to a specific shore microhabitat, form a mosaic-like pattern with narrow hybrid zones in between, over which gene flow is 10-30% of within-ecotype gene flow. Multi-locus comparisons cluster populations by geographic affinity independent of ecotype, while loci under selection group popu...

The role of phenotypic plasticity is increasingly being recognized in the field of evolutionary studies. In this paper we look at the role of genetic determination versus plastic response by comparing the protein expression profiles between two sympatric ecotypes adapted to different shore levels and habitats using two-dimensional protein maps. We...

A variant of the cDNA-AFLP method coupled to an automated sequencer was used to quantify transcripts differentially expressed between sexes of the marine snail Littorina saxatilis. First, we conducted a validation study of the technique using known concentrations of a commercial marker. Second, we analysed six replicates of males and females from a...

Natural selection can play an important role in the maintenance of genetic polymorphisms, despite ongoing gene flow. In the present study, we use previously analysed allozymic loci and perform an FST outlier-based analysis to detect the signatures of divergent selection between sympatric ecotypes of the marine snail Littorina saxatilis at different...

Additional figures. Degree of conservativeness (Figure S1) and ROC analysis (Figure S2) for the same cases as in Figure 3.

Two ecotypes of Nucella lapillus can occur allopatrically or sympatrically, according to different degrees of wave exposure and microhabitats, on rocky shores of NW Spain. We studied differences in shell size and shape in adults and families of shelled embryos captured in the wild, and molecular variation at 9 microsatellite loci and 4 mtDNA region...

We studied the relative role of genetic determination versus plastic response for traits involved in ecological adaptation of two ecotypes of Littorina saxatilis living at different shore levels. To investigate the magnitude of the plastic response across ontogeny, we compared morphological data from individuals grown in the laboratory and taken fr...

The Galician sympatric ecotypes of Littorina saxatilis have been proposed as a model system for studying parallel ecological speciation. Such a model system makes a clear prediction: candidate loci (for divergent adaptation) should present a higher level of geographical differentiation than noncandidate (neutral) loci. We used 2356 amplified fragme...

The detection of true significant cases under multiple testing is becoming a fundamental issue when analyzing high-dimensional biological data. Unfortunately, known multitest adjustments reduce their statistical power as the number of tests increase. We propose a new multitest adjustment, based on a sequential goodness of fit metatest (SGoF), which...

Question: How can we establish the biological factors that contribute to variation in assortative mating (based on a quantitative or qualitative trait)? Key assumptions: Assortative (or disassortative) mating for a particular trait can produce sexual isolation between ecotypes or incipient species. The individual contribution to population assortat...

The proteomic changes occurring during speciation are fundamental to understand this process, though they have been rarely addressed until present. Therefore, we compared the proteome of two ecotypes (RB and SU) of the marine snail Littorina saxatilis, a case of sympatric incomplete speciation, originated as a byproduct of adaptation to distinct ha...

Littorina saxatilis is an ovoviviparous organism in which shelled embryos can be directly observed in nearly all mature females captured in the wild. This characteristic has been used a number of times as an indirect estimate for fecundity of natural populations. However, there is no experimental corroboration that the number of embryos within a fe...

Two ecotypes of a marine intertidal snail (Littorina saxatilis), living at different microhabitats and shore levels, have evolved in sympatry and in parallel across the Galician rocky shore. These ecotypes differ in many traits (including size) due to differential adaptation. They meet, mate assortatively, and partially hybridize at the mid shore w...

Shell polymorphisms are widespread among those intertidal gastropods that lack a pelagic spreading stage. These polymorphisms may indicate diversifying selection in a heterogeneous habitat, but to do this the variation must be at least pardy inherited. Galician populations of Littorina saxatilis (Olivi) living in exposed rocky shores are highly pol...

AFLP markers are becoming one of the most popular tools for genetic analysis in the fields of evolutionary genetics and ecology and conservation of genetic resources. The technique combines a high-information content and fidelity with the possibility of carrying out genomewide scans. However, a potential problem with this technique is the lack of h...

The geographical genetic structure of 7 populations of the intertidal marine snail Littorina saxatilis with limited dispersal was studied in NW Spain using 3 classes of genetic markers: 840 amplified fragment length polymorphism (AFLP) loci, 3 microsatellites, and 1 morphological trait (shell size). A sharp genetic division at Cape Finisterre, as e...

In November 2002, the sinking of the Prestige cargo ship produced an oil spill of 60,000 tons that affected many areas along the Galician coast (in the northwest of Spain). In a number of rocky shore sites, most organisms (particularly marine mollusks) were nearly extinct at a local scale. We tested whether the local bottleneck/extinction that occu...

Parallel speciation can occur when traits determining reproductive isolation evolve independently in different populations that experience a similar range of environments. However, a common problem in studies of parallel evolution is to distinguish this hypothesis from an alternative one in which different ecotypes arose only once in allopatry and...

We investigated variation in shell size and shape of marine snail species of the Littorina saxatilis complex ( L. saxatilis , L. compressa and L. arcana ) using geometric morphometric methods. These morphologically similar periwinkle species that are common in the European intertidal have presented many problems for diagnosis based on morphology al...

On exposed rocky shores in northwestern Spain there is a striking polymorphism of Littorina saxatilis that has been claimed as an example of a putative sympatric ecological speciation process. Two ecotypes of this species have evolved that are adapted to different shore levels and habitats, although they meet and hybridize on the mid shore where th...

Examination of the association between reproductive isolation and genetic divergence in a variety of organisms is essential for elucidating the mechanisms causing speciation. However, such studies are lacking for hermaphrodites. We measured premating (sexual) isolation in species pairs of the hermaphroditic land snail Albinaria and we compared it w...

Populations of the marine gastropod Littorina saxatilis from exposed rocky shores of NW Spain provide one of the few putative cases of sympatric ecological speciation. Two ecotypes with large differences in shell morphology and strong assortative mating are living at different vertical levels of the shore separated by a few meters. It has been hypo...

The dogwhelk Nucella lapillus is a predatory marine gastropod living on rocky shores in the North Atlantic. As with many other gastropod species, Nucella was affected by tributyltin (TBT) pollution during the 1970s and 1980s, and local populations underwent extinction. After a partial ban on TBT in the UK in 1987, vacant sites have been recolonized...

The program includes one file with two examples of input data for JMating. Example 1: This example represents wild mating data for three ecotypes (mating types) that meet and mate in a particular hybrid zone [12]. Example 2: This example is a laboratory multiple choice experiment between two Drosophila species (mating types) that can meet and hybri...

Many different sexual isolation and sexual selection statistics have been proposed in the past. However, there is no available software that implements all these statistical estimators and their corresponding tests for the study of mating behaviour. JMATING is an easy-to-use program developed in Java for the analysis of mating frequency data to stu...

Many studies of speciation rely critically on estimates of sexual isolation obtained in the laboratory. Here we examine the sensitivity of sexual isolation to alterations in experimental design and mating environment in two sister species of Drosophila, D. santomea and D. yakuba. We use a newly devised measure of mating frequencies that is able to...

Many studies of speciation rely critically on estimates of sexual isolation obtained in the laboratory. Here we examine the sensitivity of sexual isolation to alterations in experimental design and mating environment in two sister species of Drosophila, D. santomea and D. yakuba. We use a newly devised measure of mating frequencies that is able to...

Two sympatric snail ecotypes (RB and SU) of Littorina saxatilis from exposed rocky shores of NW Spain differ in many life history traits, but classical morphometric analysis has failed to reveal significant shell shape differences between them. We used geometric morphometric methods on landmark data from digitized shell images to study size and sha...

On the NW coast of Spain, there is a hybrid zone in natural populations of L. saxatilis, where the largest ecotype is adapted to the desiccation and heat stress of the upper shore, whereas the smaller one is adapted to the wave impacts of the lower shore. The two ecotypes meet and hybridise in a mid-shore area producing intermediate individuals or...