ISTA | Evolution in Real Time
The normal response of creationists to this sort of observation is a desperate attempt to redefine evolution as something other than the scientific one of change in allele frequency over time in a population to one of their cult's childish parodies - cats turning into dogs; monkeys having human babies, etc.; or bleating forlornly about 'Macro- evolution'.
The fact remain, however, that science isn't going to change its definition to suit creationists so they can continue to misrepresent it to their credulous dupes.
Evolution happens, has been observed happening, and happens just as the Theory of Evolution predicts - in response to environmental change as environmental selectors favour some variants or combinations of variants over others, causing sorting of alleles in the population according to their differential ability to be passed down the generations into descendants.
What do you know about the marine snail, Littorina saxatilis? Littorina saxatilis, also known as the rough periwinkle, is a marine snail commonly found along rocky shores in the intertidal zone of the North Atlantic. It is well-known for its ability to withstand varying environmental conditions such as changes in salinity, temperature, and wave exposure.The Austrian-led team chose the marine snail, Littorina saxatilis as the subject of their study, starting with a distinct population which they reintroduce following the extermination of a local population by a toxic algal bloom 30 years ago. This species of snail is already known for forming local ecotypes according to local conditions and these ecotypes show signs of speciating as the establish barriers to gene flow between them.
This species is highly studied due to its remarkable phenotypic plasticity and local adaptation. Littorina saxatilis exhibits distinct ecotypes that have adapted to different microhabitats within the same shore, such as high-shore, wave-exposed regions and low-shore, sheltered areas. These ecotypes differ in shell shape and thickness, which help them survive in their respective environments—thicker shells for wave-exposed regions and lighter shells for low-energy environments.
The species is also of interest for studying reproductive isolation and the early stages of speciation, as the different ecotypes often show barriers to gene flow despite living in close proximity.
Are you interested in specific aspects of Littorina saxatilis, like its ecology or evolutionary biology?
Yes, please, both.
Ecology of Littorina saxatilis:
- Habitat and Distribution: Littorina saxatilis primarily inhabits rocky shores along the Atlantic coasts of Europe and North America. It can be found from the upper to mid-intertidal zones, enduring a wide range of environmental factors such as desiccation, salinity fluctuations, and temperature extremes during tidal changes.
- Feeding: It feeds mainly on algae, including biofilms and diatoms that grow on rock surfaces. This grazing behavior plays an important role in controlling algal growth in the intertidal zone and contributes to the overall ecology of these shorelines.
- Predators and Defenses: The snail is preyed upon by crabs, fish, and seabirds. To counter predation, Littorina saxatilis exhibits adaptations such as thicker, more robust shells in areas with high crab predation. Its ability to tightly clamp down on rocks and resist being dislodged by waves or predators is another key adaptation.
- Tolerance to Harsh Conditions: The species has a broad tolerance to environmental stressors. In the upper intertidal zones, Littorina saxatilis faces extended periods of air exposure, leading to dehydration risks, while in the lower zones, it copes with greater wave action. Its ability to adapt to these extremes has made it a highly successful organism in fluctuating coastal environments.
Evolutionary Biology of Littorina saxatilis:
- Ecotypes and Local Adaptation: One of the most remarkable aspects of Littorina saxatilis is its development of distinct ecotypes that have adapted to specific microhabitats within the same shore. These ecotypes show significant differences in shell morphology:
- High-shore ecotypes: Found in wave-exposed zones. These snails tend to have thicker, more robust shells to prevent being crushed by waves or predators like crabs.
- Low-shore ecotypes: Found in sheltered, less exposed zones. These snails have thinner shells, allowing them to move more easily and conserve energy in less turbulent environments.
- Reproductive Isolation and Speciation: Despite living in close proximity, the different ecotypes show some degree of reproductive isolation. This has made Littorina saxatilis a key species in the study of speciation. There is ongoing research into how genetic differentiation between ecotypes might lead to the evolution of new species over time. Some populations show partial reproductive barriers due to assortative mating, ecological selection, and hybrid zones.
- Hybridization and Gene Flow: Although ecotypes can interbreed, the offspring may have lower fitness, leading to reduced gene flow between ecotypes. This makes Littorina saxatilis an excellent model for studying the early stages of speciation, where populations are beginning to diverge but have not yet become fully reproductively isolated.
- Evolutionary Forces: Natural selection, particularly driven by predation pressure, wave exposure, and environmental extremes, plays a significant role in the differentiation of these ecotypes. Genetic studies show that selection can be strong enough to maintain these differences despite ongoing gene flow between the ecotypes.
Together, these ecological and evolutionary traits make Littorina saxatilis a fascinating model organism for studying adaptation, speciation, and the effects of environmental heterogeneity on evolution. Would you like to explore any of these topics in more detail?
The scientists have just published the results of their study, open access in the journal Science Advances, and explained its significance in an ISAT press release:
ISTA scientists predict—and witness—evolution in a 30-year marine snail experiment
Snails on a tiny rocky islet evolved before scientists’ eyes. The marine snails were reintroduced after a toxic algal bloom wiped them out from the skerry. While the researchers intentionally brought in a distinct population of the same snail species, these evolved to strikingly resemble the population lost over 30 years prior. The study, led by researchers from the Institute of Science and Technology Austria (ISTA) and the Norwegian Nord University, is published in Science Advances.
It is 1988. The Koster archipelago, a group of islands off the Swedish west coast near the border with Norway, is hit by a particularly dense bloom of toxic algae, wiping out marine snail populations. But why would anyone care about the fate of a bunch of snails on a three-square-meter rock in the open sea? As it turns out, this event would open up the opportunity to predict and see evolution unfolding before our eyes. Before, the islands and their small intertidal skerries—rocky islets—were home to dense and diverse populations of marine snails of the species Littorina saxatilis. While the snail populations of the larger islands—some of which were reduced to less than 1%—were restored within two to four years, several skerries could not seem to recover from this harsh blow.
From the shore to the little black dot in the sea.
The donor shore of the transplanted snail population (foreground) and the experimental skerry (little dot in the sea to the right).© Kerstin Johannesson
Marine ecologist Kerstin Johannesson from the University of Gothenburg, Sweden, saw a unique opportunity. In 1992, she re-introduced L. saxatilis snails to their lost skerry habitat—starting an experiment that would have far-reaching implications more than 30 years later. It allowed an international collaboration led by researchers from the Institute of Science and Technology Austria (ISTA), Nord University, Norway, the University of Gothenburg, Sweden, and The University of Sheffield, UK, to predict and witness evolution in the making.
Kerstin Johannesson on the experimental skerry.
Johannesson is a marine ecologist at the University of Gothenburg, Sweden.© Bo Johannesson
Wave snails and Crab snails
L. saxatilis is a common species of marine snails found throughout the North Atlantic shores, where different populations evolved traits adapted to their environments. These traits include size, shell shape, shell color, and behavior. The differences among these traits are particularly striking between the so-called Crab- and Wave-ecotype. These snails have evolved repeatedly in different locations, either in environments exposed to crab predation or on wave-exposed rocks away from crabs. Wave snails are typically small, and have a thin shell with specific colors and patterns, a large and rounded aperture, and bold behavior. Crab snails, on the other hand, are strikingly larger, have thicker shells without patterns, and a smaller and more elongated aperture. Crab snails also behave more warily in their predator-dominated environment.
The Swedish Koster archipelago is home to these two different L. saxatilis snail types, often neighboring one another on the same island or only separated by a few hundred meters across the sea. Before the toxic algal bloom of 1988, Wave snails inhabited the skerries, while nearby shores were home to both Crab and Wave snails. This close spatial proximity would prove crucial.
Rediscovering old traits
Seeing that the Wave snail population of the skerries was entirely wiped out due to the toxic algae, Johannesson decided in 1992 to reintroduce snails to one of these skerries, but of the Crab-ecotype. With one to two generations each year, she rightfully expected the Crab snails to adapt to their new environment before scientists’ eyes.
Our colleagues saw evidence of the snails’ adaptation already within the first decade of the experiment. Over the experiment’s 30 years, we were able to predict robustly what the snails will look like and which genetic regions will be implicated. The transformation was both rapid and dramatic.
Diego Garcia Castillo, lead author
Institute of Science and Technology Austria (ISTA)
Klosterneuburg, Austria.
However, the snails did not evolve these traits entirely from scratch.
Some of the genetic diversity was already available in the starting Crab population but at low prevalence. This is because the species had experienced similar conditions in the recent past. The snails’ access to a large gene pool drove this rapid evolution.
Anja Marie Westram, co-corresponding author
Institute of Science and Technology Austria (ISTA)
Klosterneuburg, Austria.
And Department of Marine Sciences
Tjärnö Marine Laboratory
University of Gothenburg, Strömstad, Sweden.
Diversity is key to adaptation
The team examined three aspects over the years of the experiment: the snails’ phenotype, individual gene variabilities, and larger genetic changes affecting entire regions of the chromosomes called “chromosomal inversions”.
In the first few generations, the researchers witnessed an interesting phenomenon called “phenotypic plasticity”: Very soon after their transplantation, the snails modified their shape to adjust to their new environment. But the population also quickly started to change genetically. The researchers could predict the extent and direction of the genetic changes, especially for the chromosomal inversions. They showed that the snails’ rapid and dramatic transformation was possibly due to two complementary processes: A fast selection of traits already present at a low frequency in the transplanted Crab snail population and gene flow from neighboring Wave snails that could have simply rafted over 160 meters to reach the skerry.
Evolution in the face of pollution and climate change
In theory, scientists know that a species with high enough genetic variation can adapt more rapidly to change. However, few studies aimed to experiment with evolution over time in the wild.
The team now wants to learn how species can adapt to modern environmental challenges such as pollution and climate change.This work allows us to have a closer look at repeated evolution and predict how a population could develop traits that have evolved separately in the past under similar conditions,.
Diego Garcia Castillo.
Not all species have access to large gene pools and evolving new traits from scratch is tediously slow. Adaptation is very complex and our planet is also facing complex changes with episodes of weather extremes, rapidly advancing climate change, pollution, and new parasites. Perhaps this research helps convince people to protect a range of natural habitats so that species do not lose their genetic variation.
Anja Marie Westram.
Now, the snails Johannesson brought to the skerry in 1992 have reached a thriving population of around 1,000 individuals.
Publication:Diego Garcia Castillo, Nick Barton, Rui Faria, Jenny Larsson, Sean Stankowski, Roger Butlin, Kerstin Johannesson, and Anja M. Westram. 2024.
Predicting rapid adaptation in time from adaptation in space: A 30-year field experiment in marine snails. Science Advances. DOI: 10.1126/sciadv.adp2102
Abstract Predicting the outcomes of adaptation is a major goal of evolutionary biology. When temporal changes in the environment mirror spatial gradients, it opens up the potential for predicting the course of adaptive evolution over time based on patterns of spatial genetic and phenotypic variation. We assessed this approach in a 30-year transplant experiment in the intertidal snail Littorina saxatilis. In 1992, snails were transplanted from a predation-dominated environment to one dominated by wave action. On the basis of spatial patterns, we predicted transitions in shell size and morphology, allele frequencies at positions throughout the genome, and chromosomal rearrangement frequencies. Observed changes closely agreed with predictions and transformation was both dramatic and rapid. Hence, adaptation can be predicted from knowledge of the phenotypic and genetic variation among populations.With that classic example of evolution being seen to occur over 30 years can we expect creationists to give up the fight and admit that it's game over?
INTRODUCTION
Populations can sometimes adapt rapidly to sudden environmental shifts, even within a few dozen generations (1, 2). For many populations, rapid adaptation will be necessary to persist amid anthropogenic environmental changes (e.g., climate change, habitat fragmentation, and pollution) as well as after naturally occurring environmental shifts. However, we are far from being able to predict whether and how fast a population will adapt and which phenotypic and genetic changes will occur (3). These questions are of great interest in basic evolutionary biology (4, 5). Adaptation relies on genetic variation, including both variation at individual base positions and larger structural variants (6, 7). The latter include chromosomal inversions, which generate large gene blocks that are inherited together and can simultaneously affect multiple traits (8, 9). Rapid adaptation particularly depends on variation already present within a species because time is not sufficient to accumulate new beneficial mutations unless population sizes are very large (10, 11) and/or generation times are very short (12).
The reliance of rapid adaptation on preexisting variation suggests that it might be possible to predict future evolutionary change from knowledge of current variation (13, 14). In particular, many temporal environmental changes, such as temperature increase, resemble a current pattern in space (e.g., a spatial temperature gradient). In this case, for a focal population experiencing an environmental change, adaptive evolution is likely to rely on genetic variation that has entered the population via past or ongoing gene flow from a population that has already adapted to a similar environment. Studies investigating phenotype-environment and genotype-environment associations often provide insights into spatial genetic variation. Can this knowledge on adaptive variation in space be used to predict how a population will respond over time after an environmental change? This principle is implicit in much conservation genetics work (15–17) but has rarely been explicitly tested (18, 19). From a practical viewpoint, predictability would mean that population responses to environmental change can be anticipated and management efforts adjusted accordingly (20). In basic research, predictability provides a test of the current understanding of a system: For example, if loci contributing to divergence between environments in space have been identified correctly, they should respond in a predictable way to changing selection pressures in time.
The intertidal snail Littorina saxatilis is a model system in which divergent adaptation in space is exceptionally well-documented (21–23). Spatial variation and local adaptation to rocky shore environments are particularly obvious in the “Wave” and “Crab” ecotypes that have been intensively studied in Sweden, UK, and Spain. The ecotypes originated repeatedly in different locations (24), in response to the selective pressures of wave action (25) and crab predation (26) on wave-exposed rocks with low crab density, and sheltered crab-rich parts of shores, respectively (Fig. 1A) (21, 27). Adaptive variation in space in this system has been studied on three levels. At the phenotypic level, the ecotypes differ in traits including size, shell shape, shell color, and behavior (21, 27, 28). The Wave ecotype is small, has a thin shell that often shows Wave-specific colors and patterns, a large and rounded aperture, and bold behavior, while the Crab ecotype is large, has a thick shell generally without patterns [but with a band patterning in Iberian Crab ecotype populations (29)], a relatively smaller and more elongated aperture, and wary behavior (Fig. 1B and fig. S1D). At the level of individual SNPs (single-nucleotide polymorphisms), highly differentiated loci likely contributing to adaptation or linked to adaptive loci are scattered across the whole genome (23, 30). At the level of large chromosomal rearrangements, several inversions differ in frequency between ecotypes (31–33) and explain variation in divergent traits between ecotypes (30, 32). These features all change over local contact zones between ecotypes, and most differences are paralleled over large geographic areas (34), strongly suggesting a role of divergent selection. Our main goal here is to test whether the observed spatial associations allow us to predict changes in time after an immediate environmental change.
While previous evolutionary experiments have demonstrated rapid change in predicted directions, they have limitations. Some have only looked at the end points of an adaptive process rather than a detailed trajectory (2, 35, 36), while others have been conducted in artificial environments (37–40). Our study is one of the few (41–43) to follow adaptation of a transplanted population in the wild from the beginning. Previous studies in stickleback (42), guppy (41), and salmon (44) primarily examined evolution in phenotypes and collinear regions. In our study, we show how natural selection reshapes phenotypes, structural variants (inversions), and collinear genes in predictable ways. In addition, disentangling the effects of selection and drift is still a challenge in evolutionary studies; we address this by explicitly inferring demographic parameters and then testing for selection against the expectation under neutrality (43, 44). Our quantitative approach also allows for a detailed understanding of the history of our study population over the full three decades it has existed.
Fig. 1. Divergence trajectory of the skerry population at the levels of phenotypes and loci in collinear genomic regions.
Years correspond to sampling points in time. (A) Cartoon of the transplant experiment showing the donor Crab ecotype on the left side, the recipient skerry in the middle, and the neighboring Wave ecotype on the right side. Figure created using graphics from Vecteezy.com under free license. (B) Shell length and shape evolution toward the Wave ecotype on the skerry. (C) Evolution of shell color, patterning, ridging, and thickness in the skerry population toward the reference Wave ecotype. Thickness represents the average thickness relative to the average thickness of the transplanted population in 1992. (D) Scatter plots of two uncorrelated quantitative traits (shell length and height growth) on a log scale, and one qualitative trait (color) reveal no bimodalities in the skerry population. (E) Genetic differentiation of the skerry versus the reference populations based on control and spatial outlier SNP loci. The reduced-LD spatial outlier dataset was used.
We assessed local adaptation in a 30-year transplant experiment on the Swedish west coast. In 1992, we collected ~700 Crab ecotype snails and relocated them to a nearby wave-exposed environment earlier occupied by a population of the Wave ecotype. This wave environment is a “skerry” (rocky islet, size approximately 1 m by 3 m), exposed to strong waves and with no evidence of crabs (Fig. 1A and fig. S1). The skerry had remained uninhabited by snails since a toxic algal bloom in 1988 killed them all (45). The skerry (current census size: ~1000 individuals) is located ~300 m away, across open sea, from the donor Crab ecotype population and ~160 m from the nearest Wave ecotype population (Supplementary Materials and Methods and fig. S1). Therefore, there are two potential sources of adaptive variation: standing genetic variation in the donor population (resulting, in part, from past gene flow from adjacent Wave populations on the same island) and posttransplant gene flow due to occasional migrants [e.g. rafted snails; see (45); the species is live-bearing and lacks pelagic dispersal] from the neighboring Wave population (or, less likely, elsewhere).
We predicted three levels of change in the skerry population. At the phenotypic level, we anticipated a transition from Crab ecotype to Wave ecotype morphology: The averages of quantitative traits (e.g., shell length and shell thickness) and the proportions of qualitative traits (e.g., shell color, patterning, and ridging) were expected to approach the values typically observed in the Wave ecotype present in the area. We formulated our prediction on the basis of the polygenic inheritance of phenotypes (30, 46) that can reach Wave optima through different pathways (both genetic and plastic) and are often under strong selection in space (47). For SNPs, we predicted an allele frequency shift over time beyond the effect of drift and neutral gene flow in at least a subset of “spatial outliers” (SNPs associated with ecotype divergence in space in previous studies in the same geographical area; see Description of the sites, the translocation, and the subsequent sampling section in Materials and Methods) toward the frequencies observed in undisturbed Wave ecotype populations. For inversions, we predicted an increase in frequency of arrangements that are more common in Wave than in Crab ecotype populations. We predicted a tendency to fix arrangements that appear fixed in the Wave ecotype (23, 30). We predicted non-fixation for inversions that are maintained polymorphic in the Wave ecotype, likely by balancing selection (33). Last, for both spatial outlier SNPs and inversions, we predicted a correlation between temporal (the start versus end of experiment) and spatial (Crab ecotype versus Wave ecotype) genetic differentiation. Overall, we expected the predictability to be higher for inversions than for SNPs because many inversions are likely to be under strong direct selection, while spatial outlier SNPs may often only be indirectly affected by selection.
Diego Garcia Castillo et al. ,
Predicting rapid adaptation in time from adaptation in space: A 30-year field experiment in marine snails
.Sci. Adv. 10, eadp2102 (2024). DOI:10.1126/sciadv.adp2102
Copyright: © 2024 The authors.
Published by American Association for the Advancement of Science. Open access.
Reprinted under a Creative Commons Attribution 4.0 International license (CC BY 4.0)
Of course not. When was creationism ever based on evidence and when did creationists ever have the honesty and intellectual integrity to accept the evidence that they are wrong? It'll never happen, not while there are fools gullible enough to keep giving the frauds money and there is a political objective behind rubbishing science and advocating fundamentalist Christianity/Islam.
What we can expect now are howl of anguish and declarations of 'cheating' by 'evilutionists', because 'evilution' is all about one species suddenly turning into another or humans growing wings and turning into birds, or monkeys giving birth to human babies. What they will never admit is that evolution is only about change in allele frequency in a population over time, and that is exactly what has been observed in this population of Littorina saxatilis on a skerry in the Koster archipelago, off the west coast of Sweden.
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