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Biological Invasions in Marine Ecosystems – the Role of Phenotypic Plasticity

Final Report Summary - ALIEN SPECIES (Biological Invasions in Marine Ecosystems – the Role of Phenotypic Plasticity)

Phenotypic plasticity is the ability of a single genotype to produce various phenotypes in several distinct environments. The resulting phenotypic flexibility may increase an organism’s fitness in a heterogeneous environment and it is a common attribute across many taxa. Understanding the dynamics of phenotypic plasticity on life history strategies, costs of plasticity and as a factor affecting the success of biological invasions is of fundamental importance in animal ecology and evolution. This project investigated the causes and consequences phenotypic plasticity may have for the invasion success on the non-indigenous species the Pacific oyster (Crassostrea gigas) in Sweden, the evolution of phenotypic plasticity in gastropods and costs and constraints of plasticity. Since the mid 2000s, C. gigas has been observed in Scandinavia and are now forming dense populations in Denmark, Sweden and Norway. A biological invasion provide an unique opportunity to study ecological and evolutionary processes as the interactions between the invader and the native fauna occur on a timescale seldom studied by evolutionary biologists – decades to hundreds of years and, further, the history of contact between species is well-defined. Consequently, we can use invasion processes to gain glimpses of the earliest micro-ecological and evolutionary responses of natural populations by studying patterns of both indigenous and non-indigenous species in space and time.

The Pacific oysters were introduced to the Swedish west coast between 1973 and 1976 as part of trials to develop an aquaculture industry. When the trials ended, oysters were left in the sea. For the next three decades the oysters were thought to be absent, until the public reported several independent sightings of the species in 2007. Because of its subtropical origin it was believed that larvae of C. gigas were unable to survive in North-European waters outside the commercial nurseries, but its present distribution range from France to Norway. In Sweden, we know of about 250 sites along the west coast with a total live biomass of 100 000 – 500 000 tonnes. In his project, the fellow has examined demographic development of C. gigas across years, as well as life history plasticity and linked these traits with recruitment success, growth and mortality (Hollander et al. in prep). Further, long periods of extremely cold conditions may push the oysters beyond their lower thermal limits and such adaptation may facilitate further migration. Such extreme thermal conditions and winter mortality in invasive C. gigas populations was assessed in Hollander et al. (in prep).

The fellow has also studied the fundamental question of how the evolution of phenotypic plasticity is constrained by different factors, such as costs of plasticity, particularly under limited resource conditions (Brönmark et al. 2012). He also examined whether an invasive species may influence native community structures. Oysters of C. gigas often assemble and construct reefs and the physical structure attracts many secondary species as the shell matrix provides attachment points and refuge. However, C. gigas also holds the potential, as a sediment stabiliser, to change the community structure among adjacent sediment-living macro fauna species. Observations showed that oyster-reefs and blue mussel-beds recruited more species and had a higher abundance of organisms compared to the bare sediment. In addition, the macrozoobenthos species composition demonstrated significant differences between oyster-reefs and mussel-beds and consistently a larger total abundance. (Hollander et al., submitted).

A consortium of oyster researchers from the three Scandinavian countries, Sweden, Norway and Denmark was recently established and in the summer of 2013 researchers from the consortium, in a joint effort, collected and sampled a large number of specimens across all countries for genetic studies. Expressed genes will be considered in terms of the level of expression and whether the same genes are expressed in response to environmental differences. Additional population genetic studies intend to study genetic variation among different geographical locations as well as potential bottlenecks. This work is presently on going.

Evolutionary studies about phenotypic plasticity often require an understanding of phenotypic change in different traits, e.g. morphology. Organismal shape data are commonly acquired from landmark-based geometric morphometrics, methods that uses the Cartesian coordinates of anatomical landmarks to generate shape data. The shape data obtained are multivariate; thus, analysis of phenotypic plasticity can be challenging. New statistical tools, such as two-state multivariate vector analysis and phenotypic trajectory analysis, have been developed to address continuous phenotypic change in multivariate data spaces. These methods describe phenotypic change as trajectories in multivariate data spaces, and use differences in geometric attributes of trajectories as test statistics. Together with Dr. Michael Collyer at Western Kentucky University, USA, the fellow has examined the two-state multivariate vector analysis and phenotypic trajectory analysis to evaluate qualities and advantages of the two methods for multi-state phenotypic change, by simulating different types of phenotypic data (Collyer & Hollander in prep.).

In order to integrate, network and further discuss phenotypic plasticity with peers, the fellow invited a group of 25 internationally acknowledged experts in the field of phenotypic plasticity for a symposium that took place at Lund university in November 2012. The symposium was organized and convened by the fellow. As a result of the symposium we will publish a Special Issue on this theme in the well-regarded journal, Heredity. The participants of the symposium are in this moment contributing to eleven papers, that will be published later this year. The fellow, together with two other researchers, act as a guest editor for this Special Issue in Heredity. He also contributes to this special issue with a meta-analysis, where papers regarding phenotypic plasticity among all aquatic and marine gastropod studies are analyzed in order to identify patterns of how plasticity evolve, costs and limits of plasticity, and to highlight topics less explored (Bourdeau et al. 2014). Finally, he has contributed to two chapters in the new book (‘Animal movement across scales’, 2014), where he discuss plasticity in more general terms, but also its consequences in the context of invasive species, and ultimately how plasticity may drive speciation.

In sum, the project has been a great success and has significantly advanced our understanding about Crassostrea gigas invasion in Sweden as well as in Scandinavia and how the species has influenced and modified the indigenous fauna (Laugen et al. 2014). His results will be of wide interest equally to those studying invasion processes and to those interested in mechanisms of phenotypic plasticity.