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Impact of the invasive three-spined stickleback (Gasterosteus aculeatus) on relative abundance and growth of native pelagic whitefish (Coregonus wartmanni) in Upper Lake Constance

  • Fisheries Research Station of Baden-Württemberg (LAZBW)
  • Fisheries Research Station of Baden-Württemberg
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Abstract and Figures

Since 2013, the pelagic zone of Upper Lake Constance (ULC) has been subject to a massive invasion of the non-native three-spined stickleback (Gasterosteus aculeatus Linnaeus, 1758). Data from monthly monitoring of pelagic whitefish (Coregonus wartmanni Bloch, 1784) were used to compare weight-at-age and abundance of pelagic whitefish for years before (1997–2012) and after the invasion (2013–2015). Growth and abundance of pelagic whitefish is shown to be heavily influenced by stickleback presence. Mean autumn weight-at-age of whitefish decreased by 33.3% after the invasion took place and a significant decline in autumn CPUE in otherwise unfished cohorts of the population was also recorded. The results imply direct effects of stickleback presence on pelagic whitefish, including interspecific competition for food leading to reduced growth and survival, and predation of eggs and larvae, hampering recruitment. These observations coincide with a sharp decline in whitefish yield. In conclusion, this study shows that the invasion of stickleback has substantially altered the pelagic fish community of ULC, with severe consequences for commercial fisheries.
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Impact of the invasive three-spined stickleback (Gasterosteus
aculeatus) on relative abundance and growth of native
pelagic whitefish (Coregonus wartmanni) in Upper Lake
Roland Ro
¨sch .Jan Baer .Alexander Brinker
Received: 8 May 2017 / Revised: 28 November 2017 / Accepted: 16 December 2017 / Published online: 28 December 2017
ÓSpringer International Publishing AG, part of Springer Nature 2017
Abstract Since 2013, the pelagic zone of Upper
Lake Constance (ULC) has been subject to a massive
invasion of the non-native three-spined stickleback
(Gasterosteus aculeatus Linnaeus, 1758). Data from
monthly monitoring of pelagic whitefish (Coregonus
wartmanni Bloch, 1784) were used to compare
weight-at-age and abundance of pelagic whitefish for
years before (1997–2012) and after the invasion
(2013–2015). Growth and abundance of pelagic
whitefish is shown to be heavily influenced by
stickleback presence. Mean autumn weight-at-age of
whitefish decreased by 33.3% after the invasion took
place and a significant decline in autumn CPUE in
otherwise unfished cohorts of the population was also
recorded. The results imply direct effects of stickle-
back presence on pelagic whitefish, including inter-
specific competition for food leading to reduced
growth and survival, and predation of eggs and larvae,
hampering recruitment. These observations coincide
with a sharp decline in whitefish yield. In conclusion,
this study shows that the invasion of stickleback has
substantially altered the pelagic fish community of
ULC, with severe consequences for commercial
Keywords Fisheries yield Decreased stock
Predation Interspecific competition
Many lakes in the alpine region have experienced
drastic changes in nutrient profile over recent years.
Anthropogenic eutrophication of these naturally olig-
otrophic systems has been followed in many cases by
managed re-oligotrophication (Jeppesen et al., 2005;
Gerdeaux et al., 2006), and with consequent changes
in fish community composition. Furthermore, the
native fish communities of all lakes are subject to
the impacts of climate change (Jeppesen et al., 2014;
Winfield et al., 2016) and aquatic invasive species
(AIS). Striking examples of the threat from invasive
species in large lakes are those of the sea lamprey
(Petromyzon marinus L. 1758) and alewife (Alosa
pseudoharengus Wilson 1811) in the Great Lakes of
North America, the arrival of which combined with
overfishing causes a massive reduction in numbers of
predatory salmonids and the collapse and ultimate
disappearance of most deepwater ciscoe species
(Brown et al., 1987; Zimmermann & Krueger,
2009). The three-spined stickleback (Gasterosteus
aculeatus) is one of several AIS to have emerged in
Upper Lake Constance (ULC). The species first
Guest editors: Nico Salmaso, Orlane Anneville,
Dietmar Straile & Pierluigi Viaroli / Large and deep perialpine
lakes: ecological functions and resource management
R. Ro
¨sch (&)J. Baer A. Brinker
Fisheries Research Station Baden-Wu
Argenweg 50/1, 88085 Langenargen, Germany
Hydrobiologia (2018) 824:243–254,-volV)(0123456789().,-volV)
Content courtesy of Springer Nature, terms of use apply. Rights reserved.
... Its adaptability, short life cycle, wide environmental tolerance, and ability to complete multiple spawning cycles per year in response to favourable conditions allow it to rapidly colonise new environments, as well as to exhibit dramatic increases in previously occupied habitats in response to altered conditions (Barber and Nettleship, 2010). In recent decades, stickleback population increases have been observed in several aquatic systems, including the White Sea (Lajus et al., 2021), Lake Constance (Germany) (Roch et al., 2018;Rösch et al., 2018) 2 A. B. Olin et al. and the above-mentioned Limfjorden (Tomczak et al., 2013). These increases have in several cases been linked to anthropogenic environmental change, such as increasing water temperatures (Lajus et al., 2021). ...
... Importantly, the stickleback not only responds rapidly to novel conditions, but may itself have substantial impacts on the ecosystem. For example, in Lake Constance, the stickleback increase is thought to explain a sharp decline of whitefish (Coregonus spp.), as the stickleback compete with whitefish for food and predate on their offspring (Roch et al., 2018;Rösch et al., 2018). As sticklebacks may via these mechanisms suppress the recruitment of their own predators, they can act to reinforce a state with low densities of predators , resulting in subsequent top-down trophic cascades (e.g. ...
... Sticklebacks along the German coastline have been found to consume substantial numbers of herring eggs, which likely results in local reductions in herring productivity (Kotterba et al., 2014). It has also been suggested that sticklebacks have a negative impact on whitefish by competing for food and predating on whitefish offspring , as observed in Lake Constance (Roch et al., 2018;Rösch et al., 2018). Finally, a strong negative relationship has been identified between juvenile abundances of stickleback and common roach along the Swedish Baltic Sea coast (U. ...
Under rapid environmental change, opportunistic species may exhibit dramatic increases in response to the altered conditions, and can in turn have large impacts on the ecosystem. One such species is the three-spined stickleback (Gasterosteus aculeatus), which has shown substantial increases in several aquatic systems in recent decades. Here, we review the population development of the stickleback in the Baltic Sea, a large brackish water ecosystem subject to rapid environmental change. Current evidence points to predatory release being the central driver of the population increases observed in some areas, while both eutrophication and climate change have likely contributed to creating more favourable conditions for the stickleback. The increasing stickleback densities have had profound effects on coastal ecosystem function by impairing the recruitment of piscivorous fish and enhancing the effects of eutrophication through promoting the production of filamentous algae. The increase poses a challenge for both environmental management and fisheries, where a substantial interest from the pelagic fisheries fleet in exploiting the species calls for urgent attention. While significant knowledge gaps remain, we suggest that the case of the Baltic Sea stickleback increase provides generalisable lessons of value for understanding and managing other coastal ecosystems under rapid change.
... However, starting in 2012/2013 the pelagic zone was invaded by sticklebacks (Gasterosteus aculeatus), which numerically dominated the fish community in recent years (Eckmann & Engesser, 2019;Hudson et al., 2021;Rösch et al., 2018). The two fish species differ strongly in morphological and behavioural specialisation to the pelagic habitat. ...
... Such changes may result for instance from differences in prey selectivity between native and invasive fish and/or changes in overall predation pressure after invasion (Beisner et al., 2003;Brooks & Dodson, 1965). In Lake Constance, the pelagic system became dominated by sticklebacks rather than the native whitefish during the 2010s (Eckmann & Engesser, 2019;Rösch et al., 2018). ...
... large zooplankton (Becker & Eckmann, 1992) thereby contributing to the postulated negative effect of the stickleback invasion on the growth of 1+ to 4+ whitefish (Rösch et al., 2018). ...
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Invasion of non‐native species might alter food web structure and the strength of top‐down control within lake ecosystems. As top‐down control exerted by fish populations is often dominated by young of the year fish, the impact of new fish species might depend on the feeding rates of the juvenile fish. Here we provide comparative analyses of feeding rates of juvenile whitefish (Coregonus wartmanni) – a native and specialised planktivore and an invasive generalist (sticklebacks, Gasterosteus aculeatus). We studied feedings rates of whitefish and sticklebacks in aquaria experiments using 2 cm to 8 cm fish feeding on seven zooplankton species common to Lake Constance. As whitefish hatch several months earlier than sticklebacks, 0+ whitefish are larger than 0+ sticklebacks throughout the year and hence are predicted to have higher feeding rates on especially large zooplankton species. We show that sticklebacks as small as 2 cm were able to feed on the largest zooplankton species of Lake Constance. Further, stickleback feeding rates were similar to both the same size 0+ whitefish and the larger 0+ whitefish co‐occurring with smaller 0+ sticklebacks. Hence, 0+ sticklebacks will compete with 0+ whitefish for the same zooplankton species, therefore the invasion of sticklebacks is unlikely to change the relative feeding pressure by individual 0+ fish on zooplankton species. The juvenile period of fish is crucial for their establishment in a new habitat as well as for the grazing impact of fish on prey communities. Here, we show that juveniles of an invasive species, sticklebacks, do have similar feeding rates on various zooplankton species compared to native whitefish despite the latter are specialized planktivores and advanced sticklebacks in growth during the seasonal course. Our results suggest that the invasion of sticklebacks and partial replacement of whitefish should not result in changing relative feeding pressures on the various zooplankton species.
... Second, an Eastern European lineage originating from the Baltic Sea Catchment currently dominates Lake Constance (Marques et al., 2019a). However, the history of stickleback in Lake Constance in terms of their time of arrival, source of colonization, and the mode of diversification into lake and stream ecotypes has been debated recently (Roesti et al., 2015;Rösch et al., 2017;Marques et al., 2019a). Notably, some authors proposed a natural postglacial colonization of the Lake Constance basin from the Danube about 9,000 years ago, similar to some other freshwater fish species of which Danube populations inhabit Lake Constance as a consequence of river capture by the Rhine catchment (Nesbø et al., 1999;Behrmann-Godel et al., 2004;Gum et al., 2005;Barluenga et al., 2006;Vonlanthen et al., 2007;Hudson et al., 2014;Gouskov and Vorburger, 2016;Lucek et al., 2018). ...
... In a recent assessment, sticklebacks in Lake Constance represent ∼28% of the fish biomass, and accounted for 96% of fish captured in the pelagic zone of the upper lake during the Projet Lac survey (Alexander et al., 2016). Despite being identified as hyper-abundant from the 1960's to the 70's (Numann, 1972), and again in littoral habitats almost two decades ago (Zimmermann, 2002) threespine sticklebacks were first recorded as bycatch in the pelagic zone of Constance by commercial fisheries in 2013 (Rösch et al., 2017). Previous reports (Numann, 1972;Deufel, 1985) indicate that stickleback have been a nuisance to fishermen in the past, with populations reaching high abundances, but then declining rapidly, presumably from parasitic infections (e.g., whitespot disease Ichthyophthirius multifiliis and carp louse Argulus foliaceus), though evidence of this is largely speculative. ...
... The massive recent increase in stickleback abundance coincides with a sharp decline in pelagic whitefish (Coregonus wartmanni, Bloch, 1784) yields, both in the number of individuals caught, and their weight-at-age (Rösch et al., 2017). Previous work has speculated that the invasive stickleback population could have a negative impact on whitefish growth and abundance, and shows that stickleback will prey on whitefish larvae in laboratory foraging experiments (Roch et al., 2018;Ros et al., 2019) or following stocking (Roch et al., 2018). ...
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Our Research Topic titled “Understanding the Impact and Invasion Success of Aquatic Non-native Species: How They Interact with Novel Environments and Native Biota,” compiled a series of research studies providing new data and approaches in assessing the invasion success and the impacts of various non-native species in the different regions of the world belonging to various groups of organisms and from various environments. A range of invasion ecology specialists endeavored to provide up-to-date information on the multifaceted issues of non-native species introductions and to map conservation priorities in terms of biological invasion. A total of 10 articles, including original pieces of research, a review, a brief research report and a hypothesis and theory, are included as part of this Research Topic. Below, an overview of these articles is provided.
... With continuing reoligotrophication since the 1980's, the relative share of copepod biomass again increased but extinct species failed to reinvade (Straile, 2015), presumably due to niche constriction by the emerged zooplankton invaders in combination with altered environmental conditions. Recently, since around 2014, Daphnia cucullata and its hybrid forms occur in the lake in high abundances, temporally coinciding with the immigration of the non-endemic three-12 spined stickleback (Gasterosteus aculeatus) in 2013 (Alexander et al., 2014;Roch et al., 2018;Rösch et al., 2018). The contemporary dominant copepod species are Eudiaptomus gracilis, Cyclops abyssorum, Cyclops vicinus, and Mesocyclops leuckarti. ...
... The fish fauna comprises around 30 species, of which three are commonly living in the pelagic zone: the lake char (Salvelinus umbla), whitefish (Coregonus wartmanni) and, since recently, the three-spined stickleback (Gasterosteus aculeatus). The latter is occurring in high numbers since 2012-2013 in the pelagic zone of Upper Lake Constance (Rösch et al., 2018;Eckmann and Engesser, 2019). Since then, the abundance of sticklebacks have increased and in 2014, they represented 96% of total abundance and 28% of the biomass of the pelagic fish (Alexander and Vonlanthen, 2016). ...
... Compared with the co-occurring species D. longispina, D. galeata is presumably less competitive at low food quantity [36] and does not perform diel vertical migration to escape vertebrate and invertebrate predation [54,55]. Other changes that were observed with oligotrophication of Lake Constance include the incursion of the three spined stickleback into the pelagic zone in about 2013 [56], and the appearance of a third Daphnia species, Daphnia cucullata, in 2014 [23]. ...
The human-caused proliferation of cyanobacteria severely impacts consumers in freshwater ecosystems. Toxicity is often singled out as the sole trait to which consumers can adapt, even though cyanobacteria are not necessarily toxic and the lack of nutritionally critical sterols in cyanobacteria is known to impair consumers. We studied the relative significance of toxicity and dietary sterol deficiency in driving the evolution of grazer resistance to cyanobacteria in a large lake with a well-documented history of eutrophication and oligo-trophication. Resurrecting decades-old Daphnia genotypes from the sediment allowed us to show that the evolution and subsequent loss of grazer resistance to cyanobacteria involved an adaptation to changes in both toxicity and dietary sterol availability. The adaptation of Daphnia to changes in cyanobacteria abundance revealed a sterol-mediated gleaner-opportunist trade-off. Genotypes from peak-eutrophic periods showed a higher affinity for dietary sterols at the cost of a lower maximum growth rate, whereas genotypes from more oligotrophic periods showed a lower affinity for dietary sterols in favour of a higher maximum growth rate. Our data corroborate the significance of sterols as limiting nutrients in aquatic food webs and highlight the applicability of the gleaner-opportunist trade-off for reconstructing eco-evolutionary processes.
... The full ecological impact of sticklebacks on the aquatic community in ULC and its tributaries is unknown. However, the results of two recent studies (Roch et al. 2018;Rösch et al. 2018) imply significant effects of stickleback presence on pelagic whitefish Coregonus wartmanni (Bloch 1784), the previously dominant pelagic fish species and the main target of local fisheries (Baer et al. 2017). The suspected reasons include interspecific competition for food leading to reduced growth and survival, and predation by sticklebacks on whitefish larvae and probably eggs, hampering recruitment (Ros et al. 2019;Baer et al. 2021). ...
Full-text available
Since 2012, a massive invasion of the three-spined stickleback ( Gasterosteus aculeatus ) has taken place into the pelagic area of Lake Constance. This species, which had previously been restricted to the littoral zone, is now the dominant pelagic fish and the previously dominant whitefish ( Coregonus wartmanni ) has suffered severe reductions in growth and recruitment. In this study, in total, 2871 sticklebacks were collected via monthly sessions over a 4-year period in pelagic and benthic areas of Lake Constance and examined for signs of infection with Schistocephalus solidus , a parasite known to be potentially fatal. The infection risk to sticklebacks increases throughout the course of the year and is size- and sex-dependent. Habitat has only a marginal impact. All parasite-induced harm is imparted after stickleback spawning and parental care is over. The results did not support the hypothesis that the invasion of the pelagic area might be driven by parasite-avoiding behaviour. Furthermore, the impact of the parasite is likely to be limited to post-reproductive adults, thereby ensuring stable reproduction of the hosts despite high rates of transmission and mortality. In consequence, stickleback stock development is independent of S. solidus infection, leading to secure coexistence of host and parasite even at extraordinary high host levels.
... The extent to which quagga mussels impact the fundamental energy pathways within the lake remains unknown, but results from elsewhere suggest that zooplankton density in the pelagic zone will have decreased due to the filtration by the quaggas while production in the littoral zone will have increased (Evans et al., 2011;Fahnenstiel et al., 2010;Vanderploeg et al., 2010). It is hypothesised that recent declines in both growth rates and catches (Rösch et al., 2018) of the most commercially important fish species in Lake Constance, the pelagic feeding whitefish Coregonus wartmanni (Bloch 1784) (Baer et al., 2022(Baer et al., , 2017 may be a result of the species being forced to feed more in littoral waters. A similar shift was previously documented for the sister species C. clupeaformis in the Great Lakes (Rennie et al., 2009). ...
Full-text available
Since the arrival of the invasive quagga mussels Dreissena rostriformis bugensis in Lake Constance, significant changes in the zooplankton and benthic invertebrate community were observed. Five years later the quagga mussel has become the dominating species of the benthic community. Its effects on other components of the food web, especially those at higher trophic levels such as fish, remain unclear around the world. To evaluate the actual impact of quaggas on the local food web of Lake Constance, the stable isotope compositions of pelagic whitefish and different benthic fish species from before and after the quagga invasion were compared. A significant increase in d 13 C was detected in pelagic whitefish one year after the establishment of the quagga mussel in the lake. This change was most likely the consequence of an increase in benthic-derived nearshore primary production and a shift towards more littoral feeding, than a change in dietary composition. Stomach content analysis of contemporary samples revealed that pelagic whitefish (Coregonus wartmanni) still feed exclusively on pelagic zooplankton. In contrast, benthic whitefish (Coregonus macrophthalmus), roach (Rutilus rutilus) and tench (Tinca tinca) show today high levels of quagga consumption. However, this behaviour alone could not explain the observed differences in d 15 N from periods before and after the quagga invasion. The results suggest that energy sources and pathways have changed considerably for both pelagic and benthic dwelling fish species in Lake Constance following the establishment of quaggas.
... All three species have been targeted by professional fishermen for centuries, but yields have declined strongly for two decades. Reasons include reduced phosphorus levels (Baer et al., 2016) and the rapid increase in numbers of three-spined stickleback in the pelagic zone, which has resulted in competition and predation effects on the whitefish larvae (Rösch et al., 2017). In addition, fisheries-induced size selection has been discussed, but appears unlikely to be a main driver (Gum et al., 2014). ...
Decreasing yields of whitefish in upper Lake Constance have prompted considerable interest in exploring the potential for local coregonid aquaculture. This study set out to assess and compare the performance of three local species (Coregonus macrophthalmus, Coregonus arenicolus and Coregonus wartmanni) with an aquaculture-adapted strain of C. lavaretus from Finland (JALO-strain, which is a hatchery-reared domestic broodstock) under standard aquaculture conditions. Larvae were raised from eggs over 100-day periods in consecutive years using standardized aquaculture conditions and a commercial pellet diet, with survival and growth monitored as performance indicators. The average egg diameters of C. arenicolus and JALO-strain were similar, and significantly larger than those of the other two local species. Growth and survival of both large-egged species was greater than in C. wartmanni. Offspring of large C. macrophthalmus spawners reached similar length and survival like C. arenicolus, but specific growth rates were significantly lower. Eggs from the JALO-strain exhibited similar survival to C. arenicolus, and JALO offspring showed significantly better growth rates than any of the three wild forms. Hence, while the offspring of wild coregonids from Lake Constance are less adapted to aquaculture conditions than JALO-strain, the potential for C. arenicolus appears promising, particularly if an optimized breeding program capable of maximizing growth can be realized.
... Invasive species that establish successful populations often have strong impacts on aquatic ecosystems through various processes including predation, disturbance, habitat modification and competition (Grabowska et al. 2009). They may alter food web structure, ecosystem functioning, water quality, and may lead to the reduction of diversity in native communities (Hall and Mills 2000;Ricciardi and MacIsaac 2011;Villéger et al. 2017;Rösch et al. 2018). Strong negative impacts of invaders on native species appear to be more frequent in freshwater ecosystems than in marine habitats (Ricciardi and Kipp 2008). ...
... For the year 2014, Alexander et al. revealed in a largescale survey that sticklebacks numerically represent 96% of the pelagic fish and 28% in terms of the total fish biomass. The emergence of sticklebacks in the pelagic zone directly affected whitefish by interspecific competition for food (Rösch et al., 2018). Whitefish are specialized in zooplankton feeding and rely on their narrow food spectrum existing in the pelagic (Eckmann et al., 2002). ...
Full-text available
Upper Lake Constance (ULC) is a large pre-alpine lake situated between Austria, Germany and Switzerland (9°18'E, 47°39'N). Along with the smaller, conjoined expanse of Lower Lake Constance, it forms the third largest lake in Europe. Its waters underwent pronounced eutrophication during the 20th century. Commercial fisheries benefitted strongly from the increased productivity during an initial mesotrophic phase, but these advantages were effectively neutralized when eutrophication became severe. By the turn of the 21 st century, internationally coordinated measures to reduce nutrient input to the lake had returned ULC to its historic reference state as an oligotrophic ecosystem. However, the remarkable success of the nutrient management program has been to the detriment of commercial fishers. Yields of most commercially important fish species have decreased, along with lake productivity. As a consequence, the high market demand for local fish products is nowadays met mainly by imports, the ecological footprint of which offsets the local benefits of environmental restoration. Responsibility for fisheries and environmental aspects of ULC managing is shared by the national and federal state administrations and in all cases, tourism, drinking water and environmental interests now take priority over fisheries. As a result, the number of fishers operating viably on Germany's largest inland water body continues to decline and the long-term viability of commercial capture operations is in doubt. Aquaculture of locally desired fish species may become an important factor in the future of the Lake Constance fisheries.
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A range of perspectives is presented from the International Fisheries Section of the American Fisheries Society on climate change effects on inland fisheries from standing and flowing waters in Africa, Asia, Australia, Europe, and Latin America. Many of the world's inland fisheries face common threats, such as eutrophication, overfishing, species introductions, and water development projects (Youn et al. 2014), which have essentially local solutions. However, most fisheries also face effects from the inherently global problem of climate change, which only can be understood and ultimately managed from a truly international perspective. The potential extent and range of such effects were illustrated by Xenopoulos et al. (2005), who, assuming the A2 model for climate change, predicted a loss of 0% to 75% of the fish species in a variety of the world's river basins but with an uncertain time lag (Tedesco et al. 2013). Here, we provide a range of perspectives from the International Fisheries Section of the American Fisheries Society on climate change effects on inland fisheries from standing and flowing waters in Africa, Asia, Australia, Europe, and Latin America.
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Ecological speciation is the process by which reproductively isolated populations emerge as a consequence of divergent natural or ecologically-mediated sexual selection. Most genomic studies of ecological speciation have investigated allopatric populations, making it difficult to infer reproductive isolation. The few studies on sympatric ecotypes have focused on advanced stages of the speciation process after thousands of generations of divergence. As a consequence, we still do not know what genomic signatures of the early onset of ecological speciation look like. Here, we examined genomic differentiation among migratory lake and resident stream ecotypes of threespine stickleback reproducing in sympatry in one stream, and in parapatry in another stream. Importantly, these ecotypes started diverging less than 150 years ago. We obtained 34,756 SNPs with restriction-site associated DNA sequencing and identified genomic islands of differentiation using a Hidden Markov Model approach. Consistent with incipient ecological speciation, we found significant genomic differentiation between ecotypes both in sympatry and parapatry. Of 19 islands of differentiation resisting gene flow in sympatry, all were also differentiated in parapatry and were thus likely driven by divergent selection among habitats. These islands clustered in quantitative trait loci controlling divergent traits among the ecotypes, many of them concentrated in one region with low to intermediate recombination. Our findings suggest that adaptive genomic differentiation at many genetic loci can arise and persist in sympatry at the very early stage of ecotype divergence, and that the genomic architecture of adaptation may facilitate this.
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Populations occurring in similar habitats and displaying similar phenotypes are increasingly used to explore parallel evolution at the molecular level. This generally ignores the possibility that parallel evolution can be mimicked by the fragmentation of an ancestral population followed by genetic exchange with ecologically different populations. Here we demonstrate such an ecological vicariance scenario in multiple stream populations of threespine stickleback fish divergent from a single adjacent lake population. On the basis of demographic and population genomic analyses, we infer the initial spread of a stream-adapted ancestor followed by the emergence of a lake-adapted population, that selective sweeps have occurred mainly in the lake population, that adaptive lake-stream divergence is maintained in the face of gene flow from the lake into the streams, and that this divergence involves major inversion polymorphisms also important to marine-freshwater stickleback divergence. Overall, our study highlights the need for a robust understanding of the demographic and selective history in evolutionary investigations.
A massive increase in the pelagic population of non-endemic three-spined sticklebacks, Gasterosteus aculeatus L. in Lake Constance has coincided with drastic declines in fishery yields. This study assesses the possible direct and indirect impact of the mass occurrence on native fish species in the lake. Laboratory foraging experiments showed that larvae of roach Rutilus rutilus L., perch Perca fluviatilis L. and whitefish Coregonus lavaretus L. are accessible to sticklebacks as food. However, distinct species effects were apparent, with whitefish showing no effective predator avoidance strategy and therefore experiencing drastically increased mortality risk compared to the other predator adapted prey species. Furthermore, in absence of larval prey, sticklebacks were shown to feed predominantly on Daphnia in the field, indicating a strong interspecific food competition with whitefish. The results suggest that sticklebacks, acting as both an invasive species and a predator in the pelagic zone where prior no predator or neozoon existed, create a unique challenge to the unadapted autochthonous fish, and thus threaten the ecological resilience of the lake. Impacts on recruitment, e.g. through larval predation and interspecific competition for zooplankton could explain recent drastic declines in fishing yields.
Enhancement stocking is a widespread but rarely evaluated practice in German vendace, Coregonus albula L. fisheries, which is precautionarily carried out to buffer yield fluctuations. However, it is assumed that stocking of larval vendace can elevate year-class strength only in the presence of substantial reproductive deficits, which so far cannot be detected prior to the spring time period when stocking is conducted by fisheries managers. Simple measures for the early quantification of natural reproduction were tested, and the efficiency of larval enhancement stocking in a lake with strong reproduction deficits was analysed. Analysis in four lakes over 3 years revealed a significant positive correlation between standardised catches of vendace larvae caught with pump-driven illuminated traps in spring and the abundance of young-of-year (YoY) vendace in the following autumn, whereas standardised catches of spawners were insufficient to forecast YoY recruitment. In a lake with low natural vendace reproduction, stocked vendace contributed 73–100% of year-class strength and fisheries yield. Accordingly, enhancement stocking can efficiently compensate for reproduction deficits, and the simple larvae sampling method may facilitate early detection of these deficits, which would allow fisheries managers to respond accordingly through larvae stocking.
Around 1350 the authorities of the Lake Constance region began to regulate the local fisheries by issuing fishermen’s ordinances and signing fisheries treaties with other principalities with the stated interest of protecting the fish stocks, which were considered a commons. The fishermen and their guilds were heavily involved in this process, since some of their practices - like the destruction of spawn and the catching of young fish - could have devastating consequences. The fishermen and their authorites decided regularly for more than four centuries to prioritise the long-term preservation of the fish stocks and not short-term profits to be made on the local fish markets. Thus, they avoided the disastrous outcome of a ‘Tragedy of the Commons’.