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A map of the round goby collection sites used in this study. Inset areas are a magni- fied view of the invasion front and established area collection sites. The initial introduction of round goby into the Trent River in 2003 is denoted with a diamond ( ). The upstream edges (USE) of the round goby population (the invasion front) between 2007 and 2010 are indicated by circles ( " ) labelled with the year the population reached the edge location. Insets: Squares ( ) represent individual sampling locations within each collection site. Invasion front round goby were sampled from 4 separate areas along the Otonabee River and round goby from the established area were collected from 3 separate areas within the Trent River.
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The role of aggression as a factor promoting invasiveness remains hotly debated. Increased aggression or a lack of tolerance for conspecifics may promote population spread. Some previous research suggests that more aggressive or bold individuals are increasingly likely to disperse and as such these individuals may be overrepresented at the invasion...
Contexts in source publication
Context 1
... goby (N. melanostomus) were collected on June 9 and June 29, 2010 from two areas in the Trent-Severn waterway (Ontario, Canada; Figure 1). Fish from an established and reliably sampled round goby population (since 2003) were caught in three locations in the Trent River centered around Hast- ings (44°17 54 N, 077°58 02 E; 44°17 43 N, 077°58 29 E; 44°18 30 N, 077°57 28 E; Figure 1 Established Area Inset, Raby et al., 2010). ...
Context 2
... were collected on June 9 and June 29, 2010 from two areas in the Trent-Severn waterway (Ontario, Canada; Figure 1). Fish from an established and reliably sampled round goby population (since 2003) were caught in three locations in the Trent River centered around Hast- ings (44°17 54 N, 077°58 02 E; 44°17 43 N, 077°58 29 E; 44°18 30 N, 077°57 28 E; Figure 1 Established Area Inset, Raby et al., 2010). Fish from the invasion front were caught at four locations in the Otonabee River (44°11 49 N, 078°14 22 E; 44°12 22 N, 078°14 22 E; 44°12 36 N, 078°14 11 E; 44°12 46 N, 078°14 01 E; Figure 1 Invasion Front Inset). ...
Context 3
... from an established and reliably sampled round goby population (since 2003) were caught in three locations in the Trent River centered around Hast- ings (44°17 54 N, 077°58 02 E; 44°17 43 N, 077°58 29 E; 44°18 30 N, 077°57 28 E; Figure 1 Established Area Inset, Raby et al., 2010). Fish from the invasion front were caught at four locations in the Otonabee River (44°11 49 N, 078°14 22 E; 44°12 22 N, 078°14 22 E; 44°12 36 N, 078°14 11 E; 44°12 46 N, 078°14 01 E; Figure 1 Invasion Front Inset). Round goby were first detected in the Otonabee River only in the spring of 2010 despite this site being previously surveyed for round goby in 2009 and earlier (Brownscombe, 2011). ...
Context 4
... that individuals on the invasion front are more aggressive than their counterparts inhabiting established areas. For example, western bluebirds ( Sialia mexicana ) were more aggressive and displaced than their less aggressive sister species, mountain bluebirds ( Sialia cur- rcoides ), and the males in new populations were more aggressive than males in older, established populations (Duckworth & Badyaev, 2007). Hence in bluebirds, aggressive individuals were driving the range expansion (Duckworth & Badyaev, 2007). Other studies suggest quite the opposite, showing that invasive populations may be populated by less aggressive individuals (Suarez et al., 1999; Cote et al., 2010b). Less competitive, or less aggressive individuals may in fact drive the range expansion simply by being displaced or competitively excluded from established optimal habitats (Holecamp & Smale, 1998; Schradin & Lamprecht, 2002; Guerra & Pollack, 2010; re- viewed in Cote et al., 2010a), and being forced to settle in potentially less ideal habitats at the edges of a species’ range. It has been argued that the general tendency for a species to have low aggression towards conspecifics may in fact help foster high densities, and help invasive species simply numerically outcompete less dense populations of native species. Invasive populations of the Argentine ant ( Liniepithema humile ) in southern California are such an example where the invasive species exhibits reduced intraspecific aggression, relative to native populations of L. humile in South America (Suarez et al., 1999), and this reduced intraspecific aggression may facilitate growth of the invasive population (Holway et al., 1998). However, in these instances, aggressivity is considered as a species- or population-wide trait, not as a trait that varies among individuals. When individual differences have been examined, asocial tendencies rather than tolerance or gregariousness appear to drive dispersal and promote invasion into new habitats. For example, in mosquitofish populations, Gambusia affinis , the least social individuals disperse (Cote et al., 2010b). The aim of our study was to determine whether there were differences in aggressive tendencies and competitive abilities between individuals from an invasion front and those from a more established area. We used the round goby ( Neogobius melanostomus ), an invasive fish in the Laurentian Great Lakes. Round goby are native to the Ponto-Caspian region of Europe (Jude et al., 1992) and have rapidly invaded North America and Western Europe. Their invasion has been mediated through unintentional human transfers in the ballast water of shipping vessels (Corkum et al., 2004). Although the saltatory appearances of the round goby through the Great Lakes over a five year period was probably aided by human-assisted dispersal (Hensler & Jude, 2007; Hayden & Miner, 2009), round goby also undergo natural range expansions in invaded habitats through unassisted dispersal (Bronnenhuber et al., 2011; Gutowsky et al., 2011; LaRue et al., 2011). Individual variation in aggressiveness and dispersal tendencies may mediate this expansion. We compared aggressiveness and competitive ability in the round goby by means of a resource contest over access to shelter. Male round goby that are reproductively active will guard a territory that contains a nest/shelter (Wickett & Corkum, 1998; MacInnis & Corkum, 2000). Round goby are strongly motivated to compete for and actively defend these shelters from heterospecifics (Dubs & Corkum, 1996; Balshine et al., 2005; Savino et al., 2007) and conspecifics (Stammler & Corkum, 2005; Sopinka et al., 2010). We predicted that if aggression is important in mediating round goby range expansions, then round goby from an invasion front would (1) be bolder than, (2) be more aggressive than and (3) outcompete round goby from established areas. However, given that round goby are highly aggressive and territorial, less competitive individuals could be forced out of prime habitat and, thus, contribute to range expansion (Ray & Corkum, 2001; Johnson et al., 2005; Brownscombe & Fox, 2012). If invasion front round goby are indeed the displaced, less competitive fish, then alternatively we predicted they would be (1) less bold, (2) less aggressive and (3) lose contests more often compared to fish from established populations. Round goby ( N. melanostomus ) were collected on June 9 and June 29, 2010 from two areas in the Trent-Severn waterway (Ontario, Canada; Figure 1). Fish from an established and reliably sampled round goby population (since 2003) were caught in three locations in the Trent River centered around Hastings (44°17 54 N, 077°58 02 E; 44°17 43 N, 077°58 29 E; 44°18 30 N, 077°57 28 E; Figure 1 Established Area Inset, Raby et al., 2010). Fish from the invasion front were caught at four locations in the Otonabee River (44°11 49 N, 078°14 22 E; 44°12 22 N, 078°14 22 E; 44°12 36 N, 078°14 11 E; 44°12 46 N, 078°14 01 E; Figure 1 Invasion Front Inset). Round goby were first detected in the Otonabee River only in the spring of 2010 despite this site being previously surveyed for round goby in 2009 and earlier (Brownscombe, 2011). The Trent River population has been there for at least seven years and is thought to have been initially established by a bait bucket transfer from one of the Great Lakes. Round goby from the Otonabee River invasion front site have spread down from the original introduction site in the Trent River near Hastings. The movement of this invasion front has tracked since 2003 (Raby et al., 2010; Brownscombe, 2011; Gutowsky & Fox, 2011). Although more established round goby populations exist in North America (for example, Lake Erie was colonized by round goby in 1993; Corkum et al., 1994), we chose to examine fish from these two nearby areas to control for environmentally induced differences in behaviour (Alvarez & Bell, 2007). The two chosen areas are within the same drainage system, and have similar habitat characteristics. Round goby were caught using angling and baited minnow traps and were then sorted by sex and reproductive status. Males and females were dis- tinguished based on urogenital papilla shape (pointed in males, square in females; Miller, 1984) and the reproductive status of males was assessed using papilla length, head width and body colouration (Marentette & Corkum, 2008; Marentette et al., 2009). Males were transported to McMaster University (Hamilton, Ontario) and held in 66 l aquaria in groups of four to six fish from the same collection site. Aquaria contained gravel to a depth of 1 cm, 15-cm sections of PVC piping as shelter, an AquaClear 50 external box filter, and a thermometer (water temperature maintained between 22 and 24°C). Round goby were fed flake food (Nutrafin) ad libitum once daily and were allowed at least 72 h to acclimate in the lab prior to behavioural testing. In total, 36 resource competition trials were conducted. Fish were placed in size-matched pairs with one competitor from the invasion front population and its opponent from the established area. We size-matched fish using body mass (to the nearest 0.01 g) because body size differences of as little as 3% have been shown to influence the outcomes of competitive interactions in this species (Stammler & Corkum, 2005). Size differences between competitors ranged from 0.01 to 2.0 g in body mass (mean difference 0.57 ± 0.49 g, paired t -test; t = 0 . 14, N = 36, p = 0 . 89). In order to further account for the effect of size differences on contest outcomes, we selected contestants such that the marginally larger individual of the pair was from the invasion front in half the trials and from the established area in the other half of the trials. To facilitate identification during the contests, each individual was marked subcutaneously with either green or yellow non-toxic acrylic paint just below the dorsal fin spines (see Wolfe & Marsden, 1998). The colour of paint used for each fish and the placement of the fish into the left versus the right end chamber of the aquarium (see below) were randomized. Twenty-four hours prior to the start of a behavioural trial, size-matched marked opponents were placed into one of two end chambers in a 66-l experimental aquarium divided into thirds by removable, black opaque barriers. Each chamber contained a black opaque shelter box (5 cm long, 15 cm wide, 5 cm high) with a small opening that was oriented to face the front of the aquarium (Figure 2A). The next morning an observer, blind to the origin of the fish, recorded all the behavioural data while seated 1 m away from the aquarium (following protocols used in Sopinka et al., 2010). Data were recorded in person and trials were also videotaped for further analyses on Mini DV cassettes using a Sony Digital Camcorder (model DVR- VX2000NTSC). Behavioural trials always began between 9:00 and 10:00 h. Each trial started when the shelters were removed from the end chambers (Figure 2B). We observed each focal fish for a 5-min post shelter removal period and recorded the time taken to initiate movement following removal of the shelter as well as all behaviours exhibited (see below). Following the 5-min boldness evaluation, we removed the two opaque barriers allowing both fish access to the central chamber and shelter and to see and interact with one another (Figure 2C). Each fish was observed for 10 min in a pre-determined, randomized order (20 min total). The identity of the fish that crossed over to the opposite side of the tank first was noted, along with which fish initiated the first aggressive act, the latency to the first aggressive act (in s), and the total duration of the first aggressive interaction that occurred (in s). All aggressive, submissive, and locomotor behaviours were recorded (see Sopinka et al., 2010 for an ethogram of the behavioural repertoire of this species). The time spent in the shelter was noted (in s) for ...
Context 5
... invasive species range, individuals with particular behavioural syndromes may be more likely to make up the population right at the invasion front and consequently mediate the colonization of new habitat (Rehage & Sih, 2004). Aggressiveness, boldness and dispersal tendency are often positively correlated and comprise a behavioural syndrome (Sih et al., 2004a,b), but the role of this syndrome in the expansion of invasion fronts is not yet clear. Some studies have suggested that individuals on the invasion front are more aggressive than their counterparts inhabiting established areas. For example, western bluebirds ( Sialia mexicana ) were more aggressive and displaced than their less aggressive sister species, mountain bluebirds ( Sialia cur- rcoides ), and the males in new populations were more aggressive than males in older, established populations (Duckworth & Badyaev, 2007). Hence in bluebirds, aggressive individuals were driving the range expansion (Duckworth & Badyaev, 2007). Other studies suggest quite the opposite, showing that invasive populations may be populated by less aggressive individuals (Suarez et al., 1999; Cote et al., 2010b). Less competitive, or less aggressive individuals may in fact drive the range expansion simply by being displaced or competitively excluded from established optimal habitats (Holecamp & Smale, 1998; Schradin & Lamprecht, 2002; Guerra & Pollack, 2010; re- viewed in Cote et al., 2010a), and being forced to settle in potentially less ideal habitats at the edges of a species’ range. It has been argued that the general tendency for a species to have low aggression towards conspecifics may in fact help foster high densities, and help invasive species simply numerically outcompete less dense populations of native species. Invasive populations of the Argentine ant ( Liniepithema humile ) in southern California are such an example where the invasive species exhibits reduced intraspecific aggression, relative to native populations of L. humile in South America (Suarez et al., 1999), and this reduced intraspecific aggression may facilitate growth of the invasive population (Holway et al., 1998). However, in these instances, aggressivity is considered as a species- or population-wide trait, not as a trait that varies among individuals. When individual differences have been examined, asocial tendencies rather than tolerance or gregariousness appear to drive dispersal and promote invasion into new habitats. For example, in mosquitofish populations, Gambusia affinis , the least social individuals disperse (Cote et al., 2010b). The aim of our study was to determine whether there were differences in aggressive tendencies and competitive abilities between individuals from an invasion front and those from a more established area. We used the round goby ( Neogobius melanostomus ), an invasive fish in the Laurentian Great Lakes. Round goby are native to the Ponto-Caspian region of Europe (Jude et al., 1992) and have rapidly invaded North America and Western Europe. Their invasion has been mediated through unintentional human transfers in the ballast water of shipping vessels (Corkum et al., 2004). Although the saltatory appearances of the round goby through the Great Lakes over a five year period was probably aided by human-assisted dispersal (Hensler & Jude, 2007; Hayden & Miner, 2009), round goby also undergo natural range expansions in invaded habitats through unassisted dispersal (Bronnenhuber et al., 2011; Gutowsky et al., 2011; LaRue et al., 2011). Individual variation in aggressiveness and dispersal tendencies may mediate this expansion. We compared aggressiveness and competitive ability in the round goby by means of a resource contest over access to shelter. Male round goby that are reproductively active will guard a territory that contains a nest/shelter (Wickett & Corkum, 1998; MacInnis & Corkum, 2000). Round goby are strongly motivated to compete for and actively defend these shelters from heterospecifics (Dubs & Corkum, 1996; Balshine et al., 2005; Savino et al., 2007) and conspecifics (Stammler & Corkum, 2005; Sopinka et al., 2010). We predicted that if aggression is important in mediating round goby range expansions, then round goby from an invasion front would (1) be bolder than, (2) be more aggressive than and (3) outcompete round goby from established areas. However, given that round goby are highly aggressive and territorial, less competitive individuals could be forced out of prime habitat and, thus, contribute to range expansion (Ray & Corkum, 2001; Johnson et al., 2005; Brownscombe & Fox, 2012). If invasion front round goby are indeed the displaced, less competitive fish, then alternatively we predicted they would be (1) less bold, (2) less aggressive and (3) lose contests more often compared to fish from established populations. Round goby ( N. melanostomus ) were collected on June 9 and June 29, 2010 from two areas in the Trent-Severn waterway (Ontario, Canada; Figure 1). Fish from an established and reliably sampled round goby population (since 2003) were caught in three locations in the Trent River centered around Hastings (44°17 54 N, 077°58 02 E; 44°17 43 N, 077°58 29 E; 44°18 30 N, 077°57 28 E; Figure 1 Established Area Inset, Raby et al., 2010). Fish from the invasion front were caught at four locations in the Otonabee River (44°11 49 N, 078°14 22 E; 44°12 22 N, 078°14 22 E; 44°12 36 N, 078°14 11 E; 44°12 46 N, 078°14 01 E; Figure 1 Invasion Front Inset). Round goby were first detected in the Otonabee River only in the spring of 2010 despite this site being previously surveyed for round goby in 2009 and earlier (Brownscombe, 2011). The Trent River population has been there for at least seven years and is thought to have been initially established by a bait bucket transfer from one of the Great Lakes. Round goby from the Otonabee River invasion front site have spread down from the original introduction site in the Trent River near Hastings. The movement of this invasion front has tracked since 2003 (Raby et al., 2010; Brownscombe, 2011; Gutowsky & Fox, 2011). Although more established round goby populations exist in North America (for example, Lake Erie was colonized by round goby in 1993; Corkum et al., 1994), we chose to examine fish from these two nearby areas to control for environmentally induced differences in behaviour (Alvarez & Bell, 2007). The two chosen areas are within the same drainage system, and have similar habitat characteristics. Round goby were caught using angling and baited minnow traps and were then sorted by sex and reproductive status. Males and females were dis- tinguished based on urogenital papilla shape (pointed in males, square in females; Miller, 1984) and the reproductive status of males was assessed using papilla length, head width and body colouration (Marentette & Corkum, 2008; Marentette et al., 2009). Males were transported to McMaster University (Hamilton, Ontario) and held in 66 l aquaria in groups of four to six fish from the same collection site. Aquaria contained gravel to a depth of 1 cm, 15-cm sections of PVC piping as shelter, an AquaClear 50 external box filter, and a thermometer (water temperature maintained between 22 and 24°C). Round goby were fed flake food (Nutrafin) ad libitum once daily and were allowed at least 72 h to acclimate in the lab prior to behavioural testing. In total, 36 resource competition trials were conducted. Fish were placed in size-matched pairs with one competitor from the invasion front population and its opponent from the established area. We size-matched fish using body mass (to the nearest 0.01 g) because body size differences of as little as 3% have been shown to influence the outcomes of competitive interactions in this species (Stammler & Corkum, 2005). Size differences between competitors ranged from 0.01 to 2.0 g in body mass (mean difference 0.57 ± 0.49 g, paired t -test; t = 0 . 14, N = 36, p = 0 . 89). In order to further account for the effect of size differences on contest outcomes, we selected contestants such that the marginally larger individual of the pair was from the invasion front in half the trials and from the established area in the other half of the trials. To facilitate identification during the contests, each individual was marked subcutaneously with either green or yellow non-toxic acrylic paint just below the dorsal fin spines (see Wolfe & Marsden, 1998). The colour of paint used for each fish and the placement of the fish into the left versus the right end chamber of the aquarium (see below) were randomized. Twenty-four hours prior to the start of a behavioural trial, size-matched marked opponents were placed into one of two end chambers in a 66-l experimental aquarium divided into thirds by removable, black opaque barriers. Each chamber contained a black opaque shelter box (5 cm long, 15 cm wide, 5 cm high) with a small opening that was oriented to face the front of the aquarium (Figure 2A). The next morning an observer, blind to the origin of the fish, recorded all the behavioural data while seated 1 m away from the aquarium (following protocols used in Sopinka et al., 2010). Data were recorded in person and trials were also videotaped for further analyses on Mini DV cassettes using a Sony Digital Camcorder (model DVR- VX2000NTSC). Behavioural trials always began between 9:00 and 10:00 h. Each trial started when the shelters were removed from the end chambers (Figure 2B). We observed each focal fish for a 5-min post shelter removal period and recorded the time taken to initiate movement following removal of the shelter as well as all behaviours exhibited (see below). Following the 5-min boldness evaluation, we removed the two opaque barriers allowing both fish access to the central chamber and shelter and to see and interact with one another (Figure 2C). Each fish was observed for 10 min in a pre-determined, randomized order (20 min total). The identity ...
Context 6
... boldness and dispersal tendency are often positively correlated and comprise a behavioural syndrome (Sih et al., 2004a,b), but the role of this syndrome in the expansion of invasion fronts is not yet clear. Some studies have suggested that individuals on the invasion front are more aggressive than their counterparts inhabiting established areas. For example, western bluebirds ( Sialia mexicana ) were more aggressive and displaced than their less aggressive sister species, mountain bluebirds ( Sialia cur- rcoides ), and the males in new populations were more aggressive than males in older, established populations (Duckworth & Badyaev, 2007). Hence in bluebirds, aggressive individuals were driving the range expansion (Duckworth & Badyaev, 2007). Other studies suggest quite the opposite, showing that invasive populations may be populated by less aggressive individuals (Suarez et al., 1999; Cote et al., 2010b). Less competitive, or less aggressive individuals may in fact drive the range expansion simply by being displaced or competitively excluded from established optimal habitats (Holecamp & Smale, 1998; Schradin & Lamprecht, 2002; Guerra & Pollack, 2010; re- viewed in Cote et al., 2010a), and being forced to settle in potentially less ideal habitats at the edges of a species’ range. It has been argued that the general tendency for a species to have low aggression towards conspecifics may in fact help foster high densities, and help invasive species simply numerically outcompete less dense populations of native species. Invasive populations of the Argentine ant ( Liniepithema humile ) in southern California are such an example where the invasive species exhibits reduced intraspecific aggression, relative to native populations of L. humile in South America (Suarez et al., 1999), and this reduced intraspecific aggression may facilitate growth of the invasive population (Holway et al., 1998). However, in these instances, aggressivity is considered as a species- or population-wide trait, not as a trait that varies among individuals. When individual differences have been examined, asocial tendencies rather than tolerance or gregariousness appear to drive dispersal and promote invasion into new habitats. For example, in mosquitofish populations, Gambusia affinis , the least social individuals disperse (Cote et al., 2010b). The aim of our study was to determine whether there were differences in aggressive tendencies and competitive abilities between individuals from an invasion front and those from a more established area. We used the round goby ( Neogobius melanostomus ), an invasive fish in the Laurentian Great Lakes. Round goby are native to the Ponto-Caspian region of Europe (Jude et al., 1992) and have rapidly invaded North America and Western Europe. Their invasion has been mediated through unintentional human transfers in the ballast water of shipping vessels (Corkum et al., 2004). Although the saltatory appearances of the round goby through the Great Lakes over a five year period was probably aided by human-assisted dispersal (Hensler & Jude, 2007; Hayden & Miner, 2009), round goby also undergo natural range expansions in invaded habitats through unassisted dispersal (Bronnenhuber et al., 2011; Gutowsky et al., 2011; LaRue et al., 2011). Individual variation in aggressiveness and dispersal tendencies may mediate this expansion. We compared aggressiveness and competitive ability in the round goby by means of a resource contest over access to shelter. Male round goby that are reproductively active will guard a territory that contains a nest/shelter (Wickett & Corkum, 1998; MacInnis & Corkum, 2000). Round goby are strongly motivated to compete for and actively defend these shelters from heterospecifics (Dubs & Corkum, 1996; Balshine et al., 2005; Savino et al., 2007) and conspecifics (Stammler & Corkum, 2005; Sopinka et al., 2010). We predicted that if aggression is important in mediating round goby range expansions, then round goby from an invasion front would (1) be bolder than, (2) be more aggressive than and (3) outcompete round goby from established areas. However, given that round goby are highly aggressive and territorial, less competitive individuals could be forced out of prime habitat and, thus, contribute to range expansion (Ray & Corkum, 2001; Johnson et al., 2005; Brownscombe & Fox, 2012). If invasion front round goby are indeed the displaced, less competitive fish, then alternatively we predicted they would be (1) less bold, (2) less aggressive and (3) lose contests more often compared to fish from established populations. Round goby ( N. melanostomus ) were collected on June 9 and June 29, 2010 from two areas in the Trent-Severn waterway (Ontario, Canada; Figure 1). Fish from an established and reliably sampled round goby population (since 2003) were caught in three locations in the Trent River centered around Hastings (44°17 54 N, 077°58 02 E; 44°17 43 N, 077°58 29 E; 44°18 30 N, 077°57 28 E; Figure 1 Established Area Inset, Raby et al., 2010). Fish from the invasion front were caught at four locations in the Otonabee River (44°11 49 N, 078°14 22 E; 44°12 22 N, 078°14 22 E; 44°12 36 N, 078°14 11 E; 44°12 46 N, 078°14 01 E; Figure 1 Invasion Front Inset). Round goby were first detected in the Otonabee River only in the spring of 2010 despite this site being previously surveyed for round goby in 2009 and earlier (Brownscombe, 2011). The Trent River population has been there for at least seven years and is thought to have been initially established by a bait bucket transfer from one of the Great Lakes. Round goby from the Otonabee River invasion front site have spread down from the original introduction site in the Trent River near Hastings. The movement of this invasion front has tracked since 2003 (Raby et al., 2010; Brownscombe, 2011; Gutowsky & Fox, 2011). Although more established round goby populations exist in North America (for example, Lake Erie was colonized by round goby in 1993; Corkum et al., 1994), we chose to examine fish from these two nearby areas to control for environmentally induced differences in behaviour (Alvarez & Bell, 2007). The two chosen areas are within the same drainage system, and have similar habitat characteristics. Round goby were caught using angling and baited minnow traps and were then sorted by sex and reproductive status. Males and females were dis- tinguished based on urogenital papilla shape (pointed in males, square in females; Miller, 1984) and the reproductive status of males was assessed using papilla length, head width and body colouration (Marentette & Corkum, 2008; Marentette et al., 2009). Males were transported to McMaster University (Hamilton, Ontario) and held in 66 l aquaria in groups of four to six fish from the same collection site. Aquaria contained gravel to a depth of 1 cm, 15-cm sections of PVC piping as shelter, an AquaClear 50 external box filter, and a thermometer (water temperature maintained between 22 and 24°C). Round goby were fed flake food (Nutrafin) ad libitum once daily and were allowed at least 72 h to acclimate in the lab prior to behavioural testing. In total, 36 resource competition trials were conducted. Fish were placed in size-matched pairs with one competitor from the invasion front population and its opponent from the established area. We size-matched fish using body mass (to the nearest 0.01 g) because body size differences of as little as 3% have been shown to influence the outcomes of competitive interactions in this species (Stammler & Corkum, 2005). Size differences between competitors ranged from 0.01 to 2.0 g in body mass (mean difference 0.57 ± 0.49 g, paired t -test; t = 0 . 14, N = 36, p = 0 . 89). In order to further account for the effect of size differences on contest outcomes, we selected contestants such that the marginally larger individual of the pair was from the invasion front in half the trials and from the established area in the other half of the trials. To facilitate identification during the contests, each individual was marked subcutaneously with either green or yellow non-toxic acrylic paint just below the dorsal fin spines (see Wolfe & Marsden, 1998). The colour of paint used for each fish and the placement of the fish into the left versus the right end chamber of the aquarium (see below) were randomized. Twenty-four hours prior to the start of a behavioural trial, size-matched marked opponents were placed into one of two end chambers in a 66-l experimental aquarium divided into thirds by removable, black opaque barriers. Each chamber contained a black opaque shelter box (5 cm long, 15 cm wide, 5 cm high) with a small opening that was oriented to face the front of the aquarium (Figure 2A). The next morning an observer, blind to the origin of the fish, recorded all the behavioural data while seated 1 m away from the aquarium (following protocols used in Sopinka et al., 2010). Data were recorded in person and trials were also videotaped for further analyses on Mini DV cassettes using a Sony Digital Camcorder (model DVR- VX2000NTSC). Behavioural trials always began between 9:00 and 10:00 h. Each trial started when the shelters were removed from the end chambers (Figure 2B). We observed each focal fish for a 5-min post shelter removal period and recorded the time taken to initiate movement following removal of the shelter as well as all behaviours exhibited (see below). Following the 5-min boldness evaluation, we removed the two opaque barriers allowing both fish access to the central chamber and shelter and to see and interact with one another (Figure 2C). Each fish was observed for 10 min in a pre-determined, randomized order (20 min total). The identity of the fish that crossed over to the opposite side of the tank first was noted, along with which fish initiated the first aggressive act, the latency to the first aggressive act (in s), and the total duration of the first aggressive ...
Citations
... This process can lead to spatial sorting of populations being adapted to dispersal at the edge, and adapted to high intraspecific competition in established populations [14]. While this was shown for morphological traits related to movement [15], the evidence for spatial sorting in behavioural traits remains equivocal, both for existence of behavioural sorting itself [16,17] as well as for the behavioural types favourable in different spatial zones of a non-native expansion [16,18,19]. ...
... This process can lead to spatial sorting of populations being adapted to dispersal at the edge, and adapted to high intraspecific competition in established populations [14]. While this was shown for morphological traits related to movement [15], the evidence for spatial sorting in behavioural traits remains equivocal, both for existence of behavioural sorting itself [16,17] as well as for the behavioural types favourable in different spatial zones of a non-native expansion [16,18,19]. ...
... While male fish and birds appear to be more aggressive at the expansion edge [16,18] the male non-native rodents observed here were more timid and risk-averse at the expansion edge, compared to those in established populations. Rodents are a taxon under high predation pressure, and have evolved to a rather hidden lifestyle, avoiding open spaces and dangerous daytimes, which seem to favour increased cryptic and timid behaviour during a colonization process. ...
Animal behaviour can moderate biological invasion processes, and the native fauna's ability to adapt. The importance and nature of behavioural traits favouring colonization success remain debated. We investigated behavioural responses associated with risk-taking and exploration, both in non-native bank voles (Myodes glareolus, N = 225) accidentally introduced to Ireland a century ago, and in native wood mice (Apodemus sylvaticus, N = 189), that decline in numbers with vole expansion. We repeatedly sampled behavioural responses in three colonization zones: established bank vole populations for greater than 80 years (2 sites), expansion edge vole populations present for 1-4 years (4) and pre-arrival (2). All zones were occupied by wood mice. Individuals of both species varied consistently in risk-taking and exploration. Mice had not adjusted their behaviour to the presence of non-native voles, as it did not differ between the zones. Male voles at the expansion edge were initially more risk-averse but habituated faster to repeated testing, compared to voles in the established population. Results thus indicate spatial sorting for risk-taking propensity along the expansion edge in the dispersing sex. In non-native prey species the ability to develop risk-averse phenotypes may thus represent a fundamental component for range expansions.
... Thus, fish from Grønsund might be considered bolder, different from our original prediction. In another study on round gobies, Groen et al. (2012) did not find any significant difference in boldness between old and new populations. Notably, our newer population was older (5 years postestablishment) than comparable studies (i.e. ...
... Notably, our newer population was older (5 years postestablishment) than comparable studies (i.e. 2-3 year; Myles-Gonzalez et al. 2015;Groen et al. 2012), so that difference observed in those studies may have been lost by the time of sampling. Traits linked to dispersal like boldness may be lost over time due to differences in density between populations: lower densities lead to selection of traits that increase reproductive rate rather than dispersal tendency (Duckworth, 2008). ...
... Traits linked to dispersal like boldness may be lost over time due to differences in density between populations: lower densities lead to selection of traits that increase reproductive rate rather than dispersal tendency (Duckworth, 2008). The type of behavioural variables being considered may also be a factor leading to our contrasting results, for example only Groen et al. (2012) measured boldness as activity after a stressful event, while Myles-Gonzalez et al. (2015) measured it as the latency to emerge from a shelter. Contrary to expectations, there was no difference between populations in their physiological stress responses. ...
The round goby (Neogobius melanostomus) is a fish native to the Ponto-Caspian region that is highly invasive through freshwater and brackish habitats in northern Europe and North America. Individual behavioural variation appears to be an important factor in their spread, for example a round goby's personality traits can influence their dispersal tendency, which may also produce variation in the behavioural composition of populations at different points along their invasion fronts. To further analyze the drivers of behavioural variation within invasive round goby populations, we focused on two populations along the Baltic Sea invasion front with closely comparable physical and community characteristics. Specifically, this study measured personality within a novel environment and predator response context (i.e., boldness), and directly analyzed links between individuals' personality traits and their physiological characteristics and stress responses (i.e., blood cortisol and lactate, brain neurotransmitters). In contrast to previous findings, the more recently established population had similar activity levels but were less bold in response to a predator cue than the older population, which suggests that behavioural compositions within our study populations may be more driven by local environmental conditions rather than being a result of personality-biased dispersal. Furthermore, we found that both populations showed similar physiological stress responses, and there also appeared to be no detectable relationship between physiological parameters and behavioural responses to predator cues. Instead, body size and body condition were important factors influencing individual behavioural responses. Overall, our results reinforce the importance of boldness traits as a form of phenotypic variation in round goby populations in the Baltic Sea. We also highlight the importance of these traits for future studies specifically testing for effects of invasion processes on phenotypic variation in the species. Nonetheless, our results also highlight that the physiological mechanisms underpinning behavioural variation in these populations remain unclear.
... In animals, a consensus is emerging around the hypothesis that particular 'pioneering' phenotypes may drive these range dynamics. Expansion populations often show improved cold tolerance, higher resting metabolic rates, heightened immune defences, more boldness and greater territorial aggression (Butin et al., 2005;Duckworth & Badyaev, 2007;Groen et al., 2012;Liebl & Martin, 2012;Martin et al., 2014Martin et al., , 2015Michelangeli et al., 2017;Myles-Gonzalez et al., 2015). They also may exhibit improved movement performance (Llewelyn et al., 2010;Lombaert et al., 2014) and have larger bodies (Bowler & Benton, 2005;Chuang & Peterson, 2016;Clobert et al., 2009). ...
Ecogeographic rules describe spatial patterns in biological trait variation and shed light on the drivers of such variation. In animals, a consensus is emerging that ‘pioneering’ traits may facilitate range shifts via a set of bold, aggressive and stress‐resilient traits. Many of these same traits are associated with more northern latitudes, and most range shifts in the northern hemisphere indicate northward movement. As a consequence, it is unclear whether pioneering traits are simply corollaries of existing latitudinal variation, or whether they override other well‐trodden latitudinal patterning as a unique ecogeographic rule of phenotypic variation.
The tree swallow Tachycineta bicolor is a songbird undergoing a southward range shift in the eastern United States, in direct opposition of the poleward movement seen in most other native species' range shifts. Because this organic range shift countervails the typical direction of movement, this case study provides for unique ecological insights on organisms and their ability to thrive in our changing world.
We sampled female birds across seven populations, quantifying behavioural, physiological and morphological traits. We also used GIS and field data to quantify a core set of ecological factors with strong ties to these traits as well as female performance.
Females at more southern expansion sites displayed higher maternal aggression, higher baseline corticosterone and more pronounced elevation of corticosterone following a standardized stressor, contrary to otherwise largely conserved latitudinal patterning in these traits. Microhabitat variation explained some quantitative phenotypic variation, but the expansion and historic ranges did not differ in openness, distance to water or breeding density.
This countervailing range shift therefore suggests that pioneering traits are not simply corollaries of existing latitudinal variation, but rather, they may override other well‐trodden latitudinal patterning as a unique ecogeographic rule of phenotypic variation.
... However, this might be counteracted by 'parasite acquisition', where native parasites infect the introduced species . Plasticity in how behavioural, physiological and/or lifehistory traits are expressed is also important following establishment, as individuals that disperse at the invasion front are predicted to have a suite of traits more suited to population expansion (e.g., boldness, high activity and exploratory behaviours, high resource acquisition) than those in the core range (Brownscombe et al., 2012;Tarkan et al., 2021). ...
Introductions of non‐native freshwater fish continue to increase globally, although only a small proportion of these introductions will result in an invasion. These invasive populations can cause ecological impacts in the receiving ecosystem through processes including increased competition and predation pressure, genetic introgression and the transmission of non‐native pathogens. Definitions of ecological impact emphasize that shifts in the strength of these processes are insufficient for characterizing impact alone and, instead, must be associated with a quantifiable decline of biological and/or genetic diversity and lead to a measurable loss of diversity or change in ecosystem functioning. Assessments of ecological impact should thus consider the multiple processes and effects that potentially occur from invasive fish populations where, for example, impacts of invasive common carp Cyprinus carpio populations are through a combination of bottom‐up and top‐down processes that, in entirety, cause shifts in lake stable states and decreased species richness and/or abundances in the biotic communities. Such far‐reaching ecological impacts also align to contemporary definitions of ecosystem collapse, given they involve substantial and persistent declines in biodiversity and ecosystem functions that cannot be recovered unaided. Thus, while not all introduced freshwater fishes will become invasive, those species that do develop invasive populations can cause substantial ecological impacts, where some of the impacts on biodiversity and ecosystem functioning might be sufficiently harmful to be considered as contributing to ecosystem collapse.
... These traits may all interact to positively influence invasion success (Juette et al. 2014;Rehage et al. 2016). Additionally, aggressiveness is also often associated with dispersal and presence at an invasion front (e.g., Groen et al. 2012). Such aggressive individuals may be better able to obtain and defend resources, thus enhancing the impacts of the invasive species. ...
Within many populations, some individuals may be more apt to move, and these individuals can substantially impact population dynamics. Invasive Silver Carp (Hypophthalmichthys molitrix) have spread throughout much of the Mississippi River Basin, and their presence has resulted in multiple negative ecosystem effects. Silver Carp are known to move hundreds of km, which has likely contributed to their rapid spread. Our study examined movement patterns and environmental cues for movement in Silver Carp based on acoustic telemetry of tagged fish that ranged widely (i.e., mobile) and those that did not range far from the site of their original capture and tagging (i.e., sedentary) in the Wabash River, USA. Sedentary and mobile designations were made based on observed extremes of mean annual ranges, and these designations were consistent within seasons and among years. Both movement groups displayed seasonal variation in movements, with mobile Silver Carp consistently moving greater distances within each season and sedentary Silver Carp exhibiting lower variability in distances moved than mobile individuals. Discharge (change in discharge) and temperature were significant predictors of mobile and sedentary individuals’ movements. Additional environmental variables (i.e., cumulative growing degree day, day of year, and change in temperature) also related to movement likelihood of sedentary individuals, whereas total length was the only additional variable that influenced movement likelihood of mobile individuals. Total length was significantly related to movement distance for both groups of Silver Carp, but the relationship was negative for sedentary fish and positive for mobile fish. Results point to differences in behavior that may require targeted management strategies to achieve agency goals to interrupt mobile individual movements that can result in range expansion. Such strategies may also limit introductions and invasions by other aquatic invasive species that exhibit similar behaviors.
... nutrient limitation), whereby the rate of primary production is reduced (Pagnucco et al. 2016), as well as facilitative interactions resulting in shifts in dominance amongst different species . Future studies should also consider multiple predator effects alongside habitat complexity treatments, such as potential intraspecific competitive interactions (Groen et al. 2012). In particular, intraspecific agonistic behaviours by N. melanostomus at higher densities might alleviate ecological impact. ...
Interactions between multiple invasive alien species (IAS) might increase their ecological impacts, yet relatively few studies have attempted to quantify the effects of facilitative interactions on the success and impact of aquatic IAS. Further, the effect of abiotic factors, such as habitat structure, have lacked consideration in ecological impact prediction for many high-profile IAS, with most data acquired through simplified assessments that do not account for real environmental complexities. In the present study, we assessed a potential facilitative interaction between a predatory invasive fish, the Ponto-Caspian round goby (Neogobius melanostomus), and an invasive bivalve, the Asian clam (Corbicula fluminea). We compared N. melanostomus functional responses (feeding-rates under different prey densities) to a co-occurring endangered European native analogue fish, the bullhead (Cottus gobio), in the presence of increased levels of habitat complexity driven by the accumulation of dead C. fluminea biomass that persists within the environment (i.e. 0, 10, 20 empty bivalve shells). Habitat complexity significantly influenced predation, with consumption in the absence of shells being greater than where 10 or 20 shells were present. However, at the highest shell density, invasive N. melanostomus maximum feeding-rates and functional response ratios were substantially higher than those of native C. gobio. Further, the Relative Impact Potential metric, by combining per capita effects and population abundances, indicated that higher shell densities exacerbate the relative impact of the invader. It therefore appears that N. melanostomus can better tolerate higher IAS shell abundances when foraging at high prey densities, suggesting the occurrence of an important facilitative interaction. Our data are thus fully congruent with field data that link establishment success of N. melanostomus with the presence of C. fluminea. Overall, we show that invader-driven benthic habitat complexity can alter the feeding-rates and thus impacts of predatory fishes, and highlight the importance of inclusion of abiotic factors in impact prediction assessments for IAS.
... Recently, N. melanostomus has been used as a model species to show how individuals at invasion fronts differ from those in established populations across a variety of traits. In addition to differences in condition, age, density, age-at-maturity, predator pressure, sex ratios, size and even trophic position (Azour et al., 2015;Brandner et al., 2013;Brandner et al., 2018;Brownscombe & Fox, 2013;Gutowsky & Fox, 2011;Gutowsky & Fox, 2012), N. melanostomus populations exhibit behavioural differences, where individuals along invasion fronts are more aggressive, active and bold than individuals from established populations (Groen et al., 2012;Myles-Gonzalez et al., 2015). The higher proportion of bold N. melanostomus found along invasion fronts could be a key driver of the invasion process for this species. ...
... Several previous studies of competition in N. melanostomus have shown that the competitive success of this species is often a result of high levels of aggressive and antagonistic behaviours towards competitors (e.g., Balshine et al., 2005;Bergstrom & Mensinger, 2009;Church et al., 2017;Dubs & Corkum, 1996;Janssen & Jude, 2001;Leino & Mensinger, 2017). Although boldness and aggression are often linked within individuals, with bolder individuals being more aggressive than shy individuals (Biro & Stamps, 2008;Sih et al., 2004), Groen et al. (2012) detected no association between boldness and aggression at the T A B L E 1 Poisson GLM analyses of "focal fish consumption" and "treatment fish consumption," and negative-binomial GLM analysis of "total interactions," based on factors "focal species," "treatment fish personality," their interaction term and the covariates "focal fish length" and "treatment fish length". Values given in bold are significant at the P < 0.05 level. ...
... Nonetheless, treatment fish length did affect treatment fish consumption, with larger N. melanostomus eating more prey than small N. melanostomus. This influence of body size on consumption by treatment fish agrees with the findings of Groen et al. (2012), who concluded that body size is a more important factor than aggression or boldness for determining the outcome of competitive interactions in N. melanostomus. ...
... Recently, N. melanostomus has been used as a model species to show how individuals at invasion fronts differ from those in established populations across a variety of traits. In addition to differences in condition, age, density, age-at-maturity, predator pressure, sex ratios, size and even trophic position (Azour et al., 2015;Brandner et al., 2013;Brandner et al., 2018;Brownscombe & Fox, 2013;Gutowsky & Fox, 2011;Gutowsky & Fox, 2012), N. melanostomus populations exhibit behavioural differences, where individuals along invasion fronts are more aggressive, active and bold than individuals from established populations (Groen et al., 2012;Myles-Gonzalez et al., 2015). The higher proportion of bold N. melanostomus found along invasion fronts could be a key driver of the invasion process for this species. ...
... Several previous studies of competition in N. melanostomus have shown that the competitive success of this species is often a result of high levels of aggressive and antagonistic behaviours towards competitors (e.g., Balshine et al., 2005;Bergstrom & Mensinger, 2009;Church et al., 2017;Dubs & Corkum, 1996;Janssen & Jude, 2001;Leino & Mensinger, 2017). Although boldness and aggression are often linked within individuals, with bolder individuals being more aggressive than shy individuals (Biro & Stamps, 2008;Sih et al., 2004), Groen et al. (2012) detected no association between boldness and aggression at the T A B L E 1 Poisson GLM analyses of "focal fish consumption" and "treatment fish consumption," and negative-binomial GLM analysis of "total interactions," based on factors "focal species," "treatment fish personality," their interaction term and the covariates "focal fish length" and "treatment fish length". Values given in bold are significant at the P < 0.05 level. ...
... Nonetheless, treatment fish length did affect treatment fish consumption, with larger N. melanostomus eating more prey than small N. melanostomus. This influence of body size on consumption by treatment fish agrees with the findings of Groen et al. (2012), who concluded that body size is a more important factor than aggression or boldness for determining the outcome of competitive interactions in N. melanostomus. ...
This study examines the impact of boldness on foraging competition of the highly invasive round goby Neogobius melanostomus Pallas 1815. Individual risk tolerance, or boldness, was measured as the time to resume movement after a simulated predation strike. Fish that resumed movement faster were categorized as “bold,” fish that took more time to resume movement were categorized as “shy” and those that fell in between these two categories were determined to have “intermediate” boldness. Competitive impacts of boldness in N. melanostomus were determined in a laboratory foraging experiment in which interspecific (juvenile Atlantic cod Gadus morhua Linnaeus 1758) and intraspecific (intermediate N. melanostomus) individuals were exposed to either bold or shy N. melanostomus competitors. G. morhua consumed fewer prey when competing with bold N. melanostomus than when competing with shy N. melanostomus, whereas intermediately bold N. melanostomus foraging was not affected by competitor boldness. Bold and shy N. melanostomus consumed similar amounts of prey, and the number of interactions between paired fish did not vary depending on the personality of N. melanostomus individuals. Therefore, intraspecific foraging competition was not found to be personality dependent. This study provides evidence that individual differences in boldness can mediate competitive interactions in N. melanostomus; nonetheless, results also show that competition is also governed by other mechanisms that require further study.
... Our observed negative correlation between boldness and movement distance may reflect the limited opportunity carp gudgeons have to disperse, creating a dynamic where permanent pools of water become a valuable resource that bolder fish stay and protect (e.g. Groen et al., 2012;Guerra & Pollack, 2010). Bold fish are often more aggressive, so shy individuals may be forced out of optimal habitat and require increased dispersal capacity to find a new pool Guerra & Pollack, 2010;Sih et al., 2004). ...
Historically, the differences in dispersal behaviour between individuals within a species has largely been ignored. Instead, we tend to assume all individuals within a population express similar phenotypes. However, evidence is growing for the importance of intraspecific variability in dispersal propensity and how this variability may influence population dynamics, as well as the role of environmental context in driving this behaviour. Individuals that are more likely to disperse can have other traits, such as being bolder or more aggressive, that collectively form behavioural syndromes. We tested for a behavioural syndrome in carp gudgeons (Hypseleotris spp.) species' complex, a type of small fish found in intermittent streams in southeastern Australia. Intermittent streams are an environment where selection may favour the evolution of different dispersal phenotypes, given the variable and unpredictable nature of flows. During dry periods, fish become isolated in refuge pools that vary in quality and persistence, and then can disperse when flow resumes. Dispersal can have costs (e.g. the risk of not finding another habitat) but also benefits (e.g. opportunity to find better habitat), meaning that different strategies (i.e. dispersing versus staying) may both be advantageous and thus evolve. Through a series of experiments that assessed these fish's latency to emergence into a novel environment and tendency to shoal, as well as movement behaviour in artificial streams, we found that (1) flow is not likely to be a movement cue, and (2) boldness, sociability and dispersal distance were repeatable, consistent with the notion that carp gudgeons exhibit personalities. To our knowledge, this is the first demonstration of a behavioural syndrome in a freshwater fish that inhabits intermittent streams. This finding contributes to our understanding of how carp gudgeons move through intermittent streams and the potential dynamics that allow these fish to persist in such harsh, hydrologically variable habitats.
... Gobies are reliant on shelters (e.g. crevices among stones) for protection from predators and access to better feeding ground (Groen et al. 2012;Grabowska et al. 2016). The male gobies also need shelters for nesting ground where they attract females and care for fertilized eggs (Groen et al. 2012). ...
... crevices among stones) for protection from predators and access to better feeding ground (Groen et al. 2012;Grabowska et al. 2016). The male gobies also need shelters for nesting ground where they attract females and care for fertilized eggs (Groen et al. 2012). The importance of shelter to these gobies leads to both intraspecific and interspecific competition for shelters resulting in displacement of less competitive fish when they are a limiting factor (van Kessel et al. 2011). ...
... To explore the difference in time spent in shelter between the different species of intruding fish, a third three-way ANOVA with replication was completed with the factors of fish sex (male, female), light conditions (day, night) and intruder species (intruding P. semilunaris, intruding N. melanostomus) for each shelter type. In addition to competition for shelter, aggressive behaviour (direct aggression, indirect aggression and guarding) for each fish pairing were compared using the Chi squared test according to Groen et al. (2012). Initial data exploration showed that behaviour was fish specific regardless of fish sex and so the data was pooled by treatment. ...
Non-indigenous western tubenose goby Proterorhinus semilunaris and round goby Neogobius melanostomus have rapidly increased in numbers and displaced native ichthyofauna in invaded ecosystems. This displacement has been predominantly linked to competition for resources and shelters. Similarly, P. semilunaris was displaced in many localities after introduction of N. melanostomus but the mechanisms of displacement are still not clear. Within the present study shelter competition laboratory studies were completed with P. semilunaris as resident fish before the introduction of either a sized matched P. semilunaris or N. melanostomus intruder. The fish competed for shelters which resembled a rock or plant. Time in shelter and accounts of direct aggression, indirect aggression and the guarding of shelter were also recorded for each fish. Shelter competitions showed P. semilunaris spent more time in plant shelters but N. melanostomus spent similar time periods in both shelter types. In intraspecific pairings, resident fish spent significantly more time in the shelters and exhibited significantly higher direct aggression and shelter guarding, especially for plant shelters. In interspecific pairings, there was no significant difference in the time spent in shelter by resident P. semilunaris and intruder N. melanostomus in either shelter type at day or night. However, in interspecific pairings, the intruder fish showed significantly higher levels of all aggression types. In intraspecific pairing, the concept of ‘resident wins’ was observed. However, in interspecific pairings, N. melanostomus was able to displace the resident fish. The higher aggression of N. melanostomus in shelter competition could account for greater invasive success and the reduction of P. semilunaris observed in the wild.
