Sandra Hudina

Differences in tolerance to anthropogenic stress between invasive and native bivalves.

Tolerance towards environmental stress has been frequently considered as one of the key determinants of invasion success. However, empirical evidence supporting the assumption that invasive species can better endure unfavorable conditions compared with native species is limited and has yielded opposing results. In this study, we examined the tolerance to different stress conditions (thermal stress and trace metal zinc pollution stress) in two phylogenetically related and functionally similar freshwater bivalve species, the native Anodonta anatina and the invasive Sinanodonta woodiana. We assessed potential differences in response to stress conditions using several cellular response assays: efficiency of the multixenobiotic resistance mechanism, respiration estimate (INT reduction capacity), and enzymatic biomarkers. Our results demonstrated that the invasive species overall coped much better with unfavorable conditions. The higher tolerance of S. woodiana was evident from (i) significantly decreased Rhodamine B accumulation indicating more efficient multixenobiotic resistance mechanism; (ii) significantly higher INT reduction capacity and (iii) less pronounced alterations in the activity of stress-related enzymes (glutathione-S-transferase, catalase) and of a neurotoxicity biomarker (cholinesterase) in the majority of treatment conditions in both stress trials. Higher tolerance to thermal extremes may provide physiological benefit for further invasion success of S. woodiana in European freshwaters, especially in the context of climate change.

Competitive interactions between co-occurring invaders: identifying asymmetries between two invasive crayfish species

Ecosystems today increasingly suffer invasions by multiple invasive species. Complex interactions between invasive species can have different fitness implications for each invader, which can in turn determine the future progression of their invasions and result in differential impacts on native species and ecosystems. To this end, through pair-wise and group scale experiments, we examined possible interaction outcomes, competition effects and their potential fitness implications for two widespread invasive species of crayfish that increasingly co-occur in freshwater ecosystems of Europe (Pacifastacus leniusulus and Orconectes limosus). In all trials, P. leniusculus demonstrated the potential to outcompete O. limosus in both staged encounters and direct resource competition, being more likely to win heterospecific agonistic encounters and to acquire shelters at a higher rate. Observed dyadic dominance was translated to a broader social context of group-scale experiments, in which dominance of P. leniusculus was further strengthened by size differential between species. O. limosus was not able to compensate for competitive pressure by the dominant P. leniusculus and suffered wet weight loss and more frequent injuries in the presence of P. leniusculus. While both species are detrimental to native ecosystems, the ability of P. leniusculus to withstand competition pressure from another successful invasive species underscores its potential to establish dominant populations. Our results highlight the importance of understanding interspecies competition in prioritizing potential management activities or control efforts in contact zones.

Differences in aggressive behaviour along the expanding range of an invasive crayfish: an important component of invasion dynamics

AbstractAggressive interactions are essential for resource distribution and population dynamics of many animal species. Aggression can also help invasive species to wrestle the resources from other species and invade new habitat. To examine the effects of intra-species aggression on range expansion, we compared aggression levels of signal crayfish (Pacifastacus leniusculus) at the core and front of the invasion range in recently invaded regions of Croatia. More pronounced aggression was observed in core populations with high population densities, indicating potentially greater importance of highly aggressive behaviour in populations with higher competitive pressure. Despite better overall physical condition, individuals at the invasion front generally displayed lower levels of aggression and regularly lost interactions to individuals from the invasion core. Rather than providing a competitive advantage during range expansion, aggression may be more expressed in established populations, priming the individuals for future expansions while also driving the dispersal outward. The observed difference in aggression along the invasion pathway demonstrates that traits that help individuals to overcome challenges of their environment, such as competition against conspecifics, can drive the invasion dynamics of a successful invader in a new environment in terms of both niche competition and intrinsic expansion dynamics.

Behavioural determinants of agonistic success in invasive crayfish

Ecosystems today increasingly suffer invasions by multiple invasive species, some of which may share similar advantageous life history traits and ecological niche. In such cases, direct competition can influence invasion success of both species, and provide insights into competition without co-evolution in species equally novel to the environment. We used two widespread crayfish invaders of freshwater ecosystems of Europe, signal crayfish (Pacifastacus leniusculus) and spiny cheek crayfish (Orconectes limosus), to investigate how behavioural decisions in agonistic encounters contribute to competitive advantages in the absence of adaptation to either opponents or an environment. In direct competition against novel but comparable opponents, the key factor for establishing clear dominance of P. leniusculus in interspecific bouts was its greater tendency towards continued engagement in high-intensity fights. With O. limosus individuals consistently retreating from staged bouts as fights became more intense, P. leniusculus individuals did not need to adapt their strategy to be successful, suggesting that their agonistic behaviour intrinsically predisposed them to win. While both species are detrimental to invaded ecosystems, our results indicate that aggressive behaviour of P. leniusculus against unfamiliar opponents could allow it to more easily outcompete other comparable species and consequently present a potentially greater threat for native ecosystems.

Aquatic Macroinvertebrates of the Sava River

The objective of this chapter is to present the data on aquatic macroinvertebrate communities along the Sava River, based on investigation performed during 2011 and 2012 at 12 sampling sites within the sector between Vrhovo (Slovenia) and Belgrade (confluence to the Danube). During our study 227 macroinvertebrate taxa were recorded in the Sava River. Having in mind that upper stretch of the Sava River was not covered by this work (alpine and subalpine stretch), as well as based on the review of previous works on the macroinvertebrate fauna of the Sava River, more than 300 species will be confirmed for the Sava River. The data on the distribution of aquatic macroinvertebrates revealed five different stretches—alpine, subalpine, Upper Sava plain, Middle Sava and Lower Sava. Physical habitat degradation, pollution and pressure caused by biological invasions were found to be the main factors of endangerment of aquatic macroinvertebrate fauna diversity. There is an obvious need for further investigation of the Sava River in order to complete the data on aquatic macroinvertebrates and to provide the basis for accurate assessment of environmental status of the river.

Species-specific differences in dynamics of agonistic interactions may contribute to the competitive advantage of the invasive signal crayfish (Pacifastacus leniusculus) over the native narrow-clawed crayfish (Astacus leptodactylus)

Abstract Species-specific differences in dynamics of agonistic interactions may influence the outcome of interspecific competition and potentially contribute to competitive advantage of one species over another. In this study, we compared the dynamics of agonistic interactions of one of the most successful crayfish invaders of European freshwater ecosystems, the signal crayfish (Pacifastacus leniusculus) and the widespread native European species currently undergoing range expansion in Croatia and Europe, the narrow-clawed crayfish (Astacus leptodactylus). Comparisons between P. leniusculus pairs and the A. leptodactylus pairs demonstrated significant differences in frequency and duration of agonistic encounters: P. leniusculus dyads engaged in fewer fights, but their duration was significantly longer. In staged interactions between size-matched interspecific pairs, agonistic behaviour of P. leniusculus individuals translated into dominance over their A. leptodactylus counterparts. This indicates that the success of P. leniusculus in agonistic encounters with the native competitor might stem from its readiness to continue fighting for a longer time period, and could lead to ecological advantages during niche competition even when facing a successful native crayfish species.

A comparative study of the physiological condition of native and invasive crayfish in Croatian rivers.

The physiological condition of two invasive crayfish species identified in Croatian rivers (Orconectes limosus and Pacifastacus leniusculus) was compared with that of native crayfish populations (Astacus astacus and A. leptodactylus). Hepatosomatic, gonadosomatic and abdominal muscle indices were examined for all four species and within a specific invadernative pair. The results demonstrate that invasive crayfish had better overall physiological condition when compared to native species, with a higher energy content of the hepatopancreas, abdominal muscle and gonads in invasive than in native species, with the exception of A. leptodactylus females which demonstrated an increased ability to allocate energy to reproduction in comparison with other species. These results also indicate that A. astacus is physiologically more unstable than A. leptodactylus and thus more likely to be outcompeted and replaced by non-indigenous crayfish species.