Abstract
BackgroundEnvironmental heterogeneity plays a major role in invasion and coexistence dynamics. Habitat segregation between introduced species and their native competitors is usually described in terms of different physiological and behavioural abilities. However little attention has been paid to the effects of behaviour in habitat partitioning among invertebrates, partially because their behavioural repertoires, especially marine benthic taxa, are extremely limited. This study investigates the effect of gaping behaviour on habitat segregation of the two dominant mussel species living in South Africa, the invasive Mytilus galloprovincialis and the indigenous Perna perna. These two species show partial habitat segregation on the south coast of South Africa, the lower and upper areas of the mussel zone are dominated by P. perna and M. galloprovincialis respectively, with overlap in the middle zone. During emergence, intertidal mussels will either keep the valves closed, minimizing water loss and undergoing anaerobic metabolism, or will periodically open the valves maintaining a more efficient aerobic metabolism but increasing the risk of desiccation.ResultsOur results show that, when air exposed, the two species adopt clearly different behaviours. M. galloprovincialis keeps the shell valves closed, while P. perna periodically gapes. Gaping behaviour increased water loss in the indigenous species, and consequently the risk of desiccation. The indigenous species expressed significantly higher levels of stress protein (Hsp70) than M. galloprovincialis under field conditions and suffered significantly higher mortality rates when exposed to air in the laboratory. In general, no intra-specific differences were observed in relation to intertidal height. The absence of gaping minimises water loss but exposes the invasive species to other stresses, probably related to anoxic respiration.ConclusionsGaping affects tolerance to desiccation, thus influencing the vertical zonation of the two species. Valve closure exposes the invasive species to higher stress and associated energy demands, but it minimizes water loss, allowing this species to dominate the upper mussel zone, where the gaping indigenous P. perna cannot survive. Thus even very simple behaviour can influence the outcome of interactions between indigenous and invasive species.
Highlights
Environmental heterogeneity plays a major role in invasion and coexistence dynamics
Several studies have shown that life in the high intertidal involves adaptation responses such as increased thermal resistance [25], heat stability of key metabolic enzymes [26], increased extracorporeal water storage, reduced evaporation [25,27] and stress-induced expression of heat stress proteins (Hsps; [28])
Laboratory experiments Mussels of Mytilus galloprovincialis and Perna perna were collected from the middle of the mussel zone in Plettenberg Bay on the south coast of South Africa (34° 22' S, 23° 22' E)
Summary
Environmental heterogeneity plays a major role in invasion and coexistence dynamics. Habitat segregation between introduced species and their native competitors is usually described in terms of different physiological and behavioural abilities. To define the dynamics of species coexistence, it is necessary to understand how different species respond to environmental stress at a physiological, ecological and a behavioural level [1,2] This is important when investigating interactions among indigenous and invasive species. Distribution and vertical zonation of intertidal communities are affected by the exceptionally steep gradients in temperature, desiccation and oxygen availability that are typical of this habitat [2124] This is true for sessile and sedentary organisms that are not capable of moving to evade environmental stresses imposed during low tide exposure to air (emersion). Previous studies have shown that Hsps induction is related to heat and hypoxic stress in several organisms, and their detection and quantification have become a sensitive and rapid mode of screening for stress responses (e.g. [30])
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
