No impact of biocontrol predator on development time or size of surviving Aedes albopictus under optimal nutritional availability

BackgroundCyclopoid copepods have been applied successfully to limit populations of highly invasive Aedes albopictus mosquitoes that can vector diseases, including chikungunya, dengue, yellow fever, and Zika, to humans. However, there is concern that changes in certain vector traits, induced by exposure to copepod predation, might increase the risk of disease transmission. In this study, we tested whether cyclopoid copepod predation has sublethal effects on the development time or adult size of Ae. albopictus under the scenario of an invasion in southeast England, which lies at the northern edge of the vector’s expanding global range.MethodsThird instar Ae. albopictus larvae, hereafter referred to as “focal individuals”, were placed in individual Petri dishes, each containing four newly-hatched Ae. albopictus larvae, which were counted, removed, and replaced daily. All focal individuals were provided with fish food ad libitum, and half were exposed to Megacyclops viridis copepod predators. The day of pupation was recorded for each focal individual, and the wing length of each focal adult was also measured.ResultsExposing late instar Ae. albopictus to predation decreased their chances of surviving to adulthood. Mortality of the focal individuals was 12.9% in the predator treatment, and 2.9% in the controls. Three focal larvae that died in the predator treatment showed signs of melanization, indicative of wounding. Among surviving Ae. albopictus, no significant difference in either pupation day or wing length was observed due to copepod predation.ConclusionsWe found that M. viridis predation on smaller Ae. albopictus larvae does not significantly affect the pupation day or adult size of surrounding larger larvae that are less vulnerable to copepod attacks. This study controlled for density effects on size by maintaining a constant number of newly-hatched prey larvae surrounding each focal larva. Those working to control Ae. albopictus populations in the field should be made aware that increased adult body size can occur if copepod biocontrol agents are applied at lower than necessary levels. The absence of a significant sublethal impact from M. viridis copepod predation on surviving later-stage larvae in this analysis supports the use of M. viridis as a biocontrol agent.Graphical abstract

Parents know best: transgenerational predator recognition through parental effects

In highly biodiverse systems, such as coral reefs, prey species are faced with predatory threats from numerous species. Recognition of predators can be innate, or learned, and can help increase the chance of survival. Research suggests that parental exposure to increased predatory threats can affect the development, behaviour, and ultimately, success of their offspring. Breeding pairs of damselfish (Acanthochromis polyacanthus) were subjected to one of three olfactory and visual treatments (predator, herbivore, or control), and their developing embryos were subsequently exposed to five different chemosensory cues. Offspring of parents assigned to the predator treatment exhibited a mean increase in heart rate two times greater than that of offspring from parents in herbivore or control treatments. This increased reaction to a parentally known predator odour suggests that predator-treated parents passed down relevant threat information to their offspring, via parental effects. This is the first time transgenerational recognition of a specific predator has been confirmed in any species. This phenomenon could influence predator-induced mortality rates and enable populations to adaptively respond to fluctuations in predator composition and environmental changes.

The behavioral response of prey fish to predators: the role of predator size

Predation is one of the key factors governing patterns in natural systems, and adjustments of prey behaviors in response to a predator stimulus can have important ecological implications for wild fish. To investigate the effects of predators on the behavior of prey fish and to test whether the possible effects varied with predator size, black carp (Mylopharyngodon piceus) and snakehead (Channa argus) (a size-matched predator treatment with a similar body size to prey fish and a larger predator treatment with approximately 2.7 times of the body mass of prey fish) were selected to function as prey and predator, respectively. Their spontaneous activities were videorecorded in a central circular arena surrounded by a ring holding the stimulus fish. The distance between prey and predator fish was approximately 200% of the distance between two prey fish, which suggested that black carp can distinguish their conspecifics from heterospecifics and probably recognize the snakehead as a potential predator. The prey fish spent substantially less time moving and exhibited an overall shorter total distance of movement after the size-matched or large predator was introduced, which possibly occurred due to increased vigilance or efforts to reduce the possibility of detection by potential predators. However, there was no significant difference in either distance or spontaneous activities between two predator treatments. These findings suggested that (1) an anti-predator strategy in black carp might involve maintaining a safe distance, decreasing activity and possibly increased vigilance and that (2) the behaviors of prey response to predators were not influenced by their relative size difference.

Restoration aquaculture of the pinto abalone (Haliotis kamtschatkana kamtschatkana Jonas): impacts of rearing method on behaviour, growth and survivorship in the hatchery

Pinto abalone (Haliotis kamtschatkana kamtschatkana) populations in Washington State (USA) and British Columbia (Canada) continue to decline despite fisheries closures. For successful recovery, supplementation may be necessary. To determine appropriate culture methods, juveniles were reared in habitat-enriched tanks (supplemented with rocks, macroalgae and sea urchins) or conventional aquaculture tanks and assessed for growth and survivorship in the laboratory over 15 months. No differences in survivorship or growth were observed. Subsequent experiments examined whether abalone behaviour (habitat selection and movement patterns) differed between rearing treatments. Abalone were exposed to one of three predator treatments (sea star arm, small crab, or no predator (control)) and filmed for 8 h. Abalone from habitat-enriched tanks changed habitats significantly more often than abalone from conventional tanks regardless of predator treatment. Significant differences in the percentage of time that abalone occupied the various habitats were also observed. Abalone in the sea star and control treatments primarily occupied the rocks, whereas abalone in the crab treatment behaved differently depending on the rearing method; conventionally reared abalone spent more time in corners, whereas abalone from habitat-enriched tanks spent more time exposed. These results demonstrate that rearing conditions can affect abalone behaviour and should be considered for abalone restoration efforts worldwide.