Sluggish Movement and Repugnant Odor Are Positively Interacting Insect Defensive Traits in Encounters with Frogs

Sluggish movement is common in chemically defended insects. We have recently shown that sluggish movement can be beneficial to prey when it fails to release the attack response of an ambush (=motion-oriented) predator. Here, we test the hypothesis that sluggish movement and chemical defense (i.e., repugnant odor) together are more defensive than either alone. We manipulated the movement and odor of lubber grasshoppers to produce four prey types: (1) sluggish-moving and high odor, (2) sluggish-moving and low odor, (3) fast-moving and high odor, and (4) fast-moving and low odor. We then offered these prey to frogs. In two independent experiments, frogs attacked prey type 1 (i.e., sluggish-moving and high-odor prey) significantly later than they attacked the other prey types. Hence, the defenses of sluggish movement and repugnant odor can act together to produce a prey that is better defended than prey with either defense alone. This may help explain why these two traits commonly cooccur in insects.     

Slow movement increases the survivorship of a chemically defended grasshopper in predatory encounters

Studies on insect defenses have investigated the benefits of noxious chemicals, aposematic coloration, and even gregariousness, but little information exists on the role of slow movement (as opposed to rapid escape movement and the absence of movement). Using the chemically defended, slow-moving lubber grasshopper (Romalea guttata) and the northern leopard frog (Rana pipiens), we investigated the role of slow movement in insect defense. In a five-day experiment, frogs did not learn an aversion to lettuce-fed lubbers; we infer that endogenous deterrent chemicals are not important in lubber defense from frogs. In experiment 2, lubbers moved significantly more slowly than crickets in the presence of frogs held under beakers. In experiment 3, control (i.e., slow-moving) lubbers suffered significantly less predation than motion-induced lubbers, and frogs attacked control lubbers significantly later than they attacked motion-induced lubbers. Hence, slow movement appears to be an important component in enhancing lubber survivorship in frog encounters. This is the first demonstration that the slow movement of an␣aposematic insect increases its survival by failing to release the attack response of certain motion-oriented predators. Received: 14 November 1997 / Accepted: 12 December 1997     

Importance of colour in the reaction of passerine predators to aposematic prey: experiments with mutants of Pyrrhocoris apterus (Heteroptera)

Persistent questions concerning the warning coloration of unpalatable insects address whether the bright aposematic colour itself or its combination with a species-specific dark pattern is the key factor in their protection against insectivorous birds, and how chromatic polymorphism originates and is maintained in aposematics. In the present study, these questions were tested experimentally, using the birds Parus major , Parus caeruleus , Erithacus rubecula , and Sylvia atricapilla as predators, and chromatically polymorphic firebug Pyrrhocoris apterus : red wild form, white, yellow, and orange mutants (all four of them with the same black melanin pattern, the mutants differing in colour of pteridine pigments only) and the nonaposematic brown-painted wild form as prey. The results show that a specific colour is essential for the birds to recognize the specific aposematic prey; the melanin pattern is not sufficient. White mutants were no better protected than nonaposematic firebugs; red wild-type and orange mutants were equally well protected against all bird species; and the reaction of birds to yellow mutants was species-specific. An evolutionary scenario of 'recurrent recessive mutations' is formulated to explain the origin of colour polymorphism in some aposematics.  © 2006 The Linnean Society of London, Biological Journal of the Linnean Society , 2006, 88 , 143–153.     

The use of auditory stimulants during swim encounters with Hector's dolphins (Cephalorhynchus hectori hectori) in Akaroa Harbour,New Zealand

The coastal distribution of Hector's dolphins and their attraction to vessels make them easily accessible to commercial tour operations. For over 25 yr, tour operators have been undertaking view and swim‐with‐dolphin trips in Akaroa Harbour, New Zealand. Since 2003, auditory stimulants, in particular stones, have been provided during such swim encounters. The potential effects associated with such stimulants have not, until now, been examined. Here, we investigate the effects of stones and other human‐induced noise on Hector's dolphin behavior. The use of stones significantly affected how dolphins interacted with swimmers. Specifically, swimmers who used stones had a greater probability of close approaches by dolphins than those who sang or simply floated on the surface of the water. The number of close and sustained approaches was also significantly higher for swimmers using stones. Dolphins were more interactive with active swimmers, approaching closer and engaging for longer than with nonactive swimmers. Dolphins socializing had a tendency to be engaged longer with swimmers. The use of stones as an auditory stimulant to sustain or enhance interactions with dolphins by artificial means may not be in the best interest of an endangered species, which already faces a range of challenges due to human activity.     

Clear water associated with biomass and nutrient variation during the growth of a Charophyte stand after a drawdown,in a tropical coastal lagoon

The community of Charophytes in the Imboassica coastal lagoon in Brazil (22° 24 S and 42° 42 W) sometimes occupies almost the entire benthic region, and presents a large variation in C:N:P ratio. The effect of drawdown on the regeneration and buildup of biomass and on the nutrient concentration of these macroalgae was studied at three different sampling sites. Drawdown results in a high level of mortality in the macroalgae stands and after the water level later rises, the process of oospore germination begins. The drawdowns occurred in November 96 and January 97, and after March 97 we took samples in order to determine biomass values and the concentration of carbon, nitrogen and phosphorus. The results indicate that the fast growth of Charophytes may absorb a great amount of the nutrients entering the lagoon. The biomass reached maximum values of between 400 and 600 g DW m^–2, and the C:N:P ratio varied from 51:7:1 to 1603:87:1, indicating that this macroalgae may grow in a wide range of nutrient concentration. The presence of this community in the Imboassica lagoon may act as one of the limiting factors controlling phytoplanktonic primary production, decreasing nutrient availability in the water column (`bottom-up' control) and keeping the water clear after drawdowns. Probably through the habitat structure produced by the great biomass reached, they provide substrate and shelter for the structuring of a community with grazing zooplankton, which acts as a `top-down' controlling mechanism on the phytoplankton.