Predator experience overrides learned aversion to heterospecifics in stickleback species pairs

Predation risk can alter female mating decisions because the costs of mate searching and selecting attractive mates increase when predators are present. In response to predators, females have been found to plastically adjust mate preference within species, but little is known about how predators alter sexual isolation and hybridization among species. We tested the effects of predator exposure on sexual isolation between benthic and limnetic threespine sticklebacks ( Gasterosteus spp.). Female discrimination against heterospecific mates was measured before and after females experienced a simulated attack by a trout predator or a control exposure to a harmless object. In the absence of predators, females showed increased aversion to heterospecifics over time. We found that predator exposure made females less discriminating and precluded this learned aversion to heterospecifics. Benthic and limnetic males differ in coloration, and predator exposure also affected sexual isolation by weakening female preferences for colourful males. Predator effects on sexual selection were also tested but predators had few effects on female choosiness among conspecific mates. Our results suggest that predation risk may disrupt the cognitive processes associated with mate choice and lead to fluctuations in the strength of sexual isolation between species.

Extent and nature of cyanide-shyness in some opulations of Australian brushtail possums in New Zealand

The proportion of possums with cyanide-shyness was assessed in four populations and ranged from 12 to 54%. These results supported anecdotal evidence of cyanide-shyness and showed that the problem could be significant in some populations. Non-toxic baiting with rhodamine dye as a marker indicated that more than 90% of possums were willing to accept the bait material, and pen trials showed that possums were able to eat the bait material but reject the cyanide paste placed in the bait. Shyness was therefore not a result of bait aversion but of direct rejection of the toxin. Attempts to induce shyness in possums by feeding them sublethal doses of cyanide, and the history of cyanide use in the trial areas, support the theory that at least in some areas cyanide-shyness is not a result of previous exposure (learned aversion) but of primary aversion. Current research to produce cyanide formulations with low emission rates of hydrogen cyanide aims to make the toxin effective even in areas where cyanide-shyness has developed.

Emesis, learned aversion, and chemical defense in octocorals: a central role for prostaglandins?

Prostaglandin A2 and its ester derivatives comprise as much as 8% of the wet tissue weight of some octocoral species such as Plexaura homomalla (phylum Cnidaria, class Anthozoa, subclass Octocorallia). These high levels of prostaglandins, although initially palatable to fish, may function as defensive toxins by inducing emesis and learned aversions in potential predators. As the fish Fundulus heteroclitus and Halichoeres garnoti gain experience through the course of experiments, they increasingly reject foods containing emetic prostaglandins, but do not alter their acceptance of untreated control foods. Emesis is also induced in fish by consumption of tissue or lipid extracts from the subtropical whip coral Leptogorgia virgulata (subclass Octocorallia, order Gorgonacea). The emetic properties of L. virgulata induce learned aversions in the fish Micropterus salmoides and Morone saxatilis. Extracts of L. virgulata do not contain high levels of prostaglandins but do, however, contain other metabolites that appear to mimic the effects of eicosanoids. Some nonprostanoid secondary metabolites may induce emesis by stimulating prostaglandin biosynthesis in the gastric mucosa of predators.

Behavioral-Response of Brushtail Possums, Trichosurus-Vulpecula, to Baits Used in Pest-Control

The behavioural responses of captive possums (Trichosurus vulpecula) were observed during first encounters with non-toxic and toxic carrot and pellet baits used in pest control programmes. Possums confronted with new baits first used smell in a highly discriminating way, and then taste, which sometimes changed their initial response. Toxic carrot baits were rejected by 27.5% of possums, equally by smell and taste aversion, and toxic pellet baits by 34% of possums, mainly by taste aversion. Few (5-7%) rejected non-toxic baits. Such non-learned aversion mechanisms therefore have an important role in the feeding behaviour of possums. A range of flavours tested, using barley as a food base, showed that only orange-flavored barley was significantly preferred to non-flavoured barley; 19 flavours had no significant effect, and 19 others significantly reduced barley consumption. Orange and cinnamon, which was ranked fourth and repels some bird species, were tested as masks for 1080 baits. Both flavours effectively masked the aversive smell and taste of 1080. The levels of toxic flavoured bait rejection were low and did not differ from those of non-toxic (flavoured or non-flavoured) baits. Very few possums were observed vomiting, a behaviour in other species that may assist survival.