Sequestration of defenses against predators drives specialized host plant associations in preadapted milkweed bugs (Heteroptera: Lygaeinae)

AbstractHost plant specialization across herbivorous insects varies dramatically, but while the molecular mechanisms of host plant adaptations are increasingly known, we often lack a comprehensive understanding of the selective forces that favor specialization. The milkweed bugs (Heteroptera: Lygaeinae) are ancestrally associated with plants of the Apocynaceae from which they commonly sequester cardiac glycosides for defense, facilitated by resistant NaNa+/K+-ATPases and adaptations for transport, storage, and discharge of toxins. Here, we show that three Lygaeinae species independently colonized four novel nonapocynaceous hosts that convergently produce cardiac glycosides. A fourth species shifted to a new source of toxins by tolerating and sequestering alkaloids from meadow saffron (Colchicum autumnale, Colchicaceae). Across three milkweed bug species tested, feeding on seeds containing toxins did not improve growth or speed of development and even impaired growth and development in two species, but sequestration mediated protection of milkweed bugs against two natural predators: lacewing larvae and passerine birds. We conclude that physiological preadaptations and convergent phytochemistry facilitated novel specialized host associations. Since toxic seeds did not improve growth but either impaired growth or, at most, had neutral effects, selection by predators on sequestration of defenses, rather than the exploitation of additional profitable dietary resources, can lead to obligatory specialized host associations in otherwise generalist insects

Differential Bird Responses to Colour Morphs of an Aposematic Leaf Beetle may Affect Variation in Morph Frequencies in Polymorphic Prey Populations

The selection of prey by predators should, theoretically, favour uniformity in the warning signals displayed by unpalatable prey. Nevertheless, some aposematically coloured species are polymorphic. We tested the hypothesis that colour morphs of unpalatable prey differ in the efficacy of their aposematic signal for birds, thereby affecting the selective advantages of these morphs. We used colour morphs (red-and-black light, red-and-black dark and metallic) of the chemically defended leaf beetle Chrysomela lapponica. In laboratory experiments, naïve great tits (Parus major) attacked live beetles of all colour morphs at the same rate. By contrast, wild-caught tits attacked light beetles at first encounter at the same rate as a novel control prey, but significantly avoided both dark and metallic beetles. Beetles of all colour morphs were similarly unpalatable for birds, and about half of the attacked beetles were released unharmed. Avoidance learning was similarly fast for all three leaf beetle morphs. However, in the next-day memory test, the dark beetles were attacked at a greater rate than beetles of two other morphs, indicating their lower memorability. A field experiment suggests that at low C. lapponica population densities, dark beetles have a survival advantage over light beetles, potentially due to the lesser conspicuousness of the dark pattern; however, when the density is high, dark beetles lose this advantage due to the low memorability of their pattern. Thus, the direction of selective bird predation on prey colour morphs may depend on prey density and thereby contribute to temporal shifts in colour morph frequencies following population fluctuations.</p

Consistency and flexibility in solving spatial tasks: different horses show different cognitive styles

Individual animals vary in their behaviour and reactions to novel situations. These differences may extend to differences in cognition among individuals. We tested twenty-six horses for their ability to detour around symmetric and asymmetric obstacles. All of the animals were able to get around the barrier to reach a food target, but varied in their approach. Some horses moved slowly but were more accurate in choosing the shortest way. Other horses acted quickly, consistently detoured in the same direction, and did not reliably choose the shortest way. The remaining horses shifted from a faster, directionally consistent response with the symmetric barrier, to a slower but more accurate response with the asymmetric barrier. The asymmetric barrier induced a reduction in heart rate variability, suggesting that this is a more demanding task. The different approaches used to solve the asymmetric task may reflect distinct cognitive styles in horses, which vary among individuals, and could be linked to different personality traits. Understanding equine behaviour and cognition can inform horse welfare and management

Territory size and habitat selection in subadult and adult males of Black Redstart (Phoenicurus ochruros) in an urban environment

Territory size, distribution of territories and habitat selection were studied in Black Redstart (Phoenicurus ochruros) populations in three urban habitats (garden city, old and new housing estates) of Prague (Czech Republic). We tested if the territory size and quality of territories occupied by adult and subadult males differed from each other. Average territory size of the adult males was 1.21 ± 0.80(SD) ha and of the subadult males 1.08 ± 0.58(SD) ha. This difference was not statistically significant. Moreover, males of particular age-class were not spatially clustered. Microhabitat analysis shows that the habitat selection depends on the presence of buildings. Apparently buildings offer a good nesting, singing and foraging places for the Black Redstart. The territory size of Black Redstarts differed between habitats, being largest in the garden city (1.98 ± 1.06 (SD) ha), intermediate in the old housing estate (1.48 ± 0.45 (SD ha) and smallest in the new housing estate (0.85 ± 0.33 (SD) ha). Our results indicate that in urban environment the relationships between adult and subadult territory owners differ from those referred to in mountain villages

Nestling diet of the Common Magpie (Pica pica) in urban and agricultural habitats

Several processes may be responsible for the urbanization of the Common Magpie (Pica pica), a species spreading widely in European towns during the last 50 years. Greater supply or better availability of food could play a role in the successful colonization of urban habitats by this species. We compared the nestling diet of Magpies within (urban) and adjacent to the city (rural) of Prague, Czech Republic, using the neck-collar method, and studied parental foraging behavior and micro-habitat associations in the city of Prague. Although the nestling diet was different between urban and rural areas, invertebrates (mainly Coleoptera) were the most frequent prey in both areas. Anthropogenic food was more abundant in urban than in rural areas. The nestling diet differed from the potentially available food supply in both urban and rural areas: Annelida and Lepidoptera were preferred, while Isopoda, Diplopoda, Orthoptera and Hymenoptera were neglected. In urban areas, Magpies foraged actively (i.e., by walking) and by perching. Prey was collected mostly from the ground. Magpies foraged mainly at sites covered with short vegetation. Utilization of short vegetation was proportional to its availability, whereas tall vegetation was used less than could be expected by availability. Short vegetation dominated the home ranges of Magpies in urban areas, while tall vegetation was more common in the Magpie home ranges in rural areas

Parental foraging strategies and feeding of nestlings in Common Redstart Phoenicurus phoenicurus

Spatial foraging activity and feeding of broods was studied in nine pairs of Common Redstart (Phoenicurus phoenicurus) breeding in nest boxes in pine forest. The effect of nestling age on feeding rate was not significant. The number of feedings per chick was similar in small and medium size broods but decreased in the largest broods. Feeding rates in individual pairs did not differ between males and females. Mean nest visit duration were longer for females. Incubation of the youngest chicks was probably the cause of sig-nificant decrease of length of feeding visits by females during the chicks' growth. The proportion of foraging techniques was different between males and females, and changed during a nestlings' life. Males foraged predominantly by perching (passive foraging mode) throughout the whole breeding period. Females also foraged mostly by perching, but with younger broods they frequently used an active foraging mode of foliage glean-ing. The active foraging mode for younger broods could be either compensation of forag-ing efficiency for the time spent brooding, or caused by differences in prey selection at dif-ferent nestling ages, or active foraging does not pay off in the exploited habitat around the nest at the end of breeding

Scared by shiny? The value of iridescence in aposematic signalling of the hibiscus harlequin bug

Studies on aposematism have generally focused on the benefits of red or yellow coloration, occasionally in contrast with green or brown, but rarely blue or orange. Furthermore, almost no studies have explicitly studied the utility of iridescent coloration in aposematism. To evaluate the survival benefit of iridescent coloration, we tested the ability of the natural colour extremes of Tectocoris diophthalmus jewelbugs to induce initial avoidance, learned avoidance, discrimination from palatable alternatives and broad generalization against avian predators: naïve hand-reared and experienced wild-caught great tits, Parus major. Artificial baits were created by hollowing out bugs and inserting pieces of mealworm. Preference tests presented iridescent and orange baits simultaneously, then birds were divided into training groups and sequentially exposed to palatable black baits alternated with iridescent or orange baits made unpalatable by soaking mealworms in quinine solution. This was followed by simultaneous black/coloured discrimination tests, then a generalization test with both previously experienced and novel baits (all palatable). All groups showed a preference for orange baits over ones with iridescent patches. For wild-caught birds, attack latencies of iridescent and orange training groups were statistically indistinguishable, although only orange caused increased attack latency over the sequence. Hand-reared birds showed no change in attack rate/latency towards iridescent bugs over the sequence. In postlearning discrimination tests, all groups showed equally strong preference for palatable black baits and their unpalatable training baits. In generalization tests, hand-reared birds were most averse towards trained baits, but increased avoidance of iridescent-and-black baits suggests iridescence alone can contribute to aposematism. Wild-caught birds showed strong aversion to iridescent and novel orange-and-black baits regardless of training, suggesting birds may be broadly generalizing experience from local red-and-black aposematic bugs. Results suggest iridescent coloration and patterning can be an effective aposematic signal, especially in the presence of alternative palatable prey and/or other aposematic species.11 page(s

Personality matters: individual variation in reactions of naive bird predators to aposematic prey

Variation in reactions to aposematic prey is common among conspecific individuals of bird predators. It may result from different individual experience but it also exists among naive birds. This variation may possibly be explained by the effect of personality—a complex of correlated, heritable behavioural traits consistent across contexts. In the great tit (Parus major), two extreme personality types have been defined. ‘Fast’ explorers are bold, aggressive and routine-forming; ‘slow’ explorers are shy, non-aggressive and innovative. Influence of personality type on unlearned reaction to aposematic prey, rate of avoidance learning and memory were tested in naive, hand-reared great tits from two opposite lines selected for exploration (slow against fast). The birds were subjected to a sequence of trials in which they were offered aposematic adult firebugs (Pyrrhocoris apterus). Slow birds showed a greater degree of unlearned wariness and learned to avoid the firebugs faster than fast birds. Although birds of both personality types remembered their experience, slow birds were more cautious in the memory test. We conclude that not only different species but also populations of predators that differ in proportions of personality types may have different impacts on survival of aposematic insects under natural conditions