Luisa Amo

Sources of individual shy-bold variations in antipredator behaviour of male Iberian rock lizards

Individual animals from the same population, sex, age and reproductive status often respond differently and consistently to predators. One important dimension of this behavioural variation is the shy–bold continuum. Innate differences in boldness might explain why individuals differ in their antipredator behaviour. In a laboratory experiment, we examined the sources of individual variation in antipredator behaviour of adult male lizards Lacerta monticola. We simulated in the laboratory repeated predatory attacks of low or high risk and analysed activity levels and refuge use in both situations. Multivariate analyses suggested the existence of two consistent and independent shy–bold continua. The first described a gradient from bold lizards that spent shorter times in the refuge after predatory approaches to shy lizards with longer emergence times, whereas the other described a gradient from bold lizards with a low propensity to hide when the predator was close but risk was low to shy lizards that hid more often. We analysed whether morphological characteristics, body condition and health (estimated from their T cell immunocompetence) of individuals might account for the differences observed. Bold individuals had smaller absolute body size, but relatively larger heads, better body condition and better health. Bold individuals with a low propensity to hide when risk was low had larger absolute body sizes, whereas relative head size, and body condition and health were not important. We suggest that the position of an individual in the shy–bold continua might reflect its optimal antipredator behaviour, which would be a function of its health, general quality and ability to evade predators.

Reliable Signaling By Chemical Cues Of Male Traits And Health State In Male Lizards, Lacerta monticola

In spite of the importance of chemoreception in social organization and sexual selection of lizards, there is a lack of general knowledge on how the characteristics of chemical signals mediate these behaviors. Moreover, it is unknown which are the mechanisms that might confer honesty to the information provided by chemical signals. We analyzed here whether characteristics of the lipophilic fraction of femoral gland secretions of Lacerta monticola male lizards can be related to the morphology, physical condition, and health state of the sender. Our results indicated that some male traits, such as body size, number of blue spots, and number of femoral pores and their level of fluctuating asymmetry, were related to variability in the relative proportions of some lipophilic chemical compounds found in secretions. Thus, conspecifics could obtain reliable information on the producer of a scent mark based on chemicals alone, and this might be the basis of female choice observed in this lizard. Moreover, only males with a greater T-cell immune response had higher proportions of two steroids (ergosterol and dehydrocholesterol) in their femoral secretions, which might suggest that the signal is honest and costly to produce. We suggest that only high-quality males could divert these compounds from metabolism to secretions in order to produce an exaggerated and honest “chemical ornament.”

Birds exploit herbivore-induced plant volatiles to locate herbivorous prey

Arthropod herbivory induces plant volatiles that can be used by natural enemies of the herbivores to find their prey. This has been studied mainly for arthropods that prey upon or parasitise herbivorous arthropods but rarely for insectivorous birds, one of the main groups of predators of herbivorous insects such as lepidopteran larvae. Here, we show that great tits (Parus major) discriminate between caterpillar-infested and uninfested trees. Birds were attracted to infested trees, even when they could not see the larvae or their feeding damage. We furthermore show that infested and uninfested trees differ in volatile emissions and visual characteristics. Finally, we show, for the first time, that birds smell which tree is infested with their prey based on differences in volatile profiles emitted by infested and uninfested trees. Volatiles emitted by plants in response to herbivory by lepidopteran larvae thus not only attract predatory insects but also vertebrate predators.

Chemical ornaments of male lizards Psammodromus algirus may reveal their parasite load and health state to females

Evidence for parasite-mediated sexual selection has been found in many species that use visual ornaments to attract females. However, in many animals, variation in female responses to scents of parasitized males suggests that parasitic infections might also affect information conveyed by pheromones (i.e., chemical ornaments). Thus, pheromones might also function in parasite-mediated sexual selection. We show here that female lizards Psammodromus algirus responded differently to femoral gland secretions of males according to the parasite load and health of these males. Scents of healthier males elicited more tongue flicks (a chemosensory behavior) by females, suggesting that these scents were more attractive. Chemical analyses showed that parasite load and the T-cell-mediated immune response were related to the variability in the proportions of some lipids in secretions of males. Further trials testing the chemosensory responses of females to chemical standards indicated that females actually discriminated the chemicals related to males’ health from other chemicals found in secretions. We suggest that these chemical ornaments may provide reliable information on the health and degree of parasitic infection of a male.

Prevalence and intensity of haemogregarine blood parasites and their mite vectors in the common wall lizard, Podarcis muralis

We describe the general field population biology of haemogregarines and mites in the wall lizard, Podarcis muralis, examining the factors that determine the prevalence and intensity of infection. The intensity of infection by haemogregarines in females was slightly lower in summer than in spring, whereas males maintained similar levels of intensity among all the seasons, probably due to immunosuppressive effects of testosterone. This is also supported because the prevalence and the infection intensity by mites were higher in males than in females. Parasite load was higher in lizards with better body condition, which could be reflecting the mortality of infected lizards with poor condition.

Sex recognition by odour and variation in the uropygial gland secretion in starlings

1. Although a growing body of evidence supports that olfaction based on chemical compounds emitted by birds may play a role in individual recognition, the possible role of chemical cues in sexual selection of birds has been only preliminarily studied. 2. We investigated for the first time whether a passerine bird, the spotless starling Sturnus unicolor, was able to discriminate the sex of conspecifics by using olfactory cues and whether the size and secretion composition of the uropygial gland convey information on sex, age and reproductive status in this species. 3. We performed a blind choice experiment during mating, and we found that starlings were able to discriminate the sex of conspecifics by using chemical cues alone. Both male and female starlings preferred male scents. Furthermore, the analysis of the chemical composition of the uropygial gland secretion by using gas chromatography-mass spectrometry (GC-MS) revealed differences between sexes, ages and reproductive status. 4. In conclusion, our study reveals for first time that a passerine species can discriminate the sex of conspecifics by relying on chemical cues and suggests that the uropygial gland secretion may potentially function as a chemical signal used in mate choice and/or intrasexual competition in this species.

Parasites and health affect multiple sexual signals in male common wall lizards, Podarcis muralis.

Multiple advertising sexual traits may either advertise different characteristics of male condition or be redundant to reinforce reliability of signals. Research has focused on multiple visual traits. However, in animals that use different multiple additional sensory systems, such as chemoreception, different types of traits might have evolved to signal similar characteristics of a male quality using different sensory channels. We examined whether ventral coloration and chemicals in femoral gland secretions of male common wall lizards, Podarcis muralis, are affected by their health state (blood-parasite load and cell-mediated immune response). Our results indicated that less parasitized lizards had brighter and more yellowish ventral colorations and also femoral secretions with higher proportions of two esters of octadecenoic acid. In addition, lizards with a greater immune response had more saturated coloration and secretions with higher proportions of octadecenoic acid methyl ester. We suggest that these signals would be reliable because only healthier males seemed able to allocate more carotenoids to coloration and presumably costly chemicals to secretions. The use of multiple sensory channels may provide more opportunities to signal a male quality under different circumstances, but also may reinforce the reliability of the signal when both types of traits may be perceived simultaneously.

Prevalence and intensity of haemogregarinid blood parasites in a population of the Iberian rock lizard, Lacerta monticola

The study of the effect of parasites on their host populations is essential for understanding their role in host population dynamics and ecology. We describe the general field population biology of haemogregarines in the Iberian rock lizard, Lacerta monticola, examining the factors that determine the prevalence and intensity of infection. Prevalence and infection intensity were higher in adults than in juvenile lizards. The prevalence rate was higher in larger lizards, probably because they were also older and had been more often in contact with parasites during their lifetime. During the mating season, the intensity of parasite infection was greater in males than in females, probably due to immunosuppressive effects of testosterone. The parasite load had a negative effect on the body condition during the reproductive season. The results suggest that the interactions between parasites and hosts are not stable in this lizard population.

Refuge use: a conflict between avoiding predation and losing mass in lizards.

Prey often respond to predation risk by increasing refuge use, but this strategy may entail a loss of body condition. Factors responsible for this loss of body condition remain unclear. Also how prey deal with refuge use to cope with predation risk without incurring costs of body condition, and how initial body condition affects refuge use remain barely known. We analyzed in the field whether adult Iberolacerta cyreni lizards modify their escape strategies and refuge use in areas with different levels of habitat deterioration and ecotourism pressure, which represent different levels of predation risk, and the consequences of changes in antipredator behavior to body condition. Lizards inhabiting deteriorated areas, where risk is higher, remained closer to refuges, but decreased time spent hidden in refuges after attacks, probably to maintain similar body condition than lizards inhabiting natural areas. We performed two laboratory experiments to isolate potential costs of refuge use that might affect the body condition of male lizards: a) a decrease of the efficiency of digestion due to low temperatures inside refuges and/or b) a reduction in food intake. Results suggest that refuge use is costly in terms of body condition due to reduced food intake, but the loss of efficiency of digestion seems unimportant. Lizards modified refuge use in relation to their body condition, with lizards with worse condition decreasing time hidden after predatory attacks. We concluded that lizards compensated for increased predation risk with flexible antipredatory strategies, coping with risk without incurring costs for body condition.

Smelling out predators is innate in birds

The role of olfaction for predation risk assessment remains barely explored in birds, although predator chemical cues could be useful in predator detection under low visibility conditions for many bird species. We examine whether Great Tits Parus major are able to use the odour of mustelids to assess predation risk when selecting cavities for roosting. We analysed whether the response to predator chemical cues is innate and assessed whether the antipredatory response is associated with exploratory behaviour, a proxy for the personality of birds. In a choice experiment in aviaries, we offered naïve adult Great Tits of known personality two nest-boxes, one control and one experimental. The experimental nest-box had the odour of a mustelid predator or a strong new odour without biological significance, the control nest-box contained no odour. When one of the cavities contained the odour of a predator, birds avoided the use of either of the two offered nest-boxes, whereas there was no avoidance of boxes when one of the nest-boxes contained a control odour. There was no relationship with exploratory behaviour. We show that the ability to use the chemical cues of predators is innate in birds, but individual differences in the response to predator chemical cues cannot be explained by the personality of the bird.