Response behaviour of native lizards and invading wall lizard to interspecific scent: implications for invasion success

The human-assisted movement of species beyond their native range facilitates novel interactions between invaders and native species that can determine whether an introduced species becomes invasive and the nature of any consequences for native communities. Avoiding costly interactions through recognition and avoidance can be compromised by the naïvety of native species to novel invaders and vice versa. We tested this hypothesis using the common wall lizard, Podarcis muralis, and the native lizard species with which it may now interact in Britain (common lizard, Zootoca vivipara, sand lizard, Lacerta agilis) and on Vancouver Island (northern alligator lizard, Elgaria coerulea) by exploring species' responses (tongue flicks, avoidance behaviour) to heterospecific scent cues in controlled experiments. The tongue flick response of P. muralis depended on the different species’ scent, with significantly more tongue flicks directed to E. coerulea scent than the other species and the control. This recognition did not result in any other behavioural response in P. muralis (i.e. attraction, aggression, avoidance). Lacerta agilis showed a strong recognition response to P. muralis scent, with more tongue flicks occurring close to the treatment stimuli than the control and aggressive behaviour directed towards the scent source. Conversely, Z. vivipara spent less time near P. muralis scent cues than the control but its tongue flick rate was higher towards this scent in this reduced time, consistent with an avoidance response. There was no evidence of E. coerulea recognition of P. muralis scent in terms of tongue flicks or time spent near the stimuli, although the native species did show a preference for P. muralis-scented refuges. Our results suggest a variable response of native species to the scent of P. muralis, from an avoidance response by Z. vivipara that mirrors patterns of exclusion observed in the field to direct aggression observed in L. agilis and an ambiguous reaction from E. coerulea which may reflect a diminished response to a cue with a low associated cost. These results have significant implications for the invasive success and potential impacts of introduced P. muralis populations on native lizards

Olfactory foraging in temperate waters: sensitivity to dimethylsulphide of shearwaters in the Atlantic Ocean and Mediterranean Sea

Many procellariiforms use olfactory cues to locate food patches over the seemingly featureless ocean surface. In particular, some of them are able to detect and are attracted by dimethylsulphide (DMS), a volatile compound naturally occurring over worldwide oceans in correspondence with productive feeding areas. However, current knowledge is restricted to sub-Antarctic species and to only one study realized under natural conditions at sea. Here, for the first time, we investigated the response to DMS in parallel in two different environments in temperate waters, the Atlantic Ocean and the Mediterranean Sea, employing Cory\u2019s (Calonectris borealis) and Scopoli\u2019s (Calonectris diomedea) shearwaters as models. To test whether these birds can detect and respond to DMS, we presented them with this substance in a Y-maze. Then, to determine whether they use this molecule in natural conditions, we tested the response to DMS at sea. The number of birds that chose DMS in the Y-maze and that were recruited at DMS-scented slicks at sea suggests that these shearwaters are attracted to DMS in both non-foraging and natural contexts. Our findings show that the use of DMS as a foraging cue may be a strategy adopted by procellariiforms across oceans but that regional differences may exist, giving a worldwide perspective to previous hypotheses concerning the use of DMS as a chemical cue

Effects of testosterone supplementation on chemical signals of male Iberian wall lizards: consequences for female mate choice

In some lizards, female mate choice is influenced by chemicals secreted by males, e.g., via the femoral glands. Secretions of the femoral glands are under direct androgenic control and vary seasonally with androgen production. However, whether increased testosterone (T) levels affect the concentration and chemical composition of secretions or their attractiveness to females is unknown. We manipulated T levels of male Iberian wall lizards, Podarcis hispanica, with silastic implants. Differential tongue-flick rates indicated that females detected and discriminated between femoral secretions of control and T-implanted males based on chemical cues alone. Females showed greater responses to secretions of T-males, which might suggest that T increased the concentration of chemical signals. Further analyses by gas chromatography–mass spectrometry indicated that T supplementation induced qualitative changes in lipid composition of femoral secretions. T-males had decreased relative proportions of cholesta-5,7-dien-3-ol in secretions, which might be related to the negative effects of T on the immune system and on lipid metabolism. However, experiments of choice of males’ scent showed that females neither preferred nor avoided the scent marks of T-males but preferred males that maintained higher proportions of cholesta-5,7-dien-3-ol in secretions, independently of the experimental manipulation. Thus, because this steroid is negatively affected by T, there might be trade-offs among increasing T levels to increase the production of chemical secretions, maintain metabolism, and attract females

Chemosensory species recognition may reduce the frequency of hybridization between native and introduced lizards

The introduction of alien species to islands by human activity can cause catastrophic consequences for small populations of island endemics. Hybridization between the endangered and endemic insular lizard Podarcis atrata (Boscá, 1916) from the Columbretes Islands (Mediterranean, Spain) and the common mainland lizard Podarcis hispanica (Steindachner, 1870) could potentially occur because mainland haplotypes have already been detected in the islands, the two species are closely genetically related, and the frequency of visitors to these islands is increasing. However, reproductive decisions of lizards are often mediated by species recognition mechanisms based on chemical cues. On the basis of this observation, even if some mainland P. hispanica lizards were introduced to the islands, interspecific recognition might make rare an eventual hybridization with the insular P. atrata. We examined interspecific chemical recognition between the insular P. atrata and the mainland P. hispanica. Our results showed that lizards of both sexes responded more strongly (i.e., directed a significantly higher number of tongue flicks) to scents of conspecific individuals than to scents of heterospecifics. Chemical recognition of conspecifics by endemic island P. atrata lizards may reduce the occurrence of hybridization with introduced mainland P. hispanica lizards and protect the insular gene pool.Peer Reviewe

Data from: Preen oil chemical composition encodes individuality, seasonal variation and kinship in black kites Milvus migrans

Evidence that bird odour can encode social information that can be used in chemical communication is growing, but is restricted to a few taxonomic groups. Among birds, diurnal raptors (i.e. birds from the Accipitriformes and Falconiformes order) have always been considered as mainly relying on their visual abilities. Although they seem to have a functional sense of smell, whether their odour can convey social information has yet to be determined. Combining gas-chromatography-mass-spectrometry (GCMS) and microsatellite data, we tested whether chemical compounds from preen gland secretions can encode sex, age, individuality, seasonal differences and genetic relatedness in the gregarious accipitriform black kite Milvus migrans. While no differences in preen oil composition were found between age classes, an individual signature was detected. While a seasonal variation was found in both sexes, compounds differ between sexes in the non-breeding season. Finally, a significant correlation between chemical proximity and genetic proximity was detected in male-male dyads and male-female dyads but not in female-female dyads. Our study provides the first evidence in raptors that preen secretion can convey information that may potentially be used in individual recognition, reproductive synchronization and inbreeding avoidance, and suggests that raptors may rely upon their olfactory abilities more than previously thought. This study opens promising avenues for further studies in raptor chemical communication

Data from: Preen oil chemical composition encodes individuality, seasonal variation and kinship in black kites Milvus migrans

Evidence that bird odour can encode social information that can be used in chemical communication is growing, but is restricted to a few taxonomic groups. Among birds, diurnal raptors (i.e. birds from the Accipitriformes and Falconiformes order) have always been considered as mainly relying on their visual abilities. Although they seem to have a functional sense of smell, whether their odour can convey social information has yet to be determined. Combining gas-chromatography-mass-spectrometry (GCMS) and microsatellite data, we tested whether chemical compounds from preen gland secretions can encode sex, age, individuality, seasonal differences and genetic relatedness in the gregarious accipitriform black kite Milvus migrans. While no differences in preen oil composition were found between age classes, an individual signature was detected. While a seasonal variation was found in both sexes, compounds differ between sexes in the non-breeding season. Finally, a significant correlation between chemical proximity and genetic proximity was detected in male-male dyads and male-female dyads but not in female-female dyads. Our study provides the first evidence in raptors that preen secretion can convey information that may potentially be used in individual recognition, reproductive synchronization and inbreeding avoidance, and suggests that raptors may rely upon their olfactory abilities more than previously thought. This study opens promising avenues for further studies in raptor chemical communication