Search

Nesting house wrens (Troglodytes aedon bonariae) use two basic alarm calls (Type I and Type II) when detect a threat near the nest. We experimentally analysed if calls distract predators or serve to recruit other birds to create a mobbing flock to deter predators. The results show that individuals preferentially position themselves in front of the threat, disclosing the location of the nest. Also, using playbacks of house wren alarm calls we found that these calls recruited both conspecific and heterospecific individuals to create a mobbing response. The alarm calls of house wrens seem to fulfil multiple functions, not only conveying information about the threat to their mates and nestling as revealed in previous studies, but also as a signal that attracts the attention of other conspecific and heterospecific individuals and can trigger a mobbing response to deter the predator. [ABSTRACT FROM AUTHOR]

Fitness can be increased dramatically by communication. So why, given the benefits of communication, would displays ever be completely lost evolutionarily? Threat displays, in particular, are relatively cheap to produce and are precursors of attack, so should be especially hard for both senders and receivers to lose completely. Here we explore an evolutionary transition in sociality, testing whether complete evolutionary loss of threat display has occurred in 'more social' hermit crab species, which interact more frequently with conspecifics. First, we synthesised literature and observations on the presence versus absence of threat display across hermit crab species, mapping this information onto a phylogenetic tree. We found that all 'less social' species — marine and terrestrial — produce threat displays, consistent with threat display being the ancestral state. But 'more social' terrestrial species, which are highly derived, do not produce a threat display, suggesting an evolutionary loss. Next, we contrasted natural interactions in the wild within a less social species (Pagurus bernhardus) versus within a more social species (Coenobita compressus), finding that the less social species, despite a lower rate of social encounter, had a higher rate of display per encounter (24%). In contrast, the more social species' rate of display per encounter was negligible (<1%), effectively indicating a loss in production. Finally, we experimentally reanimated threat display in the more social species, using postured models to test whether receivers retained any responsiveness to threat display. Starkly, receivers were not deterred by threat display, showing equal responsiveness across both threat and non-threat models, regardless of whether the models were stationary or dynamically moving. Our results thus reveal a case of complete collapse of communication involving threat display, implicating the social environment in this loss. In more social species, an extreme dependence on conspecific-derived shells likely drove a 'desperado effect', with threat displays being lost because they could not stop others from pursuing these valuable resources. [ABSTRACT FROM AUTHOR]

How ornaments that are used during mate choice and rival assessment remain reliable has been a source of contention for many years. Such signals are hypothesized to be costly (i.e., 'handicaps'), but empirical studies testing for costs of sexually selected ornaments are equivocal at best, contradictory at worst. We review recent studies finding compensation for sexually selected ornaments, in both intra- and inter-specific studies, suggesting that other traits evolve to mitigate costs of ornaments. We synthesize these studies to elucidate the role of compensatory traits in the evolution of reliable ornaments and explain how selection to reduce ornament costs may influence aspects of the phenotype that are not subjected to direct sexual selection and may obscure our ability to directly measure ornament costs. Both intraspecific studies and comparative studies in a phylogenetic framework are important for our understanding of how the costs of signals may be reduced by compensation, but each approach answers different questions about ornament evolution. We also elaborate on a general theoretical model that can be useful when testing for costs of ornaments in correlational and experimental studies. We recommend that future investigators should consider compensatory traits when testing for ornament costs, especially when manipulating ornamentation. [ABSTRACT FROM AUTHOR]

Macroevolutionary analysis of three components in the stickleback breeding system, male/female nuptial colouration, male/female courtship and male lead/female follow to the nest revealed that: (i) a change in the male lead is always coupled with a change in the female follow, although there is no correlation between changes in particular components of the leadfollow system; (ii) a change in male courtship is coupled with a change in female courtship in all taxa but Gasterosteus and Hypoptychus. Once again, there is no correlation between changes in particular courtship components except for a possible coupling of 'male pummel' and 'female sink to the substrate'; and (iii) there is no correlation between the diversification of the male and female nuptial colour signals. These different patterns of macroevolutionary co-origination and co-diversification interact to produce unique and reliable species and sex-specific signals at the beginning of courtship + tightly coupled signals involved in coordination between spawning partners at the final stages of courtship. In order to explain the preceding macroevolutionary patterns, we now need to delineate the genetic basis for the traits in each behavioural system. [ABSTRACT FROM AUTHOR]