Differential rates of phenotypic introgression are associated with male behavioral responses to multiple signals

Sexual selection on multiple signals may lead to differential rates of signal introgression across hybrid zones if some signals contribute to reproductive isolation but others facilitate gene flow. Competition among males is one powerful form of sexual selection, but male behavioral responses to multiple traits have not been considered in a system where traits have introgressed differentially. Using playbacks, mounts, and a reciprocal experimental design, we tested the hypothesis that male responses to song and plumage in two subspecies of red‐backed fairy‐wren (Malurus melanocephalus) explain patterns of differential signal introgression (song has not introgressed, whereas plumage color has introgressed asymmetrically). We found that males of both subspecies discriminated symmetrically between subspecies’ songs at a long range, but at a close range, we found that aggression was equal for both subspecies’ plumage and songs. Taken together, our results suggest that male behavioral responses hinder the introgression of song, but allow for the observed asymmetrical introgression of plumage. Our results highlight how behavioral responses are a key component of signal evolution when recently divergent taxa come together, and how differential responses to multiple signals may lead to differential signal introgression and novel trait combinations.     

Direct and indirect effects of anthropogenic bird food on population dynamics of a songbird

Anthropogenic bird foods are frequently credited with affecting avian population dynamics, but few studies have tested this assertion over broad spatial scales. Human-derived foods could directly impact population sizes or indirectly affect them by mediating the influence of another factor, such as disease. In 1994, a novel disease outbreak (mycoplasmal conjunctivitis) substantially reduced populations of the house finch (Haemorhous mexicanus) in the eastern United States, creating an opportunity to test whether bird feeding indirectly exacerbated or ameliorated the impacts of the disease. We assessed the effects of bird food availability on house finch populations using data from the National Survey on Fishing, Hunting, and Wildlife-associated Recreation and the Christmas Bird Count. House finch densities were positively related to the density of people providing food for birds prior to the spread of mycoplasmal conjunctivitis, suggesting that the availability of bird seed can limit the size of finch populations. Following the disease epidemic, house finch declines were greatest where the density of people feeding birds also fell dramatically. This pattern suggests that bird food could have a positive indirect effect on disease-related mortality. Our findings suggest that the collective actions of individual people have the potential to influence resource availability and population dynamics of wildlife in human-modified landscapes.     

Militarised natural history: tales of the avocet's return to postwar Britain

Absent as a breeding bird from Britain for at least a century, avocets (Recurvirostra avosetta) began nesting on the east coast of Britain, in Suffolk, shortly after the end of the Second World War, having honed in on two spots on Britain's coast that had been flooded for war-related reasons. The avocets' presence was surrounded in secrecy, while a dedicated few kept up a protective watch over them. As the Royal Society for the Protection of Birds (RSPB) took over responsibility for the flourishing colony, they claimed the episode as a symbol of success for British protection, later making the bird their logo. Counter to the RSPB's story of protecting a British bird, I read the narratives of events in terms of making a bird British. I show how, as postwar Britain slumped economically and spiritually and tried to rebuild itself, the birds became a vehicle for formulating national identity: of Britain as a home to which to return and belong. Exploring the themes of returning servicemen and closed territories, the paper also examines the episode in terms of the naturalisation of the military and the militarisation of nature.     

Songs differing in consistency elicit differential aggressive response in territorial birds

Acoustic signals during intrasexual interactions may help receivers to establish the cost and benefits of engaging in a confrontation versus avoiding the cost of escalation. Although birdsong repertoires have been previously suggested as providing information during agonistic encounters, the cost (time/neural resources) of assessing large repertoires may decrease the efficiency of the signal for mutual assessment. Acoustic-structural features may, therefore, be used to enable a fast and accurate assessment during this kind of encounters. Recently, it has been suggested that the consistency of songs may play a key role during intrasexual interactions in bird species. Using a playback experiment in a colour-ringed great tit population, we tested the hypothesis that songs differing in consistency may elicit a differential response, indicating that the signal is salient for the receivers. Great tit males clearly responded more aggressively towards highly consistent songs. Our findings, together with previous evidence of increased song consistency with age in the great tit, suggest that song consistency provides information on experience or dominance in this species, and this phenomenon may be more widespread than currently acknowledged.     

Host preferences in a phonotactic parasitoid of field crickets: the relative importance of host song characters

Abstract.  1. Predators, including insect parasitoids, often eavesdrop on prey signals, and as a result, predation can have important effects on the evolution of prey signalling behaviour.
2. The phonotactic parasitoid fly, Ormia ochracea , uses the calling songs of male field crickets to locate their field crickets hosts. In the western USA, this fly parasitises the variable field cricket, Gryllus lineaticeps . Previous work with one fly population suggested that female flies, like female field crickets, preferentially orient to male songs with higher chirp rates and longer chirp durations, although a limited range of male song types was used in this previous study. The current study, with a different fly population, used field-based, two-speaker choice tests to examine: (1) the effect of male chirp rate and chirp duration on fly attraction, using a natural range of song types; and (2) the relative importance of these song types in host selection by the flies.
3. Three lines of evidence suggested that chirp rate is more important than chirp duration in host selection. (a) The flies consistently preferred higher chirp rates but only sometimes preferred longer chirp durations. (b) The flies consistently preferred higher chirp rate/shorter chirp duration songs to lower chirp rate/longer chirp duration songs. (c) Preferences for longer chirp durations could be eliminated by increasing the amplitude of the less attractive song type, while preferences for higher chirp rates could only sometimes be eliminated by increasing the amplitude of the less attractive song type.
4. Fly predation may favour lower chirp rates and shorter chirp durations in G. lineaticeps , and may have resulted in stronger selection on chirp rate than on chirp duration.     

Role of structural organization in the urine concentrating mechanism of an avian kidney

The organization of tubules and blood vessels in the quail medullary cone is highly structured. This structural organization may result in preferential interactions among tubules and vessels, interactions that may enhance urine concentrating capability. In this study, we formulate a model framework for the urine concentrating mechanism of the quail kidney. The model simulates preferential interactions among renal tubules by representing two concentric cores and by specifying the fractions of tubules assigned to each of the concentric cores. The model equations are based on standard expressions for transmural transport and on solute and water conservation. Model results suggest that the preferential interactions among tubules enhance the urine concentration capacity of short medullary cones by reducing the diluting effect of the descending limbs on the region of the interstitium where the collecting ducts are located; however, the effects on longer cones are unclear.     

The vertebrate social behavior network: evolutionary themes and variations

Based on a wide variety of data, it is now clear that birds and teleost (bony) fish possess a core "social behavior network" within the basal forebrain and midbrain that is homologous to the social behavior network of mammals. The nodes of this network are reciprocally connected, contain receptors for sex steroid hormones, and are involved in multiple forms of social behavior. Other hodological features and neuropeptide distributions are likewise very similar across taxa. This evolutionary conservation represents a boon for experiments on phenotypic behavioral variation, as the extraordinary social diversity of teleost fish and songbirds can now be used to generate broadly relevant insights into issues of brain function that are not particularly tractable in other vertebrate groups. Two such lines of research are presented here, each of which addresses functional variation within the network as it relates to divergent patterns of social behavior. In the first set of experiments, we have used a sexually polymorphic fish to demonstrate that natural selection can operate independently on hypothalamic neuroendocrine functions that are relevant for (1) gonadal regulation and (2) sex-typical behavioral modulation. In the second set of experiments, we have exploited the diversity of avian social organizations and ecologies to isolate species-typical group size as a quasi-independent variable. These experiments have shown that specific areas and peptidergic components of the social behavior network possess functional properties that evolve in parallel with divergence and convergence in sociality.     

The developmental evolution of avian digit homology: An update

The identity of avian digits has been unresolved since the beginning of evolutionary morphology in the mid-19th century, i.e. as soon as questions of phylogenetic homology have been raised. The main source of concern is the persistent discrepancy between anatomical/paleontological and embryological evidence over the identity of avian digits. In this paper, recent evidence pertaining to the question of avian digit homology is reviewed and the various ideas of how to resolve the disagreement among developmental and phylogenetic evidence are evaluated. Paleontological evidence unequivocally supports the hypothesis that the fully formed digits of maniraptoran theropods are digits DI, DII, and DIII, because the phylogenetic position of Herrerasaurus is resolved, even when hand characters are excluded from the analysis. Regarding the developmental origin of the three digits of the avian hand the discovery of an anterior digit condensation in the limb bud of chickens and ostriches conclusively shows that these three digits are developing from condensations CII, CIII, and CIV. The existence of this additional anterior condensation has been confirmed in four different labs, using four different methods: Alcian blue staining, PNA affinity histochemistry, micro-capillary regression and Sox9 expression. Finally, recent evidence shows that the digit developing from condensation CII has a Hox gene expression pattern that is found in digit DI of mice forelimb and chick hind limbs. The sum of these data supports the idea that digit identity has shifted relative to the location of condensations, known as Frame Shift Hypothesis, such that condensation CII develops into digit DI and condensation CIII develops into digit DII, etc. A review of the literature on the digit identity of the Italian Three-toed Skink or Luscengola (Chalcides chalcides), shows that digit identity frame shifts may not be limited to the bird hand but may be characteristic of “adaptive” digit reduction in amniotes (sensu Steiner, H., Anders, G., 1946. Zur Frage der Entstehung von Rudimenten. Die Reduktion der Gliedmassen von Chalcides tridactylus Laur. Rev. Suisse Zool. 53, 537–546) in general. In this mode of evolution two digits are lost, in the course of the adaptation of the three anterior digits to a function that does not require the two posterior digits. This evidence suggests that the evolution of digits in tetrapods can proceed at least on two distinct levels of integration, the level of digit condensations and that of adult digits.