The effect of acoustic and visual priming stimuli on the reproductive behaviour of female zebra finches, <Emphasis Type="Italic">Taeniopygia guttata</Emphasis>

We investigated the influences of reproductive priming, using acoustic stimuli alone or a combination of acoustic and visual stimuli on egg-laying in female zebra finches (Taeniopygia guttata). One group of females was exposed during 6 days to both acoustic and visual stimuli from males while another was exposed only to acoustic stimuli; a control group was unable to see or hear males prior to the introduction of unfamiliar males for pairing. We also manipulated the amount of visual stimulation by presenting either: males with normal red bands, males with red bands without ultraviolet reflection or unadorned males. Females exposed to visual stimuli spent more time on perches near males than control females or those only hearing males. However, there were no statistically significant differences in subsequent total eggs produced, or the latency to egg-laying between females exposed to priming males with different visual characteristics; they did not significantly differ from the control females in these parameters either. Females that heard, but did not see, priming stimuli produced more eggs when paired with males than the controls. Thus, acoustic stimuli alone may have promoted reproductive condition while the acoustic and visual stimuli together did not. Our results contradict a previous report, and may reflect components of the experimental design we employed (i.e. by pairing females with unfamiliar males after their initial exposure to priming males, we may have suppressed their ability to advance their reproductive state). Females that only heard priming males may have been more willing to accept pairing males because of the absence of visual identifiers.     

Anhydrolutein in the zebra finch: a new,metabolically derived carotenoid in birds

Many birds acquire carotenoid pigments from the diet that they deposit into feathers and bare parts to develop extravagant sexual coloration. Although biologists have shown interest in both the mechanisms and function of these colorful displays, the carotenoids ingested and processed by these birds are poorly described. Here we document the carotenoid-pigment profile in the diet, blood and tissue of captive male and female zebra finches (Taeniopygia guttata). Dietary carotenoids including: lutein; zeaxanthin; and β-cryptoxanthin were also present in the plasma, liver, adipose tissue and egg-yolk. These were accompanied in the blood and tissues by a fourth pigment, 2′,3′-anhydrolutein, that was absent from the diet. To our knowledge, this is the first reported documentation of anhydrolutein in any avian species; among animals, it has been previously described only in human skin and serum and in fish liver. We also identified anhydrolutein in the plasma of two closely related estrildid finch species (Estrilda astrild and Sporaeginthus subflavus). Anhydrolutein was the major carotenoid found in zebra finch serum and liver, but did not exceed the concentration of lutein and zeaxanthin in adipose tissue or egg yolk. Whereas the percent composition of zeaxanthin and β-cryptoxanthin were similar between diet and plasma, lutein was comparatively less abundant in plasma than in the diet. Lutein also was proportionally deficient in plasma from birds that circulated a higher percentage of anhydrolutein. These results suggest that zebra finches metabolically derive anhydrolutein from dietary sources of lutein. The production site and physiological function of anhydrolutein have yet to be determined.     

PHENOTYPIC VARIATION OF GROWTH TRAJECTORIES IN FINCHES

Evolution cannot proceed without phenotypic variation for selection to act on. This is particularly true of ontogenetic parameters because it is changes in these parameters that give rise to new phenotypes. I analyzed the amount and dimensionality of phenotypic variation on growth trajectories in early ontogeny in three species of finches (Fringillidae) using the recently developed infinite-dimensional model. For two species, eight traits were analyzed, and for a third, six traits. Growth data were analyzed only up to 6 d of age in two species and 8 d of age in the third. The results were very similar for all species and traits. A very large proportion of the phenotypic variation in growth trajectories was confined to a single dimension. This dimension corresponded to a simultaneous increase/decrease at all ages in early ontogeny. The eigenfunctions, each describing a family of similar-shaped growth trajectories, were highly collinear among traits. A high covariance existed among traits at the same and different ages. If some part of the phenotypic variation has an additive genetic basis, then any selection for a change in size at one age in one trait will lead to a response in a size at subsequent ages and in the other traits. This in turn suggests that morphological evolution frequently will move along a multivariate size axis, as has indeed been found in several taxa.     

Daily rhythm of oxygen consumption and thermoregulatory responses in some European winter- or summer-acclimatized finches at different ambient temperatures

The oxygen consumption of European finches, the siskin (Carduelis spinus), the brambling (Fringilla montifringilla), the bullfinch (Pyrhulla pyrhulla), the greenfinch (Carduelis chloris) and the hawfinch (Coccothraustes coccothraustes), was recorded continuously while ambient temperature was decreased stepwise from +30 down to-75°C. The oxygen consumption, body temperature (telemetrically), and shivering (integrated pectoral electromyography) of greenfinches were measured simultaneously at ambient temperatures between +30 and-75°C. Maximum heat production, cold limit, lower critical temperature, basal metabolic rate and thermal conductance (of the greenfinch) were determined. The diurnal variation of oxygen consumption of siskins and greenfinches was recorded at thermoneutrality and below the thermoneutral zone in winter- and summer-acclimatized birds. The diurnal variation of body temperature and thermal conductance of greenfinches were also determined. The diurnal variation of heat production was not seasonal or temperature dependent in the siskin and in the greenfinch. Nocturnal reduction of oxygen consumption saved 15–33% energy in the siskin and greenfinch. Body temperature of the greenfinch was lowered by 2.5–3.4°C. The nocturnal reduction of thermal conductance in the greenfinch was 39–48%. The basal metabolic rate was lowest in the largest bird (hawfinch) and highest in the smallest bird (siskin). The values were in the expected range. The heat production capacity of finches in winter was 4.7 times basal metabolic rate in the siskin, 4.2 times in the brambling, 3.5 times in the greenfinch and 2.9 times in the bullfinch and hawfinch. The heat production capacity of the siskin and greenfinch was not significantly lower in summer. The cold limit temperatures (°C) in winter were-61.2 in the siskin,-41.3 in the greenfinch,-37.0 in the bullfinch,-35.7 in the brambling and-28.9 in the hawfinch. The cold limit was 14.3°C higher in summer than in winter in the siskin and 8.7°C in the greenfinch. Thermal insulation of the greenfinch was significantly better in winter than in summer. The shivering of the greenfinch increased linearly when ambient temperature was decreased down to-40°C. Maintenance of shivering was coincident with season. In severe cold integrated pectoral electromyography did not correlate with oxygen consumption as expected. The possible existence of non-shivering thermogenesis in birds is discussed. It is concluded that the acclimatization of European finches is primarily metabolic and only secondly affected by insulation.Abbreviations AAT avian adipose tissue - bm body mass - BMR basal metabolic rate - C _t thermal conductance - EMG electromyogram - HP heat production - HP _max maximum heat production - MR metabolic rate - NST non-shivering thermogenesis - RMR resting metabolic rate - RQ respiratory quotient - T _a ambient temperature - T _b body temperature - T _c colonic temperature - T _1c lower critical temperature - TNZ thermoneutral zone - T _st shivering threshold temperature - V oxygen consumption     

THE MITOCHONDRIAL AND NUCLEAR GENETIC HOMOGENEITY OF THE PHENOTYPICALLY DIVERSE DARWIN'S GROUND FINCHES

The most extensively studied group of Darwin's finches is the genus Geospiza, the ground finches, and yet little is known about the evolutionary history and genetic relationships of these birds. Studies using either allozyme or morphological data have been unable to resolve relationships between the six species and numerous populations of ground finches. In this paper we report the results of a study using mitochondrial control region and nuclear internal transcribed spacer (ITS) 1 sequence data. The differentiation of the ground finch species based on morphological data is not reflected in either mitochondrial or nuclear DNA sequence phylogenies. Furthermore, there is little concordance between the mitochondrial haplotypes and ITS alleles found within individuals. We suggest that the absence of species-specific lineages can be attributed to ongoing hybridization involving all six species of Geospiza. There are no long term selective pressures against hybridization within this genus, and therefore a genetically homogenous genus may be maintained indefinitely. Hybridization has apparently played a role in the adaptive radiation of Darwin's finches.     

Sex ratios and sexual selection in socially monogamous zebra finches

An experiment was performed in which adult sex ratios of zebrafinches, Taeniopygyia guttata castanotis, were varied to testpossible effects of adult population sex ratios on sexual selectionintensity and mating system dynamics in species with biparentalcare. The possibility that sex ratio influences the successof social mating patterns (leading to polygyny when males arerare and polyandry when females are rare) was not supported.Results did support the prediction of the differential allocationhypothesis that individuals of the abundant sex would increasetheir relative parental expenditure (PE). Although total (male+ female) PE did not vary between treatments, relative malePE was significantly higher in the male-biased treatment (MBT;sex ratio 64% male) than in the female-biased treatment (FBT; sexratio 36% male). In both treatments, male PE contributions contributedto female reproductive rate. Results also supported the predictionof the differential access hypothesis that individuals of theabundant sex would experience greater intensity of selectionon sexually selected attributes. Male beak color, a sexuallyselected trait, influenced male social parentage in the MBTbut not in the FBT. Finally, broods in the FBT displayed higher hatchingasynchrony and lower hatching success; we believe this was causedby early onset of incubation, a tactic used as a defense againstintraspecific brood parasitism, which was much higher in theFBT. Population sex ratios may be an important factor affectingfemale ability to influence male parental investment patterns.     

Zebra finches are sensitive to prosodic features of human speech

Variation in pitch, amplitude and rhythm adds crucial paralinguistic information to human speech. Such prosodic cues can reveal information about the meaning or emphasis of a sentence or the emotional state of the speaker. To examine the hypothesis that sensitivity to prosodic cues is language independent and not human specific, we tested prosody perception in a controlled experiment with zebra finches. Using a go/no-go procedure, subjects were trained to discriminate between speech syllables arranged in XYXY patterns with prosodic stress on the first syllable and XXYY patterns with prosodic stress on the final syllable. To systematically determine the salience of the various prosodic cues (pitch, duration and amplitude) to the zebra finches, they were subjected to five tests with different combinations of these cues. The zebra finches generalized the prosodic pattern to sequences that consisted of new syllables and used prosodic features over structural ones to discriminate between stimuli. This strong sensitivity to the prosodic pattern was maintained when only a single prosodic cue was available. The change in pitch was treated as more salient than changes in the other prosodic features. These results show that zebra finches are sensitive to the same prosodic cues known to affect human speech perception.     

Integration of palaeontological, historical, and geographical data on the extinction of koa-finches

Identifying the root causes of extinction or endangerment requires long chronological records that begin before a population started to decline and extend until its extinction or functional extinction. We present a case study of the koa‐finches, genus Rhodacanthis, an extinct group of Hawaiian honeycreepers that was specialized to feed on green pods and seeds of the koa tree or other leguminous plants. Six island populations of koa‐finches are known; four in the Holocene fossil record and two that survived until the 1890s. We document the palaeoecological context of the fossils and identify constraints on the age span of the specimen record for each population using stratigraphic contexts, associated radiometric determinations, and museum specimen data. We estimate the potential geographical range of koa‐finches at the time of human arrival using two methods: assessment of their historical and palaeo‐habitats, and geographical information system mapping of the pre‐human distribution of the koa plant (Acacia koa) and its sister species, the koai‘a plant (Acacia koaia). After integrating the foregoing data with chronological records and distributional maps of the potential forcing agents of extinction, we conclude that at least two extinctions of island populations were due to ecological change in the lowlands in the prehistorical and perhaps the early historical periods. In the same time frame, the koa‐finch populations on Hawai‘i Island became rare and restricted to upland refugia, making them vulnerable to the upland forest harvesting and degradation that was accelerating in the 1890s. Neither climatic variation nor mosquito‐vectored diseases are likely to have caused the observed extinctions. This study illustrates an approach that can be applied to many other extinct and endangered island species to better understand the causes of high extinction rates in the human era.     

Adaptive divergence in Darwin's small ground finch (Geospiza fuliginosa): divergent selection along a cline

We examine here, in a single year (2005), phenotypic divergence along a 560‐m elevation gradient in Darwin's small ground finch (Geospiza fuliginosa) in the Galápagos Islands. In this sample, four composite measures of phenotypic traits showed significant differences along the 18‐km geographical cline extending from lowlands to highlands. Compared with lowland birds, highland birds had larger and more pointed beaks, and thicker tarsi, but smaller feet and claws. Finches in an intervening agricultural zone had predominantly intermediate trait values. In a second, mark–recapture study we analyse selection on morphological traits among birds recaptured across years (2000–2005) in lowland and highland habitats. Birds were more likely to survive in the highlands and during the wet season, as well as if they had large beaks and bodies. In addition, highland birds exhibited higher survival rates if they had small feet and pointed beaks – attributes common to highland birds as a whole. Lowland birds were more likely to survive if they possessed the opposite traits. Selection therefore reinforced existing morphological divergence, which appears to reflect local adaptation to differing resources during the predominantly drought‐ridden conditions that characterized the 5‐year study. Alternative explanations – including genetic drift, matching habitat choice, deformation by parasites, and the effects of wear – received little or no support. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2013, 110 , 45–59.