'Recessive' species-specific antigens in doves and pigeons

Evidence is presented that recessive species-specific antigens are present in pigeons and doves as determined by antiserum absorptions with cells of the opposing parental and Fi birds. This confirms and extends earlier observations by M. R. Irwin and L. J. Cole and adds another species. A simple model is presented postulating a relationship between genes, enzymes, and 'dominant and recessive' antigens.     

Heterothermia in pigeons and doves reduces energetic costs

Two patterns of heterothermia were demonstrated for three species of pigeons (Columbidae): Controlled hyperthermia as a physiological strategy of the arid-adapted Australian Diamond Dove and African Namaqua Dove to minimize heat stress when exposed to high temperatures and Torpor as an energy-saving mechanism at low environmental temperatures. This mechanism was most pronounced in the fruit-eating Cloven-feathered Dove (minimal body temperature T_b=25°C, reduction of metabolic rate by 67%). Hence, heterothermia is regarded as a means of adaptation to variable and unpredictable environmental conditions, playing an important role in the ecological radiation of the Columbidae.     

Hybridization and postzygotic isolation patterns in pigeons and doves

Abstract.— The study of the patterns of reproductive isolation in relation to species divergence is critical for the understanding of the process of speciation. Comparative analyses of this kind were previously conducted in Drosophila , Lepidoptera, frogs, ducks, and birds in general. In the present study, we used information from the literature to analyze hybrid inviability in relation to species divergence in pigeons and doves. Four main patterns arose from this analysis: (1) as in the other groups studied, F₁ hybrid inviability gradually increases as species diverge, the time needed to reach total inviability being higher in birds than in the other groups; (2) as expected, the presence of geographic overlap does not influence the evolution of postzygotic isolation; (3) the percentage of unhatched eggs does not differ between hybrids of the first generation and the backcrosses, but it increases in the second hybrid generation; and (4) pigeons and doves follow Haldane's rule, as found in the other groups studied so far. The similarity between the results of this and previous studies contributes to the growing evidence suggesting that the patterns of the evolution of postzygotic isolation, and the process of speciation in general, are shared among animal groups.     

Behavioural changes and the adaptive diversification of pigeons and doves

What factors determine the extent of evolutionary diversification remains a major question in evolutionary biology. Behavioural changes have long been suggested to be a major driver of phenotypic diversification by exposing animals to new selective pressures. Nevertheless, the role of behaviour in evolution remains controversial because behavioural changes can also retard evolutionary change by hiding genetic variation from selection. In the present study, we apply recently implemented Ornstein–Uhlenbeck evolutionary models to show that behavioural changes led to associated evolutionary responses in functionally relevant morphological traits of pigeons and doves (Columbiformes). Specifically, changes from terrestrial to arboreal foraging behaviour reconstructed in a set of phylogenies brought associated shorter tarsi and longer tails, consistent with functional predictions. Interestingly, the transition to arboreality accelerated the rates of evolutionary divergence, leading to an increased morphological specialization that seems to have subsequently constrained reversals to terrestrial foraging. Altogether, our results support the view that behaviour may drive evolutionary diversification, but they also highlight that its evolutionary consequences largely depend on the limits imposed by the functional demands of the adaptive zone.     

The historic biogeography and community ecology of Polynesian pigeons and doves

The species richness, taxonomic diversity, and geographic distribution of pigeons and doves (Columbidae) have been altered irreversibly in Polynesia by 3500 years of human activity. Natural (without human influence) columbid faunas are estimated primarily by studying prehistoric bones. In all Polynesian island groups studied (except outlying Easter Island, Hawaiian Islands, or New Zealand), the prehistoric columbid faunas had more species, more genera, and more species per genus than modern faunas from the same island. Congeneric species pairs or triplets occurred on many islands for Ducula , Ptilinopus , and Gallicolumba. The losses of Polynesian columbids include the extinction of at least 9 species in the genera Ducula , Ptilinopus , Macropygia , Caloenas , Gallicolumba , and Didunculus as well as the extirpation of numerous island populations of extant species. If not for human impact, a typical East Polynesian island would support at least 5–6 species of columbids in 3–4 genera (compared to 0–3 species in 0–3 genera today). A typical West Polynesian island would support at least 6–7 species in 4–5 genera (compared to 1–6 species in 1–5 genera today). Since all Polynesian pigeons and doves are frugivorous and/or granivorous, their decline in recent millennia probably has affected the composition of Polynesian forests by limiting inter- and intra-island dispersal of plant propagules.     

Metabolic responses of homing pigeons to flight and subsequent recovery

This study examines metabolic changes occurring during short to endurance flights and during subsequent recovery in free-flying pigeons, in particular the change towards lipid utilization with increasing flight duration, lipid supply to the flight muscles, protein utilization and the time needed to metabolically recover. Eight plasma metabolite concentrations were measured in homing pigeons released from sites 20–200 km from the loft (0.3–4.8 h flight duration) just after landing and after keeping birds fasting at rest for 30 and 60 min, respectively, after their return. Birds kept in the loft fasting at rest were used as controls. Plasma free fatty acid and glycerol concentrations increased rapidly with flight duration and leveled off after about 1.5 h. This indicates a marked change towards a high and stable lipid utilization from adipose tissues within 1–2 h of flight. Plasma triglyceride levels and very-low-density lipoproteins were decreased after short flights, but subsequently regained or surpassed fasting levels at rest. This indicates that re-esterification of free fatty acids and delivery as very-low-density lipoproteins to the flight muscles to circumvent constraints of fatty acid supply, as described previously for small passerines, is not as significant in the pigeon which has a much lower mass-specific energy rate. An initial increase in plasma glucose levels and a transient decrease to fasting levels at rest was observed and may reflect the initial use and subsequent exhaustion of glycogen stores. Contrary to other birds and mammals, -hydroxy-butyrate levels increased markedly with flight duration. This may suggest a more important sparing of carbohydrates and protein as gluconeogenic precursors in the pigeon than in other species. Plasma uric acid levels increased linearly up to about 4 h flight duration. This indicates an accelerated protein breakdown during flight which may primarily serve to deliver amino acids as glucogenic precursors and citrate cycle intermediates. With increasing flight duration, the energy sources change from an initial phase based primarily on carbohydrates to a lipid-based endurance phase. It is discussed whether this metabolic change depends on the level of power output or the performed work (energy spent) since the start of flight. During the first hour of recovery, most metabolites reached or approached fasting levels at rest, indicating a marked reduction in lipolysis and protein breakdown. -hydroxy-butyrate levels remained at flight levels and glucose levels increased slightly, indicating a restoration of glycogen stores.Abbreviations VLDL very-low-density lipoproteins - FFA free fatty acids     

Nuclear and mitochondrial genes contain similar phylogenetic signal for pigeons and doves (Aves: Columbiformes)

Molecular systematic studies generally assume that gene trees are reasonable estimates of species trees. We tested the validity of this assumption in the pigeons and doves (Aves: Columbiformes) by comparing phylogenies derived from nuclear (beta-fibrinogen intron 7) and mitochondrial (cytochrome b) genes. Trees derived from the two genes when analyzed separately contained many nodes in common. A partition homogeneity test revealed no significant incongruence between trees derived from the two genes; so, we combined nuclear and mitochondrial data in subsequent phylogenetic analyses. The resulting tree, which was highly resolved and generally well supported, contained a strong biogeographic component. The rate of nucleotide substitution for the nuclear intron was approximately six times slower than that of cytochrome b. This resulted in a much higher consistency index for trees derived from the intron because of the low level of multiple substitution. However, the degree of resolution and support for trees reconstructed from the two genes was similar. We also examined the transition and transversion substitution rates for the genes. Third position transversions for cytochrome b accumulated linearly with intron divergence, suggesting low levels of multiple substitution for third position transversions.     

Metabolic physiology of the numbat (Myrmecobius fasciatus)

The numbat (Myrmecobius fasciatus) is unique amongst marsupials as it is exclusively diurnal, feeds only on termites and is semi-fossorial. This study examines the thermal and metabolic physiology of the numbat to determine if its physiology reflects its phylogeny, diet and semi-fossorial habit. Numbats (mean adult body mass 552 g) were able to regulate body temperature at ambient temperatures of 15-30 degrees C, with a body temperature at thermoneutrality (30 degrees C) of 34.1 degrees C. The thermoneutral body temperature was not significantly different from that predicted for an equivalent-sized marsupial. Basal metabolic rate, measured at 30 degrees C, was 0.389 +/- 0.025 ml O(2) g(-1) h(-1), and was slightly but not significantly lower at 82.5% of that predicted for a typical marsupial of equivalent body mass. Metabolic rate increased with decreasing ambient temperatures below 30 degrees C. Patterns of metabolic cycling observed for completely inactive numbats at ambient temperatures below 30 degrees C are likely to be related to sleep phase. Wet thermal conductance of 1.94 J g(-1) h(-1) degrees C(-1) (at 30 degrees C) was 131% of that predicted for a marsupial. Evaporative water loss of the numbat remained constant below the thermoneutral zone (<30 degrees C) at approximately 0.6 ml g(-1) h(-1), only 47.4% of that predicted for a marsupial. It increased to 1.01 +/- 0.16 ml g(-1) h(-1) at an ambient temperature of 32.5 degrees C. The thermal and metabolic physiology of the numbat is generally similar to that expected for other marsupials, and is also comparable to that of termitivorous placental mammals. Thus the reduction in body temperature and basal metabolic rate of placental termitivores is a "marsupial-like" low energy turnover physiology, and the numbat being a marsupial already has an appropriate physiology to survive exclusively on a low energy diet of termites.     

Online coverage of the literature on thermal physiology

Online searches for research topics in thermal physiology usually do not retrieve more than 40% of the existing publications. In order to determine whether this low retrieval rate is due to deficient coverage of the literature or to problems in storage and retrieval of information, a list of 25 major papers, 25 minor papers and 15 obscure papers on thermal physiology was compiled. The 65 documents were searched online in the MEDLINE database. Retrieval rate was more than 60% for obscure papers, 80% for minor papers, and 90% for major papers. It is concluded that MEDLINE has an appropriate coverage of the literature on thermal physiology and that the low retrieval rate in online searches is due mostly to problems in information processing.     

Behaviour and physiology: the thermal strategy of leatherback turtles

Background

Adult leatherback turtles (Dermochelys coriacea) exhibit thermal gradients between their bodies and the environment of ≥8°C in sub-polar waters and ≤4°C in the tropics. There has been no direct evidence for thermoregulation in leatherbacks although modelling and morphological studies have given an indication of how thermoregulation may be achieved.

Methodology/Principal Findings

We show for the first time that leatherbacks are indeed capable of thermoregulation from studies on juvenile leatherbacks of 16 and 37 kg. In cold water (< 25°C), flipper stroke frequency increased, heat loss through the plastron, carapace and flippers was minimized, and a positive thermal gradient of up to 2.3°C was maintained between body and environment. In warm water (25 – 31°C), turtles were inactive and heat loss through their plastron, carapace and flippers increased. The thermal gradient was minimized (0.5°C). Using a scaling model, we estimate that a 300 kg adult leatherback is able to maintain a maximum thermal gradient of 18.2°C in cold sub-polar waters.

Conclusions/Significance

In juvenile leatherbacks, heat gain is controlled behaviourally by increasing activity while heat flux is regulated physiologically, presumably by regulation of blood flow distribution. Hence, harnessing physiology and behaviour allows leatherbacks to keep warm while foraging in cold sub-polar waters and to prevent overheating in a tropical environment.     

Brain temperature regulation of panting and non-panting pigeons exposed to extreme thermal conditions

• 1.1. Brain (hypothalamic), skin and body temperatures were measured in hand-reared acclimated (Acc, n = 5) and non-acclimated (NAcc, n =7) rock pigeons (Columba livia, mean body mass 237 g) exposed to increasing ambient temperatures (T_a) (30–60°C) and low humidities.
• 2.2. In non-panting Acc birds, brain temperature gradually increased from 40.1 ± 0.4°C at 30°C to 41.2 ± 0.4°C at 60°C T_a. A mean body temperature (T_b) of 41.2 ± 0.2°C was measured at T_a up to 50°C; an increase of 1.1°C was observed at 60°C (T_b 42.2 ±0.6°C).
• 3.3. In Acc panting birds exposed for 2 hr to 60°C, T_hy was 41.9 ± 0.8°C and T_s was somewhat (but insignificantly) higher, i.e., 42.2 ± 0.7°C. It looks as if both values were increased as a result of a slight hyperthermia that developed (T_b = 43.5 ± 0.9°C).
• 4.4. The significance of the present results for evaluating neuronal thermoresponsiveness of birds' hypothalamus is discussed.