Flightlessness In Birds Research Articles

Anthropogenic extinctions conceal widespread evolution of flightlessness in birds

Human-driven extinctions can affect our understanding of evolution, through the nonrandom loss of certain types of species. Here, we explore how knowledge of a major evolutionary transition-the evolution of flightlessness in birds-is biased by anthropogenic extinctions. Adding data on 581 known anthropogenic extinctions to the extant global avifauna increases the number of species by 5%, but quadruples the number of flightless species. The evolution of flightlessness in birds is a widespread phenomenon, occurring in more than half of bird orders and evolving independently at least 150 times. Thus, we estimate that this evolutionary transition occurred at a rate four times higher than it would appear based solely on extant species. Our analysis of preanthropogenic avian diversity shows how anthropogenic effects can conceal the frequency of major evolutionary transitions in life forms and highlights the fact that macroevolutionary studies with only small amounts of missing data can still be highly biased.

Simultaneous Wing Molt as a Catalyst for the Evolution of Flightlessness in Birds.

AbstractComplex features, such as vision, limbs, and flight, have been lost by many groups of animals. Some groups of birds are more prone to loss of flight than others, but few studies have investigated possible reasons for this variation. I tested the hypothesis that a rare strategy of flight feather replacement is involved in rate variation in the evolution of flightlessness in birds. This strategy involves a simultaneous molt of the flight feathers of the wing, resulting in a temporary flightless condition during molt. I hypothesized that adaptations for this flightless period may serve as preadaptations for permanent flightlessness under conditions that favor permanent loss of flight. I found an elevated rate of loss of flight in lineages with simultaneous wing molt compared with loss of flight in lineages without simultaneous wing molt. This may indicate that birds with simultaneous molt are more prepared to adjust quickly to open niches that do not require flight, such as terrestrial niches on island habitats. These results illustrate how molt strategies can influence the long-term evolutionary trajectories of birds and provide insight into how phenotypic precursors may act as a mechanism of rate variation in the loss of complex traits.

Gradual evolution towards flightlessness in steamer ducks.

Flightlessness in birds is the product of changes in suites of characters-including increased body size and reduced anterior limbs-that have evolved repeatedly and independently under similar ecological conditions (generally insularity). It remains unknown whether this phenotypic convergence extends to the genomic level, partially because many losses of flight occurred long ago (such as in penguins or ratites), thus complicating the study of the genetic pathways to flightlessness. Here, we use genome sequencing to study the evolution of flightlessness in a group of ducks that are current and dynamic exemplars of this major functional transition. These recently diverged Tachyeres steamer ducks differ in their ability to fly: one species is predominantly flighted and three are mainly flightless. Through a genome-wide association analysis, we identify two narrow candidate genomic regions implicated in the morphological changes that led to flightlessness, and reconstruct the number of times flightlessness has evolved in Tachyeres. The strongest association is with DYRK1A, a gene that when knocked out in mice leads to alterations in growth and bone morphogenesis. These findings, together with phylogenetic and demographic analyses, imply that the genomic changes leading to flightlessness in Tachyeres may have evolved once, and that this trait remains functionally polymorphic in two species.

A shortening of the manus precedes the attenuation of other wing‐bone elements in the evolution of flightlessness in birds

AbstractNudds, R. L. and Slove Davidson, J. 2010. A shortening of the manus precedes the attenuation of other wing‐bone elements in the evolution of flightlessness in birds. —Acta Zoologica (Stockholm) 91: 115–122This is the first study to present evidence for a general pattern of wing‐bone attenuation during the early stages of the evolution of flightlessness. A comparative analysis using phylogenetic independent contrasts showed that in families that contain both flighted (volant) and flightless species, the volant species have shorter wings and total‐arm (humerus + ulna + manus) lengths relative to their body masses than the species within their wholly volant sister families. A shortening of the manus may typify the early stages of the evolution of flightlessness, with the humerus and ulna attenuating later, perhaps because of their role in maintaining the position of the aerodynamically important alula. A shorter wing relative to body mass was not the result of the inverse (i.e. heavier body mass relative to wing length) because mean body masses of volant members of flightless families were similar to or lower than those of their wholly volant sister families. Despite finding a common trend in the wing morphologies of volant members of flightless families, it seems unlikely that a general model of selection pressures driving the evolution of flightlessness exists. At the very least, a dichotomy between those birds that have lost the ability to fly in order to gain the ability to swim and terrestrial forms, may persist.

A new flightless gallinule (Aves: Rallidae: Gallinula) from the Oligo-Miocene of Riversleigh, northwestern Queensland, Australia

Flightlessness in birds occurs in a taxonomically diverse array of families, but is best exemplified in the rails (Rallidae). Most flightless species of rails live on islands, where the absence of native mammalian predators may make flight superfluous. Fossil rails from Oligo-Miocene sites at Riversleigh, northwestern Queensland, Australia, are considered to represent a single species of gallinule Gallinula, described here as new. Compared with four Quaternary species of Gallinula from Australasia (two volant, two non-volant), it shows similarities with the flightless species in the development of the fore- and hindlimb elements and in other characteristics of limb bone morphology associated with flightlessness. These indicate that the Riversleigh species was non-volant. Its relationships with the Quaternary species, including the flightless Gallinula mortierii, now restricted to Tasmania, but known from Plio-Pleistocene deposits in eastern mainland Australia, are considered.

Temporary flightlessness in pre‐laying Common Eiders Somateria mollissima: are females constrained by excessive wing‐loading or by minimal flight muscle ratio?

Large body size, small wings and relatively low flight muscle mass are general attributes of flightlessness in birds, but a general analysis is lacking when considering these factors simultaneously. Common Eiders Somateria mollissima are large sea ducks characterized by short, pointed wings of low surface area. Because females fast throughout incubation, they need to accumulate large body reserves prior to laying. During this pre‐laying period, many females cannot take off, and dive when approached under still‐air conditions, whereas males take off readily when disturbed. In this paper, we examine how pre‐laying female Common Eiders fit the maximum wing‐loading ratio of Meunier, the marginal flight muscle ratio (FMR) of Marden and predictions of a general model of take‐off performance (also by Marden). Wing morphology was recorded and flight muscles were dissected from specimens collected during the pre‐laying period near one breeding colony. In addition, take‐off ability, as observed during collection, was compared with the proposed thresholds for flightlessness and outputs from the general model of take‐off performance. The results indicated that half of the pre‐laying females exceeded the wing‐loading ratio of Meunier, although all females had values above 0.160, the flight muscle ratio below which take‐off would be impossible. We suggest that wing‐loading and flight muscle ratio interact in Eiders, with higher FMR compensating for excessive wing‐loading. Nevertheless, the model of take‐off performance predicted, with reasonable accuracy, the behavioural observations under still‐air conditions. Indeed, females that were predicted to be temporarily flightless could produce a specific lift of 8.8 N/kg on average (less than the 9.8 N/kg required to overcome gravity). In contrast, the average specific lift predicted for males capable of flight was estimated to be 11.4 N/kg. These results agree with our observations that female Common Eiders are at the limit of flight capability in vertebrates.

Patterns of correlated character evolution in flightless birds: a phylogenetic approach

Given a robust phylogeny for a particular higher taxon, it is possible to map the evolution of various character changes onto the phylogeny and study the extent to which they co-occur. Of particular interest are the questions of (a) whether particular morphological changes tend to accompany changes in ecology or behaviour to which they bear a functional relationship and (b) whether changes in those ‘primary’ morphological characters tend to be associated with correlated changes in other aspects of morphology, as would be expected given the high level of morphological integration that characterizes most organisms. Here we report a study of this kind, looking at morphological correlates of the evolution of flightlessness in birds, and using the concentrated changes test to determine whether associations are significant. We find that pectoral reduction, pelvic enlargement and changes in skull morphology significantly co-occur, and that these are usually achieved through heterochrony rather than other kinds of developmental reprogramming.

On the origins of birds: the sequence of character acquisition in the evolution of avian flight

Assessment of competing theories for the evolution of avian flight is problematic, and tends to rest too heavily on reconstruction of the mode of life of one or a few specimens representing still fewer species. A more powerful method is to compare the sequence of character acquisition predicted by the various theories with the empirical sequence provided by cladistic phylogeny. Arboreal and cursorial theories incorrectly predict the sequence of character acquisition for several key features of avian evolution. We propose an alternative 'pouncing proavis' model for the evolution of flight. As well as being both biologically and evolutionarily plausible, the pouncing proavis model correctly predicts the evolutionary sequence of all five key features marking the evolution of birds.

Energy Conservation and the Evolution of Flightlessness in Birds

I examine the hypothesis that energy conservation contributes to the evolution of a flightless condition in birds by comparing the factors that correlate with basal rate of metabolism in kiwis and flighted and flightless rails and ducks. Flightless rails have low basal rates, the level of which decreases with pectoral muscle mass. Kiwis also have low basal rates and small pectoral masses. The small pectoral masses found in flightless grebes, the flightless cormorant, and the flightless parrot suggest that these species have low basal rates. Penguins and flightless ducks, in contrast, have neither low basal rates nor small pectoral masses because these birds use their wings for locomotion. These data are compatible with the hypothesis that energy conservation contributes to the evolution of flightlessness in species in which pectoral muscle mass is reduced. On oceanic islands, rails have evolved a flightless condition repeatedly, usually in association with a small body size. Both adjustments reduce energy...