Convergent evolution of the tradeoff between egg size and tail fork depth in swallows and swifts

Convergent evolution provides strong evidence of the power of natural selection, particularly for distantly related taxa. Swallows and swifts are such distantly related taxa; both are specialised to feed on flying insects and have similar morphological features, such as long wings. These birds also exhibit deeply forked tails in some species, but their function remains unclear; some have argued that fork tails have evolved due to sexual selection to attract mates, while others claim that viability selection for efficient foraging favours fork tails. A recent phylogenetic analysis found the negative relationship between female tail fork depth and egg size in swallows perhaps due to foraging costs of fork tails during egg formation, but its generality remains unclear. Here, using swifts, which differ from swallows by foraging on weak‐flying insects, we found that egg size significantly decreased with increasing female fork depth. Because female fork depth was not significantly related to clutch size, clutch size would not compensate for the relationship between egg size and fork depth. The current finding using swifts, together with the previous finding in swallows, provide strong support for an evolutionary tradeoff between the female plumage ornament and reproductive investment, as predicted by sexual selection theory.     

Phylogenetic perspective on ecological niche evolution in american blackbirds (Family Icteridae)

Analysis of ecological characters on phylogenetic frameworks has only recently appeared in the literature, with several studies addressing patterns of niche evolution, generally over relatively recent time frames. In the present study, we examined patterns of niche evolution for a broad radiation of American blackbird species (Family Icteridae), exploring more deeply into phylogenetic history. Within each of three major blackbird lineages, overlap of ecological niches in principal components analysis transformed environmental space varied from high to none. Comparative phylogenetic analyses of ecological niche characteristics showed a general pattern of niche conservatism over evolutionary time, with differing degrees of innovation among lineages. Although blackbird niches were evolutionarily plastic over differing periods of time, they diverged within a limited set of ecological possibilities, resulting in examples of niche convergence among extant blackbird species. Hence, an understanding of the patterns of ecological niche evolution on broad phylogenetic scales sets the stage for framing questions of evolutionary causation, historical biogeography, and ancestral ecological characteristics more appropriately.  © 2008 The Linnean Society of London, Biological Journal of the Linnean Society , 2008, 94 , 869–878.     

Mechanisms of heterochronic change and stasis for clutch size in swifts (Apodiformes)

Since the mid‐1800s, explanations in evolution have focused on adaptivity and natural selection, largely at the expense of factors internal to the organism. Today, the importance of internal factors is no longer in dispute. Progress continues to lag, however, on the design of a framework that would allow the integration of their action in evolution. Herein, as part of a wider effort aimed at testing the functionality of the general principle based upon the embryological concepts of induction, competence, and determination (dubbed developmental determination), I present a model for the evolution of clutch size in swifts. It is structured around the physiological mechanism controlling the trait. In indeterminate laying species, it involves an exogenous signal to the female, or induction, and the acquired ability to respond to this signal, or competence. The model explains, with the action of natural selection, how a 2‐day shift in the onset of competence induces change in clutch size among species. Through the origin of induction, it predicts the evolutionary transition from indeterminate to determinate laying. Finally, in some species that are indifferent to the general increase in clutch size with latitude, it reveals how both types of developmental transformation may operate to create stasis. © 2014 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 113 , 1067–1079.     

Edaphic races and phylogenetic taxa in the Lasthenia californica complex (Asteraceae: Heliantheae): an hypothesis of parallel evolution

Lasthenia californica sensu Ornduff consists of two races that differ in their flavonoid pigments and edaphic tolerances. Recent phylogenetic studies of Lasthenia have revealed that members of L. californica sensu Ornduff belong to two phylogenetic species. The relationship of the edaphic races to these new species and to each other is the focus of this study. Characterization of flavonoid profiles and phylogenetic placement of 33 populations demonstrates that races and phylogenetic taxa are not concordant, suggesting that one or both edaphic races evolved in parallel in the two clades. We hypothesize an edaphically linked ecological role for flavonoid differences that first revealed the existence of two races.     

Convergent evolution in social swallows (Aves: Hirundinidae)

Behavioral shifts can initiate morphological evolution by pushing lineages into new adaptive zones. This has primarily been examined in ecological behaviors, such as foraging, but social behaviors may also alter morphology. Swallows and martins (Hirundinidae) are aerial insectivores that exhibit a range of social behaviors, from solitary to colonial breeding and foraging. Using a well‐resolved phylogenetic tree, a database of social behaviors, and morphological measurements, we ask how shifts from solitary to social breeding and foraging have affected morphological evolution in the Hirundinidae. Using a threshold model of discrete state evolution, we find that shifts in both breeding and foraging social behavior are common across the phylogeny of swallows. Solitary swallows have highly variable morphology, while social swallows show much less absolute variance in all morphological traits. Metrics of convergence based on both the trajectory of social lineages through morphospace and the overall morphological distance between social species scaled by their phylogenetic distance indicate strong convergence in social swallows, especially socially foraging swallows. Smaller physical traits generally observed in social species suggest that social species benefit from a distinctive flight style, likely increasing maneuverability and foraging success and reducing in‐flight collisions within large flocks. These results highlight the importance of sociality in species evolution, a link that had previously been examined only in eusocial insects and primates.     

Nuclear corroboration of DNA-DNA hybridization in deep phylogenies of hummingbirds, swifts, and passerines: the phylogenetic utility of ZENK (ii)

This paper documents the phylogenetic utility of ZENK at the avian intra-ordinal level using hummingbirds, swifts, and passerines as case studies. ZENK sequences (1.7 kb) were used to reconstruct separate gene trees containing the major lineages of each group, and the three trees were examined for congruence with existing DNA-DNA hybridization trees. The results indicate both that ZENK is an appropriate nuclear marker for resolving relationships deep in the avian tree, and that many relationships within these three particular groups are congruent among the different datasets. Specifically, within hummingbirds there was topological agreement that the major hummingbird lineages diverged in a graded manner from the "hermits," to the "mangoes," to the "coquettes," to the "emeralds," and finally to a sister relationship between the "mountain-gems" and the "bees." Concerning swifts, the deepest divergences were congruent: treeswifts (Hemiprocnidae) were sister to the typical swifts (Apodidae), and the subfamily Apodinae was monophyletic relative to Cypseloidinae. Within Apodinae, however, were short, unresolved branches among the swiftlets, spinetails, and more typical swifts; a finding which coincides with other datasets. Within passerine birds, there was congruent support for monophyly of sub-oscines and oscines, and within sub-oscines, for monophyly of New World groups relative to the Old World lineages. New World sub-oscines split into superfamilies Furnaroidea and Tyrannoidea, with the Tyrannoid relationships completely congruent among ZENK and DNA-DNA hybridization trees. Within Furnaroidea, however, there was some incongruence regarding the positions of Thamnophilidae and Formicariidae. Concerning oscine passerines, both datasets showed a split between Corvida and Passerida and confirmed the traditional membership of passerid superfamilies Muscicapoidea and Passeroidea. Monophyly of Sylvioidea, however, remained uncertain, as did the relationships among the superfamiles themselves. These results are strikingly similar to other recent findings and indicative of continuing uncertainty about the higher level relationships of oscine passerines.     

Taxonomy,skull diversity and evolution in a species complex of Myotis (Chiroptera: Vespertilionidae): a geometric morphometric appraisal

Phylogenetic relationships between taxa are not necessarily reflected by morphological data due to widespread homoplasy and convergence. However, combining morphological and molecular data provides insights into the evolution of biological forms and into the potential factors involved. Here we focus on a complex of three taxa of bats with unclear taxonomic affinities: Myotis myotis, Myotis blythii and Myotis punicus. Traditional morphometric methods failed to separate them, whereas recent molecular‐based studies suggested that they constitute separate biological species. In the present study, landmark‐based geometric morphometrics methods have been used to analyse the skull variability of 218 specimens belonging to this species complex. Patterns of size and shape delimitate three morphological groups that are congruent with the proposed taxonomic assignments, and therefore support species rank for all three major groups. These morphometrics results, however, suggest that M. myotis and M. punicus share shape characteristics in the rostrum and in the posterior part of the skull that differ from M. blythii. Because previous molecular phylogenetic analyses suggested that M. myotis and M. blythii are sister species, we interpret the similitude in skull morphology between M. myotis and M. punicus as a convergence probably related to their similar feeding habits. Within the taxon M. punicus, the skull of Corsican and Sardinian populations significantly differs from that of Maghrebian ones, suggesting the existence of further cryptic taxonomic diversity. © 2008 The Linnean Society of London, Biological Journal of the Linnean Society, 2008, 95 , 529–538.     

Tracking island colonization history and phenotypic shifts in Indian Ocean bulbuls (Hypsipetes: Pycnonotidae)

Molecular phylogenies of island organisms provide useful systems for testing hypotheses of convergent or parallel evolution, since selectively neutral molecular characters are likely to be independent of phenotype, and the existence of similar environments on multiple isolated islands provides numerous opportunities for populations to evolve independently under the same constraints. Here we construct a phylogenetic hypothesis for Hypsipetes bulbuls of the western Indian Ocean, and use this to test hypotheses of colonization pattern and phenotypic change among islands of the region. Mitochondrial sequence data were collected from all extant taxa of the region, combined with sequence data from relevant lineages in Asia. Data are consistent with a single Hypsipetes colonization of the western Indian Ocean from Asia within the last 2.6 Myr. The expansion of Hypsipetes appears to have occurred rapidly, with descendants found across the breadth of its western Indian Ocean range. The data suggest that a more recent expansion of Hypsipetes madagascariensis from Madagascar led to the colonization of Aldabra and a secondary colonization of the Comoros. Groupings of western Indian Ocean Hypsipetes according to phenotypic similarities do not correspond to mtDNA lineages, suggesting that these similarities have evolved by convergence or parallelism. The direction of phenotypic change cannot be inferred with confidence, since the primary expansion occurred rapidly relative to the rate of mtDNA substitution, and the colonization sequence remains uncertain. However, evidence from biogeography and comparison of independent colonization events are consistent with the persistence of a small grey continental bulbul in India and Madagascar, and multiple independent origins of large size and green plumage in insular island populations of the Comoros, Mascarenes and Seychelles. © 2005 The Linnean Society of London, Biological Journal of the Linnean Society, 2005, 85 , 271–287.     

The age and evolution of sociality in Stegodyphus spiders: a molecular phylogenetic perspective

Social, cooperative breeding behaviour is rare in spiders and generally characterized by inbreeding, skewed sex ratios and high rates of colony turnover, processes that when combined may reduce genetic variation and lower individual fitness quickly. On these grounds, social spider species have been suggested to be unstable in evolutionary time, and hence sociality a rare phenomenon in spiders. Based on a partial molecular phylogeny of the genus Stegodyphus, we address the hypothesis that social spiders in this genus are evolutionary transient. We estimate the age of the three social species, test whether they represent an ancestral or derived state and assess diversification relative to subsocial congeners. Intraspecific sequence divergence was high in all of the social species, lending no support for the idea that they are young, transient species. The age of the social lineages, constant lineage branching and the likelihood that social species are independently derived suggest that either the social species are 'caught in sociality' or they have evolved into cryptic species.     

Independent evolution of complex life history adaptations in two families of fishes, live-bearing halfbeaks (zenarchopteridae, beloniformes) and poeciliidae (cyprinodontiformes)

We have previously documented multiple, independent origins of placentas in the fish family Poeciliidae. Here we summarize similar analyses of fishes in the family Zenarchopteridae. This family includes three live-bearing genera. Earlier studies documented the presence of superfetation, or the ability to carry multiple litters of young in different stages of development in the same ovary, in some species in all three genera. There is also one earlier report of matrotrophy, or extensive postfertilization maternal provisioning, in two of these genera. We present detailed life-history data for approximately half of the species in all three genera and combine them with the best available phylogeny to make inferences about the pattern of life-history evolution within this family. Three species of Hemirhamphodon have superfetation but lack matrotrophy. Most species in Nomorhamphus and Dermogenys either lack superfetation and matrotrophy or have both superfetation and matrotrophy. Our phylogenetic analysis shows that matrotrophy may have evolved independently in each genus. In Dermogenys, matrotrophic species produce fewer, larger offspring than nonmatrotrophic species. In Nomorhamphus; matrotrophic species instead produce more and smaller offspring than lecithotrophic species. However, the matrotrophic species in both genera have significantly smaller masses of reproductive tissue relative to their body sizes. All aspects of these results are duplicated in the fish family Poeciliidae. We discuss the possible adaptive significance of matrotrophy in the light of these new results. The two families together present a remarkable opportunity to study the evolution of a complex trait because they contain multiple, independent origins of the trait that often include close relatives that vary in either the presence or absence of the matrotrophy or in the degree to which matrotrophy is developed. These are the raw materials that are required for either an analysis of the adaptive significance of the trait or for studies of the genetic mechanisms that underlie the evolution of the trait.     

Ectodysplasin signalling genes and phenotypic evolution in sculpins (Cottus)

Despite their deeply conserved function among vertebrates, ectodysplasin (Eda) signalling genes are involved in microevolutionary change in humans and sticklebacks. If such a dual role is common, Eda signalling genes constitute hotspots for morphological evolution. Variation in sculpin (Cottus) skin prickling and body shape resembles patterns caused by variation in Eda signalling in sticklebacks. We mapped Eda signalling genes and performed quantitative trait locus mapping in crosses between Cottus rhenanus and Cottus perifretum. A genomic region containing the Eda receptor (Edar) was strongly associated with prickling and contributed to shape. The expression of Edar in developing prickles and skeletal elements in Cottus was confirmed by in situ hybridization. Coding sequence changes between Edar alleles in C. rhenanus and C. perifretum exceeded sequence differentiation in other vertebrates. However, it is likely that additional genetic elements besides coding changes affect the phenotypic variation. Although the phenotype in a natural hybrid lineage between C. rhenanus and C. perifretum resembles C. perifretum, the respective coding Edar alleles are not fully fixed (88.6%). Hence, our results support an involvement of Eda signalling in microevolutionary changes, but imply that the Edar gene is affected by multiple evolutionary processes that vary among freshwater sculpins.     

The evolution of postcopulatory displays in dabbling ducks (Anatini): a phylogenetic perspective

Although postcopulatory displays are widespread in animals, little is known about their function or the intended receiver. The postcopulatory displays of dabbling ducks are among the best described for any animal group. We documented the presence of initial and additional postcopulatory displays in nearly all dabbling duck species. We then reconstructed the evolution of postcopulatory displays in dabbling ducks using a phylogeny derived from mitochondrial DNA sequences. The display immediately following copulation (the initial display) is highly stereotyped in most species and shows extreme phylogenetic conservation. In contrast, the performance of additional displays is less stereotyped and less phylogenetically conservative. We review the possible functions of postcopulatory displays. Using evidence from display orientation, display form and phylogenetic reconstruction, we suggest that the most likely functions of postcopulatory displays in dabbling ducks are pair bond maintenance, individual identification, or signalling a successful copulation. Copyright 2000 The Association for the Study of Animal Behaviour.     

Anatomical diversity and regressive evolution in trichomanoid filmy ferns (Hymenophyllaceae): a phylogenetic approach

To infer the anatomical evolution of the Hymenophyllaceae (filmy ferns) and to test previously suggested scenarios of regressive evolution, we performed an exhaustive investigation of stem anatomy in the most variable lineage of the family, the trichomanoids, using a representative sampling of 50 species. The evolution of qualitative and quantitative anatomical characters and possibly related growth-forms was analyzed using a maximum likelihood approach. Potential correlations between selected characters were then statistically tested using a phylogenetic comparative method. Our investigations support the anatomical homogeneity of this family at the generic and sub-generic levels. Reduced and sub-collateral/collateral steles likely derived from an ancestral massive protostele, and sub-collateral/collateral types appear to be related to stem thickness reduction and root apparatus regression. These results corroborate the hypothesis of regressive evolution in the lineage, in terms of morphology as well as anatomy. In addition, a heterogeneous cortex, which is derived in the lineage, appears to be related to a colonial strategy and likely to a climbing phenotype. The evolutionary hypotheses proposed in this study lay the ground for further evolutionary analyses that take into account trichomanoid habitats and accurate ecological preferences.     

Reconstructing plumage evolution in orioles (Icterus): repeated convergence and reversal in patterns

Several empirical studies suggest that sexually selected characters, including bird plumage, may evolve rapidly and show high levels of convergence and other forms of homoplasy. However, the processes that might generate such convergence have not been explored theoretically. Furthermore, no studies have rigorously addressed this issue using a robust phylogeny and a large number of signal characters. We scored the appearance of 44 adult male plumage characters that varied across New World orioles (Icterus). We mapped the plumage characters onto a molecular phylogeny based on two mitochondrial genes. Reconstructing the evolution of these characters revealed evidence of convergence or reversal in 42 of the 44 plumage characters. No plumage character states are restricted to any groups of species higher than superspecies in the oriole phylogeny. The high frequency of convergence and reversal is reflected in the low overall retention index (RI = 0.66) and the low overall consistency index (CI = 0.28). We found similar results when we mapped plumage changes onto a total evidence tree. Our findings reveal that plumage patterns and colors are highly labile between species of orioles, but highly conserved within the oriole genus. Furthermore, there are at least two overall plumage types that have convergently evolved repeatedly in the three oriole clades. This overall convergence leads to significant conflict between the molecular and plumage data. It is not clear what evolutionary processes lead to this homoplasy in individual characters or convergence in overall pattern. However, evolutionary constraints such as developmental limitations and genetic correlations between characters are likely to play a role. Our results are consistent with the belief that avian plumage and other sexually selected characters may evolve rapidly and may exhibit high homoplasy. The overall convergence in oriole plumage patterns is an interesting evolutionary phenomenon, but it cautions against heavy reliance on plumage characters for constructing phylogenies.     

Trends in flower symmetry evolution revealed through phylogenetic and developmental genetic advances

A striking aspect of flowering plant (angiosperm) diversity is variation in flower symmetry. From an ancestral form of radial symmetry (polysymmetry, actinomorphy), multiple evolutionary transitions have contributed to instances of non-radial forms, including bilateral symmetry (monosymmetry, zygomorphy) and asymmetry. Advances in flowering plant molecular phylogenetic research and studies of character evolution as well as detailed flower developmental genetic studies in a few model species (e.g. Antirrhinum majus, snapdragon) have provided a foundation for deep insights into flower symmetry evolution. From phylogenetic studies, we have a better understanding of where during flowering plant diversification transitions from radial to bilateral flower symmetry (and back to radial symmetry) have occurred. From developmental studies, we know that a genetic programme largely dependent on the functional action of the CYCLOIDEA gene is necessary for differentiation along the snapdragon dorsoventral flower axis. Bringing these two lines of inquiry together has provided surprising insights into both the parallel recruitment of a CYC-dependent developmental programme during independent transitions to bilateral flower symmetry, and the modifications to this programme in transitions back to radial flower symmetry, during flowering plant evolution.     

The genus Coleodactylus (Sphaerodactylinae, Gekkota) revisited: a molecular phylogenetic perspective

Nucleotide sequence data from a mitochondrial gene (16S) and two nuclear genes (c-mos, RAG-1) were used to evaluate the monophyly of the genus Coleodactylus, to provide the first phylogenetic hypothesis of relationships among its species in a cladistic framework, and to estimate the relative timing of species divergences. Maximum Parsimony, Maximum Likelihood and Bayesian analyses of the combined data sets retrieved Coleodactylus as a monophyletic genus, although weakly supported. Species were recovered as two genetically and morphological distinct clades, with C. amazonicus populations forming the sister taxon to the meridionalis group (C. brachystoma, C. meridionalis, C. natalensis, and C. septentrionalis). Within this group, C. septentrionalis was placed as the sister taxon to a clade comprising the rest of the species, C. meridionalis was recovered as the sister species to C. brachystoma, and C. natalensis was found nested within C. meridionalis. Divergence time estimates based on penalized likelihood and Bayesian dating methods do not support the previous hypothesis based on the Quaternary rain forest fragmentation model proposed to explain the diversification of the genus. The basal cladogenic event between major lineages of Coleodactylus was estimated to have occurred in the late Cretaceous (72.6+/-1.77 Mya), approximately at the same point in time than the other genera of Sphaerodactylinae diverged from each other. Within the meridionalis group, the split between C. septentrionalis and C. brachystoma+C. meridionalis was placed in the Eocene (46.4+/-4.22 Mya), and the divergence between C. brachystoma and C. meridionalis was estimated to have occurred in the Oligocene (29.3+/-4.33 Mya). Most intraspecific cladogenesis occurred through Miocene to Pliocene, and only for two conspecific samples and for C. natalensis could a Quaternary differentiation be assumed (1.9+/-1.3 Mya).     

Signal evolution and morphological complexity in hummingbirds (Aves: Trochilidae)

Understanding how animal signals are produced is critical for understanding their evolution because complexity and modularity in the underlying morphology can affect evolutionary patterns. Hummingbird feathers show some of the brightest and most iridescent colors in nature. These are produced by optically complex stacks of hollow, platelet-shaped organelles called melanosomes. Neither how these morphologies produce colors nor their evolution has been systematically studied. We first used nanoscale morphological measurements and optical modeling to identify the physical basis of color production in 34 hummingbird species. We found that, in general, the melanosome stacks function as multilayer reflectors, with platelet thickness and air space size explaining variation in hue (color) and saturation (color purity). Additionally, light rays reflected from the outer keratin surface interact with those reflected by small, superficial melanosomes to cause secondary reflectance peaks, primarily in short (blue) wavelengths. We then compared variation of both the morphological components and the colors they produce. The outer keratin cortex evolves independently and is more variable than other morphological traits, possibly due to functional constraints on melanosome packing. Intriguingly, shorter wavelength colors evolve faster than longer wavelength colors, perhaps due to developmental processes that enables greater lability of the shapes of small melanosomes. Together, these data indicate that increased structural complexity of feather tissues is associated with greater variation in morphology and iridescent coloration.     

Intron evolution in a phylogenetic perspective: Divergent trends in the two copies of the duplicated def gene in Impatiens L. (Balsaminaceae)

The history of MADS box genes is well-known in angiosperms. While duplication events and gene losses occur frequently, gene structure and intron positions are very conserved. We investigated all six introns in a duplicated MADS box gene (deficiens, def) in selected Impatiens taxa, thereby assessing intron features. For the first time, our study provides a comparison of molecular changes in all introns of a gene from a phylogenetic perspective. Interestingly, a uniform pattern of molecular evolution in the introns of each copy was not observed, but intron length increases, decreases, and size retention can be found in each copy. A tendency to accumulate long autapomorphic indels is also present, thus, a longer intron length does not reflect a higher number of parsimony-informative characters. Substitution rates vary between introns of each gene copy. While four of the six introns of def1 exhibit a change in their substitution rate, five of the six def2 introns maintain their rates throughout the genus albeit at different levels. In MADS box genes several regulatory sequences are found residing in introns. Thus, presence of putative regulatory motifs was investigated. Most of them are not conserved in position and usually present in only one of the gene copies. In addition, the potential for phylogenetic reconstruction of introns in both def copies is shortly discussed.