The skeleton flight apparatus of North American bluebirds (Sialia): Phylogenetic thrushes or functional flycatchers?

To better understand ecological traits of organisms, one can study them from two, not necessarily mutually exclusive perspectives: how the traits evolved, and their current adaptive utility. In birds, foraging behavior and associated morphological traits generally are explained by a combination of adaptive and phylogenetic predictors. The avian skeleton and more specifically, the skeletal flight apparatus is under well‐known functional and phylogenetic constraints. This is an interesting area to partition the relative contributions of adaptive correlated evolution and phylogenetic constraint to species clustering in morphological space. A prediction of convergent evolution is that nonphylogenetic morphological clustering is a characteristic of ecological similarity. We tested this using representatives of North American birds from two clades, one with a mixture of foraging modes (Turdid thrushes, solitaires, and bluebirds) and one with more canalized foraging behaviors (Tyrannid flycatchers). Nine characters on the skeletal flight apparatus from 19 species were used to characterize the morphological space and test for ecomorphological clustering. When body size and phylogeny are considered, the three bluebird species and Townsend's solitaire cluster with the ecologically similar flycatchers rather than with their phylogenetic close relatives. Furthermore, sit‐and‐wait foragers tend to exhibit relatively long distal elements and a long keel while active ground foragers have deeper keels and a longer humerus. Distal elements, expected to be relatively shorter and more bowed in the flycatchers and bluebirds, were actually longer and narrower. A reduction of distal element mass may be more important for facilitating maneuverability than surface area for insertion of wing‐rotational musculature. J. Morphol. 274:909–917, 2013. © 2013 Wiley Periodicals, Inc.     

Ecomorphological patterns of aerial feeding in oscines (Passeriformes: Passeri)

The hindlimb (myology and osteology) of swallows (Hirundinidae) is studied and compared with that of seven other passerine families to identify ecomorphological patterns. Muscular and osteological differences are found among swallow species and associations between morphology and foraging technique are examined. We explain morphological differences found in hirundinids as adaptations favouring flexion and adduction of the legs in these aerial foragers, which devote very little time to cursorial locomotion. This adaptive hypothesis is tested using a phylogenetic approach on the basis of an available molecular phylogenetic hypothesis. A clear ecomorphological pattern emerges relating foraging behaviour and pelvic morphology in hirundinids: aerial feeding technique is correlated with short distal leg segments, a large pelvis, a medial insertion of M. iliotibialis cranialis, an absence of pars accessoria of M. flexor cruris lateralis and a fused M. pubo-ischiofemoralis.     

Morphological convergence in conifer-dwelling passerines

We tested for morphological convergence in conifer specialists among 88 passerines belonging to seven different phylogenetic lineages by discriminant factor analysis. We found a parallel trend among the seven lineages in body mass and digital pad morphology, whereas no such trends existed for the feeding and flight apparatus. Compared to the control species, the conifer specialists have smaller body masses and higher digital pads with maximal widths lying more distally within each of the seven lineages. These traits are interpreted as adaptations to dwelling among coniferous needles.Communicated by: F. Bairlein     

Concordance between locomotor morphology and foraging mode in lacertid lizards

Foraging behaviors exist along a continuum from highly sedentary, ambush foraging, to more continuous searching, or active foraging. Foraging strategies, or modes, are defined based upon locomotor behaviors (e.g. percent time moving, moves per minute). In lizards, traits correlated with ambush and active foraging have been of interest for some time; however, general patterns of correlated evolution between locomotor morphology and locomotor behavior have only recently begun to be quantified. In this study, variation in hindlimb morphology is investigated in a model group of lizard species that vary between active foraging and more sedentary (or mixed) foraging mode. Canonical variates analysis reveals that the two active foraging species occupy similar regions of the morphospace, while the two more sedentary species occupy different regions. The active foraging species have a narrow pelvis with shorter tibia and femora. The more sedentary species have a wide pelvis, long tibia and femora, and slightly longer metatarsals. Phylogenetic patterns of trait variation were examined through ancestral character state reconstruction and show morphological shifts in concert with foraging mode in these species. The observed shifts in locomotor morphology are discussed in light of published data on sprint speed and endurance in these species. Together, the data show that linking morphological variation to variation in stride length and stride frequency is critical to understanding the evolution of locomotor performance. Much more stride length and frequency data are needed among ambush, mixed, and active foraging species because these parameters, and their morphological components, are likely correlated with variation in food acquisition mode.     

Ecology shapes the evolutionary trade‐off between predator avoidance and defence in coral reef butterflyfishes

Antipredator defensive traits are thought to trade‐off evolutionarily with traits that facilitate predator avoidance. However, complexity and scale have precluded tests of this prediction in many groups, including fishes. Using a macroevolutionary approach, we test this prediction in butterflyfishes, an iconic group of coral reef inhabitants with diverse social behaviours, foraging strategies and antipredator adaptations. We find that several antipredator traits have evolved adaptively, dependent primarily on foraging strategy. We identify a previously unrecognised axis of diversity in butterflyfishes where species with robust morphological defences have riskier foraging strategies and lack sociality, while species with reduced morphological defences feed in familiar territories, have adaptations for quick escapes and benefit from the vigilance provided by sociality. Furthermore, we find evidence for the constrained evolution of fin spines among species that graze solely on corals, highlighting the importance of corals, as both prey and structural refuge, in shaping fish morphology.     

Fine-scale phenotypic change across a species transition zone in the genus neotoma: disentangling independent evolution from phylogenetic history

Zones of secondary contact between closely related species provide a rare opportunity to examine evidence of evolutionary processes that reinforce species boundaries and/or promote diversification. Here, we report on genetic and morphological variation in two sister species of woodrats, Neotoma fuscipes and N. macrotis, across a 30-km transition zone in the Sierra Nevada of California. We assessed whether these lineages readily hybridize, and whether their morphology suggests ecological interactions favoring phenotypic diversification. We combined measurements of body size and 11 craniodental traits from nine populations with genetic data to examine patterns of variation within and between species. We used phylogenetic autocorrelation methods to estimate the degree to which phenotypic variation in our dataset arose from independent evolution within populations versus phylogenetic history. Although no current sympatry or hybridization was evident, craniodental morphology diverged in both lineages near their distributional limits, whereas body size converged. The shift in craniodental morphology arose independently within populations whereas body size retained a strong phylogenetic signal, yet both patterns are consistent with expectations of phenotypic change based on different models of resource competition. Our findings demonstrate the importance of examining a suite of morphological traits across contact zones to provide a more complete picture of potential ecological interactions: competition may drive both diversification and convergence in different phenotypic traits.     

Dual origins of social parasitism in North American Dialictus (Hymenoptera: Halictidae) confirmed using a phylogenetic approach

The bee subgenus Dialictus (Halictidae: Lasioglossum) displays a large array of behaviours including solitary behaviour, eusociality, and social parasitism. Socially parasitic Dialictus share a suite of morphological traits; these could result from shared ancestry, but given their functional significance, could also have resulted from adaptive convergence. A combined morphological and molecular phylogenetic approach was used to test for monophyly of North American socially parasitic Dialictus. Two data sets were used in the phylogenetic analyses. First, short mitochondrial DNA sequences from previous taxonomic studies of North American Dialictus, including six social parasites, were used because of the broad taxon sampling they provide. These data were analysed in combination with a set of 40 morphological characters, including a large proportion of characters associated with social parasitism. Phylogenetic analysis of the combined DNA barcode and morphology data set resolves two distinct lineages of social parasite. The second data set was based on three genes (cytochrome c oxidase subunit 1, elongation factor 1α, and long‐wavelength rhodopsin), but with sparser taxon sampling, including one representative from each putative social parasite‐lineage. This also supported dual origins of social parasitism among North American Dialictus. The evolution of social parasitism is discussed. © The Willi Hennig Society 2011.     

Comparative analyses suggest that information transfer promoted sociality in male bats in the temperate zone

The evolution of sociality is a central theme in evolutionary biology. The vast majority of bats are social, which has been explained in terms of the benefits of communal breeding. However, the causes for segregated male groups remain unknown. In a comparative study, we tested whether diet and morphological adaptations to specific foraging styles, two factors known to influence the occurrence of information transfer, can predict male sociality. Our results suggest that the species most likely to benefit from information transfer--namely, those preying on ephemeral insects and with morphological adaptations to feeding in open habitat--are more likely to form male groups. Our findings also indicate that solitary life was the ancestral state of males and sociality evolved in several lineages. Beyond their significance for explaining the existence of male groups in bats, our findings highlight the importance of information transfer in the evolution of animal sociality.     

Population and phylogenomic decomposition via genotyping‐by‐sequencing in Australian Pelargonium

Species delimitation has seen a paradigm shift as increasing accessibility of genomic‐scale data enables separation of lineages with convergent morphological traits and the merging of recently diverged ecotypes that have distinguishing characteristics. We inferred the process of lineage formation among Australian species in the widespread and highly variable genus Pelargonium by combining phylogenomic and population genomic analyses along with breeding system studies and character analysis. Phylogenomic analysis and population genetic clustering supported seven of the eight currently described species but provided little evidence for differences in genetic structure within the most widely distributed group that containing P. australe. In contrast, morphometric analysis detected three deep lineages within Australian Pelargonium; with P. australe consisting of five previously unrecognized entities occupying separate geographic ranges. The genomic approach enabled elucidation of parallel evolution in some traits formerly used to delineate species, as well as identification of ecotypic morphological differentiation within recognized species. Highly variable morphology and trait convergence each contribute to the discordance between phylogenomic relationships and morphological taxonomy. Data suggest that genetic divergence among species within the Australian Pelargonium may result from allopatric speciation while morphological differentiation within and among species may be more strongly driven by environmental differences.     

Trophic convergence drives morphological convergence in marine tetrapods

Marine tetrapod clades (e.g. seals, whales) independently adapted to marine life through the Mesozoic and Caenozoic, and provide iconic examples of convergent evolution. Apparent morphological convergence is often explained as the result of adaptation to similar ecological niches. However, quantitative tests of this hypothesis are uncommon. We use dietary data to classify the feeding ecology of extant marine tetrapods and identify patterns in skull and tooth morphology that discriminate trophic groups across clades. Mapping these patterns onto phylogeny reveals coordinated evolutionary shifts in diet and morphology in different marine tetrapod lineages. Similarities in morphology between species with similar diets—even across large phylogenetic distances—are consistent with previous hypotheses that shared functional constraints drive convergent evolution in marine tetrapods.     

INTENSE NATURAL SELECTION ON BODY SIZE AND WING AND TAIL ASYMMETRY IN CLIFF SWALLOWS DURING SEVERE WEATHER

Extreme climatic disturbances provide excellent opportunities to study natural selection in wild populations because they may cause measurable directional shifts in character traits. Insectivorous cliff swallows (Petrochelidon pyrrhonota) in the northern Great Plains must often endure periods of cold weather in late spring that reduce food availability, and if cold spells last four or more days, mortality due to starvation may result. We analyzed morphological shifts associated with viability selection, and how patterns of bilateral symmetry were affected by survival selection, during a four-day period of cold weather in 1992 and a six-day period in 1996 in southwestern Nebraska. Birds that died during the cold were compared to those still alive when the severe weather ended. The event in 1992 killed relatively few birds, but the cold spell in 1996 killed thousands of cliff swallows and reduced their population by about 53%. Climatological records suggest that mortality events comparable to that of 1996 have occurred in only one other year since 1875. Larger birds were favored in the 1996 event. Selection was more intense in 1996 than in 1992 because of more stressful conditions in 1996. Directional selection gradient analysis showed that measures of skeletal body size (tarsus length, culmen width and length) and wing length were targets of selection in 1996. Survivors had lower wing and outer tail asymmetry, and wing and tail asymmetry were targets of selection in both events. Mortality patterns did not differ by sex, but older birds suffered heavier mortality; morphological traits generally did not vary with age. Nonsurvivors were not in poorer apparent condition prior to the weather event than survivors, suggesting that selection acted directly on morphology independent of condition. Selection on body size in cliff swallows was more intense than in studies of body size evolution in other bird species. Larger swallows were probably favored in cold weather due to the thermal advantages of large size and the ability to store more fat. Swallows with low asymmetry were favored probably because low asymmetry in wing and tail made foraging more efficient and less costly, conferring survival advantages during cold weather. This population of cliff swallows may have undergone relatively recent body size evolution.     

Forest giants on different evolutionary branches: Ecomorphological convergence in helicopter damselflies*

The convergent evolution of analogous features is an evolutionary process occurring independently across the tree of life. From the evolution of echolocation, prehensile tail, viviparity, or winged flight, environmental factors often drive this astonishing phenomenon. However, convergent evolution is not always conspicuous or easily identified. Giant damselflies count among the largest flying insects on Earth, and have astonishing ecologies including orb‐web spider plucking and oviposition in phytotelmata. One species occurs in the Afrotropics and 18 species are found in the Neotropics. Convergent evolution was historically hypothesized based on the ecological and morphological affinities of these two geographically distant lineages but was not supported by earlier phylogenetic inferences supporting their monophyly. Using a molecular supermatrix approach and a large selection of outgroups, we revisit and reject the monophyly of Afrotropical and Neotropical giant damselflies that is otherwise supported by a morphological phylogeny. Molecular divergence time estimation suggests an origin of Afrotropical giant damselflies in the late Paleogene, and of Neotropical ones at the Cretaceous/Paleogene boundary, thereby rejecting a long‐standing West Gondwana vicariance hypothesis. The strong ecological and morphological resemblances between these two independent lineages represents an astonishing case of Amphi‐Atlantic tropical convergent evolution.     

CONVERGENT AND CORRELATED EVOLUTION OF MAJOR LIFE‐HISTORY TRAITS IN THE ANGIOSPERM GENUS LEUCADENDRON (PROTEACEAE)

Natural selection is expected to cause convergence of life histories among taxa as well as correlated evolution of different life‐history traits. Here, we quantify the extent of convergence of five key life‐history traits (adult fire survival, seed storage, degree of sexual dimorphism, pollination mode, and seed‐dispersal mode) and test hypotheses about their correlated evolution in the genus Leucadendron (Proteaceae) from the fire‐prone South African fynbos. We reconstructed a new molecular phylogeny of this highly diverse genus that involves more taxa and molecular markers than previously. This reconstruction identifies new clades that were not detected by previous molecular study and morphological classifications. Using this new phylogeny and robust methods that account for phylogenetic uncertainty, we show that the five life‐history traits studied were labile during the evolutionary history of the genus. This diversity allowed us to tackle major questions about the correlated evolution of life‐history strategies. We found that species with longer seed‐dispersal distances tended to evolve lower pollen‐dispersal distance, that insect‐pollinated species evolved decreased sexual dimorphism, and that species with a persistent soil seed‐bank evolved toward reduced fire‐survival ability of adults.     

A combined morphometric and phylogenetic analysis of an ecomorphological trend: pelagization in Antarctic fishes (Perciformes: Nototheniidae)

The Antarctic fish family Nototheniidae (Perciformes) presumably originated from a benthic ancestor, and several lineages have evolved to live or at least feed in the water column, a trend called pelagization. Here, we use information on phylogeny, allometric growth, and diet composition for an integrated analysis of morphological and ecological diversification in this group, mainly focusing on the subfamilies Trematominae and Pleuragramminae. A phylogenetic analysis of data published in earlier systematic studies produced eight equally parsimonious trees, all indicating that several previously recognized taxa are paraphyletic. These phylogenetic trees all suggest multiple origins of pelagic life styles. Multivariate morphometric analyses including nine species showed that juveniles and adults grow according to a common pattern of ontogenetic allometry. The morphometric differences among species are mosdy the result of lateral transpositions of the growth trajectories, indicating that embryonic and larval development is more important as a determinant of morphological variation than allometric growth as juveniles and adults. We studied patterns of interspecific variation with principal components and the covariation between morphometric variables and food composition with a partial least-squares analysis. Both analyses revealed a gradient from benthic to pelagic foragers. Measurements of structures involved in swimming have a prominent role in these analyses, suggesting adaptive evolution of these traits. Tracing morphometric traits on the phylogenetic trees revealed a considerable amount of evolutionary plasticity, showing that species related phylogenetically need not be morphologically similar, but can diverge considerably, perhaps as a response to natural selection and adaptation to different habitats and foraging modes. In accordance, a test of phylogenetically independent contrasts showed that bursts of increased morphological change accompanied habitat shifts.     

Evidence for a multi‐peak adaptive landscape in the evolution of trophic morphology in terapontid fishes

Using the Australian marine‐freshwater terapontid fishes as a model system, we examined the role of dietary phenotypic optima in an adaptive macro‐evolutionary landscape. Comparative modelling relying on both a priori and data‐driven identification of selective regimes suggested multi‐peak models as best describing much of the dietary phenotypic landscape of terapontids. Both approaches identified common phenotypic optima for different lineages of marine and freshwater herbivores, and minimal differentiation between carnivores and omnivores, irrespective of their phylogenetic relationships, as the model best describing morphological evolution. Significant correlations also existed between these phenotypic axes and proportions of non‐animal dietary items in species’ diets. While simulation results provided evidence for a multi‐peak adaptive landscape in the evolution of trophic morphology in terapontids, they could not rule out chance convergence in these adaptive peaks. However, they do provide scope for identifying areas for more detailed, functionally specific study of phenotypic convergence in herbivorous terapontid trophic habits. © 2014 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 113 , 623–634.     

Parallel and non‐parallel morphological divergence among foraging specialists in European whitefish (Coregonus lavaretus)

Parallel phenotypic evolution occurs when independent populations evolve similar traits in response to similar selective regimes. However, populations inhabiting similar environments also frequently show some phenotypic differences that result from non‐parallel evolution. In this study, we quantified the relative importance of parallel evolution to similar foraging regimes and non‐parallel lake‐specific effects on morphological variation in European whitefish (Coregonus lavaretus). We found evidence for both lake‐specific morphological characteristics and parallel morphological divergence between whitefish specializing in feeding on profundal and littoral resources in three separate lakes. Foraging specialists expressed similar phenotypes in different lakes in both overall body shape and selected measured morphological traits. The morphology of the two whitefish specialists resembled that predicted from other fish species, supporting the conclusion of an adaptive significance of the observed morphological characteristics. Our results indicate that divergent natural selection resulting from foraging specialization is driving and/or maintaining the observed parallel morphological divergence. Whitefish in this study may represent an early stage of divergence towards the evolution of specialized morphs.     

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.     

Trait‐based and phylogenetic associations between parasites and their hosts: a case study with small mammals and fleas in the Palearctic

We investigated the associations between ecological (density, shelter structure), morphological (body mass, hair morphology) and physiological traits (basal metabolic rate) of small mammals and ecological (seasonality of reproduction, microhabitat preferences, abundance, host specificity) and morphological (presence and number of combs) traits of their flea parasites that shape host selection processes by fleas. We adapted the extended version of the three‐table ordination and linked species composition of flea assemblages of host species with traits and phylogenies of both hosts and fleas. Fleas with similar trait values, independent of phylogenetic affinities, were clustered on the same host species. Fleas possessing certain traits selected hosts possessing certain traits. Fleas belonging to the same phylogenetic lineage were found on the same host more often than expected by chance. Certain phylogenetic lineages of hosts harbored certain phylogenetic lineages of fleas. The process of host selection by fleas appeared to be determined by reciprocal relationships between host and flea traits, as well as between host and flea phylogenies. We concluded that the connection between host and flea phylogenies, coupled with the connection between host and flea traits, suggests that the species compositions of the host spectra of fleas were driven by the interaction between historical processes and traits.     

ACCELERATED EVOLUTION OF LAND SNAILS MANDARINA IN THE OCEANIC BONIN ISLANDS: EVIDENCE FROM MITOCHONDRIAL DNA SEQUENCES

An endemic land snail genus Mandarina of the oceanic Bonin (Ogasawara) Islands shows exceptionally rapid evolution not only of morphological and ecological traits, but of DNA sequence. A phylogenetic relationship based on mitochondrial DNA (mtDNA) sequences suggests that morphological differences equivalent to the differences between families were produced between Mandarina and its ancestor during the Pleistocene. The inferred phylogeny shows that species with similar morphologies and life habitats appeared repeatedly and independently in different lineages and islands at different times. Sequential adaptive radiations occurred in different islands of the Bonin Islands and species occupying arboreal, semiarboreal, and terrestrial habitat arose independently in each island. Because of a close relationship between shell morphology and life habitat, independent evolution of the same life habitat in different islands created species possesing the same shell morphology in different islands and lineages. This rapid evolution produced some incongruences between phylogenetic relationship and species taxonomy. Levels of sequence divergence of mtDNA among the species of Mandarina is extremely high. The maximum level of sequence divergence at 16S and 12S ribosomal RNA sequence within Mandarina are 18.7% and 17.7%, respectively, and this suggests that evolution of mtDNA of Mandarina is extremely rapid, more than 20 times faster than the standard rate in other animals. The present examination reveals that evolution of morphological and ecological traits occurs at extremely high rates in the time of adaptive radiation, especially in fragmented environments.