A Phylogeny of the Gulls (Aves: Larinae) Inferred from Osteological and Integumentary Characters

Convergent evolution in dippers (Aves, Cinclidae): The only wing-propelled diving songbirds

Of the more than 6,000 members of the most speciose avian clade, Passeriformes (perching birds), only the five species of dippers (Cinclidae, Cinclus) use their wings to swim underwater. Among nonpasserine wing‐propelled divers (alcids, diving petrels, penguins, and plotopterids), convergent evolution of morphological characteristics related to this highly derived method of locomotion have been well‐documented, suggesting that the demands of this behavior exert strong selective pressure. However, despite their unique anatomical attributes, dippers have been the focus of comparatively few studies and potential convergence between dippers and nonpasseriform wing‐propelled divers has not been previously examined. In this study, a suite of characteristics that are shared among many wing‐propelled diving birds were identified and the distribution of those characteristics across representatives of all clades of extant and extinct wing‐propelled divers were evaluated to assess convergence. Putatively convergent characteristics were drawn from a relatively wide range of sources including osteology, myology, endocranial anatomy, integument, and ethology. Comparisons reveal that whereas nonpasseriform wing‐propelled divers do in fact share some anatomical characteristics putatively associated with the biomechanics of underwater “flight”, dippers have evolved this highly derived method of locomotion without converging on the majority of concomitant changes observed in other taxa. Changes in the flight musculature and feathers, reduction of the keratin bounded external nares and an increase in subcutaneous fat are shared with other wing‐propelled diving birds, but endocranial anatomy shows no significant shifts and osteological modifications are limited. Muscular and integumentary novelties may precede skeletal and neuroendocranial morphology in the acquisition of this novel locomotory mode, with implications for understanding potential biases in the fossil record of other such transitions. Thus, dippers represent an example of a highly derived and complex behavioral convergence that is not fully associated with the anatomical changes observed in other wing‐propelled divers, perhaps owing to the relative recency of their divergence from nondiving passeriforms.

Taxonomic revision and phylogenetic analysis of the flightless Mancallinae (Aves, Pan-Alcidae)

Although flightless alcids from the Miocene and Pliocene of the eastern Pacific Ocean have been known for over 100 years, there is no detailed evaluation of diversity and systematic placement of these taxa. This is the first combined analysis of morphological and molecular data to include all extant alcids, the recently extinct Great Auk Pinguinus impennis, the mancalline auks, and a large outgroup sampling of 29 additional non-alcid charadriiforms. Based on the systematic placement of Mancallinae outside of crown clade Alcidae, the clade name Pan-Alcidae is proposed to include all known alcids. An extensive review of the Mancallinae fossil record resulted in taxonomic revision of the clade, and identification of three new species. In addition to positing the first hypothesis of inter-relationships between Mancallinae species, phylogenetic results support placement of Mancallinae as the sister taxon to all other Alcidae, indicating that flightlessness evolved at least twice in the alcid lineage. Convergent osteological characteristics of Mancallinae, the flightless Great Auk, and Spheniscidae are summarized, and implications of Mancallinae diversity, radiation, and extinction in the context of paleoclimatic changes are discussed.

SONG AND PLUMAGE EVOLUTION IN THE NEW WORLD ORIOLES (ICTERUS) SHOW SIMILAR LABILITY AND CONVERGENCE IN PATTERNS

Both song and color patterns in birds are thought to evolve rapidly and exhibit high levels of homoplasy, yet few previous studies have compared the evolution of these traits systematically using the same taxa. Here we reconstruct the evolution of song in the New World orioles (Icterus) and compare patterns of vocal evolution to previously reconstructed patterns of change in plumage evolution in this clade. Individual vocal characters exhibit high levels of homoplasy, reflected in a low overall consistency index (CI = 0.27) and retention index (RI = 0.35). Levels of lability in song are comparable to those found for oriole plumage patterns using the same taxa (CI = 0.31, RI = 0.63), but are strikingly dissimilar to the conservative patterns of change seen in the songs of oropendolas (Psarocolius, Ocyalus; CI = 0.82, RI = 0.87), a group closely related to the orioles. Oriole song is also similar to oriole plumage in exhibiting repeated convergence in overall patterns, with some distantly related taxa sounding remarkably similar. Thus, both song and plumage in orioles show repeated convergence in individual elements and in overall patterns across the clade, suggesting that both of these character classes are highly labile between taxa yet highly conserved within the genus. Our results provide new insights into the tempo and mode of evolution in sexually selected traits within and across clades.

Molecular phylogenetics and diversification of the genus Sporophila (Aves: Passeriformes)

The evolutionary affinities within and among many groups of nine-primaried oscines remain unresolved. One such group is Sporophila, a large genus of New World tanager-finches. Our study focused particularly on clarifying the relationship between this genus and a closely related one, Oryzoborus, and on examining the phylogenetic affinities of the "capuchinos," a group of 11 Sporophila species that share a similar male plumage coloration pattern. Our phylogenetic analyses, based on 498 bp of mitochondrial DNA sequence, indicated that: (1) Oryzoborus is embedded within a well-supported clade containing all Sporophila species, which strongly suggests that both genera should be merged, (2) the species of capuchinos comprise a monophyletic group, implying that the plumage patterns common to all probably arose only once, and (3) the capuchinos clade is comprised of two sub-clades, one including two species that are distributed in northern South America and the other one containing eight species that are present south of the Amazon River. Mean sequence divergence among the southern capuchinos species was extremely low, suggesting a rapid radiation within the last half-million years that may be related to the high level of sexual selection present in the genus and might have been promoted by marine ingressions and egressions that occurred in some southern coastal regions of South America in the Late Pleistocene.

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.