Partial host fidelity in nest selection by the shiny cowbird (Molothrus bonariensis), a highly generalist avian brood parasite

Obligate avian brood parasites can be host specialists or host generalists. In turn, individual females within generalist brood parasites may themselves be host specialists or generalists. The shiny cowbird Molothrus bonariensis is an extreme generalist, but little is known about individual female host fidelity. We examined variation in mitochondrial control region sequences from cowbird chicks found in nests of four common Argentinean hosts. Haplotype frequency distributions differed among cowbird chicks from nests of these hosts, primarily because eggs laid in nests of house wrens Troglodytes aedon differed genetically from those laid in nests of the other three hosts (chalk-browed mockingbird Mimus saturninus, brown-and-yellow marshbird Pseudoleistes virescens, and rufous-collared sparrow Zonotrichia capensis). These differences in a maternally inherited marker indicate the presence of a nonrandom laying behaviour in the females of this otherwise generalist brood parasite, which may be guided by choice for nest type, as house wrens nest in cavities whereas the other three species are open cup nesters. © 2007 The Authors.Fil:Mahler, B. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.Fil:Confalonieri, V.A. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.Fil:Reboreda, J.C. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina

Out of Amazonia again and again: episodic crossing of the Andes promotes diversification in a lowland forest flycatcher

Most Neotropical lowland forest taxa occur exclusively on one side of the Andes despite the availability of appropriate habitat on both sides. Almost all molecular phylogenies and phylogenetic analyses of species assemblages (i.e. area cladograms) have supported the hypothesis that Andean uplift during the Late Pliocene created a vicariant barrier affecting lowland lineages in the region. However, a few widespread plant and animal species occurring in lowland forests on both sides of the Andes challenge the generality of this hypothesis. To understand the role of the Andes in the history of such organisms, we reconstructed the phylogeographic history of a widespread Neotropical flycatcher (Mionectes oleagineus) in the context of the other four species in the genus. A molecular phylogeny based on nuclear and mitochondrial sequences unambiguously showed an early basal split between montane and lowland Mionectes. The phylogeographic reconstruction of lowland taxa revealed a complex history, with multiple cases in which geographically proximate populations do not represent sister lineages. Specifically, three populations of M. oleagineus west of the Andes do not comprise a monophyletic clade; instead, each represents an independent lineage with origins east of the Andes. Divergence time estimates suggest that at least two cross-Andean dispersal events post-date Andean uplift

A 2000 km genetic wake yields evidence for northern glacial refugia and hybrid zone movement in a pair of songbirds

Hybrid zones are natural experiments that expose the forces maintaining species differences. But for cases where a trait of one of the hybridizing pair appears shifted into the range of the other, the underlying mechanism can be difficult to infer. For example, hybridization between hermit warbler (Dendroica occidentalis) and Townsend's warbler (Dendroica townsendi) is restricted to narrow hybrid zones in Washington and Oregon, yet hermit mtDNA can be found in phenotypically pure Townsend's populations up to 2000 km north along the Pacific coast. This could reflect introgression of selectively favoured hermit mitochondria north across the hybrid zones, or a neutral genetic wake left behind following southern zone movement. Hermit mitochondrial haplotypes in populations of coastal Townsend's exhibit relatively high genetic diversity and significant divergence from those found in populations of hermit warblers. This contradicts the predictions of selective introgression, but is consistent with a northern population of hermits diverging in a glacial refugium before being replaced by Townsend's via aggressive hybridization. Previous field studies showing Townsend's males to be competitively superior to hermit males support this scenario, and suggest that the extreme hybrid zone movement evidenced by the hermit mitochondrial wake represents an extinction in progress

Characterizing the phylogenetic structure of communities by an additive partitioning of phylogenetic diversity

1 Analysing the phylogenetic structure of natural communities may illuminate the processes governing the assembly and coexistence of species in ecological communities. 2 Unifying previous works, we present a statistical framework to quantify the phylogenetic structure of communities in terms of average divergence time between pairs of individuals or species, sampled from different sites. This framework allows an additive partitioning of the phylogenetic signal into alpha (within-site) and beta (among-site) components, and is closely linked to Simpson diversity. It unifies the treatment of intraspecific (genetic) and interspecific diversity, leading to the definition of differentiation coefficients among community samples (e.g. I-ST, P-ST) analogous to classical population genetics coefficients expressing differentiation among populations (e.g. F-ST, N-ST). 3 Two coefficients which express community differentiation among sites from species identity (I-ST) or species phylogeny (P-ST) require abundance data (number of individuals per species per site), and estimators that are unbiased with respect to sample size are given. Another coefficient (Pi(ST)) expresses the gain of the mean phylogenetic distance between species found in different sites compared with species found within sites, and requires only incidence data (presence/absence of each species in each site). 4 We present tests based on phylogenetic tree randomizations to detect community phylogenetic clustering (P-ST > I-ST or Pi(ST) > 0) or phylogenetic overdispersion (P-ST < I-ST or Pi(ST) < 0). In addition, we propose a novel approach to detect phylogenetic clustering or overdispersion in different clades or at different evolutionary time depths using partial randomizations. 5 I-ST, P-ST or Pi(ST) can also be used as distances between community samples and regressed on ecological or geographical distances, allowing us to investigate the factors responsible for the phylogenetic signal and the critical scales at which it appears. 6 We illustrate the approach on forest tree communities in Equatorial Guinea, where a phylogenetic clustering signal was probably due to phylogenetically conserved adaptations to the elevation gradient and was mostly contributed to by ancient clade subdivisions. 7 The approach presented should find applications for comparing quantitatively phylogenetic patterns of different communities, of similar communities in different regions or continents, or of populations (within species) vs. communities (among species).FLWINinfo:eu-repo/semantics/publishe

The West Indies as a laboratory of biogeography and evolution

Islands have long provided material and inspiration for the study of evolution and ecology. The West Indies are complex historically and geographically, providing a rich backdrop for the analysis of colonization, diversification and extinction of species. They are sufficiently isolated to sustain endemic forms and close enough to sources of colonists to develop a dynamic interaction with surrounding continental regions. The Greater Antilles comprise old fragments of continental crust, some very large; the Lesser Antilles are a more recent volcanic island arc, and the low-lying Bahama Islands are scattered on a shallow oceanic platform. Dating of island lineages using molecular methods indicates over-water dispersal of most inhabitants of the West Indies, although direct connections with what is now southern Mexico in the Early Tertiary, and subsequent land bridges or stepping stone islands linking to Central and South America might also have facilitated colonization. Species–area relationships within the West Indies suggest a strong role for endemic radiations and extinction in shaping patterns of diversity. Diversification is promoted by opportunities for allopatric divergence between islands, or within the large islands of the Greater Antilles, with a classic example provided by the Anolis lizards. The timing of colonization events using molecular clocks permits analysis of colonization–extinction dynamics by means of species accumulation curves. These indicate low rates of colonization and extinction for reptiles and amphibians in the Greater Antilles, with estimated average persistence times of lineages in the West Indies exceeding 30 Myr. Even though individual island populations of birds might persist an average of 2 Myr on larger islands in the Lesser Antilles, recolonization from within the archipelago appears to maintain avian lineages within the island chain indefinitely. Birds of the Lesser Antilles also provide evidence of a mass extinction event within the past million years, emphasizing the time-heterogeneity of historical processes. Geographical dynamics are matched by ecological changes in the distribution of species within islands over time resulting from adaptive radiation and shifts in habitat, often following repeatable patterns. Although extinction is relatively infrequent under natural conditions, changes in island environments as a result of human activities have exterminated many populations and others—especially old, endemic species—remain vulnerable. Conservation efforts are strengthened by recognition of aesthetic, cultural and scientific values of the unique flora and fauna of the West Indies