Geographic variation in morphometrics, molt, and migration suggests ongoing subspeciation in Pacific Golden-Plovers (<i>Pluvialis fulva</i>)

Breeding Pacific Golden-Plovers (Pluvialis fulva) cover 140 longitudinal degrees of Arctic tundra. Having examined 557 museum skins from across this huge distributional range, we conclude that Pacific Golden-Plovers breeding in Alaska are structurally larger than those breeding in Siberia, especially in wing length. Birds from Alaska also have more pointed wings and almost always postpone the initiation of primary molt until they reach their winter quarters, whereas many Siberian birds start primary molt in the breeding areas. These differences could have been favored by the longer transoceanic flights followed by the Alaskan populations to nonbreeding destinations in the Pacific Islands. We propose that the Alaskan and Siberian breeding birds be distinguished as distinct flyway populations to be used in conservation assessments by the international conservation community

A Model for the Development of the Rhizobial and Arbuscular Mycorrhizal Symbioses in Legumes and Its Use to Understand the Roles of Ethylene in the Establishment of these two Symbioses

We propose a model depicting the development of nodulation and arbuscular mycorrhizae. Both processes are dissected into many steps, using Pisum sativum L. nodulation mutants as a guideline. For nodulation, we distinguish two main developmental programs, one epidermal and one cortical. Whereas Nod factors alone affect the cortical program, bacteria are required to trigger the epidermal events. We propose that the two programs of the rhizobial symbiosis evolved separately and that, over time, they came to function together. The distinction between these two programs does not exist for arbuscular mycorrhizae development despite events occurring in both root tissues. Mutations that affect both symbioses are restricted to the epidermal program. We propose here sites of action and potential roles for ethylene during the formation of the two symbioses with a specific hypothesis for nodule organogenesis. Assuming the epidermis does not make ethylene, the microsymbionts probably first encounter a regulatory level of ethylene at the epidermis–outermost cortical cell layer interface. Depending on the hormone concentrations there, infection will either progress or be blocked. In the former case, ethylene affects the cortex cytoskeleton, allowing reorganization that facilitates infection; in the latter case, ethylene acts on several enzymes that interfere with infection thread growth, causing it to abort. Throughout this review, the difficulty of generalizing the roles of ethylene is emphasized and numerous examples are given to demonstrate the diversity that exists in plants

Full Access Unidirectionality in the Phylogeny of Social Organization, With Special Reference To Birds

Ecological explanations for the diversity in parental care patterns and social organization in certain taxonomic groups of birds are not fully satisfactory. They need to be supplemented by phylogenetic explanations. In this article I discussed some aspects of the latter type of explanations, especially the difference between probabilities of certain evolutionary transitions occurring in the one and in the opposite direction. To explain the diversity in parental care and mating patterns in waders and related groups, I presented a model on the phylogenetic pathways in the evolution of parental care and social organization in birds. It departs from an ancestral state with pure male parental care and social organization in birds. It departs from an ancestral state with pure male parental care which may evolve via "uniparental care" (male cares, but female cares if male deserts) and "double clutching" towards biparental care with similar roles, polyandry and pure female parental care (polygyny, promiscuity). I have argued that certain transitions in this model (especially those from uniparental care and double clutching towards biparental care with similar roles and towards pure female parental care) may easily occur in the given direction, but not in the opposite one. The model predicts that pure male parental care and related patterns may be preserved in various lineages and may be associated with several other patterns in related species. It also predicts that pure female parental care is, in many instances, a final stage in the evolution, and hence quite often combined with pure female parental in related species. To investigate the value of the model I tested its predictions for the phylogenetic trees of (1) arctic sandpipers, (2) the complete order of Charadriiformes, and (3) birds in general. All predictions were met. To investigate the likelihood of the model I considered to what extent predictions by alternative models were met. These models either ignored the effect of phylogenetic factors, or departed from alternative ancestral stages. The fit of the data seemed to be bad with the predictions of all of these models. Thus, the original model presented in this article must be considered as a probable reflection of the phylogeny of parental care and social organization in birds