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The causes of evolutionary radiations in Archipelagoes: Passerine birds in the Lesser Antilles

Smithsonian Libraries
To investigate why some lineages undergo evolutionary radiation, we compare the passerine avifaunas of the Hawaiian and Galapagos archipelagoes, which have supported well-known radiations of birds, with those of the Lesser Antilles, which have not. We focus on four steps required for the buildup of diversity through allopatric speciation and secondary sympatry: genetic divergence in isolation, persistence of island populations, recolonization of source islands, and ecological compatibility in secondary sympatry. Analysis of genetic divergence among island populations in the Lesser Antilles reveals evidence of both prolonged independent evolution and reexpansion of differentiated island populations through the archipelago but little evidence of secondary sympatry of divergent genetic lineages. Archipelagoes with high rates of colonization from continental or nearby large-island sources might fail to promote evolutionary radiations because colonists fill ecological space and constrain diversification through competition. However, morphological analysis demonstrated similar divergence between allopatric populations in species in Hawaii, Gala'pagos, and the Lesser Antilles, although the rate of divergence between secondarily sympatric species evidently is more rapid in Hawaii and the Gala'pagos. Alternatively, endemic buildup of diversity might be facilitated by the relative absence of pathogens in Hawaii and Gala'pagos that otherwise could prevent the secondary sympatry of populations owing to disease-mediated competition.

Ecological and life-history factors influencing the evolution of maternal antibody allocation: a phylogenetic comparison

Smithsonian Libraries
Maternally derived yolk antibodies provide neonates with immune protection in early life at negligible cost to mothers. However, developmental effects on the neonate's future immunity are potentially costly and thus could limit yolk antibody deposition. The benefits to neonatal immunity must be balanced against costs, which may depend on neonate vulnerability to pathogens, developmental trajectories and the immunological strategies best suited to a species' pace of life. We measured yolk antibodies and life-history features of 23 species of small Neotropical birds and assessed the evidence for each of several hypotheses for life history and ecological effects on the evolution of yolk antibody levels. Developmental period and yolk antibodies are negatively related, which possibly reflect the importance of humoral immune priming through antigen exposure, and selection to avoid autoimmunity, in species with a slower pace of life. There is also a strong relationship between body size and yolk antibody concentration, suggesting that larger species are architecturally equipped to produce and transfer higher concentrations of antibodies. These results suggest that developmental effects of maternally derived antibodies, such as imprinting effects on B-cell diversity or autoimmune effects, are important and deserve more consideration in future research.
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